SPR-based Fiber Research Articles

Advances in SPR-Based Fiber Optic Sensors for Voltage/Electric Field Measurement—A Review

Advances in SPR-Based Fiber Optic Sensors for Voltage/Electric Field Measurement—A Review

Deposition of Graphene Oxide on an SPR Fiber Refractometer for Sensor Applications.

Graphene-based materials have been increasingly incorporated to optical fiber plasmonic sensors due to the peculiar physical and chemical properties of these materials (hardness and flexibility, high electrical and thermal conductivity, and very good adsorption for many substances, etc.). In this paper, we theoretically and experimentally showed how the addition of graphene oxide (GO) to optical fiber refractometers permits the development of surface plasmon resonance (SPR) sensors with very good characteristics. We used doubly deposited uniform-waist tapered optical fibers (DLUWTs) as supporting structures because of their already proven good performance. The presence of GO as an effective third layer is useful to tune the wavelength of the resonances. In addition, the sensitivity was improved. We depict the procedures for the production of the devices and characterize the GO+DLUWTs produced in this way. We also showed how the experimental results are in agreement with the theoretical predictions and used these to estimate the thickness of deposited GO. Finally, we compared the performance of our sensors with other ones that have been recently reported, showing that our results are among the best reported. Using GO as the medium in contact with the analyte, in addition to the good overall performance of devices, permit consideration of this option as an interesting possibility for the future development of SPR-based fiber sensors.

Utilizing dip-coated graphene/nanogold to enhance SPR-based fiber optic sensor

Utilizing dip-coated graphene/nanogold to enhance SPR-based fiber optic sensor

A Novel Dual-Wavelength Method for Evaluating Temperature Effect in Fiber-Optic SPR Sensors

The temperature effect is one of the critical factors to induce the resonance wavelength shift in fiber-optic surface plasmon resonance (SPR) sensors, which leads to the inaccuracy measurement of refractive index (RI) in practical applications. In this study, a novel dual-wavelength method is presented for fiber-optic SPR sensors to measure the changes of RI and temperature simultaneously in real time. A typical model of an SPR-based fiber optical sensor is constructed for theoretical analysis of temperature effect. Both the thermo-optic effect in the fiber core and phonon–electron scattering along with electron–electron scattering in the metal layer are studied systematically in the theoretical model. The linear and independent relationship, about the dependence of defined output signals on the RI and temperature, is validated by a theoretical calculation in specific dual wavelengths. A proof-of-concept experiment is conducted to demonstrate the capability of the presented dual-wavelength technique. The experimental results indicate that the presented dual-wavelength method is technically feasible and can be applied for practical application. Since the presented method only depends on the full advantages of the transfer spectrum data, it can be applied directly to the conventional single-channel fiber-optic SPR without any specific design structure of the sensor probe. The proposed method provides a new way to detect the RI under different thermal conditions and could lead to a better design for the fiber-optic SPR sensors.

Experimental studies on the sensitivity of the propagating and localized surface plasmon resonance-based tapered fiber optic refractive index sensors.

In the present study, the sensitivities of the fiber optic propagating surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR)-based refractive index sensors have been evaluated experimentally for a tapered probe of different taper ratio. The tapering of the fiber probe has been carried out via a heating and stretching technique. The SPR probe has been fabricated by coating a thin film of silver over the core of the tapered optical fiber, while the LSPR probe has been prepared by the coating of the gold nanoparticles over the core of the tapered optical fiber. The increase in the taper ratio increases the sensitivity of both kinds of the probes. The experimentally obtained sensitivity has been compared with the sensitivity of the SPR-based fiber optic refractive index sensors fabricated using various techniques and reported in the literature.

SPR-Based Fiber Optic Sensor Using IMO Thin Film: Towards Wide Wavelength Tunability From Visible to NIR

Due to existence of free electrons, conducting metal oxides (CMOs) such as indium molybdenum oxide, can support surface plasmon resonance (SPR) at the interface of CMO and dielectric. This research provides, theoretically, the first implementation of indium molybdenum oxide (IMO) as plasmonic layer in SPR fiber optic sensor. We demonstrate how changing the oxygen contents during IMO layer deposition could tune the operational wavelength of sensing probe in a wide range from visible to NIR which has a great significance in many biological and chemical environmental applications. Moreover, sensitivity and figure of merit of the proposed sensor have been calculated and compared for IMO thin films prepared at different oxygen contents.

Simultaneous measurement of refractive index and temperature using a SPR-based fiber optic sensor

A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900nm corresponds to PDMS refractive index at 20°C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4nm/RIU and −2.850nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications.

Tuning the field distribution and fabrication of an Al@ZnO core–shell nanostructure for a SPR-based fiber optic phenyl hydrazine sensor

We report the fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor that uses coatings of silver and aluminum (Al)-zinc oxide (ZnO) core–shell nanostructure (Al@ZnO) for the detection of phenyl hydrazine (Ph-Hyd). To optimize the volume fraction (f) of Al in ZnO and the thickness of the core–shell nanostructure layer (d), the electric field intensity along the normal to the multilayer system is simulated using the two-dimensional multilayer matrix method. The Al@ZnO core–shell nanostructure is prepared using the laser ablation technique. Various probes are fabricated with different values of f and an optimized thickness of core–shell nanostructure for the characterization of the Ph-Hyd sensor. The performance of the Ph-Hyd sensor is evaluated in terms of sensitivity. It is found that the Ag/Al@ZnO nanostructure core–shell-coated SPR probe with f = 0.25 and d = 0.040 μm possesses the maximum sensitivity towards Ph-Hyd. These results are in agreement with the simulated ones obtained using electric field intensity. In addition, the performance of the proposed probe is compared with that of probes coated with (i) Al@ZnO nanocomposite, (ii) Al nanoparticles and (iii) ZnO nanoparticles. It is found that the probe coated with an Al@ZnO core–shell nanostructure shows the largest resonance wavelength shift. The detailed mechanism of the sensing (involving chemical reactions) is presented. The sensor also manifests optimum performance at pH 7.

Tailoring the Field Distribution of ZnO by Polyaniline for SPR-Based Fiber Optic Detection of Hardness of the Drinking Water

Due to the industrial development, drinking water is getting polluted by disposing several waste products of the industries. Hardness is one of the prominent impurities in drinking water which is mainly due to the presence of carbonate and bicarbonate ions (CO3 2− and HCO3 −) in it. Here, we present the synthesis of the zinc oxide (ZnO) and polyaniline (PANI) nanocomposite for the detection and estimation of hardness of the drinking water. The chemical formula of such a nanocomposite is defined in terms of the fraction of polyaniline nanoparticles reinforced in ZnO matrix and is derived as ZnO(1 − x)PANI x (0 ≤ x ≤ 0.9); x is the composition ratio. Silver and ZnO(1 − x)PANI x layers are coated over the unclad core of the optical fiber so as to create the four layer system as that of Kretschmann configuration SPR structure. The working principle involves the change in dielectric constant of (ZnO(1 − x)PANI x ) by CO3 2− or HCO3 − ions in aqueous atmosphere. Due to the strong interaction of the sensing surface to the CO3 2− and HCO3 − ions, a red shift in the SPR spectrum is observed in the concentration range 0–200 μg/l. The sensitivity of the sensor depends on the composition ratio of the nanocomposite and has been found to be maximum for the composition ratio lying in the range 0.45–0.60. This has been further confirmed in terms of the enhancement of the electric field density and found to be in agreement with the experimental value. The sensitivity of the sensor with optimum value of the composition ratio is 0.094 and 0.065 nm/(μg/l) for CO3 2− and HCO3 −, respectively. The sensor is highly selective to CO3 2− and HCO3 −. The sensor has advantages of online monitoring and remote sensing of water quality because the probe is fabricated over an optical fiber.

Performance Analysis of Bimetallic Layer With Zinc Oxide for SPR-Based Fiber Optic Sensor

We present an efficient fiber optic SPR sensor consisting of bimetallic layers of silver (Ag) and gold (Au) in coordination with zinc oxide (ZnO) for refractive-index sensing in spectral mode. The performance of the sensor is explored in terms of electric field intensity, sensitivity, and the figure of merit theoretically as well as experimentally. Four kinds of sensors with layers of Ag/ZnO, Au/ZnO, Au/Ag/ZnO, and Ag/Au/ZnO over an unclad core of the fiber are studied. For simulation, two-dimensional multilayer matrix method along with geometrical optics is used. It is found that the sensor having layers of Ag/Au/ZnO with optimized thicknesses possesses maximum electric field intensity at the interface, large shift in the resonance wavelength, sharp SPR dip, and high value of the figure of merit. In addition, the additional layers of Au and ZnO can also be used for the tuning of resonance wavelength in the visible region of the electromagnetic spectrum and for the protection of Ag layer from oxidation and; hence, can improve the durability of the sensor. Further, ZnO layer can also be used to sense some of the gases.

Monitoring of patient glucose infusion using a surface plasmon resonance-based fiber optic sensor

A surface plasmon resonance (SPR)-based optic fiber monitoring system was introduced in this paper to monitor patients’ infusion process. The SPR-based fiber optic sensor provides a dramatically enhanced flexibility during the monitoring process. The experimental results showed that the spectral shift of sensor is correlated with glucose concentration and its flowing speed. The presence of fatal air bubbles in a glucose infusion solvent is detectable in real time, so that the consequent medical accident is avoidable. This sensor can simultaneously provide the information of liquid concentration and its flowing velocity, and make a judgment on the presence of air bubbles in solution during infusion. It provides experimental guidance on designing and manufacturing a sensor for on-line clinical monitoring systems in the future.

Performance evaluation of a bilayer SPR-based fiber optic RI sensor with TiO2 using FDTD solutions

We proposed a new bilayer surface plasmon resonance-based fiber-optic refractive index sensor with silver and an over-layer of TiO2. We numerically investigated the optimal thickness of TiO2 over-layer in the proposed sensor and compared its performance to that based on typical bimetallic layers of silver-and-gold in the aqueous media using finite-difference time domain approach. We show that the use of TiO2 over-layer greatly improves the sensor performance in terms of sensitivity and signal-to-noise ratio compared to that with gold as the over-layer. Not only does the TiO2 over-layer offer a cost-effective alternative to gold for overcoming the oxidation problem, but also it allows resonance wavelength-tunability.

Design of a ultrahigh-sensitivity SPR-based optical fiber pressure sensor

We designed a novel ultrahigh-sensitivity pressure sensor based on a surface plasmon resonance (SPR) fiber optical tip embedded in a designed polymer-filled metal cylinder with an opening on one side. The calculated pressure sensitivity is dependent on two factors. One factor is the derivative of the resonance wavelength of SPR-based fiber optical sensor with respect to the refractive index of surrounding medium; another factor is the derivative of refractive index of polymer with respect to the pressure. For the polymer with Young's modulus of 1.0MPa, average vary rate of resonance wavelength with pressure of 1.75×103nm/MPa can be obtained.

Evaluation of Multi-Layered Graphene Surface Plasmon Resonance-Based Transmission Type Fiber Optic Sensor

Graphene is a zero band-gap semi-metal with remarkable electromagnetic and mechanical characteristics. This study is the first ever attempt to use graphene in the surface plasmon resonance (SPR) sensor as replacement material for gold/silver. Graphene, comprised of a single atomic layer of carbon, is a purely two-dimensional material and it is an ideal candidate for use as a biosensor because of its high surface-to-volume ratio. This sensor is based on the resonance occasion of the surface plasmon wave (SPW) according to the dielectric constants of each metal film and detected material in gas or aqueous phase. Graphene in the SPR sensor is expected to enlarge the range of analyte to bio-aerosols based on the superior electromagnetic properties of graphene. In this study, a SPR-based fiber optic sensor coated with multi-layered graphene is described. The multi-layered graphene film synthesized by chemical vapor deposition (CVD) on Ni substrate was transferred on the sensing region of an optical fiber. The graphene coated SPR sensor is used to analyze the interaction between structured DNA biotin and Streptavidin is analyzed. Transmitted light after passing through the sensing region is measured by a spectrometer and multimeter. As the light source, blue light which of 450 to 460 nm in wavelength was used. We observed the SPR phenomena in the sensor and show the contrary trends between bare fiber and graphene coated fiber. The fabricated graphene based fiber optic sensor shows excellent detection sensitivity of the interaction between structured DNA and Streptavidin.

Ultrahigh sensitivity polarimetric strain sensor based upon D-shaped optical fiber and surface plasmon resonance technology

An ultrahigh sensitivity polarimetric strain sensor is proposed based upon a four-layer D-shaped optical fiber and surface plasmon resonance (SPR) technology. In contrast to existing SPR-based sensors, which are based on changes in the refractive index of the overlayer, the sensor proposed in this study is based on the change in the refractive index of the fiber core in response to the application of an axial load. Specifically, the phase difference between the P and S waves after passing through the sensor under SPR conditions is measured using a common-path heterodyne interferometer and is used to determine the corresponding change in the refractive index of the core, from which the strain is then inversely derived. The experimental results show that the sensitivity of the proposed sensor is around 2.19×10⁴ deg/ε, i.e., degree/strain. By contrast, that of a conventional (non-SPR) polarimetric fiber sensor is just 5.2×10² deg/ε. To the best of the authors' knowledge, the sensor proposed in this study represents the first reported attempt to exploit the refractive index change of the core of an SPR-based fiber sensor for strain measurement purposes.

Surface plasmon resonance based fiber optic sensor for the IR region using a conducting metal oxide film

Theoretical modeling of a surface plasmon resonance (SPR) based fiber optic sensor with a conducting metal oxide [indium tin oxide (ITO)] as the SPR active material is proposed. The theoretical analysis reveals that the proposed sensing probe can be utilized for sensing in the IR region, where most of the gases show their absorption regime. Comparison of sensitivity predicts that an ITO-layer-coated SPR-based fiber optic sensor is about 60% more sensitive than a gold-coated fiber optic sensor. The physical reasons behind sensitivity enhancement are provided. Apart from this, various advantageous features of the ITO over the noble metals, silver and gold, are addressed.

Surface Plasmon Resonance-Based Tapered Fiber Optic Sensor: Sensitivity Enhancement by Introducing a Teflon Layer Between Core and Metal Layer

Surface plasmon resonance (SPR)-based tapered fiber optic sensor with Teflon as a dielectric sandwiched between metal and tapered fiber core is proposed. The sensitivity of the sensor has been maximized using different combinations of metal and Teflon layer thicknesses for a given taper ratio. The study shows that the sensitivity of the sensor with the introduction of dielectric (Teflon) increases with the increase in the taper ratio. The maximum sensitivity achieved for a given taper ratio is around 15 times higher than the general SPR-based fiber optic sensor.