Nanozyme-Catalyzed Colorimetric Microfluidic Immunosensor for the Filtration Enrichment and Ultrasensitive Detection of Salmonella typhimurium in Food Samples

Rapid screening of foodborne pathogens is crucial to prevent food poisoning. In this study, we proposed a nanozyme-catalyzed colorimetric microfluidic immunosensor (Nano-CMI) for the filtration enrichment and ultrasensitive detection of Salmonella typhimurium in complex matrices. Gold-core porous platinum shell nanopompoms (Au@Pt nanopompoms) were synthesized with excellent peroxidase-like activity to oxidize 3,3',5,5'-tetramethylbenzidine with significant color change. The Au@Pt nanopompoms demonstrated a large reaction area, superior catalytic property, and good stability. The microfluidic chip used in the Nano-CMI was designed based on the size disparities among S. typhi, Au@Pt nanopompoms, and the pore sizes of filters I and II. Thus, a biosensor containing pretreatment, incubation, enrichment, and detection of four-in-one functions was established and performed under the drive of a medical plastic syringe. This biosensor can accomplish ultrasensitive detection of S. typhi with a limit of detection as low as 9 cfu/mL within 20 min, which makes it suitable for point-of-care testing. The proposed Nano-CMI also possessed high specificity and good repeatability (RSD < 2.1%) and can thus be applied directly to the analysis of real food samples, suggesting its great potential for practical application in the food safety field.