Reduction of Ammineruthenium(III) by Sulfide Enables In Vivo Electrochemical Monitoring of Free Endogenous Hydrogen Sulfide

The discovery of endogenous sulfide in mammalian brain opens up a door to understanding of the physiological function of hydrogen sulfide (H2S). The transformation of different forms of sulfide (i.e., S2–, HS–, H2S, bound sulfane sulfur, et al.) in various physiological conditions hurdles the direct detection of hydrogen sulfide in vivo. Here, we find that ammineruthenium(III) (Ru(NH3)63+) can catalyze the electrochemical oxidation of free sulfide including HS– and H2S in a neutral solution (pH 7.4). This property is used to constitute an electrochemical mechanism for selective detection of hydrogen sulfide. By coupling in vivo microdialysis with selective electrochemical detection, we successfully developed an integrated microchip-based online electrochemical system (OECS) for continuous monitoring of free endogenous hydrogen sulfide in the central nervous system (CNS). The microchip-based OECS is well responsive toward hydrogen sulfide with high stability, sensitivity and selectivity. Compared with the existing methods, the OECS does not require offline treatment of brain tissue or adjustment of the detection solutions into acidic or strong basic atmosphere. These priorities essentially enable the system to accurately and reliably track dynamics of hydrogen sulfide in the CNS.