We demonstrate refractive index sensors based on single mode tapered fiber and its application as a biosensor. We utilize this tapered fiber optic biosensor, operating at 1550 nm, for the detection of protein (gelatin) concentration in water. The sensor is based on the spectroscopy of mode coupling based on core modes-fiber cladding modes excited by the fundamental core mode of an optical fiber when it transitions into tapered regions from untapered regions. The changes are determined from the wavelength shift of the transmission spectrum. The proposed fiber sensor has sensitivity of refractive index around 1500 nm/RIU and for protein concentration detection, its highest sensitivity is 2.42141 nm/%W/V.

In this work, sensitive detection of dengue virus type 2 E-proteins (DENV-2 E-proteins) was performed in the range of 0.08 pM to 0.5 pM. The successful DENV detection at very low concentration is a matter of concern for targeting the early detection after the onset of dengue symptoms. Here, we developed a SPR sensor based on self-assembled monolayer/reduced graphene oxide-polyamidoamine dendrimer (SAM/NH 2 rGO/PAMAM) thin film to detect DENV-2 E-proteins. Surface characterizations involving X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirms the incorporation of NH 2 rGO-PAMAM nanoparticles in the prepared sensor films. The specificity, sensitivity, binding affinity, and selectivity of the SPR sensor were then evaluated. Results indicated that the variation of the sensing layer due to different spin speed, time incubation, and concentration provided a better interaction between the analyte and sensing layer. The linear dependence of the SPR sensor showed good linearity (R 2 = 0.92) with the lowest detection of 0.08 pM DENV-2 E-proteins. By using the Langmuir model, the equilibrium association constant was obtained at very high value of 6.6844 TM −1 (R 2 = 0.99). High selectivity of the SPR sensor towards DENV-2 E-proteins was achieved in the presence of other competitors. Dengue virus (DENV) is the most common arthropod-borne viral disease that poses a serious global problem. According to World Health Organization (WHO), the dengue virus is the leading cause of death of 22 000, annually. As of today, the need for hospitalization and medical treatment are constantly dense due to the fact that 390 million people in the world are still infected with DENV 1. Its four distinct serotypes (DENV-1. DENV-2, DENV-3, and DENV-4) are capable of causing a range of clinical symptoms ranging from mild fevers to the severe dengue haemorrhagic fever (DHF) and be potentially life-threatening 2-10. Despite its large burden to human health, no effective vaccine and antiviral therapy are available for the virus 11,12. Early treatment for DENV is only by maintaining the body fluid of the patient, as it is critical in fighting the severe symptoms of DENV 13,14. Hence, an early, rapid, and accurate diagnosis at the onset of infection is the demand of the day in the most epidemic settings. Present discoveries in dengue diagnostics that can help in the early diagnosis are targeting the host-virus itself. DENV consists of a single-stranded positive-sense RNA virus that encodes 10 different types of proteins. Seven of

Dengue viral infection is one of the most common deadliest diseases and has become a recurrent issue for public health in tropical countries. Although the spectrum of clinical diagnosis and treatment have recently been established, the efficient and rapid detection of dengue virus (DENV) during viremia and the early febrile phase is still a great challenge. In this study, a dithiobis (succinimidyl undecanoate, DSU)/amine-functionalized reduced graphene oxide-–polyamidoamine dendrimer (DSU/amine-functionalized rGO–PAMAM) thin film-based surface plasmon resonance (SPR) sensor was developed for the detection of DENV 2 E-proteins. Different concentrations of DENV 2 E-proteins were successfully tested by the developed SPR sensor-based system. The performance of the developed sensor showed increased shift in the SPR angle, narrow full-width–half-maximum of the SPR curve, high detection accuracy, excellent figure of merit and signal-to-noise ratio, good sensitivity values in the range of 0.08–0.5 pM (S = 0.2576°/pM, R2 = 0.92), and a high equilibrium association constant (KA) of 7.6452 TM−1. The developed sensor also showed a sensitive and selective response towards DENV 2 E-proteins compared to DENV 1 E-proteins and ZIKV (Zika virus) E-proteins. Overall, it was concluded that the Au/DSU/amine-functionalized rGO–PAMAM thin film-based SPR sensor has potential to serve as a rapid clinical diagnostic tool for DENV infection.

The plethora of optical techniques have been developed to detect the dengue virus, regrettably, the existing techniques are cumbersome and have limitations to provide early identification of the lowlevel of dengue virus. For this purpose, surface plasmon resonance (SPR) optical sensor was designed with a highly sensitive thin film based on hyperbranched polymer nanocomposites for conjugation of antibodies that specifically detect the dengue virus type II (DENV). In particular, we investigate the SPR sensing performance for gold/cadmium sulfide quantum dotspolyamidoamine/antibody (Au/CdS QDs-PAMAM/IgM) sensor film in terms of linear sensitivity, binding affinity, detection accuracy, full-width-half-maximum, selectivity, and spike and recovery test. The results show a strong affinity value, good sensitivity and selectivity, high accuracy, and excellent recovery value, obeying the ideal value based on conventional assay analysis. Additionally, this Au/CdS QDs-PAMAM/IgM based SPR sensor was successfully applied for the lowest detection of 1 pM of DENV E-proteins. To this end, a highly sensitive Au/CdS QDs-PAMAM/IgM sensor film was characterized using Raman spectroscopy, ultraviolet-visible (UV-Vis-NIR) spectroscopy, and atomic force microscopy (AFM) to confirm the binding of DENV.

We report the use of a biofunctionalized tapered optical fiber based sensor with the integration of graphene oxide (GO) for the detection of Dengue virus (DENV) II E proteins. The tapered region was deposited with GO and functionalized with anti-DENV II E protein IgG antibodies to be tested with different concentrations of DENV II E proteins. The sensor obtained a detection limit of 1 pM with a sensitivity value of 12.77 nm/nM, which was better compared to previously reported studies. The sensor also showed high precision, great selectivity, and high affinity toward E protein with a dissociation constant of Kd = 1.11 × 10-9 M-1. The proposed sensor has undoubtedly exhibited the immense potential of nanomaterial integration for future advancements of dengue diagnostics.

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Surface plasmon resonance sensor coated with hydrous ferric oxide-magnetite-reduced (Fe2H2O4-Fe3O4-rGO) graphene oxide nanocomposite film was demonstrated to detect two toxic heavy metals; Arsenic (III) [As(III)] and Arsenic (V) [As(V)] in aqueous solution. The proposed nanocomposite film exhibited successful absorption of As with enhanced sensitivity and selectivity. Resultantly, when tested with different concentrations of As(III) and As(V), (0.1-1.0 ppb) the sensor ranged linearly with sensitivity of 2.196 °ppb-1 and 0.960 °ppb-1, respectively, and achieved a detection limit as low as 0.1 ppb. These results validate the potential of Fe2H2O4-Fe3O4-rGO nanocomposite material for optical sensing applications in as detection.

The surge of Dengue cases around the globe has intensified the demand for a reliable diagnostic method. The work demonstrates, to the best of our knowledge, the first label-free optical based sensor for detection of Dengue II E proteins. This was achieved by utilizing tapered optical fiber that has been functionalized with complementary recombinant antibodies. The fundamental concept of the sensor relies on the interaction between strong evanescent waves resulting from the dimensional change of the fiber and immune complex formed on the surface of the fiber when the virus is present. Sensitivity and detection limit values obtained with the sensor setup are 5.02 nm/nM and 1 pM, respectively, with a standard deviation value of no more than ±0.4. The compact and rapid sensor is a viable alternative for label-free and quantitative assessment of the infection, which may assist in providing better clinical management and understanding of the disease.