Profiling H 2 O 2 from single COS-7 cells by means of scanning electrochemical microscopy

We report quantitative determination of extracellular H O 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 H O 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 H O release value. The H O profile determined in this way gives insight into physiological activity of single live cells. In addition, intracellular H O 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 H O detection, indicating that H O generation is centered at endoplasmic reticula.