Reduced graphene oxide-based electrochemical aptasensor for the multiplexed detection of imidacloprid, thiamethoxam, and clothianidin in food samples

Neonicotinoids are a group of neurotoxic insecticides that possess significant threats not only to the environment but also to human health. This underlines the importance of developing efficient and accurate tools to detect neonicotinoids and track their behavior. Aptamers have been widely used as stable, efficient, and specific biorecognition molecules in biosensors. Nonetheless, no aptasensor was reported for the multiplexed detection of neonicotinoids. Herein, a graphene-based electrochemical biosensor was fabricated with three aptamers for the detection of imidacloprid, thiamethoxam, and clothianidin. The imidacloprid-specific aptamer underwent a truncation, which showed strong affinity with K_D = 12.8 nM compared to 20.1 nM of the original sequence when studied with differential pulse voltammetry (DPV). Screen printed electrodes were coated with graphene oxide. After electrochemical reduction, 1-pyrenebutyric acid was used to functionalize the electrodes and covalently immobilize the aptamers. The electrodes were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) to ensure successful aptasensor fabrication. The biosensor displayed excellent sensitivity compared with reported aptasensors and linear ranges from 0.01 ng/mL to 100 ng/mL for imidacloprid, thiamethoxam, and clothianidin. It also demonstrated excellent selectivity to the three analytes. Spiked extracts from tomato and rice samples were analyzed using our aptasensor, and results were validated through conventional chromatography assays. High recovery rates for all three neonicotinoids were obtained, demonstrating excellent agreement between the two methods. This study presents a cost-effective and simple multiplex detection for the sensitive, specific, and accurate on-site analysis of neonicotinoids.