Publications Cell Physics Division

The radiation pressure of two counter-propagating laser beams traps and stretches individual biological cells. Using non-focused laser beams, cells stay viable when irradiated with up to 1.4 W of 780 nm Ti-sapphire laser light for several minutes. Fluorescence microscopy has demonstrated that the essential features of the cytoskeleton, excluding stress fibres, are maintained for stretched cells in suspension. The optical stretcher provides accurate measurements of whole cell elasticity and thus can distinguish between different cells by their cytoskeletal characteristics. A model has been derived for the forces on the surface of a spherical cell that explains the observed deformations. The peak stresses on the surface of cells are 1-150 Pa for light powers of 0.2-1.4 W and depending on the refractive index of the cell trapped. Precursors of rat nerve cells exhibit a homogeneous Young's modulus E of 500 25 Pa, whereas for osmotically inflated, spherical red blood cells (RBCs) the homogeneous Young's modulus is E = 11.0 +/- 0.5 Pa. Thus, PC12 cells are about 40-50 times more elastic than RBCs.