On-off-on fluorescent nanosensing: Materials, detection strategies and recent food applications

Background: The detection of food quality and safety is important in the whole food supply chain. In recent years, fluorescent detection technology has been extensively applied in food analysis. In particular, nanomaterial-based on-off-on fluorescent sensors have received much attention because of their high sensitivity, wide detection range, strong anti-interference ability, and flexible design. Nevertheless, there is no review focusing on the onoff-on fluorescent sensors for food analysis.Scope and approach: In the current review, several common nanomaterials are introduced, including quantum dots (QDs), carbon dots (CDs), graphene quantum dots (GQDs), and metal nanoclusters (MNCs). Main detection strategies of on-off-on fluorescent sensors are elaborated, involving redox reaction, competitive reaction, DNA hybridization reaction and enzymatic reaction. In addition, recent applications of on-off-on fluorescent sensors for trace level detection of nutrients, food additives, drug residues, pesticide residues, foodborne pathogenic bacterias, mycotoxins, and heavy metal ions are also summarized. Finally, advantages, challenges and future prospects for developing the on-off-on fluorescent sensors are presented.Key findings and conclusions: The on-off-on fluorescent sensors exhibit a wide detection range, strong antiinterference ability, and excellent linear responses to various analytes. However, current detection applications are still at the laboratory stage, commercial and industrial applications are rarely reported. Future research should focus on developing high-throughput detection techniques, and portable or visual fluorescent sensors, including kits and filter papers based sensors. Apps on smartphones should also be developed in future work.

Automated summary

On-off-on fluorescent sensors based on nanomaterials have gained much attention in food analysis due to their high sensitivity, wide detection range, strong anti-interference ability, and flexible design. This review introduces common nanomaterials and elaborates the main detection strategies of on-off-on fluorescent sensors. It also summarizes recent applications of these sensors for trace level detection of various analytes in food. However, the commercial and industrial applications of these sensors are still limited, and future research should focus on developing high-throughput detection techniques and portable or visual fluorescent sensors.