Dual-signal flow measurement immunoassay based on polydopamine-coated gold nanoparticles quenching quantum dots for the simultaneous detection of clorprenaline and zilpaterol

The illicit use of clorprenaline and zilpaterol as livestock feed additives leads to harmful residues in food. With the use of polydopamine-coated gold nanoparticles (Au@PDA) quenching quantum dots (QDs), we developed a dual-signal immunochromatographic technique that allows for signal readout in 15 min using both colorimetry and fluorescence. The method exhibited high quantitative sensitivity, with limits of quantification (LOQ) of 5.5 μg/L for clorprenaline and 1.2 μg/L for zilpaterol, and limits of blank (LOB) of 0.56 μg/L and 0.24 μg/L, respectively. Notably, for potential semi-quantitative or rapid screening applications, the method demonstrated low visual limits of detection (vLOD): as low as 0.01–0.1 μg/L in fluorescence mode and 1–5 μg/L in colorimetric mode for zilpaterol and clorprenaline. The technique also showed strong stability and good specificity, with test strip findings comparable to those of commercially available ELISA kits, in spiking recovery tests, which primarily target their monitoring in pork. It was also successfully applied to swine urine. Therefore, the proposed method enables rapid detection of clorprenaline and zilpaterol, demonstrating promising potential for on-site sample screening.