The optical stretcher: A novel laser tool to micromanipulate cells

When a dielectric object is placed between two opposed, nonfocused laser be ams, the total force acting on the object is zero but the surface forces ar e additive, thus leading to a stretching of the object along the axis of th e beams. Using this principle, we have constructed a device, called an opti cal stretcher, that can be used to measure the viscoelastic properties of d ielectric materials, including biologic materials such as cells, with the s ensitivity necessary to distinguish even between different individual cytos keletal phenotypes. We have successfully used the optical stretcher to defo rm human erythrocytes and mouse fibroblasts. In the optical stretcher, no f ocusing is required, thus radiation damage is minimized and the surface for ces are not limited by the light power. The magnitude of the deforming forc es in the optical stretcher thus bridges the gap between optical tweezers a nd atomic force microscopy for the study of biologic materials.