Portable Smartphone-Based QDs for the Visual Onsite Monitoring of Fluoroquinolone Antibiotics in Actual Food and Environmental Samples.

Accurate onsite profiling of fluoroquinolone antibiotics (FQs) is of vital significance for ensuring food safety and estimating environmental pollution. Here, we propose a smartphone-based QD ratiometric fluorescence-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 the 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 yielding 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 μM. 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 onsite requirements. Interestingly, this portable device has successfully been applied for the onsite detection of GFLX in real food (i.e., milk and drinking water) and environmental (i.e., fish-farming water) samples with acceptable results. This developed platform offers a great promise for the point-of-care detection of FQ residues in practical application with the merits of being label-free, low-cost, and rapid, thus opening a new pathway for the onsite evaluation of food safety and environmental health.