Dynamics of the exofacial thiols (i.e., cell surface thiol containing membrane proteins) of a live Chinese hamster ovary (CHO) cell is probed by time-resolved confocal microscopy. For this purpose, a fluorescent probe, 7-(diethylamino)-3-(4-maleimidophenyl)-4-methylcoumarin (CPM) is covalently attached to the exofacial thiols. The emission maximum of CPM bound exofacial thiols indicates a highly exposed and polar environment. Using CPM, we studied solvation dynamics, for the first time, at the membrane of a live cell. The thiol containing membrane proteins shows ultraslow response with average solvation time, = 475 ps. CPM labeled exofacial thiols also show spontaneous, intermittent oscillation in fluorescence intensity with a period of 0.5-1.0 s. This is ascribed to reversible, intermittent changes in the structure and conformation of the membrane proteins.