Optical Tweezers

AbstractInfrared lasers focused with high numerical aperture into a microscope are used to exert and measure forces in the piconewton range. Simple light pressure and the more complex ‘gradient forces’ are exploited. Unlike any other micromanipulation tool, optical tweezers can, for example, be used to work in the interior of unopened living cells to support cell fusion, to stimulate specificity in the interaction of immune cells and to simulate heart infarction. Here, a variant of optical tweezers, erythrocyte‐mediated force application is particularly helpful. Other applications are in humanin vitrofertilisation, where hundreds of children owe their existence to optical tweezers, and blood pressure studies. Studies on infection of a single cell by a virus or bacterium and on the organisation, of one of the fundamental processes of life – the generation of motion (by the centrosome) – complement the wide field of applications of optical tweezers in the life sciences.Key Concepts:Light is focused with very high aperture into a microscope so that light pressure and gradient forces can be used to hold, manipulate and measure forces of microscopic objects.Optical tweezers can be added to most standard microscopes with only little effort.Infrared light is used, which has a large penetration depth in biological tissue. Thus, one can work in the interior of unopened objects.With red blood cells as handle, forces of optical tweezers can be fully exploited (erythrocyte‐mediated force application, EMFA).Optical tweezers can be used to establish contact between microsopic objects as well as to move particles and organelles in the interior of closed objects.The force transduction is gentle and thus also suitable for fragile targets.