Sensitivity evaluation of an optical microfiber featuring interfaces with various gold nanoparticle morphologies: Application to the GFAP detection.

Glial fibrillary acidic protein (GFAP) is a specific blood biomarker for various neurological diseases, including traumatic brain injury (TBI). In this study, we present a cost-effective, portable, and label-free biosensing method for the sensitive and rapid detection of GFAP in body fluids. As the sensitivity of current optical fiber sensors is insufficient to detect the ultralow concentration of GFAP in early body fluids, interfaces of gold nanoparticles with various morphologies were employed to improve the sensitivity of sensor. The optical microfiber sensor with gold nanostar interface demonstrated superior evanescent field enhancement compared to other gold interfaces, thereby enabling the optical microfiber sensor with gold nanostar interface to exhibit higher sensitivity. This sensor detected GFAP at concentrations ranging from 1 aM to 0.1 nM, with a limit of detection (LOD) of 0.09 aM in phosphate buffered saline (PBS) solution, being capable of detecting GFAP molecules at the single-molecule level. The compactness, portability, and high selectivity of the biosensor allow for its use in detecting GFAP in body fluids, such as serum and artificial cerebrospinal fluid (CSF), with LODs of 0.21 aM and 0.1 aM, respectively. This study introduces a valuable tool for the early diagnosis of TBI. The ultra-sensitive detection of GFAP in serum provides information on the severity of TBI in addition to imaging techniques.