Synergistic Electrochemical and SPR Fiber Sensor for Mechanistic Insights into Dimethoate Catalytic Degradation.

An optical fiber sensor based on surface plasmon resonance (SPR) is proposed for monitoring the thickness of deposited nano-thin films. A side-polished multimode SPR optical fiber sensor with an 850 nm-LD is used as the transducing element for real-time monitoring of the deposited TiO2 thin films. The SPR optical fiber sensor was installed in the TiO2 sputtering system in order to measure the thickness of the deposited sample during TiO2 deposition. The SPR response declined in real-time in relation to the growth of the thickness of the TiO2 thin film. Our results show the same trend of the SPR response in real-time and in spectra taken before and after deposition. The SPR transmitted intensity changes by approximately 18.76% corresponding to 50 nm of deposited TiO2 thin film. We have shown that optical fiber sensors utilizing SPR have the potential for real-time monitoring of the SPR technology of nanometer film thickness. The compact size of the SPR fiber sensor enables it to be positioned inside the deposition chamber, and it could thus measure the film thickness directly in real-time. This technology also has potential application for monitoring the deposition of other materials. Moreover, in-situ real-time SPR optical fiber sensor technology is in inexpensive, disposable technique that has anti-interference properties, and the potential to enable on-line monitoring and monitoring of organic coatings.

Investigation of optic fiber sensor based on surface plasmon resonance for monitoring the concentration of plasma deposited hydrophilic functional groups on material surfaces

A new D-shaped tellurite photonic crystal fiber sensor based on the four-wave mixing (FWM) effect with the surface plasmon resonance (SPR) effect is designed and optimized. The substrate of the D-shaped photonic crystal fiber (D-PCF) is tellurite glass, and the polished surface is plated with the gold film and hydrogen gas-sensitive film. An air hole of the inner cladding, which is plated with the gold film and methane gas-sensitive film, is selected as the second sensing channel to simultaneously measure the concentration of hydrogen and methane. Based on the four-wave mixing, the wavelength shifts of the Stokes and anti-Stokes spectra resulting from the variation of the gas concentration can be used to accurately detect the concentrations of methane and hydrogen. Meanwhile, it is found that the SPR effect can increase the wavelength shifts, which means the sensitivity of methane and hydrogen augment. After parameter optimization, the maximum sensitivities of methane and hydrogen are 4.03 nm/% and −14.19 nm/%, respectively. Both the linearities are up to 99.9%. The resolution of methane is 1.25×10−2% and hydrogen is 7.14×10−3%. Moreover, the fiber length of this sensor is only 20 mm, which is conducive to the construction of a compact or ultra-compact embedded FWM fiber sensor.

Abstract- -- For improving the sensitivity of a D-type SPR fiber sensor, we simulated the optimum parameters , such as, the thickness of coatings, the length of sensor, and the angle of incidence for different ranges of refractive index. These simulations are based on SPR theory and the intensity and phase methods. It is clearly that, the sensitivity is improved by increasing the length of sensor and/or the thickness of the gold film. And the sensitivity of the phase method is higher than the intensity method by two orders. It is used to detect the refractive index or concentration of gas or liquid in real-time, and it has some merits, such as, small, simple, cheaper, and in vivo test. Keywords : surface plasmon resonance (SPR), fiber sensor 1. INTRODUCTION SPR fiber sensor is very useful in many applications in resent years 1-4 , such as, physical, chemical, biophotonics, etc. Although the sensitivity is not as high as that of the SPR prism sensor, however, owing to its merits such as, low cost, smaller tested volume, convenient to operation, in-vivo testing, it is also attention-getting in the future. There are several types of optical fiber sensor (OFS) based on surface plasmon resonance had been proposed

We overview the micro- and nano-structured optical fiber sensors, directly associated with surface plasmon resonance (SPR) sensing. Fiber sensors combined with SPR technologies offer a new route to improving the sensing capability. Various approaches have been exploited and optimized. For example, D-shape, cladding-off, and tapered fiber structures as well as dielectric or metallic gratings have been introduced. These micro- and nano-structured SPR fiber sensors have received much attention due to their high sensitivity, sensor miniaturization, and the flexibility of optical fibers. Key issues for fiber SPR sensors are low loss and high overlap with sensing medium. These fiber sensors with the use of SPR have been continually studied for chemical and bio-sensing. In this chapter we will review the current status of these micro- and nano-structured optical SPR fiber sensors.KeywordsSurface Plasmon ResonancePhotonic Crystal FiberResonance WavelengthSurface Plasmon Resonance SensorSurface Plasmon WaveThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

A reflectance-based surface plasmon resonance (SPR) fiber sensor with enhanced sensitivity for biochemical sensing is reported after comparing its result with the transmittance-based SPR optical fiber sensors. The fabricated SPR sensor contains a gold-coated multimode fiber with the implementation of a standard source-sensor-spectrometer interrogation system. As the refractive index of the liquid under test is increased, a redshift of the SPR is observed. The coupling of the source to the fiber sensor is optimized by investigating the effect of an intentional misalignment in transmission-based setup. When a fiber tip coated with the silver mirror and the bifurcated fiber bundle is used, an alignment-free disposable sensor probe is achieved. A comprehensive characterization of the proposed reflectance-based SPR probe is discussed. The maximum sensitivity of 3212.19 nm/refractive index unit (RIU) is obtained.

A novel, to the best of our knowledge, type of compact pH fiber sensor combined with a hydrogel based on the whispering gallery mode (WGM) is proposed and integrates a liquid crystal (LC) microdroplet in a capillary in a compact structure as small as 180 µm. In the research, the hydrogel performs both as a supporting frame and a responsive material that causes morphological deformation of the LC microdroplet with pH variation. Moreover, a new phenomenon of pH-induced LC refractive index variation is observed and applied in the pH measurement, so that the acid itself can also lead the LC microdroplet structure transition. Thus, the WGM method is applied to detect the composite effect simultaneously to improve the sensing capability. The sensitivity of the sensor in the pH range from 4.55 to 6.86 reaches 3.19 nm/pH. The response time is short, within 60 s. The simple and compact structure of the sensor reduces the cost and enhances the stability, which is of great potential for biomedical pH measurement.

We propose a novel dual-channel Surface Plasmon Resonance (SPR) fiber sensors based on the incident angle adjusting method. By grinding fiber tip to form wedge-shape with different angles, we can easier adjust the incident angle in fiber, and then the SPR wavebands will change corresponding. The simulation and experiment demonstrate that the SPR wavebands will red-shift with increasing of the fiber grinding angle. Based on this, we cascade two fiber tips whose grinding angles are 5° and 15° respectively. Under the tests of the refractive index (RI) range from 1.333 to 1.385, the SPR wavebands are 576∼683nm and 677∼955nm respectively. Therefore, we can demodulate SPR signal by wavelength division multiplexing (WDM) technology. Sequentially, we can detect two analytes simultaneously. This dual-channel SPR fiber sensor has important significance in the fields of multichannel liquid refractive indices and temperature selfreference measurements.

Current status of micro- and nano-structured optical fiber sensors

Two unexpected experimental phenomena in transmitted and reflective heterocore optical fiber sensors are observed. The surface plasmon resonance (SPR) wavelength of the reflective SPR (R-SPR) sensor redshifts about 100nm to the transmitted SPR (T-SPR) sensor. The maximal extinction ratio is 0.60 for the T-SPR sensor and reaches 0.77 for the R-SPR sensor. For a further understanding of the generation mechanism of SPR in both sensors, the finite-element method is employed to calculate distributions of the electric fields. Accompanied with experiments, modal energy coupling among the modes as light transmits through the multimode-single-mode-multimode fiber sensor is demonstrated, and the length of the single-mode fiber (SMF) is the focus of interest. The initial dissipated energy of the higher-order TM modes breaks the dynamic coupling balance of modal energy in the SMF when SPR takes place as a significant perturbation. With increasing SMF length, extra energy couples from lower-order modes to higher-order modes, from TE modes to TM modes as well, which results in a deeper trough and a longer SPR wavelength and thus a more sensitive device. The results are promising for various applications of a broader spectrum, such as modulators and sensors.

This paper describes the fabrication of portable and robust fiber optic sensors - mainly chemical and biological sensors - on standard communication grade optical fibers. Metallic nanostructures such as nanoparticles, nanopillars, nanorods, and nanoholes in optically thick metallic films were employed to precisely control the enhancement and absorption of light so as to form sensitive and specific optical sensors based on optical fibers. The fiber-optic sensors employ localized plasmon resonances (LSPRs) of metallic nanostructures formed on the fiber end-face as well as surface plasmon resonances assoc1ated with nanoholes in optically thick metallic films as a means of transducing the input optical signal. These metallic nanostructures were formed on the cleaved end-face of multimode and single mode optical fibers and were employed in both reflection and transmission modes. Metallic nanoparticles, nanorods, and nanopillars were formed on the tip or surface of the optical fiber by either employing chemical means or by first depositing a 10-100 nm layer of metallic film on the tip or surface of the fiber and then employing focused ion beam (FIB) milling to pattern out the metallic nanoparticles and nanopillars from the film. Ordered arrays of nanoholes were formed in optically thick (150-230 nm) metallic films by employing FIB milling. Gold (Au) nanostructures are chemically stable and result in plasmon resonance related peaks in the transmission spectrum in the visible spectral region. Hence, gold was selected as the material of choice for the fabrication of the plasmon resonance sensors.

A 4-pointed gold nanostar is proposed to form the array on a fiber facet to achieve a greatly enhanced near field intensity for Surface-Enhanced Raman Scattering (SERS) detection. The proposed gold nanostar array has a Surface Plasmon Resonance (SPR) peaked at a wavelength of ∼650 nm with up to 45 times electric field intensity enhancement compared with the state-of-the-art nanorod design. It has a wideband SPR field enhancement spanned from 600 to 720 nm, which covers the wavelengths for both the excitation light (632.8 nm) and the Raman signal of the analytes (675–706 nm); With symmetrical structure it forms four hot spots in every unit cell and can detect best for light polarized horizontal or perpendicular to the waist of the nanostars. It also could be altered to tune the SPR and allows the fiber sensor to resonate at different wavelengths, as demonstrated by an example at 533 nm. All the above features make the gold nanostar-based compact and portable fiber sensor an attractive solution for SERS detection.

We demonstrated a Graphene Oxide (GO) enhanced Surface Plasmon Resonance (SPR) sensor based on silver-coated side-polished fiber. GO nano-sheets were decorated on the Octadecanethiol (ODT)-silver surface of the side-polished fiber, which enhance the interaction between the SPR wave and molecules near the sensing surface. Experimental results demonstrate that the sensitivity of the GO-modified SPR sensor enhance to 2252.0 nm/RIU, compared with the traditional silver-coated SPR sensor of 1523.5 nm/RIU, which is improved 1.48 times. Meanwhile, ODT and GO films protect the silver-based SPR sensor from degradation and improved the stability of the silver-based SPR sensor. The proposed fiber sensor can be used as promising candidate in portable testing instruments with high immobilization ability for biochemical sensing application.

A side-polished multimode fiber sensor based on surface plasmon resonance (SPR) as the transducing element with a halogen light source is proposed. The SPR fiber sensor is side polished until half the core is closed and coated with a 37 nm gold thin film by dc sputtering. The SPR curve on the optical spectrum is described by an optical spectrum analyzer and can sense a range of widths in wavelengths of SPR effects. The measurement system using the halogen light source is constructed for several real-time detections that are carried out for the measurement of the index liquid detections for the sensitivity analysis. The sensing fiber is demonstrated with a series of refractive index (RI) liquids and set for several experiments, including the stability, repeatability, and resolution calibration. The results for the halogen light source with the resolution of the measurement based on wavelength interrogation were 3 x 10(-6) refractive index units (RIUs). The SPR dip shifted in wavelength is used as a measure of the RI change at a surface, and this RI change varies directly with the number of biomolecules at the surface. The SPR dip shift in wavelength, which was hybridized at 0.1 microM of the target DNA to the probe DNA, was 8.66 nm. The all-fiber multimode SPR sensor, which has the advantages of being low cost, being disposable, having high stability and linearity, being free of labeling, and having potential for real-time detection, permit the sensor and system to be used in biochemical sensing and environmental monitoring.

A novel analysis based on surface plasmon resonance (SPR) with a side-polished multimode fiber and a white-light (halogen light) source is presented. The sensing system is a multimode optical fiber in which half of the core has been polished away and a 40 nm gold layer is deposited on to the polished surface by dc sputter. The SPR dip in the optical spectrum is investigated with an optical spectrum analyzer (OSA). In our SPR fiber sensor, the use of liquids with different refractive indices leads to a shift in the spectral dip in the SPR curve. The cross point (CP) of the two SPR spectra obtained from the refractive-index liquid and the deionized water measurements was observed with the OSA. The CP is shifted sensitively in wavelength from 630 to 1300 nm relative to a change in the refractive index of the liquid from 1.34 to 1.46. High sensitivities of 1.9 x 10(-6) refractive-index units (RIUs) in the range of the refractive index of the liquid from 1.40 to 1.44 of 5.7 x 10(-7) RIUs above the value of 1.44 are proposed and demonstrated in our novel SPR analysis.