Printed Carbon Nanotube-Based Sensors for Real-Time and Continuous Gas Detection in Simulated Human Gut Microbiota Systems

To enable sensors to operate effectively beyond controlled laboratory environments, a methodical reverse engineering approach is crucial, tailored to the unique demands of specific applications. In vitro simulators of the human gastrointestinal tract serve as invaluable platforms for studying the influence of dietary factors on gut microbiota, necessitating continuous monitoring of microbial-produced gases. However, these simulators often lack integrated, continuous gas monitoring capabilities in their harsh environments. Here, we showcase the seamless integration and inline use of fully printed carbon nanotube (CNT)-based chemiresistive gas sensors, incorporating a thin polydimethylsiloxane membrane, within the Simulator of the Human Microbial Ecosystem (SHIME). We detail our selection of materials, optimization of fabrication processes, and operational protocols for these sensors. Our results demonstrate the sensors' ability to monitor gas production phases continuously in the anaerobic, highly humid, and acidic conditions of the SHIME system over extended periods (up to 16 hours) with minimal saturation. This work advances the field by establishing a practical and tailored sensor for real-time monitoring of gaseous biomarkers in in vitro systems like SHIME. The integration of low-cost, low-energy-demand printed flexible gas sensing systems highlights their transformative potential in food biotechnology, promising energy-autonomous sensing solutions.