Local electric field measurements by optical tweezers

Abstract

We report a new technique to measure direction and amplitude of  electric fields generated by microelectrodes embedded  in polar liquid environment, as often used in microfluidic devices. The method is based on optical tweezers which act as sensitive  force transducer while a trapped charged microsphere behaves as a probe. When an electric field is applied the particles moves from its equilibrium position and finishes in a new equilibrium position where electric and optical forces are balanced. A trapped bead is moved  to explore the electric field in a wide region around the microelectrodes. In such way maps of electric fields with high spatial resolution can be reconstructed even for complex electrode geometries where numerical simulation approaches can fail. Experimental results are compared with calculations based on finite element analysis simulation.