Polydopamine-modulated anisotropic co-growth plasmonic blackbody for efficient ultra-broad-spectrum quenching to establish multicolor fluorescent immunoassay

Fluorescence quenching immunoassays have received increasing attention due to their high signal-to-noise ratio, among which multi-color fluorescence quenching methods have great advantages in detecting multiple targets. Preparing an efficient and broad-spectrum quencher is a prerequisite for establishing high-performance multicolor fluorescence quenching immunoassays. In this study, we propose a polydopamine (PDA) modulated seedless co-growth method to synthesize anisotropic plasmonic blackbody (APB) with highly branched chrysanthemum −like shape for efficient ultra-broad-spectrum quenching and utilize APB to establish a sensitive multicolor fluorescent immunoassay. The key to APB synthesis lies in the reduction of Au3+ by dopamine, which simultaneously undergoes oxidation and self-polymerization in situ to form a PDA film. This film continuously deposits on the Au crystal seeds, creating a robust end-capping effect and inducing continuous anisotropic growth of Au. The dual synergistic effects of PDA and the unique 3D-spatial structure contribute to APB's robust ultra-broad-spectrum UV absorption (6.86 × 1011 L cm−1 mol−1) from 300 to 800 nm, along with efficient ultra-broad-spectrum fluorescence quenching ability (90.1 %). This quenching ability extends to various types of fluorescence microspheres covering the range of 300–800 nm with different excitation and emission spectra. Subsequently, we applied APB in the development of a multicolor fluorescence quenching immunochromatographic assay, enabling simultaneous detection of chloramphenicol (limit of detection, LOD = 0.0045 ng/mL) and sulfadimidine (LOD = 0.038 ng/mL) in milk. This research not only offers a novel direction for designing efficient broad-spectrum quenchers but also advances the practical application of fluorescence quenching sensors.