Quantum dot-to-dye-based fluorescent ratiometric immunoassay for GFAP: a biomarker for ischaemic stroke and glioblastoma multiforme

Ischaemic stroke and glioma, as leading causes of mortality and long-term disability, pose critical challenges to healthcare systems, necessitating innovative approaches to enable early and cost-effective diagnosis for timely intervention. Glial fibrillary acidic protein (GFAP), an astrocyte-produced protein, is highly responsive to both ischaemic stroke and glioblastoma multiforme, with its levels correlating to the extent of brain damage. In this study, we present the development of an immunoassay probe for the ratiometric fluorescent detection of glial fibrillary acidic protein (GFAP), employing a monoclonal GFAP antibody-conjugated silicon quantum dots (Ab@SiQDs) and rhodamine B dye (RhB)-based immunoprobe. The developed probe exhibited a fluorescence emission shift from 580 nm to 530 nm in response to GFAP, demonstrating a linear detection range from 31.15 pg mL^-1 to 243 pg mL^-1, with a limit of detection of 0.7 pg mL^-1. Additionally, the immunoprobe showed high selectivity for GFAP, effectively discriminating it from other potential interfering biomolecules and ions. The probe was also capable of detecting GFAP in spiked serum samples, achieving a recovery rate ranging from 83% to 111%. Notably, a cost-effective paper strip assay was developed, offering significant potential for the visual detection of GFAP under ultraviolet illumination.