A colorimetric and fluorescent dual-mode biosensor based on Aloe vera polysaccharide stabilized core-shell nanoflowers and red carbon dots for organophosphorus pesticide detection.

The pesticide residues of organophosphorus pesticides (OPs) in the environment poses a threat to human health and the ecological environment. Consequently, creating a dependable and effective platform for the detection of OPs is crucial for safeguarding food safety, preserving public health, and upholding ecological equilibrium. Herein, we synthesized bimetallic nanoflowers (AP-PdPt NFs) with core-shell structure for the first time and their particle size was about 18 nm. AP-PdPt NFs facilitated the conversion of the colorless chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB), demonstrating their remarkable oxidase-like activity. The kinetics of the catalytic process adhered to the conventional Michaelis-Menten equation. In addition, we synthesized 1.36 nm red carbon dots (CDs) that can be quenched by oxTMB. Importantly, we developed a dual-mode OPs biosensor based on AP-PdPt NFs and red CDs. The biosensor can produce colorimetric and fluorescent signals for OPs in fruits and vegetables solution, and the limits of detection for dimethoate were 0.37 ng/mL in colorimetric method and 0.41 ng/mL using fluorescent mode, respectively. This dual-mode biosensor was successfully applied to the sensitive detection of dimethoate in real samples, which develops a new strategy for OPs detection.