Polymer optical fibers (POFs) have significant advantages over numerous sensing applications. The key element in developing sensor is by removing the cladding of the fiber. The use of organic solvent is one of the methods to create tapered POF in order to expose the core region. In this study, the etching chemicals involved is acetone, methyl isobutyl ketone (MIBK), and acetone-methanol mixture. The POF is immersed in 100%, 80%, and 50% of acetone and MIBK dilution. In addition, the mixture of acetone and methanol is also used for POF etching by the ratio 2:1 of the volume. Acetone has shown to be the most reactive solvent towards POF due to its fastest etching rate compared to MIBK and acetone-methanol mixture. The POF is immersed and lifted from the solution for a specific time, depending on the power loss properties for the purpose of producing unclad POF. In comparison to silica fiber optic, the advantages of POF in terms of its simple technique and easy handling enable it to produce unclad POF without damaging the core region. The surface roughness of the POF is investigated under the microscope after being immersed into different solvent. This method of chemical tapering of POF can be used as the fundamental technique for sensor development. Next, the unclad fiber is immersed into ethanol solutions in order to determine the reaction of unclad POF towards its surrounding. The findings show that this particular sensor is sensitive towards concentration changes ranging between 10 wt% to 50 wt%.

Undoped and Al-doped ZnO thin films have been prepared by the sol gel method. Zinc acetate dihydrate, ethanol and monoethanolamine were used as precursor, solvent and stabilizer, respectively. In the case of molarity study for Al-doped ZnO, aluminum nitrate nonahydrate was added to the precursor solution from 0 at. % to 6 at. % at molarity of 0.1 M, 0.2 M and 0.3 M. The optical properties were characterized using UV-Vis where the band gap of undoped ZnO increases as the annealing temperature increase and the band gap decrease as the molarity increment. Meanwhile the band gap increase upon increment of Al dopant under molarity of 0.1 M and 0.2 M due to Burstein-moss effects. Meanwhile at 0.3 M, the bandgap increase until 4 at. % of Al and suddenly decrease abruptly at 6 at. % of Al. The effect of molarity and dopant percentage on the thin film gives a different value of energy band gap.

Graphene is a carbon-based material that has attracted tremendous attention due to its eccentric chemical and physical properties. Additionally, graphene can be converted into graphene oxide (GO) or reduced graphene oxide (rGO), depending on its application. In this paper, a simple step-by-step synthetisation of GO using Modified Hummers' method is report. The synthetisation enables the production of large scale by increasing the KMnO4 ratio. The prepared GO was then characterised by FTIR spectra in order to confirm the functional groups of the prepared sample. UV-Vis characterisation was done and the results supported the FTIR results, confirming the existence of oxygen functional groups. In addition, the prepared GO was characterised using XRD, FESEM, and RAMAN to investigate its interlayer distance, surface morphology, and structural information respectively.

Optical sensor based on surface plasmon resonance are widely used for various applications. In this paper, an optimization of EM waves polarization modes for the occurrence of SPR by using a modified optical waveguiding assembly has been discussed. A 633 nm of linearly polarized He-Ne laser was appointed as a light source. The polarization modes were controlled by rotating the position of He-Ne laser. It was found that the optimum SPR signal with reflectance, R = 0.21 a. u and SPR angle, theta(SPR) = 48 degrees can be obtained as the position of laser was rotated at 90 degrees, with the presence of polarizer. The location of the critical angle was observed at theta(C) = 46 degrees. For the validation purpose, a simulation based on Fresnel equation was conducted where the percentage difference between the experimental and theoretical results were analyzed. The percentage difference between experimental and theoretical results for both theta(SPR) and theta(C) were 9.09% and 15.00% respectively. In conclusion, an excellent agreement between the theoretical and experimental findings proved the stability of this SPR setup, where the EM waves polarization can easily be controlled by manipulating the position of laser.

Nowadays, surface plasmon resonance (SPR) sensor has been widely used in biosensing applications to detect the wide diversity of biomolecular interactions. There are few parameters need to be concerned in order to optimize the performance of SPR sensors such as film thicknesses, type of thin films and their configurations. In this study, we seek to determine the optimum thicknesses of hybrid thin films which consist of gold-graphene oxide layers for the enhancement of SPR sensor sensitivity. By using a theoretical approach, a WINSPALL 3.02 simulator had been used to investigate the effects of various thicknesses of hybrid configuration's thin films towards the excitation of surface plasmon polaritons (SPP). A layer of 3 nm protein was added to compare the maximum adsorption of the SPR sensor based on their configuration. It was found that the optimum thicknesses of gold and graphene oxide are 50 nm and 0.68 nm respectively for achieving best sensitivity. Thus, the sensitivity value for gold-GO thin films is higher than silver-GO which are 19.42 degrees/RIU and 5.45 degrees/RIU with FWHM = 2.28 degrees and 0.64 degrees respectively.

The development of high sensitivity surface plasmon resonance (SPR) sensor depends on few crucial factors such as types and thicknesses of metal thin films, light coupling techniques and suitable polarization modes of EM waves. This work was carried out to investigate the effect of EM wave polarization modes on the sensing properties of SPR sensor in detecting heavy metal ions namely mercury (Hg) and plumbum (Pb). Three types of light polarization modes such as p-polarized, s-polarized and circular-polarized light were introduced. Gold and silver thin films with thicknesses of 50nm were deposited on top of SPR layer system to excite surface plasmon polaritons (SPPs). The SPR curves were analyzed by studying the FWHM, Q-factor and angle shifting characteristics. We managed to prove theoretically that the SPR phenomena able to be created by using not only the p-polarized light, yet by employing a circular-polarized light. The sensor showed positive respond for both polarization modes, where the troughs were red-shifted about 23.78% as Pb was introduced on the top of the gold-coated SPR sensor. The SPR angles were shifted about 24.45% as the sensor was exposed with Hg metal ions. Different response due to the presence of different analytes exhibited excellent criteria of high selectivity sensor. In conclusion, the combination of p-polarized light or circular-polarized light and gold thin film able to accentuate the significant role of SPR sensor in detecting heavy metal ions.

Gold nanoparticles (GNPs) have been known as an excellent characteristic for Local Surface Plasmon Resonance (LSPR) sensors due to their sensitive spectral response to the local environment of the nanoparticle surface and ease of monitoring the light signal due to their strong scattering or absorption. Prior the technologies, GNPs based LSPR has been commercialized and have become a central tool for characterizing and quantifying in various field. In this review, we presented a brief introduction on the history of surface plasmon, the theory behind the surface plasmon resonance (SPR) and the principles of LSPR. We also reported on the synthetization as well of the properties of the GNPs and the applications in current LSPR sensors.

Uric acid detection based on ZnO coated polymer optical fiber (POF) by using intensity modulation technique is proposed. Zinc oxide was prepared using sol-gel method and characterized using UV-Vis spectrometer in order to determine its optical properties such as transmittance, absorbance and refractive index. The POF cladding is removed by using acetone and the unclad length of 2 cm was coated with ZnO by using dip coating method. The unclad fiber without coating is tested under uric acid solutions for comparison purpose. As the uric acid concentration increases until 500 ppm, the power output increases for ZnO coated fiber and produces a sensitivity of 4x10(-6) mW/ppm with a slope linearity of more than 88.56 %. The refractive index of ZnO is changing due to the interaction with uric acid and allows more light to propagate inside the fiber. The sensitivity for 2 cm and 4 cm of uncoated fiber is 2x10(-6) mW/ppm and 7x10(-6) mW/ppm. The longer the length of unclad fiber, the higher the evanescent wave absorbanceas well as the number of reflections inside the fiber.