PROJECT SUMMARY/ABSTRACT The circulating gasotransmitter H₂S is endogenously produced by tightly-regulated human enzymes and exogenously produced in a diet-dependent manner by the human microbiota. Exogenous H2S production by the human gut microbiota influences human health by modulating systemic H2S bioavailability. Excessive gut microbial H2S production is hypothesized to be involved in the etiology of colorectal cancer and Ulcerative Colitis. Our understanding of how gut microbially produced H₂S affects human health remains incomplete because current measurement techniques are imprecise, invasive, require biospecimen collection, and have limited temporal resolution. In this proposal, our objective is to address this gap by developing a research- grade wearable Smart Underwear device that enables long-term real time measurements of gut microbial H₂S production in gaseous rectal effluent (flatus). Flatus are an untapped source for measuring gut microbial H2S production. We have demonstrated that the Smart Underwear v1 prototype can precisely measure physiologically-relevant concentrations of H2S in vitro. When worn by humans, the Smart Underwear v1 prototype detects flatus with an excellent signal-to-noise ratio and is able to estimate the concentration of H2S in each flatus. In the R21 phase, we propose to develop a second revision Smart Underwear prototype for clinical trials through miniaturization, software development, and incorporation of flexible materials. In addition, we propose to conduct a user experience trial to gauge the user acceptance and test the reliability of the Smart Underwear device when worn by humans. In the R33 phase, we will use the Smart Underwear v2 prototype developed in the R21 phase to test the hypothesis that the Smart Underwear device can detect diet-induced alterations in gut microbial H2S production using a randomized controlled feeding trial that contrasts gut microbial H₂S production by modulating dietary cysteine intake. The completion of the proposed goals will lead to the first wearable device that enables long-term real time measurements of gut microbial H2S production. This will facilitate the design of personalized dietary interventions to rationally modulate gut microbial H₂S production and benefit future studies seeking to untangle the complex interactions between gut microbial H2S production and disease.