Iso-dielectric Separation of Cells and Particles
- Category: MEMS & BioMEMS
- Tags: javier prieto, joel voldman
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Download as PDFThe development of new techniques to separate and characterize cells with high throughput has been essential to many of the advances in biology and biotechnology over the past few decades. 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 and, despite state-of-the-art facilities and treatments, it has a mortality rate of ~30%. Sepsis induces inflammation and organ failure; a possible treatment would require removing inflammatory agents, such as activated neutrophils, from whole blood. We used a CLP mouse model of sepsis (Figure 2a) and PMA-activated human granulocytes (Figure 2b) to monitor electrical differences between septic blood and leukocytes. With human granulocytes we saw a shift in their average isodielectric position (IDP) at high frequencies. Based on these results we did an IDP profile of leukocytes in healthy mouse blood and established a gate for the activated leukocytes. Applying the same gate under the same conditions with blood from CLP mice (n=4), we saw an increase in the number of activated leukocytes (Figure 2c). Finally we took aliquots of the same samples from healthy and CLP mice and measured common activation biomarkers with flow cytometry. Comparing both results, we see good correlation between our estimation of activated cells and the number of activated granulocytes measured in flow cytometry.
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- Figure 1: Iso-dielectric separation (IDS) microfluidic device used to measure electrical properties of the cells. The spatial conductivity gradient makes cells with different electrical properties pass through the electrodes at different positions (isodielectric point – IDP).
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- Figure 2: a) CLP intervention was used as a septic model in mice. b) At high frequencies, activated and non-activated human granulocytes show different IDP. c) A gate was defined in the IDP profile of healthy mouse blood and used to quantify the number of activated leukocytes in CLP mice. d) A good correlation of IDP results exists when compared to flow cytometry results.
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- M. D. Vahey and J. Voldman, “An Equilibrium Method for Continuous-Flow Cell Sorting Using Dielectrophoresis,” Analytical Chemistry, vol. 80, no. 9, pp. 3135-3143, 2008. [↩]
- 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. [↩]
- 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. [↩]