Visual detection of nitrite in sausage based on a ratiometric fluorescent system

A novel ratiometric fluorescence sensor based on fluorescence resonance energy transfer (FRET) between MoS2 QDs and AuNCs was developed for nitrite detection in sausages. The MoS2 QDs-AuNCs nanocomposite exhibited dual emission peaks at 430 nm and 615 nm under 365 nm excitation. With addition of nitrite, the fluorescence of AuNCs was quenched due to the agglomeration of AuNCs, whereas the emission of MoS2 QDs increased for the blocked FRET. With this strategy, nitrite was detected in the range of 0.5–20 mg/L with a detection limit of 0.67 nM. Furthermore, based on the fluorescence color change of the sensor at different nitrite concentration, a microfluidic chip combined with smartphone was developed for the fluorescent visual detection of nitrite over a range of 1.0–20 mg/L. Finally, the developed methods were applied to the determination of nitrite in sausage samples with the satisfactory recoveries of 102.6%–110.8%, indicating the potential for practical application.