Weakly ionized gold nanoparticles enhance immunoassays for ultrasensitive point-of-care sensors. Researchers developed a surface chemistry strategy using weakly ionized gold nanoparticles (AA-AuNPs) to significantly improve the sensitivity of lateral flow immunoassays (LFIAs). This approach enables ultrasensitive naked-eye detection with up to 100-fold higher sensitivity compared to traditional strongly ionized citrate-coated gold nanoparticles (Cit-AuNPs). The surface chemistry of AA-AuNPs promotes antibody adsorption and enhances the activity of adsorbed antibodies, leading to improved detection of trace biomarkers. The method simplifies the fabrication process, offers excellent reproducibility, and eliminates the need for complex nanosynthesis or additional reagents. The study demonstrates that weakly ionized AA-AuNPs can detect various biomarkers, including α-fetoprotein (AFP), C-reactive protein (CRP), and procalcitonin (PCT), with detection limits as low as 0.5 ng/ml for AFP, 1 ng/ml for CRP, and 50 pg/ml for PCT. The approach was also tested for virus detection, successfully distinguishing between wild-type SARS-CoV-2 and the B.1.1.7 mutant strain. The results show that weakly ionized AA-AuNPs provide a versatile and effective strategy for developing ultrasensitive point-of-care sensors. The study highlights the potential of surface chemistry in enhancing immunoassays for practical applications in diagnostics and healthcare.Weakly ionized gold nanoparticles enhance immunoassays for ultrasensitive point-of-care sensors. Researchers developed a surface chemistry strategy using weakly ionized gold nanoparticles (AA-AuNPs) to significantly improve the sensitivity of lateral flow immunoassays (LFIAs). This approach enables ultrasensitive naked-eye detection with up to 100-fold higher sensitivity compared to traditional strongly ionized citrate-coated gold nanoparticles (Cit-AuNPs). The surface chemistry of AA-AuNPs promotes antibody adsorption and enhances the activity of adsorbed antibodies, leading to improved detection of trace biomarkers. The method simplifies the fabrication process, offers excellent reproducibility, and eliminates the need for complex nanosynthesis or additional reagents. The study demonstrates that weakly ionized AA-AuNPs can detect various biomarkers, including α-fetoprotein (AFP), C-reactive protein (CRP), and procalcitonin (PCT), with detection limits as low as 0.5 ng/ml for AFP, 1 ng/ml for CRP, and 50 pg/ml for PCT. The approach was also tested for virus detection, successfully distinguishing between wild-type SARS-CoV-2 and the B.1.1.7 mutant strain. The results show that weakly ionized AA-AuNPs provide a versatile and effective strategy for developing ultrasensitive point-of-care sensors. The study highlights the potential of surface chemistry in enhancing immunoassays for practical applications in diagnostics and healthcare.