Miniaturized Capsule System Toward Real-Time Electrochemical Detection of H₂ S in the Gastrointestinal Tract

Hydrogen sulfide (H₂ S) is a gaseous inflammatory mediator and important signaling molecule for maintaining gastrointestinal (GI) homeostasis. Excess intraluminal H₂ S in the GI tract has been implicated in inflammatory bowel disease and neurodegenerative disorders; however, the role of H₂ S in disease pathogenesis and progression is unclear. Herein, an electrochemical gas-sensing ingestible capsule is developed to enable real-time, wireless amperometric measurement of H₂ S in GI conditions. A gold (Au) three-electrode sensor is modified with a Nafion solid-polymer electrolyte (Nafion-Au) to enhance selectivity toward H₂ S in humid environments. The Nafion-Au sensor-integrated capsule shows a linear current response in H₂ S concentration ranging from 0.21 to 4.5 ppm (R² = 0.954) with a normalized sensitivity of 12.4% ppm^-1 when evaluated in a benchtop setting. The sensor proves highly selective toward H₂ S in the presence of known interferent gases, such as hydrogen (H₂ ), with a selectivity ratio of H₂ S:H₂ = 1340, as well as toward methane (CH₄ ) and carbon dioxide (CO₂ ). The packaged capsule demonstrates reliable wireless communication through abdominal tissue analogues, comparable to GI dielectric properties. Also, an assessment of sensor drift and threshold-based notification is investigated, showing potential for in vivo application. Thus, the developed H₂ S capsule platform provides an analytical tool to uncover the complex biology-modulating effects of intraluminal H₂ S.