Profiling HO from single COS-7 cells by means of scanning electrochemical microscopy.

We report quantitative determination of extracellular HO released from single COS-7 cells with high spatial resolution, using scanning electrochemical microscopy (SECM). Our strategy of depth scan imaging in vertical x-z plane was conveniently utilized to a single cell for obtaining probe approach curves (PACs) to any positions on the membrane of a live cell by simply drawing a vertical line on one depth SECM image. This SECM mode provides an efficient way to record a batch of PACs, and visualize cell topography simultaneously. The HO concentration at the membrane surface in the center of an intact COS-7 cell was deconvoluted from apparent O, and determined to be 0.020 mM by overlapping the experimental PAC with the simulated one having a known HO release value. The HO profile determined in this way gives insight into physiological activity of single live cells. In addition, intracellular HO profile was demonstrated using confocal microscopy by labelling the cells with a luminomphore, 2',7'-dichlorodihydrofluorescein diacetate. The two methodologies have illustrated complementary experimental results of HO detection, indicating that HO generation is centered at endoplasmic reticula.