Halochromy incorporated with inner filter effect-based fluorescence quenching: A dual-response strategy for spoilage sensing of proteinous foods with rapid and irreversible readout

The lack of handy and reliable sensing strategy for non-contact freshness assessment is a problem faced by food industries. This work presented an innovative solution for freshness monitoring of proteinous foods: halochromy- and fluorescence-based dual-response sensors with rapid and irreversible readout. Sensors were prepared by the polycondensation of CdTe quantum dots (QDs)-doped silane coupling agents onto filter papers and then anchoring of pH-sensitive halochromic compounds like blueberry anthocyanin (BA) by electrostatic interaction. The as-designed sensors showed rapid (within 1 min) responsiveness on both appearance and fluorescence toward total volatile basic nitrogen (TVB-N) through pH-sensitive structural variations of BA and inner filter effect (IFE)-induced fluorescence quenching of QDs, giving a LOD as low as 0.01 ppm (ammonia) within working range of 0.001–50 ppm, and such a dual-signal response could be sustained at least for 7 days after removal of TVB-N. As a proof-of-concept, dual-response spoilage sensing of proteinous foods was experimentally proved to be highly feasible and reliable using pork, shrimps and shelled eggs as representatives of real food samples. Smartphone-based digital color information of paper sensors before and after sensing was furtherly applied to reconstruct digitized binary response, reinforcing the credibility of this strategy.