Simultaneous measurements of electrophoretic and dielectrophoretic forces using optical tweezers

TL;DR

This study uses optical tweezers to measure electrophoretic and dielectrophoretic forces on charged microbeads simultaneously, providing a detailed analysis of force distributions near electrodes with potential applications in high-curvature electrode systems.

Contribution

It introduces a method for concurrent measurement of electrophoretic and dielectrophoretic forces on microbeads using optical tweezers, with analysis of stochastic and deterministic motions.

Findings

Successfully measured force components around a tip electrode.

Demonstrated the ability to distinguish electrophoretic and dielectrophoretic forces.

Provided a framework for analyzing forces near high-curvature electrodes.

Abstract

Herein, charged microbeads handled with optical tweezers are used as a sensitive probe for simultaneous measurements of electrophoretic and dielectrophoretic forces. We first determine the electric charge carried by a single bead by keeping it in a predictable uniform electric field produced by two parallel planar electrodes, then, we examine same bead's response in proximity to a tip electrode. In this case, besides electric forces, the bead simultaneously experiences non-negligible dielectrophoretic forces produced by the strong electric field gradient. The stochastic and deterministic motions of the trapped bead are theoretically and experimentally analysed in terms of the autocorrelation function. By fitting the experimental data, we are able to extract simultaneously the spatial distribution of electrophoretic and dielectrophoretic forces around the tip. Our approach can be used for determining actual, total force components in the presence of high-curvature electrodes or metal scanning probe tips.