Gold nanolabels for enhanced electrochemical immunoanalysis of Escherichia coli

A novel nanolabel based on gold nanoparticle modified with anti-Escherichia coli (E. coli) peroxidase (HRP)-conjugated antibody has been developed. It was used for enhanced electrochemical immunoanalysis of E. coli. After the immuno-reaction, gold nanolabel, immunoparamagnetic bead (IMB) and E. coli formed a sandwich-type immunocomplex. 3,3',5,5'-Tetramethylbenzidine (TMB) was used as substrate for HRP in the presence of H₂O₂ and the enzyme activity of HRP was measured by electrochemical detection coupled with flow injection assay (FIA). The concentration of E. coli could be confirmed by amperometric response, which was in proportion to the quantity of HRP on the sandwich-type immunocomplex. Gold nanoparticles were used as carriers of antibodies resulting in the increase of antibodies attached to E. coli. Therefore, the amperometric signal was enhanced and the detection sensitivity of E. coli was improved greatly. It showed a good linear relationship between the amperometric responses and logarithmic value of E. coli concentration ranging from 1.0×10² to 5.0×10⁴ cfu·mL^-1, with a detection limit of 50 cfu·mL^-1. By introducing a pre-enrichment step, a wider detection range and lower detection limit could be obtained. The rapid detection could be finished within 1 h, shorter than other methods.