SPR is a real-time, label-free measurement of binding kinetics and affinity. Success of SPR biosensor is evident by the growing number of commercially available instruments. In the current review, development in plasmon resonance techniques such as SPR, SPR-imaging (microscope, spectroscope, Electrochemical Impedance), nanoplasmonics and microfluidics, membrane proteins: receptor studies, sensors based on polarization and interferometery, PWR, SPR–MS, Signal locked SPR, FOPPR, Mid-IR SPR, trends in protein array technology and point-of-care (POC) testing over last decade are summarized. In addition, advancement over sensor configuration, mechanism and immobilization techniques are also discussed. Advantage and disadvantage of each methodology is provided along with some of the latest accomplishments.

SPR Biosensors: Historical Perspectives and Current Challenges

The development of highly-sensitive miniaturized sensors that allow real-time quantification of analytes is highly desirable in medical diagnostics, veterinary testing, food safety, and environmental monitoring. Photonic Crystal Fiber Surface Plasmon Resonance (PCF SPR) has emerged as a highly-sensitive portable sensing technology for testing chemical and biological analytes. PCF SPR sensing combines the advantages of PCF technology and plasmonics to accurately control the evanescent field and light propagation properties in single or multimode configurations. This review discusses fundamentals and fabrication of fiber optic technologies incorporating plasmonic coatings to rationally design, optimize and construct PCF SPR sensors as compared to conventional SPR sensing. PCF SPR sensors with selective metal coatings of fibers, silver nanowires, slotted patterns, and D-shaped structures for internal and external microfluidic flows are reviewed. This review also includes potential applications of PCF SPR sensors, identifies perceived limitations, challenges to scaling up, and provides future directions for their commercial realization.

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Photonic crystal fiber based plasmonic sensors

To solve the phase matching and analyte filling problems in the microstructured optical fiber (MOF)-based surface plasmon resonance (SPR) sensors, we present the D-shaped hollow core MOF-based SPR sensor. The air hole in the fiber core can lower the refractive index of a Gaussian-like core mode to match with that of a plasmon mode. The analyte is deposited directly onto the D-shaped flat surface instead of filling the fiber holes. We numerically investigate the effect of the air hole in the core on the SPR sensing performance, and identify the sensor sensitivity on wavelength, amplitude and phase. This work allows us to determine the feasibility of using the D-shaped hollow-core MOFs to develop a high-sensitivity, real-time and distributed SPR sensor.

Surface plasmon resonance sensor based on D-shaped microstructured optical fiber with hollow core.

Surface Plasmon Resonance (SPR) fiber sensor research has grown since the first demonstration over 20 year ago into a rich and diverse field with a wide range of optical fiber architectures, plasmonic coatings, and excitation and interrogation methods. Yet, the large diversity of SPR fiber sensor designs has made it difficult to understand the advantages of each approach. Here, we review SPR fiber sensor architectures, covering the latest developments from optical fiber geometries to plasmonic coatings. By developing a systematic approach to fiber-based SPR designs, we identify and discuss future research opportunities based on a performance comparison of the different approaches for sensing applications.

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Plasmonic Fiber Optic Refractometric Sensors: From Conventional Architectures to Recent Design Trends

We numerically demonstrate a surface plasmon resonance biosensor-based on dual-polarized spiral photonic crystal fiber (PCF). Chemically stable gold material is used as the active plasmonic material, which is placed on the outer layer of the PCF to facilitate practical fabrication. Finite-element method-based numerical investigations show that the proposed biosensor shows maximum wavelength sensitivity of 4600 and 4300 nm/RIU in ${x}$ - and ${y}$ -polarized modes at an analyte refractive index of 1.37. Moreover, for analyte refractive index ranging from 1.33 to 1.38, maximum amplitude sensitivities of 371.5 RIU−1 and 420.4 RIU−1 are obtained in ${x}$ - and ${y}$ -polarized modes, respectively. In addition, the effects of changing pitch, different air hole diameter of the PCF and thickness of the gold layer on the sensing performance are also investigated. Owing to high sensitivity, improved sensing resolution and appropriate linearity characteristics, the proposed dual-polarized spiral PCF can be implemented for the detection of biological analytes, organic chemicals, biomolecules, and other unknown analytes.

Spiral Photonic Crystal Fiber-Based Dual-Polarized Surface Plasmon Resonance Biosensor

We propose a temperature sensor design based on surface plasmon resonances (SPRs) supported by filling the holes of a six-hole photonic crystal fiber (PCF) with a silver nanowire. A liquid mixture (ethanol and chloroform) with a large thermo-optic coefficient is filled into the PCF holes as sensing medium. The filled silver nanowires can support resonance peaks and the peak will shift when temperature variations induce changes in the refractive indices of the mixture. By measuring the peak shift, the temperature change can be detected. The resonance peak is extremely sensitive to temperature because the refractive index of the filled mixture is close to that of the PCF material. Our numerical results indicate that a temperature sensitivity as high as 4 nm/K can be achieved and that the most sensitive range of the sensor can be tuned by changing the volume ratios of ethanol and chloroform. Moreover, the maximal sensitivity is relatively stable with random filled nanowires, which will be very convenient for the sensor fabrication.

https://www.mdpi.com/1424-8220/14/9/16035/pdf

Surface plasmon resonance temperature sensor based on photonic crystal fibers randomly filled with silver nanowires.

We demonstrate a temperature sensor based on surface plasmon resonances supported by a six-hole microstructured optical fiber (MOF). The air holes of the MOF are coated with a silver layer and filled with a large thermo-optic coefficient liquid mixture (ethanol and chloroform). The use of all six fiber holes and their relatively large size should facilitate the coating of the silver and the filling of the liquid mixture. Temperature variations will induce changes of coupling efficiencies between the core-guided mode and the plasmonic mode, thus leading to different loss spectra that will be recorded. The refractive index of the liquid mixture is close to that of the MOF material, which will enhance the coupling efficiency and the sensitivity. Our numerical results indicate that temperature sensitivity as high as 5.6  nm/K can be achieved and that the most sensitive range of the sensor can be tuned by changing the volume ratios of ethanol and chloroform.

Simulation of surface plasmon resonance temperature sensor based on liquid mixture-filling microstructured optical fiber

We demonstrate a dual-wavelength laser based on a new laser material—Nd, Gd:YSGG, or Nd:GYSGG for short—for the first time to our knowledge. Besides its attractive properties such as antiradiation, high segregation coefficient, etc., this kind of laser crystal also shows excellent laser performance. For continuous-wave operation, the maximum output power is 10.1 W with the absorbed power of 18.45 W at 808 nm, corresponding to the slope efficiency of nearly 60%. The maximum single pulse energy and peak power reach 277 μJ and 4.6 kW (60 ns) when the absorbed pump power is 11.4 W for acousto-optic Q-switched operation.

Efficient diode-end-pumped dual-wavelength Nd, Gd:YSGG laser.

In this paper, a reflective photonic crystal fiber (PCF) sensor probe for temperature measurement has been demonstrated both theoretically and experimentally. The performance of the device depends on the intensity modulation of the optical signal by liquid mixtures infiltrated into the air holes of commercial LMA-8 PCFs. The effective mode field area and the confinement loss of the probe are both proved highly temperature-dependent based on the finite element method (FEM). The experimental results show that the reflected power exhibits a linear response with a temperature sensitivity of about 1 dB/°C. The sensor probe presents a tunable temperature sensitive range due to the concentration of the mixture components. Further research illustrates that with appropriate mixtures of liquids, the probe could be developed as a cryogenic temperature sensor. The temperature sensitivity is about 0.75 dB/°C. Such a configuration is promising for a portable, low-power and all-in-fiber device for temperature or refractive index monitoring in chemical or biosensing applications.

Ran Wang

Papers

Surface plasmon resonance sensor based on D-shaped microstructured optical fiber with hollow core.

Surface plasmon resonance temperature sensor based on photonic crystal fibers randomly filled with silver nanowires.

Simulation of surface plasmon resonance temperature sensor based on liquid mixture-filling microstructured optical fiber

Efficient diode-end-pumped dual-wavelength Nd, Gd:YSGG laser.

A Reflective Photonic Crystal Fiber Temperature Sensor Probe Based on Infiltration with Liquid Mixtures