RESUMEN
A direct competitive immunosensor for the electrochemical determination of Imidacloprid (IMD) pesticide on gold nanoparticle-modified screen-printed carbon electrodes (AuNP-SPCE) is here reported for the first time. Self-obtained specific monoclonal antibodies are immobilized on the AuNP-SPCE taking advantage of the AuNPs biofunctionalization abilities. In our biosensor design, free IMD in the sample competes with IMD conjugated with horseradish peroxidase (IMD-HRP) for the recognition by the antibodies. After that, 3,3',5,5'-Tetramethylbenzidine (TMB) is enzymatically oxidized by HRP, followed by the oxidized TMB reduction back at the surface of the SPCE. This process gives an associated catalytic current (analytical signal) that is inversely proportional to the IMD amount. The main parameters affecting the analytical signal have been optimized, reaching a good precision (repeatability with a RSD of 6%), accuracy (relative error of 6%), stability (up to one month), selectivity and an excellent limit of detection (LOD of 22â¯pmolâ¯L-1), below the maximum levels allowed by the legislation, with a wide response range (50-10000â¯pmolâ¯L-1). The detection through antibodies also allows to have an excellent selectivity against other pesticides potentially present in real samples. Low matrix effects were found when analysing IMD in tap water and watermelon samples. The electrochemical immunosensor was also validated with HPLC-MS/MS, the reference method used in official laboratories for IMD analysis, through statistical tests. Our findings make the electrochemical immunosensor as an outstanding method for the rapid and sensitive determination of IMD at the point-of-use.
Asunto(s)
Técnicas Biosensibles/métodos , Inmunoensayo/métodos , Nanopartículas del Metal/química , Neonicotinoides/análisis , Nitrocompuestos/análisis , Plaguicidas/análisis , Anticuerpos Inmovilizados/inmunología , Anticuerpos Monoclonales/inmunología , Armoracia/enzimología , Bencidinas/química , Citrullus/química , Agua Potable/análisis , Técnicas Electroquímicas/instrumentación , Técnicas Electroquímicas/métodos , Electrodos , Contaminación de Alimentos/análisis , Oro/química , Peroxidasa de Rábano Silvestre/química , Límite de Detección , Solanum lycopersicum/química , Neonicotinoides/inmunología , Nitrocompuestos/inmunología , Plaguicidas/inmunología , Contaminantes Químicos del Agua/análisis , Contaminantes Químicos del Agua/inmunologíaRESUMEN
Imidacloprid (IMD) is one of the most used pesticides worldwide as a systemic insecticide as well as for pest control and seed treatment. The toxic and potential carcinogenic character of IMD makes its monitoring of great relevance in the field of agriculture and environment, so sensitive methodologies for in field analysis are strongly required. In this context, we have developed a competitive immunoassay for the determination of IMD using specific monoclonal antibodies followed by electrochemical detection on screen-printed carbon electrodes (SPCE). The optimized immunosensor exhibited a good reproducibility (RSD of 9%) and a logarithmic response in the range 50-10 000 pM of IMD, with an estimated detection limit (LOD) of 24 pM, which was below the maximum levels allowed by the legislation. High-Performance Liquid Chromatography-Mass Spectrometry-Mass Spectrometry (HPLC-MSMS) and Enzyme-Linked Immunosorbent Assay (ELISA) analysis were also performed for comparison purposes, where the electrochemical immunosensor exhibited a wider range of response and a lower detection limit. Matrix effects below 6.5% were obtained using tap water samples. All these characteristics make our electrochemical immunosensor a valid and advantageous tool for the in field determination of IMD.