A fluorescent and ratiometric colorimetric biosensor for detection of different hazard contaminants in dairy products

The quality and safety of dairy products are directly related to public health. However, it remains challenging to achieve detection of multi-class dairy hazard contaminants. Herein, we constructed a biosensor combining Fe-doped carbon dots (Fe-CDs) with Fe3O4 @polydopamine (PDA) nanoparticles (NPs) to rapidly detect antibiotics and nitrite. Taking kanamycin (KAN) and sodium nitrite (NaNO2) as model targets, Fe-CDs were conjugated with KAN aptamers (Apt) to give aptamer-functionalized Fe-CDs (Fe-CDs-Apt). Fe-CDs-Apt could specifically recognize KAN, forming Fe-CDs-Apt-KAN complexes in the solution. Free Fe-CDs-Apt were adsorbed by subsequently added Fe3O4 @PDA NPs and separated by an external magnetic field. While, Fe-CDs-Apt-KAN kept in the supernatant and remained fluorescence intensity positively correlated with KAN concentration. NaNO2 concentration in the supernatant was monitored by ratiometric colorimetry using a nitrite-induced specific diazotization reaction. The system showed wide linear ranges of KAN (17.2 pM−343 nM) and NaNO2 (5 −5000 μM), and relatively low detection limits of 0.91 pM for KAN and 0.54 μM for NaNO2. This method could complete the detection process of the two targets within 20 min and successfully monitored KAN and NaNO2 in four kinds of dairy samples with recoveries of 92.4 − 108.7% and 90.3 − 107.2%, respectively. Biosensors based on versatile CDs and magnetic NPs appear promising in improving the analytical throughput and efficiency for food safety monitoring.