Bifunctional Strategy toward Constructing Perovskite/Upconversion Lab-on-Paper Photoelectrochemical Device for Sensitive Detection of Malathion.

Bifunctional nanocrystals which combine two kinds of materials into single nanoparticles hold great promise in photoelectrochemical (PEC) analysis, particularly for nanocrystals based on perovskite quantum dots (QDs) which generally exhibit excellent photoelectric activity yet poor stability and upconversion nanoparticles (UCNP) that normally suffer from negligible photoelectric activity. Therefore, to achieve good performance of the PEC bioassay platform, it is valuable to combine perovskite QDs with UCNP encapsulation and promote their advantages to form hybrid nanocrystals that are stable, NIR excitable, and photoelectric. Herein, the core-shell configuration of perovskite/upconversion CsPbBrI@NaYF:Yb,Tm (CPBI@UCNP) nanocrystals coupled with a NiMn-layered double hydroxide (NiMn-LDH)/CdS heterojunction to form a cascade sensitization structure was proposed to construct the lab-on-paper PEC device for ultrasensitive detection of malathion pesticides. Concretely, the bifunctional CPBI@UCNP nanocrystals that encapsulated CPBI QDs into UCNPs were employed as a nanoscale light source and sensitizer in the lab-on-paper system, which not only prevented the degradation of perovskite QDs but also overcame the negligible photoelectric performance of pristine UCNPs with the cooperation of photoactive CPBI QDs. The synergistic quenching effect, including fluorescence energy resonance transfer (FRET) and photoinduced electron transfer (PET), was created to realize enhanced PEC signal readout. Benefiting from the dynamic cascade sensitization structure of CPBI@UCNP/NiMn-LDH/CdS and synergistic quenching effect of FRET/PET, the ultrasensitive detection of malathion was achieved with high selectivity, reproducibility, and stability, which provided guidelines to employ perovskite/upconversion nanomaterials for lab-on-paper PEC analysis.