Growth‐Induced Extinction Development of Gold Nanoclusters as Signal Transducers for Quantitative Immunoassays

Abstract

Signal transducers are crucial in bioassay platforms for converting target detection into recordable signals. Commonly used color development for immunoassays involves enzymes and colorimetric substrates. However, due to cost and environmental issues, practical point‐of‐care testing requires alternative signal transducers. Growth‐induced extinction (absorption and scattering) of gold nanoclusters (AuNCs) is proposed as a novel approach for quantitative immunoassays. AuNCs devoid of localized surface plasmon resonance (LSPR) are used as seeds for growth reactions. Through reactions with a growth solution comprised of gold precursor and mild reductant, AuNCs of varying concentrations underwent controlled growth, resulting in nanoparticles of different sizes exhibiting distinct LSPR‐mediated extinction bands. Notably, the seed concentration exhibited a robust correlation with the resulting extinction of the grown particles on a small scale of 110 µL for a 96‐well microplate platform. To demonstrate this signal transduction mechanism, immunosorbent assays are performed using the conjugates of AuNC and detection antibody. The sandwich‐type assay successfully quantified a model antigen, human immunoglobulin G (hIgG), by monitoring LSPR wavelength and absorbance. This assay demonstrated a working range of 0.001–1 µg mL−1 and limit of detection of 1.19 ng mL−1. Signal transducers using the growth of AuNCs offer new alternative candidates for immunoassay platforms.