Development of a Photoelectrochemical Microelectrode\nUsing an Organic Probe for Monitoring Hydrogen Sulfide in Living Brains

Hydrogen sulfide (H<sub>2</sub>S)\nis an important bioactive molecule\nthat plays a significant role in various functions, particularly in\nthe living brain, where it is closely linked to cognition, memory,\nand several neurological diseases. Consequently, developing effective\ndetection methods for H<sub>2</sub>S is essential for studying brain\nfunctions and the underlying mechanisms of these diseases. This study\naims to construct a novel photoelectrochemical (PEC) microelectrode\nTi/TiO<sub>2</sub>@HSP for the quantitative monitoring of H<sub>2</sub>S levels in the living brain. The PEC microelectrode Ti/TiO<sub>2</sub>@HSP is formed by covalently bonding a specifically designed organic\nPEC probe HSP, which possesses a D-π–<i>A</i> structure, to the surface of TiO<sub>2</sub> nanotubes generated\nvia in situ anodic oxidation of titanium wire. The PEC probe HSP can\neffectively react with H<sub>2</sub>S and generate significant photocurrent\nresponse under long-wavelength excitation light (560 nm), thereby\nachieving quantitative detection of H<sub>2</sub>S. The sensor demonstrates\nhigh sensitivity and good selectivity. In vivo experiments utilizing\nthe PEC microelectrode Ti/TiO<sub>2</sub>@HSP enable the monitoring\nof dynamic changes in H<sub>2</sub>S levels across various regions\nof the mouse brain. The findings reveal that in normal mice, the concentration\nof H<sub>2</sub>S in the hippocampus is significantly higher than\nin the striatum and cerebral cortex. Additionally, following propargylglycine\ndrug stimulation, H<sub>2</sub>S concentrations in different brain\nregions were observed to decrease, with the most substantial reduction\nnoted in the hippocampus. This suggests that cystathionine γ-lyase\n(CSE) is the primary enzyme responsible for H<sub>2</sub>S production\nin this area, while the striatum exhibits a less pronounced decrease\nin H<sub>2</sub>S concentration, indicating a reliance on alternative\nenzymatic pathways for H<sub>2</sub>S production. Therefore, this\nstudy not only successfully develops a high-performance H<sub>2</sub>S detection sensor but also provides new experimental tools and theoretical\nfoundations for further exploring the roles of H<sub>2</sub>S in neurophysiological\nand pathological processes.