Ratiometric upconversion fluorometric turn-off nanosensor for quantification of furfural in foods

The current work puts forward a turn-off ratiometric upconversion fluorescence nanosensor for the quantification of furfural (FUR). Upconversion nanoparticles (UCNPs) containing Y3+, Yb3+, and Er3+ were synthesized; mesoporous SiO2 and amino groups were subsequently conjugated and functioned as the signal component. The p-toluidine molecule played the role of recognition molecules, which coupled with UCNPs to form a unique detection system. An absorption peak appeared when the FUR was combined with p-toluidine resulted in an obvious quenching of upconversion emission at 539 nm via inner filter effects (IFE), while the fluorescence peak at 653 nm maintained constant. Therefore, the FUR concentration was quantified by the record of fluorescence ratio I539/I653. Under optimal conditions, the proposed UCNPs-p-toluidine coupled nanosystem achieved the ratiometric fluorescence sensing toward FUR in the linear range of 0.01–100 μg/mL with a detection limit as low as 0.003 μg/mL. The accuracy of the sensor was validated by the HPLC method with preferable accuracy. Finally, the overall nanosystem showed excellent application potential in adulterated foodstuff (e.g., cookie, honey, fruit wine, milk tea, and potato chips).