Electrode fouling and passivation is an inevitable problem which seriously affects the electrode performance in cell culture and detection. Construction of photocatalytically renewable electrode by combination of nanophotocatalysts with electrochemical sensing materials could provide a promising approach for highly efficient renewal of electrode surface without damaging its micro-or nanostructures. However, the reactive oxygen species generated during photocatalysis always cause damages to cells being adhered or cultured on the electrode surface, which precludes on-line renewal of electrode during cell culture and detection. To address this issue, based on the visible light-induced renewable electrode (poly(3,4-ethylenedioxythiophene) (PEDOT)-modified TiO₂/CdS nanocomposites electrode we previously developed, a thin layer of gelatin hydrogel was spin-coated on the electrode in this work to realize efficient electrode renewal under visible light irradiation during the culture and detection of living cells. The optimized thickness (ca. 2 μm) of gelatin hydrogel was obtained by spin-coating under 3000 r/min. Benefitting from the network structure of gelatin hydrogel and the renewable performance of PEDOT@CdS/TiO₂ nanocomposites, the gelatin coating efficiently blocked the diffusion of biomacromolecules from the bulk medium to the electrode surface and thus significantly diminished the fouling caused by these macromolecules, while the pollutants derived from small molecules could be efficiently degraded under visible light irradiation. Meanwhile, gelatin coating did not induce obviously decline in detection sensitivity, and a low detection limit of 4.2 nmol/L (S/N=3) could be obtained towards electrochemical detection of nitric oxide (NO). Most importantly, the gelatin layer efficiently blocked the ultrashort-lived but highly reactive oxygen species such as OH·(generated by photocatalytic process) diffusing from the electrode surface to the cells, and the damages to the cells caused by these highly reactive species could be therefore significantly decreased. The results from live/dead cell staining demonstrated that almost all the cells (>95%) cultured on gelatin-coated electrodes maintain their viability when the electrode was irradiated by visible light for 6 h, while a considerable part of cells (>40%) culture on the uncoated electrode lost their viability under the same conditions. These features allowed on-line renewal of the electrode during cell culture and detection as well as real-time monitoring of NO released from the human umbilical vein endothelial cells (HUVECs).

Key words: nanophotocatalysts, photocatalytically renewable electrode, visible light, gelatin, human umbilical vein endothelical cells, nitric oxide, real-time monitoring