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

Hydrogen sulfide (H₂S) is an important bioactive molecule that plays a significant role in various functions, particularly in the living brain, where it is closely linked to cognition, memory, and several neurological diseases. Consequently, developing effective detection methods for H₂S is essential for studying brain functions and the underlying mechanisms of these diseases. This study aims to construct a novel photoelectrochemical (PEC) microelectrode Ti/TiO₂@HSP for the quantitative monitoring of H₂S levels in the living brain. The PEC microelectrode Ti/TiO₂@HSP is formed by covalently bonding a specifically designed organic PEC probe HSP, which possesses a D-π-<i>A</i> structure, to the surface of TiO₂ nanotubes generated via in situ anodic oxidation of titanium wire. The PEC probe HSP can effectively react with H₂S and generate significant photocurrent response under long-wavelength excitation light (560 nm), thereby achieving quantitative detection of H₂S. The sensor demonstrates high sensitivity and good selectivity. In vivo experiments utilizing the PEC microelectrode Ti/TiO₂@HSP enable the monitoring of dynamic changes in H₂S levels across various regions of the mouse brain. The findings reveal that in normal mice, the concentration of H₂S in the hippocampus is significantly higher than in the striatum and cerebral cortex. Additionally, following propargylglycine drug stimulation, H₂S concentrations in different brain regions were observed to decrease, with the most substantial reduction noted in the hippocampus. This suggests that cystathionine γ-lyase (CSE) is the primary enzyme responsible for H₂S production in this area, while the striatum exhibits a less pronounced decrease in H₂S concentration, indicating a reliance on alternative enzymatic pathways for H₂S production. Therefore, this study not only successfully develops a high-performance H₂S detection sensor but also provides new experimental tools and theoretical foundations for further exploring the roles of H₂S in neurophysiological and pathological processes.