Fluorescent Nanoprobes with Oriented Modified Antibodies to Improve Lateral Flow Immunoassay of Cardiac Troponin I

Performance of nanoprobes can often determine the detection level of Lateral immunochromatography. Traditional probes were limited by the quantity and orientation of antibodies, immune activity of the Fab region or binding strength between protein and substrate. This study developed a new efficient and robust technology to construct fluorescent nanoprobes with oriented modified antibodies, based on specific binding of the Fc region of antibody with streptococcal protein G (SPG) on the surface of polystyrene microspheres (MS) and subsequent covalent cross-linking at binding sites to firm them. Lateral flow immunoassay using these probes was applied for the detection of cardiac troponin I (cTnI). The significantly improved detection sensitivity demonstrated that antibody orientation on MS surfaces effectively enhanced immunological activities of probes compared with random immobilizing methods. Furthermore, performance evaluation results of lateral flow test strips met clinical requirements perfectly, including limit of detection (0.032 ng/mL), linearity (R > 0.99), repeatability (CV < 10%), correlation (R > 0.99), and heat aging stability. This research also employed heterophilic blocking reagent (HBR) to actively block redundant binding sites of SPG for the first time in order to eliminate false positive interferences, improving the sensitivity and precision of test results further.