Tsai, Wei-JieWei-JieTsaiChen, YehYehChenHsu, Jye-LinJye-LinHsuLin, Hsiao-ChuanHsiao-ChuanLinPO-REN HSUEHLin, Cheng-WenCheng-WenLin2026-04-212026-04-212025-09-01https://scholars.lib.ntu.edu.tw/handle/123456789/737411The ongoing COVID-19 pandemic has underscored the urgent need for rapid, sensitive, and versatile diagnostic tools. In this study, we developed a nanogold-based lateral flow immunoassay (LFIA) capable of detecting both SARS-CoV-2 nucleocapsid (N) protein antigens and anti-N IgG antibodies at the point of care. Following optimization of colloidal gold nanoparticle size, pH, and protein conjugation parameters, LFIA strips were assembled in two formats: a competitive assay for antigen detection and a sandwich assay for antibody detection. In the competitive format, gold nanoparticles (AuNPs)-conjugated N protein were used to detect varying concentrations of free N protein. The test line signal inversely correlated with antigen concentration, confirming the assay’s specificity and effectiveness. For antibody detection, the sandwich LFIA format employed immobilized anti-human IgG to capture anti-N antibodies in serum samples from COVID-19 patients. Strong test line signals were observed in samples collected ≥11 days post-symptom onset, indicating a time-dependent increase in IgG detectability. These results demonstrate that the AuNP-based LFIA platform provides a flexible, rapid, and low-cost diagnostic solution, suitable for both early antigen detection and serological monitoring during SARS-CoV-2 infection and recovery.entruejournal article10.3390/covid50901582-s2.0-105017409901