Point-of-use colorimetric detection of Escherichia coli in food matrices with DNAzyme crosslinked hydrogels

Due to the significant healthcare burden associated with foodborne illness, developing platforms suitable for the on-site detection of food pathogens is of critical importance to public health. Low-cost, equipment-free approaches are desired to allow for point-of-use contamination monitoring along the food supply chain. Here, we demonstrate the compatibility of an Escherichia coli responsive colorimetric DNAzyme-crosslinked hydrogel sensor with a wide range of food products. Sensor functionality involves an E. coli detecting DNAzyme-substrate complex that cleaves the hydrogel crosslinking in the presence of the target bacteria, resulting in a release of gold nanoparticles that is visible to the naked eye. Naked-eye detection of E. coli at concentrations of 10⁵ CFU mL^-1 has been shown in milk as well as samples extracted from produce, leafy greens, and ready-to-eat foods such as rotisserie chickens. The functionality, simplicity, and versatility of this sensing platform may improve the feasibility of frequent pathogen monitoring in the food production pipeline, with the potential to mitigate future outbreaks of foodborne illness.