In the biological systems, H₂S is an endogenously produced gasotransmitter that regulates various functions of the cardiovascular, gastrointestinal, and central nervous systems. On the one hand, elevated levels of H₂S is linked to pathology, making it as a biomarker for a range of diseases. On the other hand, H₂S drugs in some controlled doses exhibits therapeutic effects for treating neurological, ophthalmic, and carcinogenic diseases. In both the cases, accurate quantitative H₂S detection tools are vital to track H₂S to treat pathology and to study drug release kinetics. However, H₂S analysis in biological and drug samples encounters several challenges, mainly due to its low levels, sizeable interferences from complex environments, signal fluctuations due to biological fouling, and physiological pH demand. The electrochemical sensors are ideal tools to develop a straightforward H₂S sensor, because the H₂S molecules are easily oxidizable via a 2e^–/2H⁺ pathway, eliciting measureable signals. To apply the electrochemical sensors in real world analysis, we have developed nanostructured interfaces using, zinc cobaltite (ZnCo₂O₄), molybdenum disulfide (MoS₂), graphene (GR) and polymerized o-phenylenediamine (POPD) materials.

Firstly, a graphene-MoS₂/POPD modified glassy carbon electrode was fabricated from hydrothermally prepared graphene-MoS₂ hybrid, and electrochemically prepared POPD. The graphene-MoS₂/POPD modified electrode catalyzes H₂S oxidation at a minimized overpotential (+ 0.15 V vs. Ag/AgCl), and led to establish an ultrasensitive H₂S detection platform. It can detect 0.1 nM concentration of H₂S under complex biological conditions. Our experimental results indicates the synergic properties of two excellent 2D materials, graphene and MoS₂ provides signal amplifications. Moreover, POPD provides high selectivity to the interface, eliminating up to 2.5-fold surplus levels of biological interferences, and providing 98.5% anti-fouling capacity. Secondly, POPD/MoS₂/ZnCo₂O₄ modified carbon cloth electrode was developed via hydrothermal growth of ZnCo₂O₄ and MoS₂ followed by electrodeposition of POPD. The resulting sensor showed excellent sensing aptitude to H₂S, because of its rich redox chemistry and extended electrocatalytic sites. The repulsive forces between sulfur layers of MoS₂ and elemental sulfur of H₂S-oxidized product is used to alleviate sulfur passivation and to maintain a reproducible electrode surface. Using amperometric technique, both the electrodes have shown appreciable practical feasibility in human blood, serum, and urine samples at physiological pH. They were able to track real-time quantitative productions endogenous H₂S in e. coli. Future work is directed towards employing these sensors in monitoring H₂S drug release kinetics and transport in cancer cells.