Portable smartphone-based QDs for visual on-site monitoring of fluoroquinolone antibiotics in actual food and environmental samples.

Accurate on-site profiling of fluoroquinolone antibiotics (FQs) is of vital significance for ensuring food safety and estimating environmental pollution. Here, we propose a smartphone-based QDs ratiometric fluorescent sensing system to precisely report the level of FQs. As a proof of concept, we chose gatifloxacin (GFLX, a typical member of FQs) as the model for analytical target, which could effectively trigger the fluorescence color variation of QDs from bright yellow-green (~ 557 nm) to blue (~ 448 nm) through the photoinduced electron transfer (PET) process, thus emerging an evident ratiometric response. Based on this, the level of GFLX can be reported within a wide linear range from 0.85 nM to 3.6 M. Moreover, this assay owns a high sensitivity with a low detection limit of 0.26 nM for GFLX and a quick sample-to-answer monitoring time of 5.0 min, manifesting that this platform could be fully qualified for on-site requirement. Interestingly, this portable device has successfully been applied to on-site detection of GFLX in real food (i.e. milk & drinking water) and environmental (i.e. fish farming water) samples with acceptable results. This developed platform offers a great promise for point-of-care detection of FQs residues in practical application with merits of label-free, low-cost, and rapid, opening a new sight for on-site evaluating the food safety and environmental health.