LAUSR

A paper-based device, based on the fluorescence switching of water-soluble thioglycolic acid (TGA)-capped CdTe QDs, was developed for the simple, rapid and sensitive detection of organophosphorus (OP) and carbamate (CM) insecticides. A new design platform for the developed device was created, comprising a foldable sheet with a detection zone and a buffer solution loading channel, to simplify the multi-step reaction of a bi-enzyme assay with a signal enhancement system. This device was very useful for fast screening and on-site detection, without requiring many reagents. The bi-enzyme includes acetylcholinesterase (AChE), choline oxidase (ChOx) and TGA-capped CdTe QDs, which were coated on the paper-based device at the detection zone in a separated sheet, starting with an acetylcholine (ACh) substrate coating. After incubation of the sample at the detection zone, the device was closed to initiate enzyme catalyzed hydrolysis of the pre-spotted ACh. Subsequently, the buffer solution was applied to the device, allowing for the pre-spotted chemicals to mix well and importantly, result in signal enhancement. The hydrolysis of ACh was catalyzed by AChE followed by ChOx to yield H2O2, which can quench the fluorescence of the TGA-capped CdTe QDs. In the presence of OP and CM insecticides, the AChE activity was inhibited, resulting in decreased quenching of the TGA-capped CdTe QDs. The change in the fluorescence intensity of the TGA-capped CdTe QDs can be observed using the naked eye under UV-black light. Under optimized conditions, the limit of detection for pirimicarb, dichlorvos and carbaryl were found to be 0.05, 0.01 and 0.01 ppm, respectively, using visual measurements. This developed device was successfully applied to the detection of OP and CM insecticide residues in agricultural products. The data correlated well with the data obtained using gas chromatography-tandem mass spectrometry (GC-MS/MS). This developed device shows good selectivity and sensitivity for the rapid screening of insecticides and could be useful for on-site applications.