Highly Sensitive, Selective and Portable Sensor Probe Using Germanium-Doped Photosensitive Optical Fiber for Ascorbic Acid Detection.

Ascorbic acid (AA) works as an antioxidant and plays a key role in the regulation of immune system and health maintenance. Low level of AA causes disease like scurvy whereas, its higher-level induces stomach throes in human body. So, for the detection of AA, a sensitive sensor probe is fabricated by splicing a short section of highly germanium (Ge)-doped photosensitive fiber (PSF) to a single-mode fiber. In the present study, PSF’s core is easily expanded by etching with hydrofluoric acid because PSF’s core is 5-times Ge-doped. It also helps in partial removal of cladding. Thereafter, gold nanoparticles (AuNPs) are immobilized over the sensing probe for localized surface plasmon resonance (LSPR) phenomena. Further, graphene oxide (GO) is decorated over the AuNPs-coated sensor probe. The AuNPs and GO helps to increase the sensitivity and biocompatibility of sensor probe. Ascorbate oxidase from Cucurbita species has been used to increase the specificity of the sensor. The developed sensor probe has been characterized by the UV-Visible spectrophotometer, high-resolution transmission electron microscope (HR-TEM), TEM - Energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM), and SEM-EDS. The sensor exhibited a wide linear range of detection from $1~\mu \text{M}$ to 1 mM, with 3.5 %/mM of sensitivity. A detection limit of proposed sensor is found to be $15.12~\mu \text{M}$ , which is lower than the physiological AA level in serum of healthy human body (40 – $120~\mu \text{M}$). The selectivity of sensor probe has been verified by performing the experiments with various other biomolecules present in serum. The proposed LSPR sensor has many advantages such as low cost, less fragile probe, remote sensing, low electromagnetic interference, online monitoring, detection from micro-droplets, low detection limit, fast response, highly sensitive, and high specificity. [ABSTRACT FROM AUTHOR]