An integrated distance-based microfluidic aptasensor for visual quantitative detection of Salmonella with sample-in-answer-out capability

A portable distance-based microfluidic aptasensor with sample-in-answer-out capability was designed for equipment-free, in-filed, visual quantitative detection of Salmonella by microcolumns-based vortex on-line micromixing and incubation, nitrocellulose membranes fixed with single-strand binding proteins (SSBP-NCMs)-based enrichment and separation, and distance-readout based visual quantitative detection. Specifically, aptamers modified with biotin (bio-aptamers) were used as detection probes and reacted with Salmonella typhimurium. The replaceable SSBP-NCMs with high adsorbability captured free bio-aptamers, making the microfluidic chips reusable. The formed bio-aptamer-SSBP-NCMs combined with horseradish peroxidase con-jugated streptavidin (HRP-SA) which catalyzes hydrogen peroxide (H2O2) to produce oxygen (O2). O2 pushed the red gold nanoparticles (GNPs) to move a certain distance along serpentine channel. Hence, the readable distance signals were proportional to the concentrations of Salmonella in samples. The developed distance-based micro -fluidic aptasensor can detect Salmonella typhimurium as low as 3.7 x 101 cfu mL-1 and exhibited a good spec-ificity and reliability.

Automated summary

A portable and equipment-free microfluidic aptasensor was developed for on-site quantitative detection of Salmonella. This aptasensor utilized microcolumns-based vortex micromixing and incubation, nitrocellulose membranes with single-strand binding proteins (SSBP-NCMs) for enrichment and separation, and distance-readout for visual quantitative detection. The aptasensor showed good specificity and reliability, and could detect Salmonella typhimurium as low as 3.7 x 101 cfu mL-1.