Signal cascade amplification of streptavidin-biotin-modified immunofluorescence nanocapsules for ultrasensitive detection of glial fibrillary acidic protein

Glial fibrillary acidic protein (GFAP) is one of the discriminative biomarkers for diagnosing traumatic brain injury (TBI), and accurate determination of GFAP is clinically significant. In this study, a novel fluorescence immunoassay system was designed. We encapsulated carbon dots with a high fluorescence quantum yield (QY = 92.5%) inside silicon nanocapsules to serve as fluorescent markers. These markers were then integrated with the streptavidin (SA)-biotin biomagnification system and immunomagnetic separation technology for the sensitive detection of GFAP. Based on the signal cascade amplification effect of the silicon nanocapsules and SA-biotin, the fluorescence signal of the SA-biotin-modified immunofluorescence nanocapsules increased 3.6-fold compared to the carbon dot-based immunoprobe. The fluorescence immunoassay system was constructed for GFAP using SA-biotin-modified immunocapsules as the sensing probe and immunomagnetic nanoparticles as the immunorecognition probe. The fluorescence immunoassay system can specifically and ultra-sensitively quantify GFAP in blood samples, with a detection range of 10 pg/mL–10 ng/mL and detection limits of 3.2 pg/mL (serum) and 3.6 pg/mL (plasma). Moreover, the fluorescence immunoassay system exhibited prominent recoveries of 99.4%–100.4% (phosphate buffered saline), 96%–102.6% (serum), and 93.2%–110.2% (plasma), with favorable specificity and excellent stabilization. The novel fluorescence immunoassay system provides a new approach to the clinical analysis of GFAP and may serve as a potential tool for screening and diagnosing TBI.