Single Cell Viability Measured by Scanning Electrochemical Microscopy and Live/Dead Staining*
Kavita M. Jeerage, Tammy L. Oreskovic, Nikki S. Rentz, Damian S. Lauria
Based on its standard reduction potential, ferriciniummethanol can act as an alternate electron acceptor to oxygen during cellular metabolism. By locally oxidizing ferrocenemethanol at a platinum microelectrode, we probed the activity of individual human cortex adrenal cells using a scanning electrochemical microscope. Over some cells, the oxidized species generated at the microelectrode were reduced, leading to a current increase known as positive feedback. Over other cells, the cell acted primarily as a barrier to the diffusion of the reduced species to the microelectrode, leading to a current decrease known as negative feedback. In all cases, the cells probed electrochemically fluoresced green upon exposure to calcein acetoxymethyl, which indicates esterase activity in living cells with intact membranes. Electrochemical measurements using ferrocenemethanol as an indicator therefore distinguish live cells with different levels of metabolic activity. Equivalent O2 consumption rates for individual cells were calculated by converting the difference between cell and background currents using Faradays Law and are in the same range as bulk measurements (~ 5 fmol O2/min). Equivalent O2 consumption rates for cells imaged at different heights showed only a small dependence on height. Culture-level measurements of metabolic activity showed that adrenal cells in electrochemical imaging medium began to die and detach after 3 days in culture, however, this appeared to be due to the lack of fetal bovine serum rather than the addition of ferrocenemethanol.