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1

Probing the bulk viscosity of particles using aerosol optical tweezers  

NASA Astrophysics Data System (ADS)

Holographic aerosol optical tweezers can be used to trap arrays of aerosol particles allowing detailed studies of particle properties and processes at the single particle level. Recent observations have suggested that secondary organic aerosol may exist as ultra-viscous liquids or glassy states at low relative humidity, potentially a significant factor in influencing their role in the atmosphere and their activation to form cloud droplets. A decrease in relative humidity surrounding a particle leads to an increased concentration of solute in the droplet as the droplet returns to equilibrium and, thus, an increase in the bulk viscosity. We demonstrate that the timescales for condensation and evaporation processes correlate with particle viscosity, showing significant inhibition in mass transfer kinetics using ternary sucrose/sodium chloride/water droplets as a proxy to atmospheric multi-component aerosol. We go on to study the fundamental process of aerosol coagulation in aerosol particle arrays, observing the relaxation of non-spherical composite particles formed on coalescence. We demonstrate the use of bright-field imaging and elastic light scattering to make measurements of the timescale for the process of binary coalescence contrasting the rheological properties of aqueous sucrose and sodium chloride aerosol over a range of relative humidities.

Power, Rory; Bones, David L.; Reid, Jonathan P.

2012-10-01

2

Optical Tweezers  

NSDL National Science Digital Library

Learn about the principles behind the optical tweezers or optical trapping experiment. Become familiar with the use of standard optics including optical alignment, and collection of data through the use of a camera-computer system. Examine the forces on a bead trapped by a laser.

2012-01-18

3

Automation of an Optical Tweezers.  

National Technical Information Service (NTIS)

Optical tweezers is a newly developed instrument, which makes possible the manipulation of micro-optical particles under a microscope. In this paper, we present the automation of an optical tweezers which consists of a modified optical tweezers, equipped ...

B. Chang L. Hsu T. Hsieh

2000-01-01

4

Automation of optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers is a newly developed instrument, which makes possible the manipulation of micro-optical particles under a microscope. In this paper, we present the automation of an optical tweezers which consists of a modified optical tweezers, equipped with two motorized actuators to deflect a 1 W argon laser beam, and a computer control system including a joystick. The trapping of a single bead and a group of lactoacidofilus was shown, separately. With the aid of the joystick and two auxiliary cursers superimposed on the real-time image of a trapped bead, we demonstrated the simple and convenient operation of the automated optical tweezers. By steering the joystick and then pressing a button on it, we assign a new location for the trapped bead to move to. The increment of the motion 0.04 (mu) m for a 20X objective, is negligible. With a fast computer for image processing, the manipulation of the trapped bead is smooth and accurate. The automation of the optical tweezers is also programmable. This technique may be applied to accelerate the DNA hybridization in a gene chip. The combination of the modified optical tweezers with the computer control system provides a tool for precise manipulation of micro particles in many scientific fields.

Hsieh, Tseng-Ming; Chang, Bo-Jui; Hsu, Long

2000-07-01

5

Dynamic holographic optical tweezers  

Microsoft Academic Search

Optical trapping is an increasingly important technique for controlling and probing matter at length scales ranging from nanometers to millimeters. This paper describes methods for creating large numbers of high-quality optical traps in arbitrary three-dimensional configurations and for dynamically reconfiguring them under computer control. In addition to forming conventional optical tweezers, these methods also can sculpt the wavefront of each

Jennifer E. Curtis; Brian A. Koss; David G. Grier

2002-01-01

6

Optical tweezers computational toolbox  

Microsoft Academic Search

We describe a toolbox, implemented in Matlab, for the computational modelling of optical tweezers. The toolbox is designed for the calculation of optical forces and torques, and can be used for both spherical and nonspherical particles, in both Gaussian and other beams. The toolbox might also be useful for light scattering using either Lorenz–Mie theory or the T-matrix method.

Timo A. Nieminen; Vincent L. Y. Loke; Alexander B. Stilgoe; Agata M Bra?czyk; Norman R. Heckenberg; Halina Rubinsztein-Dunlop

2007-01-01

7

Theory of optical tweezers  

Microsoft Academic Search

We derive an exact partial-wave (Mie) expansion of the axial force exerted on a transparent sphere by a laser beam focused through a high numerical aperture objective. The results hold throughout the range of interest for practical applications, as well as in the Rayleigh and geometrical optics limits. They allow, in principle, an absolute calibration of optical tweezers. Starting from

P. A. Maia Neto; H. M. Nussenzveig

2000-01-01

8

Optical Tweezers and Applications  

NSDL National Science Digital Library

Did you ever imagine that you can use light to move a microscopic plastic bead? Explore the forces on the bead or slow time to see the interaction with the laser's electric field. Use the optical tweezers to manipulate a single strand of DNA and explore the physics of tiny molecular motors. Can you get the DNA completely straight or stop the molecular motor?

Simulations, Phet I.; Adams, Wendy; Dubson, Michael; Malley, Chris; Perkins, Kathy; Perkins, Thomas

2007-08-01

9

Physics in Action: Optical Tweezers  

NSDL National Science Digital Library

This website introduces the concept of an optical tweezer, a laser trap used to manipulate objects as small as single molecules. This site lists several applications of optical tweezers and explains their application in molecular biology. Diagrams and links provide further information.

2007-07-18

10

Recent Advances in Optical Tweezers  

Microsoft Academic Search

It has been over 20 years since the pioneering work of Arthur Ashkin, and in the intervening years, the field of optical tweezers has grown tremendously. Optical tweezers are now being used in the inves- tigation of an increasing number of biochemical and biophysical processes, from the basic mechanical properties of biological poly- mers to the multitude of molecular machines

Jeffrey R. Moffitt; Yann R. Chemla; Steven B. Smith; Carlos Bustamante

2008-01-01

11

Optical doughnut for optical tweezers.  

PubMed

We describe novel optical doughnuts for optical tweezers. With new phase functions, the proposed doughnut beams have dark cores in specified shapes. The technique can offer a simple method for creating a variety of beam shapes to match the trapped objects. One can rotate the beams directly by revolving their phase structures about their axes on the initial plane. The technique for generating the traditional Laguerre-Gaussian beam can be used to create these novel beams. PMID:12747724

Zhang, D W; Yuan, X C

2003-05-01

12

On chip shapeable optical tweezers  

NASA Astrophysics Data System (ADS)

Particles manipulation with optical forces is known as optical tweezing. While tweezing in free space with laser beams was established in the 1980s, integrating the optical tweezers on a chip is a challenging task. Recent experiments with plasmonic nanoantennas, microring resonators, and photonic crystal nanocavities have demonstrated optical trapping. However, the optical field of a tweezer made of a single microscopic resonator cannot be shaped. So far, this prevents from optically driven micromanipulations. Here we propose an alternative approach where the shape of the optical trap can be tuned by the wavelength in coupled nanobeam cavities. Using these shapeable tweezers, we present micromanipulation of polystyrene microspheres trapped on a silicon chip. These results show that coupled nanobeam cavities are versatile building blocks for optical near-field engineering. They open the way to much complex integrated tweezers using networks of coupled nanobeam cavities for particles or bio-objects manipulation at a larger scale.

Renaut, C.; Cluzel, B.; Dellinger, J.; Lalouat, L.; Picard, E.; Peyrade, D.; Hadji, E.; de Fornel, F.

2013-07-01

13

Interferometer Control of Optical Tweezers.  

National Technical Information Service (NTIS)

This paper discusses progress in using spatial light modulators and interferometry to control the beam profile of an optical tweezers. The approach being developed is to use a spatial light modulator (SLM) to control the phase profile of the tweezers beam...

A. J. Decker

2002-01-01

14

Optical tweezers for medical diagnostics.  

PubMed

Laser trapping by optical tweezers makes possible the spectroscopic analysis of single cells. Use of optical tweezers in conjunction with Raman spectroscopy has allowed cells to be identified as either healthy or cancerous. This combined technique is known as laser tweezers Raman spectroscopy (LTRS), or Raman tweezers. The Raman spectra of cells are complex, since the technique probes nucleic acids, proteins, and lipids; but statistical analysis of these spectra makes possible differentiation of different classes of cells. In this article the recent development of LTRS is described along with two illustrative examples for potential application in cancer diagnostics. Techniques to expand the uses of LTRS and to improve the speed of LTRS are also suggested. PMID:23559336

LaFratta, Christopher N

2013-04-05

15

Absolute calibration of optical tweezers  

SciTech Connect

As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB ('geometrical optics') approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and 'jump' effects are also confirmed.

Viana, N.B.; Mazolli, A.; Maia Neto, P.A.; Nussenzveig, H.M.; Rocha, M.S.; Mesquita, O.N. [LPO-COPEA and Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590 (Brazil); Departamento de Fisica, Instituto de Ciencias ExatasUniversidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970 (Brazil)

2006-03-27

16

Computer-generated holographic optical tweezer arrays  

Microsoft Academic Search

Holographic techniques significantly extend the capabilities of laser tweezing, making possible extended trapping patterns for manipulating large numbers of particles and volumes of soft matter. We describe practical methods for creating arbitrary configurations of optical tweezers using computer-generated diffractive optical elements. While the discussion focuses on ways to create planar arrays of identical tweezers, the approach can be generalized to

Eric R. Dufresne; Gabriel C. Spalding; Matthew T. Dearing; Steven A. Sheets; David G. Griera

2001-01-01

17

Nanometric optical tweezers based on nanostructured substrates  

Microsoft Academic Search

The ability to control the position of a mesoscopic object with nanometric precision is important for the rapid progress of nanoscience. One of the most promising tools to achieve such control is optical tweezers, which trap objects near the focus of a laser beam. However, the drawbacks of conventional tweezers include a trapping volume that is diffraction-limited and significant brownian

N. W. Roberts; M. R. Dickinson; Y. Zhang; A. N. Grigorenko

2008-01-01

18

Optical Tweezer as a Viscometer  

NASA Astrophysics Data System (ADS)

An optical tweezer (OT) has been widely used to study the mechanical properties of microscopic living biological systems like red blood cells. These studies are based on measurement of deformations caused by a force exerted directly or indirectly by an optical trap. The trap is usually pre-calibrated using Stokes viscous force of the suspension fluids for the biological system which is directly proportional to the viscosity of the fluids. Therefore, calibration of the trap depends on the viscosity of the fluid which depends on temperature. In this work, we have demonstrated that OT can be used to precisely measure the viscosity of biological fluids affected by temperature. Using a an infrared laser trap which is calibrated using silica sphere suspended in a distilled deionized water and measuring the power as function of escape velocity, we have measured the viscosities of a newborn and unborn bovine serum with a different concentration of antibodies.

Erenso, Daniel; Elrod, Samuel; Barns, Taylor; Farone, Anthony; Farone, Mary

2009-03-01

19

Quantum limited particle sensing in optical tweezers  

SciTech Connect

Particle sensing in optical tweezers systems provides information on the position, velocity, and force of the specimen particles. The conventional quadrant detection scheme is applied ubiquitously in optical tweezers experiments to quantify these parameters. In this paper, we show that quadrant detection is nonoptimal for particle sensing in optical tweezers and propose an alternative optimal particle sensing scheme based on spatial homodyne detection. A formalism for particle sensing in terms of transverse spatial modes is developed and numerical simulations of the efficacies of both quadrant and spatial homodyne detection are shown. We demonstrate that 1 order of magnitude improvement in particle sensing sensitivity can be achieved using spatial homodyne over quadrant detection.

Tay, J.W. [Jack Dodd Centre for Photonics and Ultracold Atoms, Department of Physics, University of Otago, Dunedin (New Zealand); Hsu, Magnus T. L. [School of Mathematics and Physics, University of Queensland, St. Lucia, Queensland 4072 (Australia); Bowen, Warwick P. [Jack Dodd Centre for Photonics and Ultracold Atoms, Department of Physics, University of Otago, Dunedin (New Zealand); School of Mathematics and Physics, University of Queensland, St. Lucia, Queensland 4072 (Australia)

2009-12-15

20

Optical tweezers based on polarization interferometer  

NASA Astrophysics Data System (ADS)

In this paper, we propose optical tweezers based on a biaxial crystal. To control the movement of opaque particles, we use the shift polarization interferometer. The results of experimental study of laser tweezers are shown. We demonstrates movement of a microparticle of toner using singular-optical trap, rotate a particle due to orbital momentum, conversion of two traps when changing the plane of polarizer transmission and converging of two traps.

Angelsky, Oleg V.; Maksimyak, Andrew P.; Maksimyak, Peter P.; Dominikov, Mykola M.

2013-06-01

21

Manipulation of Microobjects by Optical Tweezers  

Microsoft Academic Search

Radiation pressure from a tightly focused laser beam can be used as optical tweezers to confine, position, and transport microparticles.\\u000a Ashkin’s group first demonstrated this technique in 1986 [1]. Optical tweezers provide unique features such as remote manipulation\\u000a of micro\\/nano particles in unique features such as remote manipulation of micro\\/nano particles in liquid, noninvasive manipulation\\u000a of biological samples, precise manipulation

Shoji Maruo

22

Characterization of microparticles with driven optical tweezers.  

PubMed

We discuss how actively-driven optical tweezers may be used to characterize Brownian microparticles. Two experiments are described in detail. We follow the thermal fluctuations of a charged particle in an oscillatory electric field and demonstrate that charges as low as a few elementary charges can be measured accurately and reproducibly. Secondly, we measure the orientational dynamics of a trapped rotating droplet and use circular polarimetry within optical tweezers to determine in situ birefringence. PMID:18214111

Wood, Tiffany A; Roberts, G Seth; Eaimkhong, Sarayoot; Bartlett, Paul

2008-01-01

23

Quantum computation architecture using optical tweezers  

SciTech Connect

We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 {mu}s, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10{sup -3}. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing.

Weitenberg, Christof [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); Kuhr, Stefan [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); University of Strathclyde, Department of Physics, SUPA, Glasgow G4 0NG (United Kingdom); Moelmer, Klaus; Sherson, Jacob F. [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2011-09-15

24

The Computer Generation of Holographic Optical Tweezers  

NASA Astrophysics Data System (ADS)

Due to their ability to apply forces on a small scale, optical tweezers are useful for a variety of biological and physical applications. The utility of optical tweezers can be extended by producing multiple traps with different characteristics from a single beam. One method for achieving this is to manipulate the phase of a trapping laser's wave front with a computer generated kinoform displayed on a spatial light modulator. We compare the performance of two algorithms for kinoform calculation, a Gerchberg-Saxton algorithm and a direct search algorithm, and discuss how they address problems inherent to computer generated holographic optical tweezing.

Deceglie, Michael; Pribik, Rodd; Lyon, Jeremy; Browne, Kerry

2006-03-01

25

Micromanipulation of Retinal Neurons by Optical Tweezers  

Microsoft Academic Search

Micromanipulation by optical tweezers has been tested in cultures of mature isolated retinal cells to determine its potential for use in creating synaptic circuits in vitro. Rod and cone photoreceptors as well as other retinal nerve cell types could be optically trapped with a 980 nm diode laser mounted on an inverted light microscope using a 40x oil immersion objective

E. Townes-Anderson; R. S. St. Jules; D. M. Sherry; J. Lichtenberger; M. Hassanain

1998-01-01

26

Micro-objective manipulated with optical tweezers  

SciTech Connect

A microscope is described that uses a {mu}m-sized ball lens, which is here termed micro-objective, manipulated with optical tweezers to image the side view of the arbitrary region of a sample. Since this micro-objective is small in size, it can go into a concave region to produce a local image of the inside which the conventional microscope cannot observe. Preliminary results show good lens performance from the micro-objective when combined with optical tweezers. {copyright} {ital 1997 American Institute of Physics.}

Sasaki, M.; Kurosawa, T.; Hane, K. [Department of Mechatronics and Precision Engineering, Tohoku University, Sendai 980-77 (Japan)

1997-02-01

27

Twin-core fiber optical tweezers.  

PubMed

We present an abruptly tapered twin-core fiber optical tweezers, which is fabricated by fusing and drawing the twin-core fiber. In the twin-core fiber, the two beams are guided by the tapered fiber. At the end of the fiber tip, a larger converge angle between the two beams are made due to the abrupt tapered shape, which is formed a fast divergent optical field. The microscopic particle trapping performance of this special designed tapered twin-core fiber tip is investigated. The functionality of the proposed novel twin-core fiber optical tweezers is extended since an in-fiber integrated Mach-Zehnder interferometer has been used to control orientation of the trapped particle. The distribution of the optical field emerging from the tapered fiber tip is simulated based on the beam propagation method (BPM). By using this two-beam combination technique, a strong enough gradient forces well is obtained for microscopic particles trapping in three dimensions. The abruptly tapered twin-core fiber optical tweezers is rigid and easy to handle, especially useful for building up a multi-tweezers system for trapping and manipulating micro-scale particles. PMID:18542553

Yuan, Libo; Liu, Zhihai; Yang, Jun; Guan, Chunying

2008-03-31

28

Computational models for new fiber optic tweezers  

NASA Astrophysics Data System (ADS)

This paper discusses the calculation of the trapping forces in optical tweezers using a combination of the finite differences time domain (FDTD) method and the Lorentz force on electric dipoles. The results of 2D simulations of the trapping of a circular particle by a waveguide with a circular tip are presented and discussed.

Rodrigues Ribeiro, R. S.; Jorge, P. A. S.; Guerreiro, A.

2013-03-01

29

Tying a molecular knot with optical tweezers  

Microsoft Academic Search

, but the analysis of the buckled shape was complicated. Here we report the continuous control of the radius of curvature of a molecular strand by tying a knot in it, using optical tweezers to manipulate the strand's ends. We find that actin filaments break at the knot when the knot diameter falls below 0.4 mm. The pulling force at

Yasuharu Arai; Ryohei Yasuda; Ken-ichirou Akashi; Yoshie Harada; Hidetake Miyata; Kazuhiko Kinosita Jr; Hiroyasu Itoh

1999-01-01

30

Interactive approach to optical tweezers control  

SciTech Connect

We have developed software with an interactive user interface that can be used to generate phase holograms for use with spatial light modulators. The program utilizes different hologram design techniques, allowing the user to select an appropriate algorithm. The program can be used to generate multiple beams and can be used for beam steering. We see a major application of the program to be in optical tweezers to control the position, number, and type of optical traps.

Leach, Jonathan; Wulff, Kurt; Sinclair, Gavin; Jordan, Pamela; Courtial, Johannes; Thomson, Laura; Gibson, Graham; Karunwi, Kayode; Cooper, Jon; Laczik, Zsolt John; Padgett, Miles

2006-02-10

31

Processing carbon nanotubes with holographic optical tweezers  

Microsoft Academic Search

We report the first demonstration that carbon nanotubes can be trapped and\\u000amanipulated by optical tweezers. This observation is surprising because\\u000aindividual nanotubes are substantially smaller than the wavelength of light,\\u000aand thus should not be amenable to optical trapping. Even so, nanotube bundles,\\u000aand perhaps even individual nanotubes, can be transported at high speeds,\\u000adeposited onto substrates, untangled, and

Joseph Plewa; Evan Tanner; Daniel M. Mueth; David G. Grier

2004-01-01

32

Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy  

Microsoft Academic Search

Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. Here we describe these techniques and illustrate them with examples highlighting current capabilities and limitations.

Attila Nagy; Keir C Neuman

2008-01-01

33

Particles sorting in micro-channel system utilizing magnetic tweezers and optical tweezers  

NASA Astrophysics Data System (ADS)

This study evaluates a method for separating magnetic microparticles in a micro channel by using embedded inverted-laser tweezers, a microflow pump, and a micro magnet. Various particles were separated using optical and/or magnetic tweezers, and were identified and counted to determine the dependence of the sorting rate on the channel flow velocity. The particle sorting experiment showed good separation results when the designed channel and magnetic tweezers were used. For magnetic particles, lower flow velocities corresponded to larger separating rates with a maximum separating rate of 81%. When the designed channel and optical tweezers were used, the polystyrene particle separating rate was as high as 94%. When both the optical tweezers and the magnetic tweezers were used, the optical tweezers were more effective in trapping polystyrene particles with flow velocities between 0.09 and 0.25 ?m/s. For flow velocities between 0.09 and 0.17 ?m/s, the separating rate for polystyrene particles reached 95% and the separating rate for magnetic particles reached 85%. This hybrid system can be applied to the separation of various particles in unknown mixtures.

Chung, Yung-Chiang; Chen, Po-Wen; Fu, Chao-Ming; Wu, Jian-Min

2013-05-01

34

Optical Tweezers Array and Nimble Tweezers Probe Generated by Spatial- Light Modulator.  

National Technical Information Service (NTIS)

An optical tweezers is being developed at the NASA Glenn Research Center as a visiblelight interface between ubiquitous laser technologies and the interrogation, visualization, manufacture, control, and energization of nanostructures such as silicon carbi...

A. J. Decker B. Jassemnejad R. E. Seibel K. E. Weiland

2003-01-01

35

Kinect 4 … holographic optical tweezers  

NASA Astrophysics Data System (ADS)

The 3D position and orientation of a microtool confined in multiple optical traps needs to be controlled in order for one to perform modern, challenging experiments; for example, in order to utilize it as a scanning probe and investigate the surface of optically sensitive cells. The control interface has traditionally used the keyboard/mouse combination—limiting manipulations to a series of 1D/2D transforms. In this paper we demonstrate how the Kinect can be utilized to control the position and orientation of a microtool utilizing macroscopic models.

Muhiddin, C.; Phillips, D. B.; Miles, M. J.; Picco, L.; Carberry, D. M.

2013-07-01

36

Stretching DNA with optical tweezers  

Microsoft Academic Search

Force-extension (F-x) relationships were measured for single molecules of DNA under a variety of buffer conditions, using an optical trapping interferometer modified to incorporate feedback control. One end of a single DNA molecule was fixed to a coverglass surface by means of a stalled RNA polymerase complex. The other end was linked to a microscopic bead, which was captured and

Michelle D. Wang; Hong Yin; Robert Landick; Jeff Gelles; Steven M. Block

1997-01-01

37

Theory of Nanometric Optical Tweezers  

Microsoft Academic Search

We propose a scheme for optical trapping and alignment of dielectric particles in aqueous environments at the nanometer scale. The scheme is based on the highly enhanced electric field close to a laser-illuminated metal tip and the strong mechanical forces and torque associated with these fields. We obtain a rigorous solution of Maxwell's equations for the electromagnetic fields near the

Lukas Novotny; Randy X. Bian; X. Sunney Xie

1997-01-01

38

Theory of Nanometric Optical Tweezers  

SciTech Connect

We propose a scheme for optical trapping and alignment of dielectric particles in aqueous environments at the nanometer scale. The scheme is based on the highly enhanced electric field close to a laser-illuminated metal tip and the strong mechanical forces and torque associated with these fields. We obtain a rigorous solution of Maxwell{close_quote}s equations for the electromagnetic fields near the tip and calculate the trapping potentials for a dielectric particle beyond the Rayleigh approximation. The results indicate the feasibility of the scheme. {copyright} {ital 1997} {ital The American Physical Society}

Novotny, L.; Bian, R.X.; Xie, X.S. [Pacific Northwest National Laboratory, P.O.Box 999, Richland, Washington 99352 (United States)

1997-07-01

39

Bead movement by single kinesin molecules studied with optical tweezers  

Microsoft Academic Search

KINESIN, a mechanoenzyme that couples ATP hydrolysis to movement along microtubules, is thought to power vesicle transport and other forms of microtubule-based motility1-6. Here, microscopic silica beads7 were precoated with carrier protein8,9, exposed to low concentrations of kinesin, and individually manipulated with a single-beam gradient-force optical particle trap10-12 ('optical tweezers') directly onto microtubules. Optical tweezers greatly improved the efficiency of

Steven M. Block; Lawrence S. B. Goldstein; Bruce J. Schnapp

1990-01-01

40

Characterization of objective transmittance for optical tweezers  

SciTech Connect

We have measured the overall transmittance of a laser beam through an oil immersion objective as a function of the transverse size of the laser beam, using the dual-objective method. Our results show that the objective transmittance is not uniform and that its dependence on the radial beam's position can be modeled by a Gaussian function. This property affects the intensity distribution pattern in the sample region and should be taken into account in theoretical descriptions of optical tweezers. Moreover, one must consider this position dependence to determine the local laser power delivered at the sample region by the dual-objective method, especially when the beam overfills the objective's back entrance. If the transmittance is assumed to be uniform, the local power is overestimated.

Viana, N. B.; Rocha, M. S.; Mesquita, O. N.; Mazolli, A.; Neto, P. A. Maia

2006-06-20

41

Systematical study of the trapping forces of optical tweezers formed by different types of optical ring beams  

Microsoft Academic Search

The technique of optical tweezers has been improved a lot since its invention, which extends the application fields of optical tweezers. Besides the conventionally used Gaussian beams, different types of ring beams have also been used to form optical tweezers for different purposes. The two typical kinds of ring beams used in optical tweezers are the hollow Gaussian beam and

Sheng-Hua Xu; Yin-Mei Li; Li-Ren Lou

2006-01-01

42

Investigation of mechanical property of a cell by optical tweezers  

NASA Astrophysics Data System (ADS)

Mechanical property of a cell is investigated from reaction force generated on a particle fixed on a cell by moving with optical tweezers. This system is called as cell palpation system. By using of this system we can measure mechanical property at a desired location on a cell surface just by locating the probe particle with optical tweezers. We have investigated focal adhesion formation through mechanical property measurement after initiation of touching by the probe particle.

Sugiura, T.

2013-06-01

43

Optical capsule and tweezer array for molecular motor use.  

PubMed

A generation of optical capsules and tweezers within a modified optical add-drop filter known as PANDA ring resonator with a new concept is proposed. By using dark and bright solitons, the orthogonal tweezers can be formed within the system and observed simultaneously at the output ports. Under the resonant condition, the optical capsules and tweezers generated by dark and bright soliton pair corresponding to the left-hand and right-hand rotating solitons (tweezers) can be generated. When a soliton is interacted by an object, an angular momentum of either bright or dark tweezers is imparted to the object, in which two possible spin states known as tweezer spins are exhibited. Furthermore, an array of molecular capsules and spins, i.e., trapped molecules can be generated and detected by using the proposed system, which can be used to form large scale tweezer or capsule spins. In application, the trapped molecules can be moved and rotated securely to the required destinations, which can be useful for many applications, especially, in medical diagnosis, therapy and surgery. PMID:23955778

Yupapin, Preecha P; Kulsirirat, Kathawut; Techithdeera, Wicharn

2013-08-15

44

Surface imaging using holographic optical tweezers.  

PubMed

We present an imaging technique using an optically trapped cigar-shaped probe controlled using holographic optical tweezers. The probe is raster scanned over a surface, allowing an image to be taken in a manner analogous to scanning probe microscopy (SPM), with automatic closed loop feedback control provided by analysis of the probe position recorded using a high speed CMOS camera. The probe is held using two optical traps centred at least 10 µm from the ends, minimizing laser illumination of the tip, so reducing the chance of optical damage to delicate samples. The technique imparts less force on samples than contact SPM techniques, and allows highly curved and strongly scattering samples to be imaged, which present difficulties for imaging using photonic force microscopy. To calibrate our technique, we first image a known sample--the interface between two 8 µm polystyrene beads. We then demonstrate the advantages of this technique by imaging the surface of the soft alga Pseudopediastrum. The scattering force of our laser applied directly onto this sample is enough to remove it from the surface, but we can use our technique to image the algal surface with minimal disruption while it is alive, not adhered and in physiological conditions. The resolution is currently equivalent to confocal microscopy, but as our technique is not diffraction limited, there is scope for significant improvement by reducing the tip diameter and limiting the thermal motion of the probe. PMID:21646693

Phillips, D B; Grieve, J A; Olof, S N; Kocher, S J; Bowman, R; Padgett, M J; Miles, M J; Carberry, D M

2011-06-07

45

Optical lock-in particle tracking in optical tweezers  

NASA Astrophysics Data System (ADS)

We demonstrate a lock-in particle tracking scheme in optical tweezers based on stroboscopic modulation of an illuminating optical field. This scheme is found to evade low frequency noise sources while otherwise producing an equivalent position measurement to continuous measurement. This was demonstrated, and found to yield on average 20dB of noise suppression in the frequency range 10-5000 Hz, where low frequency laser noise and electronic noise was significant, and 35 dB of noise suppression in the range 550-710 kHz where laser relaxation oscillations introduced laser noise. The setup is simple, and compatible with any trapping optics.

Taylor, Michael A.; Knittel, Joachim; Bowen, Warwick P.

2013-04-01

46

Tunable optical tweezers for wavelength-dependent measurements  

PubMed Central

Optical trapping forces depend on the difference between the trap wavelength and the extinction resonances of trapped particles. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given application. Here we present an optical tweezer system with wavelength tunability, for the study of resonance effects. With this system, the optical trap stiffness is measured for single trapped particles that exhibit either single or multiple extinction resonances. We include discussions of wavelength-dependent effects, such as changes in temperature, and how to measure them.

Hester, Brooke; Campbell, Gretchen K.; Lopez-Mariscal, Carlos; Filgueira, Carly Levin; Huschka, Ryan; Halas, Naomi J.; Helmerson, Kristian

2012-01-01

47

Dynamic array generation and pattern formation for optical tweezers  

Microsoft Academic Search

The generalised phase contrast approach is used for the generation of optical arrays of arbitrary beam shape, suitable for applications in optical tweezers for the manipulation of biological specimens. This approach offers numerous advantages over current techniques involving the use of computer-generated holograms or diffractive optical elements. We demonstrate a low-loss system for generating intensity patterns suitable for the trapping

Paul C Mogensen; Jesper Glückstad

2000-01-01

48

High-Resolution Optical Tweezers for Single-Molecule Manipulation  

PubMed Central

Forces hold everything together and determine its structure and dynamics. In particular, tiny forces of 1-100 piconewtons govern the structures and dynamics of biomacromolecules. These forces enable folding, assembly, conformational fluctuations, or directional movements of biomacromolecules over sub-nanometer to micron distances. Optical tweezers have become a revolutionary tool to probe the forces, structures, and dynamics associated with biomacromolecules at a single-molecule level with unprecedented resolution. In this review, we introduce the basic principles of optical tweezers and their latest applications in studies of protein folding and molecular motors. We describe the folding dynamics of two strong coiled coil proteins, the GCN4-derived protein pIL and the SNARE complex. Both complexes show multiple folding intermediates and pathways. ATP-dependent chromatin remodeling complexes translocate DNA to remodel chromatin structures. The detailed DNA translocation properties of such molecular motors have recently been characterized by optical tweezers, which are reviewed here. Finally, several future developments and applications of optical tweezers are discussed. These past and future applications demonstrate the unique advantages of high-resolution optical tweezers in quantitatively characterizing complex multi-scale dynamics of biomacromolecules.

Zhang, Xinming; Ma, Lu; Zhang, Yongli

2013-01-01

49

Optical tweezers based on near infrared diode laser  

NASA Astrophysics Data System (ADS)

Emission from a single-mode 100 mW diode laser at 840 nm is used to create optical tweezers: the trapping laser beam is introduced into a microscope and focused by the objective. The microscope also allows monitoring of the motion of the trapped particles. The optical tweezers were monitored with objectives having different numerical apertures between 0.65 and 1.3. The optical trapping of polystyrene spheres with a radius between 0.11 and 7.45 micrometers and of biological objects, the flagellated alga Tetraselmis, with typical dimensions of 8 X 8 X 13 micrometers 3 were studied. The efficiency of the optical tweezers has been characterized through a parameter Q and compared with theoretical models.

Grego, S.; Arimondo, Ennio; Frediani, Carlo

1997-07-01

50

Mechanical manipulation of bone and cartilage cells with 'optical tweezers'.  

PubMed

The single beam optical gradient trap (optical tweezers) uses a single beam of laser light to non-invasively manipulate microscopic particles. Optical tweezers exerting a force of approximately 7 pN were applied to single bone and cartilage derived cells in culture and changes in intracellular calcium levels were observed using Fluo-3 labelling. Human derived osteoblasts responded to optical tweezers with an immediate increase in [Ca2+]i that was inhibited by the addition of a calcium channel blocker nifedipine. Force applied to different regions of cells resulted in a variable response. [Ca2+]i elevation in response to load was lower in rat femur derived osteoblasts, and not apparent in primary chondrocytes and the osteocytic cell line (MLO Y4). PMID:10508913

Walker, L M; Holm, A; Cooling, L; Maxwell, L; Oberg, A; Sundqvist, T; El Haj, A J

1999-10-01

51

Fundamental constraints on particle tracking with optical tweezers  

NASA Astrophysics Data System (ADS)

A general quantum limit to the sensitivity of particle position measurements is derived following the simple principle of the Heisenberg microscope. The value of this limit is calculated for particles in the Rayleigh and Mie scattering regimes, and with parameters which are relevant to optical tweezers experiments. The minimum power required to observe the zero-point motion of a levitating bead is also calculated, with the optimal particle diameter always smaller than the wavelength. We show that recent optical tweezers experiments are within two orders of magnitude of quantum limited sensitivity, suggesting that quantum optical resources may soon play an important role in high sensitivity tracking applications.

Taylor, Michael A.; Knittel, Joachim; Bowen, Warwick P.

2013-02-01

52

Assembly of 3-dimensional structures using programmable holographic optical tweezers  

Microsoft Academic Search

The micromanipulation of objects into 3-dimensional geometries within holographic optical tweezers is carried out using modified Gerchberg-Saxton (GS) and direct binary search (DBS) algorithms to produce the hologram designs. The algorithms calculate sequences of phase holograms, which are implemented using a spatial light modulator, to reconfigure the geometries of optical traps in many planes simultaneously. The GS algorithm is able

Gavin Sinclair; Pamela Jordan; Johannes Courtial; Miles Padgett; Jon Cooper; Zsolt John Laczik

2004-01-01

53

Automated trapping, assembly, and sorting with holographic optical tweezers  

PubMed Central

We combine real-time feature recognition with holographic optical tweezers to automatically trap, assemble, and sort micron-sized colloidal particles. Closed loop control will enable new applications of optical micromanipulation in biology, medicine, materials science, and possibly quantum computation.

Chapin, Stephen C.; Germain, Vincent; Dufresne, Eric R.

2008-01-01

54

Cellular viscoelasticity probed by active rheology in optical tweezers  

NASA Astrophysics Data System (ADS)

A novel approach to probe viscoelastic properties of cells based on double trap optical tweezers is reported. Frequency dependence of the tangent of phase difference in the movement of the opposite erythrocyte edges while one of the edges is forced to oscillate by optical tweezers appeared to be highly dependent on the rigidity of the cellular membrane. Effective viscoelastic parameters characterizing red blood cells with different stiffnesses (normal and glutaraldehyde-fixed) are determined. It is shown that the photo-induced effects caused by laser trapping at the power level used in the experiments are negligible giving the possibility to use the offered technique for dynamic monitoring of soft materials viscoelastic properties.

Lyubin, Evgeny V.; Khokhlova, Maria D.; Skryabina, Maria N.; Fedyanin, Andrey A.

2012-10-01

55

Magneto-optical tweezers built around an inverted microscope  

SciTech Connect

We present a simple experimental setup of magneto-optical tweezers built around an inverted microscope. Two pairs of coils placed around the focal point of the objective generate a planar-rotating magnetic field that is perpendicular to the stretching direction. This configuration allows us to control the rotary movement of a paramagnetic bead trapped in the optical tweezers. The mechanical design is universal and can be simply adapted to any inverted microscope and objective. The mechanical configuration permits the use of a rather large experimental cell and the simple assembly and disassembly of the magnetic attachment.

Claudet, Cyril; Bednar, Jan

2005-06-10

56

Marker-free cell discrimination by holographic optical tweezers  

NASA Astrophysics Data System (ADS)

We introduce a method for marker-free cell discrimination based on optical tweezers. Cancerous, non-cancerous, and drug-treated cells could be distinguished by measuring the trapping forces using holographic optical tweezers. We present trapping force measurements on different cell lines: normal pre-B lymphocyte cells (BaF3; "normal cells"), their Bcr-Abl transformed counterparts (BaF3-p185; "cancer cells") as a model for chronic myeloid leukaemia (CML) and Imatinib treated BaF3-p185 cells. The results are compared with reference measurements obtained by a commercial flow cytometry system.

Schaal, F.; Warber, M.; Zwick, S.; van der Kuip, H.; Haist, T.; Osten, W.

2009-06-01

57

Laser tweezers Raman study of optically trapped aerosol droplets of seawater and oleic acid reacting with ozone: implications for cloud-droplet properties.  

PubMed

In this communication we report the first use of the Raman laser tweezers technique to trap and hold a mixed droplet of oleic acid and water at atmospheric pressure for 30 min, oxidize the oleic acid on the droplet, follow the decay of reactants and the growth of chemical products using Raman spectroscopy, and monitor the growth in size of the droplet as it becomes more hydrophilic. We demonstrate that the oxidation of organic films on water droplets could have large climatic effects in the atmosphere. We show that cloud-droplet growth and activation of cloud condensation nuclei (to become cloud droplets) is retarded by the presence of an organic film and that chemical oxidation of this film would allow a cloud droplet to grow, reducing cloud albedo by inducing precipitation, and would allow a cloud condensation nucleus to grow to a cloud droplet, thus forming a cloud and increasing the albedo of the Earth. PMID:15612694

King, Martin D; Thompson, Katherine C; Ward, Andrew D

2004-12-29

58

Multifunctional optical tweezers using computer-generated holograms  

Microsoft Academic Search

Optical tweezers are capable of trapping microscopic particles by photon momentum transfer. The use of dynamic computer-generated holograms for beam shaping allows a high flexibility in terms of trap characteristics and features. We use a liquid crystal display (LCD) to display the holograms. Efficiency losses caused by the periodic electrode structure of the LCD have been clearly reduced by use

J. Liesener; M. Reicherter; T. Haist; H. J. Tiziani

2000-01-01

59

Investigating the thermodynamics of small biosystems with optical tweezers  

NASA Astrophysics Data System (ADS)

We present two examples of how single-molecule experimental techniques applied to biological systems can give insight into problems within the scope of equilibrium and nonequilibrium mesoscopic thermodynamics. The first example is the mapping of the free energy landscape of a macromolecule, the second the experimental verification of Crooks’ fluctuation theorem. In both cases the experimental setup comprises optical tweezers and DNA molecules.

Mossa, Alessandro; Huguet, Josep Maria; Ritort, Felix

2010-01-01

60

Multispectral optical tweezers for molecular diagnostics of single biological cells  

NASA Astrophysics Data System (ADS)

Optical trapping of single biological cells has become an established technique for controlling and studying fundamental behavior of single cells with their environment without having "many-body" interference. The development of such an instrument for optical diagnostics (including Raman and fluorescence for molecular diagnostics) via laser spectroscopy with either the "trapping" beam or secondary beams is still in progress. This paper shows the development of modular multi-spectral imaging optical tweezers combining Raman and Fluorescence diagnostics of biological cells.

Butler, Corey; Fardad, Shima; Sincore, Alex; Vangheluwe, Marie; Baudelet, Matthieu; Richardson, Martin

2012-02-01

61

Measurements of trapping efficiency and stiffness in optical tweezers  

Microsoft Academic Search

We report an experimental study concerning the radial forces of an optical tweezers acting on spherical polystyrene particles diluted in water solution. The radius of the trapped beads varied between 0.5 and 7.5 ?m, i.e., in an intermediate range between Rayleigh and geometric optics regime. As a force calibration method we used the viscous drag exerted by a fluid flow.

N. Malagnino; G. Pesce; A. Sasso; E. Arimondo

2002-01-01

62

Modified Hybrid Plasmonic Waveguides as Tunable Optical Tweezers  

NASA Astrophysics Data System (ADS)

We propose a series of modified hybrid plasmonic waveguide systems. It is found that their propagation distances and mode areas depend on their shapes notably. The optical trapping forces exerting on the dielectric nanoparticles are calculated, and the strength and range of the forces can be adjusted by altering the shapes of the waveguides. These features demonstrate the possibility of using the modified hybrid waveguide systems to design tunable nanoscale optical tweezers.

Zhang, Lu; Yang, Shu

2013-03-01

63

Superresolution imaging in optical tweezers using high-speed cameras  

Microsoft Academic Search

High-speed cameras are reliable alternatives for the direct characterization of optical trap force and particle motion in optical tweezers setups, replacing indirect motion measurements often performed by quadrant detectors. In the present approach, subpixel motion data of the trapped particle is retrieved from a high-speed low-resolution video sequence. Due to the richness structure of motion diversity of microscopic trapped particles,

Juan Pablo Staforelli; Esteban Vera; Jos'e Manuel Brito; Pablo Solano; Sergio Torres; Carlos Saavedra

2010-01-01

64

Robotic cell manipulation with optical tweezers for biomechanical characterization  

Microsoft Academic Search

In this paper, we demonstrate the effectiveness of robotic cell stretching with optical tweezers for biomechanical characterization. Optical traps serve as end-effectors to manipulate micro-beads attached to the cell surface. The dynamics of the cell-bead mixture during cell stretching is investigated for the first time. Based on our previous work, cell stiffness is extracted and biomechanical properties of cells can

Youhua Tan; Dong Sun; Shuk Han Cheng; Ronald A. Li

2011-01-01

65

Cluster formation in ferrofluids induced by holographic optical tweezers.  

PubMed

Holographic optical tweezers were used to show the interaction between a strongly focused laser beam and magnetic nanoparticles in ferrofluid. When the light intensity was high enough, magnetic nanoparticles were removed from the beam center and formed a dark ring. The same behavior was observed when focusing vortex or Bessel beams. The interactions between two or more separated rings of magnetic nanoparticles created by independent optical traps were also observed. PMID:24081086

Masajada, Jan; Bacia, Marcin; Drobczy?ski, S?awomir

2013-10-01

66

Advanced optical tweezers for the study of cellular and molecular biomechanics  

Microsoft Academic Search

Optical tweezers are an important tool for studying cellular and molecular biomechanics. We present a robust optical tweezers device with advanced features including: multiple optical traps, acousto-optic trap steering, and back focal plane interferometry position detection. We integrate these features into an upright microscope, with no compromise to its capabilities (differential interference contrast microscopy (DIC), fluorescence microscopy, etc.). Acousto-optic deflectors

Gary J. Brouhard; Henry T. Schek; Alan J. Hunt

2003-01-01

67

Sensing interactions in the microworld with optical tweezers  

NASA Astrophysics Data System (ADS)

Optical Tweezers have become a widespread tool in Cell Biology, microengineering and other fields requiring delicate micromanipulation. But for those sensitive tasks, it remains difficult to handle objects without damaging them. As the precision in position and force measurement increase, the richness of information cannot be fully exploited with simple interfaces such as a mouse or a common joystick. For this reason, we propose a haptic force-feedback optical tweezer command and a force-feedback system controlled by one hand. The system combines accurate force measurement using a fast camera and the coupling of these measured forces with a human operator. The overall transparency allows even the feeling of the Brownian motion.

Pacoret, Cécile; Bowman, Richard; Gibson, Graham; Sinan, Haliyo D.; Bergander, Arvid; Carberry, David; Régnier, Stéphane; Padgett, Miles

2009-08-01

68

Influence of gold nanoparticles' size on the trapping performance of optical tweezers  

NASA Astrophysics Data System (ADS)

Gold nanoparticles are considered to be better probes than the traditional polystyrene nanobeads in nanomaterials and nanobiotechnology. Meanwhile, optical tweezers are very popular tool for manipulation and force measurement in these fields. Gold nanoparticles with different size will receive radiation forces with different scale in optical tweezers. This paper theoretically studies the trapping performance of the optical tweezers for the gold nanoparticle with different size, and finally gives the relation curves between the radiation forces and the radius of the of the particle.

Liu, Xiaoyu; Lu, Guang

2012-11-01

69

Evidence for localized cell heating induced by infrared optical tweezers  

Microsoft Academic Search

The confinement of liposomes and Chinese hamster ovary (CHO) cells by infrared (IR) optical tweezers is shown to result in sample heating and temperature increases by several degrees centigrade, as measured by a noninvasive, spatially resolved fluorescence detection technique. For micron-sized spherical liposome vesicles having bilayer membranes composed of the phospholipid 1,2-diacyl-pentadecanoyl-glycero-phosphocholine (15-OPC), a temperature rise of â¼1.45±0.15 °C\\/100 mW

Y. Liu; D. K. Cheng; G. J. Sonek; M. W. Berns; C. F. Chapman; B. J. Tromberg

1995-01-01

70

Membrane Tether Formation from Outer Hair Cells with Optical Tweezers  

Microsoft Academic Search

Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-?m polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499±152 pN) than from OHC basal end (142±49 pN). The difference

Zhiwei Li; Bahman Anvari; Masayoshi Takashima; Peter Brecht; Jorge H. Torres; William E. Brownell

2002-01-01

71

Detection and Characterization of Individual Intermolecular Bonds Using Optical Tweezers  

Microsoft Academic Search

The development of scanning probe techniques has made it possible to examine protein-protein interactions at the level of individual molecular pairs. A calibrated optical tweezers, along with immunoglobulin G (IgG)-coated polystyrene microspheres, has been used to detect individual surface-linked Staphylococcus protein A (SpA) molecules and to characterize the strength of the noncovalent IgG-SpA bond. Microspheres containing, on average, less than

Andrea L. Stout

2001-01-01

72

Spatially resolved magnetometry using cold atoms in dark optical tweezers.  

PubMed

We use Faraday spectroscopy of atoms confined to crossed hollow beam tweezers to map magnetic fields over 3 millimeters with 200 micron resolution in a single trap loading cycle. The hollow beams are formed using spatial light modulation, and the trap location is scanned using acousto-optic deflectors. We demonstrate the technique by mapping a linear quadrupole magnetic field with 10 nT sensitivity. PMID:20174047

Fatemi, Fredrik K; Bashkansky, Mark

2010-02-01

73

The effect of Mie resonances on trapping in optical tweezers.  

PubMed

We calculate trapping forces, trap stiffness and interference effects for spherical particles in optical tweezers using electromagnetic theory. We show the dependence of these on relative refractive index and particle size. We investigate resonance effects, especially in high refractive index particles where interference effects are expected to be strongest. We also show how these simulations can be used to assist in the optimal design of traps. PMID:18795041

Stilgoe, Alexander B; Nieminen, Timo A; Knöener, Gregor; Heckenberg, Norman R; Rubinsztein-Dunlop, Halina

2008-09-15

74

Long lifetime of single atom in optical tweezer with laser cooling  

NASA Astrophysics Data System (ADS)

Single cesium atom prepared in a large-magnetic-gradient magneto-optical trap (MOT) has been efficiently loaded into a microscopic far-off-resonance optical trap (FORT, or optical tweezer), and the atom can be transferred back and forth between two traps with high efficiency. The intensity noise spectra of tweezer laser are measured and the heating mechanisms in optical tweezer are analyzed. To prolong the lifetime of single atom trapped in optical tweezer, laser cooling technique is utilized to decrease atom's kinetic energy, and the effective temperature of single atom in tweezer is estimated by the release-and-recapture (R&R) method. Thanks to laser cooling, typical lifetime of ~ 130.6 +/- 1.8 s for single atom in tweezer is obtained. These works provides a good starting point for coherent manipulation of single atom.

Wang, Junmin; He, Jun; Yang, Baodong; Zhang, Tiancai; Peng, Kunchi

2010-04-01

75

Precession mechanism of nematic liquid crystal droplet under optical tweezers  

NASA Astrophysics Data System (ADS)

Optical Tweezers are well known for manipulating and tracking microscopic particles used in many biological and microfluidic applications. Trapping birefringent particles, e.g. liquid crystal droplets, gives insight into the aspect of light polarization in optical tweezers. The outstanding properties of liquid crystal droplets are their high refractive index and birefringent property suitable for light angular momentum transfer. Under the microscope, the Maltese cross of radial nematic liquid crystal droplet was observed. Trapped under 1064 nm Optical Tweezers with power lower than 80 mW, the droplet precession around the focal point of the laser beam was observed due to circular polarization of laser. In this study we show that the precession behavior of radial nematic droplet depends on the degree of ellipticity of polarization state of light, power of the laser source and size of the radial nematic droplet, affecting the induced electrical polarization and internal reordering of the droplets. The theoretical explanation and the model of this behavior have also been determined and discussed.

Phanphak, S.; Pattanaporkratana, A.; Limtrakul, J.; Chattham, N.

2013-06-01

76

Optical sorting of particles by dual-channel line optical tweezers  

NASA Astrophysics Data System (ADS)

A novel configuration of dual-channel line optical tweezers with a ‘Y’ shape is constructed for sorting of particles within a microfluidic chip. When yeast cells with different size pass the intersection of the specially designed line optical tweezers, they are separated and transported to different channels due to a difference in the forces exerted by the line tweezers that depends on the size of the cells. The influences of some experimental conditions, such as laser power and flow velocity, on the sorting efficiency are discussed.

Ma, Baiheng; Yao, Baoli; Peng, Fei; Yan, Shaohui; Lei, Ming; Rupp, Romano

2012-10-01

77

Optical manipulation of aerosol particle arrays  

NASA Astrophysics Data System (ADS)

Aerosols play a crucial role in many areas of science, ranging from atmospheric chemistry and physics, to drug delivery to the lungs, combustion science and spray drying. The development of new methods to characterise the properties and dynamics of aerosol particles is of crucial importance if the complex role that particles play is to be more fully understood. Optical tweezers provide a valuable new tool to address fundamental questions in aerosol science. Single or multiple particles 1-15 ?m in diameter can be manipulated over indefinite timescales using optical tweezing. Linear and non-linear Raman and fluorescence spectroscopies can be used to probe a particle's composition and size. In this paper we will report on the latest developments in the use of holographic optical trapping (HOT) to study aerosols. Although widely used to trap and manipulate arrays of particles in the condensed phase, the application of HOT to aerosols is still in its infancy. We will explore the opportunities provided by the formation of complex optical landscapes for controlling aerosol flow, for comparing the properties of multiple particles, for performing the first ever digital microfluidic operations in the aerosol phase and for examining interparticle interactions that can lead to coalescence/coagulation. Although aerosol coagulation is the primary process driving the evolution of particle size distributions, it remains very poorly understood. Using HOT, we can resolve the time-dependent motion of trapped particles and the light scattering from particles during the coalescence process.

Reid, J. P.; Haddrell, A. E.; Walker, J. S.; Power, R.; Bones, D. L.; Davies, J. F.

2011-09-01

78

Frequency-dependent cell death by optical tweezers manipulation.  

PubMed

Optical tweezers were used to scan individual Chronic Myelogenous Leukemia cells to determine if the cell death depends on the scanning conditions. Although increasing the scanning frequency or amplitude means greater force applied to the cells, their effects on cell death are not a simple increasing trend, as observed in the optical microscopy. Indeed, cell death sharply increased at particular screening frequencies and amplitudes, whereas other frequencies or amplitudes were less detrimental. These results suggest that cell damage was more sensitive to certain scanning conditions, rather than simply high-applied forces. PMID:23553530

Ng, K S; Zhou, Z L; Ngan, A H W

2013-10-01

79

Hybrid optical tweezers for dynamic micro-bead arrays  

NASA Astrophysics Data System (ADS)

Dynamic micro-bead arrays offer great flexibility and potential as sensing tools in various scientific fields. Two optical trapping techniques, the GPC method using a spatial light modulator and a mechanical scanning method using galvano mirrors, are combined in a hybrid optical tweezers system to handle dynamic micro-bead arrays. This system provides greater versatility while the GPC method creates massive micro-bead arrays in a 2D space, where the trapped beads can be manipulated smoothly and very quickly in a 3D space using the mechanical scanning method. Four typical examples are demonstrated in real time.

Tanaka, Yoshio; Tsutsui, Shogo; Ishikawa, Mitsuru; Kitajima, Hiroyuki

2011-08-01

80

Full-field OCT combined with optical tweezer  

NASA Astrophysics Data System (ADS)

We present an optical tweezer technique assisted full-field optical coherence tomography (FF-OCT) system. The proposed scheme enables ultrahigh-resolution OCT imaging of a floating object optically trapped by single-beam gradient force in medium. The set up consists of a Linnik type of white light interference microscope combined with an optical tweezer system. The optical trap is formed by tightly focusing a 1064 nm Q-switching pulsed laser beam with a microscope objective lens of high numerical aperture (1.0 NA) in sample arm of the OCT interferometer. This co-sharing of probe channel between two of systems enables concurrent actions of trapping and OCT imaging for the sample. OCT imaging of the sample in depth can achieve by positioning the coherence gating with displacement of reference arm in the OCT interferometer. To demonstrate the efficacy of the system, micron-sized dielectric particles and living cells in solution are simultaneously trapped and optically sliced with cellular resolution.

Choi, Woo June; Park, Kwan Seob; Eom, Tae Joong; Oh, Myung-Kyu; Lee, Byeong-Ha

2012-02-01

81

Applications of Optical Tweezers and an Integrated Force Measurement Module for Biomedical Research.  

National Technical Information Service (NTIS)

Optical tweezers are useiul for manipulating biological samples and measuring biological forces. in the present study, we have integrated a ward atter analysis (FORSA) module into the 'single-beam gradient force optical tweezers'. The entire set-up was th...

B. Liao C. Huang D. Wang J. Tsai W. L. Hwang

2000-01-01

82

Photonic Force Microscope Based on Optical Tweezers and Two-Photon Excitation for Biological Applications  

Microsoft Academic Search

A new scanning probe microscope, the photonic force microscope (PFM), based on optical tweezers and two-photon absorption processes for biological applications is described. Optical tweezers are used to trap a fluorescent latex bead with a diameter of 200 nm in an aqueous solution in all three dimensions. The fluorescent dye is chosen to fulfill the two-photon absorption criterion for the

Ernst-Ludwig Florin; Arnd Pralle; J. K. Heinrich Hörber; Ernst H. K. Stelzer

1997-01-01

83

Stress Response in Caenorhabditis elegans Caused by Optical Tweezers: Wavelength, Power, and Time Dependence  

Microsoft Academic Search

Optical tweezers have emerged as a powerful technique for micromanipulation of living cells. Although the technique often has been claimed to be nonintrusive, evidence has appeared that this is not always the case. This work presents evidence that near-infrared continuous-wave laser light from optical tweezers can produce stress in Caenorhabditis elegans. A transgenic strain of C. elegans, carrying an integrated

Guenther Leitz; Erik Fällman; Simon Tuck; Ove Axner

2002-01-01

84

Differential Detection of Dual Traps Improves the Spatial Resolution of Optical Tweezers  

Microsoft Academic Search

The drive toward more sensitive single-molecule manipulation techniques has led to the recent development of optical tweezers capable of resolving the motions of biological systems at the subnanometer level, approaching the fundamental limit set by Brownian fluctuations. One successful approach has been the dual-trap optical tweezers, in which the system of study is held at both ends by microspheres in

Jeffrey R. Moffitt; Yann R. Chemla; David Izhaky; Carlos Bustamante

2006-01-01

85

Single DNA molecule grafting and manipulation using a combined atomic force microscope and an optical tweezer  

Microsoft Academic Search

In this letter, we report on spatially selecting and grafting a DNA-tethered bead to an atomic force microscope (AFM) cantilever, using an optical tweezer. To quantify this technique, we measure force versus extension of a single DNA molecule using AFM. For such studies, we have developed a micromanipulation approach by combining an AFM, an optical tweezer, and visualization setup. The

G. V. Shivashankar; A. Libchaber

1997-01-01

86

MatLab program for precision calibration of optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are used as force transducers in many types of experiments. The force they exert in a given experiment is known only after a calibration. Computer codes that calibrate optical tweezers with high precision and reliability in the (x,y)-plane orthogonal to the laser beam axis were written in MatLab (MathWorks Inc.) and are presented here. The calibration is based on the power spectrum of the Brownian motion of a dielectric bead trapped in the tweezers. Precision is achieved by accounting for a number of factors that affect this power spectrum. First, cross-talk between channels in 2D position measurements is tested for, and eliminated if detected. Then, the Lorentzian power spectrum that results from the Einstein-Ornstein-Uhlenbeck theory, is fitted to the low-frequency part of the experimental spectrum in order to obtain an initial guess for parameters to be fitted. Finally, a more complete theory is fitted, a theory that optionally accounts for the frequency dependence of the hydrodynamic drag force and hydrodynamic interaction with a nearby cover slip, for effects of finite sampling frequency (aliasing), for effects of anti-aliasing filters in the data acquisition electronics, and for unintended ``virtual'' filtering caused by the position detection system. Each of these effects can be left out or included as the user prefers, with user-defined parameters. Several tests are applied to the experimental data during calibration to ensure that the data comply with the theory used for their interpretation: Independence of x- and y-coordinates, Hooke's law, exponential distribution of power spectral values, uncorrelated Gaussian scatter of residual values. Results are given with statistical errors and covariance matrix. Program summary Title of program: tweezercalib Catalogue identifier: ADTV Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland. Program Summary URL: http://cpc.cs.qub.ac.uk/summaries/ADTV Computer for which the program is designed and others on which it has been tested: General computer running MatLab (MathWorks Inc.). Programming language used: MatLab (MathWorks Inc.). Uses ``Optimization Toolbox'' and ``Statistics Toolbox''. Memory required to execute with typical data: Of order 4 times the size of the data file. High speed storage required: None No. of lines in distributed program, including test data, etc.: 133183 No. of bytes in distributed program, including test data, etc.: 1043674 Distribution format: tar gzip file Nature of physical problem: Calibrate optical tweezers with precision by fitting theory to experimental power spectrum of position of bead doing Brownian motion in incompressible fluid, possibly near microscope cover slip, while trapped in optical tweezers. Thereby determine spring constant of optical trap and conversion factor for arbitrary-units-to-nanometers for detection system. Method of solution: Elimination of cross-talk between quadrant photo-diode's output channels for positions (optional). Check that distribution of recorded positions agrees with Boltzmann distribution of bead in harmonic trap. Data compression and noise reduction by blocking method applied to power spectrum. Full accounting for hydrodynamic effects: Frequency-dependent drag force and interaction with nearby cover slip (optional). Full accounting for electronic filters (optional), for ``virtual filtering'' caused by detection system (optional). Full accounting for aliasing caused by finite sampling rate (optional). Standard non-linear least-squares fitting. Statistical support for fit is given, with several plots suitable for inspection of consistency and quality of data and fit. Restrictions on the complexity of the problem: Data should be positions of bead doing Brownian motion while held by optical tweezers. For high precision in final results, data should be time series measured over a long time, with sufficiently high experimental sampling rate: The sampling rate should be well above the characteristic frequency of the trap, the so-called corner frequency. Thu

Toli?-Nørrelykke, Iva Marija; Berg-Sørensen, Kirstine; Flyvbjerg, Henrik

2004-06-01

87

Evidence for localized cell heating induced by infrared optical tweezers  

SciTech Connect

The confinement of liposomes and Chinese hamster ovary (CHO) cells by infrared (IR) optical tweezers is shown to result in sample heating and temperature increases by several degrees centigrade, as measured by a noninvasive, spatially resolved fluorescence detection technique. For micron-sized spherical liposome vesicles having bilayer membranes composed of the phospholipid 1,2-diacyl-pentadecanoyl-glycero-phosphocholine (15-OPC), a temperature rise of {similar_to}1.45{plus_minus}0.15 {degree}C/100 mW is observed when the vesicles are held stationary with a 1.064 {mu}m optical tweezers having a power density of {similar_to}10{sup 7} W/cm{sup 2} and a focused spot size of {similar_to}0.8 {mu}m. The increase in sample temperature is found to scale linearly with applied optical power in the 40 to 250 mW range. Under the same trapping conditions, CHO cells exhibit an average temperature rise of nearly 1.15{plus_minus}0.25 {degree}C/100 mW. The extent of cell heating induced by infrared tweezers confinement can be described by a heat conduction model that accounts for the absorption of infrared (IR) laser radiation in the aqueous cell core and membrane regions, respectively. The observed results are relevant to the assessment of the noninvasive nature of infrared trapping beams in micromanipulation applications and cell physiological studies. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Liu, Y.; Cheng, D.K.; Sonek, G.J. [Department of Electrical and Computer Engineering and Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92717 (United States); Berns, M.W.; Chapman, C.F.; Tromberg, B.J. [Department of Biophysics, and Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92717 (United States)

1995-05-01

88

Single atoms in optical tweezers for quantum computing  

NASA Astrophysics Data System (ADS)

Our group is interested in neutral atom quantum computing. With this goal in mind, we have recently shown how a single rubidium atom trapped in an optical tweezer can be used to store, manipulate and measure a qubit. I will detail in this talk how we trap and observe a single atom in an optical tweezer created by focusing a far-off resonant laser down to a sub-micron waist. Our qubit is encoded on the |0>=|F =1, M=0> and |1>=|F =2, M=0> hyperfine sublevels of a rubidium 87 atom. We initialize the qubit by optical pumping. We read the state of the qubit using a state selective measurement limited by the quantum projection noise. We perform single qubit operation by driving a two-photon Raman transition. We have measured the coherence time of our qubit by Ramsey interferometry. After applying a spin-echo sequence, we have found an irreversible dephasing time of about 40 ms. To perform a computation, a feature is the ability to perform a gate between two arbitrary qubits of the register. As a first step, we have demonstrated a scheme where the qubit is transfered between two tweezers with no loss of coherence and no change in the external degrees of freedom of the atom. We have then moved the atom over distances typical of the separation between atoms in an array of dipole traps, and shown that this transport does not affect the coherence of the qubit. Finally, I will present our progress towards entangling two atoms, a key ingredient towards building a two-qubit gate.

Browaeys, Antoine

2008-05-01

89

Optical Tweezers for Sample Fixing in Micro-Diffraction Experiments  

SciTech Connect

In order to manipulate, characterize and measure the micro-diffraction of individual structural elements down to single phospholipid liposomes we have been using optical tweezers (OT) combined with an imaging microscope. We were able to install the OT system at the microfocus beamline ID13 at the ESRF and trap clusters of about 50 multi-lamellar liposomes (< 10 {mu}m large cluster). Further we have performed a scanning diffraction experiment with a 1 micrometer beam to demonstrate the fixing capabilities and to confirm the size of the liposome cluster by X-ray diffraction.

Amenitsch, H.; Rappolt, M.; Sartori, B.; Laggner, P. [Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz (Austria); Cojoc, D.; Ferrari, E.; Garbin, V.; Di Fabrizio, E. [CNR-INFM, Lab TASC, Area di Ricerca, 34012 Basovizza (Italy); Burghammer, M.; Riekel, Ch. [ESRF, 6 rue Jules Horowitz, BP220, 38043 Grenoble Cedex (France)

2007-01-19

90

Multiplexed force measurements on live cells with holographic optical tweezers.  

PubMed

We describe open-loop and closed-loop multiplexed force measurements using holographic optical tweezers. We quantify the performance of our novel video-based control system in a driven suspension of colloidal particles. We demonstrate our system's abilities with the measurement of the mechanical coupling between Aplysia bag cell growth cones and beads functionalized with the neuronal cell adhesion molecule, apCAM. We show that cells form linkages which couple beads to the underlying cytoskeleton. These linkages are intermittent, stochastic and heterogeneous across beads distributed near the leading edge of a single growth cone. PMID:19365444

Mejean, Cecile O; Schaefer, Andrew W; Millman, Eleanor A; Forscher, Paul; Dufresne, Eric R

2009-04-13

91

Multiplexed force measurements on live cells with holographic optical tweezers  

PubMed Central

We describe open-loop and closed-loop multiplexed force measurements using holographic optical tweezers. We quantify the performance of our novel video-based control system in a driven suspension of colloidal particles. We demonstrate our system's abilities with the measurement of the mechanical coupling between Aplysia bag cell growth cones and beads functionalized with the neuronal cell adhesion molecule, apCAM. We show that cells form linkages which couple beads to the underlying cytoskeleton. These linkages are intermittent, stochastic and heterogeneous across beads distributed near the leading edge of a single growth cone.

Mejean, Cecile O.; Schaefer, Andrew W.; Millman, Eleanor A.; Forscher, Paul; Dufresne, Eric R.

2009-01-01

92

Mechanical properties of a giant liposome studied using optical tweezers  

NASA Astrophysics Data System (ADS)

The mechanical properties of a micrometer-sized giant liposome are studied by deforming it from the inside using dual-beam optical tweezers. As the liposome is extended, its shape changes from a sphere to a lemon shape, and finally, a tubular part is generated. The surface tension ? and the bending rigidity ? of the lipid membrane are obtained from the measured force-extension curve. In a one-phase liposome, it was found that ? increases as the charged component increases but ? remains approximately constant. In a two-phase liposome, the characteristic deformation and the force-extension curve differ from those observed for the one-phase liposome.

Shitamichi, Yoko; Ichikawa, Masatoshi; Kimura, Yasuyuki

2009-09-01

93

Axial optical trapping forces on two particles trapped simultaneously by optical tweezers  

SciTech Connect

Optical tweezers, which utilize radiation pressure to control and manipulate microscopic particles, are used for a large number of applications in biology and colloid science. In most applications a single optical tweezers is used to control one single particle. However, two or more particles can be trapped simultaneously. Although this characteristic has been used in applications, no theoretical analysis of the trapping force or the status of the trapped particles is available to our knowledge. We present our calculation, using a ray optics model, of the axial trapping forces on two rigid particles trapped in optical tweezers. The spherical aberration that results from a mismatch of the refractive indices of oil and water is also considered. The results show that the forces exerted by the optical tweezers on the two particles will cause the two particles to touch each other, and the two particles can be stably trapped at a joint equilibrium point. We also discuss the stability of axial trapping. The calculation will be useful in applications of optical tweezers to trap multiple particles.

Xu Shenghua; Li Yinmei; Lou Liren

2005-05-01

94

Optical tweezer for probing erythrocyte membrane deformability  

NASA Astrophysics Data System (ADS)

We report that the average rotation speed of optically trapped crenated erythrocytes is direct signature of their membrane deformability. When placed in hypertonic buffer, discocytic erythrocytes are subjected to crenation. The deformation of cells brings in chirality and asymmetry in shape that makes them rotate under the scattering force of a linearly polarized optical trap. A change in the deformability of the erythrocytes, due to any internal or environmental factor, affects the rotation speed of the trapped crenated cells. Here we show how the increment in erythrocyte membrane rigidity with adsorption of Ca++ ions can be exhibited through this approach.

Khan, Manas; Soni, Harsh; Sood, A. K.

2009-12-01

95

Combining confocal microscopy with precise force-scope optical tweezers  

NASA Astrophysics Data System (ADS)

We demonstrate an example of 'confocal-tweezers' wherein confocal images and precise optical force measurements, using photodiodes, are obtained simultaneously in the x-y plane without moving the objective lens. The optical trap is produced using a 1.064?m cw laser and is combined with Leica's TCS SP5 broadband confocal microscope to trap and image living cells. The unique method by which the confocal images are created facilitates the acquisition of images in areas far from the trapping location. In addition, because the scanning process involves moving galvanic mirrors independently of the objective, the trap is held stable in position and is not subject to any error in position for the x-y scan. We have successfully trapped and confocally imaged 80nm gold colloids, 150nm gold colloids and 1?m polystyrene beads whilst making quantitative measurements of the force applied by the trap on each bead. To the best of our knowledge this is the first time that anyone has combined precise force measuring optical tweezers with confocal microscopy. We also discuss some of the technical challenges involved in advancing the experimental set up to make quantitative force measurements in combination with 3D stacking. Having proven the potential of this system in 2D, we hope to develop it further to investigate the nano-mechanics of cell division through the attachment of gold beads to fluorescently labelled organelles in S. pombe yeast cells.

Richardson, Andrew C.; Reihani, Nader; Oddershede, Lene B.

2006-09-01

96

Power spectrum analysis for optical tweezers  

Microsoft Academic Search

The force exerted by an optical trap on a dielectric bead in a fluid is often found by fitting a Lorentzian to the power spectrum of Brownian motion of the bead in the trap. We present explicit functions of the experimental power spectrum that give the values of the parameters fitted, including error bars and correlations, for the best such

Kirstine Berg-Sørensen; Henrik Flyvbjerg

2004-01-01

97

Real-time control of optical tweezers  

Microsoft Academic Search

Optically trapped microshperes can be manipulated by steering the trap beam, while the object position is measured with sub-nanometer resolution. A fast steering system is required to create feedback loop for measurements at a constant force or to increase position detection precision by trap stiffening. Using a real-time re-programmable digital signal processor, we combine steering and position detection to create

Anders E. Wallin; Heikki Ojala; Anders Korsbäck; Edward Haeggström; Roman Tuma

2007-01-01

98

Peculiarities of RBC aggregation studied by double trap optical tweezers  

NASA Astrophysics Data System (ADS)

Aggregation peculiarities of red blood cells (RBCs) in autologous plasma are studied using double trap optical tweezers technique. The positions of RBCs are controlled with submicrometer accuracy by two optical traps formed by strongly focused laser beams (?=1064 nm). Quantitative measurements of interaction forces between RBCs in pair aggregates are performed. Depending on the RBCs aggregation force, four different end-points of disaggregation induced by optical trap movement are revealed. Analysis of experimental force dependence on the distance between two RBCs during disaggregation is in a good agreement with the model of ring-shaped interaction surfaces of RBCs in pair aggregate. Aggregation velocities measured are shown to be strongly different for healthy and pathologic (System Lupus Erythematosis - SLE) blood samples.

Khokhlova, Maria D.; Lyubin, Evgeny V.; Zhdanov, Alexander G.; Rykova, Sofia Yu.; Krasnova, Tatyana N.; Sokolova, Irina A.; Fedyanin, Andrey A.

2010-04-01

99

Microrheology with optical tweezers: data analysis  

NASA Astrophysics Data System (ADS)

We present a data analysis procedure that provides the solution to a long-standing issue in microrheology studies, i.e. the evaluation of the fluids' linear viscoelastic properties from the analysis of a finite set of experimental data, describing (for instance) the time-dependent mean-square displacement of suspended probe particles experiencing Brownian fluctuations. We report, for the first time in the literature, the linear viscoelastic response of an optically trapped bead suspended in a Newtonian fluid, over the entire range of experimentally accessible frequencies. The general validity of the proposed method makes it transferable to the majority of microrheology and rheology techniques.

Tassieri, Manlio; Evans, R. M. L.; Warren, Rebecca L.; Bailey, Nicholas J.; Cooper, Jonathan M.

2012-11-01

100

Antigen detection at atomolar concentration using optical tweezers  

NASA Astrophysics Data System (ADS)

Methods that avoid intermediate amplification steps to detect protein markers of pathological disturbances would be of wide interest in the clinical environment. This is particularly the case in cancer diagnosis, where protein fragments are released into the blood by the emerging cancer cells. These fragments generate an antigen-antibody reaction, and the concentration of the antigen is known to modulate this interaction. Here we report on the development of a novel optical tweezers-based procedure to measure minute amount of antigen in a biological fluid. The force was applied on a 3?m polystyrene bead coated with Bovine Serum Albumin (BSA) attached on a 1.5 ?m diameter borosilicate rod tip coated with anti-BSA antibody. First, we verified that the binding strength was dependent on the protein concentration on the bead. We then assessed the sensitivity range by finding the minimal BSA concentration in solution that can still interfere with the bead-rod linkage. On the whole, the results demonstrated that proteinous antigen present in a biological fluid could possibly be detectable at atomolar concentration through the use of an optical tweezers.

Laliberté, Mathieu; Bordeleau, François; Marceau, Normand; Sheng, Yunlong

2009-06-01

101

Optical tweezers: Characterization and systems approach to high bandwidth force estimation  

NASA Astrophysics Data System (ADS)

In recent times, the hard boundaries between classical fields of sciences have almost disappeared. There is a cross-pollination of ideas between sciences, engineering and mathematics. This work investigates a modern tool of micro-manipulation of microscopic particles that is used primarily by bio-physicists and bio-chemists for single cell, single molecule studies. This tool called the Optical Tweezers can trap microscopic dielectric particles using radiation pressure of light. Optical tweezers is increasingly being used in bio-assays as it provides a means to observe bio-molecules non invasively and offers a spatial resolution in nanometers and force resolution in femto-Newtons at millisecond timescales. In this work, physics governing the operating principle behind optical tweezers is presented, followed by a step by step procedure to build an optical tweezers system having measurement and actuation capability along with a controller logic for feedback implementation. The working of optical tweezers system is presented using a spring mass damper model and the traditional methods of optical tweezers characterization are discussed. A comprehensive view of Optical tweezers is then presented from a system theoretic perspective, underlying the limitations of traditional methods of tweezers characterization that are based on the first principle. The role of feedback in Optical tweezers is presented along with the fundamental limitations that the plant model imposes on optical tweezers performance to be used as a force sensor for fast dynamics input force. The purpose of optical tweezers as a pico-newton force probe is emphasized and a classical controls based method to improve the bandwidth of force estimation using an ad-hoc approach of system inversion is presented. The efficacy of system inversion based method in improving the force probe capability of feedback enhanced optical tweezers is validated by experimental results. It is shown experimentally that the system inversion method results in an order of magnitude improvement in the bandwidth of external force estimation. Finally, a robust control strategy is presented, where the problem of estimation of high bandwidth force is casted as an H-infinity optimization problem along with other performance objectives. This strategy is then compared with the traditional method using PI-controllers and experimental results presented. The robust control strategy is found to further improve the ability of optical tweezers as a force sensor for fast changing force profile by approximately three times over the system inversion approach.

Sehgal, Hullas

102

Study of bacterial motility using optical tweezers  

NASA Astrophysics Data System (ADS)

Bacteria are arguably the simplest of known microorganisms, forming a fundamental part of the world we live in. Many functions they perform are found in scaled-up versions in higher organisms. Among many advanced functions, bacteria possess the ability to move in search for nutrients and favorable growth conditions. Measurement of the dynamical variables associated with bacterial swimming has proven to be difficult due to the lack of an accurate and convenient tool. In the past optical traps have been used for the manipulation of microscopic objects and measurement of minute forces. Herein, I have devised techniques for use of optical traps for direct measurement of the dynamics of bacterial swimming and chemotaxis, shedding light on the propulsion apparatus and sensory systems. A detailed analysis is performed to explore the effects of non-local hydrodynamic interactions on the swimming of single cells. Due to the lack of reliable measurement techniques, experimentalists often use theoretical models to estimate bacterial dynamics, the validity of which are tested. I emphasize the shortcomings of the very popular Resistive Force Theory (RFT) and indicate how the more rigorous Slender Body Theory (SBT) is able to overcome the limitations. In addition the chemotaxis of the marine bacterial strain Vibrio alginolyticus is studied with the revelation of a previously unknown chemotactic mechanism. Direct observations showed that these cells are able to bend their flagella to impart direction changes, which is paramount for an effective search strategy. This interesting find opens several intriguing questions pertaining to chemotaxis.

Chattopadhyay, Suddhashil

103

Efficient extension of the trapping lifetime of single atoms in an optical tweezer by laser cooling  

NASA Astrophysics Data System (ADS)

Optical tweezers have become powerful tools for the confinement and manipulation of neutral atoms, molecules, mesoscopic biological molecules and living cells. In our experiment, a single caesium atom was prepared in a large-magnetic-gradient magneto-optical trap (MOT). It was then efficiently transferred back and forth between the MOT and a 1064 nm microscopic optical tweezer. The atomic transfer between the MOT and the tweezer can be employed to measure the trapping lifetime and the energy distribution of the single atom in the tweezer. In order to extend the trapping lifetime, laser cooling is used to decrease the atom's kinetic energy. The trapping lifetime was extended from ~75 to ~130 s by applying a 10 ms laser cooling phase just after the single atom is transferred into the tweezer.

He, Jun; Yang, Baodong; Zhang, Tiancai; Wang, Junmin

2011-08-01

104

Femtosecond optical tweezers for in-situ control of two-photon fluorescence  

Microsoft Academic Search

We perform a comparison of optical tweezing using continuous wave (cw) and femtosecond lasers. Measurement of the relative Q-values in the femtosecond and cw regimes shows that femtosecond optical tweezers are just as effective as cw optical tweezers. We also demonstrate simultaneous optical tweezing and in-situ control of two-photon fluorescence (at 400nm) from dye-doped polymer microspheres. By switching the 800

B. Agate; C. T. A. Brown; W. Sibbett; K. Dholakia

2004-01-01

105

High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay.  

PubMed

We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing. PMID:19466092

Hossack, William; Theofanidou, Eirini; Crain, Jason; Heggarty, Kevin; Birch, Martin

2003-08-25

106

High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay  

NASA Astrophysics Data System (ADS)

We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing.

Hossack, William J.; Theofanidou, Eirini; Crain, Jason; Heggarty, Kevin; Birch, Martin

2003-08-01

107

Raman sorting and identification of single living micro-organisms with optical tweezers  

Microsoft Academic Search

We report on a novel technique for sorting and identification of single biological cells and food-borne bacteria based on laser tweezers and Raman spectroscopy (LTRS). With this technique, biological cells of different physiological states in a sample chamber were identified by their Raman spectral signatures and then they were selectively manipulated into a clean collection chamber with optical tweezers through

Changan Xie; De Chen; Yong-Qing Li

2005-01-01

108

Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers  

Microsoft Academic Search

A cell of the bacterium Escherichia coli was tethered covalently to a glass coverslip by a single f lagellum, and its rotation was stopped by using optical tweezers. The tweezers acted directly on the cell body or indirectly, via a trapped polystyrene bead. The torque generated by the f lagel- lar motor was determined by measuring the displacement of the

RICHARD M. BERRY; HOWARD C. BERG

1997-01-01

109

High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay  

Microsoft Academic Search

We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing.

William J. Hossack; Eirini Theofanidou; Jason Crain; Kevin Heggarty; Martin Birch

2003-01-01

110

Invited Article: A review of haptic optical tweezers for an interactive microworld exploration  

NASA Astrophysics Data System (ADS)

This paper is the first review of haptic optical tweezers, a new technique which associates force feedback teleoperation with optical tweezers. This technique allows users to explore the microworld by sensing and exerting picoNewton-scale forces with trapped microspheres. Haptic optical tweezers also allow improved dexterity of micromanipulation and micro-assembly. One of the challenges of this technique is to sense and magnify picoNewton-scale forces by a factor of 1012 to enable human operators to perceive interactions that they have never experienced before, such as adhesion phenomena, extremely low inertia, and high frequency dynamics of extremely small objects. The design of optical tweezers for high quality haptic feedback is challenging, given the requirements for very high sensitivity and dynamic stability. The concept, design process, and specification of optical tweezers reviewed here are focused on those intended for haptic teleoperation. In this paper, two new specific designs as well as the current state-of-the-art are presented. Moreover, the remaining important issues are identified for further developments. The initial results obtained are promising and demonstrate that optical tweezers have a significant potential for haptic exploration of the microworld. Haptic optical tweezers will become an invaluable tool for force feedback micromanipulation of biological samples and nano- and micro-assembly parts.

Pacoret, Cécile; Régnier, Stéphane

2013-08-01

111

Invited Article: A review of haptic optical tweezers for an interactive microworld exploration.  

PubMed

This paper is the first review of haptic optical tweezers, a new technique which associates force feedback teleoperation with optical tweezers. This technique allows users to explore the microworld by sensing and exerting picoNewton-scale forces with trapped microspheres. Haptic optical tweezers also allow improved dexterity of micromanipulation and micro-assembly. One of the challenges of this technique is to sense and magnify picoNewton-scale forces by a factor of 10(12) to enable human operators to perceive interactions that they have never experienced before, such as adhesion phenomena, extremely low inertia, and high frequency dynamics of extremely small objects. The design of optical tweezers for high quality haptic feedback is challenging, given the requirements for very high sensitivity and dynamic stability. The concept, design process, and specification of optical tweezers reviewed here are focused on those intended for haptic teleoperation. In this paper, two new specific designs as well as the current state-of-the-art are presented. Moreover, the remaining important issues are identified for further developments. The initial results obtained are promising and demonstrate that optical tweezers have a significant potential for haptic exploration of the microworld. Haptic optical tweezers will become an invaluable tool for force feedback micromanipulation of biological samples and nano- and micro-assembly parts. PMID:24007046

Pacoret, Cécile; Régnier, Stéphane

2013-08-01

112

Non-conservative forces in optical tweezers and Brownian vortexes  

NASA Astrophysics Data System (ADS)

Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static, but non-conservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle's thermally-driven trajectory is not simply a deterministic response to the solenoidal component of the force, but rather reflects an interplay between advection and diffusion in which thermal fluctuations extract work from the non-conservative force field. As an example of this previously unrecognized class of stochastic machines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that non-conservative optical forces bias the particle's fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.

Sun, Bo; Grosberg, Alexander Y.; Grier, David G.

2010-02-01

113

Probing Micromechanical Properties of Biological Cells by Oscillatory Optical Tweezers  

NASA Astrophysics Data System (ADS)

We used oscillatory optical tweezers to probe the micromechanical properties of cultured alveolar epithelial cells in vitro. The frequency-dependent viscoelasticity of these cells was measured by optical trapping and forced oscillation of either a submicron endogenous intracellular organelle (intra-cellular) or a 1.5?m silica bead attached to the cytoskeleton through trans-membrane integrin receptors (extra-cellular). Both the storage modulus and the magnitude of the complex shear modulus followed weak power-law dependence with frequency. These data are comparable to data obtained by other measurement techniques. The exponents of power-law dependence of the data from the intra- and extra- cellular measurements are similar, whereas, the differences in the magnitudes of the moluli from the two measurements are statistically significant.

Zaorski, Angela; Wei, Ming-Tzo; Yalcin, Huseyin C.; Wang, Jing; Ghadiali, Samir N.; Chiou, Arthur; Ou-Yang, H. Daniel

2008-03-01

114

Dynamic excitations in membranes induced by optical tweezers.  

PubMed Central

We present the phenomenology of transformations in lipid bilayers that are excited by laser tweezers. A variety of dynamic instabilities and shape transformations are observed, including the pearling instability, expulsion of vesicles, and more exotic ones, such as the formation of passages. Our physical picture of the laser-membrane interaction is based on the generation of tension in the bilayer and loss of surface area. Although tension is the origin of the pearling instability, it does not suffice to explain expulsion of vesicles, where we observe opening of giant pores and creeping motion of bilayers. We present a quantitative theoretical framework to understand most of the observed phenomenology. The main hypothesis is that lipid is pulled into the optical trap by the familiar dielectric effect, is disrupted, and finally is repackaged into an optically unresolvable suspension of colloidal particles. This suspension, in turn, can produce osmotic pressure and depletion forces, driving the observed transformations.

Bar-Ziv, R; Moses, E; Nelson, P

1998-01-01

115

The manipulation and assembly of CuO nanorods with line optical tweezers  

Microsoft Academic Search

We present a simple technique for manipulating and assembling one-dimensional (1D) CuO nanorods. Our technique exploits the optical trapping ability of line optical tweezers to trap, manipulate and rotate nanorods without physical contact. With this simple and versatile method, nanorods can be readily arranged into interesting configurations. The optical line tweezers could also be used to manipulate an individual nanorod

Ting Yu; Fook-Chiong Cheong; Chorng-Haur Sow

2004-01-01

116

New theoretical and experimental methods for the design of fiber optic tweezers  

NASA Astrophysics Data System (ADS)

This paper presents a study of optical forces acting on dielectric particles in media of distinct refractive index. The radiation pressure forces produced by optical tweezers are calculated using the finite difference time domain method as well as the Lorentz force on electric dipoles. The model considers a 2-dimension structure composed of a waveguide and a dielectric microparticle. Furthermore, the paper presents preliminary experimental results concerning the implementation of fiber optical tweezers system based on polymeric lensed fibers.

Rodrigues Ribeiro, R. S.; Guerreiro, A.; Ecoffet, C.; Soppera, O.; Jorge, P. A. S.

2013-05-01

117

Compact microscope-based 850-nm optical tweezers  

NASA Astrophysics Data System (ADS)

Emission from a single mode 100 mW laser diode at 850 nm is used for realizing optical tweezers: the laser beam is introduced into a microscope and focused by the objective into the object plane. Injection of the beam into a 40X microscope objective has been studied and the position and the size of the waist measured. The trap performance was studied as a function of the dimensions of the trapped particles. Trapping of polystyrene latex spheres of different size (from 0.2 micrometer to 6 micrometer) was observed in different conditions of laser power and transverse velocity of the spheres. Biological objects, Tetraselmis, of large dimension (around 10 micrometer) were also studied. We demonstrate the existence of an optimal range of size of the particles to be trapped. Furthermore we measure minimum trapping power required for trapping and the maximum speed of the trapped objects as a function of the dimensions.

Frediani, Carlo; Grego, S.; Guidoni, L.; Arimondo, Ennio

1996-01-01

118

Combined holographic-mechanical optical tweezers: Construction, optimization, and calibration  

SciTech Connect

A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45 deg., smaller angles give a full 2{pi} phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.

Hanes, Richard D. L.; Jenkins, Matthew C.; Egelhaaf, Stefan U. [Condensed Matter Physics Laboratory, Heinrich-Heine University, 40225 Duesseldorf (Germany)

2009-08-15

119

Interrogating biology with force: single molecule high-resolution measurements with optical tweezers.  

PubMed

Single molecule force spectroscopy methods, such as optical and magnetic tweezers and atomic force microscopy, have opened up the possibility to study biological processes regulated by force, dynamics of structural conformations of proteins and nucleic acids, and load-dependent kinetics of molecular interactions. Among the various tools available today, optical tweezers have recently seen great progress in terms of spatial resolution, which now allows the measurement of atomic-scale conformational changes, and temporal resolution, which has reached the limit of the microsecond-scale relaxation times of biological molecules bound to a force probe. Here, we review different strategies and experimental configurations recently developed to apply and measure force using optical tweezers. We present the latest progress that has pushed optical tweezers' spatial and temporal resolution down to today's values, discussing the experimental variables and constraints that are influencing measurement resolution and how these can be optimized depending on the biological molecule under study. PMID:24047980

Capitanio, Marco; Pavone, Francesco S

2013-09-17

120

Optical tweezers with multiple optical forces using double-hologram interference  

Microsoft Academic Search

In earlier work, we introduced new ways of generating a series of interference patterns formed from Laguerre Gaussian (LG) beams, which are being used as advanced optical tweezers in creating and manipulating three-dimensional structures. In this work, we have succeeded in demonstrating, for the first time to our knowledge, double LG and LG beams with a Gaussian-beam interference using a

Woei Ming Lee; X.-C. Yuan; D. Y. Tang

2003-01-01

121

Chromosomal analysis and identification based on optical tweezers and Raman spectroscopy: comment  

NASA Astrophysics Data System (ADS)

The authors of the work: ‘Chromosomal analysis and identification based on optical tweezers and raman spectroscopy’ [Opt. Express 14, 5385 (2006], claim that they have been able to identify and differentiate between three human chromosomes with an optical-tweezer Raman Spectroscopic experimental (LTRS) set-up. The results and conclusions as they are presented in the paper are questionable, however, when the spectral data and data analysis are studied in greater detail.

Bak, Jimmy; Jørgensen, Thomas M.

2007-05-01

122

Robust control approach to force estimation in a constant position optical tweezers  

NASA Astrophysics Data System (ADS)

Feedback enhanced optical tweezers with position regulation capability enable detection and estimation of forces in the pico-Newton regime. In this article we delineate the fundamental limitations and challenges of existing approaches for regulating position and force estimation in an optical tweezer. A modern control systems approach is shown to improve the bandwidth of force estimation by three to four times which is corroborated experimentally.

Aggarwal, Tanuj; Sehgal, Hullas; Salapaka, Murti

2011-11-01

123

Measurement of interaction forces between red blood cells in aggregates by optical tweezers  

NASA Astrophysics Data System (ADS)

We have fabricated double-beam optical tweezers and demonstrated the possibility of their use for measuring the interaction forces between red blood cells (erythrocytes). It has been established experimentally that prolonged trapping of red blood cells in a tightly focused laser beam does not cause any visible changes in their shape or size. We have measured the interaction between red blood cells in the aggregate, deformed by optical tweezers.

Maklygin, A. Yu; Priezzhev, A. V.; Karmenian, A.; Nikitin, Sergei Yu; Obolenskii, I. S.; Lugovtsov, Andrei E.; Li, Kisun

2012-06-01

124

Directing growth cones of optic axons growing with laser scissors and laser tweezers  

NASA Astrophysics Data System (ADS)

We have combined a laser scissors and a laser tweezers to study, (1) the response of nerve fiber growth cones to laser-induced damage on single axons, and (2) localized microfluidic flow generated by laser-driven spinning birefringent particles. In the laser scissors study, sub-axotomy damage elicits a growth cone response whether damage is on the same or an adjacent axon. In laser tweezers study, the axon growth cones turn in response to the optically driven microfluidic flow. In summary, both the laser scissors and the laser tweezers studies elicit growth cone turning responses.o

Wu, Tao; Nieminen, Timo A.; Mohanty, Samarendra; Miotke, Jill; Meyer, Ronald L.; Rubinsztein-Dunlop, Halina; Berns, Michael W.

2012-10-01

125

Fiber-pigtailed optical tweezer for single-atom trapping and single-photon generation  

NASA Astrophysics Data System (ADS)

We demonstrate a miniature, fiber-coupled optical tweezer to trap a single atom. The same fiber is used to trap a single atom and to read out its fluorescence. To obtain a low background level, the tweezer light is chopped, and we measure the influence of the chopping frequency on the atom's lifetime. We use the single atom as a single-photon source at 780 nm and measure the second-order correlation function of the emitted photons. Because of its miniature, robust, fiber-pigtailed design, this tweezer can be implemented in a broad range of experiments where single atoms are used as a resource.

Garcia, S.; Maxein, D.; Hohmann, L.; Reichel, J.; Long, R.

2013-09-01

126

Extending a release-and-recapture scheme to single atom optical tweezer for effective temperature evaluation  

NASA Astrophysics Data System (ADS)

By recording the fluorescence fraction of the cold atoms remaining in the magneto-optical trap (MOT) as a function of the release time, the release-and-recapture (R&R) method is utilized to evaluate the effective temperature of the cold atomic ensemble. We prepare a single atom in a large-magnetic-gradient MOT and then transfer the trapped single atom into a 1064-nm microscopic optical tweezer. The energy of the single atom trapped in the tweezer is further reduced by polarization gradient cooling (PGC) and the effective temperature is evaluated by extending the R&R technique to a single atom tweezer. The typical effective temperature of a single atom in the tweezer is improved from about 105 ?K to about 17 ?K by applying the optimum PGC phase.

He, Jun; Yang, Bao-Dong; Zhang, Tian-Cai; Wang, Jun-Min

2011-07-01

127

Particle interaction measurements using laser tweezers optical trapping.  

SciTech Connect

Laser tweezers optical trapping provides a unique noninvasive capability to trap and manipulate particles in solution at the focal point of a laser beam passed through a microscope objective. Additionally, combined with image analysis, interaction forces between colloidal particles can be quantitatively measured. By looking at the displacement of particles within the laser trap due to the presence of a neighboring particle or looking at the relative diffusion of two particles held near each other by optical traps, interparticle interaction forces ranging from pico- to femto-Newtons can be measured. Understanding interaction forces is critical for predicting the behavior of particle dispersions including dispersion stability and flow rheology. Using a new analysis method proposed by Sainis, Germain, and Dufresne, we can simultaneously calculate the interparticle velocity and particle diffusivity which allows direct calculation of the interparticle potential for the particles. By applying this versatile tool, we measure difference in interactions between various phospholipid bilayers that have been coated onto silica spheres as a new type of solid supported liposome. We measure bilayer interactions of several cell membrane lipids under various environmental conditions such as pH and ionic strength and compare the results with those obtained for empty liposomes. These results provide insight into the role of bilayer fluctuations in liposome fusion, which is of fundamental interest to liposome based drug delivery schemes.

Koehler, Timothy P.; Brinker, C. Jeffrey; Brotherton, Christopher M.; Grillet, Anne M.; Molecke, Ryan A. (University of New Mexico, Albuquerque, NM)

2008-08-01

128

Manipulation of Suspended Single Cells by Microfluidics and Optical Tweezers  

PubMed Central

Chondrocytes and osteoblasts experience multiple stresses in vivo. The optimum mechanical conditions for cell health are not fully understood. This paper describes the optical and microfluidic mechanical manipulation of single suspended cells enabled by the ?PIVOT, an integrated micron resolution particle image velocimeter (?PIV) and dual optical tweezers instrument (OT). In this study, we examine the viability and trap stiffness of cartilage cells, identify the maximum fluid-induced stresses possible in uniform and extensional flows, and compare the deformation characteristics of bone and muscle cells. These results indicate cell photodamage of chondrocytes is negligible for at least 20 min for laser powers below 30 mW, a dead cell presents less resistance to internal organelle rearrangement and deforms globally more than a viable cell, the maximum fluid-induced shear stresses are limited to ~15 mPa for uniform flows but may exceed 1 Pa for extensional flows, and osteoblasts show no deformation for shear stresses up to 250 mPa while myoblasts are more easily deformed and exhibit a modulated response to increasing stress. This suggests that global and/or local stresses can be applied to single cells without physical contact. Coupled with microfluidic sensors, these manipulations may provide unique methods to explore single cell biomechanics.

Neve, Nathalie; Kohles, Sean S.; Winn, Shelley R.; Tretheway, Derek C.

2010-01-01

129

Optical trapping of a spherically symmetric sphere in the ray-optics regime: a model for optical tweezers upon cells  

SciTech Connect

Since their invention in 1986, optical tweezers have become a popular manipulation and force measurement tool in cellular and molecular biology. However, until recently there has not been a sophisticated model for optical tweezers on trapping cells in the ray-optics regime. We present a model for optical tweezers to calculate the optical force upon a spherically symmetric multilayer sphere representing a common biological cell. A numerical simulation of this model shows that not only is the magnitude of the optical force upon a Chinese hamster ovary cell significantly three times smaller than that upon a polystyrene bead of the same size, but the distribution of the optical force upon a cell is also much different from that upon a uniform particle, and there is a 30% difference in the optical trapping stiffness of these two cases. Furthermore, under a small variant condition for the refractive indices of any adjacent layers of the sphere, this model provides a simple approximation to calculate the optical force and the stiffness of an optical tweezers system.

Chang Yiren; Hsu Long; Chi Sien

2006-06-01

130

Dynamic Simulation of Trapping and Controlled Rotation of a Microscale Rod Driven by Line Optical Tweezers  

NASA Astrophysics Data System (ADS)

Since the invention of optical tweezers, several biological and engineering applications, especially in micro-nanofluid, have been developed. For example, development of optically driven micromotors, which has an important role in microfluidic applications, has vastly been considered. Despite extensive experimental studies in this field, there is a lack of theoretical work that can verify and analyze these observations. This work develops a dynamic model to simulate trapping and controlled rotation of a microscale rod under influence of the optical trapping forces. The laser beam, used in line optical tweezers with a varying trap's length, was modeled based on a ray-optics approach. Herein, the effects of viscosity of the surrounding fluid (water), gravity, and buoyancy were included in the proposed model. The predicted results are in overall agreement with the experimental observation, which make the theoretical model be a viable tool for investigating the dynamic behavior of small size objects manipulated by optical tweezers in fluid environments.

Haghshenas-Jaryani, Mahdi; Bowling, Alan; Mohanty, Samarendra

2013-03-01

131

Fiber optical tweezers for microscale and nanoscale particle manipulation and force sensing  

NASA Astrophysics Data System (ADS)

Optical tweezers have been an important tool in biology and physics for studying single molecules and colloidal systems. Most of current optical tweezers are built with microscope objectives, which are: i) expensive, ii) bulky and hard to integrate, iii) sensitive to environmental fluctuations, iv) limited in terms of working distances from the substrate, and v) rigid with the requirements on the substrate (transparent substrate made with glass and with a fixed thickness). These limitations of objective-based optical tweezers prevent them from being miniaturized. Fiber optical tweezers can provide a solution for cost reduction and miniaturization, and these optical tweezers can be potentially used in microfluidic systems. However, the existing fiber optical tweezers have the following limitations: i) low trapping efficiency due to weakly focused beams, ii) lack of the ability to control the positions of multiple particles simultaneously, and iii) limited functionalities. The overall objective of this dissertation work is to further the fundamental understanding of fiber optical tweezers through experimental study and modeling, and to develop novel fiber optical tweezers systems to enhance the capability and functionalities of fiber optical tweezers as microscale and nanoscale manipulators/sensors. The contributions of this dissertation work are summarized as follows. i) An enhanced understanding of the inclined dual-fiber optical tweezers (DFOTs) system has been achieved. Stable three dimensional (3D) optical trapping of a single micron-sized particle has been experimentally demonstrated. This is the first time that the trapping efficiency has been calibrated and the stiffness of the trap has been obtained in the experiments, which has been carried out by using two methods: the drag force method and power spectrum analysis. Such calibration enables the system to be used as a picoNewton-level force sensor in addition to a particle manipulator. The influence of system parameters on the trapping performance has been carefully investigated through both experimental and numerical studies. ii) Multiple traps have been created and carefully studied with the inclined DFOTs for the first time. Three traps, one 3D trap and two 2D traps, have been experimentally created at different vertical levels with adjustable separations and positions. iii) Multiple functionalities have been achieved and studied for the first time with the inclined DFOTs. Particle separation, grouping, stacking, rod alignment, rod rotation, and optical binding have been experimentally demonstrated. The multiple functionalities allow the inclined DFOTs to find applications in the study of interaction forces in colloidal systems as well as parallel particle manipulation in drug delivery systems. iv) Far-field superfocusing effect has been investigated and successfully demonstrated with a fiber-based surface plasmonic (SP) lens for the first time. A planar SP lens with a set of concentric nanoscale rings on a fiber endface has been developed. For the first time, a focus size that is comparable to the smallest achievable focus size of high NA objective lenses has been achieved with the fiber-based SP lens. The fiber-based SP lens can bridge the nanoscale particles/systems and the macroscale power sources/detectors, which has been a long standing challenge for nanophotonics. In addition to optical trapping, the fiber-based SP lens will impact many applications including high-resolution lithography, high-resolution fluorescence detection, and sub-wavelength imaging. v) Trapping ability enhanced with the fiber-based SP lens has been successfully demonstrated. With the help of the fiber-based SP lens, the trapping efficiency of fiber optical tweezers has been significantly enhanced, which is comparable with that of objective-based optical tweezers. A submicron-sized bacterium has been successfully trapped in three dimensions for the first time with optical tweezers based on single fibers.

Liu, Yuxiang

132

Mapping force of interaction between PLGA nanoparticle with cell membrane using optical tweezers  

NASA Astrophysics Data System (ADS)

Drug delivery using magnetic (Fe3O4) Poly Lactic-co-Glycolic Acid (PLGA) nanoparticles is finding increasing usage in therapeutic applications due to its biodegradability, biocompatibility and targeted localization. Since optical tweezers allow non-contact, highly sensitive force measurement, we utilized optical tweezers for studying interaction forces between the Fe3O4-PLGA nanoparticles with prostate cancer PC3 cells. Presence of Fe3O4 within the PLGA shell allowed efficient trapping of these nanoparticles in near-IR optical tweezers. The conglomerated PLGA nanoparticles could be dispersed by use of the optical tweezers. Calibration of trapping stiffness as a function of laser beam power was carried out using equipartition theorem method, where the mean square displacement was measured with high precision using time-lapse fluorescence imaging of the nanoparticles. After the trapped PLGA nanoparticle was brought in close vicinity of the PC3 cell membrane, displacement of the nanoparticle from trap center was measured as a function of time. In short time scale (< 30sec), while the force of interaction was within 0.2 pN, the force increased beyond 1pN at longer time scales (˜ 10 min). We will present the results of the time-varying force of interactions between PLGA nanoparticles with PC3 cells using optical tweezers.

Chhajed, Suyash; Gu, Ling; Homayoni, Homa; Nguyen, Kytai; Mohanty, Samarendra

2011-03-01

133

Silicon photonics for functional on-chip optical tweezers devices and circuits  

NASA Astrophysics Data System (ADS)

Silicon photonics using waveguide- and microresonator-based devices are finding technologically important applications in the field of optofluidics. By integrating microfluidic channels on top of silicon-based planar devices, silicon photonic devices can function as on-chip optical tweezers to manipulate micro/nanoparticles. In this paper, we will highlight our recent progress in the field of optofluidics using silicon nitride devices for on-chip optical manipulation including the experimental demonstrations of: (i) planar optical tweezers using waveguide junctions with and without tapers, (ii) microparticle buffering and dropping on microring resonator devices upon linearly polarized light and (iii) microparticle trapping and assembling on circular microdisk resonators. Such devices can function as basic building blocks for "optical tweezers circuits" in lab-on-chip applications.

Cai, Hong; Wang, Jiawei; Poon, Andrew W.

2013-02-01

134

A computational tool to characterize particle tracking measurements in optical tweezers  

NASA Astrophysics Data System (ADS)

Here, we present a computational tool for optical tweezers which calculates the particle tracking signal measured with a quadrant detector and the shot-noise limit to position resolution. The tool is a piece of Matlab code which functions within the freely available Optical Tweezers Toolbox. It allows the measurements performed in most optical tweezer experiments to be theoretically characterized in a fast and easy manner. The code supports particles with arbitrary size, any optical fields and any combination of objective and condenser, and performs a full vector calculation of the relevant fields. Example calculations are presented which show the tracking signals for different particles, and the shot-noise limit to position sensitivity as a function of the effective condenser NA.

Taylor, Michael A.; Bowen, Warwick P.

2013-08-01

135

Investigating intermolecular forces associated with thrombus initiation using optical tweezers  

NASA Astrophysics Data System (ADS)

Thrombus formation occurs when a platelet membrane receptor, glycoprotein (GP) Ib-IX-V complex, binds to its ligand, von Willebrand factor (vWf), in the subendothelium or plasma. To determine which GP Ib-IX-V amino acid sequences are critical for bond formation, we have used optical tweezers to measure forces involved in the binding of vWf to GP Ib-IX-V variants. Inasmuch as GP Ib(alpha) subunit is the primary component in human GP Ib-IX-V complex that binds to vWf, and that canine GP Ib(alpha) , on the other hand, does not bind to human vWf, we progressively replaced human GP Ib(alpha) amino acid sequences with canine GP Ib(alpha) sequences to determine the sequences essential for vWf/GP Ib(alpha) binding. After measuring the adhesive forces between optically trapped, vWf-coated beads and GP Ib(alpha) variants expressed on mammalian cells, we determined that leucine- rich repeat 2 of GP Ib(alpha) was necessary for vWf/GP Ib-IX- V bond formation. We also found that deletion of the N- terminal flanking sequence and leucine-rich repeat 1 reduced adhesion strength to vWf but did not abolish binding. While divalent cations are known to influence binding of vWf, addition of 1mM CaCl2 had no effect on measured vWf/GP Ib(alpha) bond strengths.

Arya, Maneesh; Lopez, Jose A.; Romo, Gabriel M.; Dong, Jing-Fei; McIntire, Larry V.; Moake, Joel L.; Anvari, Bahman

2002-05-01

136

Rate of growth pattern of yeast cells studied under optical tweezers  

NASA Astrophysics Data System (ADS)

Cell growth and division has been of scientists' interest for over generations. Several mathematical models have been reported derived from conventional method of cell culture. Here we applied optical tweezers to guide cell division directionally. The patterns of Saccharonmyces bayanus yeast growth was studied under 1064 nm line optical tweezers generated by time-shared multiple optical traps. Yeast growth was found following the path of the generated laser patterns in linear, circular, square and L shapes, speculatively as a result of localized heating effect due to absorption at the focal point.

Charrunchon, Sookpichaya; Limtrakul, Jumras; Chattham, Nattaporn

2013-06-01

137

Graded-index fiber tip optical tweezers: numerical simulation and trapping experiment.  

PubMed

Optical fiber tweezers based on a graded-index multimode fiber (GIMMF) tip is proposed. Light propagation characteristics and gradient force distribution near the GIMMF tip are numerically investigated, which are further compared with that of optical fiber tips based on conventional single mode fibers. The simulated results indicated that by selecting optimal GIMMF length, the gradient force of the GIMMF tip tweezers is about 4 times higher than that of the SMF tip tweezers with a same shape. To prove the feasibility of such a new concept, optical trapping of yeast cells with a diameter of ~5 ?m using the chemically-etched GIMMF tip is experimentally demonstrated and the trapping force is also calculated. PMID:23842403

Gong, Yuan; Ye, Ai-Yan; Wu, Yu; Rao, Yun-Jiang; Yao, Yao; Xiao, Song

2013-07-01

138

Tapered fiber optical tweezers for microscopic particle trapping: fabrication and application  

Microsoft Academic Search

A novel single tapered fiber optical tweezers is proposed and fabricated by heating and drawing technology. The microscopic particle tapping performance of this special designed tapered fiber probe is demonstrated and investigated. The distribution of the optical field emerging from the tapered fiber tip is numerically calculated based on the beam propagation method. The trapping force FDTD analysis results, both

Zhihai Liu; Chengkai Guo; Jun Yang; Libo Yuan

2006-01-01

139

Mechanical properties of stored red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

We have developed a method for measuring the red blood cell (RBC) membrane overall elasticity ? by measuring the deformation of the cells when dragged at a constant velocity through a plasma fluid by an optical tweezers. The deformability of erythrocytes is a critical determinant of blood flow in the microcirculation. We tested our method and hydrodynamic models, which included the presence of two walls, by measuring the RBC deformation as a function of drag velocity and of the distance to the walls. The capability and sensitivity of this method can be evaluated by its application to a variety of studies, such as, the measurement of RBC elasticity of sickle cell anemia patients comparing homozygous (HbSS), including patients taking hydroxyrea (HU) and heterozygous (HbAS) with normal donors and the RBC elasticity measurement of gamma irradiated stored blood for transfusion to immunosupressed patients as a function of time and dose. These studies show that the technique has the sensitivity to discriminate heterozygous and homozygous sickle cell anemia patients from normal donors and even follow the course of HU treatment of Homozygous patients. The gamma irradiation studies show that there is no significant change in RBC elasticity over time for up to 14 days of storage, regardless of whether the unit was irradiated or not, but there was a huge change in the measured elasticity for the RBC units stored for more than 21 days after irradiation. These finds are important for the assessment of stored irradiated RBC viability for transfusion purposes because the present protocol consider 28 storage days after irradiation as the limit for the RBC usage.

Fontes, Adriana; Alexandre de Thomaz, Andre; de Ysasa Pozzo, Liliana; de Lourdes Barjas-Castro, Maria; Brandao, Marcelo M.; Saad, Sara T. O.; Barbosa, Luiz Carlos; Cesar, Carlos Lenz

2005-08-01

140

Red blood cell micromanipulation with elliptical laser beam profile optical tweezers in different osmolarity conditions  

NASA Astrophysics Data System (ADS)

In this work optical tweezers with elliptical beam profiles have been developed in order to examine the effect of optical force on fresh red blood cells (RBC) in isotonic, hypertonic and hypotonic buffer solutions. Considering that the optical force depends essentially on the cell surface and the cytoplasmic refractive index, it is obvious that biochemical modifications associated with different states of the cell will influence its behaviour in the optical trap. Line optical tweezers were used to manipulate simultaneously more than one red blood cell. After we have been manipulated a RBC with an elliptical laser beam profile in an isotonic or hypertonic buffer, we noticed that it rotates by itself when gets trapped by optical tweezers and undergoes folding. Further shape deformations can be observed attributed to the competition between alignment and rotational torque which are transferred by laser light to the cell. In hypotonic buffer RBCs become spherical and do not rotate or fold since the resultant force due to rays emerging from diametrically opposite points of the cell leads to zero torque. Manipulation of fresh red blood cells in isotonic solution by line optical tweezers leads to folding and elongation of trapped RBCs. Membrane elasticity properties such as bending modulus can be estimated by measuring RBC's folding time in function with laser power.

Spyratou, E.; Makropoulou, M.; Serafetinides, A. A.

2011-06-01

141

Mechanical and electrical properties of red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are a very sensitive tool, based on photon momentum transfer, for individual, cell by cell, manipulation and measurements, which can be applied to obtain important properties of erythrocytes for clinical and research purposes. Mechanical and electrical properties of erythrocytes are critical parameters for stored cells in transfusion centers, immunohematological tests performed in transfusional routines and in blood diseases. In this work, we showed methods, based on optical tweezers, to study red blood cells and applied them to measure apparent overall elasticity, apparent membrane viscosity, zeta potential, thickness of the double layer of electrical charges and adhesion in red blood cells.

Fontes, A.; Barjas Castro, M. L.; Brandão, M. M.; Fernandes, H. P.; Thomaz, A. A.; Huruta, R. R.; Pozzo, L. Y.; Barbosa, L. C.; Costa, F. F.; Saad, S. T. O.; Cesar, C. L.

2011-04-01

142

On-site manipulation of single whole-genome DNA molecules using optical tweezers  

NASA Astrophysics Data System (ADS)

In this letter, we describe a noninvasive methodology for manipulating single Mb-size whole-genome DNA molecules. Cells were subjected to osmotic shock and the genome DNA released from the burst cells was transferred to a region of higher salt concentration using optical tweezers. The transferred genome DNA exhibits a conformational transition from a compact state into an elongated state, accompanied by the change in its environment. The applicability of optical tweezers to the on-site manipulation of giant genome DNA is suggested, i.e., lab-on-a-plate.

Oana, Hidehiro; Kubo, Koji; Yoshikawa, Kenichi; Atomi, Haruyuki; Imanaka, Tadayuki

2004-11-01

143

Applications of optical tweezers and an integrated force measurement module for biomedical research  

NASA Astrophysics Data System (ADS)

Optical tweezers are useful for manipulating biological samples and measuring biological forces. In the present study, we have integrated a forward scatter analysis (FORSA) module in the single-beam gradient force optical tweezers. The entire set-up was then incorporated onto an inverted microscope. In the FORSA module an Helium-Neon probing laser was spotted (at a slightly out-of-focus way) onto the object being trapped by the infrared laser-based tweezers and generated a diffraction pattern. Imagines of the diffraction pattern were captured by a charge- coupled device (CCD), and digitized and processed by a computer. Wed demonstrated that tracking the amplified diffraction pattern war much more precise to determine the movement of the object within the trap than analyzing the minute motion of the object itself. Displacement of the object could then be translated into the force being applied by the tweezers. Also, using an algorithm developed in the lab, we were able to follow the movement of the scattering pattern at a temporal resolution close to video rate. We have used this system to investigate the binding force associate with cell-cell interactions and modular interactions. In these studies. A cell was carefully positioned to make contact with another cell or a microparticle coated with proteins of interest by optical tweezers in a well-controlled manner. During these events, we noted a progressive increase of cell adhesion at the immediate early period (i.e., a few minutes after initial contact) of cell-cell interactions. Also, binding of a disintegrin, rhodostomin, and its mutant to the counterpart integrin on the cell surface could be assessed with great convenience and accuracy. Our results demonstrated that addition of the forward scatter analysis module to convention optical tweezers provides an effective and convenient way for monitoring biological activities in situ and measuring changes of biological forces with precision.

Tsai, Jin-Wu; Liao, Bing-Yao; Huang, Chun-Cheng; Hwang, Wen-Liang; Wang, Da-Wei; Chiou, Arthur E.; Lin, Chi-Hung

2000-07-01

144

Analysis of optical trap mediated aerosol coalescence  

NASA Astrophysics Data System (ADS)

The use of optical tweezers for the analysis of aerosols is valuable for understanding the dynamics of atmospherically relevant particles. However to be able to make accurate measurements that can be directly tied to real-world phenomena it is important that we understand the influence of the optical trap on those processes. One process that is seemingly straightforward to study with these techniques is binary droplet coalescence, either using dual beam traps, or by particle collision with a single trapped droplet. This binary coalescence is also of interest in many other processes that make use of dense aerosol sprays such as spray drying and the use of inhalers for drug delivery in conditions such as asthma or hay fever. In this presentation we discuss the use of high speed (~5000 frames per second) video microscopy to track the dynamics of particles as they approach and interact with a trapped aqueous droplet and develop this analysis further by considering elastic light scattering from droplets as they undergo coalescence. We find that we are able to characterize the re-equilibration time of droplets of the same phase after they interact and that the trajectories taken by airborne particles influenced by an optical trap are often quite complex. We also examine the role of parameters such as the salt concentration of the aqueous solutions used and the influence of laser wavelength.

Mistry, N. S.; Power, R.; Anand, S.; McGloin, D.; Almohamedi, A.; Downie, M.; Reid, J. P.; Hudson, A. J.

2012-10-01

145

Construction of a cost effective optical tweezers for manipulation of birefringent materials using circularly polarized light  

Microsoft Academic Search

Light manipulation is a very powerful tool in physics, biology, and chemistry. There are several physical principles underlying the apparatus known as the ``optical tweezers,'' the term given to using focused light to manipulate and control small objects. By carefully controlling the orientation and position of a focused laser beam, dielectric particles can be effectively trapped and manipulated. We have

Allison McMahon; Toni Sauncy

2008-01-01

146

Physical Properties of Escherichia coli P Pili Measured by Optical Tweezers  

Microsoft Academic Search

The mechanical behavior of individual P pili of uropathogenic Escherichia coli has been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ?103 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. They are particularly important in the pathogenesis of E. coli colonizing the upper

Jana Jass; Staffan Schedin; Erik Fällman; Jörgen Ohlsson; Ulf J. Nilsson; Bernt Eric Uhlin; Ove Axner

2004-01-01

147

Nonlinear Elastic and Viscoelastic Deformation of the Human Red Blood Cell with Optical Tweezers  

Microsoft Academic Search

Studies of the deformation characteristics of single biological cells can offer insights into the connec- tions among mechanical state, biochemical response and the onset and progression of diseases. Deformation im- posed by optical tweezers provides a useful means for the study of single cell mechanics under a variety of well-controlled stress-states. In this paper, we first crit- ically review recent

J. P. Mills; L. Qie; M. Dao; C. T. Lim; S. Suresh

2004-01-01

148

Mechanics of the human red blood cell deformed by optical tweezers  

Microsoft Academic Search

The mechanical deformation characteristics of living cells are known to influence strongly their chemical and biological functions and the onset, progression and consequences of a number of human diseases. The mechanics of the human red blood cell (erythrocyte) subjected to large deformation by optical tweezers forms the subject of this paper. Video photography of the cell deformed in a phosphate

M. Dao; C. T. Lim; S. Suresh

2003-01-01

149

Elasticity of the Red Cell Membrane and Its Relation to Hemolytic Disorders: An Optical Tweezers Study  

Microsoft Academic Search

We have used optical tweezers to study the elasticity of red cell membranes; force was applied to a bead attached to a permeabilized spherical ghost and the force-extension relation was obtained from the response of a second bead bound at a diametrically opposite position. Interruption of the skeletal network by dissociation of spectrin tetramers or extraction of the actin junctions

John Sleep; David Wilson; Robert Simmons; Walter Gratzer

1999-01-01

150

Distinct Membrane Mechanical Properties of Human Mesenchymal Stem Cells Determined Using Laser Optical Tweezers  

Microsoft Academic Search

The therapeutic efficacy of mesenchymal stem cells (MSCs) in tissue engineering and regenerative medicine is determined by their unique biological, mechanical, and physicochemical characteristics, which are yet to be fully explored. Cell membrane mechanics, for example, has been shown to critically influence MSC differentiation. In this study, we used laser optical tweezers to measure the membrane mechanics of human MSCs

Igor Titushkin; Michael Cho

2006-01-01

151

Optical tweezers with fluorescence detection for temperature-dependent microrheological measurements  

NASA Astrophysics Data System (ADS)

We introduce a setup of optical tweezers, capable of carrying out temperature-dependent rheological measurements of soft materials. In our setup, the particle displacement is detected by imaging a bright spot due to fluorescence emitted from a dye-labeled particle against a dark background onto a quadrant photodiode. This setup has a relatively wide space around the sample that allows us to further accessorize the optical tweezers by a temperature control unit. The applicability of the setup was examined on the basis of the rheological measurements using a typical viscoelastic system, namely a worm-like micelle solution. The temperature and frequency dependences of the local viscoelastic functions of the worm-like micelle solution obtained by this setup were in good accordance with those obtained by a conventional oscillatory rheometer, confirming the capability of the optical tweezers as a tool for the local rheological measurements of soft materials. Since the optical tweezers measurements only require a tiny amount of sample (~40 ?L), the rheological measurements using our setup should be useful for soft materials of which the available amount is limited.

Shundo, Atsuomi; Hori, Koichiro; Penaloza, David P.; Tanaka, Keiji

2013-01-01

152

Micromanipulation of statoliths in gravity-sensing Chara rhizoids by optical tweezers  

Microsoft Academic Search

Infrared laser traps (optical tweezers) were used to micromanipulate statoliths in gravity-sensing rhizoids of the green alga Chara vulgaris Vail. We were able to hold and move statoliths with high accuracy and to observe directly the effects of statolith position on cell growth in horizontally positioned rhizoids. The first step in gravitropism, namely the physical action of gravity on statoliths,

G. Leitz; E. Schnepf; K. O. Greulich

1995-01-01

153

Optical tweezers study of viscoelastic properties in the outer hair cell plasma membrane  

Microsoft Academic Search

An optical tweezers system was used to study the mechanical characteristics of the outer hair cell (OHC) lateral wall by forming plasma membrane tethers. A 2nd order generalized Kelvin model was applied to describe the viscoelastic behavior of OHC membrane tethers. The measured parameters included equilibrium tethering force, (Feq), force relaxation times (tau), stiffness values (kappa), and coefficients of friction

David R. Murdock; Sergey A. Ermilov; Feng Qian; William E. Brownell; Bahman Anvari

2004-01-01

154

High-resolution, long-term characterization of bacterial motility using optical tweezers  

Microsoft Academic Search

We present a single-cell motility assay, which allows the quantification of bacterial swimming in a well-controlled environment, for durations of up to an hour and with a temporal resolution greater than the flagellar rotation rates of ?100 Hz. The assay is based on an instrument combining optical tweezers, light and fluorescence microscopy, and a microfluidic chamber. Using this device we

Taejin L Min; Patrick J Mears; Lon M Chubiz; Christopher V Rao; Yann R Chemla; Ido Golding

2009-01-01

155

Mechanical characterization of human red blood cells by robotic manipulation with optical tweezers  

Microsoft Academic Search

Human red blood cells (RBCs) are responsible to transport oxygen and carbon dioxide for human bodies. The physiological functions of RBCs are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. In this paper, to understand the correlation between the cell properties and their osmotic environments, robotic manipulation technology with optical tweezers is

Youhua Tan; Dong Sun; Wenhao Huang; Hanxiong Li

2009-01-01

156

Thermodynamic DNA Looping by a Two-Site Restriction Endonuclease Studied using Optical Tweezers  

Microsoft Academic Search

Many enzyme-DNA interactions involve multimeric protein complexes that bind at two distant sites such that the DNA is looped. An example is the type IIe restriction enzyme Sau3AI, which requires two recognition sites to cleave the DNA. Here we study this process at the single DNA level using force measuring optical tweezers. We characterize cleavage rates of single DNA molecules

Gregory J. Gemmen

2005-01-01

157

Holographic optical tweezers obtained by using the three-dimensional Gerchberg-Saxton algorithm  

NASA Astrophysics Data System (ADS)

An extension of the Gerchberg-Saxton algorithm from two dimensions to three is used to configure a continuous optical trap geometry. Intensity tailoring in a continuous, three-dimensional (3D) volume rather than in multiple discrete two-dimensional planes yields flexible 3D holographic optical tweezers. A numerical simulation and optical demonstrations of continuous 3D beam shaping and particle trapping confirm the capabilities of the method.

Chen, Hao; Guo, Yunfeng; Chen, Zhaozhong; Hao, Jingjing; Xu, Ji; Wang, Hui-Tian; Ding, Jianping

2013-03-01

158

RBCs under optical tweezers as cellular motors and rockers: microfluidic applications  

NASA Astrophysics Data System (ADS)

Recently, we have reported self-rotation of normal red blood cells (RBC), suspended in hypertonic buffer, and trapped in unpolarized laser tweezers. Here, we report use of such an optically driven RBC-motor for microfluidic applications such as pumping/centrifugation of fluids. Since the speed of rotation of the RBC-motor was found to vary with the power of the trapping beam, the flow rate could be controlled by controlling the laser power. In polarized optical tweezers, preferential alignment of trapped RBC was observed. The aligned RBC (simulating a disk) in isotonic buffer, could be rotated in a controlled manner for use as a microfluidic valve by rotation of the plane of polarization of the trapping beam. The thickness of the discotic RBC could be changed by changing the osmolarity of the solution and thus the alignment torque on the RBC due to the polarization of the trapping beam could be varied. Further, in polarized tweezers, the RBCs in hypertonic buffer showed rocking motion while being in rotation. Here, the RBC rotated over a finite angular range, stopped for some time at a particular angle, and then started rotating till it was back to the aligned position and this cycle was found repetitive. This can be attributed to the fact that though the RBCs were found to experience an alignment torque to align with plane of polarization of the tweezers due to its form birefringence, it was smaller in magnitude as compared to the rotational torque due to its structural asymmetry in hypertonic solution. Changes in the laser power caused a transition from/to rocking to/from motor behavior of the RBC in a linearly polarized tweezers. By changing the direction of polarization caused by rotation of an external half wave plate, the stopping angle of rocking could be changed. Further, RBCs suspended in intermediate hypertonic buffer and trapped with polarized tweezers showed fluttering about the vertical plane.

Mohanty, Samarendra; Mohanty, Khyati; Gupta, Pradeep

2006-09-01

159

Flexible particle manipulation techniques with conical refraction-based optical tweezers  

NASA Astrophysics Data System (ADS)

We present an optimized optical tweezers system based upon the conical refraction of circularly polarized light in a biaxial crystal. The described optical arrangement avoids distortions to the Lloyd plane rings that become apparent when working with circularly polarized light in conventional optical tweezers. We demonstrate that the intensity distribution of the conically diffracted light permits optical manipulation of high and low refractive index particles simultaneously. Such trapping is in three dimensions and not limited to the Lloyd plane rings. By removal of a quarter waveplate the system also permits the study of linearly polarized conical refraction. We show that particle position in the Raman plane is determined by beam power, and indicates that true optical tweezing is not taking place in this part of the beam.

McDougall, C.; Henderson, Robert; Carnegie, David J.; Sokolovskii, Grigorii S.; Rafailov, Edik U.; McGloin, David

2012-10-01

160

Refractive multiple optical tweezers for parallel biochemical analysis in micro-fluidics  

NASA Astrophysics Data System (ADS)

We present a multiple laser tweezers system based on refractive optics. The system produces an array of 100 optical traps thanks to a refractive microlens array, whose focal plane is imaged into the focal plane of a high-NA microscope objective. This refractive multi-tweezers system is combined to micro-fluidics, aiming at performing simultaneous biochemical reactions on ensembles of free floating objects. Micro-fluidics allows both transporting the particles to the trapping area, and conveying biochemical reagents to the trapped particles. Parallel trapping in micro-fluidics is achieved with polystyrene beads as well as with native vesicles produced from mammalian cells. The traps can hold objects against fluid flows exceeding 100 micrometers per second. Parallel fluorescence excitation and detection on the ensemble of trapped particles is also demonstrated. Additionally, the system is capable of selectively and individually releasing particles from the tweezers array using a complementary steerable laser beam. Strategies for high-yield particle capture and individual particle release in a micro-fluidic environment are discussed. A comparison with diffractive optical tweezers enhances the pros and cons of refractive systems.

Merenda, Fabrice; Rohner, Johann; Pascoal, Pedro; Fournier, Jean-Marc; Vogel, Horst; Salathé, René P.

2007-02-01

161

Algorithms for On-Line Monitoring of Micro Spheres in an Optical Tweezers-Based Assembly Cell  

Microsoft Academic Search

Optical tweezers have emerged as a powerful tool for micro and nanomanipulation. Using optical tweezers to perform automated assembly requires on-line monitoring of components in the assembly workspace. This paper presents algorithms for estimating 3-dimensional positions of micro-spheres in the assembly workspace. Algorithms presented in this paper use images obtained by optical section microscopy. The images are first segmented to

Tao Peng; Arvind Balijepalli; Satyandra K. Gupta; Tom LeBrun

2007-01-01

162

An SLM-based Shack-Hartmann wavefront sensor for aberration correction in optical tweezers  

NASA Astrophysics Data System (ADS)

Holographic optical tweezers allow the creation of multiple optical traps in 3D configurations through the use of dynamic diffractive optical elements called spatial light modulators (SLMs). We show that, in addition to controlling traps, the SLM in a holographic tweezers system can be both the principal element of a wavefront sensor and the corrective element in a closed-loop adaptive optics system. This means that aberrations in such systems can be estimated and corrected without altering the experimental setup. Aberrations are estimated using the Shack-Hartmann method, where an array of spots is projected into the sample plane and the distortion of this array is used to recover the aberration. The system can recover aberrations of up to ten wavelengths peak-peak, and is sensitive to aberrations much smaller than a wavelength. The spot pattern could also be analysed by eye, as a tool for aligning the system.

Bowman, Richard W.; Wright, Amanda J.; Padgett, Miles J.

2010-12-01

163

High-resolution optical tweezers for investigating DNA-binding/translocating molecular motors  

NASA Astrophysics Data System (ADS)

A double-trap optical tweezers instrument was constructed and its spatial resolution measured. The instrument features real-time control that allows feedback based position- and force-clamping experiments. To study RNA-polymerization by QDE-1, an RNA-dependent RNA-polymerase, we tethered a 7250 nt single-stranded DNA molecule between two optically trapped microspheres. Preliminary constant-force extension trajectories and force-extension curves were collected.

Wallin, Anders E.; Ojala, Heikki; Ziedaite, Gabija; Degerth, Linda; Bamford, Dennis; Haeggström, Edward

2009-08-01

164

Optical levitation and manipulation of stuck particles with pulsed optical tweezers  

NASA Astrophysics Data System (ADS)

We report on optical levitation and manipulation of microscopic particles that are stuck on a glass surface with pulsed optical tweezers. An infrared pulse laser at 1.06 ?m was used to generate a large gradient force (up to 10^-9 N) within a short duration (~45 ?s) that overcomes the adhesive interaction between the particles and the glass surface. Then a low-power continuous-wave diode laser at 785 nm was used to capture and manipulate the levitated particle. We have demonstrated that both stuck dielectric and biological micrometer-sized particles, including polystyrene beads, yeast cells, and Bacillus cereus bacteria, can be levitated and manipulated with this technique. We measured the single-pulse levitation efficiency for 2.0 ?m polystyrene beads as a function of the pulse energy and of the axial displacement from the stuck particle to the pulsed laser focus, which was as high as 88%.

Ashok Ambardekar, Amol; Li, Yong-Qing

2005-07-01

165

Improved direct binary search-based algorithm for generating holograms for the application of holographic optical tweezers  

NASA Astrophysics Data System (ADS)

This paper presents an improved direct binary search (DBS)-based algorithm for generating holograms to holographic optical tweezers. The simulations show that the improved algorithm greatly enhances computation speed while maintaining high hologram efficiency and high-intensity homogeneous target spots. The improved algorithm was applied to generate holographic optical tweezers in several experiments. The experiments demonstrate that real-time trap and manipulation can be realized with the improved algorithm if the number of trapped microparticles is small.

Zhao, Xudong; Li, Jing; Tao, Tao; Long, Qian; Wu, Xiaoping

2012-01-01

166

Differential detection of dual traps improves the spatial resolution of optical tweezers  

PubMed Central

The drive toward more sensitive single-molecule manipulation techniques has led to the recent development of optical tweezers capable of resolving the motions of biological systems at the subnanometer level, approaching the fundamental limit set by Brownian fluctuations. One successful approach has been the dual-trap optical tweezers, in which the system of study is held at both ends by microspheres in two separate optical traps. We present here a theoretical description of the Brownian limit on the spatial resolution of such systems and verify these predictions by direct measurement in a Brownian noise-limited dual-trap optical tweezers. We find that by detecting the positions of both trapped microspheres, correlations in their motions can be exploited to maximize the resolving power of the instrument. Remarkably, we show that the spatial resolution of dual optical traps with dual-trap detection is always superior to that of more traditional, single-trap designs, despite the added Brownian noise of the second trapped microsphere.

Moffitt, Jeffrey R.; Chemla, Yann R.; Izhaky, David; Bustamante, Carlos

2006-01-01

167

Red blood cell membrane viscoelasticity, agglutination and zeta potential measurements with double optical tweezers  

NASA Astrophysics Data System (ADS)

The red blood cell (RBC) viscoelastic membrane contains proteins and glycolproteins embedded in, or attached, to a fluid lipid bilayer and are negatively charged, which creates a repulsive electric (zeta) potential between the cells and prevents their aggregation in the blood stream. There are techniques, however, to decrease the zeta potential to allow cell agglutination which are the basis of most of the tests of antigen-antibody interactions in blood banks. This report shows the use of a double optical tweezers to measure RBC membrane viscosity, agglutination and zeta potential. In our technique one of the optical tweezers trap a silica bead that binds strongly to a RBC at the end of a RBCs rouleaux and, at the same time, acts as a pico-Newton force transducer, after calibration through its displacement from the equilibrium position. The other optical tweezers trap the RBC at the other end. To measure the membrane viscosity the optical force is measured as a function of the velocity between the RBCs. To measure the adhesion the tweezers are slowly displaced apart until the RBCs disagglutination happens. The RBC zeta potential is measured in two complimentary ways, by the force on the silica bead attached to a single RBC in response to an applied electric field, and the conventional way, by the measurement of terminal velocity of the RBC after released from the optical trap. These two measurements provide information about the RBC charges and, also, electrolytic solution properties. We believe this can improve the methods of diagnosis in blood banks.

Fontes, Adriana; Fernandes, Heloise P.; Barjas-Castro, Maria L.; de Thomaz, André A.; de Ysasa Pozzo, Liliana; Barbosa, Luiz C.; Cesar, Carlos L.

2006-03-01

168

Optical tweezers induced photodamage in living cells quantified with digital holographic phase microscopy  

NASA Astrophysics Data System (ADS)

Optical tweezers are a versatile technique to manipulate living biological specimen in a contact-less way. The interaction with living cells can be performed, for example, through direct manipulation of cell organelles or by movement of an internalized particle within the cytoplasm. However, the risk of damage that the trapping beam may induce in the biological sample due to the energy deposition has to be considered. This optically induced damage or photodamage depends mainly on the wavelength of the trapping beam, the exposure time and the biological specimen that is investigated. In this work, we explore a method to analyse the photo damage in living cells in a multimodal biophotonic workstation that is based on combining a holographic optical tweezers (HOT) microscope with a self-interference digital holographic microscopy (DHM) module. A time-dependent investigation shows that no observable changes in the cell morphology are induced at room conditions with the used laser power of the trapping beam during periods of time < 20 min of laser application. In addition, results from investigations of the photodamage increasing the working temperature to 37°C demonstrate that the optical tweezers beam can provoke severe but reversible morphology changes in the cell.

Barroso Peña, Álvaro; Kemper, Björn; Woerdemann, Mike; Vollmer, Angelika; Ketelhut, Steffi; von Bally, Gert; Denz, Cornelia

2012-05-01

169

Internal Structure, Fluctuations and Micromechanical Properties of Bovine Arterial Endothelial Cells: An Optical Tweezers Study  

NASA Astrophysics Data System (ADS)

The purpose of this study is to probe the micromechanical properties of cultured bovine arterial endothelial cells by using optical tweezers to trap endogenous granular structures in the cells. A novel application of oscillating optical tweezers and coherent detection of the forced oscillation of the trapped particle enables us to measure the viscoelastic properties in soft matter with a broad frequency range and with a high data sampling rate. This study was designed to determine the difference between the viscoelasticity of the cytoskeleton around granular structures in close vicinity of the nucleus and around the cell's edge. Time dependent measurements of the mechanical properties at a fixed oscillation frequency revealed pronounced fluctuation in living cells, indicating local dynamics of the cytoskeleton around the probed particle. Possible causes for the fluctuations will be discussed.

Perretta, Carolyn; Farrell, Sheena; Latinovic, Olga; Ou-Yang, H. Daniel

2006-03-01

170

Construction of a cost effective optical tweezers for manipulation of birefringent materials using circularly polarized light  

NASA Astrophysics Data System (ADS)

Light manipulation is a very powerful tool in physics, biology, and chemistry. There are several physical principles underlying the apparatus known as the ``optical tweezers,'' the term given to using focused light to manipulate and control small objects. By carefully controlling the orientation and position of a focused laser beam, dielectric particles can be effectively trapped and manipulated. We have designed a cost efficient and effective undergraduate optical tweezers apparatus by using standard ``off the shelf'' components and starting with a standard undergraduate laboratory microscope. Images are recorded using a small CCD camera interfaced to a computer and controlled by LabVIEW^TM software. By using wave plates to produce circular polarized light, rotational motion can be induced in small particles of birefringent materials such as calcite and mica.

McMahon, Allison; Sauncy, Toni

2008-10-01

171

Kinetics of Microtubule-AtMAP65-1 Bond Studied with Dual-Optical Tweezers  

Microsoft Academic Search

The unbinding force of microtubule-AtMAP65-1 bond is measured with dual-optical tweezers. Force histograms reveal quantized force distributions under physiological condition and with 100 mM NaCl treatment. Based on Bell-Evans-model of multiple bonds, histograms are fitted and kinetic parameters are obtained. Under the force loading rate of 9 pN\\/s, the most probable unbinding forces for the single bond are 16.8± 0.8

E Qu; Honglian Guo; Chunhua Xu; Zhaolin Li; Ming Yuan; Bingying Cheng; Daozhong Zhang

2007-01-01

172

3D manipulation of particles into crystal structures using holographic optical tweezers  

Microsoft Academic Search

We have developed holographic optical tweezers that can manipulate many particles simultaneously in three dimensions in order to create micro-crystal structures that extend over many tens of microns. The technique uses specific hologram-design algorithms to create structures that can be dynamically scaled or rotated about arbitrary axes. We believe the generation and control of pre-determined crystal-like structures have significant potential

Jonathan Leach; Gavin Sinclair; Pamela Jordan; Johannes Courtial; Miles J. Padgett; Jon Cooper; Zsolt J. Laczik

2004-01-01

173

A New Determination of the Shear Modulus of the Human Erythrocyte Membrane Using Optical Tweezers  

Microsoft Academic Search

Optical tweezers are used to apply calibrated forces to human erythrocytes, via small silica beads bound to their membrane. The shear modulus ? of the membrane is inferred from measurements of the cell deformation in the small strain linear regime. We find the same result ?=2.5±0.4?N\\/m for both discotic and nearly spherical swollen cells. This value is smaller than the

Sylvie Hénon; Guillaume Lenormand; Alain Richert; François Gallet

1999-01-01

174

Short-term binding of fibroblasts to fibronectin: optical tweezers experiments and probabilistic analysis  

Microsoft Academic Search

The biophysical properties of the interaction between fibronectin and its membrane receptor were inferred from adhesion tests\\u000a on living cells. Individual fibroblasts were maintained on fibronectin-coated glass for short time periods (1–16?s) using\\u000a optical tweezers. After contact, the trap was removed quickly, leading to either adhesion or detachment of the fibroblast.\\u000a Through a stochastic analysis of bond kinetics, we derived

Olivier Thoumine; Pierre Kocian; Arlette Kottelat; Jean-Jacques Meister

2000-01-01

175

COMBINING OPTICAL TWEEZERS AND MICROPIPETTES FOR DNA STRETCHING: ELASTICITY OF MICROPIPETTE CRUCIAL  

Microsoft Academic Search

Optical tweezers are often used in connection with other techniques to study physical properties of biological systems. In\\u000a particular, this combination has often been used to study elastic properties of individual strands of nucleic acids. The DNA\\u000a used in this study is the shortest so far reported, only 1.1 ?m, 20 times its persistence length. We use two different experimental

THOMAS MØLLER HANSEN; NADER REIHANI; LENE ODDERSHEDE

176

Optical tweezers to study single Protein A\\/Immunoglobulin G interactions at varying conditions  

Microsoft Academic Search

Optical tweezers (OT) are ideally suited to study the interaction of single receptor-ligand bonds. Here we introduce a newly\\u000a developed assay using OT to investigate the interactions between Protein A from Staphylococcus\\u000a aureus and Immunoglobulin G from rabbit serum (RIgG). We demonstrate that the rupture forces depend on the loading rate and on the\\u000a sodium chloride concentration. The measured loading

Mathias Salomo; Ulrich F. Keyser; Marc Struhalla; Friedrich Kremer

2008-01-01

177

Optical tweezers: Characterization and systems approach to high bandwidth force estimation  

Microsoft Academic Search

In recent times, the hard boundaries between classical fields of sciences have almost disappeared. There is a cross-pollination of ideas between sciences, engineering and mathematics. This work investigates a modern tool of micro-manipulation of microscopic particles that is used primarily by bio-physicists and bio-chemists for single cell, single molecule studies. This tool called the Optical Tweezers can trap microscopic dielectric

Hullas Sehgal

2010-01-01

178

Chromosomal analysis and identification based on optical tweezers and Raman spectroscopy  

NASA Astrophysics Data System (ADS)

The ability to identify specific chromosomes with certainty has been established by the development of several cytogenetic techniques based on staining. Here, we report the use of a new optical technique, laser tweezers and Raman spectroscopy (LTRS), to capture and manipulate chromosomes in order to obtain their spectral patterns for molecular analysis without the need for staining. The purpose of this study was to obtain Raman spectroscopy patterns for chromosomes number 1, 2, and 3 and to test if the Raman spectroscopy pattern could be used to distinguish these three chromosomes. In our experiment, optical tweezers were used to capture the individual chromosomes and the Raman spectral patterns were collected for the trapped chromosomes. Then, the captured chromosome was manipulated with the optical tweezers and moved to another chamber through a micro - channel, in which the chromosomes were G banded for positive identification as chromosome number 1, 2, or 3. Generalized discriminate analysis (GDA) was used to compare the Raman signatures. This analysis revealed that chromosomes 1, 2, and 3 could be distinguished and identified based on their Raman spectra. Development of this approach will lead to more rapid automatic methods for chromosome analysis and identification without the use of prior staining. Moreover, the Raman spectral patterns may lend themselves to more detailed analysis of chromosomal structure than is currently available with standard staining protocols. Such analysis may some day be useful for rapid, automated screening and diagnosis for certain cancers.

Ojeda, Jenifer F.; Xie, Changan; Li, Yong-Qing; Bertrand, Fred E.; Wiley, John; McConnell, Thomas J.

2006-06-01

179

Single-cell optoporation and transfection using femtosecond laser and optical tweezers  

PubMed Central

In this paper, we demonstrate a new single-cell optoporation and transfection technique using a femtosecond Gaussian laser beam and optical tweezers. Tightly focused near-infrared (NIR) femtosecond laser pulse was employed to transiently perforate the cellular membrane at a single point in MCF-7 cancer cells. A distinct technique was developed by trapping the microparticle using optical tweezers to focus the femtosecond laser precisely on the cell membrane to puncture it. Subsequently, an external gene was introduced in the cell by trapping and inserting the same plasmid-coated microparticle into the optoporated cell using optical tweezers. Various experimental parameters such as femtosecond laser exposure power, exposure time, puncture hole size, exact focusing of the femtosecond laser on the cell membrane, and cell healing time were closely analyzed to create the optimal conditions for cell viability. Following the insertion of plasmid-coated microparticles in the cell, the targeted cells exhibited green fluorescent protein (GFP) under the fluorescent microscope, hence confirming successful transfection into the cell. This new optoporation and transfection technique maximizes the level of selectivity and control over the targeted cell, and this may be a breakthrough method through which to induce controllable genetic changes in the cell.

Waleed, Muhammad; Hwang, Sun-Uk; Kim, Jung-Dae; Shabbir, Irfan; Shin, Sang-Mo; Lee, Yong-Gu

2013-01-01

180

Single-cell optoporation and transfection using femtosecond laser and optical tweezers.  

PubMed

In this paper, we demonstrate a new single-cell optoporation and transfection technique using a femtosecond Gaussian laser beam and optical tweezers. Tightly focused near-infrared (NIR) femtosecond laser pulse was employed to transiently perforate the cellular membrane at a single point in MCF-7 cancer cells. A distinct technique was developed by trapping the microparticle using optical tweezers to focus the femtosecond laser precisely on the cell membrane to puncture it. Subsequently, an external gene was introduced in the cell by trapping and inserting the same plasmid-coated microparticle into the optoporated cell using optical tweezers. Various experimental parameters such as femtosecond laser exposure power, exposure time, puncture hole size, exact focusing of the femtosecond laser on the cell membrane, and cell healing time were closely analyzed to create the optimal conditions for cell viability. Following the insertion of plasmid-coated microparticles in the cell, the targeted cells exhibited green fluorescent protein (GFP) under the fluorescent microscope, hence confirming successful transfection into the cell. This new optoporation and transfection technique maximizes the level of selectivity and control over the targeted cell, and this may be a breakthrough method through which to induce controllable genetic changes in the cell. PMID:24049675

Waleed, Muhammad; Hwang, Sun-Uk; Kim, Jung-Dae; Shabbir, Irfan; Shin, Sang-Mo; Lee, Yong-Gu

2013-08-07

181

Optical determination of motility forces in human spermatozoa with laser tweezers  

NASA Astrophysics Data System (ADS)

Laser tweezers may act as optical force transducers. We report on the determination of intrinsic motility forces of human spermatozoa by employing an 800 nm optical trap. The cellular forces were calculated from calibrated trapping forces. The determination of trapping forces based on a hydrodynamic model for ellipsoidal specimens, the measurement of the minimum laser power required to confine a single cell in the trap, and the calculation of viscus forces during the movement of optically trapped sperm heads through a laminar fluid. A mean motility force of 44 plus or minus 24 pN was calculated for spermatozoa of healthy donors.

Koenig, Karsten; Svaasand, Lars O.; Tadir, Yona; Tromberg, Bruce J.; Berns, Michael W.

1996-12-01

182

Scanning a DNA molecule for bound proteins using hybrid magnetic and optical tweezers.  

PubMed

The functional state of the genome is determined by its interactions with proteins that bind, modify, and move along the DNA. To determine the positions and binding strength of proteins localized on DNA we have developed a combined magnetic and optical tweezers apparatus that allows for both sensitive and label-free detection. A DNA loop, that acts as a scanning probe, is created by looping an optically trapped DNA tether around a DNA molecule that is held with magnetic tweezers. Upon scanning the loop along the ?-DNA molecule, EcoRI proteins were detected with ~17 nm spatial resolution. An offset of 33 ± 5 nm for the detected protein positions was found between back and forwards scans, corresponding to the size of the DNA loop and in agreement with theoretical estimates. At higher applied stretching forces, the scanning loop was able to remove bound proteins from the DNA, showing that the method is in principle also capable of measuring the binding strength of proteins to DNA with a force resolution of 0.1 pN/[Formula: see text]. The use of magnetic tweezers in this assay allows the facile preparation of many single-molecule tethers, which can be scanned one after the other, while it also allows for direct control of the supercoiling state of the DNA molecule, making it uniquely suitable to address the effects of torque on protein-DNA interactions. PMID:23755219

van Loenhout, Marijn T J; De Vlaminck, Iwijn; Flebus, Benedetta; den Blanken, Johan F; Zweifel, Ludovit P; Hooning, Koen M; Kerssemakers, Jacob W J; Dekker, Cees

2013-06-03

183

Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers  

PubMed Central

A cell of the bacterium Escherichia coli was tethered covalently to a glass coverslip by a single flagellum, and its rotation was stopped by using optical tweezers. The tweezers acted directly on the cell body or indirectly, via a trapped polystyrene bead. The torque generated by the flagellar motor was determined by measuring the displacement of the laser beam on a quadrant photodiode. The coverslip was mounted on a computer-controlled piezo-electric stage that moved the tether point in a circle around the center of the trap so that the speed of rotation of the motor could be varied. The motor generated ?4500 pN nm of torque at all angles, regardless of whether it was stalled, allowed to rotate very slowly forwards, or driven very slowly backwards. This argues against models of motor function in which rotation is tightly coupled to proton transit and back-transport of protons is severely limited.

Berry, Richard M.; Berg, Howard C.

1997-01-01

184

Raman sorting and identification of single living micro-organisms with optical tweezers  

NASA Astrophysics Data System (ADS)

We report on a novel technique for sorting and identification of single biological cells and food-borne bacteria based on laser tweezers and Raman spectroscopy (LTRS). With this technique, biological cells of different physiological states in a sample chamber were identified by their Raman spectral signatures and then they were selectively manipulated into a clean collection chamber with optical tweezers through a microchannel. As an example, we sorted the live and dead yeast cells into the collection chamber and validated this with a standard staining technique. We also demonstrated that bacteria existing in spoiled foods could be discriminated from a variety of food particles based on their characteristic Raman spectra and then isolated with laser manipulation. This label-free LTRS sorting technique may find broad applications in microbiology and rapid examination of food-borne diseases.

Xie, Changan; Chen, De; Li, Yong-Qing

2005-07-01

185

Electrochemical detection of single microbeads manipulated by optical tweezers in the vicinity of ultramicroelectrodes.  

PubMed

Latex micrometric beads are manipulated by optical tweezers in the vicinity of an ultramicroelectrode (UME). They are optically trapped in solution and approached the electrode surface. After the electrochemical measurement, they are optically removed from the surface. The residence time of the particle on the electrode is thus controlled by the optical tweezers. The detection is based on diffusional hindrance by the insulating objects which alters the fluxes of the redox Ru(NH3)6(3+) species toward the UME and thus its mass-transfer limited current. We have optically deposited successively 1, 2, and 3 beads of 3-?m radius on the UME surface, and we have recorded the variations of the current depending on their landing locations that were optically controlled. Finally we decreased the current by partially blocking the electroactive surface with a six-bead assembly. The variation of the steady-state current and the approach curves allow for the indirect electrochemical localization of the bead in the vicinity of the UME, not only when the bead is in contact but also when it is levitated at distances lower than the UME radius. These experiments show that single particles or more complex structures may be manipulated in situ in a contactless mode near the UME surface. From comparison with simulations, the electrochemical detection affords an indirect localization of the object in the UME environment. The developed approach offers a potential application for interrogating the electrochemical activity of single cells and nanoparticles. PMID:24020821

Suraniti, Emmanuel; Kanoufi, Frédéric; Gosse, Charlie; Zhao, Xuan; Dimova, Rumiana; Pouligny, Bernard; Sojic, Neso

2013-09-16

186

Optical tweezers and cell biomechanics in macro- and nano-scale  

NASA Astrophysics Data System (ADS)

The mechanical properties of cells, as well as their dysfunction, have been implicated in many aspects of human physiology and patho-physiology. Hence, new biophysical techniques, as optical tweezers, are of great importance for biomechanical measurements in both cells and cell simulators (e.g. liposomes). Liposomes are used, among other applications, as drug delivery nanosystems in cancer therapy. In this work, experimental measurements of the optical forces exerted by line optical tweezers on trapped cells (erythrocytes) and liposomes, using the dielectrophoresis method for calibration, are presented. Folding and elongation of trapped red blood cells was observed, in the direction of the electric field of incident beam, while, upon removal of the optical trap, the red blood cells were observed to unfold to their original biconcave shape. By measuring the folding and unfolding times, membrane elasticity properties such as bending modulus were estimated. Shear and bending modulus of liposomes were also estimated by measuring the liposome deformations, induced by optical forces along the beam long axis. The optical force is quasi-linearly increased with the increase of liposome diameter. In the elasticity regime, when the laser was turned off, the liposome acquired gradually its initial shape without any hysteresis.

Serafetinides, Alexander A.; Makropoulou, Mersini; Spyratou, Ellas

2013-03-01

187

3D multiple optical tweezers based on time-shared scanning with a fast focus tunable lens  

NASA Astrophysics Data System (ADS)

Three-dimensional controlled manipulation of individual micro-objects requires multiple optical tweezers that can be independently controlled in a 3D working space with high spatiotemporal resolution. Here, the author presents 3D multiple optical tweezers based on a time-shared scanning technique with an electrically focus tunable lens for axial steering and a two-axis steering mirror for lateral steering. Four typical examples of 3D controlled manipulation, including the rotation of a single bead on its axis, are demonstrated in real time. The optical system design and the control method are also described.

Tanaka, Yoshio

2013-02-01

188

Apparatus for Using Optical Tweezers to Manipulate Materials.  

National Technical Information Service (NTIS)

A method and apparatus for control of optical trap arrays and formation of particle arrays using light that is in the visible portion of the spectrum. The method and apparatus provides a laser and a time variable diffractive optical element to allow dynam...

B. A. Koss D. G. Grier E. R. Dufresne J. E. Curtis

2004-01-01

189

Probing interactions between colloidal particles with oscillating optical tweezers  

Microsoft Academic Search

The potential of optical traps for the study of weak interactions in colloidal systems is well recognized. In this paper, a theoretical model is developed for two oscillating interacting hard spheres in a fluid in the low Reynolds number limit. The amplitude of oscillation of the particle and the phase lag between the motion of the particles and the optical

Christopher D. Mellor; Melissa A. Sharp; Colin D. Bain; Andrew D. Ward

2005-01-01

190

Counter-propagating dual-trap optical tweezers based on linear momentum conservation  

NASA Astrophysics Data System (ADS)

We present a dual-trap optical tweezers setup which directly measures forces using linear momentum conservation. The setup uses a counter-propagating geometry, which allows momentum measurement on each beam separately. The experimental advantages of this setup include low drift due to all-optical manipulation, and a robust calibration (independent of the features of the trapped object or buffer medium) due to the force measurement method. Although this design does not attain the high-resolution of some co-propagating setups, we show that it can be used to perform different single molecule measurements: fluctuation-based molecular stiffness characterization at different forces and hopping experiments on molecular hairpins. Remarkably, in our setup it is possible to manipulate very short tethers (such as molecular hairpins with short handles) down to the limit where beads are almost in contact. The setup is used to illustrate a novel method for measuring the stiffness of optical traps and tethers on the basis of equilibrium force fluctuations, i.e., without the need of measuring the force vs molecular extension curve. This method is of general interest for dual trap optical tweezers setups and can be extended to setups which do not directly measure forces.

Ribezzi-Crivellari, M.; Huguet, J. M.; Ritort, F.

2013-04-01

191

In situ microparticle analysis of marine phytoplankton cells with infrared laser-based optical tweezers  

NASA Astrophysics Data System (ADS)

We describe the application of infrared optical tweezers to the in situ microparticle analysis of marine phytoplankton cells. A Nd:YAG laser (lambda=3D 1064 nm) trap is used to confine and manipulate single Nannochloris and Synechococcus cells in an enriched seawater medium while spectral fluorescence and Lorenz-Mie backscatter signals are simultaneously acquired under a variety of excitation and trapping conditions. Variations in the measured fluorescence intensities of chlorophyll a (Chl a) and phycoerythrin pigments in phytoplankton cells are observed. These variations are related, in part, to basic intrasample variability, but they also indicate that increasing ultraviolet-exposure time and infrared trapping power may have short-term effects on cellular physiology that are related to Chl a photobleaching and laser-induced heating, respectively. The use of optical tweezers to study the factors that affect marine cell physiology and the processes of absorption, scattering, and attenuation by individual cells, organisms, and particulate matter that contribute to optical closure on a microscopic scale are also described. (c)1995 Optical Society of America

Sonek, G. J.; Liu, Y.; Iturriaga, R. H.

1995-11-01

192

Direct integration of micromachined pipettes in a flow channel for single DNA molecule study by optical tweezers  

Microsoft Academic Search

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of ?-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of

Cristina Rusu; Oever van't Ronny; M. J. de Boer; Henri V. Jansen; J. W. Berenschot; Martin L. Bennink; Johannes S. Kanger; B. G. de Grooth; Miko Elwenspoek; Jan Greve; Jürgen Brugger; Berg van den Albert

2001-01-01

193

The design and biological applications of dual-beam oscillating optical tweezer-based imaging cytorheometer  

NASA Astrophysics Data System (ADS)

Because of its non-invasive nature, optical tweezers have emerged as a popular tool for the studies of complex fluids and biological cells and tissues. The capabilities of optical tweezer-based experimental instruments continue to evolve for better and broader applications, through new apparatus designs and integrations with microscopic imaging techniques. In this paper, we present the design, calibration and applications of a powerful microrheometer that integrates a novel high temporal and spatial resolution dual-beam oscillating optical tweezer-based cytorheometer (DOOTC) with spinning disk confocal microscopy. The oscillating scheme detects the position of micron-size probe particles via a phase-sensitive lock-in amplifier to greatly enhance sensitivity. The dual-beam scheme ensures that the cytorheometer is insensitive to sample specimen background parameter variances, and thus enables the investigation of micromechanical properties of biological samples, which are intrinsically inhomogeneous. The cytorheometer system is demonstrated to be capable of measuring dynamic local mechanical moduli in the frequency range of 0.1-150 Hz at up to 2 data point per second and with nanometer spatial resolutions, while visualizing and monitoring structural properties in situ. We report the results of system applications in the studies of bovine skin gelatin gel, purified microtubule assemblies, and human alveolar epithelial cells. The time evolution of the storage moduli G' and the loss moduli G'' of the gel is recorded for undisturbed gel-forming process with high temporal resolution. The micromechanical modulus G* of polymerized microtubule network as a function of frequency are shown to be both inhomogeneous and anisotropic consistent with local structures revealed by confocal imaging. The mechanical properties of A549 human lung cells as a function of temperature will be reported showing significant decrease in cell stiffness at higher temperature.

Ou-Yang, H. D.; Wang, J.

2006-09-01

194

Stratospheric aerosol optical depths, 1850-1990  

Microsoft Academic Search

A global stratospheric aerosol database employed for climate simulations is described. For the period 1883-1990, aerosol optical depths are estimated from optical extinction data, whose quality increases with time over that period. For the period 1850-1882, aerosol optical depths are more crudely estimated from volcanological evidence for the volume of ejecta from major known volcanoes. The data set is available

Makiko Sato; James E. Hansen; M. Patrick McCormick; James B. Pollack

1993-01-01

195

Virtual Environment for Manipulating Microscopic Particles with Optical Tweezers.  

National Technical Information Service (NTIS)

In this paper, virtual reality techniques are used to define an intuitive interface to a nanoscale manipulation device. This device utilizes optical methods to focus laser light to trap and reposition nano-to-microscopic particles. The underlying physics ...

Y. G. Lee K. W. Lyons T. W. LeBrun

2003-01-01

196

Radiation trapping forces on microspheres with optical tweezers  

SciTech Connect

Axial trapping forces exerted on microspheres are predicted using a Gaussian beam electromagnetic field model and a ray-optics model, and compared with experimental measurements. Ray-optics predicts a maximum trapping efficiency [ital Q]= [minus]0.14 for optically trapped polystyrene microspheres in water, compared to a measured value of [minus]0.12 [plus minus] 0.014 for 10 [mu]m diam microspheres. When the microspheres are composed of amorphous silica, the predicted ray-optics [ital Q] decreases to [minus]0.11, compared to a [ital Q] = [minus]0.034 predicted by the electromagnetic field model, and a measured value of [minus]0.012 [plus minus] 0.001 for 1 [mu]m diam microspheres. These results indicate that the two models have applicability in two different size regimes, and thus, are complementary.

Wright, W.H.; Sonek, G.J. (Department of Electrical and Computer Engineering ( ) Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92717 (United States)); Berns, M.W. (Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92717 (United States))

1993-08-09

197

The self-orientation of mammalian cells in optical tweezers—the importance of the nucleus  

NASA Astrophysics Data System (ADS)

Here we present the first evidence showing that eukaryotic cells can be stably trapped in a single focused Gaussian beam with an orientation that is defined by the nucleus. A mammalian eukaryotic cell (in suspension) is trapped and is re-oriented in the focus of a linearly polarized Gaussian beam with a waist of dimension smaller than the radius of the nucleus. The cell reaches a position relative to the focus that is dictated by the nucleus and nuclear components. Our studies illustrate that the force exerted by the optical tweezers at locations within the cell can be predicted theoretically; the data obtained in this way is consistent with the experimental observations.

Perney, Nicolas M. B.; Horak, Peter; Hanley, Neil A.; Melvin, Tracy

2012-04-01

198

Measuring stall forces in vivo with optical tweezers through light momentum changes  

NASA Astrophysics Data System (ADS)

The stall forces of processive molecular motors have been widely studied previously in vitro. Even so, in vivo experiments are required for determining the actual performance of each molecular motor in its natural environment. We report the direct measurement of light momentum changes in single beam optical tweezers as a suitable technique for measuring forces inside living cells, where few alternatives exist. The simplicity of this method, which does not require force calibration for each trapped object, makes it convenient for measuring the forces involved in fast dynamic biological processes such us intracellular traffic. Here we present some measurements of the stall force of processive molecular motors inside living Allium cepa cells.

Mas, J.; Farré, A.; López-Quesada, C.; Fernández, X.; Martín-Badosa, E.; Montes-Usategui, M.

2011-09-01

199

Probing cell biophysical behavior based on actin cytoskeleton modeling and stretching manipulation with optical tweezers  

NASA Astrophysics Data System (ADS)

This letter presents an approach to utilizing the actin cytoskeleton model and optical tweezers technology to probe the distinct underlying F-actin remodeling mechanism and showing quantitatively how cell mechanical behavior is associated with alterations in the cell functions. The structural parameters of F-actin were extracted by fitting the modeling results with the experimental results obtained by cell stretching manipulation. Alterations of cell mechanical behaviors under distinct diseased cellular stages were further interpreted. Jurkat and K562 cells were used as sample cells. This letter successfully illustrates the correlation of the cell mechanical behavior and cell functional alterations in a quantitative way.

Wang, Kaiqun; Cheng, Jinping; Han Cheng, Shuk; Sun, Dong

2013-08-01

200

Simultaneous rotation, orientation and displacement control of birefringent microparticles in holographic optical tweezers.  

PubMed

We report the experimental implementation of a new method for generating multiple dynamical optical tweezers, where each one of them is generated with an independent linear polarization state with arbitrary orientation. This also allows an independent simultaneous polarization-rotation control. The laser beam, both for generating multiple traps and polarization control, has been modulated using a single reflective nematic liquid crystal with parallel alignment. We present experimental results of controlled displacement, orientation and rotation of birefringent particles. In addition, a simple method for estimating and canceling out the primary astigmatism present in the system is presented. PMID:23388900

Arias, A; Etcheverry, S; Solano, P; Staforelli, J P; Gallardo, M J; Rubinsztein-Dunlop, H; Saavedra, C

2013-01-14

201

Laser-induced fusion of human embryonic stem cells with optical tweezers  

NASA Astrophysics Data System (ADS)

We report a study on the laser-induced fusion of human embryonic stem cells (hESCs) at the single-cell level. Cells were manipulated by optical tweezers and fused under irradiation with pulsed UV laser at 355 nm. Successful fusion was indicated by green fluorescence protein transfer. The influence of laser pulse energy on the fusion efficiency was investigated. The fused products were viable as gauged by live cell staining. Successful fusion of hESCs with somatic cells was also demonstrated. The reported fusion outcome may facilitate studies of cell differentiation, maturation, and reprogramming.

Chen, Shuxun; Cheng, Jinping; Kong, Chi-Wing; Wang, Xiaolin; Han Cheng, Shuk; Li, Ronald A.; Sun, Dong

2013-07-01

202

Trapping volume control in optical tweezers using cylindrical vector beams.  

PubMed

We present the result of an investigation into the optical trapping of spherical microparticles using laser beams with a spatially inhomogeneous polarization direction [cylindrical vector beams (CVBs)]. We perform three-dimensional tracking of the Brownian fluctuations in the position of a trapped particle and extract the trap spring constants. We characterize the trap geometry by the aspect ratio of spring constants in the directions transverse and parallel to the beam propagation direction and evaluate this figure of merit as a function of polarization angle. We show that the additional degree of freedom present in CVBs allows us to control the optical trap strength and geometry by adjusting only the polarization of the trapping beam. Experimental results are compared with a theoretical model of optical trapping using CVBs derived from electromagnetic scattering theory in the T-matrix framework. PMID:23282827

Skelton, S E; Sergides, M; Saija, R; Iatì, M A; Maragó, O M; Jones, P H

2013-01-01

203

An interactive optical tweezers simulation for science education  

NASA Astrophysics Data System (ADS)

We developed a freely available interactive simulation of optical traps and their biological applications (phet.colorado.edu). The target audience is undergraduate majors as well as more advanced researchers. The simulation has three panels: optical traps, manipulating DNA, and measuring molecular motors. Each panel has options that allow students to interactively explore key physical ideas. For instance, viscosity can be turned off to see the critical aspect of dissipation, or time can be slowed down to see the oscillating electric field and the induced charge separation. An overview of the simulation and specific exercises suitable for an undergraduate class are discussed.

Perkins, Thomas T.; Malley, Christopher V.; Dubson, Michael A.; Perkins, Katherine K.

2010-08-01

204

Combined versatile high-resolution optical tweezers and single-molecule fluorescence microscopy  

PubMed Central

Optical trapping and single-molecule fluorescence are two major single-molecule approaches. Their combination has begun to show greater capability to study more complex systems than either method alone, but met many fundamental and technical challenges. We built an instrument that combines base-pair resolution dual-trap optical tweezers with single-molecule fluorescence microscopy. The instrument has complementary design and functionalities compared with similar microscopes previously described. The optical tweezers can be operated in constant force mode for easy data interpretation or in variable force mode for maximum spatiotemporal resolution. The single-molecule fluorescence detection can be implemented in either wide-field or confocal imaging configuration. To demonstrate the capabilities of the new instrument, we imaged a single stretched ? DNA molecule and investigated the dynamics of a DNA hairpin molecule in the presence of fluorophore-labeled complementary oligonucleotide. We simultaneously observed changes in the fluorescence signal and pauses in fast extension hopping of the hairpin due to association and dissociation of individual oligonucleotides. The combined versatile microscopy allows for greater flexibility to study molecular machines or assemblies at a single-molecule level.

Sirinakis, George; Ren, Yuxuan; Gao, Ying; Xi, Zhiqun; Zhang, Yongli

2012-01-01

205

Combined versatile high-resolution optical tweezers and single-molecule fluorescence microscopy  

NASA Astrophysics Data System (ADS)

Optical trapping and single-molecule fluorescence are two major single-molecule approaches. Their combination has begun to show greater capability to study more complex systems than either method alone, but met many fundamental and technical challenges. We built an instrument that combines base-pair resolution dual-trap optical tweezers with single-molecule fluorescence microscopy. The instrument has complementary design and functionalities compared with similar microscopes previously described. The optical tweezers can be operated in constant force mode for easy data interpretation or in variable force mode for maximum spatiotemporal resolution. The single-molecule fluorescence detection can be implemented in either wide-field or confocal imaging configuration. To demonstrate the capabilities of the new instrument, we imaged a single stretched ? DNA molecule and investigated the dynamics of a DNA hairpin molecule in the presence of fluorophore-labeled complementary oligonucleotide. We simultaneously observed changes in the fluorescence signal and pauses in fast extension hopping of the hairpin due to association and dissociation of individual oligonucleotides. The combined versatile microscopy allows for greater flexibility to study molecular machines or assemblies at a single-molecule level.

Sirinakis, George; Ren, Yuxuan; Gao, Ying; Xi, Zhiqun; Zhang, Yongli

2012-09-01

206

Dynamics of Interaction of RBC with optical tweezers  

NASA Astrophysics Data System (ADS)

It has recently been shown that a red blood cell (RBC) can be used as optically driven motor. The mechanism for rotation is however not fully understood. While the dependence on osmolarity of the buffer led us to conclude that the osmolarity dependent changes in shape of the cell are responsible for the observed rotation, role of ion gradients and folding of RBC to a rod shape has been invoked by Dharmadhikari et al to explain their observations. In this paper we report results of studies undertaken to understand the dynamics of a RBC when it is optically tweezed. The results obtained support our earlier conjecture that osmolarity dependent changes in shape of the cell are responsible for the observed rotation.

Mohanty, Samarendra K.; Mohanty, Khyati S.; Gupta, Pradeep Kumar

2005-06-01

207

Optimizing active and passive calibration of optical tweezers  

NASA Astrophysics Data System (ADS)

To obtain quantitative information from optical trapping experiments it is essential to perform a precise force calibration. Therefore, sources of noise should be pinpointed and eliminated. Fourier analysis is routinely used to calibrate optical trapping assays because it is excellent for pinpointing high frequency noise. In addition, Allan variance analysis is particularly useful for quantifying low frequency noise and for predicting the optimal measurement time. We show how to use Allan variance in combination with Fourier analysis for optimal calibration and noise reduction in optical trapping assays. The methods are applied to passive assays, utilizing the thermal motion of a trapped particle, and to active assays where the bead is harmonically driven. The active method must be applied in assays where, for example, the viscoelastic properties of the medium or the size or shape of the trapped object are unknown. For measurement times shorter than the optimal calibration time the noise is larger in active than in the passive assays. For times equal to or longer than the optimal measurement time, though, the noise on passive and active assays is identical. As an example, we show how to quantify the influence on measurement noise of bead size and chamber geometry in active and passive assays.

Andersson, M.; Czerwinski, F.; Oddershede, L. B.

2011-04-01

208

Optical Tweezers as a New Biomedical Tool to Measure Zeta Potential of Stored Red Blood Cells  

PubMed Central

During storage, red blood cells (RBCs) for transfusion purposes suffer progressive deterioration. Sialylated glycoproteins of the RBC membrane are responsible for a negatively charged surface which creates a repulsive electrical zeta potential. These charges help prevent the interaction between RBCs and other cells, and especially among each RBCs. Reports in the literature have stated that RBCs sialylated glycoproteins can be sensitive to enzymes released by leukocyte degranulation. Thus, the aim of this study was, by using an optical tweezers as a biomedical tool, to measure the zeta potential in standard RBCs units and in leukocyte reduced RBC units (collected in CPD-SAGM) during storage. Optical tweezers is a sensitive tool that uses light for measuring cell biophysical properties which are important for clinical and research purposes. This is the first study to analyze RBCs membrane charges during storage. In addition, we herein also measured the elasticity of RBCs also collected in CPD-SAGM. In conclusion, the zeta potential decreased 42% and cells were 134% less deformable at the end of storage. The zeta potential from leukodepleted units had a similar profile when compared to units stored without leukoreduction, indicating that leukocyte lyses were not responsible for the zeta potential decay. Flow cytometry measurements of reactive oxygen species suggested that this decay is due to membrane oxidative damages. These results show that measurements of zeta potentials provide new insights about RBCs storage lesion for transfusion purposes.

Silva, Carlos A. L.; Fernandes, Heloise P.; Filho, Milton M.; Lucena, Sheyla C.; Costa, Ana Maria D. N.; Cesar, Carlos L.; Barjas-Castro, Maria L.; Santos, Beate S.; Fontes, Adriana

2012-01-01

209

Formation of an artificial blood vessel: adhesion force measurements with optical tweezers  

NASA Astrophysics Data System (ADS)

We are investigating the formation of a tissue capsule around a foreign body. This tissue capsule can be used as an autologous graft for the replacement of diseased blood vessels or for bypass surgery. The graft is grown in the peritoneal cavity of the recipient and the formation starts with the adhesion of cells to the foreign body. We identify the cell type and measure the adhesion of these cells to foreign materials using optical tweezers. Cell adhesion to macroscopic samples and microspheres is investigated. No difference in the adhesion force was measurable for polyethylene, silicon and Tygon on a scale accessible to optical tweezers. The density of adherent cells was found to vary strongly, being highest on polyethylene. The mean rupture forces for cell-microsphere adhesion ranged from 24 to 39 pN and changed upon preadsorption of bovine serum albumin. For plain microspheres, the highest mean rupture force was found for PMMA, which also showed the highest adhesion probability for the cell-microsphere interaction.

Knoener, Gregor; Campbell, Julie H.; Heckenberg, Norman R.; Rubinsztein-Dunlop, Halina

2004-10-01

210

Investigation of the mechanical property of individual cell using axial optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers is a technique that can trap and manipulate small objects using a highly focused laser beam. Because optical tweezers can also be used to measure small forces, it has been extensively used for the measurement of the mechanical forces of cells. Previous research works typically study particle manipulation and cell force measurement in the lateral direction, hence excluding valuable insights about the axial mechanical properties of cells. Other works that investigate axial cell force measurements utilize spatial light modulators and other devices that are expensive and complicate the setup. Thus, in our study, we designed a simple scheme that can axially manipulate particles by adjusting the position of one lens, called L1-lens, in our setup. Image processing techniques were utilized to determine the changes in the axial particle translation, providing nanometer sensitivity. We investigated the capability of our system using two different-sized particles and results show that for a given L1-lens default position and movement, a 2-micron particle and a 4.26-micron particle were moved axially for 7.68 µm and 4.83 µm, respectively. Axial trapping stiffness was also measured for the stated bead sizes in different magnification. Using the computed trapping sti_ness, we will investigate the axial reactive forces of cells.

Dy, Mary-Clare; Sugiura, Tadao; Minato, Kotaro

2013-02-01

211

Simulation of heart infarction by laser microbeams and induction of arrhythmias by optical tweezers  

NASA Astrophysics Data System (ADS)

Laser microbeam and optical tweezers were used for micromanipulation of a heart tissue model consisting of embryonic chicken cardiomyocytes and bibroblasts. Using the laser microbeam a would was created, i.e. a sort of artificial heart infarction was generated. The first steps of wound repair were observed by live cell imaging. A complete filling of teh would primarily by migrating fibroblasts but not by cardiomyocytes was detected 18 hours after wounding. In another set of experiments erythrocyte mediated force application (EMFA) by optical tweezers was applied for optomechanical manipulatoin of cardiomyocytes and fibroblasts. Here we demonstrate induction of dramatic distrubances of calcium waves in a group of synchronously beating cardiomyocytes by an optomechanical input that results in cellular deformation. Surprisingly, it was found that putatively non-excitable fibroblasts respond to this mechanical stress with calcium oscillations. The results reported here indicate that the induction of artificial heart infarction can provide insights into healing processes after mycardial injury. EMFA is capable to examine effects of myocardial overload and to provide important information about processes triggered by mechanical stress on the level of single or very few cells. As a perspective, the preseneted techniques may be used to study the influence of drugs on wound healing and coordination of beating in the heart.

Perner, Birgit; Monajembashi, Shamci; Rapp, Alexander; Wollweber, Leo; Greulich, Karl Otto

2004-10-01

212

Optical Tweezers Experiments Resolve Distinct Modes of DNA-Protein Binding  

PubMed Central

Optical tweezers are ideally suited to perform force microscopy experiments that isolate a single biomolecule, which then provides multiple binding sites for ligands. The captured complex may be subjected to a spectrum of forces, inhibiting or facilitating ligand activity. In the following experiments, we utilize optical tweezers to characterize and quantify DNA binding of various ligands. High Mobility Group Type B (HMGB) proteins, which bind to double-stranded DNA, are shown to serve the dual purpose of stabilizing and enhancing the flexibility of double stranded DNA. Unusual intercalating ligands are observed to thread into and lengthen the double-stranded structure. Proteins binding to both double- and single-stranded DNA, such as the alpha polymerase subunit of E. coli Pol III, are characterized and the subdomains containing the distinct sites responsible for binding are isolated. Finally, DNA binding of bacteriophage T4 and T7 single-stranded DNA (ssDNA) binding proteins are measured for a range of salt concentrations, illustrating a binding model for proteins that slide along double-stranded DNA, ultimately binding tightly to ssDNA. These recently developed methods quantify both the binding activity of the ligand as well as the mode of binding.

McCauley, Micah J.; Williams, Mark C.

2009-01-01

213

Optical tweezers experiments resolve distinct modes of DNA-protein binding.  

PubMed

Optical tweezers are ideally suited to perform force microscopy experiments that isolate a single biomolecule, which then provides multiple binding sites for ligands. The captured complex may be subjected to a spectrum of forces, inhibiting or facilitating ligand activity. In the following experiments, we utilize optical tweezers to characterize and quantify DNA binding of various ligands. High mobility group type B (HMGB) proteins, which bind to double-stranded DNA, are shown to serve the dual purpose of stabilizing and enhancing the flexibility of double stranded DNA. Unusual intercalating ligands are observed to thread into and lengthen the double-stranded structure. Proteins binding to both double- and single-stranded DNA, such as the alpha polymerase subunit of E. coli Pol III, are characterized, and the subdomains containing the distinct sites responsible for binding are isolated. Finally, DNA binding of bacteriophage T4 and T7 single-stranded DNA (ssDNA) binding proteins is measured for a range of salt concentrations, illustrating a binding model for proteins that slide along double-stranded DNA, ultimately binding tightly to ssDNA. These recently developed methods quantify both the binding activity of the ligand as well as the mode of binding. PMID:19173290

McCauley, Micah J; Williams, Mark C

2009-04-01

214

Design of hybrid optical tweezers system for controlled three-dimensional micromanipulation  

NASA Astrophysics Data System (ADS)

Three-dimensional (3D) micro/nano-manipulation using optical tweezers is a significant technique for various scientific fields ranging from biology to nanotechnology. For the dynamic handling of multiple/individual micro-objects in a true 3D working space, we present an improved hybrid optical tweezers system consisting of two multibeam techniques. These two techniques include the generalized phase contrast method with a spatial light modulator and the time-shared scanning method with a two-axis steering mirror and an electrically focus-tunable lens. Unlike our previously reported system that could only handle micro-objects in a two and half dimensional working space, the present system has high versatility for controlled manipulation of multiple micro-objects in a true 3D working space. The controlled rotation of five beads forming a pentagon, that of four beads forming a tetrahedron about arbitrary axes, and the fully automated assembly and subsequent 3D translation of micro-bead arrays are successfully demonstrated as part of the 3D manipulation experiment.

Tanaka, Yoshio; Tsutsui, Shogo; Kitajima, Hiroyuki

2013-04-01

215

Measuring integrated cellular mechanical stress response at focal adhesions by optical tweezers  

NASA Astrophysics Data System (ADS)

The ability of cells to sustain mechanical stress is largely modulated by the cytoskeleton. We present a new application of optical tweezers to study cell's mechanical properties. We trap a fibronectin-coated bead attached to an adherent H4II-EC3 rat hepatoma cell in order to apply the force to the cell surface membrane. The bead position corresponding to the cell's local mechanical response at focal adhesions is measured with a quadrant detector. We assessed the cell response by tracking the evolution of the equilibrium force for 40 cells selected at random and selected a temporal window to assess the cell initial force expression at focal adhesions. The mean value of the force within this time window over 40 randomly selected bead/cell bounds was 52.3 pN. Then, we assessed the responses of the cells with modulation of the cytoskeletons, namely the ubiquitous actin-microfilaments and microtubules, plus the differentiation-dependent keratin intermediate filaments. Notably, a destabilization of the first two networks led to around 50 and 30% reductions in the mean equilibrium forces, respectively, relative to untreated cells, whereas a loss of the third one yielded a 25% increase. The differences in the forces from untreated and treated cells are resolved by the optical tweezers experiment.

Bordeleau, François; Bessard, Judicael; Marceau, Normand; Sheng, Yunlong

2011-09-01

216

Using electrical and optical tweezers to facilitate studies of molecular motors†  

PubMed Central

Dielectrophoresis was used to stretch and suspend actin filaments across a trench etched between two electrodes patterned on a glass slide. Optical tweezers were used to bring a motor protein-coated bead into close proximity to a pre-selected, suspended actin filament, facilitating the attachment of the myosin-coated bead to the filament. The clearance beneath the filament allowed the bead to move freely along and around its filamentous track, unhindered by solid surfaces. Using defocused images, the three-dimensional position of the bead was tracked as a function of time to obtain its trajectory. Experiments were carried out with myosin V and myosin X. Both motor proteins followed left-handed helical paths with the myosin X motor exhibiting a shorter pitch than the myosin V. The combined use of electrostatic and optical tweezers facilitates the preparation of motility assays with suspended tracks. Variants of this technique will enable higher complexity experiments in vitro to better understand the behavior of motors in cells.

Arsenault, Mark E.; Sun, Yujie; Bau, Haim H.; Goldman, Yale E.

2013-01-01

217

Elastic light scattering measurements from multiple red blood cells in elliptical optical tweezers  

NASA Astrophysics Data System (ADS)

Different theoretical models have been developed to understand light propagation in biological media and to facilitate the analysis of experimental data, both at the cellular level and in bulk tissues. Optical tweezers, combined with a light scattering measurement facility, enable the measurement of elastic light scattering distributions from single particles and cells. The aim of this paper is to present elastic light scattering measurement results from several red blood cells (RBCs) held in elliptical optical tweezers and to compare these results with theoretical predictions found in literature. Both faceon and rim-on incidence of He-Ne laser light (vertical polarization) in relation to the measured RBCs was considered. In the face-on case, light scattering intensity was larger from two RBCs than from one, but almost no difference was found when using three RBCs instead of two. In rim-on incidence, clear changes in the shape of the scattering light intensity field were found when the number of RBCs was increased from one to two. These results are supported by modelling results from literature.

Kauppila, Antti; Kinnunen, Matti; Karmenyan, Artashes; Myllylä, Risto

2011-09-01

218

Comparison of a high-speed camera and a quadrant detector for measuring displacements in optical tweezers  

Microsoft Academic Search

We compare the performance of a high-speed camera and a quadrant detector for measuring the displacement of micron-sized particles in optical tweezers. For trapping powers up to 100 mW, the standard deviation of the particle displacements measured by the two techniques shows excellent agreement. This comparison also provides a method for calibrating one technique against the other.

S. Keen; J. Leach; G. Gibson; M. J. Padgett

2007-01-01

219

Optically-driven red blood cell rotor in linearly polarized laser tweezers  

NASA Astrophysics Data System (ADS)

We have constructed a dual trap optical tweezers set-up around an inverted microscope where both the traps can be independently controlled and manipulated in all the three dimensions. Here we report our observations on rotation of red blood cells (RBCs) in a linearly polarized optical trap. Red blood cells deform and become twisted in hypertonic phosphate buffer saline and when trapped, experience an unbalanced radiation pressure force. The torque generated from the unbalanced force causes the trapped RBC to rotate. Addition of Ca^{++} ions in the solution, keeping the osmolarity same, makes the cell membranes stiffer and the cells deform less. Thus the speed of rotation of the red blood cells can be controlled, as less deformation and in turn less asymmetry in shape produces less torque under the radiation pressure resulting in slower rotation at the same laser power.

Khan, Manas; Mohanty, Samarendra K.; Sood, A. K.

2005-11-01

220

A general method for manipulating DNA sequences from any organism with optical tweezers  

PubMed Central

Mechanical manipulation of single DNA molecules can provide novel information about DNA properties and protein–DNA interactions. Here we describe and characterize a useful method for manipulating desired DNA sequences from any organism with optical tweezers. Molecules are produced from either genomic or cloned DNA by PCR using labeled primers and are tethered between two optically trapped microspheres. We demonstrate that human, insect, plant, bacterial and viral sequences ranging from ?10 to 40 kilobasepairs can be manipulated. Force-extension measurements show that these constructs exhibit uniform elastic properties in accord with the expected contour lengths for the targeted sequences. Detailed protocols for preparing and manipulating these molecules are presented, and tethering efficiency is characterized as a function of DNA concentration, ionic strength and pH. Attachment strength is characterized by measuring the unbinding time as a function of applied force. An alternative stronger attachment method using an amino–carboxyl linkage, which allows for reliable DNA overstretching, is also described.

Fuller, Derek N.; Gemmen, Gregory J.; Rickgauer, John Peter; Dupont, Aurelie; Millin, Rachel; Recouvreux, Pierre; Smith, Douglas E.

2006-01-01

221

The stiffness of rabbit skeletal actomyosin cross-bridges determined with an optical tweezers transducer.  

PubMed Central

Muscle contraction is brought about by the cyclical interaction of myosin with actin coupled to the breakdown of ATP. The current view of the mechanism is that the bound actomyosin complex (or "cross-bridge") produces force and movement by a change in conformation. This process is known as the "working stroke." We have measured the stiffness and working stroke of a single cross-bridge (kappa xb, dxb, respectively) with an optical tweezers transducer. Measurements were made with the "three bead" geometry devised by Finer et al. (1994), in which two beads, supported in optical traps, are used to hold an actin filament in the vicinity of a myosin molecule, which is immobilized on the surface of a third bead. The movements and forces produced by actomyosin interactions were measured by detecting the position of both trapped beads. We measured, and corrected for, series compliance in the system, which otherwise introduces large errors. First, we used video image analysis to measure the long-range, force-extension property of the actin-to-bead connection (kappa con), which is the main source of "end compliance." We found that force-extension diagrams were nonlinear and rather variable between preparations, i.e., end compliance depended not only upon the starting tension, but also upon the F-actin-bead pair used. Second, we measured kappa xb and kappa con during a single cross-bridge attachment by driving one optical tweezer with a sinusoidal oscillation while measuring the position of both beads. In this way, the bead held in the driven optical tweezer applied force to the cross-bridge, and the motion of the other bead measured cross-bridge movement. Under our experimental conditions (at approximately 2 pN of pretension), connection stiffness (kappa con) was 0.26 +/- 0.16 pN nm-1. We found that rabbit heavy meromyosin produced a working stroke of 5.5 nm, and cross-bridge stiffness (kappa xb) was 0.69 +/- 0.47 pN nm-1.

Veigel, C; Bartoo, M L; White, D C; Sparrow, J C; Molloy, J E

1998-01-01

222

Analysis of RBC damage using laser tweezers Raman spectroscopy (LTRS) during femtosecond laser optical trapping  

NASA Astrophysics Data System (ADS)

We monitored cell viability and damage under femtosecond laser irradiation using aser weezers Raman pectroscopy (LTRS) which is becoming a powerful tool for the analysis of biological materials. Femtosecond lasers are more frequently used as a light source for optical tweezers since they enable nonlinear optical phenomena such as two-photon absorption or second harmonic generation trapping. Femtosecond laser optical trapping similar to thee CW laser optical trapping except that optical damage can be easily induced due to extremely high peak power of femtosecond pulses. We monitored the Raman signal changes as a marker for optical damage. We used red blood cell (RBC) as a target sample and first used the CW laser beams to trap the RBC from the bottom of the chamber. After the trapped RBC is moved to a desired depth, we switched the laser mode to mode-locked mode and monitored the Raman signals as a function of the laser irradiation time. It was observed that the Raman shift at 1543 cm-1 may be a good marker for optical damage both for CW and femtosecond laser trapping.

Ju, Sung-bin; Pyo, Jin-woo; Jang, Jae-young; Lee, Seungduk; Kim, Beop-Min

2008-03-01

223

One-dimensional jumping optical tweezers for optical stretching of bi-concave human red blood cells.  

PubMed

We report the experimental demonstration of optical stretching of individual bio-concave human red blood cells (RBCs) with one-dimensional jumping optical tweezers. We trapped a RBC in isotonic buffer solution in a conventional stationary single-beam gradient-force optical trap and discretely scanned the trapping beam with an acousto-optic modulator such that the focal point of the trapping beam jumped back-and-forth between two fixed points. At the jumping frequency on the order of a 100 Hz and higher, and the jumping distance in the range of a few microns, the bi-concave RBC was stably trapped and stretched. The elongation of the stretched RBC was measured as a function of the beam-scanning amplitude, and the experimental results were explained qualitatively by a theoretical model. PMID:18542279

Liao, Guan-Bo; Bareil, Paul B; Sheng, Yunlong; Chiou, Arthur

2008-02-01

224

Optical tweezers based force measurement system for quantitating binding interactions: system design and application for the study of bacterial adhesion  

Microsoft Academic Search

An optical force measurement system for quantitating forces in the pN range between micrometer-sized objects has been developed. The system was based upon optical tweezers in combination with a sensitive position detection system and constructed around an inverted microscope. A trapped particle in the focus of the high numerical aperture microscope-objective behaves like an omnidirectional mechanical spring in response to

Erik Fällman; Staffan Schedin; Jana Jass; Magnus Andersson; Bernt Eric Uhlin; Ove Axner

2004-01-01

225

Coherence and Raman Sideband Cooling of a Single Atom in an Optical Tweezer  

NASA Astrophysics Data System (ADS)

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n¯x=n¯y=0.01, n¯z=8) even for a trap beam waist as small as w=900nm. The small atomic wave packet with ?x=?y=24nm and ?z=270nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces.

Thompson, J. D.; Tiecke, T. G.; Zibrov, A. S.; Vuleti?, V.; Lukin, M. D.

2013-03-01

226

Force between colloidal particles in a nematic liquid crystal studied by optical tweezers  

NASA Astrophysics Data System (ADS)

We measure the dependence of the interparticle force F on the distance R between two colloidal particles with hyperbolic hedgehog defects in a nematic liquid crystal using optical tweezers. The particle-defect pair can be regarded as an elastic “dipole” in the electrostatic analogy. In a parallel configuration, where the dipole vectors are parallel with each other, F is attractive and proportional to R-4 . However, F becomes repulsive at small R due to the existence of a defect between the particles. In an antiparallel configuration, where the particles directly face each other, F is repulsive over the whole range of R and proportional to R-3.6 . In another antiparallel configuration, where two hyperbolic hedgehog defects directly face each other, F is proportional to R-3.6 and F at small R turns out to be attractive upon tilting the dipoles. Furthermore, we yield the force between particles connected by a stringlike defect called a bubblegum defect.

Takahashi, Kenji; Ichikawa, Masatoshi; Kimura, Yasuyuki

2008-02-01

227

Coherence and Raman sideband cooling of a single atom in an optical tweezer.  

PubMed

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n(x)=n(y)=0.01, n(z)=8) even for a trap beam waist as small as w=900??nm. The small atomic wave packet with ?x=?y=24??nm and ?z=270??nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces. PMID:23581312

Thompson, J D; Tiecke, T G; Zibrov, A S; Vuleti?, V; Lukin, M D

2013-03-26

228

Active Microrheology Using Optical Tweezers to Characterize Viscoelastic Properties of Entangled DNA  

NASA Astrophysics Data System (ADS)

We use active microrheology techniques to investigate the frequency-dependent linear elastic and viscous moduli (G', G'') of entangled DNA. Utilizing optical tweezers, single microspheres, embedded within solutions of entangled DNA of varying molecular lengths and solution concentrations, are driven sinusoidally over a frequency range of 0.6 - 95 Hz, while fluorescence microscopy is used to simultaneously visualize the deformation of a sparse number of DNA molecules entangled in the solution. DNA lengths of 11 kbp -- 115 kbp and solution concentrations of 1.0 -- 2.5 mg/ml are probed to determine the dependence of the viscoelasticity of entangled DNA on solution concentration and, for the first time, molecular length. Results are compared to theoretical predictions for entangled polymers, as well as previously reported macrorheology results.

Chapman, Cole D.; Lee, Kent; Henze, Dean; Smith, Douglas E.; Anderson, Rae M.

2013-03-01

229

3D Manipulation of Protein Microcrystals with Optical Tweezers for X-ray Crystallography  

NASA Astrophysics Data System (ADS)

In some synchrotron facilities such as SPring-8, X-ray microbeams have been utilized for protein crystallography, allowing users to collect diffraction data from a protein microcrystal. Usually, a protein crystal is picked up manually from a crystallization droplet. However it is very difficult to manipulate the protein microcrystals which are very small and fragile against a shock and changes of temperature and solvent condition. We have been developing an automatic system applying the optical tweezers with two lensed fiber probes to manipulate the fragile protein microcrystal. The system succeeded in trapping a crystal and levitating it onto the cryoloop in the solvent. X-ray diffraction measurement for the manipulated protein microcrystals indicated that laser irradiation and trap with 1064nm wavelength hardly affected the result of X-ray structural analysis.

Hikima, T.; Hashimoto, K.; Murakami, H.; Ueno, G.; Kawano, Y.; Hirata, K.; Hasegawa, K.; Kumasaka, T.; Yamamoto, M.

2013-03-01

230

Optical tweezers study of viscoelastic properties in the outer hair cell plasma membrane  

NASA Astrophysics Data System (ADS)

An optical tweezers system was used to study the mechanical characteristics of the outer hair cell (OHC) lateral wall by forming plasma membrane tethers. A 2nd order generalized Kelvin model was applied to describe the viscoelastic behavior of OHC membrane tethers. The measured parameters included equilibrium tethering force, (Feq), force relaxation times (?), stiffness values (?), and coefficients of friction (?). An analysis of force relaxation in membrane tethers indicated that the force decay is a biphasic process containing both an elastic and a viscous phase. In general, we observed an overall negative trend in the measured parameters upon application of the cationic amphipath chlorpromazine (CPZ). CPZ was found to cause up to a 40 pN reduction in Feq in OHCs. A statistically significant reduction in relaxation times and coefficients of friction was also observed, suggesting an increase in rate of force decay and a decrease in plasma membrane viscosity.

Murdock, David R.; Ermilov, Sergey A.; Qian, Feng; Brownell, William E.; Anvari, Bahman

2004-06-01

231

Inferring kinetic pathways, rates, and force dependence from nonprocessive optical tweezers experiments: a maximum likelihood approach  

NASA Astrophysics Data System (ADS)

Optical tweezers experiments allow us to probe the role of force and mechanical work in a variety of biochemical processes. However, observable states do not usually correspond in a one-to-one fashion with the internal state of an enzyme or enzyme-substrate complex. Different kinetic pathways yield different distributions for the dwells in the observable states. Furthermore, the dwell-time distribution will be dependent upon force, and upon where in the biochemical pathway force acts. I will present a maximum-likelihood method for identifying rate constants and the locations of force-dependent transitions in transcription initiation by T7 RNA Polymerase. This method is generalizable to systems with more complicated kinetic pathways in which there are two observable states (e.g. bound and unbound) and an irreversible final transition.

Kalafut, Bennett; Visscher, Koen

2008-10-01

232

Measurement of the membrane elasticity of red blood cell with osmotic pressure by optical tweezers.  

PubMed

Cells have to undergo many changes in osmotic pressure during their long-term preservation, and will have injuries before they return to their normal states. Mechanics of a cell with deformation, either small or large, is usually used to describe the change of the cell quantitatively. However, there are few reports on the deformation of cells subjected to the change of osmotic pressures during preservation. Here, we report our study of the elasticity of the human red blood cells under osmotic pressures using optical tweezers. We find that the deformation characteristics of erythrocytes are strongly dependent on the osmotic pressure. We also find the RBCs will become stiff with increasing osmotic pressure, suggesting a potential reason for membrane injury during preservation. PMID:19448857

Wu, Jianguang; Li, Yinmei; Lu, Di; Liu, Zhong; Cheng, Zhengdong; He, Liqun

233

Development of microfluidic system and optical tweezers for electrophysiological investigations of an individual cell  

NASA Astrophysics Data System (ADS)

We present a new approach of combining Lab-on-a-chip technologies with optical manipulation technique for accurate investigations in the field of cell biology. A general concept was to develop and combine different methods to perform advanced electrophysiological investigations of an individual living cell under optimal control of the surrounding environment. The conventional patch clamp technique was customized by modifying the open system with a gas-tight multifunctional microfluidics system and optical trapping technique (optical tweezers). The system offers possibilities to measure the electrical signaling and activity of the neuron under optimum conditions of hypoxia and anoxia while the oxygenation state is controlled optically by means of a spectroscopic technique. A cellbased microfluidics system with an integrated patch clamp pipette was developed successfully. Selectively, an individual neuron is manipulated within the microchannels of the microfluidic system under a sufficient control of the environment. Experiments were performed to manipulate single yeast cell and red blood cell (RBC) optically through the microfluidics system toward an integrated patch clamp pipette. An absorption spectrum of a single RCB was recorded which showed that laser light did not impinge on the spectroscopic spectrum of light. This is promising for further development of a complete lab-on-a-chip system for patch clamp measurements.

Alrifaiy, A.; Bitaraf, N.; Lindahl, O.; Ramser, K.

2010-08-01

234

Single-molecule manipulation of double-stranded DNA using optical tweezers: Interaction studies of DNA with RecA and YOYO-1  

Microsoft Academic Search

By using optical tweezers and a specially designed flow cell with an integrated glass micropipette, we constructed a setup similar to that of Smith et al. (Science 271:795-799, 1996) in which an individual double-stranded DNA (dsDNA) molecule can be captured between two polystyrene beads. The first bead is immobilized by the optical tweezers and the second by the micropipette. Movement

Martin L. Bennink; Orlando D. Scharer; Ronald Kanaar; Kumiko Sakata-Sogawa; Juleon M. Schins; Johannes S. Kanger; Grooth de Bart G; Jan Greve

1999-01-01

235

Multiple trap Laguerre-Gaussian holographic optical tweezers using a multiplexed ferroelectric SLM  

NASA Astrophysics Data System (ADS)

A holographic optical tweezers system is constructed using time-shared multiplexing to generate multiple optical traps. Computer generated Fresnel zone plates are used to produce the required laser focuses for standard optical traps while helical zone plates are used to generate Laguerre-Gaussian (LG) laser modes that produce doughnut shaped focuses. Standard Fresnel zone plates are used for trapping non-biological matter whereas LG modes are used in trapping delicate biological matter that is susceptible to damage from excessive laser radiation. A reflective high speed ferroelectric spatial light modulator (SLM), which is used to display the zone plate images, is capable of multiplexing a maximum of 24 binary images at a refresh rate of up to 1440Hz. By programming the SLM to display one binary hologram per bit plane, a commercial 24 bit colour SLM is used to provide 24 multiplexed traps. The ferroelectric holographic system enables multiple independently movable traps using time-shared multiplexing without the need for mechanical movement within the system. The software developed to display the zone plates uses Open GL acceleration to allow fast smooth movement in real time. Open GL utilises the graphics processing unit (GPU) common on many computers today which greatly increases the frame rate of the images displayed on the SLM. Use of the apparatus is demonstrated by the trapping and manipulation of colloidal particles and yeast cells. Preliminary results indicate that the use of LG zone plates for trapping biological cells results in significantly less damage than standard Fresnel zone plates.

Lafong, A.; Hossack, W. J.; Arlt, J.; Nowakowski, T. J.; Read, N. D.

2006-09-01

236

Manipulating CD4+ T cells by optical tweezers for the initiation of cell-cell transfer of HIV-1  

PubMed Central

Cell-cell interactions through direct contact are very important for cellular communication and coordination – especially for immune cells. The human immunodeficiency virus type I (HIV-1) induces immune cell interactions between CD4+ cells to shuttle between T cells via a virological synapse. A goal to understand the process of cell-cell transmission through virological synapses is to determine the cellular states that allow a chance encounter between cells to become a stable cell-cell adhesion. Here we demonstrate the use of optical tweezers to manipulate uninfected primary CD4+ T cells near HIV Gag-iGFP transfected Jurkat T cells to probe the determinants that induce stable adhesion. When combined with fast 4D confocal fluorescence microscopy, optical tweezers can be utilized to not only facilitate cell-cell contact, but to also allow one to simultaneously track the formation of a virological synapse, and ultimately to enable us to precisely determine all events preceding virus transfer. HIV-1 infected T cell (green) decorated with uninfected primary T cells (red) by manipulating the primary cells with an optical tweezers system

McNerney, Gregory P.; Hubner, Wolfgang; Chen, Benjamin K.; Huser, Thomas

2011-01-01

237

Calibration of optical tweezers with positional detection in the back focal plane  

SciTech Connect

We explain and demonstrate a new method of force and position calibrations for optical tweezers with back-focal-plane photodetection. The method combines power spectral measurements of thermal motion and the response to a sinusoidal motion of a translation stage. It consequently does not use the drag coefficient of the trapped object as an input. Thus, neither the viscosity, nor the size of the trapped object, nor its distance to nearby surfaces needs to be known. The method requires only a low level of instrumentation and can be applied in situ in all spatial dimensions. It is both accurate and precise: true values are returned, with small error bars. We tested this experimentally, near and far from surfaces in the lateral directions. Both position and force calibrations were accurate to within 3%. To calibrate, we moved the sample with a piezoelectric translation stage, but the laser beam could be moved instead, e.g., by acousto-optic deflectors. Near surfaces, this precision requires an improved formula for the hydrodynamical interaction between an infinite plane and a microsphere in nonconstant motion parallel to it. We give such a formula.

Tolic-Noerrelykke, Simon F.; Schaeffer, Erik; Howard, Jonathon; Pavone, Francesco S.; Juelicher, Frank; Flyvbjerg, Henrik [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany) and European Laboratory for Non-linear Spectroscopy, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence (Italy) and Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden (Germany); European Laboratory for Non-linear Spectroscopy, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence (Italy); Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany); Isaac Newton Institute for Mathematical Sciences, Cambridge CB3 0EH (United Kingdom); Biosystems Department, Risoe National Laboratory, DK-4000 Roskilde (Denmark) and Danish Polymer Centre, Risoe National Laboratory, DK-4000 Roskilde (Denmark)

2006-10-15

238

Combined optical tweezers and laser dissector for controlled ablation of functional connections in neural networks  

NASA Astrophysics Data System (ADS)

Regeneration of functional connectivity within a neural network after different degrees of lesion is of utmost clinical importance. To test pharmacological approaches aimed at recovering from a total or partial damage of neuronal connections within a circuit, it is necessary to develop a precise method for controlled ablation of neuronal processes. We combined a UV laser microdissector to ablate neural processes in vitro at single neuron and neural network level with infrared holographic optical tweezers to carry out force spectroscopy measurements. Simultaneous force spectroscopy, down to the sub-pico-Newton range, was performed during laser dissection to quantify the tension release in a partially ablated neurite. Therefore, we could control and measure the damage inflicted to an individual neuronal process. To characterize the effect of the inflicted injury on network level, changes in activity of neural subpopulations were monitored with subcellular resolution and overall network activity with high temporal resolution by concurrent calcium imaging and microelectrode array recording. Neuronal connections have been sequentially ablated and the correlated changes in network activity traced and mapped. With this unique combination of electrophysiological and optical tools, neural activity can be studied and quantified in response to controlled injury at the subcellular, cellular, and network level.

Difato, Francesco; Dal Maschio, Marco; Marconi, Emanuele; Ronzitti, Giuseppe; Maccione, Alessandro; Fellin, Tommasso; Berdondini, Luca; Chieregatti, Evelina; Benfenati, Fabio; Blau, Axel

2011-05-01

239

Biomechanics and dynamics of red blood cells probed by optical tweezers and digital holographic microscopy  

NASA Astrophysics Data System (ADS)

Red blood cells (RBC), with their unique viscoelastic properties, can undergo large deformations during interaction with fluid flow and migration through narrow capillaries. Both local and overall viscoelastic property is important for cellular function and change in these properties indicate diseased condition. Though biomechanics of the cells have been studied using variety of physical techniques (AFM, optically-trapped anchoring beads and microcapilary aspiration) in force regime > 10pN, little is studied at low force regime <1pN. Such perturbations are not only hard to exercise on the cell membrane, but quantification of such deformations becomes extremely difficult. By application of low power optical tweezers directly on cell membrane, we could locally perturb discotic RBC along the axial direction, which was monitored dynamically by digital holographic microscopy-a real time, wide-field imaging method having nm axial resolution. The viscoelastic property of the RBC at low force regime was found to be significantly different from that of high-force regime. The results were found to be in good agreement with the simulation results obtained using finite element model of the axially-stretched RBC. The simulations and results of viscoelestic measurements will be presented.

Cardenas, Nelson; Thomas, Pattrick; Yu, Lingfeng; Mohanty, Samarendra

2011-03-01

240

Inducing trauma into neuroblastoma cells and synthetic neural networks using optical tweezers  

NASA Astrophysics Data System (ADS)

The laser tweezers have become a very useful tool in the fields of physics, chemistry, and biology. My intent is to use the laser tweezers to induce trauma into neuroblastoma cells, cells that resemble neural cells when treated with retinoic acid, to try to surmise what happens when neural cells and networks are disrupted or destroyed. The issues presented will deal with the obtaining, maintenance, and differentiation of the cells, as well as the inner operations of the laser tweezers themselves, and what kind of applications it has been applied to, as well as to my work in this project.

Schneider, Patrick William

241

Femtosecond single optical fiber tweezers enabled two-photon fluorescence excitation of trapped microscopic objects  

NASA Astrophysics Data System (ADS)

Analysis of trapped microscopic objects using fluorescence and Raman spectroscopy is gaining considerable interest. We report on the development of single fiber femto second optical tweezers and its use in two-photon fluorescence (TPF) excitation of trapped fluorescent particles. Trapping of the floating objects led to stable fluorescence emission intensity over a long period of time, suitable for spectroscopic measurements. Trapping depth of few cm was achieved inside colloidal sample with TPF from the trapped particle being visible to the naked eye. Furthermore, the fiber optic trapping was so stable that the trapped particle could be moved in 3D even by holding the fiber in hand and slow maneuvering of the same. Owing to the propagation distance of the Bessel-like beam emerging from the axicon-fiber tip, a relatively longer streak of fluorescence was observed along the microsphere length. The cone angle of axicon was engineered so as to provide better trapping stability and high axial confinement of TPF. The theoretical simulation of fiber optical microbeam profiles emerging from the axicon tip and trapping force estimations was found to be in good agreement with the experimentally observed stiffness and TPF patterns. Apart from miniaturization capability into lab-on- a-chip micro-fluidic devices, the proposed non-invasive micro axicon tipped optical fiber can be used in multifunctional mode for in-depth trapping, rotation, sorting and ablation as well as for two-photon fluorescence excitation of motile sample which will revolutionize biophysics and research in material science.

Mishra, Yogeshwar N.; Pinto, Mervyn; Ingle, Ninad; Mohanty, Samarendra K.

2011-02-01

242

On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers.  

PubMed

This paper demonstrates local pH measurement in a microchip using a pH-sensing gel-microbead. To achieve this, the gel-microbead made of a hydrophilic photo-crosslinkable resin was functionalized with the pH indicator bromothymol blue (BTB). The primary constituent of this photo-crosslinkable resin is poly(ethylene glycol). Gel-microbeads impregnated with BTB were obtained by stirring the mixture solution, which was composed of the resin, BTB, and an electrolyte solution. The gel-microbead is polymerized by UV illumination. The polymerized gel-microbead can be manipulated by optical tweezers and made to adhere to a glass surface. The local pH was measured from the color of the gel-microbead impregnated with BTB by calibrated color information in the YCrCb color space. We succeeded in measuring the local pH value using the pH-sensing gel-microbead by manipulating and positioning it at the desired point in the microchip. PMID:18231676

Maruyama, Hisataka; Arai, Fumihito; Fukuda, Toshio

2007-11-27

243

Interaction of Oxazole Yellow Dyes with DNA Studied with Hybrid Optical Tweezers and Fluorescence Microscopy  

PubMed Central

Abstract We have integrated single molecule fluorescence microscopy imaging into an optical tweezers set-up and studied the force extension behavior of individual DNA molecules in the presence of various YOYO-1 and YO-PRO-1 concentrations. The fluorescence modality was used to record fluorescent images during the stretching and relaxation cycle. Force extension curves recorded in the presence of either dye did not show the overstretching transition that is characteristic for bare DNA. Using the modified wormlike chain model to curve-fit the force extension data revealed a contour length increase of 6% and 30%, respectively, in the presence of YO-PRO-1 and YOYO-1 at 100 nM. The fluorescence images recorded simultaneously showed that the number of bound dye molecules increased as the DNA molecule was stretched and decreased again as the force on the complex was lowered. The binding constants and binding site sizes for YO-PRO-1 and YOYO-1 were determined as a function of the force. The rate of YO-PRO-1 binding and unbinding was found to be 2 orders of magnitude larger than that for YOYO-1. A kinetic model is proposed to explain this observation.

Murade, C.U.; Subramaniam, V.; Otto, C.; Bennink, Martin L.

2009-01-01

244

Probing Protein Folding Kinetics with High-resolution, Stabilized Optical Tweezers  

NASA Astrophysics Data System (ADS)

Single-molecule techniques provide a powerful means of exploring molecular transitions such as the unfolding and refolding of a protein. However, the quantification of bi-directional transitions and near-equilibrium phenomena poses unique challenges, and is often limited by the detection resolution and long-term stability of the instrument. We have developed unique optical tweezers methods that address these problems, including an interference-based method for high-resolution 3D bead tracking (˜1 nm laterally, ˜0.3 nm vertically, at > 100 Hz), and a continuous autofocus system that stabilizes the trap height to within 1-2 nm longterm [1,2]. We have used our instruments to quantify the force-dependent unfolding and refolding kinetics of single protein domains (e.g. spectrin in collaboration with E. Evans). These single-molecule studies are presented, together with the accompanying probabilistic analysis that we have developed. References: 1. W.P. Wong, V. Heinrich, E. Evans, Mat. Res. Soc. Symp. Proc., 790, P5.1-P5.10 (2004). 2. V. Heinrich, W.P. Wong, K. Halvorsen, E. Evans, Langmuir, 24, 1194-1203 (2008).

Wong, Wesley; Halvorsen, Ken

2009-03-01

245

The interaction of Escherichia coli with its surrounding three dimensional substrate measured by oscillatory optical tweezers  

NASA Astrophysics Data System (ADS)

It has been known that the shape, the locomotion, and the growth of cells and bacteria are often affected by their interactions with extra cellular matrix (ECM). However, it is difficult to quantify such interactions with conventional biochemical methods. In this paper we report the application of oscillatory optical tweezers to trap and oscillate three types of E. coli, in 0.2% LB agar substrate to quantify the E. coli - substrate interactions in terms of the elasticity modulus G'. The three types of E. coli are BW25113 (wild-type, normal with flagellum), BW25113 (normal with flagellum, but subjected to UV light exposure for 1 hr to deactivate the flagellum), and JW1923 (a null-flagellum mutant of BW25113). Our results indicate that the value of G' for the later two is significantly higher than that for the normal wild-type (WT). We speculated that the interaction with the surrounding is perturbed, and hence reduced, mainly by the motion of the flagellum in the case of the WT.

Yen, Pei-Wen; Su, Pin-Tzu; Hung, Li-Jen; Wei, Ming-Tzo; Syu, Wan-Jr; Chiou, Arthur

2009-08-01

246

STED nanoscopy combined with optical tweezers reveals protein dynamics on densely covered DNA.  

PubMed

Dense coverage of DNA by proteins is a ubiquitous feature of cellular processes such as DNA organization, replication and repair. We present a single-molecule approach capable of visualizing individual DNA-binding proteins on densely covered DNA and in the presence of high protein concentrations. Our approach combines optical tweezers with multicolor confocal and stimulated emission depletion (STED) fluorescence microscopy. Proteins on DNA are visualized at a resolution of 50 nm, a sixfold resolution improvement over that of confocal microscopy. High temporal resolution (<50 ms) is ensured by fast one-dimensional beam scanning. Individual trajectories of proteins translocating on DNA can thus be distinguished and tracked with high precision. We demonstrate our multimodal approach by visualizing the assembly of dense nucleoprotein filaments with unprecedented spatial resolution in real time. Experimental access to the force-dependent kinetics and motility of DNA-associating proteins at biologically relevant protein densities is essential for linking idealized in vitro experiments with the in vivo situation. PMID:23934077

Heller, Iddo; Sitters, Gerrit; Broekmans, Onno D; Farge, Géraldine; Menges, Carolin; Wende, Wolfgang; Hell, Stefan W; Peterman, Erwin J G; Wuite, Gijs J L

2013-08-11

247

Optical tweezers reveal a dynamic mechanical response of cationic peptide-DNA complexes  

NASA Astrophysics Data System (ADS)

Nonviral carriers have been developed to deliver nucleic acids by forming nanoscale complexes; however, there has been limited success in achieving high transfection efficiency. Our hypothesis is that a factor affecting gene delivery efficiency is the mechanical response of the condensed complex. To begin to test this hypothesis, we directly measured the mechanical properties of DNA-carrier complexes using optical tweezers. Histidine-lysine (HK) polymer, Asparagine-lysine (NK) polymer and poly-L-lysine were used to form complexes with a single DNA molecule. As carriers were introduced, a sudden decrease in DNA extension occurrs at a force level which is defined as critical force (Fc). Fc is carrier and concentration dependent. Pulling revealed reduction in DNA extension length for HK-DNA complexes. The characteristics of force profiles vary by agent and can be dynamically manipulated by changes in environmental conditions such as ionic strength of the buffer as well as pH. Heparin can remove cationic reagents which are otherwise irreversibly bound to DNA. The implications for optimizing molecular interactions to enhance transfection efficiency will be discussed.

Lee, Amy; Zheng, Tai; Sucayan, Sarah; Chou, Szu-Ting; Tricoli, Lucas; Hustedt, Jason; Kahn, Jason; Mixson, A. James; Seog, Joonil

2013-03-01

248

Optical tweezers based measurement of PLGA-NP interaction with prostate cancer cells  

NASA Astrophysics Data System (ADS)

In order to quantify the binding capacities of polymeric, biodegradable and biocompatible poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), conjugated with either R11 peptides or Folic Acid, the strength by detach from prostate cancer cells (PCCs) was measured via optical tweezers based measurements. Specific nanoparticle drug delivery eliminates the previously used diffuse, full-body application of potent cancer drugs by localizing drug delivery to malignant cells. Precise monitoring of NP position in the trap near the PCC membrane using a fluorescence imaging based method enabled calibration of the trap stiffness and subsequent force measurements. By defining the force with which the many diverse conjugates and coatings of different types of NPs bind the vast array of cancer cell types, chemotherapeutic drugs can be delivered in a specific manner with the optimal particle and corresponding conjugates. Further, and most significantly, the rupture force measurements will reveal whether or not targeted nanoparticles can overcome the force of blood attempting to pull the particle from designated cells. Our preliminary study revealed that the binding between PLGA-NPs and prostate cancer cells is enhanced by coating with folic acid or R11 peptides. These conjugates increase the force required to detach the particle thus allowing particles to overcome drag force of the blood in prostate capillary systems.

Blesener, Thea; Mondal, Argha; Menon, Jyothi U.; Nguyen, Kytai T.; Mohanty, Samarendra

2013-02-01

249

Uncoiling mechanism of Klebsiella pneumoniae type 3 pili measured by using optical tweezers  

NASA Astrophysics Data System (ADS)

Pili are bacterial appendages that play many important roles in bacterial behaviors, physiology and interaction with hosts. Via pili, bacteria are able to adhere to, migrate onto, and colonize on host cells, mechanically. Different from the most studied type 1 and P type pili, which are rigid and thick with an average of 6~7 nm in diameter, type 3 pili are relatively tiny (3-5 nm in diameter) and flexible, and their biophysical properties remains unclear. By using optical tweezers, we found that the elongation processes of type 3 pili are divided into three phases: (1) elastic elongation, (2) uncoiling elongation, and (3) intrinsic elongation, separately. Besides, the uncoiling force of the recombinant pili displayed on the surface of E. coli [pmrkABCDV1F] is measured 20 pN in average stronger than that of E. coli [pmrkABCDV1]. This suggests that pilin MrkF is involved in determining the mechanical properties of the type 3 pili.

Chen, Feng-Jung; Chan, Chia-Han; Liu, Kuo-Liang; Huang, Ying-Jung; Peng, Hwei-Ling; Chang, Hwan-You; Yew, Tri-Rung; Hsu, Ken Y.; Hsu, Long

2007-09-01

250

Removal forces and adhesion properties of Saccharomyces cerevisiae on glass substrates probed by optical tweezer  

NASA Astrophysics Data System (ADS)

In agroindustry, the hygiene of solid surfaces is of primary importance in order to ensure that products are safe for consumers. To improve safety, one of the major ways consists in identifying and understanding the mechanisms of microbial cell adhesion to nonporous solid surfaces or filtration membranes. In this paper we investigate the adhesion of the yeast cell Saccharomyces cerevisiae (about 5 ?m in diameter) to a model solid surface, using well-defined hydrophilic glass substrates. An optical tweezer device developed by Piau [J. Non-Newtonian Fluid Mech. 144, 1 (2007)] was applied to yeast cells in contact with well-characterized glass surfaces. Two planes of observation were used to obtain quantitative measurements of removal forces and to characterize the corresponding mechanisms at a micrometer length scale. The results highlight various adhesion mechanisms, depending on the ionic strength, contact time, and type of yeast. The study has allowed to show a considerable increase of adhering cells with the ionic strength and has provided a quantitative measurement of the detachment forces of cultured yeast cells. Force levels are found to grow with ionic strength and differences in mobility are highlighted. The results clearly underline that a microrheological approach is essential for analyzing the adhesion mechanisms of biological systems at the relevant local scales.

Castelain, Mickaël; Pignon, Frédéric; Piau, Jean-Michel; Magnin, Albert; Mercier-Bonin, Muriel; Schmitz, Philippe

2007-10-01

251

Single-molecule kinetics under force: probing protein folding and enzymatic activity with optical tweezers  

NASA Astrophysics Data System (ADS)

Weak non-covalent bonds between and within single molecules govern many aspects of biological structure and function (e.g. DNA base-paring, receptor-ligand binding, protein folding, etc.) In living systems, these interactions are often subject to mechanical forces, which can greatly alter their kinetics and activity. My group develops and applies novel single-molecule manipulation techniques to explore and quantify these force-dependent kinetics. Using optical tweezers, we have quantified the force-dependent unfolding and refolding kinetics of different proteins, including the cytoskeletal protein spectrin in collaboration with E. Evans's group [1], and the A2 domain of the von Willebrand factor blood clotting protein in collaboration with T. Springer's group [2]. Furthermore, we have studied the kinetics of the ADAMTS13 enzyme acting on a single A2 domain, and have shown that physiolgical forces in the circulation can act as a cofactor for enzymatic cleavage, regulating hemostatic activity [2]. References: 1. E. Evans, K. Halvorsen, K. Kinoshita, and W.P. Wong, Handbook of Single Molecule Biophysics, P. Hinterdorfer, ed., Springer (2009). 2. X. Zhang, K. Halvorsen, C.-Z. Zhang, W.P. Wong, and T.A. Springer, Science 324 (5932), 1330-1334 (2009).

Wong, Wesley

2010-03-01

252

Induction of sustained glycolytic oscillations in single yeast cells using microfluidics and optical tweezers  

NASA Astrophysics Data System (ADS)

Yeast glycolytic oscillations have been studied since the 1950s in cell free extracts and in intact cells. Until recently, sustained oscillations have only been observed in intact cells at the population level. The aim of this study was to investigate sustained glycolytic oscillations in single cells. Optical tweezers were used to position yeast cells in arrays with variable cell density in the junction of a microfluidic flow chamber. The microfluidic flow chambers were fabricated using soft lithography and the flow rates in the different inlet channels were individually controlled by syringe pumps. Due to the low Reynolds number, the solutions mixed by diffusion only. The environment in the junction of the chamber could thus be controlled by changing the flow rates in the inlet channels, with a complete change of environment within 2 s. The optimum position of the cell array was determined by simulations, to ensure complete coverage of the intended solution without any concentration gradients over the cell array. Using a DAPI filter set, the NADH auto fluorescence could be monitored in up to 100 cells simultaneously. Sustained oscillations were successfully induced in individual, isolated cells within specific flow rates and concentrations of glucose and cyanide. By changing the flow rates without changing the surrounding solution, it was found that the cell behavior was dependent on the concentration of chemicals in the medium rather than the flow rates in the range tested. Furthermore, by packing cells tightly, cell-to-cell interaction and synchronization could be studied.

Gustavsson, Anna-Karin; Adiels, Caroline B.; Goksör, Mattias

2012-10-01

253

Optical tweezers reveal relationship between microstructure and nanoparticle penetration of pulmonary mucus  

PubMed Central

In this study, the mobility of nanoparticles in mucus and similar hydrogels as model systems was assessed to elucidate the link between microscopic diffusion behavior and macroscopic penetration of such gels. Differences in particle adhesion to mucus components were strongly dependent on particle coating. Particles coated with 2 kDa PEG exhibited a decreased adhesion to mucus components, whereas chitosan strongly increased the adhesion. Despite such mucoinert properties of PEG, magnetic nanoparticles of both coatings did not penetrate through native respiratory mucus, resisting high magnetic forces (even for several hours). However, model hydrogels were, indeed, penetrated by both particles in dependency of particle coating, obeying the theory of particle mobility in an external force field. Comparison of penetration data with cryogenic scanning EM images of mucus and the applied model systems suggested particularly high rigidity of the mucin scaffold and a broad pore size distribution in mucus as reasons for the observed particle immobilization. Active probing of the rigidity of mucus and model gels with optical tweezers was used in this context to confirm such properties of mucus on the microscale, thus presenting the missing link between micro- and macroscopical observations. Because of high heterogeneity in the size of the voids and pores in mucus, on small scales, particle mobility will depend on adhesive or inert properties. However, particle translocation over distances larger than a few micrometers is restricted by highly rigid structures within the mucus mesh.

Kirch, Julian; Schneider, Andreas; Abou, Berengere; Hopf, Alexander; Schaefer, Ulrich F.; Schneider, Marc; Schall, Christian; Wagner, Christian; Lehr, Claus-Michael

2012-01-01

254

Thermodynamic DNA Looping by a Two-Site Restriction Endonuclease Studied using Optical Tweezers  

NASA Astrophysics Data System (ADS)

Many enzyme-DNA interactions involve multimeric protein complexes that bind at two distant sites such that the DNA is looped. An example is the type IIe restriction enzyme Sau3AI, which requires two recognition sites to cleave the DNA. Here we study this process at the single DNA level using force measuring optical tweezers. We characterize cleavage rates of single DNA molecules in the presence of Sau3AI as a function of enzyme concentration, incubation time, and the fractional extension of the DNA molecule. Activity is completely inhibited by tensions of a few picoNewtons. By replacing Mg^2+ with Ca^2+, the Sau3AI dimers form but do not cleave the DNA, thus trapping DNA loops. We are able to pull apart these loops, measuring the force needed and the length of DNA released for each. We also characterize the number and length distributions of these loops as a function of incubation time and DNA fractional extension. The results of these studies are discussed in the context of a Brownian dynamics model of DNA looping.

Gemmen, Gregory J.

2005-03-01

255

Aerosol Optical Properties Observed during CHAPS  

NASA Astrophysics Data System (ADS)

During the CHAPS, the DOE Gulfstream-1 aircraft was used to make in-situ measurements of aerosol optical properties. The flight pattern was designed to allow for measurements below cloud, within the cloud layer, and above the clouds in the vicinity of Oklahoma City. Two different inlets were used on the G-1: an isokinetic inlet for sampling dry aerosols smaller than approximately 2 ?m in diameter, and a Counterflow Virtual Impactor (CVI) that excluded unactivated aerosols, but which allows cloud droplets to enter. A suite of paired instruments, including a nephelometer, Particle Soot Absorption Photometer (PSAP), and Aerosol Mass Spectrometer (AMS), was used to measure the aerosol optical properties from both sampling streams. Below the clouds, the single-scattering albedo measured inside the Oklahoma City plume was generally smaller than that observed outside of the plume. Within the cloud layer, but far from the clouds, there is little difference in the aerosol scattering measured inside and outside of the plume. These observations indicate that the vertical transport by the shallow clouds is very localized. Both aerosol extensive and intensive properties are discussed. For example, the total aerosol scattering and the mass-scattering efficiency measured inside the clouds was slightly larger for clouds that have roots within the Oklahoma City plume. Using data from the AMS in conjunction with the CVI inlet reveals that these in-cloud aerosols also have a relatively large amount of nitrate. Possible explanations for this increase nitrate will be discussed.

Berg, L. K.; Berkowitz, C. M.; Ogren, J. A.; Andrews, E.; Hubbe, J. M.; Lee, Y.; Yu, X.

2008-12-01

256

Effect of salicylate on outer hair cell plasma membrane viscoelasticity: studies using optical tweezers  

NASA Astrophysics Data System (ADS)

The plasma membrane (PM) of mammalian outer hair cells (OHCs) generates mechanical forces in response to changes in the transmembrane electrical potential. The resulting change in the cell length is known as electromotility. Salicylate (Sal), the anionic, amphipathic derivative of aspirin induces reversible hearing loss and decreases electromotile response of the OHCs. Sal may change the local curvature and mechanical properties of the PM, eventually resulting in reduced electromotility or it may compete with intracellular monovalent anions, particularly Cl-, which are essential for electromotility. In this work we have used optical tweezers to study the effects of Sal on viscoelastic properties of the OHC PM when separated from the underlying composite structures of the cell wall. In this procedure, an optically trapped microsphere is brought in contact with PM and subsequently pulled away to form a tether. We measured the force exerted on the tether as a function of time during the process of tether growth at different pulling rates. Effective tether viscosity, steady-state tethering force extrapolated to zero pulling rate, and the time constant for tether growth were estimated from the measurements of the instantaneous tethering force. The time constant for the tether growth measured for the OHC basal end decreased 1.65 times after addition of 10 mM Sal, which may result from an interaction between Sal and cholesterol, which is more prevalent in the PM of OHC basal end. The time constants for the tether growth calculated for the OHC lateral wall and control human embryonic kidney cells as well as the other calculated viscoelastic parameters remained the same after Sal perfusion, favoring the hypothesis of competitive inhibition of electromotility by salicylate.

Ermilov, Sergey A.; Brownell, William E.; Anvari, Bahman

2004-06-01

257

Gobal Aerosol Optical Models and Lookup Tables for the New MODIS Aerosol Retrieval over Land.  

National Technical Information Service (NTIS)

Since 2000, MODIS has been deriving aerosol properties over land from MODIS observed spectral reflectance, by matching the observed reflectance with that simulated for selected aerosol optical models, aerosol loadings, wavelengths and geometrical conditio...

L. A. Remer O. Dubovik R. C. Levy

2007-01-01

258

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Manipulation of Nanoparticles Using Dark-Field-Illumination Optical Tweezers with Compensating Spherical Aberration  

NASA Astrophysics Data System (ADS)

Based on our previous investigation of optical tweezers with dark field illumination [Chin. Phys. Lett. 25(2008)329], nanoparticles at large trap depth are better viewed in wide field and real time for a long time, but with poor forces. Here we present the mismatched tube length to compensate for spherical aberration of an oil-immersion objective in a glass-water interface in an optical tweezers system for manipulating nanoparticles. In this way, the critical power of stable trapping particles is measured at different trap depths. It is found that trap depth is enlarged for trapping nanoparticles and trapping forces are enhanced at large trap depth. According to the measurement, 70-nm particles are manipulated in three dimensions and observed clearly at large appropriate depth. This will expand applications of optical tweezers in a nanometre-scale colloidal system.

Zhou, Jin-Hua; Tao, Run-Zhe; Hu, Zhi-Bin; Zhong, Min-Cheng; Wang, Zi-Qiang; Cai, Jun; Li, Yin-Mei

2009-06-01

259

Force mapping during the formation and maturation of cell adhesion sites with multiple optical tweezers.  

PubMed

Focal contacts act as mechanosensors allowing cells to respond to their biomechanical environment. Force transmission through newly formed contact sites is a highly dynamic process requiring a stable link between the intracellular cytoskeleton and the extracellular environment. To simultaneously investigate cellular traction forces in several individual maturing adhesion sites within the same cell, we established a custom-built multiple trap optical tweezers setup. Beads functionalized with fibronectin or RGD-peptides were placed onto the apical surface of a cell and trapped with a maximum force of 160 pN. Cells form adhesion contacts around the beads as demonstrated by vinculin accumulation and start to apply traction forces after 30 seconds. Force transmission was found to strongly depend on bead size, surface density of integrin ligands and bead location on the cell surface. Highest traction forces were measured for beads positioned on the leading edge. For mouse embryonic fibroblasts, traction forces acting on single beads are in the range of 80 pN after 5 minutes. If two beads were positioned parallel to the leading edge and with a center-to-center distance less than 10 µm, traction forces acting on single beads were reduced by 40%. This indicates a spatial and temporal coordination of force development in closely related adhesion sites. We also used our setup to compare traction forces, retrograde transport velocities, and migration velocities between two cell lines (mouse melanoma and fibroblasts) and primary chick fibroblasts. We find that maximal force development differs considerably between the three cell types with the primary cells being the strongest. In addition, we observe a linear relation between force and retrograde transport velocity: a high retrograde transport velocity is associated with strong cellular traction forces. In contrast, migration velocity is inversely related to traction forces and retrograde transport velocity. PMID:23372781

Schwingel, Melanie; Bastmeyer, Martin

2013-01-25

260

Nonequilibrium thermodynamics of single DNA hairpins in a dual-trap optical tweezers setup  

NASA Astrophysics Data System (ADS)

We use two counter propagating laser beams to create a dual trap optical tweezers setup which is free from cross interference between the beams and provides great instrumental stability. This setup works by direct measurement of light momentum, separately for each trap, and is based on the Minitweezers design [1]. The dual trap setup has many applications: it can be used to study the force-dependent unfolding kinetics of single molecules and to address fundamental problems in nonequilibrium thermodynamics of small systems [2]. Recent progress in statistical physics has shown the importance of considering large energy deviations in the beahvior of systems that are driven out-of-equilibrium by time-dependent forces. Prominent examples are nonequilibrium work relations (e.g. the Jarzynski equality [3]) and fluctuation theorems. By repeated measurement of the irreversible work the Jarzynski equality allows us to recover the free energy difference between two thermodynamic states, AF, by taking exponential averages of the work W done by the external agent on the system, e-??F =

Crivellari, M. Ribezzi; Huguet, J. M.; Ritort, F.

2011-03-01

261

Force Unfolding Kinetics of RNA Using Optical Tweezers. I. Effects of Experimental Variables on Measured Results  

PubMed Central

Experimental variables of optical tweezers instrumentation that affect RNA folding/unfolding kinetics were investigated. A model RNA hairpin, P5ab, was attached to two micron-sized beads through hybrid RNA/DNA handles; one bead was trapped by dual-beam lasers and the other was held by a micropipette. Several experimental variables were changed while measuring the unfolding/refolding kinetics, including handle lengths, trap stiffness, and modes of force applied to the molecule. In constant-force mode where the tension applied to the RNA was maintained through feedback control, the measured rate coefficients varied within 40% when the handle lengths were changed by 10-fold (1.1–10.2 Kbp); they increased by two- to threefold when the trap stiffness was lowered to one-third (from 0.1 to 0.035 pN/nm). In the passive mode, without feedback control and where the force applied to the RNA varied in response to the end-to-end distance change of the tether, the RNA hopped between a high-force folded-state and a low-force unfolded-state. In this mode, the rates increased up to twofold with longer handles or softer traps. Overall, the measured rates remained with the same order-of-magnitude over the wide range of conditions studied. In the companion article on pages 3010–3021, we analyze how the measured kinetics parameters differ from the intrinsic molecular rates of the RNA, and thus how to obtain the molecular rates.

Wen, Jin-Der; Manosas, Maria; Li, Pan T. X.; Smith, Steven B.; Bustamante, Carlos; Ritort, Felix; Tinoco, Ignacio

2007-01-01

262

Three-dimensional light-scattering and deformation of individual biconcave human blood cells in optical tweezers.  

PubMed

For studying the elastic properties of a biconcave red blood cell using the dual-trap optical tweezers without attaching microbeads to the cell, we implemented a three-dimensional finite element simulation of the light scattering and cell's deformation using the coupled electromagnetic and continuum mechanics modules. We built the vector field of the trapping beams, the cell structure layout, the hyperelastic and viscoelastic cell materials, and we reinforced the constraints on the cell constant volume in the simulation. This computation model can be useful for studying the scattering and the other mechanical properties of the biological cells. PMID:23736438

Yu, Lingyao; Sheng, Yunlong; Chiou, Arthur

2013-05-20

263

Modeling highly focused laser beam in optical tweezers with the vector Gaussian beam in the T-matrix method.  

PubMed

The vector Gaussian beam with high-order corrections is used to describe accurately the laser beam up to numerical aperture NA=1.20 in the optical tweezers for trapping nanoparticles. The beam is then expanded in the T-matrix method into the vector spherical wave function (VSWF) series using the point matching method with a new selection of the matching points. The errors in the beam description and in the VSWF expansion are much lower than those that occur in the paraxial Gaussian beam model. PMID:23455996

Bareil, Paul B; Sheng, Yunlong

2013-01-01

264

Video-based analysis of the rotational behaviour of rod-shaped, self-propelled bacteria in holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Utilising the versatility of holographic optical tweezers and high speed video analysis, we present a scheme for the analysis of the rotational properties of multiple rod-shaped bacteria directly from video microscopy data. The bacterial body and flagella rotation frequency of Bacillus subtilis are determined by temporally resolved monitoring of the position of the bacterial body. In contrast to established methods, the video-based approach can be extended to the simultaneous analysis of several bacteria within the field of view. Monitoring multiple bacteria simultaneously will allow resolving the role of hydrodynamic interactions of multiple flagella motors on their mutual dynamics.

Dewenter, Lena; Alpmann, Christina; Woerdemann, Mike; Denz, Cornelia

2012-05-01

265

Aerosol optical properties during the Lindenberg Aerosol Characterization Experiment (LACE 98)  

Microsoft Academic Search

The optical properties of atmospheric aerosol particles were measured close to ground level using different methods at Lindenberg\\/Falkenberg (Germany) during the Lindenberg Aerosol Characterization Experiment (LACE 98), 13 July 1998 to 14 August 1998 [Ansmann et al., 2002]. The experimental setup consisted of (a) an aerosol photometer, which measured a complete set of aerosol optical properties, such as extinction, scattering,

U. Bundke; G. Hänel; H. Horvath; W. Kaller; S. Seidl; H. Wex; A. Wiedensohler; M. Wiegner; V. Freudenthaler

2002-01-01

266

The Reno Aerosol Optics Study: An Evaluation of Aerosol Absorption Measurement Methods  

Microsoft Academic Search

The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative

Patrick J. Sheridan; W. Patrick Arnott; John A. Ogren; Elisabeth Andrews; Dean B. Atkinson; Hans Moosmüller; Andreas Petzold; Beat Schmid; Anthony W. Strawa; Ravi Varma; Aki Virkkula

2005-01-01

267

Optical Tweezers and Optical Trapping Improved for Future Automated Micromanipulation and Characterization.  

National Technical Information Service (NTIS)

Optical trap arrays are being developed at the NASA Glenn Research Center for holding, manipulating, and optically interrogating arrays of nanotube sensors. The trap arrays, for example, might be used to arrange arrays of chemical sensors for insertion on...

S. Y. Wrbanek A. J. Decker

2005-01-01

268

Dye lasing in optically manipulated liquid aerosols.  

PubMed

We report lasing in airborne, rhodamine B-doped glycerol-water droplets with diameters ranging between 7.7 and 11.0 ?m, which were localized using optical tweezers. While being trapped near the focal point of an infrared laser, the droplets were pumped with a Q-switched green laser. Our experiments revealed nonlinear dependence of the intensity of the droplet whispering gallery modes (WGMs) on the pump laser fluence, indicating dye lasing. The average wavelength of the lasing WGMs could be tuned between 600 and 630 nm by changing the droplet size. These results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium. PMID:23938905

Karadag, Y; Aas, M; Jonáš, A; Anand, S; McGloin, D; Kiraz, A

2013-05-15

269

Amines and optical properties of Titan's aerosols  

NASA Astrophysics Data System (ADS)

This work deals with the optical characterization of Titan aerosol analogues or "tholins". Those have been produced in different N2-CH4 gaseous mixtures to study the effect of the initial methane concentration on their optical properties. We studied the FIR- and MID-IR absorption properties on the SMIS beamline of the French SOLEIL synchrotron. And we determined the UV-visible-near IF optical indices by using the spectroscopic ellipsometry technique in the 370-1000 nm wavelength range.

Carrasco, N.; Mahjoub, A.; Gautier, T.; Dahoo, P. R.; Szopa, C.; Cernogora, G.

2012-09-01

270

Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae  

NASA Astrophysics Data System (ADS)

A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper.

Castelain, Mickaël; Rouxhet, Paul G.; Pignon, Frédéric; Magnin, Albert; Piau, Jean-Michel

2012-06-01

271

Mechanical characterization of human red blood cells under different osmotic conditions by robotic manipulation with optical tweezers.  

PubMed

The physiological functions of human red blood cells (RBCs) play a crucial role to human health and are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. The osmotic condition is an important factor to the physiological environment, but its effect on RBCs has been little studied. To investigate this effect, robotic manipulation technology with optical tweezers is utilized in this paper to characterize the mechanical properties of RBCs in different osmotic conditions. The effectiveness of this technology is demonstrated first in the manipulation of microbeads. Then the optical tweezers are used to stretch RBCs to acquire the force-deformation relationships. To extract cell properties from the experimental data, a mechanical model is developed for RBCs in hypotonic conditions by extending our previous work , and the finite element model is utilized for RBCs in isotonic and hypertonic conditions. Through comparing the modeling results to the experimental data, the shear moduli of RBCs in different osmotic solutions are characterized, which shows that the cell stiffness increases with elevated osmolality. Furthermore, the property variation and potential biomedical significance of this study are discussed. In conclusion, this study indicates that the osmotic stress has a significant effect on the cell properties of human RBCs, which may provide insight into the pathology analysis and therapy of some human diseases. PMID:20176536

Tan, Youhua; Sun, Dong; Wang, Jinzhi; Huang, Wenhao

2010-02-18

272

Measuring nanoscale interactions and dynamics of DNA-grafted colloids with line optical tweezers  

NASA Astrophysics Data System (ADS)

Much of the excitement regarding nanotechnology stems from the idea of "bottom-up" self-assembly: the possibility of spontaneously growing complex structures or devices out of molecular scale components rather than using conventional microfabrication. Realizing such goals requires a reliable method for inducing specific interactions between multiple particle species. The preferred method for inducing such interactions is to use hybridization, the sequence-specific assembly of single stranded DNA grafted onto the particles into double strands. Linking bridges of DNA can either glue two objects together strongly or cause them to weakly and reversibly adhere. While the strong adhesion limit has been studied, the weak reversible interactions required for equilibrium self-assembly and annealing remain poorly characterized, hindering experimental and theoretical progress. All previous attempts to assemble non-DNA objects using DNA interactions have created highly disordered aggregates rather than the hoped for crystal-like structures. Here we report the first direct measurements of such DNA-induced colloidal interactions, as well as the first colloidal crystals assembled using them. The pair interactions measured with our optical tweezer method can be modeled in detail by well-known statistical physics and chemistry, boding well for their application to directed self-assembly. The microspheres' binding dynamics, however, have a surprising power-law scaling that can significantly slow annealing and crystallization. We separated effects due to multiple bridge kinetics from those due to individual DNA hybridization by adjusting the microspheres' DNA surface density. The process of DNA hybridization requires the traversing of a multitude of intermediate steps to get from two random coil oligonucleotides to a tidy duplex DNA. We probed the nature of these intermediate states by measuring the lifetime distribution of single 16-bp duplexes subject to thermal dissociation under effectively zero tension. Unlike comparable single molecule experiments performed at finite tension, we find an unusual stretched exponential lifetime distribution, suggesting that thermal dissociation proceeds via a number of competing intermediate pathways. Similar measurements with higher DNA density indicate that multiple-bridged states are highly unstable, indicating that the duplexes are extremely force sensitive. Our power-law kinetics are a likely consequence of the exquisite force sensitivity and nonexponential dissociation kinetics of the DNA bridges.

Biancaniello, Paul Louis

273

Aerosol Radiative Forcing Derived from SeaWiFS-Retrieved Aerosol Optical Properties  

Microsoft Academic Search

To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the earth's radiation budgets [aerosol radiative forcing (ARF)] are computed using a radiative transfer model. It is found that the distribution of the SeaWiFS-retrieved aerosol optical thickness is distinctively zonal.

Ming-Dah Chou; Pui-King Chan; Menghua Wang

2002-01-01

274

Combining optical tweezers, single-molecule fluorescence microscopy, and microfluidics for studies of DNA-protein interactions.  

PubMed

The technically challenging field of single-molecule biophysics has established itself in the last decade by granting access to detailed information about the fate of individual biomolecules, unattainable in traditional biochemical assays. The appeal of single-molecule methods lies in the directness of the information obtained from individual biomolecules. Technological improvements in single-molecule methods have made it possible to combine optical tweezers, fluorescence microscopy, and microfluidic flow systems. Such a combination of techniques has opened new possibilities to study complex biochemical reactions on the single-molecule level. In this chapter, we provide general considerations for the development of a combined optical trapping, fluorescence microscopy, and microfluidics instrument, along with methods to solve technical issues that are critical for designing successful experiments. Finally, we present several experiments to illustrate the power of this combination of techniques. PMID:20627167

Gross, Peter; Farge, Géraldine; Peterman, Erwin J G; Wuite, Gijs J L

2010-01-01

275

Lipid Bilayer-Integrated Optoelectronic Tweezers for Nanoparticle Manipulations.  

National Technical Information Service (NTIS)

Remotely manipulating a large number of microscopic objects is important to soft-condensed matter physics, biophysics, and nanotechnology. Optical tweezers and optoelectronic tweezers have been widely used for this purpose but face critical challenges whe...

S. Ota S. Wang X. Yin X. Zhang Y. Wang

2013-01-01

276

Impairment of cytoskeleton-dependent vesicle and organelle translocation in green algae: combined use of a microfocused infrared laser as microbeam and optical tweezers.  

PubMed

A Nd-YAG laser at 1064 nm is used as optical tweezers to move intracellular objects and a laser microbeam to cause impairment of cytoskeleton tracks and influence intracellular motions in desmidiaceaen green algae. Naturally occurring migrations of large nuclei are inhibited in Micrasterias denticulata and Pleurenterium tumidum when the responsible microtubules are targeted with a laser microbeam generating 180 mW power in the focal plane. Impairment of the microtubule tracks appears to be irreversible, as the nucleus cannot pass the former irradiated area in Pleurenterium or remains abnormally dislocated in Micrasterias. The actin filament-dependent movement of secretory vesicles and smaller particles can be manipulated by the same IR-laser at 90 mW when functioning as optical tweezers. In Closterium lunula particles are displaced from their cytoplasmic tracks for up to 10 micro m but return to their tracks immediately after removing the light pressure gained by the optical tweezers. The cytoplasmic tracks consist of actin filament cables running parallel to the longitudinal axis of Closterium cells as depicted by Alexa phalloidin staining and confocal laser scanning microscopy. Dynamics and extensibility of the cytoplasmic strands connecting particles to the tracks are also demonstrated in the area of large vacuoles which are surrounded by actin filament bundles. In Micrasterias trapping of secretory vesicles by the optical tweezers causes irreversible malformations of the cell shape. The vesicle accumulation itself dissipates within 30 s after removing the optical tweezers, also indicating reversibility of the effects induced, in the case of actin filament-mediated processes. PMID:12423258

Holzinger, A; Monajembashi, S; Greulich, K O; Lütz-Meindl, U

2002-11-01

277

Aerosol Radiative Forcing Derived From SeaWIFS - Retrieved Aerosol Optical Properties.  

National Technical Information Service (NTIS)

To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the Earth's radiation budgets (aerosol r...

M. D. Chou P. K. Chan M. Wang

2000-01-01

278

Atmospheric Aerosol Optical Properties in the Persian Gulf  

Microsoft Academic Search

Aerosol optical depth measurements over Bahrain acquired through the ground-based Aerosol Robotic Network (AERONET) are analyzed. Optical depths obtained from ground-based sun\\/sky radiometers showed a pronounced temporal trend, with a maximum dust aerosol loading observed during the March-July period. The aerosol optical depth probability distribution is rather narrow with a modal value of about 0.25. The Ångström parameter frequency distribution

Alexander Smirnov; Brent N. Holben; Oleg Dubovik; Norm T. O'Neill; Thomas F. Eck; Douglas L. Westphal; Andreas K. Goroch; Christophe Pietras; Ilya Slutsker

2002-01-01

279

Optical Properties of Atmospheric Aerosol in Maritime Environments  

Microsoft Academic Search

Systematic characterization of aerosol over the oceans is needed to understand the aerosol effect on climate and on transport of pollutants between continents. Reported are the results of a comprehensive optical and physical characterization of ambient aerosol in five key island locations of the Aerosol Robotic Network (AERONET) of sun and sky radiometers, spanning over 2-5 yr. The results are

Alexander Smirnov; Brent N. Holben; Yoram J. Kaufman; Oleg Dubovik; Thomas F. Eck; Ilya Slutsker; Christophe Pietras; Rangasayi N. Halthore

2002-01-01

280

Calibrating bead displacements in optical tweezers using acousto-optic deflectors  

SciTech Connect

Displacements of optically trapped particles are often recorded using back-focal-plane interferometry. In order to calibrate the detector signals to displacements of the trapped object, several approaches are available. One often relies either on scanning a fixed bead across the waist of the laser beam or on analyzing the power spectrum of movements of the trapped bead. Here, we introduce an alternative method to perform this calibration. The method consists of very rapidly scanning the laser beam across the solvent-immersed, trapped bead using acousto-optic deflectors while recording the detector signals. It does not require any knowledge of solvent viscosity and bead diameter, and works in all types of samples, viscous or viscoelastic. Moreover, it is performed with the same bead as that used in the actual experiment. This represents marked advantages over established methods.

Vermeulen, Karen C.; Mameren, Joost van; Stienen, Ger J.M.; Peterman, Erwin J.G.; Wuite, Gijs J.L.; Schmidt, Christoph F. [Laser Centre and Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands); Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam (Netherlands); Laser Centre and Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands)

2006-01-15

281

Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration  

SciTech Connect

Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3 W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.

Andersson, Martin; Madgavkar, Ashwin; Stjerndahl, Maria; Wu, Yanrong; Tan, Weihong; Duran, Randy; Niehren, Stefan; Mustafa, Kamal; Arvidson, Kristina; Wennerberg, Ann [Department of Chemistry, University of Florida, Gainesville, Florida 32611 (United States); Molecular Machines and Industries GmbH, Breslauerstrasse 2, 85386 Eching (Germany); Center for Clinical Dental Research, University of Bergen, N-5009 Bergen (Norway); Department of Prosthodontics/Dental Material Science, University of Goeteborg, S-40530 Goeteborg, Sweden and Department of Biomaterials, University of Goeteborg, S-40530 Goeteborg (Sweden)

2007-07-15

282

An emerging ground-based aerosol climatology: Aerosol optical depth from AERONET  

Microsoft Academic Search

Long-term measurements by the AERONET program of spectral aerosol optical depth, precipitable water, and derived Angstrom exponent were analyzed and compiled into an aerosol optical properties climatology. Quality assured monthly means are presented and described for 9 primary sites and 21 additional multiyear sites with distinct aerosol regimes representing tropical biomass burning, boreal forests, midlatitude humid climates, midlatitude dry climates,

B. N. Holben; D. Tanré; A. Smirnov; T. F. Eck; I. Slutsker; N. Abuhassan; W. W. Newcomb; J. S. Schafer; B. Chatenet; F. Lavenu; Y. J. Kaufman; J. Vande Castle; A. Setzer; B. Markham; D. Clark; R. Frouin; R. Halthore; A. Karneli; N. T. O'Neill; C. Pietras; R. T. Pinker; K. Voss; G. Zibordi

2001-01-01

283

Optofluidic tweezer on a chip  

PubMed Central

A novel method to realize an optical tweezer involving optofluidic operation in a microchannel is proposed. To manipulate the optical tweezer, light from an optical fiber is passed through both PDMS (polydimethylsiloxane)-air surface lenses and an optofluidic region, which is located in a control channel. Two liquids with different refractive indices (RIs) are introduced into the control channel to form two different flow patterns (i.e., laminar and segmented flows), depending on the liquid compositions, the channel geometry, and the flow rates. By altering the shapes of the interface of the two liquids in the optofluidic region, we can continuously or intermittently control the optical paths of the light. To demonstrate the functionality of the proposed method, optical tweezer operations on a chip are performed. Changing the flow pattern of two liquids with different RIs in the optofluidic region results in successful trapping of a 25 ?m diameter microsphere and its displacement by 15 ?m.

Ono, K.; Kaneda, S.; Shiraishi, T.; Fujii, T.

2010-01-01

284

Applying Combined Optical Tweezers and Fluorescence Microscopy Technologies to Manipulate Cell Adhesions for Cell-to-Cell Interaction Study.  

PubMed

Cell-to-cell interactions are important for the regulation of various cell activities, such as proliferation, differentiation, and apoptosis. This paper presents an approach to studying cell-to-cell interactions at a single-cell level through manipulating cell adhesions with optical tweezers. Experiments are performed on leukemia cancer cells and stromal cells to demonstrate the feasibility of this method. After the adhesion properties of leukemia cells on stromal cells are characterized, fluorescence intensity is used as a label to study the Wnt signaling pathway of leukemia cells. The activities of the Wnt signaling pathway of K562 cells on M210B4 and HS5 cells are examined based on fluorescence analysis. The reliability of the fluorescence imaging is confirmed through comparison with traditional flow cytometry analysis. The proposed approach will offer new avenues to investigate otherwise inaccessible mechanisms in cell-to-cell interactions. PMID:23549881

Gou, Xue; Han, Ho Chun; Hu, Songyu; Leung, Anskar Y H; Sun, Dong

2013-03-28

285

Optical Properties of Aerosols and Clouds: The Software Package OPAC  

Microsoft Academic Search

The software package OPAC (Optical Properties of Aerosols and Clouds) is described. It easily provides optical properties in the solar and terrestrial spectral range of atmospheric particulate matter. Microphysical and optical properties of six water clouds, three ice clouds, and 10 aerosol components, which are considered as typical cases, are stored as ASCII files. The optical properties are the extinction,

M. Hess; P. Koepke; I. Schult

1998-01-01

286

Optical closure experiments for biomass smoke aerosols  

NASA Astrophysics Data System (ADS)

A series of laboratory experiments at the Fire Laboratory at Missoula (FLAME) investigated chemical, physical, and optical properties of fresh smoke samples from combustion of wildland fuels that are burned annually in the western and southeastern US The burns were conducted in the combustion chamber of the US Forest Service Fire Sciences Laboratory in Missoula, Montana. Here we discuss retrieval of optical properties for a variety of fuels burned in FLAME 2, using nephelometer-measured scattering coefficients, photoacoustically-measured aerosol absorption coefficients, and size distribution measurements. Uncertainties are estimated from various instrument characteristics and instrument calibration studies. Our estimates of single scattering albedo for different dry smoke samples varied from 0.428 to 0.990, indicative of observed wide variations in smoke aerosol chemical composition. In selected case studies, we retrieved the complex refractive index from measurements but show that these are highly sensitive to uncertainties in measured size distributions.

Mack, L. A.; Levin, E. J. T.; Kreidenweis, S. M.; Obrist, D.; Moosmüller, H.; Lewis, K. A.; Arnott, W. P.; McMeeking, G. R.; Sullivan, A. P.; Wold, C. E.; Hao, W.-M.; Collett, J. L., Jr.; Malm, W. C.

2010-09-01

287

Optical closure experiments for biomass smoke aerosols  

NASA Astrophysics Data System (ADS)

The FLAME experiments were a series of laboratory studies of the chemical, physical, and optical properties of fresh smokes from the combustion of wildland fuels that are burned annually in the western and southeastern US. The burns were conducted in the combustion chamber of the USFS Fire Sciences Laboratory in Missoula, Montana. Here we discuss the retrieval of optical properties for a variety of fuels burned in FLAME 2, using nephelometer-measured scattering coefficients, photoacoustically-measured aerosol absorption coefficients, and size distribution measurements. Uncertainties are estimated from the various instrument characteristics and from instrument calibration studies. Our estimates of single scattering albedo for different dry smokes varied from 0.43-0.99, indicative of the wide variations in smoke aerosol chemical composition that were observed. In selected case studies, we retrieved the complex refractive index from the measurements, but show that these are highly sensitive to the uncertainties in measured size distributions.

Mack, L. E.; Levin, E. J. T.; Kreidenweis, S. M.; Obrist, D.; Moosmüller, H.; Lewis, K. A.; Arnott, W. P.; McMeeking, G. R.; Sullivan, A. P.; Wold, C. E.; Hao, W.-M.; Collett, J. L., Jr.; Malm, W. C.

2010-03-01

288

Oxidation of biogenic and water-soluble compounds in aqueous and organic aerosol droplets by ozone: a kinetic and product analysis approach using laser Raman tweezers.  

PubMed

The results of an experimental study into the oxidative degradation of proxies for atmospheric aerosol are presented. We demonstrate that the laser Raman tweezers method can be used successfully to obtain uptake coefficients for gaseous oxidants on individual aqueous and organic droplets, whilst the size and composition of the droplets is simultaneously followed. A laser tweezers system was used to trap individual droplets containing an unsaturated organic compound in either an aqueous or organic (alkane) solvent. The droplet was exposed to gas-phase ozone and the reaction kinetics and products followed using Raman spectroscopy. The reactions of three different organic compounds with ozone were studied: fumarate anions, benzoate anions and alpha-pinene. The fumarate and benzoate anions in aqueous solution were used to represent components of humic-like substances, HULIS; alpha-pinene in an alkane solvent was studied as a proxy for biogenic aerosol. The kinetic analysis shows that for these systems the diffusive transport and mass accommodation of ozone is relatively fast, and that liquid-phase diffusion and reaction are the rate determining steps. Uptake coefficients, gamma, were found to be (1.1 +/- 0.7) x 10(-5), (1.5 +/- 0.7) x 10(-5) and (3.0-7.5) x 10(-3) for the reactions of ozone with the fumarate, benzoate and alpha-pinene containing droplets, respectively. Liquid-phase bimolecular rate coefficients for reactions of dissolved ozone molecules with fumarate, benzoate and alpha-pinene were also obtained: kfumarate = (2.7 +/- 2) x 10(5), kbenzoate = (3.5 +/- 3) x 10(5) and kalpha-pinene = (1-3) x 10(7) dm3 mol(-1) s(-1). The droplet size was found to remain stable over the course of the oxidation process for the HULIS-proxies and for the oxidation of alpha-pinene in pentadecane. The study of the alpha-pinene/ozone system is the first using organic seed particles to show that the hygroscopicity of the particle does not increase dramatically over the course of the oxidation. No products were detected by Raman spectroscopy for the reaction of benzoate ions with ozone. One product peak, consistent with aqueous carbonate anions, was observed when following the oxidation of fumarate ions by ozone. Product peaks observed in the reaction of ozone with alpha-pinene suggest the formation of new species containing carbonyl groups. PMID:18214104

King, Martin D; Thompson, Katherine C; Ward, Andrew D; Pfrang, Christian; Hughes, Brian R

2008-01-01

289

Measurements and modeling of water transport and osmoregulation in a single kidney cell using optical tweezers and videomicroscopy.  

PubMed

With an optical tweezer installed in our optical microscope we grab a single Madin Darby Canine kidney cell and keep it suspended in the medium without touching the glass substrate or other cells. Since the optically trapped cell remains with a closely round shape, we can directly measure its volume by using videomicroscopy with digital image analysis. We submit this cell to a hyperosmotic shock (up-shock) and video record the process: the cell initially shrinks due to osmotic efflux of water and after a while, due to regulatory volume increase (RVI), an osmoregulation response, it inflates again (water influx) until it reaches a new volume (the regulatory volume VR). In addition to considering standard osmotic water transport, we model RVI using a simple phenomenological model. We obtain an expression for cell volume variation as a function of time that fits very well with our experimental data, where two characteristic times appear naturally: one related to water transport and the other related to RVI. From the fit we obtain water permeability, osmolyte influx rate for RVI, and regulatory volume. With the addition of the hormone vasopressin, water permeability increases while the regulatory volume decreases until inhibition of RVI. In summary, we present a technique to measure directly volume changes of a single isolated kidney cell under osmotic shock and a phenomenological analysis of water transport that takes into account osmoregulation. PMID:14682972

Lúcio, A D; Santos, R A S; Mesquita, O N

2003-10-10

290

Using optical tweezers to examine the chemotactic force to a single inflammatory cell--eosinophil stimulated by chemoattractants prepared from Toxocara Canis larvae  

NASA Astrophysics Data System (ADS)

Granulocytes are a group of white blood cells belonging to the innate immune system in human and in murine in which eosinophils play an important role in worm infection-induced inflammation. The migration of these cells is well characterized and has been separated into four steps: rolling, adhesion, transendothelial migration, and chemotaxis, however, the physical characteristics of the chemotactic force to eosinophils from worm component remain largely unknown. Note that optical tweezers are featured in the manipulation of a single cell and the measurement of biological forces. Therefore, we propose to use optical tweezers to examine the chemotactic force to a eosinophil from a T. canis lavae preparation in terms of distance during the migration of eosinophil.

Shih, Po-Chen; Su, Yi-Jr; Chen, Ke-Min; Jen, Lin-Ni; Liu, Cheng-tzu; Hsu, Long

2005-08-01

291

Aerosol optical depth characteristics in Yinchuan area  

NASA Astrophysics Data System (ADS)

Sand dust aerosol is the main component of aerosol in troposphere atmosphere of East Asia, which can produce the extensive influence on the ecosystem, atmosphere environment and atmosphere chemistry through intensive sand dust weather process. For investigation of the aerosol optical depth (AOD) and its temporal-spatial evolution over this area, a series of observation experiments were carried out by a sun photometer CE-318 located at Beifang University of Nationality( 106°E, 38°29'N ), Yinchuan Ningxia province of China from September 2012 to April 2013 and many direct solar radiation datum were obtained. The experiments results were analyzed in detail and some conclusions are obtained as follows: (1) For daily evolution of AOD, the variation trend are divided into four types: ?the AOD values are relatively steady in whole day; ? the AOD values increase from morning to afternoon; ? the AOD values are greater at noon than that in the morning and afternoon; ?there is a peak in the variation trends of AOD from 9:00~12:00 in the morning, but it is small at other time. (2) For month evolution, the minimum AOD average value appears in September and the maximum one appears in April. (3) For the seasonal changes trend, the average AOD values in the April are bigger than that in the autumn. (4) In addition, during the observation period, one dust weather process was observed and the change characteristic of AOD of dust aerosol was obtained and analyzed.

Zhang, Yaya; Mao, Jiandong; Rao, Zhimin; Zhang, Fan

2013-08-01

292

Interactive application in holographic optical tweezers of a multi-plane Gerchberg-Saxton algorithm for three-dimensional light shaping  

Microsoft Academic Search

Phase-hologram patterns that can shape the intensity distribution of a light beam in several planes simultaneously can be calculated with an iterative Gerchberg-Saxton algorithm [T. Haist et al., Opt. Commun. 140, 299 (1997)]. We apply this algorithm in holographic optical tweezers. This allows us to simultaneously trap several objects in individually controllable arbitrary 3-dimensional positions. We demonstrate the interactive use

Gavin Sinclair; Jonathan Leach; Pamela Jordan; Graham Gibson; Eric Yao; Zsolt John Laczik; Miles J. Padgett; Johannes Courtial

2004-01-01

293

Contribution of different aerosol species to the global aerosol extinction optical thickness: Estimates from model results  

Microsoft Academic Search

We combine global distributions of aerosol loading resulting from transport models for soil dust, sulfate, sea salt, and carbonaceous aerosol. From the aerosol distributions we estimate optical thickness and compare them with Sun photometer measurements and satellite retrievals, thereby revealing problems with both model results and comparisons with such measurements. Globally, sulfate, dust, and carbonaceous particles appear to contribute equally

Ina Tegen; Peter Hollrig; Mian Chin; Inez Fung; Daniel Jacob; Joyce Penner

1997-01-01

294

Instrument calibration and aerosol optical depth validation of the China Aerosol Remote Sensing Network  

Microsoft Academic Search

This paper introduced the calibration of the CE-318 sunphotometer of the China Aerosol Remote Sensing Network (CARSNET) and the validation of aerosol optical depth (AOD) by AOD module of ASTPWin software compared with the simultaneous measurements of the Aerosol Robotic Network (AERONET)\\/Photométrie pour le Traitement Opérationnel de Normalization Satellitaire (PHOTONS) and PREDE skyradiometer. The results show that the CARSNET AOD

Huizheng Che; Xiaoye Zhang; Hongbin Chen; Bahaiddin Damiri; Philippe Goloub; Zhengqiang Li; Xiaochun Zhang; Yao Wei; Huaigang Zhou; Fan Dong; Deping Li; Tianming Zhou

2009-01-01

295

Case studies and comparisons of the CALIPSO aerosol optical depth measurements and aerosol type estimates  

Microsoft Academic Search

The CALIPSO Level II data are analyzed to assess the veracity of the CALIPSO aerosol type identification algorithm and generate distributions of aerosol types and their respective optical characteristics. The distributions show that the classification algorithm has no surface type or diurnal dependencies. For this initial assessment of algorithm performance, we analyze global distributions of the CALIPSO aerosol types, along

Ali Omar; Mark Vaughan; Chieko Kittaka; Dave Winker

2008-01-01

296

Estimation of aerosol optical depth over ocean: Intercept technique  

Microsoft Academic Search

The study of atmospheric aerosols is an important element to understand the earth's solar radiation budget, water cycle balance, and climate change dynamics. Estimating aerosol properties is also one of the first steps in generating high-level land and ocean surface products from satellite observations. In this paper, a simple method to estimate the aerosol optical depth (AOD) over ocean is

Abd Rahman Mat Amin; Khiruddin Abdullah; Mohd Rivaie

2011-01-01

297

Optical Properties of Atmospheric Aerosol in Maritime Environments  

Microsoft Academic Search

Atmospheric aerosol optical properties over the oceans based on the AERONET data are presented. The results are compared with the historical shipborne data acquired over the last 30 years. A model of the maritime aerosol component derived using AERONET data from island locations in the Pacific, Atlantic and Indian Ocean is presented. Maritime aerosol properties in the Central Pacific are

Alexander Smirnov; B. N. Holben; O. Dubovik; T. F. Eck; I. Slutsker

2004-01-01

298

Aerosol optical depth over Europe: Satellite retrieval and modeling  

NASA Astrophysics Data System (ADS)

Aerosol optical depth (AOD) and A?ngström coefficients over Europe retrieved from satellite data for August 1997 provide information on the spatial variations of these aerosol properties. The AOD results are compared with initial results from model calculations, showing the relative influences of sulphate and nitrate aerosol. .

Gonzalez, C. Robles; de Leeuw, G.; Veefkind, J. P.; Builtjes, P. J. H.; van Loon, M.; Schaap, M.

2000-08-01

299

Optical Properties of Titan's Aerosol Analogues  

NASA Astrophysics Data System (ADS)

In the upper Titan's atmosphere its main constituents, CH4 and N2, are photolyzed and radiolyzed by solar photons and magnetospheric electrons. The primary products of these chemical interactions evolve to heavier organic compounds which are likely to associate to form the haze layers observed on Titan's upper atmosphere. Different theories and models have been used to explain the physical, chemical and optical properties of the haze material, but only with limited success. Among the parameters involved in these models, the complex refractive index is one of the most critical due to the influence that chemical composition and structural organization of the solid have on the n and k values. As part of a continued systematical study for the synthesis and characterization of Titan's aerosol analogues initiated in our group, we have subjected mixtures of CH4 in N2 to laser irradiation to produce layer of aerosol analogues. A set of optical properties values directly calculated from the transmission and reflectance curves, as well as a chemical characterization, by tandem mass spectroscopy, of the laboratory analogues will be presented. Our experimental protocol avoids some of the difficulties usually faced on laboratory simulations (over-irradiation, contamination with atmospheric oxygen, accurate ratio of initial gas mixture), porosity influences will also be discussed. The optical values can be used to determine how the chemical and optical properties of these aerosols influence the matching with the observed geometric albedo spectrum and how they participate in the radiative equilibrium processes in Titan's atmosphere. They will certainly help in the interpretation of the observations made by the Huygens descend through Titan's atmosphere last January and in all the new information about Titan generated since then. Financial support from CONACyT (40449) and PROMEP (103.5/03/1134) is acknowledged. SIRJ acknowledges a travel grant from PIFI 3.2.

Ramirez, Sandra I.; Contreras, G.; Agarwal, V.

2006-09-01

300

Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the UK  

NASA Astrophysics Data System (ADS)

Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and hence its climate impact, but few in situ observations of mixing state exist. We present airborne single particle soot photometer (SP2) measurements of refractory BC (rBC) mass concentrations and mixing state coupled with aerosol composition and optical properties measured in urban plumes and regional pollution over the UK. All data were obtained using instrumentation flown on the UK's BAe-146-301 large Atmospheric Research Aircraft (ARA) operated by the Facility for Airborne Atmospheric Measurements (FAAM). We measured sub-micron aerosol composition using an aerosol mass spectrometer (AMS) and used positive matrix factorization to separate hydrocarbon-like (HOA) and oxygenated organic aerosols (OOA). We found a higher number fraction of thickly coated rBC particles in air masses with large OOA relative to HOA, higher ozone-to-nitrogen oxides (NOx) ratios and large concentrations of total sub-micron aerosol mass relative to rBC mass concentrations. The more ozone- and OOA-rich air masses were associated with transport from continental Europe, while plumes from UK cities had higher HOA and NOx and fewer thickly coated rBC particles. We did not observe any significant change in the rBC mass absorption efficiency calculated from rBC mass and light absorption coefficients measured by a particle soot absorption photometer despite observing significant changes in aerosol composition and rBC mixing state. The contributions of light scattering and absorption to total extinction (quantified by the single scattering albedo; SSA) did change for different air masses, with lower SSA observed in urban plumes compared to regional aerosol (0.85 versus 0.9-0.95). We attribute these differences to the presence of relatively rapidly formed secondary aerosol, primarily OOA and ammonium nitrate, which must be taken into account in radiative forcing calculations.

McMeeking, G. R.; Morgan, W. T.; Flynn, M.; Highwood, E. J.; Turnbull, K.; Haywood, J.; Coe, H.

2011-05-01

301

Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the United Kingdom  

NASA Astrophysics Data System (ADS)

Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and hence its climate impact, but few in situ observations of mixing state exist. We present airborne single particle soot photometer (SP2) measurements of refractory BC (rBC) mass concentrations and mixing state coupled with aerosol composition and optical properties measured in urban plumes and regional pollution over the United Kingdom. All data were obtained using instrumentation flown on the UK's BAe-146-301 large Atmospheric Research Aircraft (ARA) operated by the Facility for Airborne Atmospheric Measurements (FAAM). We measured sub-micron aerosol composition using an aerosol mass spectrometer (AMS) and used positive matrix factorization to separate hydrocarbon-like (HOA) and oxygenated organic aerosols (OOA). We found a higher number fraction of thickly coated rBC particles in air masses with large OOA relative to HOA, higher ozone-to-nitrogen oxides (NOx) ratios and large concentrations of total sub-micron aerosol mass relative to rBC mass concentrations. The more ozone- and OOA-rich air masses were associated with transport from continental Europe, while plumes from UK cities had higher HOA and NOx and fewer thickly coated rBC particles. We did not observe any significant change in the rBC mass absorption efficiency calculated from rBC mass and light absorption coefficients measured by a particle soot absorption photometer despite observing significant changes in aerosol composition and rBC mixing state. The contributions of light scattering and absorption to total extinction (quantified by the single scattering albedo; SSA) did change for different air masses, with lower SSA observed in urban plumes compared to regional aerosol (0.85 versus 0.9-0.95). We attribute these differences to the presence of relatively rapidly formed secondary aerosol, primarily OOA and ammonium nitrate, which must be taken into account in radiative forcing calculations.

McMeeking, G. R.; Morgan, W. T.; Flynn, M.; Highwood, E. J.; Turnbull, K.; Haywood, J.; Coe, H.

2011-09-01

302

Optical tweezers studies of viral DNA packaging: Motor function and DNA confinement in Bacteriophages phi29, lambda, and T4  

NASA Astrophysics Data System (ADS)

In the assembly of many viruses a powerful molecular motor translocates the genome into a pre-assembled capsid. We use optical tweezers to directly measure translocation of a single DNA molecule into the viral capsid. Improved techniques allow us to measure initiation and early stages of packaging. With phi29 the DNA terminal protein was found to cause large variations in the starting point of packaging. Removal of this protein results in terminal initiation, permitting more accurate assessment of motor function and DNA confinement forces. We investigated the role of electrostatic repulsion by varying ionic screening of the DNA. The observed trends are in accord with those theoretically expected considering counter-ion competition; however the forces are larger than expected in comparison with recent theories and DNA ejection measurements. We have recently succeeded in extending our methods to study two other phages: lambda and T4. These systems have unique structural and functional features, presenting an opportunity for comparative studies in this family of molecular motors. Initial measurements show that lambda and T4 translocate DNA several times faster than the phi29 motor, but are more sensitive to applied load.

Smith, Douglas

2007-03-01

303

Studies of viral DNA packaging motors with optical tweezers: a comparison of motor function in bacteriophages ?29, ?, and T4  

NASA Astrophysics Data System (ADS)

A key step in the assembly of many viruses is the packaging of double-stranded DNA into a viral procapsid (an empty protein shell) by the action of an ATP-powered portal motor complex. We have developed methods to measure the packaging of single DNA molecules into single viral proheads in real time using optical tweezers. We can measure DNA binding and initiation of translocation, the DNA translocation dynamics, and the filling of the capsid against resisting forces. In addition to studying bacteriophage ?29, we have recently extended these methods to study the E. coli bacteriophages ? and T4, two important model systems in molecular biology. The three systems have different capsid sizes/shapes, genome lengths, and biochemical and structural differences in their packaging motors. Here, we compare and contrast these three systems. We find that all three motors translocate DNA processively and generate very large forces, each exceeding 50 piconewtons, ~20x higher force than generated by the skeletal muscle myosin 2 motor. This high force generation is required to overcome the forces resisting the confinement of the stiff, highly charged DNA at high density within the viral capsids. However, there are also striking differences between the three motors: they exhibit different DNA translocation rates, degrees of static and dynamic disorder, responses to load, and pausing and slipping dynamics.

Smith, Douglas E.; Fuller, Derek N.; Raymer, Dorian M.; Rickgauer, Peter; Grimes, Shelley; Jardine, Paul J.; Anderson, Dwight L.; Catalano, Carlos E.; Kottadiel, Vishal; Rao, Venigalla B.

2007-09-01

304

Experimental study of the Stokes-Einstein relation by using oscillating optical tweezers and a position tracking method  

NASA Astrophysics Data System (ADS)

Transportation and delivery of microscopic materials in very small and complex systems such as biological organisms are mainly done by physical diffusion. This phenomenon in a fluid system with a low Reynolds number can be explained using the Stokes-Einstein relation D = k B T/?, where D is the diffusion coefficient, T is the temperature of the system, and ? is the viscous friction coefficient of the background fluid. For a spherical particle with radius a in a fluid of viscosity ?, ? = 6 ??a. As far as we know, all the experimental tests of this relation before ours measured only D, ?, a, and T due to the experimental difficulties in measuring ? directly. In this research, we tested this relation from a different perspective. The diffusion coefficient D and the viscous friction coefficient ? were experimentally measured in the same system by using a position tracking method and an oscillating optical tweezers technique, respectively. We found that our experimental results supported the Stokes-Einstein relation very well.

Ha, Chungil; Kim, Sung-Jin; Pak, Hyuk Kyu

2013-02-01

305

FACS-sorted particles reduce the data variance in optical tweezers-assisted dynamic force spectroscopy measurements.  

PubMed

By combining optical tweezers-assisted dynamic force spectroscopy experiments with fluorescence activated cell sorting (FACS), we demonstrate a new approach to reducing the data variance in measuring receptor-ligand interactions on a single molecule level by ensuring similar coating densities. Therefore, the carboxyfluorescein-labelled monophosphorylated peptide tau226-240[pThr231] is anchored on melamine resin beads and these beads are sorted by FACS to achieve a homogeneous surface coverage. To quantify the impact of the fluorescence dye on the bond parameters between the phosphorylated peptide and the corresponding phosphorylation specific anti-human tau monoclonal antibody HPT-104, we perform dynamic force spectroscopy and compare the results to data using unsorted beads covered with the non-fluorescence peptide analogue. Finally, we demonstrate that the data variance of the relative binding frequency is significantly decreased by a factor of 3.4 using pre-sorted colloids with a homogeneous ligand coating compared to using unsorted colloids. PMID:23788010

Stangner, T; Singer, D; Wagner, C; Gutsche, C; Ueberschär, O; Hoffmann, R; Kremer, F

2013-06-20

306

Probing the effect of elevated cholesterol on the mechanical properties of membrane-cytoskeleton by optical tweezers  

NASA Astrophysics Data System (ADS)

The composition of the cell membrane and the surrounding physiological factors determine the nature and dynamics of membrane-cytoskeleton coupling. Mechanical strength of a cell is mainly derived from such coupling. In this article, we investigate the effect of extra cellular cholesterol on the membrane-cytoskelaton connectivity of single cell endothelium and consequent remodeling of its mechanical properties. Using optical tweezers as a force probe, we have measured membrane stiffness (km), membrane microviscosity (?eff ) and the two-dimensional shear modulus (G'(f)) as a function of extracellular cholesterol in the range of 0.1mM to 6mM. We find that membrane stiffness and shear modulus are dependent on cholesterol-induced membrane-cytoskeletal organization. Further, by disrupting the membranecytoskeletal connectivity with Cytochalasin D, an actin delpolymerizing molecule, we recover pure membrane behaviour devoid of any cytoskeleton attachment. However, behaviour of ?eff was found to be unaffected by disruption of membrane-cytoskeleton organization. We infer that cholesterol is playing a distinct role in modulating membrane organization and membrane-cytoskeleton connectivity independently. We further discuss implications of our approach in characterizing cellular mechanics.

Rajkumar, Arun S.; Muley, Ajit; Chatterjee, Suvro; Jaffar Ali, B. M.

2010-08-01

307

Direct measurement of DNA molecular length in solution using optical tweezers: detection of looping due to binding protein interactions.  

PubMed

DNA looping is caused by the interaction between DNA binding proteins located at separate positions on a DNA molecule and may play an important role in transcription regulation. We have developed a system to stretch single DNA molecules and to measure changes in molecular length. DNA molecules were prepared and 5' end-labeled by PCR amplification. Two beads and the intervening DNA molecule were trapped and manipulated independently with dual trap optical tweezers. The trapped DNA molecule was then stretched and the extension (the distance between the two beads) was measured. The extension at the specific tension force of 30 pN was calculated and used as a molecular length. The molecular length was found to be proportional to the base pair number. The rise per residue was calculated to be 3.31 +/- 0.05 A. The length measurement was applied to DNA fragments containing GC box sequences at two different locations separated by a distance of 2.428 kbp. The addition of GC box binding transcription factor Sp1 shortened the molecular length, suggesting DNA looping forms as a result of interaction between transcription factors. PMID:9463890

Sakata-Sogawa, K; Kurachi, M; Sogawa, K; Fujii-Kuriyama, Y; Tashiro, H

1998-01-01

308

Laser microbeams for DNA damage induction, optical tweezers for the search on blood pressure relaxing drugs: contributions to ageing research  

NASA Astrophysics Data System (ADS)

One essential cause of human ageing is the accumulation of DNA damages during lifetime. Experimental studies require quantitative induction of damages and techniques to visualize the subsequent DNA repair. A new technique, the "immuno fluorescent comet assay", is used to directly visualize DNA damages in the microscope. Using DNA repair proteins fluorescently labeled with green fluorescent protein, it could be shown that the repair of the most dangerous DNA double strand breaks starts with the inaccurate "non homologous end joining" pathway and only after 1 - 1 ½ minutes may switch to the more accurate "homologous recombination repair". One might suggest investigating whether centenarians use "homologous recombination repair" differently from those ageing at earlier years and speculate whether it is possible, for example by nutrition, to shift DNA repair to a better use of the error free pathway and thus promote healthy ageing. As a complementary technique optical tweezers, and particularly its variant "erythrocyte mediated force application", is used to simulate the effects of blood pressure on HUVEC cells representing the inner lining of human blood vessels. Stimulating one cell induces in the whole neighbourhood waves of calcium and nitric oxide, known to relax blood vessels. NIFEDIPINE and AMLODIPINE, both used as drugs in the therapy of high blood pressure, primarily a disease of the elderly, prolong the availability of nitric oxide. This partially explains their mode of action. In contrast, VERAPAMILE, also a blood pressure reducing drug, does not show this effect, indicating that obviously an alternative mechanism must be responsible for vessel relaxation.

Grigaravicius, P.; Monajembashi, S.; Hoffmann, M.; Altenberg, B.; Greulich, K. O.

2009-08-01

309

Climatology of aerosol optical properties in Southern Africa  

NASA Astrophysics Data System (ADS)

A thorough regionally dependent understanding of optical properties of aerosols and their spatial and temporal distribution is required before we can accurately evaluate aerosol effects in the climate system. Long term measurements of aerosol optical depth, Angstrom exponent and retrieved single scattering albedo and size distribution, were analyzed and compiled into an aerosol optical properties climatology for southern Africa. Monitoring of aerosol parameters have been made by the AERONET program since the middle of the last decade in southern Africa. This valuable information provided an opportunity for understanding how aerosols of different types influence the regional radiation budget. Two long term sites, Mongu in Zambia and Skukuza in South Africa formed the core sources of data in this study. Results show that seasonal variation of aerosol optical thicknesses at 500 nm in southern Africa are characterized by low seasonal multi-month mean values (0.11 to 0.17) from December to May, medium values (0.20 to 0.27) between June and August, and high to very high values (0.30 to 0.46) during September to November. The spatial distribution of aerosol loadings shows that the north has high magnitudes than the south in the biomass burning season and the opposite in none biomass burning season. From the present aerosol data, no long term discernable trends are observable in aerosol concentrations in this region. This study also reveals that biomass burning aerosols contribute the bulk of the aerosol loading in August-October. Therefore if biomass burning could be controlled, southern Africa will experience a significant reduction in total atmospheric aerosol loading. In addition to that, aerosol volume size distribution is characterized by low concentrations in the non biomass burning period and well balanced particle size contributions of both coarse and fine modes. In contrast high concentrations are characteristic of biomass burning period, combined with significant dominance of fine mode particles.

Queface, Antonio J.; Piketh, Stuart J.; Eck, Thomas F.; Tsay, Si-Chee; Mavume, Alberto F.

2011-06-01

310

An investigation of aerosol optical properties: Atmospheric implications and influences  

NASA Astrophysics Data System (ADS)

An experimental, observational, and theoretical investigation of aerosol optical properties has been made in this work to study their implications and influences on the atmosphere. In the laboratory the scientific and instrumental methodology consisted of three parts, namely, aerosol generation, optical and mass concentration measurements, and computational calculations. In particular the optical properties of ammonium sulfate and caffeine aerosol were derived from measurements made with a transmissometer cell-reciprocal- integrating nephelometer (TCRIN), equipped with a laser beam at 632.8 nm, and by applying a Mie theory computer code The aerosol generators, optical equipment and calibration procedures were reviewed. The aerosol shape and size distribution were studied by means of scanning electron microscopy and the Gumprecht- Sliepcevich/Lipofsky-Green extinction-sedimentation method. In particular the spherical and cylindrical shape were considered. During this investigation, an alternative method for obtaining the optical properties of monodisperse spherical non-absorbing aerosol using a cell-transmissometer, which is based on a linearisation of the Lambert-Beer law, was found. In addition, adapting the TCRIN to electrooptical aerosol studies, the optical properties of a circular-cylindrical aerosol of caffeine were undertaken under the condition of random orientation in relation with the laser beam, and perpendicular orientation to it. A theoretical study was conducted to assess the sensitivity of aerosol to a change of shape under different polarisation modes. The aerosol optical properties, obtained previously in the laboratory, were then used to simulate the direct radiative forcing. The calculations and results were obtained by applying a one- dimensional energy-balance box model. The influence of atmospheric aerosol on the sky brightness due to a total solar eclipse was studied using the photometric and meteorological observations made during the eclipse of 26 February 1998 which occurred in Venezuela. With additional data, a comparison could be made between this eclipse and the other one which took place in the same country on 3 February 1916.

Penaloza-Murillo, Marcos A.

311

Parallel transport of biological cells using individually addressable VCSEL arrays as optical tweezers  

Microsoft Academic Search

We have demonstrated the use of vertical cavity surface emitting lasers (VCSELs) for optical trapping and active manipulation of live biological cells and microspheres. We have experimentally verified that the Laguerre–Gaussian laser mode output from the VCSEL functions just as well as the traditional Gaussian fundamental laser mode for optically trapping biological cells and may be preferable since the highest

Richard A. Flynn; Aaron L. Birkbeck; Matthias Gross; Mihrimah Ozkan; Bing Shao; Mark M. Wang; Sadik C. Esener

2002-01-01

312

Novel cost effective carbon nanotubes deposition technique using optical tweezer effect  

Microsoft Academic Search

Carbon nanotubes (CNTs) have been intensively studied for optical applications because of their useful characteristics. However, handling of the CNTs is one of the largest problems for device applications. Several methods have been reported to fabricate optical devices, such as spray method, direct synthesis method, and polymer embedding method. These methods require complicated process and dissipate excessive amount of CNTs.

Ken Kashiwagi; Shinji Yamashita; Sze Yun Set

2007-01-01

313

Near infrared optical tweezers and nanosecond ablation on yeast and algae cells  

NASA Astrophysics Data System (ADS)

In recent years, lasers for optical trapping and micromanipulation of microscopic particles or cells and sub cellular structures, both in vivo and in vitro, have gained remarkable interest in biomedical research and applications. Although the principles and the mechanisms of pulsed laser ablation have been well described for macroscopic interventions, the microbeam operation under microscopic guidance necessitates further investigation. In this work, we present the research and development efforts towards a pulsed ultraviolet microbeam laser system, the design and realization efforts towards a near infrared laser trapping device and the results obtained on yeast cells and algae by the combined system. We investigated the optical dissection of the cells versus the presence of optical trapping forces and the presence of rhodamine dye. We characterized the optical ablation of the cell walls and resulting cavitation as plasma formation effects which create shock waves due to their occurrence only in nanosecond pulse irradiation mode. We estimated the minimum energy of the microbeam for optical dissection of yeast cell, under the influence of optical trapping forces, as lower as 3 ?J, while in the presence of rhodamine as lower as 2 ?J. Lastly, using the techniques of optical microsurgery we demonstrated the minimum energy value for sub cellular dissection on an algae cell equal to 27 ?J.

Kotsifaki, D. G.; Makropoulou, M.; Serafetinides, A.

2013-03-01

314

The study of adhesive forces between the type-3 fimbriae of Klebsiella pneumoniae and collagen-coated surfaces by using optical tweezers  

NASA Astrophysics Data System (ADS)

Adherence to host cells by a bacterial pathogen is a critical step for establishment of infection. It will contribute greatly to the understanding of bacterial pathogenesis by studying the biological force between a single pair of pathogen and host cell. In our experiment, we use a calibrated optical tweezers system to detach a single Klebsiella pneumoniae, the pathogen, from collagen, the host. By gradually increasing the laser power of the optical tweezers until the Klebsiella pneumoniae is detached from the collagen, we obtain the magnitude of the adhesive force between them. This happens when the adhesive force is barely equal to the trapping force provided by the optical tweezers at that specific laser power. This study is important because Klebsiella pneumoniae is an opportunistic pathogen which causes suppurative lesions, urinary and respiratory tract infections. It has been proved that type 3 fimbrial adhesin (mrkD) is strongly associated with the adherence of Klebsiella pneumoniae. Besides, four polymorphic mrkD alleles: namely, mrkDv1, v2, v3, and v4, are typed by using RFLP. In order to investigate the relationship between the structure and the function for each of these variants, DNA fragments encoding the major fimbrial proteins mrkA, mrkB, mrkC are expressed together with any of the four mrkD adhesins in E. coli JM109. Our study shows that the E. coli strain carrying the mrkDv3 fimbriae has the strongest binding activity. This suggests that mrkDv3 is a key factor that enhances the adherence of Klebsiella Pneumoniae to human body.

Chan, Chiahan; Fan, Chia-chieh; Huang, Ying-Jung; Peng, Hwei-Ling; Long, Hsu

2004-10-01

315

Parallel Transport of Biological Cells using Individually Addressable VCSEL Arrays as Optical Tweezers.  

National Technical Information Service (NTIS)

We have demonstrated the use of vertical cavity surface emitting lasers (VCSELs) for optical trapping and active manipulation of live biological cells and microspheres.We have experimentally verified that the Laguerre Gaussian laser mode output from the V...

A. L. Birkbeck B. Shao M. Gross M. Ozhan R. A. Flynn

2005-01-01

316

An algorithm for improved control of trap intensities in holographic optical tweezers  

NASA Astrophysics Data System (ADS)

The use of phase only spatial light modulators for holographic optical trapping results in the appearance of ghost orders, creating unwanted traps with uncontrolled intensity and causing variations in the intensity of the desired traps. By introducing dummy areas in the diffraction plane during the hologram optimization, the intensity in the ghost orders can be significantly reduced. By directing a variable fraction of the light to the dummy area, the optical power in the traps can be controlled independently and kept constant also while moving traps to different arrangements. We present and evaluate an algorithm for hologram generation which utilizes dummy areas and allows arbitrary spot positioning in three dimensions. The method enables the use of holographic optical trapping for applications requiring precise control of the intensity in traps, such as optical force measurement.

Persson, Martin; Engström, David; Goksör, Mattias

2012-10-01

317

In vitro motility of immunoadsorbed brain myosin-V using a Limulus acrosomal process and optical tweezer-based assay.  

PubMed

To facilitate functional studies of novel myosins, we have developed a strategy for characterizing the mechanochemical properties of motors isolated by immunoadsorption directly from small amounts of crude tissue extracts. In this initial study, silica beads coated with an antibody that specifically recognizes the tail of myosin-V were used to immunoadsorb this motor protein from brain extracts. The myosin-containing beads were then positioned with optical tweezers onto actin filaments nucleated from Limulus sperm acrosomal processes and observed for motility using high resolution video DIC microscopy. The addition of brush border spectrin to the motility chamber enabled the growth of stable actin filament tracks that were approximately 4-fold longer than filaments grown in the absence of this actin crosslinking protein. The velocity of myosin-V immunoadsorbed from brain extracts was similar to that observed for purified myosin-V that was antibody-linked to beads or assessed using the sliding actin filament assay. Motile beads containing myosin-V immunoadsorbed from brain extracts bound poorly to nucleated actin filaments and were incapable of linear migrations following the addition of a different antibody that specifically recognizes the motor-containing head domain of myosin-V. Myosin-V motility was most robust in the absence of Ca2+. Interestingly, skeletal muscle tropomyosin and brush border spectrin had no detectable effect on myosin-V mechanochemistry. Myosin-V containing beads were also occasionally observed migrating directly on acrosomal processes in the absence of exogenously added actin.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7615669

Wolenski, J S; Cheney, R E; Mooseker, M S; Forscher, P

1995-04-01

318

Parametric study of the forces on microspheres held by optical tweezers  

Microsoft Academic Search

Optical-trapping forces exerted on polystyrene microspheres are predicted and measured as a function of sphere size, laser spot size, and laser beam polarization. Axial and transverse forces are in good and excellent agreement, respectively, with a ray-optics model when the sphere diameter is [ge]10 [mu]m. Results are compared with results from an electromagnetic model when the sphere size is [le]1

W. H. Wright; G. J. Sonek; M. W. Berns

1994-01-01

319

Aerosol Optical Properties in Southeast Asia From AERONET Observations  

NASA Astrophysics Data System (ADS)

There is little published data available on measured optical properties of aerosols in the Southeast Asian region. The AERONET project and collaborators commenced monitoring of aerosol optical properties in February 2003 at four sites in Thailand and two sites in Viet Nam to measure the primarily anthropogenic aerosols generated by biomass burning and fossil fuel combustion/ industrial emissions. Automatic sun/sky radiometers at each site measured spectral aerosol optical depth in 7 wavelengths from 340 to 1020 nm and combined with directional radiances in the almucantar, retrievals were made of spectral single scattering albedo and aerosol size distributions. Angstrom exponents, size distributions and spectral single scattering albedo of primarily biomass burning aerosols at rural sites are compared to measurements made at AERONET sites in other major biomass burning regions in tropical southern Africa, South America, and in boreal forest regions. Additionally, the aerosol single scattering albedo and size distributions measured in Bangkok, Thailand are compared with those measured at other urban sites globally. The influences of aerosols originating from other regions outside of Southeast Asia are analyzed using trajectory analyses. Specifically, cases of aerosol transport and mixing from Southern China and from India are presented.

Eck, T. F.; Holben, B. N.; Boonjawat, J.; Le, H. V.; Schafer, J. S.; Reid, J. S.; Dubovik, O.; Smirnov, A.

2003-12-01

320

Comparisons of the TOMS aerosol index with Sun-photometer aerosol optical thickness: Results and applications  

NASA Astrophysics Data System (ADS)

A nearly 20-year global data set (1979-1994 and 1996 to the present) of tropospheric absorbing aerosols has been developed from total ozone mapping spectrometer (TOMS) backscattered radiance measurements in the range from 331 to 380 nm. The occurrence of aerosols is derived directly from measured backscattered radiances and is represented by a quantity known as the aerosol index. Previous theoretical model simulations have demonstrated that the aerosol index depends on aerosol optical thickness (AOT), single scattering albedo, and aerosol height and that the AOT can be determined provided that the microphysical properties and height of aerosols are known. In this paper we show that the TOMS aerosol index measurements are linearly proportional to the AOT derived independently from ground-based Sun-photometer instruments over regions of biomass burning and regions covered by African dust. We also show how this linear relationship can be used to directly convert the aerosol index into AOT for smoke and dust aerosols for the regions near the Sun-photometer sites and how information about aerosol height can be inferred from the results. Finally, we apply this method to the TOMS data over the last two decades and find a significant increase in the amount of biomass burning smoke in the African savanna regions during the 1990s in addition to the more obvious increase in South America.

Hsu, N. C.; Herman, J. R.; Torres, O.; Holben, B. N.; Tanre, D.; Eck, T. F.; Smirnov, A.; Chatenet, B.; Lavenu, F.

1999-03-01

321

Retrieval of Spectral Aerosol Optical Properties and Their Relationship to Aerosol Chemistry During ARCTAS  

NASA Astrophysics Data System (ADS)

Aerosols are known to both absorb and scatter radiation at UV wavelengths with the degree of absorption/scattering largely dependent on aerosol chemistry. The interactions of aerosols with the UV radiation field were examined during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS). Analysis focused on two case studies; one flight from the first phase of ARCTAS over Alaska and the Arctic ocean (Flight 10, April 2008) and the other from the second phase over northern Canada (Flight 17, June 2008). These flights were chosen based on availability of aircraft profiles through pollution layers and biomass burning smoke plumes with high loadings of organic aerosol during flight. Aerosol single scattering albedo (?) was retrieved at near-UV (350-400nm) wavelengths at 1nm resolution from spectral actinic flux data collected aboard the NASA DC-8 aircraft during ARCTAS using two CCD Actinic Flux Spectroradiometers. Retrievals were performed using the Tropospheric Ultraviolet Model version 4.6 (TUV 4.6). Inputs of trace gas (e.g., NO2, SO2) concentrations, aerosol optical depth, location, time, pressure, etc. required by TUV were determined from ancillary aircraft measurements made from the DC-8. Values of ? were subsequently used to determine absorption optical depth (?abs) for each of the examined flights. Retrieval and calculation results were compared to aerosol optical properties in the visible (calculated from measurements of absorption and scattering aboard the DC-8) and the spectral dependencies characterized. Spectral ? and ?abs were compared with aerosol chemistry data collected by an Aerosol Mass Spectrometer (AMS) to provide insight into the role of aerosol composition on absorption in the UV wavelength range. In particular, spectral dependencies were compared to the oxidation state of the organic aerosol (determined from AMS data) to examine the impact of aerosol processing/aging on spectral ? and ?abs.

Corr, C. A.; Hall, S. R.; Ullmann, K.; Shetter, R.; Anderson, B. E.; Beyersdorf, A. J.; Thornhill, K. L.; Cubison, M.; Jimenez, J. L.; Dibb, J. E.

2010-12-01

322

Using optical tweezers for the characterization of polyelectrolyte solutions with very low viscoelasticity.  

PubMed

Recently, optical tweezing has been used to provide a method for microrheology addressed to measure the rheological properties of small volumes of samples. In this work, we corroborate this emerging field of microrheology by using these optical methods for the characterization of polyelectrolyte solutions with very low viscoelasticity. The influence of polyelectrolyte (i.e., polyacrylamide, PAM) concentration, specifically its aging, of the salt concentration is shown. The close agreement of the technique with classical bulk rheological measurements is demonstrated, illustrating the advantages of the technique. PMID:23786307

Pommella, Angelo; Preziosi, Valentina; Caserta, Sergio; Cooper, Jonathan M; Guido, Stefano; Tassieri, Manlio

2013-07-11

323

Complex field-induced nematic defect structures in Laguerre-Gaussian optical tweezers  

NASA Astrophysics Data System (ADS)

Complex optical field-induced defect structures are presented in nematic and chiral nematic liquid crystals, as imprinted by Laguerre-Gaussian (LG) laser beams. Our modeling study is based on the phenomenological free energy approach, which dielectrically couples the nematic optical axis with the polarization of the LG beams. The symmetry of the presented structures proves to be conditioned by the beam helical indices. The beam intensity, strength of the nematic elastic constant, and local intensity-induced control of the nematic order via absorption of the light are demonstrated as possible mechanisms for producing, imprinting, and tuning of the field-induced complex defect structures in achiral and chiral nematics.

Žumer, Slobodan; Porenta, Tine; Ravnik, Miha

2012-10-01

324

Using Optical Tweezers for the Characterization of Polyelectrolyte Solutions with Very Low Viscoelasticity  

PubMed Central

Recently, optical tweezing has been used to provide a method for microrheology addressed to measure the rheological properties of small volumes of samples. In this work, we corroborate this emerging field of microrheology by using these optical methods for the characterization of polyelectrolyte solutions with very low viscoelasticity. The influence of polyelectrolyte (i.e., polyacrylamide, PAM) concentration, specifically its aging, of the salt concentration is shown. The close agreement of the technique with classical bulk rheological measurements is demonstrated, illustrating the advantages of the technique.

2013-01-01

325

Measurement of the atom number distribution in an optical tweezer using single-photon counting  

NASA Astrophysics Data System (ADS)

We demonstrate in this paper a method to reconstruct the atom number distribution of a cloud containing a few tens of cold atoms. The atoms are first loaded from a magneto-optical trap into a microscopic optical dipole trap and then released in a resonant light probe where they undergo a Brownian motion and scatter photons. We count the number of photon events detected on an image intensifier. Using the response of our detection system to a single atom as a calibration, we extract the atom number distribution when the trap is loaded with more than one atom. The atom number distribution is found to be compatible with a Poisson distribution.

Fuhrmanek, A.; Sortais, Y. R. P.; Grangier, P.; Browaeys, A.

2010-08-01

326

Calibration of nonspherical particles in optical tweezers using only position measurement.  

PubMed

Nonspherical probe particles are an attractive choice for optically-trapped scanning probe microscopy. We show that it is possible to calibrate a trap with a nonspherical particle using only position measurements, without requiring measurement of orientation, using a pseudopotential based on the position occupation probability. It is not necessary to assume the force is linear with displacement. PMID:23595446

Bui, Ann A M; Stilgoe, Alexander B; Nieminen, Timo A; Rubinsztein-Dunlop, Halina

2013-04-15

327

Unzipping DNA with Optical Tweezers: High Sequence Sensitivity and Force Flips  

Microsoft Academic Search

Force measurements are performed on single DNA molecules with an optical trapping interferometer that combines subpiconewton force resolution and millisecond time resolution. A molecular construction is prepared for mechanically unzipping several thousand-basepair DNA sequences in an in vitro configuration. The force signals corresponding to opening and closing the double helix at low velocity are studied experimentally and are compared to

U. Bockelmann; Ph. Thomen; B. Essevaz-Roulet; V. Viasnoff; F. Heslot

2002-01-01

328

The Influence of Aerosol Chemistry on Spectral Aerosol Optical Properties During ARCTAS  

NASA Astrophysics Data System (ADS)

Aerosols are noted to both absorb and scattering radiation at UV wavelengths with the degree of absorption/scattering largely dependent on aerosol chemistry. The interactions of aerosols with the UV radiation field were examined for several flights during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign in summer 2008. Aerosol single scattering albedo (?) was retrieved at near-UV (300-400nm) wavelengths from spectral actinic flux data collected aboard the NASA DC-8 aircraft during ARCTAS using two CCD Actinic Flux Spectroradiometers. Retrievals were performed using the Tropospheric Ultraviolet Model versus 4.6 (TUV 4.6). TUV inputs of trace gas (e.g., NO2, SO2) concentrations, aerosol optical depth, location, time, pressure, etc. were determined from ancillary aircraft measurements made during ARCTAS. Values of ? were used to determine absorption optical depth (?abs) for each of the examined flights. Retrieval and calculation results were compared to aerosol optical properties in the visible and the spectral dependencies characterized. Additionally, comparisons of spectral ? and ?abs with aerosol chemical data collected by an Aerosol Mass Spectrometer and teflon filters were performed and provide insight into the role of chemistry and enhanced absorption in the UV wavelength range.

Corr, C. A.; Hall, S. R.; Ullmann, K.; Shetter, R.; Anderson, B.; Cubison, M.; Jimenez, J. L.; Scheuer, E. M.; Dibb, J. E.; Wennberg, P. O.

2009-12-01

329

Parametric study of the forces on microspheres held by optical tweezers  

SciTech Connect

Optical-trapping forces exerted on polystyrene microspheres are predicted and measured as a function of sphere size, laser spot size, and laser beam polarization. Axial and transverse forces are in good and excellent agreement, respectively, with a ray-optics model when the sphere diameter is [ge]10 [mu]m. Results are compared with results from an electromagnetic model when the sphere size is [le]1 [mu]m. Axial trapping performance is found to be optimum when the numerical aperture of the objective lens is as large as possible, and when the trapped sphere is located just below the chamber cover slip. Forces in the transverse direction are not as sensitive to parametric variations as are the axial forces. These results are important as a first-order approximation to the forces that can be applied either directly to biological objects or by means of microsphere handles attached to the biological specimen.

Wright, W.H.; Sonek, G.J. (Beckman Laser Institute and Medical Clinic, University of California, Irvine, Irvine, California 92715 (United States) Department of Electrical and Computer Engineering, University of California, Irvine (United States)); Berns, M.W. (Beckman Laser Institute and Medical Clinic, University of California, Irvine, Irvine, California 92715 (United States))

1994-03-20

330

Optical tweezers position measurement - comparing position sensitive detectors and high-speed cameras  

NASA Astrophysics Data System (ADS)

The design and construction of a low-cost optical trapping system is described. Trapping is performed on 1 micron diameter silica beads using 785 nm light from a diode laser. The particle position is measured using visible 633 nm light imaged onto a position sensitive lateral effect photodiode. We simultaneously acquire images of the trapped particle with a high-speed CCD camera and compare the accuracy of the camera to that obtained with the position sensitive detector. )

Sparks, Laura; Sharpe, John

2010-02-01

331

Studies on erythrocytes in malaria infected blood sample with Raman optical tweezers  

NASA Astrophysics Data System (ADS)

Raman spectroscopy was performed on optically trapped red blood cells (RBCs) from blood samples of healthy volunteers (h-RBCs) and from patients suffering from P. vivax infection (m-RBCs). A significant fraction of m-RBCs produced Raman spectra with altered characteristics relative to h-RBCs. The observed spectral changes suggest a reduced oxygen-affinity or right shifting of the oxygen-dissociation curve for the intracellular hemoglobin in a significant fraction of m-RBCs with respect to its normal functional state.

Dasgupta, Raktim; Shanker Verma, Ravi; Ahlawat, Sunita; Uppal, Abha; Kumar Gupta, Pradeep

2011-07-01

332

To Study the Effect of Paclitaxel on the Cytoplasmic Viscosity of Murine Macrophage Immune Cell RAW 264.7 Using Self-Developed Optical Tweezers System  

NASA Astrophysics Data System (ADS)

In recent years, optical tweezers have become one of the tools to measure the mechanical properties of living cells. In this study, we first constructed an optical tweezers to investigate the cytoplasmic viscosity of immune cells. In addition to measuring viscosity of cells in a normal condition, we also treated cells with anti-cancer drug, Paclitaxel, and in order to study its effect on the cytoplasmic viscosity. The results showed that the viscosity decreased dramatically during the first 3 h. After 3 h, the change started to slow down and it remained nearly flat by the end of the experiment. In addition, we used the confocal laser scanning microscope to observe the cytoskeleton of the cell after drug treatment for 3 and 5 h, respectively, and found that actin filaments were disrupted and that the nucleus had disintegrated in some drug-treated cells, similar to the process of apoptosis. This study presents a new way for measuring the changes in cytoplasmic viscosity, and to determine if a cell is going into apoptosis as a result of a drug treatment.

Chen, Ying-chun; Wu, Chien-ming

2012-12-01

333

Variability of aerosol optical depth and aerosol forcing over India  

Microsoft Academic Search

Over the Indian continent, population is growing day by day and it is expected that soon India will become one of the worlds most populated countries. With the growing population, industrialization and urbanization, the aerosol loading in India is increasing that has significant impact on the weather\\/climatic conditions. The present paper discusses the analysis of the temporal and spatial variations

S. Sarkar; R. Chokngamwong; G. Cervone; R. P. Singh; M. Kafatos

2005-01-01

334

Variability of aerosol optical depth and aerosol forcing over India  

Microsoft Academic Search

Over the Indian continent, population is growing day by day and it is expected that soon India will become one of the world’s most populated countries. With the growing population, industrialization and urbanization, the aerosol loading in India is increasing that has significant impact on the weather\\/climatic conditions. The present paper discusses the analysis of the temporal and spatial variations

S. Sarkar; R. Chokngamwong; G. Cervone; R. P. Singh; M. Kafatos

2006-01-01

335

Unzipping DNA with optical tweezers: high sequence sensitivity and force flips.  

PubMed Central

Force measurements are performed on single DNA molecules with an optical trapping interferometer that combines subpiconewton force resolution and millisecond time resolution. A molecular construction is prepared for mechanically unzipping several thousand-basepair DNA sequences in an in vitro configuration. The force signals corresponding to opening and closing the double helix at low velocity are studied experimentally and are compared to calculations assuming thermal equilibrium. We address the effect of the stiffness on the basepair sensitivity and consider fluctuations in the force signal. With respect to earlier work performed with soft microneedles, we obtain a very significant increase in basepair sensitivity: presently, sequence features appearing at a scale of 10 basepairs are observed. When measured with the optical trap the unzipping force exhibits characteristic flips between different values at specific positions that are determined by the base sequence. This behavior is attributed to bistabilities in the position of the opening fork; the force flips directly reflect transitions between different states involved in the time-averaging of the molecular system.

Bockelmann, U; Thomen, Ph; Essevaz-Roulet, B; Viasnoff, V; Heslot, F

2002-01-01

336

Dynamic measurements of forces between thrombus-inducing proteins using optical tweezers  

NASA Astrophysics Data System (ADS)

Both hemostasis and thrombosis occur as a result of platelet adhesion to the subendothelial matrix, platelet activation, and platelet aggregation. The first stage in hemostasis and thrombosis is the binding of the platelet membrane receptor, glycoprotein (GP) Ib-IX complex, to its ligand, von Willebrand factor (VWF), in the subendothelium. In particular, the A1 domain of VWF is responsible for binding GP Ib-IX. After immobilizing A1 on a 2.0 ?m diameter polystyrene bead, we optically trapped the bead using a titanium-sapphire laser tuned to 830 nm. The A1-coated bead was then moved towards a transfected Chinese hamster ovary cell which expressed the GP Ib-IX complex, and allowed to adhere to the cell. We subsequently detached the cell from the bead at different constant loading rates, ranging over three orders of magnitude, by using a piezoelectrically-driven translational stage. Displacement of the bead was simultaneously monitored from the trapping center using a quadrant photodetector to determine the force required to detach A1 from GP Ib-IX. These dynamic measurements of unbinding force emphasize the important role that shear rate plays in the initial stage of thrombus formation.

Arya, Maneesh; Romo, Gabriel M.; López, Jose A.; Anvari, Bahman

2003-06-01

337

Spatiotemporal Analysis of Cell Response to a Rigidity Gradient: A Quantitative Study Using Multiple Optical Tweezers  

PubMed Central

Abstract We investigate the dynamic response of single cells to weak and local rigidities, applied at controlled adhesion sites. Using multiple latex beads functionalized with fibronectin, and each trapped in its own optical trap, we study the reaction in real time of single 3T3 fibroblast cells to asymmetrical tensions in the tens of pN · ?m?1 range. We show that the cell feels a rigidity gradient even at this low range of tension, and over time develops an adapted change in the force exerted on each adhesion site. The rate at which force increases is proportional to trap stiffness. Actomyosin recruitment is regulated in space and time along the rigidity gradient, resulting in a linear relationship between the amount of recruited actin and the force developed independently in trap stiffness. This time-regulated actomyosin behavior sustains a constant and rigidity-independent velocity of beads inside the traps. Our results show that the strengthening of extracellular matrix-cytoskeleton linkages along a rigidity gradient is regulated by controlling adhesion area and actomyosin recruitment, to maintain a constant deformation of the extracellular matrix.

Allioux-Guerin, Myriam; Icard-Arcizet, Delphine; Durieux, Christiane; Henon, Sylvie; Gallet, Francois; Mevel, Jean-Claude; Masse, Marie-Jo; Tramier, Marc; Coppey-Moisan, Maite

2009-01-01

338

Sources of optically active aerosol particles over the Amazon forest  

NASA Astrophysics Data System (ADS)

Size-fractionated ambient aerosol samples were collected at a pasture site and a primary rainforest site in the Brazilian Amazon Basin during two field campaigns (April-May and September-October 1999), as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis (PIXE), for equivalent black carbon (BC e) by a light reflectance technique and for mass concentration by gravimetric analysis. Additionally, we made continuous measurements of absorption and light scattering by aerosol particles. The vertical chemical composition gradients at the forest site have been discussed in a companion article (Journal of Geophysical Research-Atmospheres 108 (D18), 4591 (doi:4510.1029/2003JD003465)). In this article, we present the results of a source identification and quantitative apportionment study of the wet and dry season aerosols, including an apportionment of the measured scattering and absorption properties of the total aerosol in terms of the identified aerosol sources. Source apportionments (obtained from absolute principal component analysis) revealed that the wet and dry season aerosols contained the same three main components, but in different (absolute and relative) amounts: the wet season aerosol consisted mainly of a natural biogenic component, whereas pyrogenic aerosols dominated the dry season aerosol mass. The third component identified was soil dust, which was often internally mixed with the biomass-burning aerosol. All three components contributed significantly to light extinction during both seasons. At the pasture site, up to 47% of the light absorption was attributed to biogenic particles during the wet season, and up to 35% at the tower site during the wet-to-dry transition period. The results from the present study suggest that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin.

Guyon, Pascal; Graham, Bim; Roberts, Gregory C.; Mayol-Bracero, Olga L.; Maenhaut, Willy; Artaxo, Paulo; Andreae, Meinrat O.

339

Atmospheric optical effect of aerosols in large fires  

SciTech Connect

The relative concentration of submicron and supermicron size particles and high turbulence in large fire plumes can radically change the aerosol size evolution in the fire plume. These size changes affect the potential for visibility reduction and long range transport. We have developed a coupled hydrodynamic plume aerosol coagulation model including condensation in the first hour of the aerosol evolution in the fire. We have extended aerosol plume evolution calculations beyond the first hour of the plume to several days transport times. This was done with a 10 level model with parameterized vertical and horizontal diffusion, sedimentation and coagulation. The optical effects of the evolving concentration and size distributions were modeled assuming Mie scattering and absorption. We have also tested the hydrodynamic part of the modeling with wind convergence measurements in a large jet fuel pool fire. These studies have pointed to the potential importance of supermicron scavenging of submicron aerosol by turbulent processes in the active fire plume.

Porch, W.M.; Atherton, C.S.; Penner, J.E.

1987-04-07

340

Raman-tweezers spectroscopy of single biological cells and organelles  

NASA Astrophysics Data System (ADS)

Raman tweezers, also called laser tweezers Raman spectroscopy (LTRS), is an instrument that combines optical tweezers and confocal Raman microscopy for simultaneous manipulation and analysis of single biological cells or organelles in a physiological solution without the need of introducing biochemical tags. The optical tweezers part of the LTRS system uses a tightly focused near-infrared beam to capture and immobilize a biological particle in a liquid medium by the gradient force. The Raman spectroscopy part can generate vibrational spectra of the trapped particle to provide composition and conformation information of molecules based on measuring molecular vibrations from the scattered light. In this talk, we will present the physical principle and instrumentation of optical tweezers and micro-Raman spectroscopy system. Applications in rapid detection and identification of microorganisms, sorting of living cells, and real-time measurement of the dynamical changes in biochemical properties of macromolecules within living cells, and detection of recombinant proteins in transgenic cells will be presented.

Li, Yongqing

2004-11-01

341

Aerosol optical properties and their radiative effects in northern China  

NASA Astrophysics Data System (ADS)

As a fast developing country covering a large territory, China is experiencing rapid environmental changes. High concentrations of aerosols with diverse properties are emitted in the region, providing a unique opportunity for understanding the impact of environmental changes on climate. Until very recently, few observational studies were conducted in the source regions. The East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE) attempts to characterize the physical, optical and chemical properties of the aerosols and their effects on climate over China. This study presents some preliminary results using continuous high-quality measurements of aerosol, cloud and radiative quantities made at the first EAST-AIRE baseline station at Xianghe, about 70 km east of Beijing over a period of one year (September 2004 to September 2005). It was found that the region is often covered by a thick layer of haze (with a yearly mean aerosol optical depth equal to 0.82 at 500 nm and maximum greater than 4) due primarily to anthropogenic emissions. An abrupt "cleanup" of the haze often took place in a matter of one day or less because of the passage of cold fronts. The mean single scattering albedo is approximately 0.9 but has strong day-to-day variations with maximum monthly averages occurring during the summer. Large aerosol loading and strong absorption lead to a very large aerosol radiative effect at the surface (the annual 24-hour mean values equals 24 W m-2), but a much smaller aerosol radiative effect at the top of the atmosphere (one tenth of the surface value). The boundary atmosphere is thus heated dramatically during the daytime, which may affect atmospheric stability and cloud formation. In comparison, the cloud radiative effect at the surface is only moderately higher (-41 W m-2) than the aerosol radiative effect at the surface.

Li, Zhanqing; Xia, Xiangao; Cribb, Maureen; Mi, Wen; Holben, Brent; Wang, Pucai; Chen, Hongbin; Tsay, Si-Chee; Eck, T. F.; Zhao, Fengsheng; Dutton, E. G.; Dickerson, R. E.

2007-11-01

342

Columnar aerosol optical properties at AERONET sites in central eastern Asia and aerosol transport to the tropical mid-Pacific  

Microsoft Academic Search

The column-integrated optical properties of aerosol in the central eastern region of Asia and midtropical Pacific were investigated based on Sun\\/sky radiometer measurements made at Aerosol Robotic Network (AERONET) sites in these regions. Characterization of aerosol properties in the Asian region is important due to the rapid growth of both population and economic activity, with associated increases in fossil fuel

T. F. Eck; B. N. Holben; O. Dubovik; A. Smirnov; P. Goloub; H. B. Chen; B. Chatenet; L. Gomes; X.-Y. Zhang; S.-C. Tsay; Q. Ji; D. Giles; I. Slutsker

2005-01-01

343

Is there evidence for an aerosol indirect effect during the recent aerosol optical depth decline in Europe?  

Microsoft Academic Search

Aerosol indirect effects are some of the largest uncertainties of anthropogenic climate change. To estimate the first aerosol indirect radiative effect (or cloud albedo effect), we analyzed global solar irradiance measurements under completely overcast skies during the recent period of aerosol optical depth decline in Europe. Although measurements from 15 Swiss and 8 northern German sites show clear evidence for

Christian Ruckstuhl; Joel R. Norris; Rolf Philipona

2010-01-01

344

Effect of wind speed on columnar aerosol optical properties at Midway Island  

Microsoft Academic Search

Aerosol optical properties over Midway Island in the central Pacific Ocean are considered in conjunction with the information on surface wind speed. In general, optical conditions over Midway resemble aerosol found over other maritime locations in the Pacific Ocean (Lanai, Tahiti, and Nauru). The most frequently occurring values of aerosol optical depth at 500-nm wavelength and Angstrom parameter are 0.06

A. Smirnov; B. N. Holben; T. F. Eck; O. Dubovik; I. Slutsker

2003-01-01

345

Measurement of aerosol optical depth in the Pacific Ocean and the North Atlantic  

Microsoft Academic Search

The results of spectral aerosol optical depth measurments in the Pacific Ocean and in the North Atlantic are presented. Comparisons of aerosol optical depth spectra indicate that the optical properties of the maritime aerosols influencing Pacific Ocean measurements are substantially different than those of the North Atlantic data. The values of the Angstrom parameter calculated in the 461-to 1016-nm range

Yu. V. Villevalde; A. V. Smirnov; N. T. O'Neill; S. P. Smyshlyaev; V. V. Yakovlev

1994-01-01

346

Reproducing the optical properties of fine desert dust aerosols using ensembles of simple model particles  

Microsoft Academic Search

Single scattering optical properties are calculated for a proxy of fine dust aerosols at a wavelength of 0.55?m. Spherical and spheroidal model particles are employed to fit the aerosol optical properties and to retrieve information about the physical parameters characterising the aerosols. It is found that spherical particles are capable of reproducing the scalar optical properties and the forward peak

Michael Kahnert

2004-01-01

347

Identification of stepped changes of binding affinity during interactions between the disintegrin rhodostomin and integrin ?IIb?3 in living cells using optical tweezers  

NASA Astrophysics Data System (ADS)

Integrin receptors serve as both mechanical links and signal transduction mediators between the cell and its environment. Experimental evidence demonstrates that conformational changes and lateral clustering of the integrin proteins may affect their binding to ligands and regulate downstream cellular responses; however, experimental links between the structural and functional correlations of the ligand-receptor interactions are not yet elucidated. In the present report, we utilized optical tweezers to measure the dynamic binding between the snake venom rhodostomin, coated on a microparticle and functioned as a ligand, and the membrane receptor integrin alpha(IIb)beta(3) expressed on a Chinese Hamster Ovary (CHO) cell. A progressive increase of total binding affinity was found between the bead and CHO cell in the first 300 sec following optical tweezers-guided contact. Further analysis of the cumulative data revealed the presence of "unit binding force" presumably exerted by a single rhodostomin-integrin pair. Interestingly, two such units were found. Among the measurements of less total binding forces, presumably taken at the early stage of ligand-receptor interactions, a unit of 4.15 pN per molecule pair was derived. This unit force dropped to 2.54 pN per molecule pair toward the later stage of interactions when the total binding forces were relatively large. This stepped change of single molecule pair binding affinity was not found when mutant rhodostomin proteins were used as ligands (a single unit of 1.81 pN per pair was found). These results were interpreted along with the current knowledge about the conformational changes of integrins during the "molecule activation" process.

Hsieh, Chia-Fen; Chang, Bo-Jui; Pai, Chyi-Huey; Chen, Hsuan-Yi; Chi, Sien; Hsu, Long; Tsai, Jin-Wu; Lin, Chi-Hung

2004-10-01

348

Toward Investigating Optically Trapped Organic Aerosols with CARS Microspectroscopy  

NASA Astrophysics Data System (ADS)

The Intergovernmental Panel on Climate Change notes the huge uncertainty in the effect that atmospheric aerosols play in determining overall global temperature, specifically in their ability to nucleate clouds. To better understand aerosol chemistry, the novel coupling of gradient force optical trapping with broad bandwidth coherent anti-Stokes Raman scattering (CARS) spectroscopy is being developed to study single particles suspended in air. Building on successful designs employed separately for the techniques, this hybrid technology will be used to explain how the oxidation of organic compounds changes the chemical and physical properties of aerosols. By trapping the particles, an individual aerosol can be studied for up to several days. Using a broad bandwidth pulse for one of the incident beams will result in a Raman vibrational spectrum from every laser pulse. Combined with signal enhancement due to resonance and coherence of nonlinear CARS spectroscopy, this technique will allow for acquisition of data on the millisecond time scale, facilitating the study of dynamic processes. This will provide insights on how aerosols react with and absorb species from the gas phase. These experiments will increase understanding of aerosol oxidation and growth mechanisms and the effects that aerosols have on our atmosphere and climate. Progress in efforts developing this novel technique to study model systems is presented.

Voss, L. F.

2009-12-01

349

Seasonal variations in aerosol optical properties over China  

NASA Astrophysics Data System (ADS)

Seasonal variations in background aerosol optical depth (AOD) and aerosol type are investigated over various ecosystems in China based upon three years' worth of meteorological data and data collected by the Chinese Sun Hazemeter Network. In most parts of China, AODs are at a maximum in spring or summer and at a minimum in autumn or winter. Minimum values (0.10˜0.20) of annual mean AOD at 500 nm are found in the Qinghai-Tibetan Plateau, the remote northeast corner of China, the northern forest ecosystems and Hainan Island. Annual mean AOD ranges from 0.25 to 0.30 over desert and oasis areas, as well as the desertification grasslands in northern China; the annual mean AOD over the Loess Plateau is moderately high at 0.36. Regions where the highest density of agricultural and industrial activities are located and where anthropogenic sulphate aerosol and soil aerosol emissions are consistently high throughout the whole year (e.g., the central-eastern, southern and eastern coastal regions of China) experience annual mean AODs ranging from 0.50˜0.80. Remarkable seasonal changes in the main types of aerosol over northern China (characterized by the Angstrom exponent, ?) are seen. Due to biomass and fossil fuel burning from extensive agricultural practices in northern rural areas, concentrations of smoke and soot aerosols rise dramatically during autumn and winter (high ?), while the main types of aerosol during spring and summer are dust and soil aerosols (low ?). Over southeastern Asia, biomass burning during the spring leads to increases in smoke and soot emissions. Over the Tibetan Plateau and Hainan Island where the atmosphere is pristine, the main types of aerosol are dust and sea salt, respectively.

Wang, Yuesi; Xin, Jinyuan; Li, Zhanqing; Wang, Shigong; Wang, Pucai; Hao, Wei Min; Nordgren, Bryce L.; Chen, Hongbin; Wang, Lili; Sun, Yang

2011-09-01

350

Seasonal variations in aerosol optical properties over China  

NASA Astrophysics Data System (ADS)

The seasonal variations in background aerosol optical depth (AOD) and aerosol type are investigated over various ecosystems in China based upon three years' worth of meteorological data and data collected by the Chinese Sun Hazemeter Network. In most parts of China, AODs are at a maximum in spring or summer and at a minimum in autumn or winter. Minimum values (0.10~0.20) of annual mean AOD at 500 nm are found in the Qinghai-Tibetan Plateau, which is located in the remote northeast corner of China, the northern forest ecosystems and Hainan Island. Annual mean AOD ranges from 0.25 to 0.30 over desert and oasis areas as well as the desertification grasslands in northern China; the annual mean AOD over the Loess Plateau is moderately high at 0.36. Regions where the highest density of agricultural and industrial activities are located and where anthropogenic sulphate aerosol and soil aerosol emissions are consistently high throughout the whole year (e.g. the central-eastern, southern and eastern coastal regions of China) experience annual mean AODs ranging from 0.50~0.80. Remarkable seasonal changes in the main types of aerosol over northern China (characterized by the Angstrom exponent, ?) are seen. Due to biomass and fossil fuel burning from extensive agricultural practices in northern rural areas, concentrations of smoke and soot aerosols rise dramatically during autumn and winter (high ?), while the main types of aerosol during spring and summer are dust and soil aerosols (low ?). Over southeast Asia, biomass burning during the spring leads to increases in smoke and soot emissions. Over the Tibetan Plateau and Hainan Island where the atmosphere is pristine, the main types of aerosol are dust and sea salt, respectively.

Wang, Y.; Xin, J.; Li, Z.; Wang, S.; Wang, P.; Hao, W. M.; Nordgren, B. L.; Chen, H.; Wang, L.; Sun, Y.

2008-05-01

351

Modeled optical thickness of sea-salt aerosol  

NASA Astrophysics Data System (ADS)

We simulate the generation and microphysical evolution of sea-salt aerosol using a climatologically driven 3-D microphysical model for the year 2006. We then apply Mie theory to calculate the extinction and scattering efficiencies of our transported, size-resolved sea-salt aerosol, accounting for hygroscopic growth due to changes in ambient relative humidity. We calculate the column optical thickness of our modeled sea-salt aerosol for comparison to three previously published wind speed-dependent clean marine air optical thickness formulations. Variously derived from optical thickness measurements and retrievals taken from the Midway Island AERONET site, the satellite-based MODIS instruments, and the Global Atmospheric Watch (GAW) site at Mace Head, Ireland, the three formulations report similar background levels of clean marine AOT at zero wind speed but significantly different functional dependencies for nonzero wind speeds. We find that our modeled sea-salt aerosol optical thickness very closely depends on the square of surface wind speed under steady state conditions. This relationship is consistent across all latitudes. However, due to the fact that steady state winds are seldom maintained, the 24 h mean wind is more frequently applicable to calculations of sea-salt AOT, with only slightly diminished accuracy.

Madry, William L.; Toon, Owen B.; O'Dowd, C. D.

2011-04-01

352

Optical Properties and Associated Hygroscopicity of Clay Aerosols  

Microsoft Academic Search

Airborne mineral dust particles contribute a significant fraction to the total aerosol mass, thus they make a substantial contribution to the Earth's radiative budget by direct scattering and absorption of radiation. Quantifying their contribution is complicated by the variability of optical properties as a function of water uptake. To improve understanding, we directly measured the relative humidity (RH) dependence of

Alexis Rae Attwood; Margaret E. Greenslade

2010-01-01

353

Aerosol optical depth trends over different regions of India  

NASA Astrophysics Data System (ADS)

Seasonal and annual mean trends in aerosol optical depths (AODs) for the last decade are derived using MODerate resolution Imaging Spectroradiometer (MODIS) Level 2 10 km × 10 km remote sensing data over different locations in India. AODs have increased across India in the last decade. AOD trends exhibit spatial, seasonal and annual mean variations. Annual mean AODs have increased by >40% during 2000-2009 in Jaipur, Hyderabad and Bengaluru. The increase in AODs over Hyderabad and Bengaluru, major high-tech cities, can be ascribed to the increase in urbanization. An increase in AODs over New Delhi where manmade aerosols are dominant can be attributed to an increase in the amount of aerosols from fossil fuel and biomass burning, while an increasing trend in AODs in the northeast, indicates an increase in the amount of aerosols produced from biomass burning and forest fires. AODs decreased in the high altitude sites of Shimla and Dehradun. AODs and wind speeds increased over Jaipur, while they decreased in Trivandrum during the last decade. An increase in wind speeds led to an increase in soil derived dust particles over Jaipur, an arid site, while a decrease in wind speeds over Trivandrum, contributed to a decrease in sea spray aerosols thereby causing a decrease in AOD. Annual rainfall increased by ?1% in most locations. Both AODs and rainfall have increased in the last decade over most study locations. These findings become important and useful in the context of regional and global climate change due to aerosols.

Ramachandran, S.; Kedia, Sumita; Srivastava, Rohit

2012-03-01

354

Aerosol characteristics at a high-altitude location in central Himalayas: Optical properties and radiative forcing  

Microsoft Academic Search

Collocated measurements of the mass concentrations of aerosol black carbon (BC) and composite aerosols near the surface were carried out along with spectral aerosol optical depths (AODs) from a high-altitude station, Manora Peak in central Himalayas, during a comprehensive aerosol field campaign in December 2004. Despite being a pristine location in the Shivalik Ranges of central Himalayas and having a

P. Pant; P. Hegde; U. C. Dumka; Ram Sagar; S. K. Satheesh; K. Krishna Moorthy; Auromeet Saha; M. K. Srivastava

2006-01-01

355

New Techniques For Predicting Optical Properties Of Nonspherical Multicomponent Aerosols Using Single Particle Measurements  

Microsoft Academic Search

Better understanding of diverse effects of atmospheric aerosols on climate and atmospheric chemistry requires more realistic treatments of physical and chemical properties of aerosol particles. Recent measurements demonstrate that a large fraction of aerosol particles has complex chemical composition and exhibits a variety of shapes. This paper presents new techniques for predicting the optical properties of nonspherical multicomponent aerosols containing

I. N. Sokolik; J. R. Anderson; S. A. Guazzotti; K. A. Prather

2003-01-01

356

Titan aerosols - Optical properties and vertical distribution  

Microsoft Academic Search

An analysis of Titan's solar phase variation as a function of wavelength together with the continuum geometric albedo makes it possible to set limits on the real part of the refractive index and on the average particle size of the aerosol component of Titan's atmosphere of between about 1.5 and 2.0 and between 0.20 microns and about 0.35 microns, respectively.

K. Rages; J. B. Pollack

1980-01-01

357

Improving Radiative Assessments of Aerosol Chemical, Physical and Optical Properties Through Aerosol Volatility Studies Over Optically Effective Sizes  

Microsoft Academic Search

In order to interpret in-situ and satellite observations of complex aerosol mixtures such as those encountered during ACE-ASIA and TRACE-P as well as to model them, optical effects due to each component of particles in a given size needs to be determined. Here we present recently refined techniques applied to particles with optically effective sizes over 0.1 - 14 mum.

Y. Shinozuka; A. Clarke; S. Howell; V. Kapustin

2002-01-01

358

Effect of Dust and Anthropogenic Aerosols on Columnar Aerosol Optical Properties over Darjeeling (2200 m asl), Eastern Himalayas, India  

PubMed Central

Background The loading of atmospheric particulate matter (aerosol) in the eastern Himalaya is mainly regulated by the locally generated anthropogenic aerosols from the biomass burning and by the aerosols transported from the distance sources. These different types of aerosol loading not only affect the aerosol chemistry but also produce consequent signature on the radiative properties of aerosol. Methodology/Principal Findings An extensive study has been made to study the seasonal variations in aerosol components of fine and coarse mode aerosols and black carbon along with the simultaneous measurements of aerosol optical depth on clear sky days over Darjeeling, a high altitude station (2200 masl) at eastern Himalayas during the year 2008. We observed a heavy loading of fine mode dust component (Ca2+) during pre-monsoon (Apr – May) which was higher by 162% than its annual mean whereas during winter (Dec – Feb), the loading of anthropogenic aerosol components mainly from biomass burning (fine mode SO42? and black carbon) were higher (76% for black carbon and 96% for fine mode SO42?) from their annual means. These high increases in dust aerosols during pre-monsoon and anthropogenic aerosols during winter enhanced the aerosol optical depth by 25 and 40%, respectively. We observed that for every 1% increase in anthropogenic aerosols, AOD increased by 0.55% during winter whereas for every 1% increase in dust aerosols, AOD increased by 0.46% during pre-monsoon. Conclusion/Significance The natural dust transport process (during pre-monsoon) plays as important a role in the radiation effects as the anthropogenic biomass burning (during winter) and their differential effects (rate of increase of the AOD with that of the aerosol concentration) are also very similar. This should be taken into account in proper modeling of the atmospheric environment over eastern Himalayas.

Chatterjee, Abhijit; Ghosh, Sanjay K.; Adak, Anandamay; Singh, Ajay K.; Devara, Panuganti C. S.; Raha, Sibaji

2012-01-01

359

Aerosol optical depth determination from ground based irradiance ratios  

SciTech Connect

The atmospheric optical depth serves as an input parameter to atmospheric correction procedures in remote sensing and as an index of atmospheric opacity or constituent columnar abundance for meteorological applications. Its measurement, typically performed by means of a small field of view radiometer centered on the solar disk, is sensitive to the absolute calibration accuracy of the instrument. In this paper a simple technique is presented which permits the extraction of aerosol optical depth from the ratio of total to direct irradiance measurements. An error analysis performed on the results of radiative transfer simulations and field measurements indicates that the technique generates values of aerosol optical depth which are sufficiently accurate for many applications. This method thus represents a useful alternative to standard sunphotometer measurements.

Miller, J. R.; O'Neill, N. T.; Boyer, A.

1989-08-01

360

An operational retrieval algorithm for determining aerosol optical properties in the ultraviolet  

Microsoft Academic Search

This paper describes a number of practical considerations concerning the optimization and operational implementation of an algorithm used to characterize the optical properties of aerosols across part of the ultraviolet (UV) spectrum. The algorithm estimates values of aerosol optical depth (AOD) and aerosol single scattering albedo (SSA) at seven wavelengths in the UV, as well as total column ozone (TOC)

Thomas E. Taylor; Tristan S. L'Ecuyer; James R. Slusser; Graeme L. Stephens; Christian D. Goering

2008-01-01

361

Biomass burning aerosol size distribution and modeled optical properties  

NASA Astrophysics Data System (ADS)

Satellite remote sensing of smoke aerosol and estimates of aerosol forcing of climate require knowledge of the aerosol optical properties. A smoke aerosol physical and optical model is developed from a database of over 800 volume size distributions inverted from sky radiance data measured by the AERONET radiometer network in Brazil over a 3-year period. The model represents total column, ambient conditions during the burning season in the Amazon Basin and cerrado region of Brazil. The mean volume size distributions are bimodal and can be represented by two lognormals. Accumulation mode modal radius is 0.13±0.02 ?m with ? = 0.60 ± 0.04, and coarse-mode modal radius ranges from 6 to 40 ?m, with a mean of 11.5 ?m and ? = 1.26 ± 0.23. The volume of each mode varies with optical thickness, causing the ratio of accumulation mode and coarse mode to vary as well, but the effect on the optical properties is negligible. Refractive index is taken to be 1.43-0.0035i, and single scattering albedo is assumed to be 0.90, which is modeled with an external mixing of black carbon. The optical properties in the visible are dominated by the accumulation mode. Accumulation mode characteristics do not vary from year to year, from forest to cerrado region, with optical thickness or with precipitable water vapor. At one test location, accumulation mode characteristics do vary with air mass trajectory origin. The model is tested with independent data and can accurately predict the scattering phase function and path radiance in the backscattering direction that determines remote sensing properties and is responsible for scattering sunlight back to space.

Remer, L. A.; Kaufman, Y. J.; Holben, B. N.; Thompson, A. M.; McNamara, D.

1998-12-01

362

Cytoplasmic Regulation of the Movement of E-Cadherin on the Free Cell Surface as Studied by Optical Tweezers and Single Particle Tracking: Corralling and Tethering by the Membrane Skeleton  

Microsoft Academic Search

The translational movement of E-cadherin, a calcium-dependent cell-cell adhesion molecule in the plasma membrane in epithelial cells, and the mecha- nism of its regulation were studied using single particle tracking (SPT) and optical tweezers (OT). The wild type (Wild) and three types of artificial cytoplasmic mutants of E-cadherin were expressed in L-cells, and their movements were compared. Two mutants were

Yasushi Sako; Akira Nagafuchi; Shoichiro Tsukita; Masatoshi Takeichi; Akihiro Kusumi

1998-01-01

363

Tropospheric aerosols in the Mediterranean: 1. Microphysical and optical properties  

NASA Astrophysics Data System (ADS)

Measurements of the aerosol properties were carried out at the island of Lampedusa, in the Mediterranean, in May 1999, as part of the Photochemical Activity and Ultraviolet Radiation modulating factors II campaign. Data from ground-based lidar and Sun photometer, and particle counters aboard an instrumented ultralight aircraft, are used in this study. Three different cases, when all the measurements were available in cloud-free conditions, were identified to derive the aerosol microphysical and optical properties. In one of these cases (18 May) the airmasses originated from Africa, and were loaded with a large amount of desert dust. In the other two cases (25 May and 27 May) the airmasses passed over Europe before reaching Lampedusa from North. The microphysical and optical properties of the aerosol strongly depend on the origin of the airmasses. The amount of particles in the 1-6 ?m range of radii and the average aerosol surface area per unit volume are larger in the desert dust case than on 25 May and 27 May. The real part of the refractive index of the desert dust at 532 nm is between 1.52 and 1.58; its imaginary part is 5-7 × 10-3 and the single scattering albedo is about 0.7-0.75. The aerosol layer of 18 May closest to the surface, that probably contains a mixture of desert dust and marine aerosol, displays a smaller imaginary part (1.2 × 10-3) and a larger single scattering albedo (0.91). The aerosols originating from the North Atlantic and Europe have a real part of the refractive index between 1.35 and 1.49, and an imaginary part ranging from 8 × 10-4 to 1.8 × 10-2; the single scattering albedo at 532 nm (0.78-0.95) is larger than for desert dust values. The smallest value of the single scattering albedo (0.69) corresponds to an airmass originating from North, characterized by a large imaginary part of the refractive index. The asymmetry factor of the desert dust appears consistently larger for the desert dust (0.75-0.8) than for the other cases (0.61-0.72). The extinction-to-backscattering ratio, also derived from the measurements, is about 40 sr for the desert dust, and between 60 and 81 sr for the aerosol of northern origin. Simple estimates of the aerosol average direct shortwave radiative forcing at the top of the atmosphere indicate that all considered aerosol types induce a cooling. The radiative forcing per unit optical depth of the aerosol originating from North is about -37 Wm-2 over ocean and -(12-17) Wm-2 over land, while is -29 Wm-2 over ocean and -8 Wm-2 over land for desert dust. The largest forcing is however produced by the desert aerosols that generally display a considerably larger optical depth.

di Iorio, T.; di Sarra, A.; Junkermann, W.; Cacciani, M.; Fiocco, G.; Fuã, D.

2003-05-01

364

Optical characterization of continental and biomass-burning aerosols over Bozeman, Montana: A case study of the aerosol direct effect  

NASA Astrophysics Data System (ADS)

Atmospheric aerosol optical properties were observed from 21 to 27 September 2009 over Bozeman, Montana, during a transitional period in which background polluted rural continental aerosols and well-aged biomass-burning aerosols were the dominant aerosol types of extremely fresh biomass-burning aerosols resulting from forest fires burning in the northwestern United States and Canada. Aerosol optical properties and relative humidity profiles were retrieved using an eye-safe micropulse water vapor differential absorption lidar (DIAL) (MP-DIAL), a single-channel backscatter lidar, a CIMEL solar radiometer as part of the Aerosol Robotic Network (AERONET), a ground-based integrating nephelometer, and aerosol products from Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua. Aerosol optical depths (AODs) measured during the case study ranged between 0.03 and 0.17 (0.015 and 0.075) at 532 nm (830 nm) as episodic combinations of fresh and aged biomass-burning aerosols dominated the optical depth of the pristinely clean background air. Here, a pristinely clean background refers to very low AOD conditions, not that the aerosol scattering and absorption properties are necessarily representative of a clean aerosol type. Diurnal variability in the aerosol extinction to backscatter ratio (Sa) of the background atmosphere derived from the two lidars, which ranged between 55 and 95 sr (50 and 90 sr) at 532 nm (830 nm), showed good agreement with retrievals from AERONET sun and sky measurements over the same time period but were consistently higher than some aerosol models had predicted. Sa measured during the episodic smoke events ranged on average from 60 to 80 sr (50 to 70 sr) at 532 nm (830 nm) while the very fresh biomass-burning aerosols were shown to exhibit significantly lower Sa ranging between 20 and 40 sr. The shortwave direct radiative forcing that was due to the intrusion of biomass-burning aerosols was calculated to be on average -10 W/m2 and was shown to compare favorably with regional-scale forcing calculations using MODIS-Terra and AERONET data in an effort to assess the accuracy of estimating the regional-scale aerosol direct radiative forcing effect using aerosol optical properties measured from a single rural site such as Bozeman, Montana.

Nehrir, Amin R.; Repasky, Kevin S.; Reagan, John A.; Carlsten, John L.

2011-11-01

365

Aerosol particle vertical distributions and optical properties over Singapore  

NASA Astrophysics Data System (ADS)

As part of the Seven Southeast Asian Studies (7SEAS) program, an Aerosol Robotic Network (AERONET) sun photometer and a Micro-Pulse Lidar Network (MPLNET) instrument have been deployed at Singapore to study the regional aerosol environment of the Maritime Continent (MC). Using coincident AERONET Level 2.0 and MPLNET Level 2.0a data from 24 September 2009 to 31 March 2011, the seasonal variability of aerosol particle vertical distributions and optical properties is examined. On average, the bulk (˜65%) of aerosol extinction is found below 1.5 km with substantial aerosol loading (˜35%) above. Possibly due to the transition from El Niño to La Niña conditions and subsequent reduction in fire events, the MPLNET mean integrated aerosol extinction is observed to be the lowest for July-September 2010, which coincides with the typical MC biomass burning season. On the other hand, the highest mean integrated extinctions are derived for January-March 2010 and 2011, which can be attributed to off-season MC biomass burning smoke and anthropogenic pollution. The seasonal lidar ratios also show higher occurrences ?60 sr, which are indicative of biomass burning smoke, for October 2009-June 2010, but such occurrences decrease from July 2010 to March 2011 when La Niña conditions prevail. In addition, principal component analysis (PCA) identifies five primary aerosol vertical profile types over Singapore, i.e. strongly-capped/deep near-surface layer (SCD; 0-1.35 km), enhanced mid-level layer (EML; 1.35-2.4 km), enhanced upper-level layer (EUL; 2.4-3.525 km), deep contiguous layer (DCL; 3.525-4.95 km) and deep multi-layer (DML; >4.95 km). PCA also identifies an off-season MC biomass burning smoke event from 22 February to 8 March 2010, which is subsequently examined in detail.

Chew, Boon Ning; Campbell, James R.; Salinas, Santo V.; Chang, Chew Wai; Reid, Jeffrey S.; Welton, Ellsworth J.; Holben, Brent N.; Liew, Soo Chin

2013-11-01

366

Investigating Molecular Level Stress-Strain Relationships in Entangled F-Actin Networks by Combined Force-Measuring Optical Tweezers and Fluorescence Microscopy  

NASA Astrophysics Data System (ADS)

Actin is an important cytoskeletal protein involved in cell structure and motility, cancer invasion and metastasis, and muscle contraction. The intricate viscoelastic properties of filamentous actin (F-actin) networks allow for the many dynamic roles of actin, thus warranting investigation. Exploration of this unique stress-strain/strain-rate relationship in complex F-actin networks can also improve biomimetic materials engineering. Here, we use optical tweezers with fluorescence microscopy to study the viscoelastic properties of F-actin networks on the microscopic level. Optically trapped microspheres embedded in various F-actin networks are moved through the network using a nanoprecision piezoelectric stage. The force exerted on the microspheres by the F-actin network and subsequent force relaxation are measured, while a fraction of the filaments in the network are fluorescent-labeled to observe filament deformation in real-time. The dependence of the viscoelastic properties of the network on strain rates and amplitudes as well as F-actin concentration is quantified. This approach provides the much-needed link between induced force and deformation over localized regimes (tens of microns) and down to the single molecule level.

Lee, Kent; Henze, Dean; Robertson-Anderson, Rae M.

2013-03-01

367

Seasonal variability of aerosol optical depth over Indian subcontinent  

USGS Publications Warehouse

Ganga basin extends 2000 km E-W and about 400 km N-S and is bounded by Himalayas in the north. This basin is unequivocally found to be affected by high aerosols optical depth (AOD) (>0.6) throughout the year. Himalayas restricts movement of aerosols toward north and as a result dynamic nature of aerosol is seen over the Ganga basin. High AOD in this region has detrimental effects on health of more than 460 million people living in this part of India besides adversely affecting clouds formation, monsoonal rainfall pattern and Normalized Difference Vegetation Index (NDVI). Severe drought events (year 2002) in Ganga basin and unexpected failure of monsoon several times, occurred in different parts of Indian subcontinent. Significant rise in AOD (18.7%) over the central part of basin (Kanpur region) have been found to cause substantial decrease in NDVI (8.1%) since 2000. A negative relationship is observed between AOD and NDVI, magnitude of which differs from region to region. Efforts have been made to determine general distribution of AOD and its dominant departure in recent years spatially using Moderate Resolution Imaging Spectroradiometer (MODIS) data. The seasonal changes in aerosol optical depth over the Indo-Gangetic basin is found to very significant as a result of the increasing dust storm events in recent years. ?? 2005 IEEE.

Prasad, A. K.; Singh, R. P.; Singh, A.; Kafatos, M.

2005-01-01

368

Cloud-Driven Changes in Aerosol Optical Properties - Final Technical Report  

SciTech Connect

The optical properties of aerosol particles are the controlling factors in determining direct aerosol radiative forcing. These optical properties depend on the chemical composition and size distribution of the aerosol particles, which can change due to various processes during the particles’ lifetime in the atmosphere. Over the course of this project we have studied how cloud processing of atmospheric aerosol changes the aerosol optical properties. A counterflow virtual impactor was used to separate cloud drops from interstitial aerosol and parallel aerosol systems were used to measure the optical properties of the interstitial and cloud-scavenged aerosol. Specifically, aerosol light scattering, back-scattering and absorption were measured and used to derive radiatively significant parameters such as aerosol single scattering albedo and backscatter fraction for cloud-scavenged and interstitial aerosol. This data allows us to demonstrate that the radiative properties of cloud-processed aerosol can be quite different than pre-cloud aerosol. These differences can be used to improve the parameterization of aerosol forcing in climate models.

Ogren, John A.; Sheridan, Patrick S.; Andrews, Elisabeth

2007-09-30

369

Accuracy assessments of aerosol optical properties retrieved from Aerosol Robotic Network (AERONET) Sun and sky radiance measurements  

Microsoft Academic Search

Sensitivity studies are conducted regarding aerosol optical property retrieval from radiances measured by ground-based Sun-sky scanning radiometers of the Aerosol Robotic Network (AERONET). These studies focus on testing a new inversion concept for simultaneously retrieving aerosol size distribution, complex refractive index, and single-scattering albedo from spectral measurements of direct and diffuse radiation. The perturbations of the inversion resulting from random

O. Dubovik; A. Smirnov; B. N. Holben; M. D. King; Y. J. Kaufman; T. F. Eck; I. Slutsker

2000-01-01

370

Chemical apportionment of aerosol column optical depth off the mid-Atlantic coast of the United States  

Microsoft Academic Search

Aerosol column optical depths derived from airborne Sun photometer and in situ measurements of aerosol properties in 14 vertical profiles off the mid-Atlantic coast of the United States in June show excellent agreement. Simultaneous measurements of the chemical compositions of the aerosol allows an assessment of the chemical apportionment of the aerosol column optical depths. The optical depths had essentially

Dean A. Hegg; John Livingston; Peter V. Hobbs; T. Novakov; Philip Russell

1997-01-01

371

Optical characteristics of aerosol in the coastal area  

NASA Astrophysics Data System (ADS)

The paper continues our previous investigations, based on the backscattering coefficient distribution, of the optical properties of aerosol in a coastal zone. The material presents some results of an elastic-backscattering lidar experiment carried out in the Bulgarian Black Sea coastal area in September 1992. The lidar experimental results are presented as 2-D images of the cross-sections of the variation of the extinction as a function of the height and the distance along the sounded path at different elevations. The value of the volume extinction coefficient is calculated according to Klett's inversion method, based on single elastic scattering of the laser emission. Along with the lidar measurements a conventionally measured meteorological parameters are presented. The experimental data considered in the paper demonstrates the lidar sensitivity to underlying surface influence over the optical characteristics of the aerosol.

Skakalova, Toni; Grigorov, Ivan; Parvanov, Orlin; Kolev, Ivan N.

1998-01-01

372

Evaluating UVA Aerosol Optical Depth using a Smartphone Camera.  

PubMed

This research evaluates a smartphone complementary metal oxide semiconductor (CMOS) image sensor's ability to detect and quantify incident solar UVA radiation and subsequently, aerosol optical depth at 340 and 380 nm. Earlier studies revealed that the consumer grade CMOS sensor has inherent UVA sensitivities, despite attenuating effects of the lens. Narrow bandpass and neutral density filters were used to protect the image sensor and to not allow saturation of the solar images produced. Observations were made on clear days, free from clouds. The results of this research demonstrate that there is a definable response to changing solar irradiance and aerosol optical depth can be measured within 5% and 10% error margins at 380 and 340 nm respectively. The greater relative error occurs at lower wavelengths (340 nm) due to increased atmospheric scattering effects, particularly at higher air masses and due to lower signal to noise ratio in the image sensor. The relative error for solar irradiance was under 1% for observations made at 380 nm. The results indicate that the smartphone image sensor, with additional external narrow bandpass and neutral density filters can be used as a field sensor to evaluate solar UVA irradiance and aerosol optical depth. PMID:23581749

Igoe, Damien P; Parisi, Alfio V; Carter, Brad

2013-05-20

373

Columnar Aerosol Optical Properties during "El Arenosillo 2004 Summer Campaign"  

SciTech Connect

A detailed analysis of the microphysical and radiative columnar aerosol parameters has been carried out for data collected during the “El Arenosillo 2004” summer campaign. These data are derived from a Cimel sun-photometer, as part of the PHOTONS-AERONET network at the El Arenosillo site in south-western Spain, over the period 1 June to 31 October 2004. The aim of this campaign was to obtain a more complete set of data on aerosol microphysical, optical/radiative, and chemical properties for use in closure studies. Previous papers addressed the climatology of the AOD-alpha parameters at this site. In this paper, we focus on the characterization of the particle size distribution and associated microphysical parameters, such as volume concentration, effective radius, etc., in order to define the features and ranges of these physical parameters associated with both fine and coarse particle modes. The requirement of high AOD values for using the optical inversion technique puts significant constraints on the estimation of these parameters and, thus, necessitates great care in the analysis. As a result, only the characterizations for desert dust events are considered reliable. Moreover, summer 2004 had the most frequent desert dust intrusions, including the most intense event, ever recorded at the El Arensillo site. We summarize the results for the intensive summer campaign in terms of the range of values of the physical and optical parameters of the mixed aerosol types present in this area of Spain.

Prats, N.; Cachorro, V. E.; Sorribas, M.; Mogo, S.; Berjon, A.; Toledano, C.; de Frutos, A. M.; de la Rosa, J.; Laulainen, Nels S.; de la Morena, B. A.

2008-04-14

374

Nighttime Aerosol Optical Depth Variability From Astronomical Photometry  

NASA Astrophysics Data System (ADS)

A technique for determination of the short-term (6 minutes intervals) variability of the aerosol optical depth (AOD) during nighttime from broadband visible measurements of star irradiances during clear nights was developed for the instrument called the Whole Sky Imager (WSI), placed at the Atmospheric Radiation Measurement (ARM) observation site in Oklahoma. The AOD is inferred indirectly from simultaneous observations of extinction of stars having different colors (spectra) and different elevations above the horizon, and takes into account the other sources for starlight attenuation in the atmosphere which might be present and which are measured by other instruments at the site at compatible timescales (e.g., precipitable water vapor content, columnar ozone amount, observed atmospheric stratification). The total error of the new method is a combination of the absolute star flux measurement error with the WSI and a systematic error in the models assumed for the other atmospheric components causing the starlight extinction. The relative error in the aerosol optical depth determined through this method is found to be below 4%. For the validation of the results, the comparison of the aerosol optical depth measured with the Lidar at 10 minutes intervals (at 355nm) with the AOD determined from WSI (in visible) shows a good agreement for the data in the interval studied (1999-2003).

Musat, I. C.; Ellingson, R. G.

2006-12-01

375

Improved retrieval of aerosol optical depth by satellite  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols are of major concern for public health and climate change, but their sources and atmospheric distributions remain poorly constrained. Satellite-borne radiometers offer a new constraint on aerosol sources and processes by providing global aerosol optical depth (AOD) retrievals. However, quantitative evaluation of chemical transport models (CTMs) with AOD products retrieved from satellite backscattered reflectances can be compromised by inconsistent assumptions of aerosol optical properties and errors in surface reflectance estimates. We present an improved AOD retrieval algorithm for the MODIS satellite instrument using locally derived surface reflectances and CTM aerosol optical properties. Assuming negligible atmospheric reflectance at 2.13 in cloud-free conditions, we derive 0.47/2.13 and 0.65/2.13 surface reflectance ratios at 1°x1.25° horizontal resolution for the continental United States in summer 2004 from the subset of top-of-atmosphere (TOA) reflectance data with minimal aerosol reflectance. We find higher ratios over arid regions than those assumed in the operational MODIS AOD retrieval algorithm, explaining the high AOD bias found in these regions. We simulate TOA reflectances for each MODIS scene using local aerosol optical properties from the GEOS-Chem CTM, and fit these reflectances to the observed MODIS TOA reflectances for a best estimate of AODs for each scene. Comparison with coincident ground-based (AERONET) AOD observations in the western and central United States during the summer of 2004 shows considerable improvement over the operational MODIS AOD products in this region. We find the AOD retrieval is more accurate at 0.47 than at 0.65 mum because of the higher signal to noise ratio, and that the correlation between MODIS and AERONET AODs improves as averaging time increases. We further improve the AOD retrieval method using an extensive ensemble of aircraft, ground-based, and satellite aerosol observations during the ICARTT field campaign over eastern North America in summer 2004. The aircraft measurements show narrower aerosol size distributions than those typically assumed in models, and correcting this leads to higher model and satellite retrieved AODs. We find that single scattering albedos calculated assuming externally mixed aerosol more closely represent observations than those calculated assuming internal mixing. Our improved MODIS AOD retrieval compares well to the ground-based AERONET data (R = 0.84, slope = 1.02), significantly improving on the MODIS operational products. Inference of surface PM2.5 from our MODIS AOD retrieval shows good correlation to the EPA-AQS data (R = 0.78) but a high regression slope (slope = 1.48). The high slope is seen in all AOD inferred PM2 5 concentrations (AERONET: slope = 2.04; MODIS c005: slope = 1.51) and is caused by an overestimate of PM2 5 over strong source regions which could reflect the mid day peak in sulfate concentrations corresponding to AOD sampling times.

Drury, Easan Evans

376

Optical and Hygroscopic Studies of Aerosols In Simulated Planetary Atmospheres  

NASA Astrophysics Data System (ADS)

Basic characteristics of the early Earth climate, the only known environment in the Universe in which life has been known to emerge and thrive, remain a mystery. In particular, little is understood about the Earth's atmosphere 2.8 billion years ago. From climate models and laboratory studies, it is postulated that an organic haze, much like that found on Saturn's largest moon Titan, covered the early Earth. This haze, generated from photolysis of carbon dioxide (CO2) and methane (CH4), may have had profound climatic consequences. Climate models of the early Earth that include this haze have had to rely upon optical properties of a Titan laboratory analog. Titan haze, though thought to be similar, is formed from a different combination of precursor gases and by different energy sources than early Earth haze. This thesis examines the direct and indirect radiative effects of aerosol on early Earth climate by studying the optical and hygroscopic properties of a laboratory analog. A Titan analog is studied for comparison and to better understand spacecraft-retrieved haze chemical and optical properties from Titan. The properties of the laboratory analogs, generated in a flowing reactor cell with a continuum ultraviolet (UV) light source, were primarily measured using cavity ringdown aerosol extinction spectroscopy and UV-visible (UV-Vis) transmission spectroscopy. We find that the optical properties of our early Earth analog are significantly different than those of the Titan analog from Khare et al. (1984). In both the UV and visible, when modeled as fractals, particles with the optical properties of the early Earth analog have approximately 30% larger extinction efficiencies than particles with Khare et al. (1984) values. This result implies our early Earth haze analog would provide a more efficient UV shield and have a stronger antigreenhouse effect than the Khare et al. (1984) Titan analog. Our Titan analog has significantly smaller imaginary refractive index values in the UV-Vis than Khare et al. (1984) values. These results may imply that (a) photolysis is not the dominant source of aerosol on Titan, and/or (b) the optical retrievals are dominated by the more absorbing and scattering electric discharge generated aerosol. For the hygroscopicity studies, the optical growth of the early Earth analog at various relative humidities (RH) was measured, as well as a Titan analog for comparison. The retrieved hygroscopic parameter for the early Earth analog indicates that a humidified early Earth aerosol could have contributed to a larger antigreenhouse effect on the early Earth atmosphere than previously modeled with dry aerosol. Such effects would be important in regions where RH is greater than 50% because such high humidities are needed for significant amounts of water to be on the aerosol. The retrieved hygroscopicity parameter also indicates that the particles could activate into cloud droplets at reasonable supersaturations. In regions where the haze was dominant, it is expected that low particle concentrations, once activated into cloud droplets, would create short-lived, optically thin clouds. Such clouds, if predominant on the early Earth, would have a lower albedo than clouds today, thereby warming the planet relative to current day clouds.

Hasenkopf, Christa A.

2011-08-01

377

Optical Properties of Mixed Black Carbon, Inorganic and Secondary Organic Aerosols  

SciTech Connect

Summarizes the achievements of the project, which are divided into four areas: 1) Optical properties of secondary organic aerosols; 2) Development and of a polar nephelometer to measure aerosol optical properties and theoretical approaches to several optical analysis problems, 3) Studies on the accuracy of measurements of absorbing carbon by several methods, and 4) Environmental impacts of biodiesel.

Paulson, S E

2012-05-30

378

Direct measurements of the axial displacement and evolving size of optically trapped aerosol droplets  

Microsoft Academic Search

The axial displacement of optically tweezed liquid aerosol droplets has been studied directly through the application of side imaging at 90° to the trapping laser beam. In conjunction with imaging in the plane of the optical trap and cavity-enhanced Raman spectroscopy (CERS), the optical forces experienced by a trapped aerosol have been interrogated. By varying the power of the trapping

K. J. Knox; J. P. Reid; K. L. Hanford; A. J. Hudson; L. Mitchem

2007-01-01

379

Direct measurements of the axial displacement and evolving size of optically trapped aerosol droplets  

Microsoft Academic Search

The axial displacement of optically tweezed liquid aerosol droplets has been studied directly through the application of side imaging at 90 to the trapping laser beam. In conjunction with imaging in the plane of the optical trap and cavity-enhanced Raman spectroscopy (CERS), the optical forces experienced by a trapped aerosol have been interrogated. By varying the power of the trapping

K J Knox; J P Reid; K L Hanford; A J Hudson; L Mitchem

2007-01-01

380

Aerosol optical properties in the marine boundary layer during the First Aerosol Characterization Experiment (ACE 1) and the underlying chemical and physical aerosol properties  

Microsoft Academic Search

Measurements were made onboard the NOAA R\\/V Discoverer during the First Aerosol Characterization Experiment (ACE 1) to understand the optical properties of a minimally perturbed natural aerosol system in terms of its chemical and physical properties. ACE I took place during November and December of 1995 in the Southern Ocean region south of Australia. Reported here are observations at a

P. K. Quinn; D. J. Coffman; V. N. Kapustin; T. S. Bates

1998-01-01

381

Aerosol optical properties at Lampedusa (Central Mediterranean) 1. Influence of transport and identification of different aerosol types  

Microsoft Academic Search

Aerosol optical depth andÅngström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001-September 2003. The average aerosol optical depth at 495.7 nm, tau, is 0.24±0.14; the averageÅngström exponent, alpha, is 0.86±0.63. The observed values of tau range from 0.03 to 1.13, and

G. Pace; A. di Sarra; D. Meloni; S. Piacentino; P. Chamard

2005-01-01

382

Aerosol optical properties at Lampedusa (Central Mediterranean). 1. Influence of transport and identification of different aerosol types  

Microsoft Academic Search

Aerosol optical depth and Ångström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001-September 2003. The average aerosol optical depth at 495.7 nm, tau, is 0.24±0.14; the average Ångström exponent, alpha, is 0.86±0.63. The observed values of tau range from 0.03 to

G. Pace; A. di Sarra; D. Meloni; S. Piacentino; P. Chamard

2006-01-01

383

Aerosol physical and optical properties and their relationship to aerosol composition in the free troposphere at Izaña, Tenerife, Canary Islands, during July 1995  

Microsoft Academic Search

Aerosol physical, optical, and chemical properties were measured at 2360 m above sea level over the Canary Islands during July 1995. Five aerosol size modes were observed. Nucleation aerosols 160 Mm-1 at relative humidities <30%. The lowest scattering was in air masses from the northwest whose aerosols were mostly pollutants. Air masses with North African mineral dust had the highest

H. Maring; D. L. Savoie; M. A. Izaguirre; C. McCormick; R. Arimoto; J. M. Prospero; C. Pilinis

2000-01-01

384

Climatology of aerosol optical properties in Northern Norway and Svalbard  

NASA Astrophysics Data System (ADS)

We present comparisons between estimates of the aerosol optical thickness and the Ångström exponent in Northern Norway and Svalbard based on data from AERONET stations at Andenes (69° N, 16° E, 379 m altitude) and Hornsund (77° N, 15° E, 10 m altitude) for the period 2008-2010. The three-year annual mean values for the aerosol optical thickness at 500 nm ?(500) at Andenes and Hornsund were 0.11 and 0.10, respectively. At Hornsund, there was less variation of the monthly mean value of ?(500) than at Andenes. The annual mean values of the Ångström exponent ? at Andenes and Hornsund were 1.18 and 1.37, respectively. At Andenes and Hornsund ? was found to be larger than 1.0 in 68% and 93% of the observations, respectively, indicating that fine-mode particles were dominating at both sites. Both sites had a similar seasonal variation of the aerosol size distribution although one site is in an Arctic area while the other site is in a sub-arctic area.

Chen, Y.-C.; Hamre, B.; Frette, Ø.; Stamnes, J. J.

2012-10-01

385

Using molecular tweezers to move and image nanoparticles  

NASA Astrophysics Data System (ADS)

The ability to manipulate nanoparticles is significant in nanoscale science and technology. As sizes of the objects scale down to the sub-10 nm regime, it imposes a great challenge for the conventional optical tweezers. There has been much effort to explore alternative manipulation methods including using nanostructures, electron beams, scanning probes, etc. In this paper, an overview of the latest advances in trapping and manipulation of nanoparticles with a focus on the emergent electron tweezers is provided.

Zheng, Haimei

2013-05-01

386

Using molecular tweezers to move and image nanoparticles.  

PubMed

The ability to manipulate nanoparticles is significant in nanoscale science and technology. As sizes of the objects scale down to the sub-10 nm regime, it imposes a great challenge for the conventional optical tweezers. There has been much effort to explore alternative manipulation methods including using nanostructures, electron beams, scanning probes, etc. In this paper, an overview of the latest advances in trapping and manipulation of nanoparticles with a focus on the emergent electron tweezers is provided. PMID:23592008

Zheng, Haimei

2013-05-21

387

Optical and microphysical properties of atmospheric aerosols in Moldova  

NASA Astrophysics Data System (ADS)

Measurements of aerosol properties in Kishinev, Moldova are being carried out within the framework of the international AERONET program managed by NASA/GSFC since 1999. Direct solar and sky diffuse radiances are measured by using of sunphotometer Cimel-318. Aerosol optical properties are retrieved from measured radiances by using of smart computational procedures developed by the AERONET's team. The instrument is situated at the ground-based solar radiation monitoring station giving the opportunity to make simultaneous spectral (win sunphotometer) and broadband (with the set of sensors from radiometric complex) solar radiation. Detailed description of the station and investigations in progress can be found at the http://arg.phys.asm.md. Ground station is placed in an urban environment of Kishinev city (47.00N; 28.56E; 205 m a.s.l). Summary of aerosol optical and microphysical properties retrieved from direct solar and diffuse sky radiance observations at Moldova site from September 1999 to June 2009 are presented below. Number of measurements (total): 1695 Number of measurements (for ?o, n, k): 223 Range of aerosol optical depth (AOD) @440 nm: 0.03 < ?(440) < 2.30, < ?(440)>=0.25 Range of Ångström parameter < ?440_870 >: 0.14 < ? < 2.28 Asymmetry factor (440/670/870/1020): 0.70/0.63/0.59/0.58 ±0.04 Refraction (n) and absorption (k) indices@440 nm: 1.41 ± 0.06; 0.009 ± 0.005 Single scattering albedo < ?o >(440/670/870/1020): 0.93/0.92/0.90/0.89 ±0.04 Parameters of volume particle size distribution function: (fine mode) volume median radius r v,f , ?m: 0.17 ± 0.06 particle volume concentration Cv,f, ?m3/?m2: 0.04 ± 0.03 (coarse mode) volume median radius rv,c , ?m: 3.08 ± 0.64 particle volume concentration Cv,c, ?m3/?m2: 0.03 ± 0.03 Climatic norms of AOD@500 nm and Ångström parameter < ?440_870 > at the site of observation are equal to 0.21 ± 0.06 and 1.45 ± 0.14, respectively. The aerosol type in Moldova may be considered as 'urban-industrial and mixed' in accordance with the classification of aerosol type models systematized and developed by AERONET team (O.Dubovik et al., 2002, J. Atmosph. Sci., 59, 590-608) on the basis of datasets acquired from worldwide observations at the network of sunphotometers. It should be noted the presence of increased value of absorption index and reduced values of albedo. This may be due to influence of absorptive aerosols (soot). These aerosols are originated from local dust sources and exhausts from intensive urban traffic, from sources of biomass and household garbage burning both in and around the city, and from long-range transport over regions with high loading of aerosols (dust, smoke).

Aculinin, Alexandr; Smicov, Vladimir

2010-05-01

388

Relation between optical and chemical properties of dust aerosol over Beijing, China  

Microsoft Academic Search

Characteristics of optical and chemical properties of dust aerosol over Beijing and their relation were studied in the spring dust season, 2006 to understand the impact of dust and anthropogenic aerosol on the regional climate. Two dust plumes (DS1 and DS2) were identified with contrasting physicochemical properties. Strong absorbing of aerosol at 439 nm was observed, probably due to the

Kan Huang; Guoshun Zhuang; Yanfen Lin; Juan Li; Yele Sun; Wenjie Zhang; Joshua S. Fu

2010-01-01

389

Physical and optical properties of aerosols over an urban location in western India: Seasonal variabilities  

Microsoft Academic Search

We present results on various physical and optical properties of aerosols measured over Ahmedabad, an urban location in western India, from 2002 to 2005 and discuss their seasonal and interannual variabilities. Aerosol parameters which have been studied include AOD spectra, aerosol mass concentration, size distribution, BC concentration, wavelength dependency in absorption, scattering coefficient, single scattering albedo and their vertical distribution

Dilip Ganguly; A. Jayaraman; H. Gadhavi

2006-01-01

390

Aerosol chemical and optical properties over the Paris area within ESQUIF project  

Microsoft Academic Search

Aerosol chemical and optical properties are extensively investigated for the first time over the Paris Basin in July 2000 within the ESQUIF project. The measurement campaign offers an exceptional framework to evaluate the performances of the chemistry-transport model CHIMERE in simulating concentrations of gaseous and aerosol pollutants, as well as the aerosol-size distribution and composition in polluted urban environments against

A. Hodzic; R. Vautard; P. Chazette; L. Menut; B. Bessagnet

2006-01-01

391

Tropospheric Aerosol Optical Thickness from the GOCART Model and Comparisons with Satellite and Sun Photometer Measurements  

Microsoft Academic Search

The Georgia Institute of Technology-Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model is used to simulate the aerosol optical thickness for major types of tropospheric aerosols including sulfate, dust, organic carbon (OC), black carbon (BC), and sea salt. The GOCART model uses a dust emission algorithm that quantifies the dust source as a function of the degree of

Mian Chin; Paul Ginoux; Stefan Kinne; Omar Torres; Brent N. Holben; Bryan N. Duncan; Randall V. Martin; Jennifer A. Logan; Akiko Higurashi; Teruyuki Nakajima

2002-01-01

392

Microphysical and optical properties of aerosol particles in urban zone during ESCOMPTE  

Microsoft Academic Search

Microphysical and optical properties of the main aerosol species on a peri-urban site have been investigated during the ESCOMPTE experiment. Ammonium sulfate (AS), nitrate (N), black carbon (BC), particulate organic matter (POM), sea salt (SS) and mineral aerosol (D) size distributions have been used, associated with their refractive index, to compute, from the Mie theory, the key radiative aerosol properties

M. Mallet; J. C. Roger; S. Despiau; O. Dubovik; J. P. Putaud

2003-01-01

393

The Optical Constants of Several Atmospheric Aerosol Species: Ammonium Sulfate, Aluminum Oxide, and Sodium Chloride  

Microsoft Academic Search

The optical constants of substances composing atmospheric aerosols are required to evaluate properly the effects of aerosols on the earth's radiation balance. We briefly review techniques for determining optical constants and also discuss pitfalls in using measured optical constants to simulate the optical constants of the real particles found in the atmosphere. We then compile the optical constants of (NH4hSO4,

Owen B. Toon; James B. Pollack; Bishun N. Khare

1976-01-01

394

Microcrystal manipulation with laser tweezers.  

PubMed

X-ray crystallography is the method of choice to deduce atomic resolution structural information from macromolecules. In recent years, significant investments in structural genomics initiatives have been undertaken to automate all steps in X-ray crystallography from protein expression to structure solution. Robotic systems are widely used to prepare crystallization screens and change samples on synchrotron beamlines for macromolecular crystallography. The only remaining manual handling step is the transfer of the crystal from the mother liquor onto the crystal holder. Manual mounting is relatively straightforward for crystals with dimensions of >25?µm; however, this step is nontrivial for smaller crystals. The mounting of microcrystals is becoming increasingly important as advances in microfocus synchrotron beamlines now allow data collection from crystals with dimensions of only a few micrometres. To make optimal usage of these beamlines, new approaches have to be taken to facilitate and automate this last manual handling step. Optical tweezers, which are routinely used for the manipulation of micrometre-sized objects, have successfully been applied to sort and mount macromolecular crystals on newly designed crystal holders. Diffraction data from CPV type 1 polyhedrin microcrystals mounted with laser tweezers are presented. PMID:23793156

Wagner, Armin; Duman, Ramona; Stevens, Bob; Ward, Andy

2013-06-13

395

Vertical Profiles of Cloud Condensation Nuclei, Condensation Nuclei, Optical Aerosol, Aerosol Optical Properties, and Aerosol Volatility Measured from Balloons.  

National Technical Information Service (NTIS)

Under the support of this grant a balloon-borne gondola containing a variety of aerosol instruments was developed and flown from Laramie, Wyoming, (41 deg N, 105 deg W) and from Lauder, New Zealand (45 deg S, 170 deg E). The gondola includes instruments t...

G. Vali J. R. Snider T. Deshler

1998-01-01

396

Evaluation of OMI Aerosol Type and Extinction Optical Depth With AERONET Ground Measurements  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV) aerosol products (OMAERUV) including Aerosol Index (AI), aerosol extinction optical depth, single scattering albedo, and absorption optical depth from the Ozone Monitoring Instrument (OMI) onboard the Aura spacecraft provide unique information for understanding the global effect of absorbing aerosols on Earth's radiation budget. Recently we have released a new data set with significant improvements by reducing uncertainties in retrievals due in part to the inaccuracies of aerosol type identification, layer height estimates, and the spectral dependence of aerosol absorption properties. These improvements include the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol layer height data, Atmospheric Infrared Sounder (AIRS) carbon monoxide data which is used to distinguish smoke from dust type aerosols in conjunction with OMI UVAI, updated carbonaceous aerosol models that account for the presence of organics, and a better optimization of the algorithm. In this study, we will demonstrate how a combined multi-sensors approach can be used for improving OMI aerosol products and evaluate them with AERONET Angstrom exponent and aerosol optical depth data at selected sites and regions.

Ahn, C.; Torres, O.; Bhartia, P. K.; Chen, Z.; Jethva, H. T.

2011-12-01

397

Aircraft observations of the microphysical and optical properties of major aerosol species  

NASA Astrophysics Data System (ADS)

We summarise the microphysical and optical parameters of some principal aerosol species obtained by instrumentation on the UK Met Office C-130 aircraft during international field campaigns since 1996. The aerosol species include Saharan dust, biomass burning aerosol, European continental pollution, eastern seaboard USA pollution, and clean maritime aerosol. The typical structure of the aerosol in the vertical from each airmass type is described. Microphysical parameters are described that comprise the mode radius and geometric standard deviation associated with 2-3 lognormal fits to the mean observed aerosol size distributions spanning the accumulation and coarse modes. Optical parameters comprising the aerosol single scattering albedo (which was both measured and derived from Mie theory), specific extinction coefficient, and asymmetry factor (which were derived from Mie theory) are also presented. Where available, evolution of the physical and optical properties of the aerosol has been highlighted. Comparisons with long-term ground-based AERONET aerosol retrievals show reasonable agreement. Our observations provide useful data for validating and improving global circulation models (GCMs) that use physically based aerosol representation and for validating satellite retrievals of the physical and optical properties of aerosols.

Osborne, S. R.; Haywood, J. M.

2005-02-01

398

Aerosol optical properties affected by a strong dust storm over central and northern China  

Microsoft Academic Search

Aerosol observational data at 8 ground-based observation sites in the Chinese Sun Hazemeter Network (CSHNET) were analyzed\\u000a to characterize the optical properties of aerosol particles during the strong dust storm of 16–21 April 2005. The observational\\u000a aerosol optical depth (AOD) increased significantly during this dust storm at sites in Beijing city (86%), Beijing forest\\u000a (84%), Xianghe (13%), Shapotou (27%), Shenyang

Jinyuan Xin; Wupeng Du; Yuesi Wang; Qingxian Gao; Zhanqing Li; Mingxing Wang

2010-01-01

399

Ground-based observation of aerosol optical properties in Lanzhou, China  

Microsoft Academic Search

Aerosol optical properties from August 2006 to July 2007 were obtained from ground-based and sky radiance measurements in Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL), China. High aerosol optical thickness (AOT) associated with low Ångström exponent (?) was mainly observed in spring, which was consistent with the seasonal dust production from Hexi Corridor. The maximum monthly average value

Xingna YU; Bin ZHU; Shuxian FAN; Yan YIN; Xiaoli BU

2009-01-01

400

Aerosol Size Distributions Obtained by Inversions of Spectral Optical Depth Measurements  

Microsoft Academic Search

Columnar aerosol size distributions have been inferred by numerically,inverting particulate optical depth measurements as a function of wavelength. An inversion formula which explicitly includes the magnitude of the measurement variances is derived and applied to optical depth measurements obtained in Tucson with a solar radiometer. It is found that the individual size distributions of the aerosol particles (assumed spher- ical),

Michael D. King; Dale M. Byrne; Benjamin M. Herman; John A. Reagan

1978-01-01

401

Images of optically thick artificial aerosol clouds in the near-Earth space  

NASA Astrophysics Data System (ADS)

The images were constructed for three aerosol cloud distribution types: uniform, one with a cavity in the center (shell) and one with a dense core (core with 'wings'). Differences between images of optically thich and optically thin clouds for these three distribution types of particles and various view angles are discussed. Calculated results are compared with experimental data from aerosol clouds observations.

Belikov, Yu. E.; Gurvich, A. V.

1995-04-01

402

High-resolution laser-based detection for magnetic tweezers  

NASA Astrophysics Data System (ADS)

Magnetic tweezers are a versatile and powerful single-molecule manipulation technique capable of applying force and torque on single bio-molecules. They afford several unique advantages over other single-molecule manipulation techniques such as optical tweezers or atomic force microscopy. The hallmark of magnetic tweezers is the ability to twist bio-molecules without the need for complex optical instrumentation. Perhaps less known but of equal significance, magnetic tweezers rely on a slowly decaying magnetic field gradient (1 mm) to impose force so they are intrinsically configured in a passive force clamp mode. These features make magnetic tweezers particularly well suited for the study of nucleic acid structure, DNA topology, and protein-nucleic acid interactions. The one downside to most magnetic tweezers to date is that they rely on video tracking methods to determine the position of the particle. Despite recent progress, the spatial and temporal resolution and accuracy are fundamentally limited by image tracking techniques. I will describe recent improvements utilizing laser-based detection to overcome these limitations. We implemented back-scattered laser-based detection combined with video image tracking to achieve high-resolution, high-bandwidth, three-dimensional position tracking.

Neuman, Keir

2011-03-01

403

Improving Radiative Assessments of Aerosol Chemical, Physical and Optical Properties Through Aerosol Volatility Studies Over Optically Effective Sizes  

NASA Astrophysics Data System (ADS)

In order to interpret in-situ and satellite observations of complex aerosol mixtures such as those encountered during ACE-ASIA and TRACE-P as well as to model them, optical effects due to each component of particles in a given size needs to be determined. Here we present recently refined techniques applied to particles with optically effective sizes over 0.1 - 14 ?m. These provide constraints on the real and imaginary refractive indices, as required for both scattering and absorbing particles. We will also demonstrate the application of this approach to ACE-Asia and TRACE-P data. The size distribution during ACE-Asia was measured by Optical Particle Counter (OPC, custom LAS-X, Particle Measurement Systems) with thermal analysis at 150°C and 300°C that inferred the volatile and refractory components of the particles. Calibrations of this optical measurement based upon wide-angle scattering provided the optically effective diameters of particles sized by the OPC rather than physical diameters. This allows direct Mie modeling of optical properties and reduces related uncertainties common to instruments that size particles based on other techniques (eg. aerodynamic - problematic for nonspherical particles and uncertain refractive index; forward scattering instruments - uncertain for large aerosol and very sensitive to refractive index ; impactors - uncertainties due to size cuts and inversions and refractive index; etc.). These optically effective size distributions are then used in the following manner: 1) Integration of optical sizes over scattering angles seen by a nephelometer provides a direct closure without having to make estimated nephelometer truncation corrections. For large particle dust events these approaches indicate that standard truncation corrections for nephelometer data appear to underestimate required corrections. 2) Volatility is related to concurrently measured soluble species (PILS-particle in liquid sampler, R. Weber) providing chemical characterization and associated refractive indices for the volatile component. This also allows correction of effective optical sizes to actual physical sizes if needed. 3) Submicrometer refractory (300°C) component is linked to the absorbing soot and dust components to refine effective refractive index for this size class. 4) The calculated optical properties enable us to provide a constrained estimate of the actual refractive indices of the dust and soot components through comparison with direct measurements of scattering by nephelometer and absorption by Particle Soot Absorption Photometer (PSAP). 5) If measurements such as f(RH) are available, this size-resolved volatility can also be used to predict this humidity response and confirming the approach for modeling properties at ambient humidity as required for closure and satellite comparisons.

Shinozuka, Y.; Clarke, A.; Howell, S.; Kapustin, V.

2002-12-01

404

Retrieval of aerosol optical thickness over snow using AATSR observations  

NASA Astrophysics Data System (ADS)

Remote sensing of aerosols experiences lack of products over very bright surfaces, such as deserts and snow, due to difficulties with the subtraction of the surface reflection contribution, when a small error in accounting for surface reflectance can cause a large error in retrieved aerosol optical thickness (AOT). Cloud screening over bright surface is also not easy because of low contrast between clouds and surface in visible range of spectrum, and additional infrared chan-nels are not always available. Luckily, AATSR instrument onboard ENVISAT has necessary features to solve both of these problems. In current work we present an improved version of discussed earlier [1,2] dual-view algorithm to retrieve AOT over snow. The retrieval algorithm still consists of cloud screening, based on spectral shape analysis of AATSR pixel in order to extract clear snow pixels, and of AOT retrieval over snow and water. Current version of AOT retrieval over open ocean now contains improved accounting for ocean reflectance (in previous version the ocean was assumed to be absolutely black). The AOT retrieval over snow has been improved to account more accurately for the bidirectional features of the surface reflection function. For this we now use the approach described in [4] instead of [3], which has been used in the previous version of the retrieval. The accuracy of both approaches [3] and [4] has been evaluated via comparison to forward radiative-transfer model for the case of a very bright surface. The new algorithm has been applied to various scenes in European Arctic and Alaska in different scales, up to global AOT maps. The correspondence of AOT over snow to AOT over water is quite good, which proves the reliability of the retrieval. The algorithm has been validated against AERONET and other Arctic ground based AOT data and shows reasonably good correlation. The presented cloud screening method has been validated via comparison to MODIS cloud mask and Micro Pulse Lidar data. 1. L.G. Istomina, W. Von Hoyningen-Huene, A.A.Kokhanovsky, V.V. Rozanov, M. Schreier, K. Dethloff, M.Stock, R. Treffeisen, A. Herber, J.P.Burrows (2008). Sensitivity study of the dual-view algorithm for aerosol optical thickness retrieval over snow and ice, Proceedings of the 2nd MERIS/(A)ATSR User Workshop, 22-26 September 2008, ESRIN, Frascati, Italy. 2. L.G. Istomina, W. Von Hoyningen-Huene, A.A. Kokhanovsky, J.P. Burrows (2009) Retrieval of aerosol optical thickness in Arctic region using dual-view AATSR observations, Proceedings of ESA Atmospheric Science Conference, 9-11 September 2009, Barcelona, Spain. 3. Y.R. Kaufman, D. Tanre, H.R. Gordon, T. Nakajima, J. Lenoble, R. Frouin, H. Grassl, B.M. Herman, M.D. King, P.M. Teillet (1997) Passive remote sensing of tropospheric aerosol and atmorpheric correction for the aerosol effect. J. Geophys. Res. 102, 16.815-16.830 4. D.Tanre, M. Herman, P.Y.Deschamps, A. De Leffe (1979) Atmosperic modeling for space measurements of ground reflectances, including bidirectional properties. Appl. Optics, 18, 21. 3587-3594

Istomina, Larysa; von Hoyningen-Huene, Wolfgang; Rozanov, Vladimir; Kokhanovsky, Alexander; Burrows, John P.

405

The Smallest Tweezers in the World  

ERIC Educational Resources Information Center

|A pair of fine tweezers and a steady hand may well be enough to pick up a grain of sand, but what would you use to hold something hundreds of times smaller still, the size of only one micron? The answer is to use a device that is not mechanical in nature but that relies instead on the tiny forces that light exerts on small particles: "optical

Lewalle, Alexandre

2008-01-01

406

AERONET-based microphysical and optical properties of smoke-dominated aerosol near source regions and transported over oceans, and implications for satellite retrievals of aerosol optical depth  

NASA Astrophysics Data System (ADS)

Smoke aerosols from biomass burning are an important component of the global aerosol cycle. Analysis of Aerosol Robotic Network (AERONET) retrievals of size distribution and refractive index reveals variety between biomass burning aerosols in different global source regions, in terms of aerosol particle size and single scatter albedo (SSA). Case studies of smoke transported to coastal/island AERONET sites also mostly lie within the range of variability at near-source sites. Two broad ''families'' of aerosol properties are found, corresponding to sites dominated by boreal forest burning (larger, broader fine mode, with midvisible SSA ∼0.95), and those influenced by grass, shrub, or crop burning with additional forest contributions (smaller, narrower particles with SSA ∼0.88-0.9 in the midvisible). The strongest absorption is seen in southern African savannah at Mongu (Zambia), with average SSA ∼0.85 in the midvisible. These can serve as candidate sets of aerosol microphysical/optical properties for use in satellite aerosol optical depth (AOD) retrieval algorithms. The models presently adopted by these algorithms over ocean are often insufficiently absorbing to represent these biomass burning aerosols. A corollary of this is an underestimate of AOD in smoke outflow regions, which has important consequences for applications of these satellite datasets.

Sayer, A. M.; Hsu, N. C.; Eck, T. F.; Smirnov, A.; Holben, B. N.

2013-09-01

407

Evaluation of sulfate aerosol optical depths over the North Atlantic and comparison with satellite observations  

SciTech Connect

It has been postulated that scattering of sunlight by aerosols can significantly reduce the amount of solar energy absorbed by the climate system. Aerosol measurement programs alone cannot provide all the information needed to evaluate the radiative forcing due to anthropogenic aerosols. Thus, comprehensive global-scale aerosol models, properly validated against surface-based and satellite measurements, are a fundamental tool for evaluating the impacts of aerosols on the planetary radiation balance. Analyzed meteorological fields from the European Centre for Medium-Range Weather Forecasts are used to drive a modified version of the PNL Global Chemistry Model, applied to the atmospheric sulfur cycle. The resulting sulfate fields are used to calculate aerosol optical depths, which in turn are compared to estimates of aerosol optical depth based on satellite observations.

Berkowitz, C.M.; Ghan, S.J. [Pacific Northwest Lab., Richland, WA (United States); Benkovitz, C.M.; Wagener, R.; Nemesure, S.; Schwartz, S.E. [Brookhaven National Lab., Upton, NY (United States)

1993-11-01

408

High aerosol optical depth biomass burning events: A comparison of optical properties for different source regions  

NASA Astrophysics Data System (ADS)

The optical properties of aerosols such as smoke from biomass burning vary due to aging processes and these particles reach larger sizes at high concentrations. We compare the spectra of aerosol optical depth (?a), column-integrated volume size distributions, refractive indices, and single scattering albedo retrieved from AERONET observations for four selected events of very high smoke optical depth (?a ~ 2 at 500 nm). Two case studies are from tropical biomass burning regions (Brazil and Zambia) and two are cases of boreal forest and peat fire smoke transported long distances to sites in the US and Moldova. Smoke properties for these extreme events can be significantly different from those reported in more typical plumes. In particular, large differences in smoke fine mode particle radius (~0.17 to 0.25 ?m) and single scattering albedo (~0.88 to 0.99 at 440 nm) were observed as a result of differences in fuels burned, combustion phase, and aging.

Eck, T. F.; Holben, B. N.; Reid, J. S.; O'Neill, N. T.; Schafer, J. S.; Dubovik, O.; Smirnov, A.; Yamasoe, M. A.; Artaxo, P.

2003-10-01

409

Influence of observed diurnal cycles of aerosol optical depth on aerosol direct radiative effect  

NASA Astrophysics Data System (ADS)

The diurnal variability of aerosol optical depth (AOD) can be significant, depending on location and dominant aerosol type. However, these diurnal cycles have rarely been taken into account in measurement-based estimates of aerosol direct radiative forcing (ADRF) or aerosol direct radiative effect (ADRE). The objective of our study was to estimate the influence of diurnal aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global ADRE estimates. While focusing also in more detail on some selected sites of strongest impact, our goal was to also see the possible impact regionally. We calculated ADRE with different assumptions about the daily AOD variability: taking the observed daily AOD cycle into account and assuming diurnally constant AOD. Moreover, we estimated the corresponding differences in ADREs, if the single AOD value for the daily mean was taken from the the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra or Aqua overpass times, instead of accounting for the true observed daily variability. The mean impact of diurnal AOD variability on 24 h ADRE estimates, averaged over all AERONET sites, was rather small and it was relatively small even for the cases when AOD was chosen to correspond to the Terra or Aqua overpass time. This was true on average over all AERONET sites, while clearly there can be much stronger impact in individual sites. Examples of some selected sites demonstrated that the strongest observed AOD variability (the strongest morning afternoon contrast) does not typically result in a significant impact on 24 h ADRE. In those cases, the morning and afternoon AOD patterns are opposite and thus the impact on 24 h ADRE, when integrated over all solar zenith angles, is reduced. The most significant effect on daily ADRE was induced by AOD cycles with either maximum or minimum AOD close to local noon. In these cases, the impact on 24 h ADRE was typically around 0.1-0.2 W m-2 (both positive and negative) in absolute values, 5-10% in relative ones.

Eck, T. F.; Huttunen, J.; Lehtinen, K. E. J.; Lindfors, A. V.; Myhre, G.; Smirnov, A.; Tripathi, S. N.; Yu, H.

2013-08-01

410

Validation of MODIS aerosol optical depth over the Mediterranean Coast  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols, due to their high spatial and temporal variability, are considered one of the largest sources of uncertainty in different processes affecting visibility, air quality, human health, and climate. Among their effects on climate, they play an important role in the energy balance of the Earth. On one hand they have a direct effect by scattering and absorbing solar radiation; on the other, they also have an impact in precipitation, modifying clouds, or affecting air quality. The application of remote sensing techniques to investigate aerosol effects on climate has advanced significatively over last years. In this work, the products employed have been obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS). MODIS is a sensor located onboard both Earth Observing Systems (EOS) Terra and Aqua satellites, which provide almost complete global coverage every day. These satellites have been acquiring data since early 2000 (Terra) and mid 2002 (Aqua) and offer different products for land, ocean and atmosphere. Atmospheric aerosol products are presented as level 2 products with a pixel size of 10 x 10 km2 in nadir. MODIS aerosol optical depth (AOD) is retrieved by different algorithms depending on the pixel surface, distinguishing between land and ocean. For its validation, ground based sunphotometer data from AERONET (Aerosol Robotic Network) has been employed. AERONET is an international operative network of Cimel CE318 sky-sunphotometers that provides the most extensive aerosol data base globally available of ground-based measurements. The ground sunphotometric technique is considered the most accurate for the retrieval of radiative properties of aerosols in the atmospheric column. In this study we present a validation of MODIS C051 AOD employing AERONET measurements over different Mediterranean coastal sites centered over an area of 50 x 50 km2, which includes both pixels over land and ocean. The validation is done comparing spatial statistics from MODIS with corresponding temporal statistics from AERONET, as proposed by Ichoku et al. (2002). Eight Mediterranean coastal sites (in Spain, France, Italy, Crete, Turkey and Israel) with available AERONET and MODIS data have been used. These stations have been selected following QA criteria (minimum 1000 days of level 2.0 data) and a maximum distance of 8 km from the coast line. Results of the validation over each site show analogous behaviour, giving similar results regarding to the accuracy of the algorithms. Greatest differences are found for the AOD obtained over land, especially for drier regions, where the surface tends to be brighter. In general, the MODIS AOD has better a agreement with AERONET retrievals for the ocean algorithm than the land algorithm when validated over coastal sites, and the agreement is within the expected uncertainty estimated for MODIS data. References: - C. Ichoku et al., "A spatio-temporal approach for global validation and analysis of MODIS aerosol products", Geophysical Research Letters, 219, 12, 10.1029/2001GL013206, 2002.

Díaz-Martínez, J. Vicente; Segura, Sara; Estellés, Víctor; Utrillas, M. Pilar; Martínez-Lozano, J. Antonio

2013-04-01

411

Spatial variation of aerosol optical properties in North China Plain  

NASA Astrophysics Data System (ADS)

The column-integrated optical properties of aerosol in Beijing and Xianghe situated at North China Plain were investigated based on Sun/sky radiometer measurements made at Aerosol Robotic Network (AERONET) sites. Only version 2 and level 2 quality-assured data were presented and analyzed in this paper. Time intervals differ for the two sites, with Beijing having 9 years of data (Mar.-May, 2001; Apr., 2002-Dec., 2011),while Xianghe having 6 years of data (Mar.-Apr., 2001;Sep., 2004-Dec.,2011). Monthly mean 500 nm AOT values reach a maximum in June (0.95) and exceed 0.55 from March through September, and the minimum values occur during the late fall and winter months of November through February at Beijing. The monthly mean AOT values at Xianghe are very close to those measured at Beijing. The absolute differences of AOT between the two sites are less than 0.1 except in June and July. The reason of large difference in June and July is the frequently cloud contamination in summer result in the monthly means over the two sites computed from a large number of measurements of different date. The monthly averaged AOT with the same date in June and July are re-computed and the absolute difference of AOT between Beijing and Xianghe reduced to 0.01 and 0.03 in June and July respectively. The monthly mean Angstrom Exponent (AE) in Beijing and Xianghe sites are very close, with the absolute difference less than 0.075. The monthly mean AE in the two sites varied between ~1.0 and ~1.3 except in spring (March-May), therefore clearly dominated by fine mode aerosol for most of the year. All monthly averaged SSA at Beijing showed much lower value as compared to Xianghe though the seasonal variations are similar for the two sites, which indicates that aerosol absorption is greater in Beijing. All monthly averaged imaginary part of refractive index at Beijing has much higher value than Xianghe. The absolute differences of SSA between the two sites range from 0.016 to 0.037 except that the difference in September is only 0.0005. All the significant differences but September exceed the 95% confidence level based on t-test technique. This very large difference in SSA over a relatively small distance (~70 km) suggests the significant variability in aerosol absorption between Beijing and Xianghe and the reasons for this difference should be investigated.

Fan, Xuehua

2013-04-01

412

Satellite and ground-based study of optical properties of 1997 Indonesian Forest Fire aerosols  

NASA Astrophysics Data System (ADS)

Optical properties of biomass burning aerosols in the event of Indonesian forest fires in 1997 were studied by groundbased sky radiometry and satellite remote sensing with AVHRR and TOMS radiometers. The AVHRR-derived optical thickness distribution agreed with the distribution of TOMS-derived UV-absorbing aerosol index and with the optical thickness measured by sky radiometry and sunphotometry. The single scattering albedo of aerosols was fairly constant as 0.9 in the September-October period. Relationship between Ångström turbidity factor and exponent supported the polydispersion consisted of aged small particles. This observation was consistent with the fact that the retrieved volume size distribution by sky radiometry has a distinct accumulation mode with a peak radius of 0.25 µm. Those optical properties of smoke aerosols seem to reflect the specific chemical structure of Indonesian forest fire aerosols, i.e., a mixture of carbonaceous and sulfate particles.

Nakajima, Teruyuki; Higurashi, Akiko; Takeuchi, Nobuo; Herman, Jay R.

413

Nanoscale Molecular Tweezers  

NSDL National Science Digital Library

The featured molecules for this month are drawn from the "Research Advances" column by Angela G. King, and represent some of the structures from the research on molecular tweezers (published in J. Am. Chem. Soc. 2004, 126, 8124). The structures below are based on the figure on page 1690 showing two types of receptors that switch between U and W shapes upon coordination of soft metal cations, acting in the manner of mechanical tweezers. When viewing these molecules in Chime you must render in ball and stick or space filling modes in order to see the incorporated metal ions. In several cases the torsion angles connecting the anthracene substituents to the rest of the molecule are not well defined and have been drawn as either coplanar or orthogonal to the central ring system. At a moderate level of theory, the torsion angle in those instances where it has been set to 90° displays a broad minimum ranging for 50?130°.

414

Relative humidity and its effect on aerosol optical depth in the vicinity of convective clouds  

NASA Astrophysics Data System (ADS)

The hygroscopic growth of aerosols is controlled by the relative humidity (RH) and changes the aerosols’ physical and hence optical properties. Observational studies of aerosol–cloud interactions evaluate the aerosol concentration using optical parameters, such as the aerosol optical depth (AOD), which can be affected by aerosol humidification. In this study we evaluate the RH background and variance values, in the lower cloudy atmosphere, an additional source of variance in AOD values beside the natural changes in aerosol concentration. In addition, we estimate the bias in RH and AOD, related to cloud thickness. This provides the much needed range of RH-related biases in studies of aerosol–cloud interaction. Twelve years of radiosonde measurements (June–August) in thirteen globally distributed stations are analyzed. The estimated non-biased AOD variance due to day-to-day changes in RH is found to be around 20% and the biases linked to cloud development around 10%. Such an effect is important and should be considered in direct and indirect aerosol effect estimations but it is inadequate to account for most of the AOD trend found in observational studies of aerosol–cloud interactions.

Altaratz, O.; Bar-Or, R. Z.; Wollner, U.; Koren, I.

2013-09-01

415

Optical Tweezers-Assisted Cross-Correlation Analysis for a Non-intrusive Fluid Temperature Measurement in Microdomains  

NASA Astrophysics Data System (ADS)

An image-based approach to predict the fluid temperature in microfluidic flow cell is presented. We apply Fourier-based cross-correlation processing to determine the lateral displacement of the optically trapped bead; therefore, both the mean square displacement (MSD) and the diffusion coefficient (D) can be obtained. On the other hand, applying the Stokes--Einstein equation, together with Faxen's law correction, the theoretical relation showed that D is proportional to (T/?), where T and ? are temperature and temperature-dependent fluid viscosity, respectively. Hence, the fluid temperature can be determined by MSD-based thermometry.

Cheng, Chih-Ming; Chang, Ming-Chih; Chang, Yu-Fen; Wang, Wei-Ting; Hsu, Chien-Ting; Tsai, Jing-Shin; Liu, Chia-Yeh; Wu, Chien-Ming; Ou, Keng-Liang; Yang, Tzu-Sen

2012-06-01

416

Hemoglobin degradation in human erythrocytes with long-duration near-infrared laser exposure in Raman optical tweezers  

NASA Astrophysics Data System (ADS)

Near-infrared laser (785-nm)-excited Raman spectra from a red blood cell, optically trapped using the same laser beam, show significant changes as a function of trapping duration even at trapping power level of a few milliwatts. These changes in the Raman spectra and the bright-field images of the trapped cell, which show a gradual accumulation of the cell mass at the trap focus, suggest photoinduced aggregation of intracellular heme. The possible role of photoinduced protein denaturation and hemichrome formation in the observed aggregation of heme is discussed.

Dasgupta, Raktim; Ahlawat, Sunita; Verma, Ravi Shanker; Uppal, Abha; Gupta, Pradeep Kumar

2010-09-01

417

A decadal regional and global trend analysis of the aerosol optical depth using a data-assimilation grade over-water MODIS and Level 2 MISR aerosol products  

Microsoft Academic Search

Using the ten-year (2000-2009) DA quality Terra MODIS and MISR aerosol products, as well as 7 years of Aqua MODIS, we studied both regional and global aerosol trends over oceans. This included both natural and data assimilation grade versions of the products. Contrary to some of the previous studies that showed a decreasing trend in aerosol optical depth (AOD) over

J. Zhang; J. S. Reid

2010-01-01

418

Aerosol optical properties over the midcontinental United States  

NASA Astrophysics Data System (ADS)

Solar and sky radiation measurements were analyzed to obtain aerosol properties such as the optical thickness and the size distribution. The measurements were conducted as part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) during the second intensive field campaign (IFC) from June 25 to July 14, 1987, and the fifth IFC from July 25 to August 12, 1989, on the Konza Prairie near Manhattan, Kansas. Correlations with climatological and meteorological parameters show that during the period of observations in 1987, two types of air masses dominated the area: an air mass with low optical thickness and low temperature air associated with a northerly breeze, commonly referred to as the continental air, and an air mass with a higher optical thickness and higher temperature air associated with a southerly wind which we call "Gulf air." The size distributions show a predominance of the larger size particles in Gulf air. Because of the presence of two contrasting air masses, correlations with parameters such as relative humidity, specific humidity, pressure, temperature, and North Star sky radiance reveal some interesting aspects. In 1989, clear distinctions between continental and Gulf air cannot be made; the reason for this will be discussed.

Halthore, Rangasayi N.; Markham, Brian L.; Ferrare, Richard A.; Aro, Theo. O.

1992-11-01

419

Multiwavelength solar radiometer network and features of aerosol spectral optical depth at Trivandrum  

NASA Astrophysics Data System (ADS)

Five multiwavelength solar radiometers have been developed and deployed at Trivandrum, Mysore, Waltair, Jodhpur and New Delhi establishing a network during Indian Middle Atmosphere Program. The instruments measure atmospheric columnar optical depth at nine wavelengths in the visible and near infrared enabling studies on physical features of aerosols and integrated content of atmospheric water vapor. Using this instrument, measurements of aerosol optical depth and atmospheric water vapor have been made at Trivandrum since November 1985. The monthly, seasonal and spectral variations of aerosol optical depth are studied and their implications are discussed in the light of earlier findings.

Krishna Moorthy, K.; Nair, Prabha R.; Krishna Murthy, B. V.

1989-12-01

420

Global error maps of aerosol optical properties: an error propagation analysis  

NASA Astrophysics Data System (ADS)

Among the numerous atmospheric constituents, aerosols play a unique role on climate, due to their scattering and absorbing capabilities, visibility degradation and their effect on incoming and outgoing radiation. The most important optical properties are the aerosol optical depth (AOD), the asymmetry parameter (g) and the single scattering albedo (SSA). Uncertainties in aerosol microphysics in global models, which in turn affect their optical properties, propagate to uncertainties on the effect of aerosols on climate. This study aims to estimate the uncertainty of AOD, g and SSA attributable to the aerosol representation in models, namely mixing state, aerosol size and aerosol associated water. As a reference, the monthly mean output of the general circulation model LMDz-INCA from the international comparison exercise AEROCOM B was used. For the optical properties calculations, aerosols were considered either externally mixed, homogeneously internally mixed or coated spheres. The radius was allowed to vary by 20% (with 2% intervals) and the aerosol water content by 50% (with 5% intervals) with respect to the reference model output. All of these possible combinations were assumed to be equally likely and the optical properties were calculated for each one of them. A probability density function (PDF) was constructed at each model grid point for AOD, g and SSA. From this PDF, the 1 sigma and 2 sigma uncertainties of the AOD, g and SSA were calculated and are available as global maps for each month. For the range of the cases studied, we derive a maximum 2 sigma uncertainty range in AOD of 70%, while for g and SSA the maxima reach 18% and 28% respectively. The mixing state was calculated to be important, with the aerosol absorption and SSA being the most affected properties when absorbing aerosols are present. chem-phys-discuss.net/8/16027/2008/

Tsigaridis, K.; Balkanski, Y.; Schulz, M.; Benedetti, A.

2008-12-01