Cascaded Gravity-Driven Microfluidic Chip with Tilt-Actuated Siphon Valves for Rapid Detection of <i>Salmonella</i> Typhimurium

In recent years, urgent food safety issues have heightened the demand for rapid detection technologies for foodborne pathogens, especially biosensors featuring simplicity, rapidity, and high sensitivity. Yet despite a booming surge in related published studies, commercializing these biosensors remains a constant challenge and persistent objective for researchers. In this study, a gravity-driven microfluidic chip with tilt-actuated siphon valves was developed, integrating silica magnetic beads based nucleic acid separation and recombinase-aided amplification (RAA) detection of <i>Salmonella</i> Typhimurium by simple operations along with a portable biosensing device. By chip inclination, the balance between gravity of reagents and capillary force around siphon valves is altered; thus, simple tilting operations could provide a driving force for fluid flow without the need for external pumps. Siphon valves were designed geometrically with surface modifications to generate comfortable tilting angles, and a chip holder with a built-in angle guide was designed to ensure consistent operational performance. A smartphone app was developed to monitor fluorescence signals for quantitative detection of <i>S</i>. Typhimurium. Experimental results showed that this portable biosensing device could detect <i>S</i>. Typhimurium in spiked chicken samples at concentrations as low as 1.1 × 10¹ CFU/mL within 60 min, with recovery rates ranging from 91.54% to 117.27%. The siphon valves also demonstrated compatibility with diverse liquid properties, offering scalability and adaptability for various detection scenarios and potential for the detection of various pathogens in food safety and clinical diagnostics by using related nucleic acid probes and reagents.