Fluorescent Nanosensor for Indole-3-Propionic Acid Detection in Gut Health Monitoring.

The gut microbiota plays a pivotal role in bio-transforming dietary components, including tryptophan, an essential amino acid that undergoes microbial metabolism. Microbial metabolism of tryptophan yields indole-3-propionic acid (IPA), an emerging biomarker for gut inflammation. Current IPA detection relies on expensive, time-consuming mass spectrometry. To address this limitation, a fluorescent nanosensor system is presented that uniquely features two optical modalities: one utilizing near-infrared (NIR) emission of a central single-walled carbon nanotube (SWNT), and a separate, visible emission from the corona phase polymer, a cationic conjugated polyelectrolyte (CP3). Selective IPA molecular recognition occurs at the latter, but the binding is optically reported via quenching in both the visible and NIR emission channels. The two modalities provide complementary advantages: CP3-SWNTs' NIR channel enables detection in strongly scattering tissue environments due to reduced Rayleigh scattering at longer wavelengths. Conversely, CP3 visible channel facilitates future rapid, cost-effective point-of-care biological sample screening. Functionality of both modalities is maintained within a gelatin metacrylate hydrogel offering potential for future continuous in vivo monitoring of IPA dynamics. The sensor reveals significant differences in plasma IPA levels between healthy controls and patients with active gut inflammation: ulcerative colitis and Crohn's disease, highlighting its promise in rapid gut health assessment.