Optic Surface Plasmon Resonance Sensor Research Articles

SPR based fiber-optic sensor with enhanced electric field intensity and figure of merit using different single and bimetallic configurations

We present numerical simulations of electric field intensity, sensitivity and figure of merit (FOM) for different single and bimetallic configured surface plasmon resonance (SPR) fiber optic sensors. The metals considered are gold (Au), silver (Ag), copper (Cu) and aluminum (Al). The overall performance of the sensor is evaluated in terms of electric field intensity, sensitivity, FOM, chemical stability and the cost of fabrication of the sensor. More specifically, in terms of the sensing parameters, Al and Cu bimetallic configuration is found to be much better than the single and the other bimetallic configured sensors. The bimetallic configuration of Al and Cu for fiber optic SPR sensor is also evaluated experimentally. Additionally, the film adhesion capability of both the materials gets improved when used in bimetallic combination which further improves the chemical stability of the sensor; this is a serious problem with Al and Cu in their single layer configuration. The combinations which possess gold as outer layer are more chemically stable but found to be weaker in terms of sensing parameters and cost of fabrication as gold is highly expensive.

Refractive Index Measurement in Sucrose Solution and Beverage Using Surface Plasmon Resonance Sensor Based on Hetero-core Structured Fiber Optic

The surface plasmon resonance (SPR) sensor was fabricated by depositing silver thin film on the surface of hetero-core structured fiber optic. The SPR sensor based on hetero-core structured fiber optic was applied to measure refractive index of sucrose solution and fruit juices. The sensor part was immersed in sucrose solution and/or juice and the propagating light spectra were measured. It was shown that the fiber optic SPR sensor showed a good agreement with that measured by conventional refractometer.

A wavelength selective application for an optical fiber surface plasmon resonance sensor

In this paper, a wavelength selective optical fiber surface plasmon resonance sensor, which provides a flexible detection capability, has been experimentally investigated. The light reflected from the sensor tip in response to flowing water and ethanol are monitored at several single wavelengths. The reflected light transient modulated by flowing solvent has an exponential form, which the change in magnitude and response time are dependent on the monitoring wavelength. Optimal wavelength best suited for measurement was determined by investigating the dynamic response curve. Rather than wavelength and angular interrogation methods commonly used in SPR measurement, this single wavelength monitoring scheme is a low-cost, flexible and reliable method.

Resolution enhancement of optical surface plasmon resonance sensor using metamaterial

In this paper, we present and discuss a path to extend the enhancement of the resolution of an optical surface plasmon resonance (SPR) sensor. Basically, our approach is to combine bi-metamaterial layers to design the SPR sensor. The calculation shows that the proposed SPR sensor structure has a preference over the conventional SPR sensors and bimetallic SPR sensors since it gives a much sharper reflectance dip and can achieve considerable sensitivity improvement when compared to the recently reported investigations. The effects of the metamaterial permittivity, permeability, and thickness on the reflectance curve are studied. It is also seen that metamaterial layers improve the field of the proposed SPR structure, which may provide a novel tool to significantly enhance the sensitivity and resolution of the sensors.

Surface plasmon resonance biochemical sensor based on light guiding flexible fused silica capillary tubing

A fiber optic surface plasmon resonance (SPR) sensor based on light guiding flexible fused silica tubing with its cladding stripped and coated with gold film as SPR sensing area is presented. Theoretical simulate of the proposed sensing structure for different sensing area length and different film thickness of sensors is done to obtain the suitable parameters, and the simulation for different refractive index is carried out. Meanwhile, the experiments for refractive index (RI) measurement have been demonstrated using the developed sensor, 400μm optical fiber sensor and 125μm optical fiber sensor. Experimental results have shown the capillary sensor has advantage in terms of sensitivity and resolution. The capillary sensor is also used for detecting and monitoring biochemical binding and dissociation processes of the RNase B and Con A. It is proved that the sensor with chemical modification can be implemented for specific biochemical sensing

An Exposed-Core Grapefruit Fibers Based Surface Plasmon Resonance Sensor.

To solve the problem of air hole coating and analyte filling in microstructured optical fiber-based surface plasmon resonance (SPR) sensors, we designed an exposed-core grapefruit fiber (EC-GFs)-based SPR sensor. The exposed section of the EC-GF is coated with a SPR, supporting thin silver film, which can sense the analyte in the external environment. The asymmetrically coated fiber can support two separate resonance peaks (x- and y-polarized peaks) with orthogonal polarizations and x-polarized peak, providing a much higher peak loss than y-polarized, also the x-polarized peak has higher wavelength and amplitude sensitivities. A large analyte refractive index (RI) range from 1.33 to 1.42 is calculated to investigate the sensing performance of the sensor, and an extremely high wavelength sensitivity of 13,500 nm/refractive index unit (RIU) is obtained. The silver layer thickness, which may affect the sensing performance, is also discussed. This work can provide a reference for developing a high sensitivity, real-time, fast-response, and distributed SPR RI sensor.

Boronic acid modified fiber optic SPR sensor and its application in saccharide detection

To extend the application of fiber-optic surface plasmon resonance (SPR) sensing technology, the chemical molecular, 2-(((6-aminohexyl)(benzyl)amino)methyl) phenyl boronic acid (ABA-PBA), is prepared as the recognition monolayer and immobilized on the fiber-optic SPR probe. The boronic acid moiety in ABA-PBA monolayer can covalently bond with 1, 2- or 1, 3- diols moiety of sugar. A monolayer of ABA-PBA is assembled on the SPR sensing region and confirmed by surface enhanced Raman scattering (SERS) technique. Spectrophotometric method is used to determine the pKa of ABA-PBA. The interaction between ABA-PBA monolayer and saccharide can induce the shift of resonance wavelength. By using the miniature fiber-optic SPR sensor, saccharide concentration can be monitored in real time. It shows good selectivity to fructose at low concentrations (10–50mM).

Fibre optic surface plasmon resonance sensor system designed for smartphones.

A fibre optic surface plasmon resonance (SPR) sensor system for smartphones is reported, for the first time. The sensor was fabricated by using an easy-to-implement silver coating technique and by polishing both ends of a 400 µm optical fibre to obtain 45° end-faces. For excitation and interrogation of the SPR sensor system the flash-light and camera at the back side of the smartphone were employed, respectively. Consequently, no external electrical components are required for the operation of the sensor system developed. In a first application example a refractive index sensor was realised. The performance of the SPR sensor system was demonstrated by using different volume concentrations of glycerol solution. A sensitivity of 5.96·10(-4) refractive index units (RIU)/pixel was obtained for a refractive index (RI) range from 1.33 to 1.36. In future implementations the reported sensor system could be integrated in a cover of a smartphone or used as a low-cost, portable point-of-care diagnostic platform. Consequently it offers the potential of monitoring a large variety of environmental or point-of-care parameters in combination with smartphones.

A super continuum characterized high-precision SPR fiber optic sensor for refractometry

Here we introduce a high sensitive side-polished fiber optic based surface plasmon resonance (SPR) sensor for refractometry in liquids for 1.32–1.37 Refractive Index Unit (RIU). In fabrication, a Controllable Hybrid Polishing Method (CHPM) was used to make high quality D-shaped fibers. For characterization, a super continuum (SC) light source was used in the measurement setup. The sensor has a spectral sensitivity of 5200nm/RIU with a Limit of Detection (LOD) of 5.8×10−6 RIU. Also, we have demonstrated that by reducing the intensity noise in our light source, a Signal-to-Noise Ratio (SNR) of 12.6dB and a Limit of Detection (LOD) of 3.7×10−6 RIU is achievable in an intensiometric approach.

Affinity based glucose measurement using fiber optic surface plasmon resonance sensor with surface modification by borate polymer

An affinity based method of glucose measurement using a fiber optic surface plasmon resonance (FO-SPR) sensor with surface modification by a borate polymer was proposed. In this method, the sensor is able to obtain the glucose concentration by detecting the surface refractive index of the sensor, which could avoid the impact of bioelectricity from viable tissues when applied for implantable measurement. A biocompatible borate polymer, PAA-ran-PAAPBA, which is capable of associating and dissociating with glucose molecules dynamically, performed non-consumption measurement of glucose, thereby enabling the possibility of glucose detection in hypoglycemic situations. Numerical simulation was performed based on the FO-SPR theory, and an online-transmission FO-SPR sensor with optimized structural parameters was fabricated. PAA-ran-PAAPBA was synthesized and immobilized onto the surface of the FO-SPR sensor using layer-by-layer self-assembly technique. An experimental system was built, and contrast-measurement experiment for 1–10 and 10–300mg/dL glucose solutions was performed; the FO-SPR sensor bonded with the borate polymer exhibited higher accuracy, especially for low-concentration detection. This study laid a technical foundation for further exploration of implantable measurement systems for blood glucose.

Gas-Clad Two-Way Fiber Optic SPR Sensor: a Novel Approach for Refractive Index Sensing

We propose and study the characteristics of a novel gas-clad surface plasmon resonance (SPR)-based fiber optic sensor. The proposed fiber optic probe not only senses change in the refractive index of the environment surrounding the outer layer of the probe but also shows the potential of detecting different gases in cladding holes. We have carried out the study of sensing probe of gas-clad fiber with nitrogen gas filled in air holes of the primary cladding. Silica is used as a second cladding of the gas-clad fiber with ITO film over this secondary cladding as a plasmonic metal layer. To optimize the probe design, figure of merit (FOM) and detection accuracy (DA) are calculated for varying thicknesses of different layers.

Theoretical Study of Phase-Interrogated Surface Plasmon Resonance Based on Optical Fiber Sensors with Metallic and Oxide Layers

This work reports the theoretical investigation of optical fiber surface plasmon resonance sensors incorporating an internal metallic layer of silver covered with an oxide layer. This research is supported by the application of an effective analytical model combining geometrical optics with the transfer matrix theory for stratified optical media. Different oxide materials like titanium dioxide, silicon dioxide, and aluminum oxide are considered aiming to achieve increased/enhanced sensitivity to refractive index variations of the external medium, particularly when addressing phase interrogation. It is shown that the combination of a 50-nm thickness silver inner layer with a dielectric titanium oxide layer of a specific thickness enables high-performance phase sensitivity reading and is compatible with tailoring the sensor working region to the third telecommunication wavelength window around 1550 nm.

Theoretical analysis of tapered fiber optic surface plasmon resonance sensor for voltage sensitivity

The geometry dependent reflecting spectrum, resonance wavelength and sensitivity of surface plasmon resonance (SPR)-based tapered fiber optic sensor have been investigated. It is observed that as the tip end diameter decreases, the refractive index sensitivity of proposed sensor monotonically increases. However, the voltage sensitivity increases with the tip end diameter decreasing to a certain value. The relationship between the tip end diameter and refractive index sensitivity, voltage sensitivity present here gives a guideline to use tapered fiber optic SPR sensor targeting specific applications.

Sensing Properties of Long Period Fiber Grating Coated by Silver Film

In long period fiber gratings (LPFGs), the fiber modes guided by the core layer can excite surface plasmon resonance (SPR) in the metallic thin-film coated on the cylindrical surface of fibers. In this letter, the LPFG-based fiber optic SPR sensor is analyzed numerically by unconjugated form of coupled mode method. According to the mode analysis, the EH modes can couple with surface plasmon mode and are suitable for refractive index sensing application. In wavelength interrogation, the transmission dip caused by SPR is sensitive to the environmental refractive index. The sensitivity of the sensor achieves 1660 nm/RIU in the aqueous solution.

Multiplexing of Surface Plasmon Resonance Sensing Devices on Etched Single-Mode Fiber

It is proposed the multiplexing of optical fiber-based surface plasmon resonance (SPR) sensors deployed in a ladder topology, addressed in wavelength by combining each sensor with specific fiber Bragg gratings (FBGs) and considering intensity interrogation. In each branch of the fiber layout, the FBGs are located after the sensor and the peak optical power reflected by the FBGs is a function of the relative spectral position between the SPR sensor and the FBG resonances, with the former dependent on the refractive index of the surrounding medium. The concept is tested for the multiplexing of two SPR sensors fabricated in an etched region of a single-mode fiber showing intrinsic refractive index sensitivity up to 5000 nm/RIU, which translates into a sensitivity of ∼829 dB/RIU from the interrogation approach considered. The obtained refractive index resolution is in the order of 10−4 RIU, and the crosstalk level between the sensors was found negligible.

Analysis of Phase Interrogated SPR Fiber Optic Sensors With Bimetallic Layers

An effective analytical model combining geometrical optics with the transfer-matrix theory for stratified optical media is applied to investigate the sensing properties of tapered optical fiber surface plasmon resonance (SPR) sensors incorporating Ag-Au bimetallic layers, particularly in the context of phase interrogation. The performance of the sensing structures is studied as a function of the tapering parameters and thickness of the metallic layers. It is shown that the Ag-Au bimetallic combination is capable of improving the resolution and tuning working region of SPR fiber-optic sensors and that by tapering the sensing structures enhanced sensitivity can be achieved when phase interrogation is considered.

A High Sensitivity Surface Plasmon Resonance D-Shaped Fiber Sensor Based on a Waveguide-Coupled Bimetallic Structure: Modeling and Optimization

A D-shaped optical fiber surface plasmon resonance sensor based on waveguide coupled mode using a bimetallic structure is proposed. Finite difference time domain method is used to examine the proposed structure and to improve its sensitivity. Maximum sensitivity of about 6140.2 nm/RIU is achieved. The sensor has some advantages, including high speed and sensitivity, easy construction, easy connection to other devices due to high numerical aperture optical fiber, small size, and in vivo test capability.

Surface Plasmon Resonance Sensor Based on an Angled Optical Fiber

Optical fiber-based surface plasmon resonance (SPR) sensors show great promise in applications for biochemistry detection. In this paper, a SPR sensor employing the angled optical fiber tip with a constant incident angle is reported. The incident angle and light interaction have been theoretical analyzed. The sensing probe has been fabricated via polishing the fiber tip to a specific angle. The process to achieve the smooth polished surface is also presented. The SPR spectra of solutions with different refractive indexes are obtained by collecting the light reflected by the angled fiber with metal coating. There is a red shift with the increase of analytes' refractive index. Slightly different from the theoretical value 8300 nm/RIU, the sensitivity obtained in the experiment is 7650 nm/RIU.

Sensitivity of tapered optical fiber surface plasmon resonance sensors

The sensitivity of surface plasmon resonance based tapered optical waveguide sensors having various profile is analyzed and compared. Using ray approach the change of resonance wavelength with taper ratio is obtained and hence the variations of sensitivity with taper ratio for each considered tapered profile are presented. It is observed that as the taper ratio decreases the sensitivity of proposed sensor for each profile increases up to certain taper ratio where the plasmonic condition is satisfied. Also, the effect of profiles on the sensitivity is significant for lower taper ratio. In all considered cases the maximum sensitivity is obtained for sinusoidal tapered profile.

Double‐layer silver nanoparticle arrays‐based localised surface plasmon resonance optical sensor for sensitive detection of concanavalin A

A localised surface plasmon resonance (LSPR) optical sensor with double-layer silver nanoparticle (Ag NP) arrays has been developed for the sensitive detection of concanavalin A (ConA). Based on the principle of carbohydrate–protein interactions, double-layer dextran capped Ag NP arrays were initially constructed. The increase of adsorption apparent mass and LSPR coupling between the two Ag NP arrays can effectively enhance the LSPR spectral shift response. Compared with the single-layer Ag NP arrays configuration, the double-layer Ag NP arrays configuration improves the limitation of detection of ConA concentration from 3.42 to ∼1.14 µg/ml.