Integrated sample-in-result-out microfluidic biosensor for rapid ultrasensitive detection of Salmonella typhimurium...

Salmonella typhimurium (S. typhimurium)-induced contamination is emerging as a severe threat to food safety. Therefore, rapid and sensitive detection of S. typhimurium is urgently required. Conventional detection methodologies exhibit persistent limitations. The combination of microfluidic chips with magnetic beads (MBs) for isolating bacteria such as S. typhimurium has emerged as a prominent research focus. However, flexible and tunable magnetic field control methods for optimizing MB chain formation and enhancing the capture efficiency of the target bacteria are lacking. We developed a microfluidic fluorescent biosensor to achieve an efficient on-site detection of S. typhimurium using magnetic bead (MB) chains for continuous-flow electromagnetic separation, a dual-aptamer recognition method for specifically labeling S. typhimurium, and a customized smartphone-based real-time fluorescence system for quantitative detection. Aptamer-conjugated MBs in the separation channel were distributed into high-density bead chains in a high-intensity gradient magnetic field generated by an electromagnetic actuation module. The samples continuously flew through the separation channel, in which the target bacteria were specifically captured by aptamer-conjugated MBs. Aptamer-functionalized fluorescent labels were passed through the separation channel to form bacteria-MB-fluorescent label complexes for quantitative detection. Under optimal conditions, the microfluidic biosensor completed sample-in-result-out detection within 30 min, with a detection limit of 2 colony-forming unit/mL for S. typhimurium. This biosensor can be potentially applied for detecting food pathogens, making it suitable for supervising food production and monitoring catering hygiene.