Fiber Surface Plasmon Resonance Sensor Research Articles

Twisted fiber SPR sensor for copper ion detection

A novel fiber surface plasmon resonance (SPR) sensor for the detection of copper ions was reported in this paper. The twisted region was fabricated on the single-mode fiber by using the fiber hot melt torsion technology, and the light transmitted in the core was coupled to the cladding. The cladding was coated with nano gold film, and the cladding mode totally reflected at the interface between the cladding and the gold film, which excited the SPR effect. After optimizing the fabrication parameters of the twisted region, the twisted fiber with a pitch of 123 µm was selected to construct the SPR sensor probe, and its refractive index sensitivity is 2689.06 nm/RIU. Furthermore, the self-assembled chitosan / polyacrylic acid film was immobilized on the surface of the sensor layer by layer, and the concentration of copper ion was detected. The test results indicate that with the increase of Cu2+ concentration from 15.7 nM to 1.57 mM, the SPR resonance valley moves towards the long wavelength direction, the detection sensitivity is 3.46 nm/lgC, and the limit of detection (LOD) is 10.10 nM. The proposed fiber SPR sensor is simple to manufacture, which provides a new idea for heavy metal ion detection by fiber sensor.

High-sensitivity biconical optical fiber SPR salinity sensor with a compact size by fiber grinding technique

For seawater salinity measurement, a high-sensitivity, ultra-compact, and corrosion-resistant biconical optical fiber surface plasmon resonance (SPR) sensor deposited with a 40 nm thick gold film based on fiber grinding technique was fabricated and demonstrated in this article. The ultra-compact biconical sensing structure with different grinding angles were fabricated by applying the optical fiber grinding machine, and the length of the sensing region was only hundreds of microns. The experimental results indicated that when the grinding angle was 14°, the sensor showed the highest sensitivity: a high refractive index sensitivity of 3965 nm/RIU and a high salinity sensitivity of 0.6898 nm/‰. Meanwhile, this biconical sensor had acceptable repeatability and stability. Therefore, this article demonstrated the feasibility of the biconical structure to improve the sensitivity of fiber-based SPR sensors, and provided a novel and practical solution for seawater salinity measurement.

A Dual-Parameter Optical Fiber SPR Sensor for Simultaneous Measurement of Glucose and Cholesterol Concentrations

A surface plasmon resonance (SPR) dual-parameter sensor is designed and fabricated. It was electroless plated with silver on the surface of the core of the plastic-clad optical fiber and a gold film was plated near the end face side to produce the double SPR resonance valleys. 4-mercaptophenylboronic acid (4-MPBA) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -cyclodextrin ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -CD) were coated separately on the surface of the silver and gold films. 4-MPBA can selectively recognize the structures of cis-vicinal diols, and thus can capture glucose that contains such structures. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -CD is a class of cyclic oligosaccharides whose unique hydrophilic outer surface and lipophilic central cavity help facilitate the formation of inclusion complexes with cholesterol through multiple interactions. The sensor can detect 0–4 mM glucose and 0–500 nM cholesterol, and it has a linear response in the concentration range of 0–0.1 mM glucose and 0–15 nM cholesterol. The sensitivity of glucose and cholesterol concentration of the sensor is 89.6 and 0.994 nm/nM, respectively. The detection limits for quantifying glucose and cholesterol are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.12~\mu \text{M}$ </tex-math></inline-formula> and 0.1 nM, respectively. The experimental results also show that the sensor has good selectivity and stability. The proposed technique can be further applied in medicine, environment, and biology monitoring.

Dual-channel fiber-optic surface plasmon resonance sensor with cascaded coaxial dual-waveguide D-type structure and microsphere structure

To address the restriction of fiber-optic surface plasmon resonance (SPR) sensors in the field of multi-sample detection, a novel dual-channel fiber-optic SPR sensor based on the cascade of coaxial dual-waveguide D-type structure and microsphere structure is proposed in this paper. The fiber sidepolishing technique converts the coaxial dual-waveguide fiber into a D-type one, and the evanescent wave in the ring core leaks, generating a D-type sensing region; the fiber optic fused ball push technology converts the coaxial dual waveguides into microspheres, and the stimulated cladding mode evanescent wave leaks, producing the microsphere sensing region. By injecting light into the coaxial dual-waveguide middle core alone, the sensor can realize single-stage sensing in the microsphere sensing area; it can also realize dual-channel sensing in the D-type sensing area and microsphere sensing area by injecting light into the ring core. The refractive index measurement ranges for the two channels are 1.333–1.365 and 1.375–1.405, respectively, with detection sensitivities of 981.56 nm/RIU and 4138 nm/RIU. The sensor combines wavelength division multiplexing and space division multiplexing technologies, presenting a novel research concept for multi-channel fiber SPR sensors.

Single-mode D-shaped photonic crystal fiber surface plasmon resonance sensor with open microchannel

Accessible microchannels that allow microscale fluid control and microparticle-filtering are promising tools for advanced biological and chemical sensing and analysis. To this end, we proposed a d-shaped photonic crystal fiber surface plasmon resonance sensor with open microchannel. The optical characteristics of the sensor were numerically investigated using the Finite Element Method and the fiber structure was then fabricated using a standard stack-and-draw method. The numerical results demonstrate that the d-shaped photonic crystal fiber can be applied as a sensor with wide refractive index detection range between 1.330 and 1.435, a maximum sensitivity of 28400 nm/RIU, finest resolution of 3.52 × 10−6 RIU, and maximum figure-of-merit of 592 RIU−1. The sensor operates in the single-mode regime, has good linearity range, requires simple fabrication, has high coupling efficiency with conventional single-mode fibers, and has low losses, making it a practical candidate for wide range of applications in chemical and biological testing.

Multimode fiber surface plasmon resonance sensor based on a down-up taper.

A multimode fiber surface plasmon resonance sensor based on a down-up taper for refractive index measurement is proposed and demonstrated. The device is fabricated by splicing two multimode fibers in a heating and pushing process to form an up taper, followed by heating and pulling the fiber adjacent to the up-taper area to form a down taper, and then using a magnetron sputtering technique to deposit a Cr + Ag layer of 50 nm on the surface of the down-up taper. Such a structure effectively increases the taper ratio and hence improves the measurement sensitivity. The experimental results obtained show that in the refractive index range of 1.345-1.375, the refractive index sensitivity achieved is ∼3264.01 nm/RIU. The device has a compact size and its entire length is ∼2.75 mm. Moreover, the robustness of the device is better than that of the previously reported fiber surface plasmon resonance sensors due to its relatively large waist diameter of 40 µm for the down taper. The device is expected to have potential applications in biological and chemical sensing.

A D-shaped elliptical hollow core fiber SPR sensor

A D-shaped elliptical hollow core fiber surface plasmon resonance (SPR) sensor is proposed and analyzed here using gold and titanium oxide (TiO2) layer. The fiber geometry consists of a doped elliptical core with a concentric central elliptical air hole. A finite element method-based simulation software COMSOL Multiphysics is used for numerical analysis. Both gold and TiO2 layers are optimized. The sensor responds over a wide range of refractive index (RI) from 1.33 to 1.40. The average sensitivity obtained for the designed sensor is 4142.85nm/RIU (RI Unit) whereas that for a single mode fiber (SMF) is only 897.55nm/RIU. So, our designed sensor gives more than 4 times enhanced sensitivity and proves to be a potential alternative of SMF based low cost, compatible SPR sensors by covering the low sensitivity issue suffered by SMF sensors.

Multi-channel Optical Fiber Surface Plasmon Resonance Sensor with Narrow FWHM, High Figure of Merit, and Wide Detection Range

Multi-channel Optical Fiber Surface Plasmon Resonance Sensor with Narrow FWHM, High Figure of Merit, and Wide Detection Range

High-Sensitivity Triple-Channel Optical Fiber Surface Plasmon Resonance Sensor

Optical fiber surface plasmon resonance (SPR) sensors are widely used for refractive index (RI) sensing, thanks to their high sensitivity. However, with the increasing demand for multiple analytes detection and sensor integration, a traditional single-channel optical fiber SPR sensor is outdated. We propose and demonstrate a novel triple-channel optical fiber SPR sensor with high sensitivity. The sensor is fabricated with side-polished single-mode fiber (SMF), where the sensing film consists of a layer of gold nanofilm and a layer of TiO2 nanofilm. The resonance wavelength range of the SPR sensing zone can be adjusted significantly by changing the TiO2 nanofilm thickness. Experimentally, by cascading three sensing zones whose TiO2 nanofilm thicknesses are 10, 30, and 60 nm, respectively, a triple-channel SPR sensor is realized. The average sensitivities of three sensing channels reach up to 2637.8, 3962.2, and 6097.3 nm/RIU in the RI range of 1.333–1.370 RIU, which is superior to most current multichannel SPR sensors. Besides, three sensing channels are independent without crosstalk. The proposed triple-channel SPR sensor has great potential in biological and chemical sensing fields, especially in multiple analytes detection applications.

D-Shaped Fiber Surface Plasmon Resonance Refractive Index Sensor Enhanced By MXene (Ti3C2Tx)

A D-shaped fiber-optic surface plasmon resonance (SPR) sensor with MXene (Ti3C2Tx) is proposed as the sensing enhancement material. A spin coating method was used to cover the gold film D-shaped fiber SPR sensor with a layer of MXene. Experimentally, the sensor's sensitivity, full width at half maximum (FWHM), and figure of merit (FOM) are discussed. The effect of various MXene concentrations on D-shaped fiber SPR sensors was investigated. The results demonstrate that as the MXene concentration increases, the sensitivity, FWHM, and FOM value of the D-shaped fiber SPR sensor increase as well. The MXene-based D-shaped fiber SPR sensor exhibits the highest sensitivity, measuring 3143 nm/RIU, and the highest FOM value, 15.26. Compared to the Au-film D-shaped fiber SPR sensor, Sensitivity is increased by 53.6%. The results indicate that MXene could be used to enhance the performance of SPR refractive index sensors.

A novel ultra-low refractive index photonic crystal fiber sensor based on surface plasmon resonance

Since many biopharmaceuticals have low refractive indexes, the demand for corresponding low refractive index photonic crystal fiber surface plasmon resonance (PCF-SPR) sensors increasing rapidly. In this paper, a novel ultra-low refractive indexes PCF sensor based on SPR is proposed. The sensor structure is simple photonic crystal fiber without grinding. The gold pillars are filled in the y-direction pores. The effect of gold pillars of different shapes, positions and sizes on sensitivity is discussed. The effect of two pores size and pitch are also investigated. The sensitivity increases with the dimension of two pores. However, the sensitivity increases first and then decreases with cycle. As a result, the sensor can monitor the analyte refractive index in 1.21–1.49. The maximum x-polarization sensitivity is 5200 nm/RIU, and the maximum y-polarization sensitivity is 4700 nm/RIU in near-infrared wavelength region. Moreover, the corresponding y-polarization and x-polarization linear fits are 0.9999 and 0.9998, respectively. The proposed ultra-low RI PCF-SPR sensor also works well with wide range refractive indexes.

Ultra-sensitive mid-infrared copper based fiber surface plasmon resonance sensor using two-dimensional transition metal dichalcogenides

In this paper, a copper (Cu) based fiber surface plasmon resonance (SPR) sensor using two-dimensional (2D) transition metal dichalcogenides (TMDs) is studied theoretically. As the number of layers of TMDs increases, the sensitivity first increases and then decreases, exhibiting a maximum value for each TMDs based fiber SPR sensor. The maximum sensitivities of the fiber SPR sensors with WS2, MoS2, WSe2 and MoSe2 are up to 47.664 µm/RIU, 44.164 µm/RIU, 46.704 µm/RIU and 48.816 µm/RIU, while their resonance wavelengths are 3481.1 nm, 3592.2 nm, 3500.8 nm and 3435.1 nm. In addition, the growth rate of sensitivity in the mid-infrared regime is obviously higher than that in the visible or near-infrared regime. The proposed Cu based fiber SPR sensor with 2D TMDs exhibits ultra-high sensitivity in the mid-infrared regime, and can be used for highly sensitive bio-sensing.

S-type fiber surface plasmon resonance strain sensor.

The fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index detection, and there are few reports on SPR sensors used for strain measurement. In this paper, we propose and demonstrate an S-type fiber strain sensor based on SPR. The simulation and testing results indicate that the smaller the vertical axis offset of S-type fiber is, the larger the incidence angle of SPR is, and the closer the working band of SPR is to the shorter wavelength direction. By electrofusion, we fabricated an S-type structure on the single-mode fiber, and by the S-type structure, the high-order cladding mode was excited. A 50 nm gold film was coated on the surface of the fiber cladding behind the S-type structure. The evanescent field of the cladding mode contacted the gold film to produce SPR, and the strain can change the vertical axis offset of the S-type fiber and further change the incidence angle of SPR; hence an S-type fiber strain sensor based on SPR was realized. When the refractive index of the ambient medium is 1.345 RIU, the vertical axis offset and length of the S-shaped structure are 87 and 501 µm, respectively, the resonance wavelength of the fiber SPR strain sensor changes from 648.06 to 631.77 nm with a strain detection range of 0-1200µε, and its sensitivity is -14.38pm/µε. The proposed sensor provides a new solution for the strain measurement of the fiber SPR sensor, which is expected to be used in the fields of engineering, health monitoring, and early warning.

Surface plasmon resonance sensor using a polarization-maintaining fiber on a hetero-core optical fiber structure with gold thin film.

This study experimentally demonstrated the effects of two polarization-maintaining fibers (PMFs) as a sensing region instead of conventional single-mode fiber (SMF) using Au-coated hetero-core optical fiber surface plasmon resonance (SPR) sensor. We experimentally observed that the SPR resonant wavelength is shifted toward longer wavelength with refractive index (RI) increasing from 1.332 to 1.396. A PMF sensor exhibits the broad SPR spectra, resulting in a higher sensitivity with a 1.5-fold change in the light intensity at 850 nm relative to RI, compared with the SMF case. Discussions most likely responsible for this effect are given by the lower angular distribution peak in the hetero-core region of PMFs.

Hyperbolic-Metamaterials-Based SPR Temperature Sensor Enhanced by a Nanodiamond-PDMS Hybrid for High Sensitivity and Fast Response.

A high-performance surface plasmon resonance (SPR) fiber sensor is proposed with hyperbolic metamaterials (HMMs), nanodiamonds (NDs), and polydimethylsiloxane (PDMS) to enhance the temperature sensitivity and response time. The HMM with tunable dispersion can break through the structural limitations of the optical fiber to improve the refractive index (RI) sensitivity, while NDs and PDMS with large thermo-optic coefficients enable to induce significant RI change under varied thermal fields. The ternary composite endows the sensor with a high temperature sensitivity of -9.021 nm/°C, which is 28.6 times higher than that of the conventional gold film-based SPR sensor. Furthermore, NDs with high thermal conductivity (2200 W/mK) effectively expedite the thermal response of PDMS, which reduces the response time from 80 to 6 s. It is believed that the proposed sensors with high sensitivity, fast response time, and compact size have great potential for applications in industrial production, healthcare, environmental monitoring, etc.

A High-FOM surface plasmon resonance sensor based on MMF-TUMMF-MMF structure of optical fiber

The figure of merit (FOM) of conventional surface plasmon resonance (SPR) sensors is low due to the low sensitivity and wide full width at half maxima (FWHM) caused by many low-intensity high-order cladding modes. To address this problem, this paper proposes a SPR sensor based on U-shaped tapered arm cascade of multimode fiber (TUMMF). The U-shaped macro-bend increases the intensity of the light field leaking into the cladding, and the tapered area makes the number of higher-order modes smaller to achieve high sensitivity and narrow FWMH sensing performance. Through simulation and experimental verification, the sensitivity of the sensor is proportional to the fiber curvature and taper ratio, and the FWMH is inversely proportional. Therefore, the parameters of the sensor are optimized by integrating the FOM and the mechanical strength of the sensor. The optimized sensor parameters are 3 mm bending diameter, 0.85 taper ratio, and 152 nm gold film thickness. The sensor was tested in the refractive index (RI) sensing range of 1.3324–1.3731 and showed a sensitivity of 4816.092 nm/RIU and a FWMH of 97.54 nm. The FOM of the proposed sensor is 49.37 /RIU, which is 3.18 times higher than that of the U-shaped multimode fiber SPR sensor. The probe has the advantages of simple fabrication, high environmental stability and easy modification, and has a wide range of applications in bioenvironmental and other fields.

Theoretical study of distance-dependent optical fiber SPR sensor based on MoS2 nanosheets

Sandwich assay employing gold nanoparticles and DNA is a common signal amplification strategy designed for surface plasmon resonance sensor. To further improve the sensitivity employing sandwich assay, sandwich-structured optical fiber surface plasmon resonance sensors based on AuNPs and MoS2 nanosheets has been theoretically studied. Au film deposited on fiber core is the bottom nanomaterial of sandwich structure while AuNPs and MoS2 nanosheets are optional used as top nanomaterials. Top and bottom nanomaterials are separated by double stranded DNA, which allows solvent to perform as a spacer. The thickness of spacer is able to be tuned by the number of base pairs of double stranded DNA. Spacer thickness and nanomaterials play important roles to regulate the performance of optical fiber surface plasmon resonance sensor. The refractive index sensitivity has been found to be enhanced by the presence of MoS2 nanosheets compared to AuNPs. Large spacer thickness supported by long double stranded DNA further improves the performance of sensor. This study yields new insight into the structural design of optical fiber surface plasmon resonance sensor enhanced by sandwich structure and will open exciting avenues to apply sandwich-like assay for biosensing.

Experimental study of the copper-coated hollow fiber surface plasmon resonance sensor

A novel optical fiber surface plasmon resonance (SPR) sensor based on the copper-coated hollow fiber structure was proposed. The simple chemical liquid phase deposition method was developed to coat the thin copper film on the inner surface of the hollow fiber to fabricate the proposed sensor. The performance of the hollow fiber SPR sensors with different copper film thickness were investigated experimentally by measuring the transmission spectra of the sensors filled by sensed liquid media with different refractive indices. Theoretical analysis based on the ray transmission model was also carried out for comparison. The experimental and theoretical results agree well with each other. The factors which affect the sensor performance are discussed. The sensor achieves a maximum sensitivity of 7111 nm/RIU, which is relatively high in the copper film based optical fiber SPR sensors and comparable to the silver-coated hollow fiber sensors. Moreover, the fabrication process of the proposed sensor is much simpler than other copper based optical fiber SPR sensors, which make it more practical. The copper film deposition method presented in this paper is also applicable to the fabrication of some microstructured optical fiber or photonic crystal fiber based sensors with copper film.

Transition metal dichalcogenides boost the performance of optical fiber SPR sensors

We show the active role that the transition metal dichalcogenide MoS2 plays in enhancing the sensing performance of optical fiber sensors based on surface plasmon resonance (SPR). This is proved experimentally suggesting that the optical fiber SPR sensor with the MoS2 has an about 24 percent increase in the bulk refractive index sensitivity compared to the one without the MoS2. Also, we investigate the surface sensing performance of the sensor using self-assembly monolayers of polyelectrolytes with well-defined thickness and refractive index.

Single-mode fiber curvature sensor based on SPR.

A fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index measurement, but there is less research on curvature measurement. In this paper, a single-mode fiber curvature sensor based on SPR is designed and fabricated. By employing bending, the transmitted light in the fiber core leaks into the cladding. A 50 nm gold film is coated outside the cladding, and the evanescent field of the cladding after bending contacts the gold film to cause SPR. When the curvature changes, the coupled cladding mode and intensity are different; that is, the SPR incident angle and evanescent field intensity are different, so as to realize the dual parameters of SPR resonance wavelength and depth of the resonance valley changing with curvature. By experiments, the influence of different cutoff wavelengths of single-mode fiber on the performance of the sensor is studied. The testing results indicate that with the decrease in cutoff wavelength of the single-mode fiber, the valley depth sensitivity of the sensor increases, and the half height width (FWHM) decreases. When the cutoff wavelength of the single-mode fiber is 630 nm, the valley depth sensitivity of the sensor is 0.0088a.u/m-1, the wavelength sensitivity is 0.26nm/m-1, and the average FWHM is only 21 nm. The proposed single-mode fiber curvature sensor based on SPR has a narrow FWHM and an opening threshold. It can also realize no opening threshold by introducing a coreless fiber, which provides a new solution, to the best of our knowledge, for the diversified detection of fiber SPR sensors.