A colorimetric biosensor for Escherichia coli detection in food based on aptamer-enhanced oxidase-mimicking activity of octahedral Ag₂O nanoparticles

Abstract

Escherichia coli (E. coli) poses a grave threat to food safety, underscoring the need for expeditious and precise detection methodologies. Conventional colorimetric approaches are simple, but they frequently lack accuracy and stability. This study constructed an aptamer-based colorimetric biosensor, leveraging the enzyme-mimicking activity of octahedral Ag₂O nanoparticles (NPs), mediated by oligonucleotides, aiming for highly sensitive foodborne E. coli detection. The P12-55 aptamer can be adsorbed onto the octahedral Ag₂O NPs surface, thereby significantly enhancing their oxidase-mimicking activity. The aptamer enhances activity by promoting ·O₂⁻ generation, and accelerating electron transfer to the 3,3',5,5'-tetramethylbenzidine (TMB) substrate. In the presence of E. coli in the sensing system, the aptamer exhibits a preferential binding affinity for the bacteria, thereby restoring the oxidase-mimicking activity and enabling the transduction of the detection signal. The biosensor exhibited a range of linear detection of 3 × 10²–3 × 10⁸ CFU·mL⁻¹, and the limit of detection (LOD) was as low as 4 CFU·mL⁻¹. Recovery rates of 99.1% to 104% were achieved in milk and tap water samples, demonstrating outstanding practicality and reliability. This study proposes a novel and efficient method for the rapid detection of harmful bacteria in food, which is of significant importance for food safety assurance.

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