Dual-mode biosensing system based on stimuli-responsive DNA hydrogel and polyadenine-AuNPs for sensitive and rapid detection of Escherichia coli O157:H7.

Escherichia coli O157:H7 (E. coli O157:H7) poses public health risks due to its low infectious dose and high pathogenicity, highlighting the need for rapid, sensitive detection methods. We report a dual-mode colorimetric/fluorescent biosensor based on a stimuli-responsive DNA hydrogel and polyadenine (polyA)-gold nanoparticles (AuNPs) for detecting E. coli O157:H7. A polyacrylamide/DNA hybrid hydrogel with a FAM-labeled, polyA10-extended aptamer serves as the matrix. Target recognition induces aptamer release and hydrogel disassembly, triggering AuNP dispersion via polyA10 strands and fluorescence enhancement by aptamers. The sensor shows linear colorimetric and fluorescent responses over 1 × 103-1 × 109 CFU/mL, with detection limits of 97 CFU/mL (colorimetric) and 1 CFU/mL (fluorescent). In milk, mutton, and fish samples, recoveries of 95.6%-108.3% with relative standard deviations (RSDs) below 2.3% confirm high accuracy and reproducibility. This study introduces a dual-mode detection approach, combining "homologous activation and heterogeneous output," enabling rapid screening and quantitative analysis, offering a method for pathogen monitoring in food.