A near-infrared crosstalk-free FRET fluorescent probe for highly specific detection of sulfite and viscosity as well as its multi-applications.

Sulfur dioxide (SO2) serves as a crucial signaling molecule in biological systems and a common preservative in food products, while viscosity variations reflect microenvironment alterations in pathological states and plant stress responses. To address detection challenges in these dual analytes, a near-infrared FRET probe PPTC was architected by the hybridization of a phenanthroimidazole donor and a piperazine-benzene-thiophene-cyanine acceptor strcture. The engineered architecture achieved a significant 250 nm emission separation (510/760 nm) effectively preventing spectral crosstalk, while incorporating dual-response ratiometric mechanisms. Specifically, nucleophilic C=C cleavage triggered a pronounced enhancement at 510 nm within 4 min, and viscosity-restricted rotation augmented the emission at 760 nm. Based on this dual-response design, a nanomolar sensitivity for SO2 (61.88 nM) was attained. Functional validation spanned multiple domains with food safety monitoring attaining 95.33-103.33% SO2 recovery in dried samples, environmental surveillance utilizing smartphone-hydrogel platforms, plant studies resolving synchronous viscosity-SO2 co-regulation in salt-stressed rice sprouts, and cellular barrier penetration in onion epidermis. Cross-kingdom functionality of simultaneous viscosity-SO2 detection was further evidenced through mitochondrial colocalization (Pearson's coefficient 0.87) and inflammation tracking in zebrafish and living cells. Collectively, these findings highlight the considerable promise of PPTC as a dual-analyte probe for SO2 and viscosity in intricate biological environments and foodstuffs.