Impedimetric sensing of cells on polypyrrole-based conducting polymers

Polypyrrole (PPy) is a conducting polymer that may be electrochemically generated with the incorporation of any anionic species, including net-negatively charged biological molecules such as proteins and polysaccharides. In this article, dermatan and chloride-loaded PPy films were prepared on gold sputter-coated coverslips and various skin derived cells were studied on them by electrochemical impedance spectroscopy. Impedance spectra in the frequency range 1-100 kHz were either determined at specific times or impedance was monitored continuously at specific frequencies. An equivalent impedance circuit was fitted to the recorded impedance spectra to obtain parameters whose contributions could be mapped to intracellular and intercellular current pathways, and the membrane properties of cells. Results show cell-induced impedance changes were detected over PPy modified electrodes and were dependent on cell density and type, monitoring frequency, material composition, and treatment. Lower cell densities were detected on PPy when compared with bare gold. Keratinocyte confluence, as determined by impedimetric analysis, was reached more rapidly on PPy than on gold. This was consistent with previous, more cumbersome, biochemical assays. Electrical equivalent circuit analysis provided evidence that the technique may be extended to discriminate cell type because of the intracellular and intercellular resistance, and cell membrane capacitance being related to cell morphology.