Entropy-driven assembly of DNA networks coupled with polarity-flipping effect: PEC-CL dual-mode synergy for ultrasensitive detection of Staphylococcus aureus.

Foodborne pathogens pose a serious threat to food safety, often leading to foodborne illnesses and even death. The most effective way to prevent disease outbreaks is to implement rapid, sensitive, and accurate detection methods. Here, we develop a dual-mode biosensor based on the synergistic mechanism of entropy-driven DNA network self-assembly and photoelectrochemical polarity reversal for the highly sensitive detection of Staphylococcus aureus. The sensor is activated by target bacteria, which trigger an entropy-driven DNA circuit and initiate cascaded assembly of DNA networks that efficiently load Cu2O-CuO nanocomposites. These nanocomposites precisely modulate the interfacial band structure of the In2S3-MXene heterojunction, induce a reversal in the direction of photogenerated charge carrier migration, and enable a pronounced anodic-to-cathodic polarity flip in the photoelectrochemical response. This transformation yields a detection signal with an enhanced signal-to-noise ratio. Concurrently, the DNA network assembly activates a catalytic hairpin self-assembly reaction, generates G-quadruplex/Hemin DNAzymes that catalyze the chromogenic reaction of TMB, and produces a visual colorimetric signal. This dual-mode platform enables orthogonal signal validation. Under optimized conditions, the biosensor achieves a linear detection range from 1 to 1 × 109 CFU/mL for S. aureus, with detection limits of 1.11 CFU/mL (photoelectrochemical mode) and 2.03 CFU/mL (colorimetric mode). The sensor also demonstrates​high selectivity and robust anti-interference performance. By integrating DNA network assembly with polarity modulation, this work provides a novel approach for the high-performance detection of foodborne pathogens.