Designing Optical Traps from the Bottom Up

Optical trapping is a highly dexterous method of manipulating and interrogating nano- and micro-components. It has wide range of application, from fundamental biology and biomedical studies at the cellular and subcellular levels, to studies of colloid and surface chemistry as well as controlled studies of aerosol chemistry relevant to climate change models, to fundamental physics connected to our understanding of the statistical mechanics of small systems, with opportunities of working towards the macroscopic quantum limit. To allow greater flexibility of design we have supplemented our lab’s use of a commercial fluorescence microscope with a new, open-source hardware microscope, of our own design, incorporating x-, y-, and z-motion of the sample stage, piezoelectric fine-scale control of microfluidic chambers within the workstation, Köhler illumination, a CMOS camera, automated tracking of microparticles, and provisions for alignment and calibration (in three dimensions) of optical traps. Here we describe our analysis of the two-dimensional potential well created by a single-beam laser gradient trap, and discuss algorithms for compensating for any factors that might otherwise limit the quality of the optical trap