The Dielectrophoresis Network
at the University of Surrey
Dielectrophoresis primarily offers the opportunity to discover and exploit the electrical properties- - or electrophysiology - of cells. Unlike other methods of electrophysiological analysis (see the electrophysiology primer in Resources for more) we look at static electrophysiology (invariant over scales of seconds or longer) rather than the transients caused by action potentials; however, its simplicity and ease of use allows it to be applied to many more scenarios than conventional methods allow.
We have benchmarked the system against other methods used in electrophysiology - our work with Chris Fry and Rita Jabr - both electrophysiologists at Surrey - showed that the system produces the same values for the cytoplasmic resistance of cardiac cells as gold standard techniques using tissue preparations. That work also developed a new medium composition best suited for stabilising cells in low conductivity (a medium that is now available from Labtech - se the Resources page). We have also developed a system for using dielectrophoresis to place single neurons into an electrode grid, in order to take conventional electrode recordings from neurons when interacting in a defined manner.
We have performed studies on drug resistance in both cancer cells and bacteria. In the former case, the key advantage of DEP is speed - we were able to show that antibiotic action could be detected in 4 hours, reducing the time required to select an appropriate treatment. In cancer cells, we have shown that DEP can elucidate an entire mechanism of drug action by studying the effects of P-gp blocker agents on K562 cells using a combination of DEP and flow cytometry. The work also examined the differences between drug sensitive and drug resistant cancer strains, and found a direct correlation between the degree of resistance, the cytoplasm conductivity, and the membrane potential. Building on this work, and using DEP spectra of cells treated with ion channel blockers, we were able to go further and isolate the quantities of free ions in the cytoplasms of drug-sensitive and drug-resistant cells and identifying P-gp's secondary function as a chloride channel.
We have also used DEP to examine apoptosis in cells, particularly in cancer cells. Using a new analytical technique to extract multiple population data from a single DEP spectrum - allowing the identification of cells in a healthy, apoptotic and necrotic states, as well as apoptotic body debris - we have shown that dielectrophoresis can track the progress of apopotosis more rapidly than flow cytometry, and more accurately (since cells are handled in a much less aggressive manner in DEP). This was later developed in successive systems using the DEP-Wells and finally a multi-channel DEP-dot that could track the progress of apoptosis on a minute-by-minute basis, identifying the first changes in the cell population 23 minutes after exposure.
More recently, we have extended this work to look at IC50 - the measure of the toxic threshold of a drug (or efficacy, in the case of those cells intended to be killed by the action of the drug). We began by successfully examining algae as a function of water quality, and have since analysed the IC50 of drugs such as staurosporine, benchmarked against gold standard methods such as annexin - but more rapidly and at substantially lower cost.
Relevant papers in the archive:
23, 24, 26, 30, 32, 33, 35, 38, 40, 42, 49, 55, 56