Interface coordination achieving excellent optical properties of three-dimensional dendritic gold nanoparticles for immunochromatographic performance

The replacement of traditional 30 – 40 nm gold nanoparticles (AuNPs) by large-sized AuNPs can only limitedly improve the signal intensity of immunochromatographic assay (ICA) due to the conventional seed growth method which requires the perfect lattice matching of Au atom and Au seed to achieve layer-by-layer growth and obtain large-sized AuNP with low absorption and high scattering. In this study, dopamine was introduced to replace sodium citrate as the reductant and polydopamine (PDA) as the stabilizer to prepare 3D dendritic AuNPs (PDA-AuNPs) with high absorption and low scattering, which is crucial in enhancing the sensitivity of the ICA. The dendritic PDA-AuNPs with excellent solubility and broadband absorption at 40, 80, 110, 140, and 170 nm were precisely synthesized by regulating the concentrations of Au seed, and the effect of optical intensity and binding efficiency relative to particle size of PDA-AuNPs on the detection sensitivity of Escherichia coli O157:H7 was further analyzed. The ICA based on 170 nm PDA-AuNPs has the lowest detection limit of 200 CFU/mL, which is over 20 times lower than that of the traditional AuNPs. PDA-AuNPs, the simple-to-prepare labeling materials with high optical performance, show great promise in low-cost and high-performance immunochromatographic platforms.