An impedance-based chemiresistor for the real-time, simultaneous detection of gut microbiota-generated short-chain fatty acids

Abstract

Short-chain fatty acids (SCFAs) are key molecules, produced by gut bacteria in the intestine, that are absorbed into the bloodstream and strongly influence human health. SCFA disruption and imbalances have been linked to many diseases; however, SCFAs are seldom used diagnostically as their detection requires extensive sample preparation and expensive equipment. In this work, an electrochemical sensor was developed to enable real-time (requiring less than 2 min per measurement), quantitative measurement of SCFAs from complex samples in liquid phase without the need for extraction, evaporation, or destruction. An impedance-based sensor for in vitro detection of acetic acid, propionic acid, and butyric acid (accounting for more than 85% of SCFAs in the intestine) was fabricated by the deposition of ZnO and polyvinyl alcohol (PVA) on the surface of a microfabricated interdigitated gold electrode. The sensor was first exposed to a broad, physiologically relevant range of concentrations of SCFAs in isolation (0.5–20 mg/ml in electroanalytical cell), and, unlike previously published SCFA sensors that could detect only in gas form with the aid of evaporation, it was able to detect them directly in the liquid phase at room temperature. Subsequently, Electrochemical Impedance Spectroscopy (EIS) analysis was utilized in a complex medium, accompanied by Fe(CN)63−/4−. This was applied to a mixture of SCFAs, prepared in varying ratios and concentrations spanning from 0.5 to 10 mg/ml. The analysis successfully demonstrated the sensor's capacity to accurately measure SCFAs in a mixture of experimental relevance. The recorded faradaic responses were then used to train a fit-to-data model to screen human bacterial isolates and detect which species secrete SCFAs in vitro. This research paves the way for swift, non-destructive assessment of SCFA levels in complex biological samples. The end product is a miniaturized sensor that is highly stable and sensitive, making it ideal for real-time monitoring applications.