Optical fiber technology, in association with the phenomenon of surface plasmon resonance (SPR), has opened a new gateway for quick, easier, and accurate sensing of various chemical, biochemical, and biological parameters. Continuous efforts can be seen in the direction of increasing the sensitivity of the optical fiber biosensors; thus, many hybrid nanostructured optical fiber biosensors composing different nanomaterials, nanomaterial combinations, and different 2D materials have been proposed in the past few decades. This paper discusses the synthesis, characterization, and applications of nanoparticles to the most favorable noble metal for SPR biosensing, i.e., gold. The gold nanoparticles (AuNPs) were prepared by the Turkevich method, and the optical property of AuNPs was characterized using the UV-visible spectrophotometer and transmission electron microscopy (TEM) technique. In addition, the synthesis, characterization, and application of the oxide form the most explored 2D material, i.e., graphene, are also presented in this paper. The graphene oxide was synthesized using an easier and economical method, i.e., a modified Hummer’s method, and an evaluation of the characteristics has been done by a UV-visible spectrophotometer and TEM results.

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Ascorbic acid, genreally known as Vitamin ‘C’, is a nutrient, which is responsible for numerous biological functions like collagen formation, iron absorption, growth and repair of cells, tissues, bones, cartilages, teeth etc. It plays a promising role in providing a healthy immunity against bacterial and viral infections. It also helps in making several chemical messenger and hormones, thus playing importance in the nervopus system of body. Thus, ascorbic acid is a biomarker for the detection of various malfunctionings of the body like weakened immunity, scurvy, cardiovascular diseases, Alzheimer’s and Parkinson’s disease. In this work, a straightforward and effectual sensor model is proposed to detect the presence of ascorbic acid samples found in human body. Etched single mode fiber-multimode fiber-single mode fiber (E-SMS) is used for developing the sensor with the application of localized surface plasmon resonance (LSPR) phenomenon. For achieving LSPR and better sensitivity, the E-SMS are coated with gold nanoparticles (AuNPs). The different concentration of ascorbic acid solution alters the refractive index and the spectrum thus recorded and evaluated. The experimental results shows that the proposed E-SMS-based LSPR biosensors can detect the presence of ascorbic acid in human body and thus have significant application in the field of biosensing.

Dopamine, an important neurotransmitter, can play both excitatory as well as inhibitory role in human body by either exciting the receptors on postsynaptic membrane or by inhibiting or suppressing them. It plays crucial roles in the working of renal, central-nervous, hormonal and cardiovascular system. An elevated level of dopamine results in cardio-toxicity that leads to rapid increase in heart rates, hypertension, drug addiction and heart failure. The low level of dopamine, on the other hand, may cause stress, depression, ailments such as schizophrenia, Alzheimer's disease, Parkinson's disease and many more. Thus, monitoring of dopamine measures in body in real time is vital for observing its impact on biological process and mechanism. In this work, a straightforward and efficient sensor model is proposed to detect the presence of dopamine in human body. Etched optical fiber with an overlayer of one of the most promising 2D material-graphene oxide (GO) is used for developing the sensor with the lossy mode resonance (LMR) approach. The sensor probe was analyzed for its performance in terms of stability. The experimental results show that the proposed etched LMR biosensor has immense capacity to sense the presence of dopamine in human and thus have significant application in real time detection and monitoring of dopamine.