Palladium-platinum bimetallic nanomaterials and their application in Staphylococcus aureus detection on paper-based devices

In this study, we demonstrate how palladium@platinum nanoparticles (Pd@Pt NPs) can be used as a nanozyme for the detection of Staphylococcus aureus (S. aureus) on a paper-based analytical device. Pt was doped with Pd to form bimetallic NPs that serve as a peroxidase mimetic, which can enhance the reaction area with a substrate (3, 3', 5, 5'-tetramethylbenzidine, TMB). After material characterization, we show the peroxidase-like activity of the Pd@Pt NPs featured a 13-times higher binding affinity value (K_m) for TMB compared to horseradish peroxidase, which is currently widely used in immunoassays. By incorporating the Pd@Pt NPs in a paper-based immunoassay, we can detect protein A, the biomarker of S. aureus, within 30 min with a detection limit of 9.56 ng/mL. We have also successfully validated this nanozyme-immobilized paper-based analytical device (nPAD) for the detection of human immunoglobulin G to demonstrate the capability of the Pd@Pt NPs for different target analytes. This highly sensitive, rapid, and portable nPAD design has the potential for personalized medicine and point-of-care testing, which could expand on-site prognoses in resource-limited settings.