Quantification of pH gradients and implications in insulator-based dielectrophoresis of biomolecules

Aytug Gencoglu, Fernanda Camacho-Alanis, Vi Thanh Nguyen, Asuka Nakano, Alexandra Ros, Adrienne R. Minerick

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Direct current (DC) insulator-based dielectrophoretic (iDEP) microdevices have the potential to replace traditional alternating current dielectrophoretic devices for many cellular and biomolecular separation applications. The use of large DC fields suggest that electrode reactions and ion transport mechanisms can become important and impact ion distributions in the nanoliters of fluid in iDEP microchannels. This work tracked natural pH gradient formation in a 100μm wide, 1cm-long microchannel under applicable iDEP protein manipulation conditions. Using fluorescence microscopy with the pH-sensitive dye FITC Isomer I and the pH-insensitive dye TRITC as a reference, pH was observed to drop drastically in the microchannels within 1min in a 3000V/cm electric field; pH drops were observed in the range of 6-10min within a 100V/cm electric field and varied based on the buffer conductivity. To address concerns of dye transport impacting intensity data, electrokinetic mobilities of FITC were carefully examined and found to be (i) toward the anode and (ii) 1 to 2 orders of magnitude smaller than H+ transport which is responsible for pH drops from the anode toward the cathode. COMSOL simulations of ion transport showed qualitative agreement with experimental results. The results indicate that pH changes are severe enough and rapid enough to influence the net charge of a protein or cause aggregation during iDEP experiments. The results also elucidate reasonable time periods over which the phosphate buffering capacity can counter increases in H+ and OH- for unperturbed iDEP manipulations.

Original languageEnglish (US)
Pages (from-to)2436-2447
Number of pages12
Issue number18
StatePublished - Sep 2011


  • Electroosmotic flow
  • FITC fluorescence
  • Insulator-based dielectrophoresis
  • Natural pH gradients

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry


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