Magnetic nanochains-enhanced finger-actuated microfluidic biosensor for rapid Salmonella detection

Salmonella Typhimurium, a major foodborne pathogen, poses significant threats to public health and food safety, highlighting the need for rapid, sensitive, and field-deployable detection tools. Here, we present a portable microfluidic biosensor that uniquely integrates magnetic chain-assisted enrichment, nanozyme-catalyzed colorimetric detection, and smartphone readout into a single, finger-actuated platform. First, magnetic nanobeads were self-assembled into ordered magnetic nanochains (Magchains) under a uniform magnetic field, enabling effectively stationary, high-surface-area capture probes. Rotational flow around these anchored chains created high-frequency probe-target collisions, overcoming diffusion limitations. Second, Au@Pt nanozymes provided robust and stable peroxidase-mimicking activity, enabling sensitive and visually stable colorimetric readouts. Finally, the chip's pneumatic control allowed sequential enrichment, washing, and detection without external pumps or complex instrumentation. The biosensor achieved a broad linear range (6.3 × 10¹-6.3 × 10⁶ CFU/mL) and a detection limit of 32 CFU/mL within 30 min. Tests with spiked chicken samples confirmed high accuracy and reproducibility in complex food matrices. This platform offers a promising solution for point-of-care detection of foodborne pathogens in resource-limited settings.