Self-Assembled Carbazole Amphiphiles for Postharvest Monitoring of Pest Infestation through Uric Acid Detection

Abstract

Two carbazole-based fluorescent amphiphilic probes were synthesized and systematically investigated for the selective recognition of uric acid (UA). The probes exhibit a distinctive concentration-dependent dual fluorescence response toward UA, originating from a hierarchical binding mechanism. At low UA concentrations, electrostatic association between protonated piperazine units and urate anions induces fluorescence quenching, while at higher concentrations, cooperative hydrogen bonding and π–π stacking interactions involving carbazole moieties lead to pronounced fluorescence enhancement through excimer-state redistribution. Probe 2 shows a detection limit as low as ~0.6 µM. Detailed spectroscopic, lifetime, and mechanistic studies confirm the formation of static probe-UA complexes and modulation between monomeric, partially overlapped, and fully overlapped excimer emissions. Importantly, the sensing platform remains operational in complex food matrices; fluorescence titrations performed in rice and other cereal extracts display excellent linearity and selectivity toward UA with negligible interference from common cereal constituents. Quantitative estimation of UA in real rice and wheat extracts correlates strongly with conventional enzymatic uricase assays, validating the reliability of this non-enzymatic, multiparametric fluorescence strategy. The method provides a rapid, interference-free, and field-deployable approach for early detection of pest infestation and contamination in stored cereals, supporting sustainable postharvest management.