Multi‐emitting fluorescent system–assisted lab‐in‐a‐syringe device for on‐site and background‐free detection of 2,4‐dichlorophenoxyacetic acid

Abstract

AbstractHerbicide residuals have posed severe threat to food safety and public health; thus, the development of smart, portable, efficient, and accurate on‐site detection system is in urgent demand. Here, a multi‐emitting fluorescent system‐assisted lab‐in‐a‐syringe (LIS) device was developed for the on‐site and background‐free determination of 2,4‐dichlorophenoxyacetic acid (2,4‐D). 2,4‐D‐responsive cascade reactions were constructed: 2,4‐D could specifically suppress alkaline phosphatase (ALP) activity and restrain the generation of ascorbic acid (AA), MnO2 nanosheets would oxidize AA into dehydroascorbic acid that subsequently reacts with o‐phenylenediamine (OPD) to generate blue‐emission product (λem, 435 nm), whereas remained MnO2 nanosheets and OPD further produced yellow‐emission product (λem, 570 nm). Red‐emission carbon dots (RCDs, λem, 680 nm), synthesized via the solvothermal treatment of cilantro, were introduced to construct a multi‐emitting fluorescent system. Then, four paper pads, respectively, dropped with ALP, sodium l‐ascorbyl‐2‐phosphate, MnO2 nanosheets + RCDs, and OPD were held into reusable plastic filters and assembled paper‐based LIS device to trigger cascade reactions (total analysis time, 65 min) and eliminate background interference. As a result, with the support of color recognizer application in smartphone, fluorescent color on detection pads from blue–purple to red to yellow was achieved for the sensitive and visual detection of 2,4‐D with LOD of 5.0 μg L−1, recoveries of 94.6%–106.8%, and relative standard deviations of 2.3%–6.8%. Obviously, this strategy provides a robust, visual, and background‐free platform for 2,4‐D detection, which expands application prospects in the field of herbicide analysis.