Photoelectrochemical analysis of the alkaline phosphatase activity in single living cells.

Conventional photoelectrochemical (PEC) analysis mostly utilizes photoactive material modified planar indium tin oxides (ITOs) to obtain photocurrent responses for the measurement of analytes in solution. In this work, a CdS quantum dot (QD) modified nanopipette was prepared for the PEC analysis of the alkaline phosphatase (ALP) activity in single MCF-7 cells. The nanopipette was filled with ascorbic acid 2-phosphate (AAP) that was egressed outside the nanopipette by electrochemical pumping. Next, AAP was catalyzed by ALP to generate ascorbic acid (AA), which is an efficient electron donor for CdS QDs under illumination. Based on the result that the nanopipette showed a linear photocurrent response to AA, a nearly linear correlation between the photocurrent and the activity of ALP was established. Accordingly, using these CdS QD modified nanopipettes, the ALP activity in single MCF-7 cells was determined to be 0.12 U mL-1 by PEC analysis. This work does not expand the application of PEC bioanalysis, but offers a new strategy for single cell analysis.