A microfluidic colorimetric biosensor for in-field detection of Salmonella in fresh-cut vegetables using thiolated polystyrene microspheres, hose-based microvalve and smartphone imaging APP

A microfluidic colorimetric biosensor was developed using thiolated polystyrene microspheres (SH-PSs) for aggregating of gold nanoparticles (AuNPs), a novel hose-based microvalve for controlling the flow direction, and a smartphone imaging APP for monitoring colorimetric signals. Aptamer-PS-cysteamine conjugates were used as detection probes and reacted with Salmonella in samples. Complementary DNA - magnetic nanoparticle (cDNA - MNP) conjugates were used as capture probes, reacted with the free aptamer-PS-cysteamine conjugates. AuNPs were aggregated on the surface of Salmonella-aptamer-PS-cysteamine conjugates, resulting in a visible color change in the detection chamber, which indicating different concentrations of Salmonella. The limit of detection was low to 6.0 × 101 cfu/mL. The microfluidic biosensor exhibited a good specificity. It was evaluated by analyzing salad samples spiked with Salmonella. The recoveries ranged from 91.68% to 113.76%, which indicated its potential application in real samples.