Development of an electrochemical immunosensor for the determination of molinate by using phages labeled with CdS nanocrystals as a novel strategy to signal amplification

Research on immunoassays and immunosensors is currently focused mainly on the development of strategies to amplify the resulting signal. In this sense, the development of new hapten tracers that allow simpler, more sensitive, and more reliable immunoassays is desirable. Therefore, we present the development of an electrochemical immunosensor using viral particles (phages) bound with dozens of CdS nanocrystals (CdS NCs) as an outperforming alternative to conventional competitive hapten conjugates. This allows us to obtain an multiplicator effect in signal obtained. Therefore, as proof of concept, an electrochemical immunosensor was developed for the detection of the molinate in river water samples, based on a noncompetitive immunoassay using recombinant M13 phage particles labeled with CdS NCs (CdS NCs-phage). The phage particles have on its surface peptides that recognize the molinate/antibody immune complex. Molinate determination was performed by square wave anodic stripping voltammetry of Cd2+ release from CdS NCs. The limit of detection and the midpoint sensitivity obtained were 34 pg mL-1 and 0.43 ng mL-1, respectively. In addition, other very good analytical parameters were obtained, where percent coefficient of variation (%CV) between 5 % and 25 %, and recovery percentages close to 99 % were found. Results obtained were compared with those determined by HPLC-UV visible, obtaining an excellent correlation between both methods. This electrochemical immunosensor was successfully used to analyze molinate in river water samples without pre-treatment, obtaining excellent recoveries.