The μPIVOT:: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (mu PIV) and optical tweezers (OT). This instrument, the mu PIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (similar to 70 pN mu m(-1) for a 20 mu m polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R-2 = 0.988, RMS error = 13.04 mu m s(-1)). Interaction between both techniques is shown to be negligible for 15 mu m to 35 mu m diameter trapped particles subjected to fluid velocities from 50 mu m s(-1) to 500 mu m s(-1) even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle-particle hydrodynamics.