Electrochemical bioassay based on l-lysine-modified magnetic nanoparticles for Escherichia coli detection: Descriptive results and comparison with other commercial magnetic beads

Abstract

This paper describes the synthesis and biofunctionalization of magnetic nanoparticles (MNPs) of about 10 nm obtained by the coprecipitation method under alkaline conditions. These homemade nanoparticles were conveniently modified with l-lysine and glutaraldehyde and used as solid support for the immunochemical determination of Escherichia coli. Biofunctionalized MNPs were characterized by X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), Atomic Force Microscopy (AFM), and thermogravimetric analysis. Electrochemical detection was based on a sandwich Enzyme-Linked Immuno Magnetic Electrochemical (ELIME) method using a primary antibody (capture antibody, Ab1) and an HRP-labeled antibody (secondary, Ab-HRP). The enzymatic by-product was measured by constant potential amperometry. In the work described here, a quantitative determination of E. coli was achieved with a linear working range between 266 and 1 × 106 CFU mL−1 and a detection limit of ca. 80 CFU/mL. The sensitivity and the cross-reactivity of the proposed method against E. coli were tested using other commercial magnetic beads such as epoxy and undecaldehyde-modified MNPs and various potential interferences such as Pseudomonas aeruginosa, Enterococcus faecalis, Salmonella enterica, and Acinetobacter baumannii. The results showed similar analytical properties between the different commercial approaches and the homemade MNPs. This fact makes the MNP-Lys a very promising material for its integration into electrochemical sensing platforms.