Nanozyme-Catalyzed Colorimetric Microfluidic Immunosensor for the Filtration Enrichment and Ultrasensitive Detection of <i>Salmonella typhimurium</i> 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 <i>Salmonella typhimurium</i> 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 <i>S. typhi</i>, 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 <i>S. typhi</i> 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.