Rapid detection of brucellosis by a two-signal vertical flow immunoassay based on sea urchin-like gold nanoparticles.

Brucellosis, a chronic zoonotic disease caused by Brucella, poses a significant threat to global public health and safety. While vertical flow immunoassay (VFI) is an effective tool for detecting brucellosis, its low sensitivity and poor quantitative ability significantly limit its application in brucellosis detection. Therefore, in this study, a dual-mode signal output technique was designed for rapid detection of brucellosis using the photothermal properties of sea urchin-like gold particles (ULGNs). ULGNs were prepared using the hydroquinone reduction method, and their localized surface plasmon resonance (LSPR) peaks could be easily tuned to the near-infrared (NIR) range by controlling the surface spikes. Subsequently, the ULGNs were detected using a Staphylococcus aureus protein A(SPA) probe coupled to the ULGNs. The colorimetric signal, observed by the naked eye, could show the results within 10 min, and its minimum detection limit was 2 IU mL. In addition, the ULGNs, irradiated at 808 nm, increased the temperature rapidly. Detecting the temperature difference at the T-points, with the minimum detection limit of 0.8 IU mL, which was 2.5-fold amplified compared with the colorimetric signal, enabled the rapid output of the photothermal signals. In addition, based on the temperature change of the T-point, it is possible to preliminarily quantify the antibody level in the patient's body, providing a rapid preventive effect. Therefore, ULGNs-VFI effectively improved the detection sensitivity and quantitative accuracy. The method has no cross-reactivity with human S. aureus, sheep enterococcus faecalis, human mycobacterium tuberculosis-positive serum samples, as well as rabbit E. coli, and has exceptional specificity and stability. Therefore, ULGNs-VFI has the potential for practical application in brucellosis POCT detection.