Ultra-thin CoAg-MOFNs for SERS to rapid analysis of imidacloprid pesticide residues in citrus

Abstract

In this study, ultra-thin metal-organic framework nanosheets (MOFNs) was used for preparing the enhanced substrate to rapidly detect the imidacloprid residues in citrus based on Surface-Enhanced Raman Scattering (SERS) technology. Ultrasonic stripping method was used to prepare Co-MOFNs nanosheets. And CoAg-MOFNs enhanced substrate was made by loading AgNPs on the Co-MOFNs nanosheets to enhance SERS signal. The effects of the concentration of AgNPs, the ratio of Co-MOFNs to AgNPs, the mixing time between the prepared enhanced base and imidacloprid standard solution on SERS peak intensity were investigated, which showed that when the concentrated volume of AgNPs was 20 times, and the mixed volume ratio of Co-MOFNs and AgNPs was 1:1, the prepared CoAg-MOFNs had good SERS enhanced effect. And the SERS response was the best when the CoAg-MOFNs nanocomposite was mixed with imidacloprid pesticide for 1 min. Utilizing density functional theory (DFT), four Raman characteristic peaks, specifically at 764, 784, 942 and 1035 cm–1, were identified for the qualitative and quantitative assessment of imidacloprid pesticide residues in citrus fruits. A quantitative analysis curve representing imidacloprid residues was developed, correlating the intensity at 1035 cm–1 over a range of 0.5 to 50 mg kg–1 (y = 2.7964x + 26.211, R2 = 0.9923), demonstrating a strong linear relationship. The limit of detection (LOD) was 0.5 mg kg–1, and the limit of quantitation (LOQ) was 0.5 mg kg–1. which can meet the maximum residue limit (MRL) of 1 mg kg–1 stipulated by the Codex Alimentarius Commission (CAC) and European Union (EU). The recoveries were 93.02% ~ 101.07%, and RSD was 2.57% ~ 7.71%, indicating that the prepared CoAg-MOFNs nanocomposite combined with SERS method for analysis of imidacloprid pesticide residues in citrus was feasible.