Measuring the pressures across microfluidic droplets with an optical tweezer.

We introduce a novel technique that enables pressure measurements to be made in microfluidic chips using optical trapping. Pressure differentials across droplets in a microfluidic channel are determined by monitoring the displacements of a bead in an optical trap. We provide physical interpretation of the results. Our experiments reveal that our device has high sensitivity and can be operated over a wide range of pressures from several Pascals to several thousand Pascals.