Development of a pH-responsive ratiometric fluoroprobe based on GSH-CuNCs-Ce3+ and N-CQDs for rapid/sensitive malathion detection in fruit juices

Herein, we engineered a novel pH-responsive ratiometric assay by virtue of the composite system of Ce3+-enhanced glutathione-encapsulated copper nanoclusters (GSH-CuNCs-Ce3+) and N-doped carbon quantum dots (N-CQDs). The GSH-CuNCs-Ce3+ and N-CQDs were fabricated using one-pot chemical reduction and hydrothermal approaches, respectively, and their morphologies as well as physical and chemical properties were testified in detail by a series of characterization techniques. At 350-nm excitation wavelength, the GSH-CuNCs-Ce3+/N-CQDs system (GCC-NC) featured the 440/650-nm dual-emitting property. The ratios of fluorescence intensities (F650/F440) demonstrated a strong pH-dependence from 3.0 to 5.0 with coefficient of determination of 0.9982. Consequently, the GCC-NC system was feasible for constructing a pH-responsive dual-emitting fluoroprobe. Based on the catalytic effect of acetylcholinesterase on acetylcholine to yield acetic acid and further trigger varying solution pH, the as-constructed GCC-NC fluoroprobe was satisfactorily applied for detecting malathion. Under optimized conditions, the newly developed GCC-NC fluoroprobe supplied wider linear range (0.25-200 μM), lower detection limit (0.075 μM), satisfactory recoveries (96.3-106.2%) and higher precision for malathion in several kinds of fruit juice samples. The fortified experiments by malathion's structural analogues and metal ions provided compelling evidence that this fluoroprobe had strong anti-interference capacity and high specificity for malathion. These findings render us to believe that the as-constructed pH-responsive dual-emitting fluoroprobe holds great promising in trace malathion assay in food matrices.