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. Author manuscript; available in PMC: 2006 Sep 12.
Published in final edited form as: Am J Phys. 2003 Mar;71(3):201–215. doi: 10.1119/1.1532323

Resource Letter: LBOT-1: Laser-based optical tweezers

Matthew J Lang 1,a), Steven M Block 1
PMCID: PMC1564163  NIHMSID: NIHMS11347  PMID: 16971965

Abstract

This Resource Letter provides a guide to the literature on optical tweezers, also known as laser-based, gradient-force optical traps. Journal articles and books are cited for the following main topics: general papers on optical tweezers, trapping instrument design, optical detection methods, optical trapping theory, mechanical measurements, single molecule studies, and sections on biological motors, cellular measurements and additional applications of optical tweezers.

I. INTRODUCTION

The field of optical tweezers has enjoyed a wide range of applications since its inception in the early 1970s. By using light to trap microscopic objects noninvasively, optical tweezers provide a flexible tool for ultrafine positioning, measurement, and control. In practice, forces up to 200 pN or thereabouts may be applied with sub-pN resolution on objects whose characteristic dimensions are similar to the wavelength of light. Particle positioning and detection capabilities are therefore on a spatial scale of micrometers down to angstroms. The emerging applications of laser-based optical traps are quite diverse and extensive, ranging from atomic physics to the medical sciences. As a result, optical tweezers have been a focal point for interdisciplinary science.

Trapping apparatus ranges from simple, lens-based traps to complex instrumentation integrating multiple optical technologies. A variety of novel techniques have been developed for rapid position detection, trap stiffness determination, and applying controlled, calibrated forces. Instrument advances, such as the use of multiple laser beams, computerized automation of laser beams and sample positioning, and optical tweezers used in combination with other methodologies, such as fluorescence spectroscopy, micropipettes, and optical microbeams, have all helped to make optical tweezers an extremely versatile tool.

Owing to their exquisitely controllable force-exerting properties, optical tweezers are useful for a variety of nano-mechanical measurements, particularly those with biological applications. Objects such as biopolymers (e.g., microtubules, DNA molecules), lipid membranes, intact or fractionated cells, and single biological macromolecules have all been studied successfully with optical tweezers. There are many broad areas of current research in biophysics, including the mechanical unfolding and refolding of proteins or nucleic acids, the strength of receptor-ligand bonding interactions, and the nanoscale mechanics of biological motors, which are especially well suited to work with optical tweezers.

Optical tweezers are also useful purely as manipulators and positioning devices. Tweezers can be used to confine or constrain microscopic objects, as well as to organize, assemble, locate, or modify them. In addition to studies of single proteins, biological applications such as intracellular particle tracking and positioning, selective cell harvesting, and probing the mechanics of cell membranes have all been pursued with vigor. Laser-based tweezers also have been used to study the interactions of many-particle systems, e.g., colloids and quasi-crystals.

A full theory of optical tweezers, covering the full range of spatial scales and levels of sophistication, has evolved comparatively slowly over the years, and lags somewhat behind experimental work at the present. Variations in the size, shape, and composition of trapped objects, the nonuniformity of the trapping light distribution, the fact that dimensions of trapped objects are often comparable to the wavelength of light, combined with the large numerical apertures employed (which preclude scalar paraxial approximations, necessitating a full vector treatment), have all conspired to make general theories difficult to develop. However, there has been much current progress, and many papers combine limited aspects of trapping theory with experiment.

Our goal for this Resource Letter is to provide a guide to the literature. Our strategy has been to organize selected papers into a few main categories, rather than to provide a comprehensive review of all literature. Thus, numerous articles were omitted, some of which can be found among the citations papers in the papers we list. We apologize to colleagues whose work may thereby have been under-represented. Inevitably, some of the literature can be classified under multiple categories. Therefore, we strongly encourage reader to browse related titles and topics. For example, sections of research reports frequently include design details not necessarily covered in specific instrument papers.

We present a general section on optical tweezers first, including books and reviews on the subject. However, we caution readers that this is a fast-moving area, and much of the material found in books and early reviews is not particularly up-to-date. A focus on the earliest literature follows, including the seminal papers on optical tweezers. Papers relevant to optical instrument construction, calibration, and detection are listed next, followed by papers that deal mainly with optical trapping theory. The remaining sections are geared towards specific biological applications, including uses with cells, molecular motors, and additional applications of optical tweezers.

II. JOURNALS

The following are selected journals carrying articles on optical tweezers:

Applied Optics

Applied Physics Letters

Biophysical Journal

Cytometry

Experimental Cell Research

Fertility and Sterility

Human Reproduction

Journal of Applied Physics

Journal of Modern Optics

Methods in Cell Biology

Nature

Optics Letters

Physical Review Letters

Proceedings of the National Academy of Sciences Science

Acknowledgments

We sincerely thank Susan LaCoste and Jolande Murray for their invaluable help in compiling, listing, and formatting the many references assembled here.

III. BOOKS, REVIEWS, AND GENERAL PAPERS

  • 1.Sheetz MP. Laser Tweezers in Cell Biology. In: Wilson L, Matsudaira P, editors. Methods in Cell Biology. Vol. 55. San Diego: Academic; 1998. Includes a number of topics in laser tweezers and applications. (I,A,E) [PubMed] [Google Scholar]
  • 2.Block SM. Optical Tweezers: A New Tool for Biophysics. In: Satir BH, editor. Noninvasive Techniques in Cell Biology. New York: Wiley-Liss; 1990. pp. 375–402. pp. The working principle of optical tweezers is described, including details on instrument construction. Examples of trapped cells and inner structures are presented. A good all-around introduction. (E) [Google Scholar]
  • 3.Laser Manipulations of Atoms and Particles. Chu S. Science. 1991;253:861–866. doi: 10.1126/science.253.5022.861. Discussion of applications to atoms and particles. (E) [DOI] [PubMed] [Google Scholar]
  • 4.Making light work with optical tweezers. Block SM. Nature. 1992;360(6403):493–495. doi: 10.1038/360493a0. A short review with basic principles. (E) [DOI] [PubMed] [Google Scholar]
  • 5.Laser Trapping of Neutral Particles. Chu S. Sci Am. 1992;268(2):71–76. Good introduction to trapping capabilities. (E) [Google Scholar]
  • 6.Optical tweezers in cell biology. Kuo SC, Sheetz MP. Trends Cell Biol. 1992;2:116–118. doi: 10.1016/0962-8924(92)90016-g. A short review. (E) [DOI] [PubMed] [Google Scholar]
  • 7.Optical Tweezers: Glasperlenspiel—II. Simmons RM, Finer JT. Curr Biol. 1993;3(5):309–311. doi: 10.1016/0960-9822(93)90188-t. A general discussion of optical tweezers is provided. (E) [DOI] [PubMed] [Google Scholar]
  • 8.Biological applications of optical forces. Svoboda K, Block SM. Annu Rev Biophys Biomol Struct. 1994;23:247–285. doi: 10.1146/annurev.bb.23.060194.001335. This review provides a good foundation for general understanding of optical tweezers for the serious reader. Includes an introduction to instrument construction, trapping theory, calibration and detection methods, and a table of objective transmittances in the near infrared. (I) [DOI] [PubMed] [Google Scholar]
  • 9.Optical trapping and manipulation of microscopic particles and biological cells by laser beams. Sato S, Inaba H. Opt Quantum Electron. 1996;28:1–16. Review of basic principles and features of single beam optical trapping of cells, latex spheres, crystals, and metal particles. A review. (E) [Google Scholar]
  • 10.Optical trapping and manipulation of neutral particles using lasers. Ashkin A. Proc Natl Acad Sci USA. 1997;94(10):4853–4860. doi: 10.1073/pnas.94.10.4853. Outlines the history and recent developments of optical trapping. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Laser scissors and tweezers. Berns MW. Sci Am. 1998;278(4):62–67. doi: 10.1038/scientificamerican0498-62. (E) [DOI] [PubMed] [Google Scholar]
  • 12.Versatile optical traps with feedback control. Visscher K, Block SM. Methods Enzymol. 1998;298:460–489. doi: 10.1016/s0076-6879(98)98040-5. (I) [DOI] [PubMed] [Google Scholar]
  • 13.Single-molecule biomechanics with optical methods. Mehta AD, Rief M, Spudich JA, Smith DA, Simmons RM. Science. 1999;283(5408):1689–1695. doi: 10.1126/science.283.5408.1689. A review that describes a number of single molecule methods using optical tweezers. (E) [DOI] [PubMed] [Google Scholar]
  • 14.History of optical trapping and manipulation of small-neutral particle, atoms, and molecules. Ashkin A. IEEE J Sel Top Quantum Electron. 2000;6(6):841–856. A review. (I) [Google Scholar]
  • 15.Single molecule nanomanipulation of biomolecules. Ishii Y, Ishijima A, Yanagida T. Trends Biotechnol. 2001;19(6):211–216. doi: 10.1016/s0167-7799(01)01635-3. A good introduction to combined single molecule imaging and manipulation techniques for the study of molecular motors. (E) [DOI] [PubMed] [Google Scholar]
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  • 17.Using optics to measure biological forces and mechanics. Kuo SC. Traffic. 2001;2(11):757–763. doi: 10.1034/j.1600-0854.2001.21103.x. A review including optical stretching. (I) [DOI] [PubMed] [Google Scholar]

IV. OPTICAL TWEEZERS, CURRENT RESEARCH TOPICS

A. Earlier works on radiation pressure

  • 18.Optical levitation by radiation pressure. Ashkin A, Dziedzic JM. Appl Phys Lett. 1971;19:283–285. Glass spheres are levitated with radiation pressure in air and vacuum. (I) [Google Scholar]
  • 19.Acceleration and trapping of particles by radiation pressure. Ashkin A. Phys Rev Lett. 1970;24(4):156–159. The first observation of the acceleration of suspended particles using radiation pressure. (I) [Google Scholar]
  • 20.Optical Levitation of Liquid Drops by Radiation Pressure. Ashkin A, Dziedzic JM. Science. 1975;187(4181):1073–1075. doi: 10.1126/science.187.4181.1073. Drops in the size range of 1 to 40 micrometers are levitated and manipulated with the trap. (I) [DOI] [PubMed] [Google Scholar]
  • 21.Optical Levitation in High-Vacuum. Ashkin A, Dziedzic JM. Appl Phys Lett. 1976;28(6):333–335. Optical levitation down to a pressure of 10−6 Torr was observed under high-vacuum. (I) [Google Scholar]
  • 22.Feedback Stabilization of Optically Levitated Particles. Ashkin A, Dziedzic JM. Appl Phys Lett. 1977;30(4):202–204. (I) [Google Scholar]
  • 23.Trapping of atoms by resonance radiation pressure. Ashkin A. Phys Rev Lett. 1978;40(12):729–732. A method for trapping, cooling, and manipulating sodium atoms is described. (I) [Google Scholar]
  • 24.Applications of Laser Radiation Pressure. Ashkin A. Science. 1980;210(5):1081–1088. doi: 10.1126/science.210.4474.1081. Radiation pressure is discussed for neutral particles, including applications for microscopic particles and atoms. (I) [DOI] [PubMed] [Google Scholar]
  • 25.Observation of light scattering from nonspherical particles using optical levitation. Ashkin A, Dziedzic JM. Appl Opt. 1980;19(5):660–668. doi: 10.1364/AO.19.000660. Objects including spheroids, spherical doublets, triplets, etc. were studied. (I) [DOI] [PubMed] [Google Scholar]
  • 26.Continuous-wave self-focusing and self-trapping of light in artificial Kerr media. Ashkin A, Dziedzic JM, Smith PW. Opt Lett. 1982;7(6):276–278. doi: 10.1364/ol.7.000276. Beam trajectory and shapes arising from self-trapping are presented for laser modes exhibiting self-focusing in suspensions of submicroscopic particles. (I) [DOI] [PubMed] [Google Scholar]

B. Seminal studies on optical tweezers

  • 27.Observation of a Single-Beam Gradient Force Optical Trap for Dielectric Particles. Ashkin A, Dziedzic JM, Bjorkholm JE, Chu S. Opt Lett. 1986;11(5):288–290. doi: 10.1364/ol.11.000288. This is the original paper describing the invention of optical tweezers. Trapping of particles ranging from 10 μm to ~25 nm was observed in this single beam trap. (I) [DOI] [PubMed] [Google Scholar]
  • 28.Optical trapping and manipulation of viruses and bacteria. Ashkin A, Dziedzic JM. Science. 1987;235(4795):1517–1520. doi: 10.1126/science.3547653. Tobacco mosaic virus and single Escherichia coli bacteria. One of the first reports of biological applications of optical traps. (E) [DOI] [PubMed] [Google Scholar]
  • 29.Optical trapping and manipulation of single cells using infrared laser beams. Ashkin A, Dziedzic JM, Yamane T. Nature. 1987;330(6150):769–771. doi: 10.1038/330769a0. One of the first reports of biological applications of optical trapping including the manipulation of particles within the cytoplasm of cells. (E) [DOI] [PubMed] [Google Scholar]

C. Instrument design

The most common and straightforward method of building optical tweezers instrumentation is to custom-fit an optical microscope that already incorporates imaging capabilities and a good objective lens used for forming a trap. Attention to stable instrument construction and alignment details will improve the usability of the instrument. When deciding where to place an instrument, minimizing room temperature variations, acoustical noise, and mechanical vibrations should all be considered.

The references below describe a range of instruments from simple, single-beam traps to sophisticated multi-component systems. The incorporation of technologies in optical tweezers designs, frequently requiring ingenuity, has led to powerful new experimental methods. A broad range of components including trapping lasers, lenses, detection systems, calibration methods, and beam steering solutions has been incorporated into tweezers designs. Technologies for beam steering and multiple trap generation, including acoustooptic deflectors and galvanometer scanning mirrors, are outlined in some of the following papers. Computer control, automation, and data acquisition are critical components of optical tweezers experiments. The experimental requirements (speed of a motor, required position sensitivity, force regime desired) should provide a guide for optimizing the design of an instrument. Multiple feedback methods for force and position clamping have been implemented. Note that many research papers, found in other sections of this Resource Letter, contain instrument design details outlined in materials and methods sections.

  • 30.Block SM. Constructing optical tweezers. In: Spector D, Goldman R, Leinward L, editors. Cell Biology: A Laboratory Manual. NY: Cold Spring Harbor, Cold Spring Harbor; 1998. A good place to start. (E) [Google Scholar]
  • 31.Single beam optical trapping integrated in a confocal microscope for biological applications. Visscher K, Brakenhoff GJ. Cytometry. 1991;12(6):486–491. doi: 10.1002/cyto.990120604. Includes trapping theory, force calculation, and a description of the principle of trap manipulation by objective lens movement. (I) [DOI] [PubMed] [Google Scholar]
  • 32.Optical tweezers using a diode laser. Afzal RS, Treacy EB. Rev Sci Instrum. 1992;63(4):2157–2163. Straightforward demonstration of using a diode laser to form an optical trap. (E) [Google Scholar]
  • 33.Optical-Trapping Micromanipulation Using 780-Nm Diode-Lasers. Schut TCB, Schipper EF, de Grooth BG, Greve J. Opt Lett. 1993 E;18(6):447–449. doi: 10.1364/ol.18.000447. [DOI] [PubMed] [Google Scholar]
  • 34.Micromanipulation by ‘multiple’ optical traps created by a single fast scanning trap integrated with the bilateral confocal scanning laser microscope. Visscher K, Brakenhoff GJ, Krol JJ. Cytometry. 1993;14(2):105–114. doi: 10.1002/cyto.990140202. Includes a description of the instrument with fast scanning by acoustooptic modulation and galvanometric scan mirrors. (A) [DOI] [PubMed] [Google Scholar]
  • 35.Beam Magnification and the Efficiency of Optical Trapping with 790-nm AlGaAs Laser Diodes. Escandon GJ, Liu Y, Sonek GJ, Berns MW. IEEE Photonics Technol Lett. 1994;6(5):597–600. Discussion of trap efficiency with respect to input beam shape. Includes correction of diode output elipticity using anamorphic prisms. (E) [Google Scholar]
  • 36.Constructions and Applications of a Simple Optical Tweezers. Jong YC, Chen HM, Hsu JH, Fann WS. Zool Stu. 1995;34(S1):209–210. (E) [Google Scholar]
  • 37.Construction of multiple-beam optical traps with nanometer-resolution position sensing. Visscher K, Gross SP, Block SM. IEEE J Sel Top Quantum Electron. 1996;2(4):1066–1076. This paper discusses two types of optical tweezers instruments. Includes calibration methods, time-shared traps, instrument construction details, and a discussion of general desired features. (I) [Google Scholar]
  • 38.Quantitative measurements of force and displacement using an optical trap. Simmons RM, Finer JT, Chu S, Spudich JA. Biophys J. 1996;70(4):1813–1822. doi: 10.1016/S0006-3495(96)79746-1. Includes a schematic of the optical trap and detection system along with circuits with feedback arrangements. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.Interferometric optical tweezers. Chiou AE, Wang W, Sonek GJ, Hong J, Berns MW. Opt Commun. 1997;133(1–6):7–10. Two beams generate an interference fringe for trapping and micromanipulation. (I) [Google Scholar]
  • 40.Design for fully steerable dual-trap optical tweezers. Fallman E, Axner O. Appl Opt. 1997;36(10):2107–2113. doi: 10.1364/ao.36.002107. A detailed recipe for the construction is provided. (E) [DOI] [PubMed] [Google Scholar]
  • 41.Optical tweezers based on near infrared diode laser. Grego S, Arirnondo E, Frediani C. J Biomed Opt. 1997;2(3):332–339. doi: 10.1117/12.275449. A single-mode 100 mW diode operating at 840 nm was used. (E) [DOI] [PubMed] [Google Scholar]
  • 42.Self-aligned dual-beam optical laser trap using photorefractive phase conjugation. Wang W, Chiou AE, Sonek GJ, Berns MW. J Opt Soc Am B. 1997;14(4):697–704. Phase conjugation in a crystal is used to form a dual trap in a counterpropagating arrangement. Includes a description of the instrument, theoretical analysis, and a performance comparison against a single beam trap. (A) [Google Scholar]
  • 43.Optical tweezer arrays and optical substrates created with diffractive optics. Dufresne ER, Grier DG. Rev Sci Instrum. 1998;69(5):1974 –1977. A diffractive optical element is used to create multiple optical tweezers from a single laser beam. (I) [Google Scholar]
  • 44.Inexpensive optical tweezers for undergraduate laboratories. Smith SP, Bhalotra SR, Brody AL, Brown BL, Boyda EK, Prentiss M. Am J Phys. 1999;67(1):26–35. General introduction to setting up an instrument. (E) [Google Scholar]
  • 45.Optical tweezers for confocal microscopy. Hoffmann A, Meyerzu Horste G, Pilarczyk G, Monajembashi S, Uhl V, Greulich KO. Appl Phys B. 2000;71(5):747–753. doi: 10.1046/j.1365-2818.2000.00698.x. A method is presented to keep the trap fixed while doing 3D z-sectioning imaging. (I) [DOI] [PubMed] [Google Scholar]
  • 46.Multi-functional optical tweezers using computer-generated holograms. Liesener J, Reicherter M, Haist T, Tiziani HJ. Opt Commun. 2000;185(1–3):77–82. Seven spheres are trapped independently. (I) [Google Scholar]
  • 47.Design of a scanning laser optical trap for multiparticle manipulation. Mio C, Gong T, Terray A, Marr DWM. Rev Sci Instrum. 2000;71(5):2196–2200. Scanning is achieved using a piezo-actuated mirror. Details of the experimental arrangement and demonstration of trapping of multiple particles simultaneously is provided. (I) [Google Scholar]
  • 48.Construction of an optical tweezers: Calculation and experiments. Sun W, Wang YQ, Gao CM. Chin Phys. 2000;9(11):855–860. (I) [Google Scholar]
  • 49.An integrated laser trap/flow control video microscope for the study of single biomolecules. Wuite GJL, Davenport RJ, Rappaport A, Bustamante C. Biophys J. 2000;79(2):1155–1167. doi: 10.1016/S0006-3495(00)76369-7. Detailed description of an instrument that combines optical tweezers and micropipettes to perform experiments deep within a flow chamber. Video microscopy and deflection are used for detection. Forces are applied with optical tweezers and a computer-controlled flow system. Used to study the transcription of RNA polymerase. (A) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 50.Computer-generated holographic optical tweezer arrays. Dufresne ER, Spalding GC, Dearing MT, Sheets SA, Grier DG. Rev Sci Instrum. 2001;72(3):1810–1816. An adaptive-additive algorithm method is presented for creating planar arrays of holographic optical tweezers. (A) [Google Scholar]
  • 51.Design and construction of a space-borne optical tweezer apparatus. Resnick A. Rev Sci Instrum. 2001;72(11):4059–4065. Optical tweezers in space; a rugged design is detailed. (E) [Google Scholar]
  • 52.An Automated 2D Force Clamp for Single Molecule Studies. Lang MJ, Asbury CL, Shaevitz JW, Block SM. Biophys J. 2002;83:491–501. doi: 10.1016/S0006-3495(02)75185-0. This paper describes a fully-automated trapping instrument used as a two-dimensional force clamp for kinesin motility mesurements. The instrument is capable of simultaneous optical tweezers and single molecule fluorescence. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]

1. Detection method: video, quadrant photodiode, interferometry, and others

Position detection may be achieved in many ways including video, quadrant photodiode, and interferometric methods. Time response and position sensitivity should be considered when deciding on a detection method. Video microscopy is straightforward and can be used to track a particle with sub-pixel resolution. Video detection has limited time response and is not as convenient for systems requiring fast positional feedback. Quadrant photodiodes, placed in either an image or back focal plane, can be used for two- or three-dimensional position sensing. Quadrant-photodiode detection, which in some instances utilizes a separate detector beam for convenience, has both a faster time response and greater position sensitivity. Interferometry is another sensitive position-sensing method that is used to detect displacement along one axis.

  • 53.Direct Measurement of Nanometric Displacement under an Optical Microscope. Kamimura S. Appl Opt. 1987;26(16):3425–3427. doi: 10.1364/AO.26.003425. (I) [DOI] [PubMed] [Google Scholar]
  • 54.Optical measurement of picometer displacements of transparent microscopic objects. Denk W, Webb WW. Appl Opt. 1990;29(16):2382–2391. doi: 10.1364/AO.29.002382. Description of the instrument and interferometer including signal detection and amplification circuitry. (A) [DOI] [PubMed] [Google Scholar]
  • 55.High-resolution axial and lateral position sensing using two-photon excitation of fluorophores by a continuous-wave Nd:YAG laser. Florin EL, Horber JKH, Stelzer EHK. Appl Phys Lett. 1996;69(4):446–448. Changes in fluorescence due to displacement are used as a spatial sensor. Includes a fluorescence intensity versus z-position graph. (I) [Google Scholar]
  • 56.Determination of the force constant of a single-beam gradient trap by measurement of backscattered light. Friese MEJ, Rubinsztein-Dunlop H, Heckenberg NR, Dearden EW. Appl Opt. 1996;35(36):7112–7116. doi: 10.1364/AO.35.007112. Model of the trap as a harmonic oscillator with measurements. (I) [DOI] [PubMed] [Google Scholar]
  • 57.Improved nm displacement detector for microscopic beads at frequencies below 10 Hz. Li DQ, Schnapp BJ. Rev Sci Instrum. 1997;68(5):2195–2199. Laser interferometry detection is outlined in this paper. (E) [Google Scholar]
  • 58.Detection of single-molecule interactions using correlated thermal diffusion. Mehta AD, Finer JT, Spudich JA. Proc Natl Acad Sci USA. 1997;94(15):7927–7931. doi: 10.1073/pnas.94.15.7927. Methods are described to detect and correlate the motion of optically trapped beads attached to both ends of a single actin filament. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 59.Three-dimensional potential analysis of radiation pressure exerted on a single microparticle. Sasaki K, Tsukima M, Masuhara H. Appl Phys Lett. 1997;71(1):37–39. Total internal reflection microscopy is used in this three-dimensional position sensing method. (I) [Google Scholar]
  • 60.Interference model for back-focal-plane displacement detection in optical tweezers. Gittes F, Schmidt CF. Opt Lett. 1998;23(1):7–9. doi: 10.1364/ol.23.000007. Description including a model comparison with experiment for the signal of back-focal-plane imaging using a quadrant photodiode. (A) [DOI] [PubMed] [Google Scholar]
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  • 62.Three-dimensional imaging with optical tweezers. Friese MEJ, Truscott AG, Rubinsztein-Dunlop H, Heckenberg NR. Appl Opt. 1999;38(31):6597–6603. doi: 10.1364/ao.38.006597. This paper reports that features of approximately 200 nm can be resolved with a sensitivity of 5 nm. (I) [DOI] [PubMed] [Google Scholar]
  • 63.Nanometer-displacement detection of optically trapped metallic particles based on critical angle method for small force detection. Higurashi E, Sawada R, Ito T. Rev Sci Instrum. 1999;70(7):3068–3073. Detection is based on critical-angle prisms where angle changes originating from trapped particle motion provide a sensitive measure of position. (I) [Google Scholar]
  • 64.3D single-particle tracking and optical trap measurements on adhesion proteins. Peters IM, vanKooyk Y, van Vliet SJ, de Grooth BG, Figdor CG, Greve J. Cytometry. 1999;36(3):189–194. doi: 10.1002/(sici)1097-0320(19990701)36:3<189::aid-cyto7>3.3.co;2-v. Cell adhesion studies. (I) [DOI] [PubMed] [Google Scholar]
  • 65.Three-dimensional high-resolution particle tracking for optical tweezers by forward scattered light. Pralle A, Prummer M, Florin EL, Stelzer EHK, Horber JKH. Microsc Res Tech. 1999;44(5):378–386. doi: 10.1002/(SICI)1097-0029(19990301)44:5<378::AID-JEMT10>3.0.CO;2-Z. The ratio of the intensity of scattered light to the total amount of light is used for axial position determination. A model for the position signal is presented. (A) [DOI] [PubMed] [Google Scholar]

2. Calibration

The force exerted on an object by an optical trap depends both on the trap (shape and intensity) and the object (size and composition). Detailed knowledge of the force exerted on a particle is a critical quantity in biochemical, kinetic, and mechanical trapping experiments. Force calibration is achieved by a number of methods, each with different advantages. The drag or escape force method is performed by moving an object or stage while monitoring an “escape” velocity, and is particularly useful to check the linearity of trapping potential in regions far from the trap center. The equipartition method, which is straightforward and fast, measures thermal fluctuations in position of a trapped particle. The power spectral method provides stiffness information in addition to a diagnostic for noise sources at various frequencies. In addition to the methods having different advantages, multiple methods provide a good consistency check of the overall trap stiffness.

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  • 67.Measurement of small forces using an optical trap. Ghislain LP, Switz NA, Webb WW. Rev Sci Instrum. 1994;65:2762–2768. Includes calibration using drag force and signal source considerations. (A) [Google Scholar]
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  • 69.Optical Trapping and Fluorescence Detection in Laminar-Flow Streams. Wang W, Liu Y, Sonek GJ, Berns MW, Keller RA. Appl Phys Lett. 1995;67(8):1057–1059. Escape velocities are measured relative to the position within the flow stream. (A) [Google Scholar]
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3. Fiber-based traps

Light exiting from a fiber, because of its steep spatial gradient, can be used to trap objects, provided that the repulsive scattering force is more than balanced. The most common fiber-based trap involves two counter-propagating beams, to neutralize the scattering force in the central region. Because there are no local lenses, fiber-based traps have the advantage of being able to penetrate deep into solution. Fiber-based traps have also been used for cell stretching studies.

  • 73.Demonstration of a fiberoptic light-force trap. Constable A, Kim J, Mervis J, Zarinetchi F, Prentiss M. Opt Lett. 1993;18(21):1867–1869. doi: 10.1364/ol.18.001867. Single-mode fibers. Includes sample cell construction information. (I) [DOI] [PubMed] [Google Scholar]
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D. Theory of optical tweezers

A wide range of models and degrees of sophistication have been applied to the theory of optical tweezers. The size, shape, and composition of an object are important quantities when determining an appropriate theory. Laser focusing properties such as the mode, input beam diameter, and numerical aperture of the lens are also critical. Theories have been developed for describing the expected signal detection shapes. Many of the references below include both theory and experiments.

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E. Experiments using optical tweezers

1. Mechanical and single molecule measurements

Mechanical properties such as elasticity, stiffness, rigidity, and torque can be measured using optical tweezers. Light is easily manipulated and relatively noninvasive, making laser-based mechanical measurements straightforward for studying biological systems. Cells, intracellular structures, filaments, and single molecules have all been probed. Multiple traps can be used to construct additional geometries for mechanical measurements. Combinations of optical tweezers and other methods, such as micropipettes, fluorescence microscopy, and microsurgery, provide very powerful tools for studying biological systems.

Single molecule mechanical measurements using optical tweezers, including biological motor motility, protein-protein unbinding, and protein unfolding, have experienced a tremendous growth in recent years. Throughout these papers, assay development remains a critical component, including details of slide/flow cell construction, methods for attaching samples to microspheres, and general assay conditions.

  • 103.Buckling of a Single Microtubule by Optical Trapping Forces: Direct Measurement of Microtubule Rigidity. Kurachi M, Hoshi M, Tashiro H. Cell Motil Cytoskeleton. 1995;30(3):221–228. doi: 10.1002/cm.970300306. The microtubule rigidity was found to be dependent on length. (I) [DOI] [PubMed] [Google Scholar]
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  • 106.Strength and lifetime of the bond between actin and skeletal muscle alpha-actinin studied with an optical trapping technique. Miyata H, Yasuda R, Kinosita K., Jr Biochim Biophys Acta. 1996;1290(1):83–88. doi: 10.1016/0304-4165(96)00003-7. Suggestion of two classes of actin-actinin bonds, based on unbinding time measurements. (I) [DOI] [PubMed] [Google Scholar]
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  • 108.Torsional rigidity of single actin filaments and actin-actin bond breaking force under torsion measured directly by in vitro micromanipulation. Tsuda Y, Yasutake H, Ishijima A, Yanagida T. Proc Natl Acad Sci USA. 1996;93(23):12937–12942. doi: 10.1073/pnas.93.23.12937. This study includes the use of optical tweezers and fluorescent beads to measure rotational Brownian motion. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
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  • 113.A method for determination of stiffness of collagen molecules. Luo ZP, Bolander ME, An KN. Biochem Biophys Res Commun. 1997;232(1):251–254. doi: 10.1006/bbrc.1997.6268. (I) [DOI] [PubMed] [Google Scholar]
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  • 119.Short-term binding of fibroblasts to fibronectin: optical tweezers experiments and probabilistic analysis. Thoumine O, Kocian P, Kottelat A, Meister JJ. Eur Biophys J with Biophys Lett. 2000;29(6):398–408. doi: 10.1007/s002490000087. Adhesion tests of fibroblasts on fibronectin-coated glass. (I) [DOI] [PubMed] [Google Scholar]
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  • 123.Detection and characterization of individual intermolecular bonds using optical tweezers. Stout AL. Biophys J. 2001;80(6):2976–2986. doi: 10.1016/S0006-3495(01)76263-7. Details of the instrument, technique and geometry for rupture force measurements are shown. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
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2. Biological motors

Biological motors are excellent model systems for observing protein motions and conformational changes, and are a subject of intense research. Motor properties such as speed, force, processivity, working stroke distance, and substrate should be considered when designing an experiment. Many technological developments, including force clamping, the three-bead assay, and computer automation of trap and sample positioning have been used in biological motor research. We encourage the reader to explore experimental innovations implemented in multiple motor systems.

a. General motors
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b. Kinesin

Kinesin, which hydrolyzes ATP to move along microtubules, is a processive motor that takes about 100 steps before detaching. Kinesin’s processivity makes it ideal for optical tweezers studies. Optical tweezers measurements have identified that kinesin steps in discrete, 8 nm increments and hydrolyzes one ATP per step. Instrumental innovations specifically geared towards measuring kinesin motility have led to a number of advances in optical tweezers.

  • 139.Bead movement by single kinesin molecules studied with optical tweezers. Block SM, Goldstein LS, Schnapp BJ. Nature. 1990;348(6299):348–352. doi: 10.1038/348348a0. (E) [DOI] [PubMed] [Google Scholar]
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c. Myosin

Myosin, which moves on an actin substrate, is the subject of intense research. A three-bead assay has been developed to measure the properties of skeletal muscle myosin, a nonprocessive motor. In this geometry, two trapped beads suspend an actin filament above a third motor-coated bead. Motor interaction and power stroke movement of the filament can be detected by monitoring fluctuations and movement of the double bead system. Many innovations have been implemented to both simultaneously generate multiple traps and detect position in this geometry. More recently, processive myosins have been discovered (myosin V being an example) with properties somewhat similar to kinesin, and therefore amenable to many of the same techniques.

  • 157.Actin cores of hair-cell stereocilia support myosin motility. Shepherd GM, Corey DP, Block SM. Proc Natl Acad Sci USA. 1990;87(21):8627–8631. doi: 10.1073/pnas.87.21.8627. Optical tweezers were used to deposit myosin-coated beads on actin cores of hair-cell stereocilia in an in vitro assay. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
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d. Nucleic acid-based enzymes

RNA- and DNA-based enzymes with motor-like properties also have been studied with optical tweezers. Multiple geometries for motility assays have been implemented. The stretching properties of DNA have been used as a centering tool and as a ruler to monitor the progress of nucleotide motors. These motor studies have benefited enormously from powerful biochemical, as well as biophysical, methods available for manipulating nucleic acids.

  • 179.RNA Polymerase gets very pushy. O’Brien C. Science. 1995;70:1568. doi: 10.1126/science.270.5242.1568. An introduction to a polymerase, optical tweezers measurement. (E) [DOI] [PubMed] [Google Scholar]
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e. Flagellar motors
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3. Measurements involving DNA

DNA stretching studies have been the subject of much experimental and theoretical development. Measurements ranging from base pair interactions to chromosome mobility have been studied.

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  • 198.RecA polymerization on double-stranded DNA by using single-molecule manipulation: The role of ATP hydrolysis. Shivashankar GV, Feingold M, Krichevsky O, Libchaber A. Proc Natl Acad Sci USA. 1999;96(14):7916–7921. doi: 10.1073/pnas.96.14.7916. Force extension is used to study the polymerization of RecA on DNA. A model for nucleation and growth is presented. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
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  • 202.Direct integration of micromachined pipettes in a flow channel for single DNA molecule study by optical tweezers. Rusu C, van’t Oever R, de Boer MJ, Jansen HV, Berenschot JW, Bennink ML, Kanger JS, de Grooth BG, Elwenspoek M, Greve J, Brugger J, van den Berg A. J Micromech Sys. 2001;10(2):238–246. Various shaped micropipettes are presented. (I) [Google Scholar]
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  • 205.Effect of pH on the overstretching transition of double-stranded DNA: Evidence of force-induced DNA melting. Williams MC, Wenner JR, Rouzina L, Bloomfield VA. Biophys J. 2001;80(2):874 –881. doi: 10.1016/S0006-3495(01)76066-3. Solution pH from 6.0 to 10.6 was studied. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
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F. Cells and optical tweezers

Optical tweezers have numerous cell biology applications. Intracellular materials including organelles and chromosomes have been probed using optical tweezers. Cell function, in particular mitosis and motility, have been studied by methods such as laser inactivation and tweezers-assisted chromosome movement. Localized studies of membrane rigidity and fluidity have increased our understanding of cell morphology. Many cellular measurements involve combinations of optical tweezers with other methodologies, such as microsurgery and fluorescence characterization, to form powerful tools for cell research.

1. General cells

Cell types including mammalian cells, Escherichia coli, red blood cells, nerve cells and gametes have been studied.

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  • 227.Optically controlled collisions of biological objects to evaluate potent polyvalent inhibitors of virus-cell adhesion. Mammen M, Helmerson K, Kishore R, Choi SK, Phillips WD, Whitesides GM. Chem Biol. 1996;3(9):757–763. doi: 10.1016/s1074-5521(96)90252-5. Two particles are caused to collide using independently controlled optical tweezers. (I) [DOI] [PubMed] [Google Scholar]
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  • 229.Micromanipulation of retinal neurons by optical tweezers. Townes-Anderson E, St Jules RS, Sherry DM, Lichtenberger J, Hassanain M. Mol Vis. 1998;4:12. Optical tweezers are used to position and group neuron cells. The outgrowth of manipulated cells is compared to unmanipulated cells. (I) [PubMed] [Google Scholar]
  • 230.Keratocytes pull with similar forces on their dorsal and ventral surfaces. Galbraith CG, Sheetz MP. J Cell Biol. 1999;147(6):1313–1323. doi: 10.1083/jcb.147.6.1313. A laser trap was used to place and hold a fibronectin-coated bead on the lamella of a keratocyte to monitor cellular force and displacement. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 231.Elasticity of the red cell membrane and its relation to hemolytic disorders: an optical tweezers study. Sleep J, Wilson D, Simmons R, Gratzer W. Biophys J. 1999;77(6):3085–3095. doi: 10.1016/S0006-3495(99)77139-0. Two beads were used to measure the force-extension relation of red cell membranes. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 232.A diffusion barrier maintains distribution of membrane proteins in polarized neurons. Winckler B, Forscher P, Mellman I. Nature. 1999;397(6721):698–701. doi: 10.1038/17806. In this study, optical tweezers are used to measure the lateral mobility of membrane proteins. (I) [DOI] [PubMed] [Google Scholar]
  • 233.Changes in Hechtian strands in cold-hardened cells measured by optical microsurgery. Buer CS, Weathers PJ, Swartzlander GA. Plant Physiol. 2000;122(4):1365–1377. doi: 10.1104/pp.122.4.1365. In this study concanavalin-coated spheres were inserted through an ablated hole in the cell wall and attached to a hechtian strand. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 234.Measuring the forces involved in polyvalent adhesion of uropathogenic Escherichia coli to mannose-presenting surfaces. Liang MN, Smith SP, Metallo SJ, Choi IS, Prentiss M, Whitesides GM. Proc Natl Acad Sci USA. 2000;97(24):13092–13096. doi: 10.1073/pnas.230451697. Optical tweezers are used to orient the bacteria relative to a surface of functionalized self assembled monolayers. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 235.Optical deformability of soft biological dielectrics. Guck J, Ananthakrishnan R, Moon TJ, Cunningham CC, Kas J. Phys Rev Lett. 2000;84(23):5451–5454. doi: 10.1103/PhysRevLett.84.5451. Includes some information on damage. (I) [DOI] [PubMed] [Google Scholar]
  • 236.Cell spreading and lamellipodial extension rate is regulated by membrane tension. Raucher D, Sheetz MP. J Cell Biol. 2000;148(1):127–136. doi: 10.1083/jcb.148.1.127. Optical tweezers were used to determine membrane tension in a tether-force measurement. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 237.Chiral self-propulsion of growing bacterial macrofibers on a solid surface. Mendelson NH, Sarlls JE, Wolgemuth CW, Goldstein RE. Phys Rev Lett. 2000;84(7):1627–1630. doi: 10.1103/PhysRevLett.84.1627. Optical tweezers were used to measure the Young’s modulus of the bacterial cell wall. (I) [DOI] [PubMed] [Google Scholar]
  • 238.Micromanipulation of chloroplasts using optical tweezers. Bayoudh S, Mehta M, Rubinsztein-Dunlop H, Heckenberg NR, Critchley C. J Microsc. 2001;203(Pt 2):214 –222. doi: 10.1046/j.1365-2818.2001.00843.x. Dual optical tweezers were used to probe chloroplast arrangement. (I) [DOI] [PubMed] [Google Scholar]
  • 239.Direct measurement of the area expansion and shear moduli of the human red blood cell membrane skeleton. Lenormand G, Henon S, Richert A, Simeon J, Gallet F. Biophys J. 2001;81(1):43–56. doi: 10.1016/S0006-3495(01)75678-0. Galvanometric mirrors form the traps in this three-bead measurement. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 240.Cell traction forces on soft biomaterials. I. Microrheology of Type I collagen gels. Velegol D, Lanni F. Biophys J. 2001;81(3):1786–1792. doi: 10.1016/S0006-3495(01)75829-8. A refraction plate on a galvanometric scanner was used to translate the trapped particle. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 241.Stretching biological cells with light. Guck J, Ananthakrishnan R, Casey Cunningham C, Kas J. J Phys: Condens Matter. 2002 A description of the experimental setup is provided Cell viability is also discussed I;14:4843–4856. [Google Scholar]

2. Gamete cells

Optical tweezers can be used to manipulate and determine the force generation and swimming properties of sperm. Implantation and fertilization developments use combinations of zonal drilling with short-wavelength (blue-to-UV) lasers and manipulation with optical tweezers. Laser-assisted hatching has also been investigated to possibly improve implantation efficiency.

  • 242.Micromanipulation of sperm by a laser generated optical trap. Tadir Y, Wright WH, Vafa O, Ord T, Asch RH, Berns MW. Fertil Steril. 1989;52:870–873. (E) [PubMed] [Google Scholar]
  • 243.Force generated by human sperm correlated to velocity and determined using a laser generated optical trap. Tadir Y, Wright WH, Vafa O, Ord T, Asch RH, Berns MW. Fertil Steril. 1990;53(5):944 –947. doi: 10.1016/s0015-0282(16)53539-0. (I) [DOI] [PubMed] [Google Scholar]
  • 244.Micromanipulation of gametes using laser microbeams. Tadir Y, Wright WH, Vafa O, Liaw LH, Asch R, Berns MW. Hum Reprod. 1991;6(7):1011–1016. doi: 10.1093/oxfordjournals.humrep.a137451. A review. (E) [DOI] [PubMed] [Google Scholar]
  • 245.Controlled micromanipulation of human sperm in three dimensions with an infrared laser optical trap: effect on sperm velocity. Colon JM, Sarosi P, McGovern PG, Askin A, Dziedzic JM, Skurnick J, Weiss G, Bonder EM. Fertil Steril. 1992;57(3):695–698. doi: 10.1016/s0015-0282(16)54926-7. (I) [DOI] [PubMed] [Google Scholar]
  • 246.Lasers for gamete micromanipulation: basic concepts. Tadir Y, Neev J, Ho P, Berns MW. J Assist Reprod Genet. 1993;10(2):121–125. doi: 10.1007/BF01207733. A review. (E) [DOI] [PubMed] [Google Scholar]
  • 247.Exposure of human spermatozoa to the cumulus oophorus results in increased relative force as measured by a 760 nm laser optical trap. Westphal LN, el Dansasouri I, Shimizu S, Tadir Y, Berns MW. Hum Reprod. 1993;8(7):1083–1086. doi: 10.1093/oxfordjournals.humrep.a138197. (I) [DOI] [PubMed] [Google Scholar]
  • 248.Relative force of human epididymal sperm. Araujo E, Jr, Tadir Y, Patrizio P, Ord T, Silber S, Berns MW, Asch RH. Fertil Steril. 1994;62(3):585–590. (I) [PubMed] [Google Scholar]
  • 249.Optical manipulations of human gametes. Conia J, Voelkel S. Biotechniques. 1994;17(6):1162–1165. Male gamete selection and laser-assisted fertilization is described using a commercially available system. (E) [PubMed] [Google Scholar]
  • 250.Zona drilling and sperm insertion with combined laser microbeam and optical tweezers. Schutze K, Clement-Sengewald A, Ashkin A. Fertil Steril. 1994;61(4):783–786. Demonstration of combined micromachine optical tweezers used to transport a sperm through a UV laser-drilled hole. (I) [PubMed] [Google Scholar]
  • 251.Effect of freezing on the relative escape force of sperm as measured by a laser optical trap. Dantas ZN, Araujo E, Jr, Tadir Y, Berns MW, Schell MJ, Stone SC. Fertil Steril. 1995;63(1):185–188. Clinical trial. (I) [PubMed] [Google Scholar]
  • 252.Spatiotemporal relationships among early events of fertilization in sea urchin eggs revealed by multiview microscopy. Suzuki K, Tanaka Y, Nakajima Y, Hirano K, Itoh H, Miyata H, Hayakawa T, Kinosita K., Jr Biophys J. 1995;68(3):739–748. doi: 10.1016/S0006-3495(95)80289-4. A multiview microscopy system for both polarization and fluorescence wavelength imaging was implemented. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 253.Zona thinning with the use of laser: a new approach to assisted hatching in humans. Antinori S, Panci C, Selman HA, Caffa B, Dani G, Versaci C. Hum Reprod. 1996;11(3):590–594. doi: 10.1093/humrep/11.3.590. Clinical trial. (I) [DOI] [PubMed] [Google Scholar]
  • 254.Animal experimentation. Fertilization of bovine oocytes induced solely with combined laser microbeam and optical tweezers. Clement-Segenwald A, Schutze K. J Assist Reprod Gen. 1996;13:259–265. doi: 10.1007/BF02065947. (I) [DOI] [PubMed] [Google Scholar]
  • 255.Determination of motility forces of human spermatozoa using an 800 nm optical trap. Konig K, Svaasand L, Liu YG, Sonek G, Patrizio P, Tadir Y, Berns MW, Tromberg BJ. Cell Mol Biol. 1996;42(4):501–509. (I) [PubMed] [Google Scholar]
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  • 257.Effect of pentoxifylline on the intrinsic swimming forces of human sperm assessed by optical tweezers. Patrizio P, Liu Y, Sonek GJ, Berns MW, Tadir Y. J Androl. 2000;21(5):753–756. (I) [PubMed] [Google Scholar]

3. Cell damage

In general, optical tweezers are much more “cell friendly” than many alternative methods because of the noninvasive character of light. Cell photodamage remains an issue, however, one that has been investigated for various systems using a range of trapping wavelengths. The papers below discuss a number of relevant issues, and possible solutions to tweezers-induced cell damage.

  • 258.Evidence for localized cell heating induced by infrared optical tweezers. Liu Y, Cheng DK, Sonek GJ, Berns MW, Chapman CF, Tromberg BJ. Biophys J. 1995;68(5):2137–2144. doi: 10.1016/S0006-3495(95)80396-6. Environmental and temperature-sensitive dye was used with spatially-resolved fluorescence in this study. A heat conduction model is also presented. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 259.In-situ microparticle analysis of marine phytoplankton cells using infrared laser-based optical tweezers. Sonek GJ, Liu Y, Iturriga RH. Appl Opt. 1995;34:7731–7741. doi: 10.1364/AO.34.007731. Spectroscopic observation of cellular physiology related to chlorophyll in the presence of the optical trap. (A) [DOI] [PubMed] [Google Scholar]
  • 260.Cell damage in near-infrared multimode optical traps as a result of multiphoton absorption. Konig K, Liang H, Berns MW, Tromberg BJ. Opt Lett. 1996;21(14):1090–1092. doi: 10.1364/ol.21.001090. Cell damage is shown to be greater in lasers that have unstable temporal power outputs. (I) [DOI] [PubMed] [Google Scholar]
  • 261.Effects of ultraviolet exposure and near infrared laser tweezers on human spermatozoa. Konig K, Tadir Y, Patrizio P, Berns MW, Tromberg BJ. Hum Reprod. 1996;11(10):2162–2164. doi: 10.1093/oxfordjournals.humrep.a019069. (I) [DOI] [PubMed] [Google Scholar]
  • 262.Wavelength dependence of cell cloning efficiency after optical trapping. Liang H, Vu KT, Krishnan P, Trang TC, Shin D, Kimel S, Berns MW. Biophys J. 1996;70(3):1529–1533. doi: 10.1016/S0006-3495(96)79716-3. Wavelengths from 700 to 900 nm and 1064 nm were investigated. Includes growth by exposure time and wavelength for various durations. Lasers include a Nd:YAG and Ti:sapphire. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 263.Physiological monitoring of optically trapped cells: assessing the effects of confinement by 1064-nm laser tweezers using microfluorometry. Liu Y, Sonek GJ, Berns MW, Tromberg BJ. Biophys J. 1996;71(4):2158–2167. doi: 10.1016/S0006-3495(96)79417-1. Two-photon excited fluorescence is collected to monitor the physiology of optically trapped cells. (A) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 264.Characterization of photodamage to Escherichia coli in optical traps. Neuman KC, Chadd EH, Liou GF, Bergman K, Block SM. Biophys J. 1999;77(5):2856–2863. doi: 10.1016/S0006-3495(99)77117-1. A study of cell damage through the wavelength range of (790–1064 nm) using a tunable Ti:sapphire laser by measuring the rotation rates of Escherichia coli cells tethered to glass. Includes a table and curves for microscope objective transmission. (A) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 265.Cell viability and DNA denaturation measurements by two-photon fluorescence excitation in CWAl:GaAs diode laser optical traps. Zhang ZX, Sonek GJ, Wei XB, Sun C, Berns MW, Tromberg BJ. J Biomed Opt. 1999;4(2):256–259. doi: 10.1117/1.429948. (I) [DOI] [PubMed] [Google Scholar]
  • 266.Cell viability in optical tweezers: high power red laser diode versus Nd:YAG laser. Schneckenburger H, Hendinger A, Sailer R, Gschwend MH, Strauss WSL, Bauer M, Schutze K. J Biomed Opt. 2000;5(1):40–44. doi: 10.1117/1.429966. (I) [DOI] [PubMed] [Google Scholar]

4. Tools for cells

  • 267.Automated single-cell manipulation and sorting by light trapping. Buican TN, Smyth MJ, Crissman HA, Salzman GC, Stewart C, Martin JC. Appl Opt. 1987;26(24):5311–5316. doi: 10.1364/AO.26.005311. Optical tweezers are used to sort and transport cells automatically without mechanical contact or significant fluid flow. (I) [DOI] [PubMed] [Google Scholar]
  • 268.Optical Trapping, Cell Manipulation, and Robotics. Buican TN, Neagley DL, Morrison WC, Upham BD. New Technol Cytom. 1989;1063:190–197. A tool for cytometry; image analysis is used to locate particles inside an enclosed manipulation chamber. Automated positioning and biological microrobotic applications are presented. (I) [Google Scholar]
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  • 270.Laser microbeam as a tool in cell biology. Berns MW, Wright WH, Wiegand Steubing R. Int Rev Cytol. 1991;129:1–44. doi: 10.1016/s0074-7696(08)60507-0. Gives a general introduction to optical tweezers, construction tips, and applications to cell biology, including combinations with micro-beam methods. (E) [DOI] [PubMed] [Google Scholar]
  • 271.Application of laser optical tweezers in immunology and molecular genetics. Seeger S, Monajembashi S, Hutter KJ, Futterman G, Wolfrum J, Greulich KO. Cytometry. 1991;12(6):497–504. doi: 10.1002/cyto.990120606. Microsorting and trap-induced cell contact is presented. (I) [DOI] [PubMed] [Google Scholar]
  • 272.Laser induced cell fusion in combination with optical tweezers: the laser cell fusion trap. Wiegand-Steubing R, Cheng S, Wright WH, Numajiri Y, Berns MW. Cytometry. 1991;12(6):505–510. doi: 10.1002/cyto.990120607. The optical trap is used to bring the cells together while a UV beam initiates the cell fusion. (I) [DOI] [PubMed] [Google Scholar]
  • 273.The light microscope on its way from an analytical to a preparative tool. Greulich KO, Weber G. J Microsc. 1992;167(2):127–151. Description and applications of a combined microbeam and optical trap instrument. (I) [Google Scholar]
  • 274.Manipulation of cells, organelles, and genomes by laser microbeam and optical trap. Weber G, Greulich KO. Int Rev Cytol. 1992;133:1–41. doi: 10.1016/s0074-7696(08)61857-4. The working principle of the optical trap is presented along with biological applications including cell fusion and cell wall perforation. Microdissection of chromosomes is also presented as a tool. Organelle movement is also presented. Includes many references. (I) [DOI] [PubMed] [Google Scholar]
  • 275.Laser micromanipulators for biotechnology and genome research. Ponelies N, Scheef J, Harim A, Leitz G, Greulich KO. J Biotechnol. 1994;35(2–3):109–120. doi: 10.1016/0168-1656(94)90030-2. A review. (E) [DOI] [PubMed] [Google Scholar]
  • 276.Catch and move—cut or fuse. Schutze K, Clement-Sengewald A. Nature. 1994;368(6472):667–669. doi: 10.1038/368667a0. A review that provides a general introduction to microbeam, tweezers methods, and applications. (E) [DOI] [PubMed] [Google Scholar]
  • 277.Optical tweezers-based immunosensor detects femtomolar concentrations of antigens. Helmerson K, Kishore R, Phillips WD, Weetall HH. Clin Chem. 1997;43(2):379–383. Optical tweezers are used to measure antigen-antibody bonds forces. (I) [PubMed] [Google Scholar]
  • 278.Cut out or poke in—the key to the world of single genes: laser micromanipulation as a valuable tool on the look-out for the origin of disease. Schutze K, Becker I, Becker KF, Thalhammer S, Stark R, Heckl WM, Bohm M, Posl H. Genet Anal. 1997;14(1):1–8. doi: 10.1016/s1050-3862(96)00169-6. Review article discussing microbeam and optical tweezers applications. (E) [DOI] [PubMed] [Google Scholar]
  • 279.Laser tweezers and optical microsurgery in cellular and molecular biology. Working principles and selected applications. Greulich KO, Pilarczyk G. Cell Mol Biol (Noisy-le-grand) 1998;44(5):701–710. (E) [PubMed] [Google Scholar]
  • 280.Greulich KO. Basel: Birkhauser; 1999. Micromanipulation by Light in Biology and Medicine: The Laser Microbeam and Optical Tweezers. This book provides a broad introduction to optical tweezers topics and related methods. (E,I) [Google Scholar]
  • 281.Micromanipulation by laser microbeam and optical tweezers: from plant cells to single molecules. Greulich KO, Pilarczyk G, Hoffmann A, Meyer Zu Horste G, Schafer B, Uhl V, Monajembashi S. J Microsc. 2000;198(Pt 3):182–187. doi: 10.1046/j.1365-2818.2000.00698.x. A review. (E) [DOI] [PubMed] [Google Scholar]
  • 282.Laser-guided direct writing of living cells. Odde DJ, Renn MJ. Biotechnol Bioeng. 2000;67(3):312–318. doi: 10.1002/(sici)1097-0290(20000205)67:3<312::aid-bit7>3.0.co;2-f. (I) [DOI] [PubMed] [Google Scholar]
  • 283.A new microsystem for automated electrorotation measurements using laser tweezers. Reichle C, Schnelle T, Muller T, Leya T, Fuhr G. Biochim Biophys Acta. 2000;1459(1):218–229. doi: 10.1016/s0005-2728(00)00150-x. Optical tweezers are used as a bearing system for rotational studies for determining cytoplasmic properties. (I) [DOI] [PubMed] [Google Scholar]
  • 284.Greulich KO. Micromanipulation by laser microbeam and optical tweezers. In: Hawes C, Satiat-Jeunemaitre B, editors. Plant Cell Biology: A Practical Approach. Oxford: Oxford U. P.; 2001. pp. 159–169. pp. (E) [Google Scholar]
  • 285.Automated single-cell sorting system based on optical trapping. Grover SC, Skirtach AG, Gauthier RC, Grover CP. J Biomed Opt. 2001;6(1):14 –22. doi: 10.1117/1.1333676. (I) [DOI] [PubMed] [Google Scholar]

G. Trapping various objects

1. Particles, hard spheres, gels, and polymers

  • 286.Laser Manipulation and Ablation of a Single Microcapsule in Water. Misawa H, Kitamura N, Masuhara H. J Am Chem Soc. 1991;113:7859–7863. Deformation of a trapped particle with a pulse of light from a second laser. (A) [Google Scholar]
  • 287.Spatial Pattern-Formation, Size Selection, and Directional Flow of Polymer Latex-Particles by Laser Trapping Technique. Misawa H, Koshioka M, Sasaki K, Kitamura N, Masuhara H. Chem Lett. 1991;(3):469–472. Ring and line image patterns are shown. (I) [Google Scholar]
  • 288.Three-dimensional optical trapping and laser ablation of a single polymer latex particle in water. Misawa H, Koshioka M, Sasaki K, Kitamura N, Masuhara H. J Appl Phys. 1991;70(7):3829–3836. Includes microscope hole drilling in a PMMA latex particle. (I) [Google Scholar]
  • 289.Optical trapping of small particles using a 1.3-μm compact In-GaAsP diode laser. Sato S, Ohyumi M, Shibata H, Inaba H, Ogawa Y. Opt Lett. 1991;16(5):282–284. doi: 10.1364/ol.16.000282. Calibration of this diode laser trap using Stokes’ law is presented. (E) [DOI] [PubMed] [Google Scholar]
  • 290.Optical trapping of a metal particle and a water droplet by a scanning laser beam. Sasaki K, Koshioka M, Misawa H, Kitamura N, Masuhara H. Appl Phys Lett. 1992;60(7):807–809. A scanning laser trap is used to construct a potential well “cage” around the metal particle. (A) [Google Scholar]
  • 291.Poly(N-isopropylacrylamide) Microparticle Formation in Water by Infrared Laser-Induced Photo-Thermal Phase Transition. Ishikawa M, Misawa H, Kitamura N, Masuhara H. Chem Lett. 1993:481–484. Local heating promotes the phase transition and trap-induced formation of the microparticle. (I) [Google Scholar]
  • 292.Laser Manipulation and Assembling of Polymer Latex Particles in Solution. Misawa H, Sasaki K, Koshioka M, Kitamura N, Masuhara H. Macromolecules. 1993;26(2):282–286. Presentation of spatial alignment of particles in arbitrary shapes in addition to molecular structures for radical formation. (A) [Google Scholar]
  • 293.Optical trapping of microscopic metal particles. Sato S, Harada Y, Waseda Y. Opt Lett. 1994;19(22):1807–1809. doi: 10.1364/ol.19.001807. Trapping of bronze, silver, and gold. (I) [DOI] [PubMed] [Google Scholar]
  • 294.Optical trapping of metallic rayleigh particles. Svoboda K, Block SM. Opt Lett. 1994;19(13):930–932. doi: 10.1364/ol.19.000930. (I) [DOI] [PubMed] [Google Scholar]
  • 295.Optical trapping of metallic particles by a fixed Gaussian beam. Furukawa H, Yamaguchi I. Opt Lett. 1998;23(3):216–218. doi: 10.1364/ol.23.000216. Gold particles were used in this study. (I) [DOI] [PubMed] [Google Scholar]
  • 296.Rubinsztein-Dunlop H, Nieminen TA, Friese MEJ, Heckenberg NR. Optical trapping of absorbing particles. In: Löwdin PO, editor. Advances in Quantum Chemistry, 30, Modern Trends in Atomic Physics. San Diego: Academic; 1998. pp. 469–493. pp. Includes a comparison of trapping force and torque for Gaussian and doughnut beams. (I) [Google Scholar]
  • 297.Photophysics and photochemistry of a laser manipulated microparticle. Misawa H, Juodkazis S. Prog Polym Sci. 1999;24(5):665–697. Scanning laser micromanipulation is surveyed. Includes methods for caging particles. A review. (I) [Google Scholar]
  • 298.Effects associated with bubble formation in optical trapping. Berry DW, Heckenberg NR, Rubinsztein-Dunlop H. J Mod Opt. 2000;47(9):1575–1585. (I) [Google Scholar]
  • 299.Reversible phase transitions in polymer gels induced by radiation forces. Juodkazis S, Mukai N, Wakaki R, Yamaguchi A, Matsuo S, Misawa H. Nature. 2000;408(6809):178–181. doi: 10.1038/35041522. (I) [DOI] [PubMed] [Google Scholar]

2. Vesicles and membranes

  • 300.Lateral movements of membrane glycoproteins restricted by dynamic cytoplasmic barriers. Edidin M, Kuo SC, Sheetz MP. Science. 1991;254(5036):1379–1382. doi: 10.1126/science.1835798. Antibody-coated gold particles were moved across the cell surface with tweezers until a barrier was encountered. (I) [DOI] [PubMed] [Google Scholar]
  • 301.Instability and ‘pearling’ states produced in tubular membranes by competition of curvature and tension. Bar-Ziv R, Moses E. Phys Rev Lett. 1994;73(10):1392–1395. doi: 10.1103/PhysRevLett.73.1392. Tweezers initiate an instability in tubular membranes. A model is used to interpret the observations. “Pearls” are formed at high amplitudes. (I) [DOI] [PubMed] [Google Scholar]
  • 302.Entropic Expulsion in Vesicles. Bar-Ziv R, Frisch T, Moses E. Phys Rev Lett. 1995;75(19):3481–3484. doi: 10.1103/PhysRevLett.75.3481. After pressurization with optical tweezers, inner vesicles pierce through and exit larger encapsulating vesicles. (I) [DOI] [PubMed] [Google Scholar]
  • 303.Local Unbinding of Pinched Membranes. Bar-Ziv R, Menes R, Moses E, Safran SA. Phys Rev Lett. 1995;75(18):3356–3359. doi: 10.1103/PhysRevLett.75.3356. Tweezing produces local swelling of bound membranes. Theoretical explanations are presented. (I) [DOI] [PubMed] [Google Scholar]
  • 304.Critical dynamics in the pearling instability of membranes. Bar-Ziv R, Tlusty T, Moses E. Phys Rev Lett. 1997;79(6):1158–1161. (I) [Google Scholar]
  • 305.Spontaneous expulsion of giant lipid vesicles induced by laser tweezers. Moroz JD, Nelson P, Bar-Ziv R, Moses E. Phys Rev Lett. 1997;78(2):386–389. Includes quantative theoretical models. (I) [Google Scholar]
  • 306.Dynamic excitations in membranes induced by optical tweezers. Bar-Ziv R, Moses E, Nelson P. Biophys J. 1998;75(1):294 –320. doi: 10.1016/S0006-3495(98)77515-0. Includes the demonstration and a quantitative framework for pearling instability, expulsion of vesicles, and other shape transformations excited with optical tweezers. (A) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 307.Hard spheres in vesicles: curvature-induced forces and particle-induced curvature. Dinsmore AD, Wong DT, Nelson P, Yodh AG. Phys Rev Lett. 1998;80(2):409–412. Entropic forces due to the curvature of a vesicle wall are studied. (I) [Google Scholar]
  • 308.Giant vesicles: Micromanipulation of membrane bilayers. Menger FM, Keiper JS. Adv Mater. 1998;10(11):888–890. (E) [Google Scholar]
  • 309.A new determination of the shear modulus of the human erythrocyte membrane using optical tweezers. Henon S, Lenormand G, Richert A, Gallet F. Biophys J. 1999;76(2):1145–1151. doi: 10.1016/S0006-3495(99)77279-6. Includes a scheme of the optical tweezers experimental setup that uses galvanometric mirrors to position multiple beads. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 310.Characteristics of a membrane reservoir buffering membrane tension. Raucher D, Sheetz MP. Biophys J. 1999;77(4):1992–2002. doi: 10.1016/S0006-3495(99)77040-2. The elongation rate was studied for membrane-attached beads to identify different phases of formation. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]
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3. Colloids

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  • 313.Forces on a colloidal particle in a polymer solution: A study using optical tweezers. Valentine MT, Dewalt LE, OuYang HD. J Phys: Condens Matter. 1996;8(47):9477–9482. Sinusoidal motion of a particle with optical tweezers is employed in this study. (I) [Google Scholar]
  • 314.Entropic control of particle motion using passive surface microstructures. Dinsmore AD, Yodh AG, Pine DJ. Nature. 1996;383:239–242. Entropic forces at step edges are studied using tweezers and measurement of particle motions. (I) [Google Scholar]
  • 315.Localized dynamic light scattering: Probing single particle dynamics at the nanoscale. Bar-Ziv R, Meller A, Tlusty T, Moses E, Stavans J, Safran SA. Phys Rev Lett. 1997;78(1):154 –157. Dynamic light scattering is collected from a single particle held with optical tweezers. (A) [Google Scholar]
  • 316.Optical tweezers in colloid and interface science. Grier DG. Curr Opin Colloid Interface Sci. 1997;2(3):264 –270. A review. (E) [Google Scholar]
  • 317.Entropic colloidal interactions in concentrated DNA solutions. Verma R, Crocker JC, Lubensky TC, Yodh AG. Phys Rev Lett. 1998;81(18):4004 –4007. Interparticle potentials of colloidal particles with DNA were studied using line optical tweezers. (I) [Google Scholar]
  • 318.Entropic attraction and repulsion in binary colloids probed with a line optical tweezer. Crocker JC, Matteo JA, Dinsmore AD, Yodh AG. Phys Rev Lett. 1999;82(21):4352–4355. An introduction to line optical tweezers and “equilibrium” measurements. (I) [Google Scholar]
  • 319.Tailored surfaces using optically manipulated colloidal particles. Mio C, Marr DWM. Langmuir. 1999;15(25):8565–8568. (I) [Google Scholar]
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  • 321.Direct measurement of static and dynamic forces between a colloidal particle and a flat surface using a single-beam gradient optical trap and evanescent wave light scattering. Clapp AR, Dickinson RB. Langmuir. 2001;17(7):2182–2191. (I) [Google Scholar]
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  • 323.Colloidal interactions in suspensions of rods. Lin K, Crocker JC, Zeri AC, Yodh AG. Phys Rev Lett. 2001;87(8):088301. doi: 10.1103/PhysRevLett.87.088301. Rod flexibility, rod ahesion, and bridging are studied. (I) [DOI] [PubMed] [Google Scholar]
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H. Nonstandard traps and trapped objects

1. Alternate trap shapes

  • 325.Optical Matter: Crystallization and Binding in Intense Optical Fields. Burns MM, Fournier JM, Golovchenko JA. Science. 1990;249:749–754. doi: 10.1126/science.249.4970.749. Standing-wave optical fields create arrays of trapped structures. (I) [DOI] [PubMed] [Google Scholar]
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  • 328.Helical Beams Give Particles a Whirl. Bains S. Science. 1996;273:36. Discussion on making particles spin with light. (E) [Google Scholar]
  • 329.Optical angular-momentum transfer to trapped absorbing particles. Friese MEJ, Enger J, Rubinsztein-Dunlop H, Heckenberg NR. Phys Rev A. 1996;54(2):1593–1596. doi: 10.1103/physreva.54.1593. Rotation of particles in a doughnut beam via input polarization. (I) [DOI] [PubMed] [Google Scholar]
  • 330.Optical tweezers and optical spanners with Laguerre-Gaussian modes. Simpson NB, Allen JL, Padgett MJ. J Mod Opt. 1996;43(12):2485–2491. Models of trapping forces from these modes. (A) [Google Scholar]
  • 331.Mechanical equivalence of spin and orbital angular momentum of light: an optical spanner. Simpson NB, Dholakia K, Allen L, Padgett MJ. Opt Lett. 1997;22(1):52–54. doi: 10.1364/ol.22.000052. Demonstration of transfer of orbital angular momentum to a trapped particle. (A) [DOI] [PubMed] [Google Scholar]
  • 332.Optical alignment and spinning of laser-trapped microscopic particles. Friese MEJ, Nieminen TA, Heckenberg NR, Rubinsztein-Dunlop H. Nature. 1998;394(6691):348–350. Rotation of a trapped calcite crystal due to an elliptically polarized trapping beam is shown in successive frames. (I) [Google Scholar]
  • 333.Optical torque controlled by elliptical polarization. Friese MEJ, Nieminen TA, Heckenberg NR, Rubinsztein-Dunlop H. Opt Lett. 1998;23(1):1–3. doi: 10.1364/ol.23.000001. Rotation frequency is measured and calculated. (I) [DOI] [PubMed] [Google Scholar]
  • 334.Force measurements of optical tweezers in electro-optical cages. Fuhr G, Schnelle T, Muller T, Hitzler H, Monajembashi S, Greulich KO. Appl Phys A. 1998;67(4):385–390. (I) [Google Scholar]
  • 335.Optical trapping of Rayleigh particles using a Gaussian standing wave. Zemanek P, Jonas A, Sramek L, Liska M. Opt Commun. 1998;151(4 –6):273–285. (I) [Google Scholar]
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  • 337.Optical particle trapping with computer-generated holograms written on a liquid-crystal display. Reicherter M, Haist T, Wagemann EU, Tiziani HJ. Opt Lett. 1999;24(9):608–610. doi: 10.1364/ol.24.000608. Use of a liquid-crystal display as an optical element to generate arbitrary traps. (I) [DOI] [PubMed] [Google Scholar]
  • 338.Optical trapping of nanoparticles and microparticles by a Gaussian standing wave. Zemanek P, Jonas A, Sramek L, Liska M. Opt Lett. 1999;24(21):1448–1450. doi: 10.1364/ol.24.001448. (I) [DOI] [PubMed] [Google Scholar]
  • 339.Dynamic array generation and pattern formation for optical tweezers. Mogensen PC, Gluckstad J. Opt Commun. 2000;175(1–3):75–81. (I) [Google Scholar]
  • 340.Combined dielectrophoretic field cages and laser tweezers for electrorotation. Schnelle T, Muller T, Reichle C, Fuhr G. Appl Phys B. 2000;70(2):267–274. (A) [Google Scholar]
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2. Alternate trapped objects

  • 342.Optical trapping of low-refractive-index microfabricated objects using radiation pressure exerted on their inner walls. Higurashi E, Ohguchi O, Ukita H. Opt Lett. 1995;20(19):1931–1933. doi: 10.1364/ol.20.001931. Trapping of a ring-shaped object. (I) [DOI] [PubMed] [Google Scholar]
  • 343.Trapping model for the low-index ring-shaped micro-object in a focused, lowest-order Gaussian laser-beam profile. Gauthier RC. J Opt Soc Am B. 1997;14(4):782–789. (I) [Google Scholar]
  • 344.Beth’s experiment using optical tweezers. Moothoo DN, Arlt J, Conroy RS, Akerboom F, Voit A, Dholakia K. Am J Phys. 2001;69(3):271–276. Birefringent calcite particles are made to rotate with circularly polarized light. (E) [Google Scholar]
  • 345.Cell manipulation by use of diamond microparticles as handles of optical tweezers. Sun CK, Huang YC, Cheng PC, Liu HC, Lin BL. J Opt Soc Am B. 2001;18(10):1483–1489. Irregularly shaped diamond microparticles were used. (I) [Google Scholar]

I. Optical tweezers and other technologies

  • 346.Laser Trapping, Spectroscopy, and Ablation of a Single Latex Particle in Water. Misawa H, Koshioka M, Sasaki K, Kitamura N, Masuhara H. Chem Lett. 1990;(11):1479–1482. (I) [Google Scholar]
  • 347.Two-color trapped-particle optical microscopy. Malmqvist L, Hertz HM. Opt Lett. 1994;19(12):853–855. doi: 10.1364/ol.19.000853. A trapped lithium niobate particle is used to generate the second color. (I) [DOI] [PubMed] [Google Scholar]
  • 348.Second-harmonic and sum-frequency generation from optically trapped KTiOPO4 microscopic particles by use of Nd:YAG and Ti:Al2O3 lasers. Sato S. Opt Lett. 1994;19(13):927–929. doi: 10.1364/ol.19.000927. Particles of nonlinear, optically-active materials are trapped and shown to generate the second-harmonic and sum-frequency of trapping wavelengths. (A) [DOI] [PubMed] [Google Scholar]
  • 349.Autofluorescence spectroscopy of optically trapped cells. Konig K, Liu Y, Sonek GJ, Berns MW, Tromberg BJ. Photochem Photobiol. 1995;62(5):830–835. doi: 10.1111/j.1751-1097.1995.tb09143.x. Includes a description of the instrument where a CCD array is used to collect the fluorescence spectrum. (I) [DOI] [PubMed] [Google Scholar]
  • 350.Combined Near-infrared Raman Microprobe and Laser Trapping System: Application to the Analysis of a Single Organic Microdroplet in Water. Ajito K. Appl Spectrosc. 1998;52(3):339–342. Use of a Ti:sapphire laser for simultaneous trapping and Raman spectroscopy. (I) [Google Scholar]
  • 351.Transmission and confocal fluorescence microscopy and time-resolved fluorescence spectroscopy combined with a laser trap: Investigation of optically trapped block copolymer micelles. Gensch T, Hofkens J, vanStam J, Faes H, Creutz S, Tsuda K, Jerome R, Masuhara H, DeSchryver FC. J Phys Chem B. 1998;102(43):8440–8451. (I) [Google Scholar]
  • 352.Imaging and spectroscopic analysis of single microdroplets containing p-cresol using the near-infrared laser tweezers Raman microprobe system. Ajito K, Morita M. Surf Sci. 1999;428:141–146. (I) [Google Scholar]
  • 353.Investigation of the molecular extraction process in single subpicoliter droplets using a near-infrared laser Raman trapping system. Ajito K, Morita M, Torimitsu K. Anal Chem. 2000;72(19):4721–4725. doi: 10.1021/ac0002994. (I) [DOI] [PubMed] [Google Scholar]
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  • 356.Microelectrophoresis of a bilayer-coated silica bead in an optical trap: Application to enzymology. Galneder R, Kahl V, Arbuzova A, Rebecchi M, Radler JO, McLaughlin S. Biophys J. 2001;80(5):2298–2309. doi: 10.1016/S0006-3495(01)76201-7. A field/trap apparatus is described and discussed. (I) [DOI] [PMC free article] [PubMed] [Google Scholar]

1. Two-photon generation

  • 357.2-Photon Fluorescence Excitation in Continuous-Wave Infrared Optical Tweezers. Liu Y, Sonek GJ, Berns MW, Konig K, Tromberg BJ. Opt Lett. 1995;20(21):2246–2248. doi: 10.1364/ol.20.002246. A Nd:YAG laser (1064 nm) is used to excite Propidium Iodine and Snarf in human sperm and hamster ovary cells. (I) [DOI] [PubMed] [Google Scholar]
  • 358.Laser tweezers are sources of two-photon excitation. Konig K. Cell Mol Biol. 1998;44(5):721–733. (I) [PubMed] [Google Scholar]
  • 359.Multiphoton fluorescence excitation in continuous-wave infrared optical traps. Zhang ZX, Sonek GJ, Liang H, Berns MW, Tromberg BJ. Appl Opt. 1998;37(13):2766–2773. doi: 10.1364/ao.37.002766. The BO-DIPY dye is used. (I) [DOI] [PubMed] [Google Scholar]
  • 360.Laser tweezers and multiphoton microscopes in life sciences. Konig K. Histochem Cell Biol. 2000;114(2):79–92. doi: 10.1007/s004180000179. Focuses on optical tweezers and multiphoton, femtosecond microscopes. (I) [DOI] [PubMed] [Google Scholar]

2. Optical probe microscopy

  • 361.Scanning-force microscope based on an optical trap. Ghislain LP, Webb WW. Opt Lett. 1993;18(19):1678–1680. doi: 10.1364/ol.18.001678. Imaging with a glass stylus is described using optical tweezers including ~20 nm features. (I) [DOI] [PubMed] [Google Scholar]
  • 362.Photonic force microscope based on optical tweezers and two-photon excitation for biological applications. Florin EL, Pralle A, Horber JKH, Stelzer EHK. J Struct Biol. 1997;119(2):202–211. doi: 10.1006/jsbi.1997.3880. Includes two-photon excitation and images using this technique. (I) [DOI] [PubMed] [Google Scholar]

J. Additional applications of optical tweezers

  • 363.Pattern formation and flow control of fine particles by laser-scanning micromanipulation. Sasaki K, Koshioka M, Misawa H, Kitamura N, Masuhara H. Opt Lett. 1991;16(19):1463–1465. doi: 10.1364/ol.16.001463. Pattern formation of ~50 particles by scanning with galvanometer mirrors. (I) [DOI] [PubMed] [Google Scholar]
  • 364.Multibeam laser manipulation and fixation of microparticles. Misawa H, Sasaki K, Koshioka M, Kitamura N, Masuhara H. Appl Phys Lett. 1992;60(3):310–312. Demonstration of construction by ordering particles and linking them with photopolymerization fixation. (I) [Google Scholar]
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  • 366.Simultaneous Manipulation and Lasing of a Polymer Microparticle Using a CW 1064 nm Laser Beam. Misawa H, Fujisawa R, Sasaki K, Kitamura N, Masuhara H. Jpn J Appl Phys. 1993;32:L788–L790. Report of two-photon pumped lasing of a rhodamine-640 doped polystyrene particle in an optical trap. (A) [Google Scholar]
  • 367.Optical Thermal Ratchet. Faucheux LP, Bourdieu LS, Kaplan PD, Libchaber AJ. Phys Rev Lett. 1995;74(9):1504 –1507. doi: 10.1103/PhysRevLett.74.1504. The trap intensity is modulated to present an asymmetric potential that induces directed motion of a Brownian particle. (I) [DOI] [PubMed] [Google Scholar]
  • 368.Micro-objective manipulated with optical tweezers. Sasaki M, Kurosawa T, Hane K. Appl Phys Lett. 1997;70(6):785–787. A 25-μm diameter sphere is trapped and used as a lens in a micro-objective application. (I) [Google Scholar]
  • 369.Optical tweezers in pharmacology. Zahn M, Seeger S. Cell Mol Biol. 1998;44(5):747–761. (I) [PubMed] [Google Scholar]
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