Carbon dot-modified silver nanoparticle electrochemical sensors for the ultrasensitive detection of total malachite green and leucomalachite green residues in fish.

Owing to its low cost and high effectiveness as a biocide in aquaculture, malachite green (MG) and its residue leucomalachite green (LMG) are commonly found in aquatic resources. However, they are known to be hazardous contaminants to both the ecosystem and humans. Their side effects on the environment threaten fishery resources and food safety. In this perspective, designing a suitable tool for the quantitative and real-time detection of MG and LMG in foodstuffs is extremely crucial. Herein, we report an ultrasensitive differential pulse voltammetry (DPV) method using a gold (Au) electrode modified with a mixture of silver nanoparticles and carbon dots (AgCDs) to enhance its catalytic properties for the redox reaction of MG and LMG. Carbon dots (CDs) ecologically synthesized from pineapple peel juice via a hydrothermal method were used as reducing and stabilizing agents for the synthesis of silver nanoparticles (AgNPs). Besides the resulting AgCDs solution used to modify the Au electrode via immersion, a portable electrochemical workstation was used, making field monitoring and real-time detection easier. The synergistic effect of Au and AgCDs makes the modified AgCDs/Au electrode highly effective for the trace detection of total MG and LMG residues. Under optimized parameters and in a Na2SO4 electrolyte solution, a linear range from 6 pg mL-1 to 100 pg mL-1 with a detection limit of around 5 pg mL-1 was obtained. Furthermore, its precision, accuracy, and application studies on catfish, carp, red carp, and sheatfish suggest that the AgCDs/Au electrode can be used to monitor and determine traces of these contaminants in foodstuffs.