Dual-truncated-cone structure for quasi-distributed multichannel fiber surface plasmon resonance sensor

Wave type fiber SPR sensor for rapid and highly sensitive detection of hyperoside

The fiber surface plasmon resonance (SPR) sensor used for the detection of active ingredients in traditional Chinese medicine has the problems of low sensitivity and difficult specific recognition. This paper proposed a wave type fiber SPR sensor, which reduced the mode of transmitted light through a periodic wave structure and caused concentrated and total reflection of the transmitted beam at the interface between the bent peak cladding and the air. A 50 nm gold film was coated on the surface of the cladding in the wave structure area to form the SPR sensing area. By controlling the width and height of the wave structure to control the total reflection angle of the transmitted light, i.e., the SPR incidence angle, the sensitivity of the fiber SPR sensor was effectively improved to 4972 nm/RIU. Furthermore, HSP90AA protein was modified on the gold film of the sensor to achieve specific detection of hyperoside. The longest single detection time was only 3 minutes, and the detection sensitivity was 0.53 nm/(µg/ml), with a detection limit as low as 0.68µg/ml, which is comparable to liquid chromatography. The proposed wave type fiber SPR sensor is fast in production and has high structural mechanical strength, providing a new approach for the rapid, highly sensitive, and specific detection of active ingredients in traditional Chinese medicine.

SPR sensor based on Bessel-like beam

A proposal toward the enhancement in the sensitivity of a fiber-based surface plasma resonance (SPR) refractive index (RI) sensor is explored experimentally using a Bessel-like beam as the input source. We splice a section of single-mode fiber and a section of multimode fiber to construct the Bessel-like beam, which contains a series of concentric rings for the consistency of the resonance angle configuration to improve the performance of the SPR sensor. We fabricate a dual-truncated-cone (DTC) structure of the fiber to excite and receive the SPR signals. The larger the number of concentric rings, the higher the sensitivity. The number of concentric ring is determined by the length of the multimode fiber. When the grinding angle of the DTC-sensing probe is 15^° and the length of the multimode fiber is 500 µm, the maximum testing average sensitivity is 6908.3 nm/RIU, which is more sensitive than the previous SPR sensor introduced by the Gaussian beam as the input source in multimode fibers.

Dielectric layer thickness insensitive EVA/Ag-coated hollow fiber temperature sensor based on long-range surface plasmon resonance

A novel hollow fiber temperature sensor (HFTS) based on long-range surface plasmon resonance is presented. The HFTS consists of a dielectric/Ag-coated hollow fiber filled with the thermosensitive liquid and two multimode fibers connected at both ends. By measuring the transmission spectra under different temperatures, the performances, including sensitivity and figure of merit (FOM) of the sensors with different structural parameters, such as thermosensitive liquid property, ethylene-vinyl acetate (EVA) and silver layer thicknesses, were investigated experimentally. The results shows that the sensitivity of the optimized HFTS is 1.60nm/°C to 5.21nm/°C in the range from 20°C to 60°C, and the FOM is up to 0.0453°C^-1. Both performances are higher than most reported optical fiber temperature sensors based on surface plasmon resonance. Moreover, the performance of the HFTS is not sensitive to the dielectric layer thickness, which greatly reduces the difficulty of fabrication.

In-situ dual-channel surface plasmon resonance fiber sensor for temperature-compensated detection of glucose concentration

External temperature variations inevitably affect the accuracy of surface plasmon resonance (SPR) biosensors. To that end, we propose an ultra-compact label-free dual-channel SPR fiber sensor (DSPRFS) that can simultaneously measure the glucose concentration and ambient temperature in real-time. The proposed sensor is based on a unique dual-channel structure fabricated by etching a side-hole fiber (SHF), and has significantly higher spatial sensitivity than traditional SPR biosensors. After coating with silver and zinc oxide films, one channel was filled with polydimethylsiloxane (PDMS) to sense the ambient temperature, and the other channel was immobilized with glucose oxidase (GOx) enzyme for glucose sensing. The proposed sensor is analyzed theoretically, fabricated and characterized. Glucose concentration sensitivity and temperature sensitivity of the manufactured sensor sample were found to be as high as 6.156 nm/mMand -1.604 nm/°C with limits of detection (LOD) of 16.24 µM and 0.06 °C, respectively. The proposed sensor has an extremely compact structure, enables temperature compensation, and is suitable for in-situ monitoring and high-precision sensing of glucose and other biological analytes.

Surface-Plasmon-Resonance-Based Optical Fiber Curvature Sensor with Temperature Compensation by Means of Dual Modulation Method

Curvature measurement plays an important role in many fields. Aiming to overcome shortcomings of the existing optical fiber curvature sensors, such as complicated structure and difficulty in eliminating temperature noise, we proposed and demonstrated a simple optical fiber curvature sensor based on surface plasmon resonance. By etching cladding of the step-index multimode fiber and plating gold film on the bare core, the typical Kretschmann configuration is implemented on fiber, which is used as the bending-sensitive region. With increases in the curvature of the optical fiber, the resonance wavelength of the SPR (Surface Plasmon Resonance) dip linear red-shifts while the transmittance decreases linearly. In the curvature range between 0 and 9.17 m⁻¹, the wavelength sensitivity reached 1.50 nm/m⁻¹ and the intensity sensitivity reached −3.66%/m⁻¹. In addition, with increases in the ambient temperature, the resonance wavelength of the SPR dips linearly blueshifts while the transmittance increases linearly. In the temperature range between 20 and 60 °C, the wavelength sensitivity is −0.255 nm/°C and the intensity sensitivity is 0.099%/°C. The sensing matrix is built up by combining the aforementioned four sensitivities. By means of the dual modulation method, the cross-interference caused by temperature change is eliminated. Additionally, simultaneous measurement of curvature and temperature is realized.

Surface-plasmon-resonance-based optical-fiber temperature sensor with high sensitivity and high figure of merit

We propose and demonstrate a novel and compact optical-fiber temperature sensor with a high sensitivity and high figure of merit (FOM) based on surface plasmon resonance (SPR). The sensor is fabricated by employing a single-mode twin-core fiber (TCF), which is polished as a circular truncated cone and coated with a layer of gold film and a layer of polydimethylsiloxane (PDMS). Owing to the high refractive index sensitivity of SPR sensors and high thermo-optic coefficient of PDMS, the sensor realizes a high temperature sensitivity of -4.13  nm/°C to -2.07  nm/°C in the range from 20°C to 70°C, transcending most other types of optical-fiber temperature sensors. Owing to the fundamental mode beam transmitting in the TCF, the sensor realizes a high FOM of up to 0.034/°C, more than twice that of SPR sensors based on multimode fiber. The proposed temperature sensor is meaningful and will have potential applications in many fields, such as biomedical and biomaterial.