Au@Ag, Au@Pd, Au@Pt and Au@Ir Nanoparticles as Colorimetric and Peroxidase-Like Labels for Lateral Flow Assays

Lateral flow assays (LFAs) are an indispensable point-of-care (POC) diagnostic tool. While it is fast, accessible, and user-friendly, LFAs often suffer from limited sensitivity (high limit of detection – LOD). One widely adopted strategy to overcome this limitation involves replacing conventional gold nanoparticle (Au NP) labels with alternative nanomaterials. Utilizing more efficient colorimetric labels preserves all the advantages of LFA as a POC method while improving LOD. Alternative nanomaterial-based labels may exhibit catalytic activities, allowing for signal amplification and further improvement in sensitivity. In this study, we investigated the optical and catalytic properties of core@shell NPs to evaluate their performance as labels for LFAs. A total of 67 core@shell NPs, comprising Au cores and Ag, Pd, Pt, or Ir shells with varying thicknesses (0.5–50 nm) were synthesized. For the first time, we comprehensively examined the relationship between composition, morphology, optical behavior, and catalytic performance across these core@shell NPs. We used two parameters for evaluating nanoparticles as LFA labels: integrated extinction in the visible range (380–750 nm) and specific peroxidase-like activity. Based on these parameters, we concluded that their LOD values on nitrocellulose membranes do not improve significantly through optical enhancement alone. A substantial improvement in sensitivity of two to 3 orders of magnitude is associated with NPs exhibiting high peroxidase-like activity. This work has demonstrated the universal applicability of the proposed parameters as reliable descriptors for nanoparticle performance in LFAs.