Use of bimetallic PtAu nanoraspberries as novel labels in lateral flow immunoassays: application for a chronic wound biomarker detection

Lateral flow immunoassays (LFIAs) are widely used point-of-care (POC) diagnostic tools due to their rapid response and ease of naked-eye detection. Gold nanoparticles (AuNPs) are commonly employed for colorimetric readout. However, these AuNP-based systems suffer from a relatively low sensitivity, which limits their application for the detection of low-abundance biomarkers. In this study, we propose the use of bimetallic platinum-gold (PtAu) nanoraspberries (NRs), consisting of a platinum shell surrounded by gold protuberances, as novel detection tags in LFIAs. The PtAu NRs surface morphology allows to enhance the nanoparticle:antibody conjugation ratio and to minimize unspecific absorptions, compared to that of the traditional AuNPs. Moreover, the intense purple coloration of the PtAu NRs provides superior visual contrast against the white background of lateral flow strips. All these features lead to improved performance in terms of sensitivity and specificity compared to the use of AuNPs. We also demonstrate the application of the PtAu NRs in an LFIA platform for the detection of myeloperoxidase (MPO), a key biomarker of chronic wound infection, at clinically relevant levels in artificial wound exudates with also high selectivity versus potential interferents. In addition, semi-quantitative analysis using a smartphone and ImageJ software showed a linear correlation between the normalized color intensity and the logarithm of MPO concentrations over the 50–5000 ng/mL range, achieving an estimated limit of detection of 1.8 ng/mL. These findings highlight the potential of PtAu NRs to improve LFIA performance and lay the groundwork for their use in multiplexed POC diagnostics.