Immuno-capture and in situ detection of Salmonella typhimurium on a novel microfluidic chip

• A novel microfluidic chip and a LIF microsystem were designed and fabricated.
• Salmonella typhimurium was captured and labeled by specific immuno-capture on chip.
• CdSe/ZnS quantum dots-labeled bacteria were detected by in situ analysis using LIF microsystem.
• The proposed method has potential application in practice.

The new method presented in this article achieved the goal of capturing Salmonella typhimurium via immunoreaction and rapid in situ detection of the CdSe/ZnS quantum dots (QDs) labeled S. typhimurium by self-assembly light-emitting diode-induced fluorescence detection (LIF) microsystem on a specially designed multichannel microfluidic chip. CdSe/ZnS QDs were used as fluorescent markers improving detection sensitivity. The microfluidic chip developed in this study was composed of 12 sample channels, 3 mixing zones, and 6 immune reaction zones, which also acted as fluorescence detection zones. QDs–IgG–primary antibody complexes were generated by mixing CdSe/ZnS QDs conjugated secondary antibody (QDs–IgG) and S. typhimurium antibody (primary antibody) in mixing zones. Then, the complexes went into immune reaction zones to label previously captured S. typhimurium in the sandwich mode. The capture rate of S. typhimurium in each detection zone was up to 70%. The enriched QDs-labeled S. typhimurium was detected using a self-assembly LIF microsystem. A good linear relationship was obtained in the range from 3.7 × 10 to 3.7 × 105 cfu mL−1 using the equation I = 0.1739 log (C) − 0.1889 with R2 = 0.9907, and the detection limit was down to 37 cfu mL−1. The proposed method of online immunolabeling with QDs for in situ fluorescence detection on the designed multichannel microfluidic chip had been successfully used to detect S. typhimurium in pork sample, and it has shown potential advantages in practice.

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