Electrical biosensors

Electrical biosensors for individual living cells were described at the March meeting of the American Physical Society. Cells are complex networks of interacting molecules, and are usually studied with optical techniques. Electrical measurements, however, can provide complementary information. Toward that end, Lydia Sohn of Princeton University described several new biosensors. With one, she measured the amount of DNA in a single living cell passed through a small fluid chamber between two metal electrodes. The cell changed the system’s capacitance in a way that reflected the amount of the cell’s negatively charged DNA but not its other ions. Sohn reported that the technique can identify the stage of a cell’s development (since cells can contain different amounts of DNA at different stages) and can potentially distinguish cancerous cells from healthy ones. Sohn also described a biosensor that can detect small amounts of a specific protein in live E. coli cells. The eventual goal of Sohn’s lab is to take inventory of a living cell’s protein contents—something that cannot be done with current protein assay techniques, which require the destruction of cells. (http://www.aps.org/meet/MAR02/baps/vpr/layf7-003.html .)