Optical tweezers single-molecule studies

Experimental techniques based on the application of mechanical forces to single molecules in small assemblies have been applied to study the binding properties of biomolecules and their response to external mechanical manipulations. Among such techniques are atomic force microscopy (AFM), optical tweezers, biomembrane force probe, and surface force apparatus experiments (Binning et al., 1986 Block and Svoboda, 1994 Evans et ah, 1995 Israelachvili, 1992). These techniques have inspired us and others (see also the chapters by Eichinger et al. and by Hermans et al. in this volume) to adopt a similar approach for the study of biomolecules by means of computer simulations. 

Observing single molecules. A major advance in the study of molecular motors has been the development of ways to observe and study single macromolecules. The methods make use of optical traps (optical "tweezers") that can hold a very small ( 1 pm diameter) polystyrene or silica bead near the waist of a laser beam focused through a microscope objective. ° ... 

Block SM, Goldstein LSB, Schnapp BJ. 1990. Bead movement by single kinesin molecules studied with optical tweezers. Nature 348 348. 

Optical tweezers have proved useful for the study of lateral heterogeneity and order in cell structure and protein motion. For example, Bustamante, et al. (88) studied the single molecule mechanics of DNA uncoiling. The use of optical tweezers has proved especially useful for the study of lateral heterogeneity and order of lipid layers (89), and a host of problems relating to protein motions see Section 14.11.4. 

Since their invention, optical tweezers have proved themselves to be very powerful interdisciplinary tools. Today they are used extensively in biophysics, as they serve as delicate tools to manipulate and study single molecules of DNA [8, 9]. Optically trapped beads have been successfully used to measure local elasticities and viscosities, for example inside cells. Ashkin [5] provides an overview of the diverse uses of optical traps as an important tool in the important areas of research. Isolation and detection of sparse cells concentration of cells from dilute suspensions separation of cells according to specific properties and trapping and positioning of individual cells for characterization are the key areas of research due to their possible impact. The non-invasive nature of particle manipulation being a key requirement, forces like hydrodynamic, optical, ultrasonic and electromagnetic have been employed for such purposes. Successful examples of the use of these optical forces for biological applications are determination... 

Manipulation of these biomoleeules ean be eonducted by using a glass-microneedle (Ishijima e/a/, 1996). Many studies, however, have used laser trapping of microbeads by optical tweezers, where a single molecule is attached to a microbead (Prasad, 2003). 

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