Figure 2. Clausius-Mossotti calculations and yeast-cell separation.

Calculated CM factors for (A) viable and (B) non-viable yeast cells as a function of SAW-DEP frequency and media conductivity. Red lines correspond to positive values of CM factor (pDEP) and blue to negative (nDEP). (C) Ratio of viable:non-viable CM factors, where a ratio of between −0.95 and −1.05 (green) corresponds to conditions under which the pDEP and nDEP forces are approximately equal and opposite. (D) Image of latex beads, which experience nDEP under all tested conditions, used to calibrate the location of nDEP alignment within the channel. (E) An optical micrograph of live and dead yeast cells separated using a SAW-DEP device, operating at 20 MHz in 0.15 S/m buffer conductivity. Dead cells, stained with Trypan blue, align at regions of low electric field gradient (nDEP) owing to their reduced polarizability with respect to the surrounding medium, and vice versa. Pearl chaining of the live cells along the electric field lines occurs owing to mutual DEP and dipole-dipole interactions.