In-depth imaging of dielectrophoresis by digital in-line holographic microscopy

Abstract

Dielectrophoresis is usually viewed using traditional microscopy, basically in plane since the depth of focus is short. However, a basic dielectrophoretic platform induces particle mobility not only in electrode plane but also in the depth dimension as well. The electric field gradient also has depth dimension. Therefore it is essential to measure dielectrophoresis in that depth dimension as well. In this study we demonstrate negative dielectrophoresis; the phenomenon is imaged with digital in-line holographic microscopy. The imaging method requires a full platform transparency, which is realized with transparent indium-tin-oxide electrodes. The negative dielectrophoresis demonstrations utilized polystyrene carboxylate particles 4.08 μm in diameter in a potassium chloride dilution 5 mM in concentration. The size of the active region of the platform was 65 μm in diameter. By negative dielectrophoresis, particles approach the trap at the center of the electrode tips. Intense particle movement was also observed outside of the platform’s active region. This was a result of AC electro-osmosis or electro thermal flow.