Portable Smartphone-Assisted Graphene Quantum Dots Sensing Platform for the Detection of Gut Microbial Metabolites

Metabolomics research is gaining traction lately as there is a growing interest in studying the global relationship between human diseases and the metabolite network. The presence and concentration of beneficial gut-derived metabolites depends on the individual's microbiota composition and diet, with direct metabolite-based supplementation being an appealing option for those unable to produce them. This work serves as an approach in the direct detection of gut-derived metabolites through a smartphone-based approach, as a faster and cheaper alternative to more traditional techniques such as chromatography or the study of gut bacteria culture. Urolithin, a beneficial gut microbial metabolite, was successfully detected with our developed smartphone-based optical assay with low limits of detection of 0.257-0.422 mu M that were comparable to those measured with a fluorescence spectrophotometer or even better than some reported HPLC methods. On top of a good sensitive detection with a reduced analysis time, the proposed "turn off-to-on" fluorescence sensing strategy that employed graphene quantum dots coupled with copper(II) ions also distinguished urolithin metabotypes and exhibited good selectivity in the presence of other reducing compounds and phenolic analogues. Our developed approach has demonstrated its versatility in direct gut-derived metabolite detection in commercial dietary supplements, making it a user-friendly tool for food and pharmaceutical product analysis.