The development of new techniques to separate and characterize cells with high throughput has been essential to many advances in biology and biotechnology.  We are developing a novel method for the simultaneous separation and characterization of cells based upon their electrical properties.  This method, iso-dielectric separation (IDS), uses dielectrophoresis (the force on a polarizable object ^[1] ) and a medium with spatially varying conductivity to sort electrically distinct cells while measuring their effective conductivity (Figure 1).  It is similar to iso-electric focusing except that it uses DEP instead of electrophoresis to concentrate cells and particles to the region in a conductivity gradient where their polarization charge vanishes ^{[2] [3] [4]} .

Sepsis is a clinical condition caused by infection; despite state-of-the-art facilities and treatments, sepsis has a mortality rate of ~30%. Sepsis induces inflammation and organ failure and a possible treatment would require removing inflammatory agents from whole blood such as activated neutrophils. Using an automated IDS system (see Figure 2a) we could see electrical differences between white and red blood cells (Figure 2b). Furthermore, we measured the electrical properties of activated vs. non-activated neutrophils (see Figure 2c). The populations show differences that indicate that the populations are amenable to efficient separation. Using the position as a classifier to determine if a neutrophil is activated or non-activated yields receiver operating characteristic (ROC) curves with high area-under-curve (AUC), which would result in good specificity (see Figure 2d).

1. H. A. Pohl and J. S. Crane, “Dielectrophoresis of cells,” Biophysical Journal, vol. 11, pp. 711-727, 1971.
2. M. D. Vahey and J. Voldman, “An equilibrium method for continuous-flow cell sorting using cielectrophoresis,” Analytical Chemistry, vol. 80, no. 9, pp. 3135-3143, 2008.
3. M. D. Vahey and J. Voldman,  “Iso-dielectric separation: A new method for the continuous-flow screening of cells,” Micro Total Analysis Systems ’06, vol. 2, pp. 1058-1060, 2006.
4. M. D. Vahey and J. Voldman, “High-throughput cell and particle characterization using isodielectric separation,” Analytical Chemistry, vol. 81, no. 7, pp. 2446-2455, 2009.