Satyendra K. Mishra

Surface plasmon resonance-based fiber optic hydrogen sulphide gas sensor utilizing Cu–ZnO thin films

We report an experimental study on a surface plasmon resonance (SPR)-based fiber optic hydrogen sulphide gas sensor with a thin metal oxide (zinc oxide (ZnO)) layer as the additional layer. This zinc oxide layer is grown over the copper layer to support surface plasmons at the metal-dielectric interface at room temperature. The wavelength interrogation mode of operation has been used to characterize the sensor. The thin film of zinc oxide over the copper film was deposited on the unclad portion of the fiber by the thermal evaporation technique. Experiments were performed for the detection of concentrations of hydrogen sulphide gas varying from 0 to 100 ppm around the probe. The unpolarized light from a polychromatic source is launched from one end of the fiber and the corresponding SPR spectrum is recorded at the other end. The recorded SPR spectrum shows a shift in the resonance wavelength on a change in the hydrogen sulphide gas concentration, which is considered as a detectable signal for the characterization of the sensor. Further, the optimization of the performance of the sensor was achieved by varying the thickness of the zinc oxide film. The sensor possesses a very fast response time and high sensitivity. Since the sensor utilizes optical fibers it has additional advantages of remote sensing, online monitoring, light weight and low cost.

Surface Plasmon Resonance-Based Fiber Optic Methane Gas Sensor Utilizing Graphene-Carbon Nanotubes-Poly(Methyl Methacrylate) Hybrid Nanocomposite

Fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor using graphene-carbon nanotubes/poly(methyl methacrylate) (GCNT/PMMA) hybrid composites for the detection of methane gas have been carried out. Four kinds of probes with different over-layers on the silver-coated unclad core of the fiber have been fabricated to achieve the best performance of the sensor. The over-layers used are of reduced graphene oxide (rGO), carbon nanotubes (CNT), reduced graphene oxide-carbon nanotubes (GCNT), and GCNT/PMMA hybrid nanocomposite. The sensing ability of all the probes has been tested for the following gases: methane, ammonia, hydrogen sulfide, chlorine, carbon dioxide, hydrogen, and nitrogen. The SPR spectra of all the probes for different concentrations of gases have been determined. A red shift in the resonance wavelength has been observed with increasing concentration of gases around the probes. Out of all the probes, the one with GCNT/PMMA hybrid nanocomposite over-layer has been found to be highly selective towards methane gas. For maximum sensitivity, the performance of the probe has been evaluated using different doping concentrations of GCNT in GCNT/PMMA nanocomposite. The doping concentration of 5 wt.% has been found to give maximum sensitivity of the sensor. Since the probe has been fabricated on optical fiber, apart from high selectivity and sensitivity, it has additional advantages such as miniaturized probe, low cost, capability of online monitoring and remote sensing, and immunity to electromagnetic field interference.

Surface Plasmon Resonance-Based Fiber Optic Sensor for the Detection of Low Concentrations of Ammonia Gas

Fabrication and characterization of a highly sensitive surface plasmon resonance-based fiber optic sensor for the detection of low concentrations of ammonia gas have been reported. The sensor probe is fabricated by coating an unclad core of the optical fiber with successive layers of indium tin oxide (ITO) and bromocresol purple (BCP). Increase in the concentration of ammonia gas around the sensing probe increases the resonance wavelength linearly implying that the absorption of ammonia gas by BCP layer increases its refractive index. In addition, ITO layer also contributes to the increase in the resonance wavelength because it is porous and has grains, which allow the reaction products to enter the pores of the ITO layer causing swelling of the layer resulting in mechanical stress and hence increase in the refractive index. To achieve maximum sensitivity of the sensor, the thickness of the BCP layer is optimized and is found to be 70 nm. The sensitivity of the sensor with optimized thickness of BCP layer is 1.891 nm/ppm and is larger than the sensitivity values obtained in the cases of Ag/BCP and Cu/BCP-coated probes for the concentration range 1-10 ppm of the ammonia gas. The selectivity of the probe is checked by carrying out experiments on the probe with different gases and it is observed that the probe is highly selective for ammonia gas. The sensor has many advantages, such as low cost, online monitoring, and remote sensing, due to the fabrication of the surface plasmon resonance probe on an optical fiber.

Localized and propagating surface plasmon resonance based fiber optic sensor for the detection of tetracycline using molecular imprinting

In the present study we report a novel approach for the fabrication of localized and propagating surface plasmon resonance based fiber optic sensor for the detection of tetracycline using molecular imprinting (MIP) technique. The sensor is fabricated by coating layers of silver film, silver nanoparticles and MIP film prepared using tetracycline molecule as template over an unclad core of the multimode optical fiber. Nanoparticles of sizes in the range 10–30 nm are synthesized by hydrothermal process. A polychromatic light source is used to launch the light from one end of the fiber and the absorption spectrum for a given concentration of the tetracycline solution around the probe is measured at the other end of the fiber using a spectrometer interfaced with a computer. The absorption spectra are recorded for the concentration range of tetracycline from 10−8 M to 10−5 M. A shift of 102 nm in peak absorbance wavelength is obtained for this concentration range. The sensor works in the promising concentration range of tetracycline found in foods etc. The sensor has various advantages such as high sensitivity, low cost, fast response and capability of online monitoring and remote sensing. Further, the sensitivity of the sensor is about double the sensor based on localized surface plasmon resonance and molecular imprinting.

Fabrication and Characterization of a SPR Based Fiber Optic Sensor for the Detection of Chlorine Gas Using Silver and Zinc Oxide

A fiber optic chlorine gas sensor working on surface plasmon resonance (SPR) technique fabricated using coatings of silver and zinc oxide films over unclad core of the optical fiber is reported. The sensor probe is characterized using wavelength interrogation and recording SPR spectra for different concentrations of chlorine gas around the probe. A red shift is observed in the resonance wavelength on increasing the concentration of the chlorine gas. The thickness of the zinc oxide film is optimized to achieve the maximum sensitivity of the sensor. In addition to wavelength interrogation, the sensor can also work on intensity modulation. The selectivity of the sensor towards chlorine gas is verified by carrying out measurements for different gases. The sensor has various advantages such as better sensitivity, good selectivity, reusability, fast response, low cost, capability of online monitoring and remote sensing.

Zinc oxide thin film/nanorods based lossy mode resonance hydrogen sulphide gas sensor

We report a fiber optic hydrogen sulfide gas sensor based on lossy mode resonance utilizing a coating of zinc oxide thin film along with nanorods over the unclad core of the fiber. The sensor is characterized in terms of peak absorbance wavelength determined from the recorded lossy mode resonance spectra for different concentrations of the hydrogen sulfide gas. To achieve the maximum sensitivity of the sensor, the growing period of the nanorods is optimized. It is found that the sensitivity of the sensor depends on the concentration of the gas. Further, the sensor is best suited for low concentrations (less than 60 ppm) of the gas. Experiments are also performed on the probe fabricated with zinc oxide nanorods grown over the unclad portion of the fiber. On comparison, it is found that the probe with layers of zinc oxide thin film and its nanorods is more sensitive than the probe that has layer of nanorods only. This is because of the large active surface area available in the probe fabricated with zinc oxide thin film and its nanorods. In addition, the probe with zinc oxide thin film and its nanorods is highly selective to hydrogen sulfide gas.

Surface Plasmon Resonance-Based Fiber Optic Chlorine Gas Sensor Utilizing Indium-Oxide-Doped Tin Oxide Film

Fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic chlorine gas sensor are carried out. The fiber optic probe is fabricated by depositing a thin layer of indium-oxide-doped tin oxide over a silver-coated unclad core of the fiber. The SPR spectra of the chlorine gas for its different concentrations are obtained. It is observed that the resonance wavelength increases as the concentration of the chlorine gas increases and appears to saturate for higher concentrations of the gas. The sensitivity of the sensor depends on the thickness and the doping concentration of the indium-oxide-doped tin oxide film. The optimum thickness and the atomic weight percent doping concentration of the film are found to be 12 nm and 6 at. wt.%, respectively. To compare the performance, experiments are also carried out on probes coated with indium oxide and tin oxide layers over silver coated unclad core of the fiber. The performance of both the probes is found to be inferior to the one coated with indium-oxide-doped tin oxide layer. Further, the indium oxide doped tin oxide layer based probe is highly sensitive to chlorine gas for low concentrations. The sensor has low response time and is reversible. The proposed probe has advantages of online monitoring and remote sensing.

Gas-Clad Two-Way Fiber Optic SPR Sensor: a Novel Approach for Refractive Index Sensing

We propose and study the characteristics of a novel gas-clad surface plasmon resonance (SPR)-based fiber optic sensor. The proposed fiber optic probe not only senses change in the refractive index of the environment surrounding the outer layer of the probe but also shows the potential of detecting different gases in cladding holes. We have carried out the study of sensing probe of gas-clad fiber with nitrogen gas filled in air holes of the primary cladding. Silica is used as a second cladding of the gas-clad fiber with ITO film over this secondary cladding as a plasmonic metal layer. To optimize the probe design, figure of merit (FOM) and detection accuracy (DA) are calculated for varying thicknesses of different layers.

A lossy mode resonance-based fiber optic hydrogen gas sensor for room temperature using coatings of ITO thin film and nanoparticles

In this article, the idea of employing lossy mode resonances (LMR) concertedly for gas sensing along with the reversible interaction of metal oxides with gases has been investigated. Fabrication and characterization of a LMR-based fiber optic probe with successive coatings of indium-tin oxide (ITO) film and nanoparticles over the unclad core of the fiber have been carried out for the detection of hydrogen gas (H2). The results have been compared with the probes having individual coatings of ITO thin film and nanoparticles. For calibrating and comparing, the wavelength interrogative spectra have been recorded for varying concentrations of H2 gas exploiting the sensor probes. A red shift of the spectrum has been observed with the increase in the concentration of the gas. The results uphold the fact that the LMR-based sensor with both thin film and nanoparticles layer has better sensitivity to H2 gas than the probes with the layer of either nanoparticles or thin film. A collective study on the three probes for different gases has predicted a maximum level of sensitivity for the probe with layers of thin film and nanoparticles along with the high selectivity and repeatability of the results for H2 gas. In addition to high sensitivity and selectivity, the proposed sensor can be used for online monitoring and remote sensing of the gas because of the fabrication of the probe on the optical fiber.

Surface plasmon resonance based fiber optic sensor for the detection of CrO42− using Ag/ITO/hydrogel layers

Surface plasmon resonance based fiber optic sensor for the detection of CrO42− in aqueous samples is reported. The probe is fabricated by coating layers of silver, indium-tin oxide (ITO) and hydrogel with (3-acrylamidopropyl)-trimethylammonium chloride (ATAC) over the unclad core of the optical fiber. The layers of silver and ITO over the unclad core of the fiber are deposited using a thermal evaporation technique, while the hydrogel with ATAC layer is coated using a dip-coating method. For the characterization of the sensor, samples of different concentrations of CrO42− are prepared in aqueous solution of sodium chloride. The sensor is based on the principle of shrinkage/swelling of the hydrogel layer when the concentration of the CrO42− sample around the hydrogel layer is increased/decreased. The shrinkage of the hydrogel layer occurs because of the polymerization of ATAC present in the hydrogel due to the formation of its ion pair with CrO42− anion present in the aqueous solution. The sensor is based on the wavelength interrogation technique. The SPR spectra recorded for different concentrations of CrO42− show that as the concentration of CrO42− increases the resonance wavelength increases. To achieve the maximum shift in resonance wavelength and the maximum sensitivity of the sensor, the concentrations of ATAC in hydrogel, pH and concentration of sodium chloride in water and the thickness of the ITO layer are optimized. The selectivity of the sensor is investigated using samples of other anions and it is found that the present sensor is more selective for low concentrations of CrO42−. The sensor has a low limit of detection and has several advantages, such as immunity to electromagnetic interference, miniaturized probe, low cost, fast response, capability of online monitoring and remote sensing, due to the fabrication of the probe on an optical fiber.