Signal Enhancement in Immunoassays via Coupling to Catalytic Nanoparticles.

Early diagnosis is vital for effective disease management, selection of appropriate treatment regimes, and surveillance and control of disease transmission. There is a growing need for point-of-need diagnostic platforms, such as lateral flow immunoassays (LFIAs), to reduce healthcare burdens, particularly in low-resource settings. However, LFIAs often suffer from inadequate sensitivity and exhibit limited dynamic ranges, leading to late-stage diagnosis or misdiagnosis. Here, we present a signal enhancement platform for use in both plate- and paper-based immunoassays, based on the formation of a coupled nanoparticle network. We demonstrate the coupling of an antigen-targeting detection probe with a secondary, catalytically active nanoparticle by utilizing secondary antibody interactions. Here, we show that signal enhancement is achieved through two functional mechanisms: network formation, facilitated by the secondary nanoparticle increasing the relative concentration of nanoparticles immobilized at the test zone; and the inclusion of catalytically active nanoparticles, which catalyze the oxidation of a chromogenic substrate at the test zone. Through this approach, we yielded a 40-fold improvement in the limit of detection (LOD) using 40 nm gold nanoparticle detection probes in spiked pooled human saliva. Further, the signal enhancement platform can be utilized alongside a range of detection probes, including gold nanoparticles, commonly employed for use in LFIAs. This work concludes by showcasing that the signal enhancement mechanism is compatible for use with complex sample matrices, such as human saliva.