Colorimetric and handheld pH meter dual-signal readout platform for E. coli detection based on a cascade reaction.

A dual-signal readout has been designed detecting platform based on a cascade reaction for Escherichia coli (E. coli) detection by using colorimetric approach and a handheld pH meter. The immunoreaction was conducted using polydopamine@copper ferrite-Ag nanoparticles (PDA@CuFe2O4-Ag NP) and a glucose oxidase (GOD)–conjugated graphene oxide-gold nanosheet composite (GOD-GO/Au NS) to synthesize a sandwich complex mode between targets. Together with the formation of immune complexes, the GOD-GO/Au NS can catalyze glucose to produce gluconic acid and hydrogen peroxide (H2O2). The gluconic acid produced altered the pH of the detection solution. Since the PDA@CuFe2O4-Ag NP have good peroxidase-like activity, they can catalyze the oxidation of TMB to the blue product oxTMB once H2O2 is produced in the reaction system, and the absorbance change of oxTMB at 652 nm can be recorded using ultraviolet–visible (UV–Vis) spectroscopy. Interestingly, the PDA@CuFe2O4-Ag NP composites can consume the generated H2O2, and can create a reaction cycle that promotes glucose oxidation. Under optimal conditions, the proposed dual-channel signal platform is proportional to the logarithm of the E. coli concentration within a range of 102–107 cfu mL−1. Additionally, the devised approach was successfully used to detect E. coli at the required levels in real samples. This dual-mode detection method notably enhances the accuracy and diversity of detection, and curbs the false negative and positive rates. [ABSTRACT FROM AUTHOR]