Electrochemical monitoring of cell behaviour in vitro: a new technology

This article describes a novel electrochemical technique for the real-time monitoring of changes in the behaviour of adherent human cells in vitro: i.e., a biosensor that combines a biological recognition mechanism with a physical transduction technique, described collectively as Oncoprobe. Confluent viable cells adherent to gold electrodes (sensors) modify the extracellular microenvironment at the cell:sensor interface to produce a change in the electrochemical potential compared to that measured in the absence of cells. The potential was measured as an open circuit potential (OCP) with respect to a saturated calomel reference in the bulk culture medium. Typical OCP values for confluent cultures of human breast carcinoma cells, 8701-BC, approximated -100 mV compared with cell-free values of approximately -15 mV. The OCP for 8701-BC cells was modified in response to temperature changes over the range 32 to 40 degrees C and also to treatments with phytohemagglutinin (PHA, 25 microg/mL), cycloheximide (30 microM) and interleukin-1 beta (IL-1, 0.5 ng/mL) over 24 h. Cultures of synovial fibroblasts also responded to the same treatments with similar responses, producing negative shifts in the OCP signal with PHA and IL-I, but a positive shift in OCP signal with cycloheximide, all relative to the untreated control cultures. From experimental data and theoretical considerations it is proposed that the cell-derived signals are mixed electrode potentials reflecting a "conditioned," more reducing environment at the cell:sensor interface. Only viable cells caused a negative shift in the OCP signal, this being lost when cells were rendered nonviable by formalin exposure. This technology appears unique in its ability to passively "listen in" on cell surface activities, suggesting numerous applications in the fields of drug discovery, chemotherapy, and cell behaviour.