A reusable QCM biosensor with stable antifouling nano-coating for on-site reagent-free rapid detection of E. coli O157:H7 in food products

Numerous biosensors have shown exceptional analytical performance under laboratory conditions, yet only a few are capable of on-site use with complex, non-model samples while exhibiting reliable analytical performance. Here, we present a new portable biosensor for the rapid (30 min) and accurate detection of bacterial agents in "real-world" food samples, which are originally in either solid or liquid form. The biosensor combines well-established quartz crystal microbalance (QCM) technology, with innovative terpolymer brush nano-coatings on the sensing surface to efficiently reduce non-specific fouling from food samples. Following reagent-free sample preparation, where solid food samples are homogenized, we validated the sensor's detection capabilities on native pathogenic Escherichia coli O157:H7 (E. coli O157:H7) in hamburgers, Czech dumplings, and milk. We achieved limits of detection (LOD), as low as 7.5 × 102 CFU/mL in milk, a value approaching fundamental QCM limits, using a simple direct detection assay format. The biosensor's exceptional reusability was demonstrated through 60 sequential hamburger sample injections, resulting in only a minor LOD shift toward the end of the series. A 10-minute sonication treatment during sample preparation significantly enhanced sensitivity for E. coli O157:H7 in hamburgers and dumplings, yielding LODs as low as 3.1 × 10³ CFU/mL and 2.6 × 10⁴ CFU/mL, respectively. For on-site analysis, we integrated the nano-coated sensing chip into a custom-built four-channel portable QCM biosensor with an optimized microfluidic system, which can be produced on a scale suitable for practical deployment.