Optical trapping of microspheres as a model for biological cells

Abstract
An analytical model has been developed to predict, in three dimensions, the forces exerted on dielectric microspheres in an optical trap. Results for a single-beam gradient force trap predict the existence of a stable trapping location and an effective trapping range. A minimum trapping power of approximately 5 mW, and an effective axial range of approximately 9 mu m, have been measured for polystyrene microspheres suspended in water and are in reasonable agreement with theoretical results. Applications of the model to the optical trapping of biological cells and chromosomes are described.