Self-induced rotation of pigmented cells by dielectrophoretic force field

We discuss in this paper a novel observation of self-induced rotational motion of pigmented biological cells in a dielectrophoretic force field. The experimental platform for our work is basically a microfluidic system fabricated with Au microelectrode on the glass substrate with PDMS microchannel irreversibly bonded on top of it. To investigate the cell movement in this microfluidic system due to electric field gradient, dielectrophoresis (DEP) force field was generated by applying an AC electrical field on between the electrodes in the microfluidic system. During our cell manipulation experiments of three types of pigment and two types of non-pigment cells respectively, the self-rotation of certain cells while under positive DEP force have been observed. Noticeably, only pigment cells exhibited self-rotation that was not only stable, repeatable, but also controllable in terms of the rotation speed. We found that the variation of DEP parameters, such as frequency, voltage and waveforms, would change the rotation speed accordingly. We suspected that the unbalance distribution of melanin inside the pigment cells is mainly responsible for this self-rotation phenomenon. Therefore, experiments have also been conducted to compare the cell rotation behavior of different passages (i.e., different melanin content in the cell) of the same type of pigment cells (e.g., Melan-a cells). A potential application for this novel observation is to use the self-induced rotation phenomenon as a bio-marker to separate pigment and non-pigment cells.