Optical tweezer for micro and nano scale rheology of biomaterials

Abstract

Since the first proposal and demonstration of an optical trap to hold micron sized particles by Ashkin in 1986, optical tweezer-based techniques for control and manipulation of particles has seen tremendous progress and enabled the exploration of the structure and dynamics of materials at the nano length scale. In biophysical applications, these techniques have enabled a range of activities from measurements of very small forces (at sub-pN levels) at operation within cells thus assisting in the elucidation of intracellular transport mechanisms, to obtaining elastic parameters of biomolecules. The techniques have helped in gaining insights on the viscoelastic properties at micro and nano length scales of a range of soft materials such as colloids, polymer melts, bio membranes etc. The paper describes some of the studies carried out by us to understand polymer structure and elasticity of these materials in solution. The domains of "passive" and "active" rheology are explained with examples of studies undertaken to address these domains. The work using video microscopy to study silk fibroin solutions is used to exemplify the domain of passive rheology. We present recent work on bacterial solutions wherein live bacteria influence the optical trap region and thereby help us study the local viscoelasticity of such a medium. © 2010 IACS.