Water-soluble noncovalently engineered graphene-neutral red nanocomposite with photocurrent generating capacity

A non-enzymatic electrochemical immunoassay for quantitative detection of Escherichia coli O157:H7 using Au@Pt and graphene

Herein, a non-enzymatic sandwich-type electrochemical immunoassay was fabricated for quantitative monitoring of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated Fe₃O₄ magnetic nanoparticles (Fe₃O₄@SiO₂) were modified with mouse anti-E. coli O157:H7 monoclonal antibody (Ab₁) to act as capture probes to reduce detection time and increase the sensitivity of the immunoassay. The Au@Pt nanoparticles were loaded on neutral red (NR) functionalized graphene to form composite complex rGO-NR-Au@Pt. rGO-NR-Au@Pt has high specific surface area and good biocompatibility. rGO-NR-Au@Pt was used as the carriers of detection antibodies (Ab₂). Au@Pt catalyzed the reduction of hydrogen peroxide (H₂O₂) to detection of E. coli O157:H7 with the thionine (TH) as electron mediator to effectually amply the current signal. Under the optimized conditions, a linear relationship between the reduction peak current change (ΔI_pc) and the logarithm of the E. coli O157:H7 concentration is obtained in the range from 4.0 × 10³ to 4.0 × 10⁸ CFU mL^-1 and the limit of detection (LOD) is 4.5 × 10² CFU mL^-1 at a signal-to-noise ratio of 3. The immunoassay exhibits acceptable specificity, reproducibility and stability on the detection of E. coli O157:H7. Furthermore, the immunoassay showed good performance in pork and milk samples. The results suggest that this immunoassay will be promising in the food safety area.