Direct dielectrophoretic characterization of particles in the high-density microwell array using optical tweezers

In this work, a quantitative and intuitive measurement of dielectrophoresis (DEP) behavior in a high-density dielectrophoretic microwell array chip was accomplished in assistance with the holographic optical tweezers. A one-dimensional force balance system with high reliability was achieved between the transverse optical trapping (TOT) force and the DEP force. The value of the DEP force was inferred by accurately calculating the TOT force, and the direction of the DEP force was observed with high-magnification microscopy. In order to estimate the availability and operability of the DEP force measurement system, we systematically investigated the influences of various external factors on the DEP behaviors of microspheres and live cells. All the quantitative measurement results, which agree well with the theory, showed that this system could serve as an accurate research tool for DEP behavior characterizations to optimize and improve the DEP-based manipulations of microparticles and live cells for a broad range of applications. The system also provides an approach to quantitatively obtain important parameters such as Clausius-Mossotti factors for cells in mediums, which could potentially be used to understand the dielectric properties of different types of cells for cell differentiation and diagnosis at the single-cell level.