Optic Surface Plasmon Resonance Sensor Research Articles

Performance analysis of optical fiber surface plasmon resonance sensor in single-mode operation region

Abstract A new approach for studying the performance of single-mode optical fiber surface plasmon resonance sensor for refractive index sensing is presented. Intensity interrogation technique is used to observe and examine the effect of changing the value of the operating wavelength, within the single-mode operation region, on sensor performance. Effect of changing metal thickness, which is a critical parameter of the sensor structure, is also investigated. The results show that the selected operating wavelength within the mentioned region plays a very important role and has a significant impact on the sensor sensitivity. As the operating wavelength increases beyond the cut-off wavelength, above which the first higher-order mode disappears, the sensitivity increases while the refractive index range, for which the sensitivity is above its half maximum value, becomes narrower. In the proposed sensor structure, for a metal thickness of 25 nm, the maximum sensitivity reaches 2554 RIU−1 for analyte refractive index of 1.439 at a wavelength of 1500 nm. This sensitivity corresponds to a resolution of order 106 RIU by assuming 1% minimum reflectivity variation. The operating wavelength should be carefully selected and changed according to the refractive index values intended to be measured to ensure high sensor sensitivity at these values. The analysis provided in this paper enables to select and change the desired range of the sensed refractive index using low cost technique by just changing the operating wavelength in the single-mode operation region.

Fabrication and Measurement of Fiber Optic Surface Plasmon Resonance Sensor Based on Polymer Microtip and Gold Nanoparticles Composite

Fiber optic surface plasmon resonance (FO SPR) sensor offers attractive advantages over the conventional prism-based SPR platforms, such as simplicity, cost-effectiveness, and miniaturization. To improve the performance of the existing FO SPR sensor which has been fabricated by depositing a gold thin film on the flat fiber cross-section or side surface, we propose to fabricate the polymer microtip array on optical fiber using simple cost-effective soft and imprint lithography because SPR instruments mainly depend on the structural aspect of the thin metal plasmonic film deposited on the optical fiber substrate. The fabricated microstructures are also combined with the gold nanoparticles to expand the sensing area. The proposed sensor displayed 175% improved sensitivity with linear response according to refractive index changes, when developed FO SPR sensor and conventional FO SPR sensor without microtip array were applied to refractive index measurement, respectively. Based on the obtained results, the proposed FO SPR sensor can ultimately be used in various applications, ranging from food safety, environmental monitoring, and biomarker analysis.

Lossy mode resonance-based uniform core tapered fiber optic sensor for sensitivity enhancement

A lossy mode resonance (LMR)-supported fiber optic sensor in which a uniform fiber core is placed among two identical tapered regions, is investigated numerically. Indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO) are considered as LMR active materials used to excite several lossy modes and gold and silver are used as surface plasmon resonance (SPR) active materials. In this probe design, a central uniform core coated with ITO/AZO is the active sensing region, whereas tapered regions are meant for bringing the incident angle close to the critical angle. The sensitivity of the present fiber optic bio-sensor is evaluated for first two LMRs utilizing both ITO and AZO separately, along with its variation with the taper ratio (TR). For ITO, the maximum sensitivity values are observed to be 18.425 μm RIU−1 (refractive index unit) and 0.825 μm RIU−1, corresponding to the first and second LMRs, respectively, at a TR of 1.6 and for AZO, equivalent values are 0.79 μm RIU−1 and 0.35 μm RIU−1, respectively, at a TR of 2.0. The results illustrate that the first LMR is more sensitive than the second LMR and the ITO-coated probe possesses greater sensitivity than the AZO-coated probe for both LMRs. Similarly, for the fiber optic SPR sensor, the maximum value of sensitivity is 5.6425 μm RIU−1, in the case of gold and 5.0615 μm RIU−1 in the case of silver, at a TR of 1.6. Hence, the result shows that the sensor with the present fiber optic probe design has around a 3-fold enhancement in sensitivity compared with conventional SPR sensors. This study will have applications in many sensing schemes where the requirement of large sensitivity is vital.

Comparison of measurement protocol for biosensors using fiber optic localized surface plasmon resonance sensor

Abstract In an immunoassay test, which is a representative analytical method for evaluating the performance of a biosensor, the change of the sensor’s output with respect to the continuous change of the measurement target concentration is represented by a graph and defined as the characteristic curve of the sensor. In most studies using biosensors (disposable or not disposable), the characteristic curve of the sensor is obtained by accumulating and successively changing the concentration of the target using a single sensor (consecutive measurement using a single sensor: CS protocol). However, the CS protocol has an inherent error because the accumulated measurement results for a single sensor that continuously varies with the concentration of the target material are considered as the sensor’s output at each concentration level. In this paper, we obtain the characteristic curve of the sensor by measuring the different concentrations of the target using different sensors (separate measurement using the individual sensor: SI protocol). By comparing this characteristic curve with the characteristic curve obtained using the CS protocol, we prove that the widely used method based on CS protocol is inaccurate as a measurement protocol for biosensors.

HER2 breast cancer biomarker detection using a sandwich optical fiber assay

Optical fiber-based surface plasmon resonance (OF-SPR) sensors have demonstrated high versatility and performances over the last years, which propelled the technique to the heart of numerous and original biosensing concepts. In this work, we contribute to this effort and present our recent findings about the detection of breast cancer HER2 biomarkers through OF-SPR optrodes. 1 cm-long sections of 400 μm core-diameter optical fibers were covered with a sputtered gold film, yielding enhanced sensitivity to surface refractive index changes. Studying the impacts of the gold film thickness on the plasmonic spectral response, we improved the quality and reproducibility of the sensors. These achievements were correlated in two ways, using both the central wavelengths of the plasmon resonance and its influence on the bulk refractive index sensitivity. Our dataset was fed by additional biosensing experiments with a direct and indirect approach, relying on aptamers and antibodies specifically implemented in a sandwich layout. HER2 biomarkers were specifically detected at 0.6 μg/mL (5.16 nM) in label-free while the amplification with HER2-antibodies provided a nearly hundredfold signal magnification, reaching 9.3 ng/mL (77.4 pM). We believe that these results harbinger the way for their further use in biomedical samples.

Hg2+ Optical Fiber Sensor Based on LSPR with PDDA-Templated AuNPs and CS/PAA Bilayers

An optical fiber localized surface plasmon resonance (LSPR) sensor was proposed and experimentally demonstrated to detect Hg2+ ions by functionalizing the optical fiber surface with gold nanoparticles (AuNPs) and chitosan (CS)/poly acrylic acid (PAA) bilayers. A flame-brushing technology was proposed to post-process the polydimethyl diallyl ammonium chloride(PDDA)-templated nanoparticles, avoiding the aggregation of AuNPs and achieving well-dispersed AuNPs arrays. LSPR stimulated by the AuNPs is sensitive to changes in the refractive index induced by Hg2+ ions absorption on the CS/PAA bilayers. Experimental results demonstrated that the LSPR peak wavelength linearly shifts with the concentrations of Hg2+ ions from 1 to 30 μM with a sensitivity of around 0.51 nm/ppm. The sensor also exhibits good specificity and longtime stability.

Detection of adulteration in pure honey utilizing Ag-graphene oxide coated fiber optic SPR probes.

Fiber optic surface plasmon resonance (SPR) sensor utilizing silver (Ag) and Ag-graphene oxide (GO) is designed and developed for the detection of adulteration of glucose and fructose in pure honey. The concentration range of the two adulterants in pure honey is varied from 4% to 20% with a step change of 4%. The experiments were performed with two different fiber optic probes viz. Probe 1 and Probe 2. Probe 1 is fabricated by coating 50nm Ag film on unclad optical fiber portion and Probe 2 is fabricated by modifying Ag film with GO for sensitivity improvement. The study confirms that using GO modified fiber optic probe, the sensitivity is enhanced to 24% and 37% for glucose and fructose adulterated honey samples respectively. The technique presented in this study is easy, rapid, label free and shows high prospective for the detection of adulterants in pure honey.

Highly sensitive fiber optic surface plasmon resonance sensor employing 2D nanomaterials

Optical fiber-based surface plasmon resonance sensors using, silver layer (Ag), platinum (Pt), and indium tin oxide in addition to 2D nanomaterials such as graphene are presented in this research. In terms of sensitivity (S) and figure of merit (FoM), the performance analysis of the proposed and configured sensor has been demonstrated. The proposed sensors are based on the scheme of Kretschmann for obtaining the transmitted power using the transfer matrix method and the equations of Fresnel. With theoretical and numerical studies, the reported sensor exhibits a good wavelength sensitivity which is improved to the maximum value of 4150 nm/RIU. Full width half maximum values are minimized to be 59 nm and the FoM is optimized to be 70 RIU−1 which gives better sensing properties in comparison with other published articles.

Beating the shot-noise limit with optical fiber quantum sensors for salinity measurement

An ultra-resolution optical salinity quantum sensor depended on the tapered hetero-core structure coated with a gold film (around 50 nm) is proposed and demonstrated in this paper. Single photons which work as an input source are used for exciting surface plasmon polaritons at the interface between the metal and the seawater. We exploit the statistical analysis method to get the transmission spectroscopy and quantify its estimation error. Experiment results show that the detected estimation errors of the proposed quantum sensor are completely in agreement with the quantum theory. Though various external interference and experimental defects exist, the error bars are beyond the standard quantum limit. The salinity sensitivity of this proposed sensor is about 0.02204/‰. The resolution of this proposed sensor is 0.0016‰, which is one order of magnitude higher than that of traditional optical fiber surface plasmon resonance (SPR) sensors. The resolution and the sensitivity of the quantum sensor can be further enhanced by modifying the metal coating and the structural parameters. This work realizes the combination of optical fiber sensing technology and quantum plasmonic technology, which will pave the way for the development of high-resolution and high-sensitivity sensor.

Theoretical and experimental characterization of a salinity and temperature sensor employing optical fiber surface plasmon resonance (SPR)

A reflective seawater salinity and temperature sensor based on surface plasmon resonance (SPR) effect with multimode single-mode (MS) fiber structure has been proposed and demonstrated. Firstly, the sensing mechanism of the optical fiber SPR sensor was analyzed. Next, the influence of the type of metal, the thickness of the metal film, and the length of sensing area upon the SPR spectrum were simulated and compared. Based on these measurements, a reflective and highly-sensitive refractive index sensor was fabricated and experimentally demonstrated. Finally, a dual-parameter SPR sensor for the simultaneous measurement of seawater salinity and temperature was proposed by coating polydimethylsiloxane (PDMS) on half of the sensor as a temperature sensitive material, whose sensitivities were demonstrated to be 0.31 nm/‰ and -2.02 nm/°C, respectively. The proposed sensor not only resolves the cross-sensitivity problem between salinity and temperature, but also provides a simple structure with low cost and high sensitivity.

Fabrication of a Chemical Sensor Based on Surface Plasmon Resonance via Plastic Optical Fiber

In this work, a chemical optical fiber sensor based on Surface Plasmon Resonance (SPR) was designed and implemented using plastic optical fiber. The sensor is used for estimating refractive indices and concentrations of various chemical materials (methanol, distilled water, ethanol, kerosene) as well as for evaluating the performance parameters such as sensitivity, signal to noise ratio, resolution and the figure of merit of the fabricated sensor. It was found that the value of the sensitivity of the optical fiber-based SPR sensor, with 40 nm thick and 10 mm long Au metal film of exposed sensing region, was 3μm/RIU, while the SNR was 0.24, the figure of merit was 20, and the resolution was 0.00066. The sort of optical fiber utilized in this work is plastic optical fiber with a core diameter of 980 μm, a fluorinated polymer cladding of 20μm and a numerical aperture of 0.51.

The temperature responsive mechanism of fiber surface plasmon resonance sensor

The temperature responsive mechanism of the optical fiber Surface Plasmon Resonance (SPR) sensor is analyzed. It is found that, both the gold film and the fiber core change with increasing temperature and affect the temperature sensitivity of the SPR sensor, but the main factor of the intrinsic temperature sensitivity of the sensor is the temperature dependent SPR response of the gold coating. The gold film plasma frequency plays a critical role in the temperature response mechanism of the sensor. Experimental and simulation results show that the SPR wavelength shift due to the change of the gold film temperature contributes 19.6 % to the total, as the sensor surrounded with ethanol and the environment temperature increases from 0°C to 50°C. The reason is that the plasma frequency of the gold film rises significantly as the external temperature increases. The rising rate of plasma frequency with temperature is related to the morphology and the deposition method of the gold film. This result has provided a novel insight on the physical properties of optical fiber SPR sensors and has improved the capability of SPR sensors for measuring signals in a temperature-changing environment.

Surface plasmon resonance‐based fiber optic sensor prepared from bilayers of indium tin oxide‐indium oxide

AbstractExperimental investigations on fiber optic surface plasmon resonance (SPR) sensor with ITO (indium tin oxide)‐IO (indium oxide) layers are reported. Sensitivity ascends with increase in IO layer thickness till a definite thickness and begins descending with further enhancement in IO layer thickness. Maximum rise in sensitivity is observed for sensor fabricated from 40 nm ITO to 30 nm IO layers.

Enhanced sensitivity of bimetallic optical fiber SPR sensor based on MoS2 nanosheets

In this paper, we have fabricated and characterized a bimetallic optical fiber surface plasmon resonance (SPR) sensor, followed by molybdenum disulfide (MoS2) nanosheets have been coated on the surface of metal film. The performance of the sensor is discussed in terms of the sensitivity and the figure of merit (FOM) theoretically and experimentally. The effect of different thickness of Au/Ag film on the performance of the sensor was studied. The results indicate that the FOM of sensor with silver film is much higher than that with gold film, although gold film is conducive to the sensitivity improvement. Two types of sensors are fabricated, which are the sensor with silver layer and the sensor with bimetallic layers of silver and gold. The sensitivity of the sensor with silver film and the sensor with bimetallic layers are 2141 nm/RIU and 2487 nm/RIU, respectively; and the FOM values are 19.44 RIU−1 and 18.47 RIU−1, respectively. Then, it is theoretically confirmed that MoS2 has the potential to promote the sensitivity of SPR sensor, and the sensitivity is tuned by the number of layers of MoS2 nanosheets. MoS2 nanosheets successfully bridged the gold film with the help of chemical bonds. The sensitivity of the sensor with MoS2 nanosheets is 3061 nm/RIU, and its FOM value is 23.29 RIU−1.

MoSe2-Au Based Sensitivity Enhanced Optical Fiber Surface Plasmon Resonance Biosensor for Detection of Goat-Anti-Rabbit IgG

Surface Plasmon resonance (SPR) provides an efficacious and label-free detection method for optical fiber bio-sensing. MoSe 2 is one of the transition metal dichalcogenides (TMDCs) which has broad applications in detecting specific reactions. Cysteamine hydrochloride with enriched groups can generate self-assemble films for tight attachment. In this study we aimed to combine the rapid response of optical fiber SPR sensors with the enhanced sensitivity of MoSe 2 nano-films. An optical fiber SPR biosensor with MoSe 2 -Au nanostructure was proposed and implemented, and a sensitivity of 2821.81 nm/RIU was achieved, which was approximately 98.7% higher than that of conventional SPR sensor without using MoSe 2 nanostructure. Furthermore, Bovine Serum Albumin (BSA) was utilized as the target molecule to test the bioaffinity of the biosensor with MoSe 2 deposition cycles from 0 to 8. Weighing the sensitivity and the figure of merit (FOM), the best deposition cycle of MoSe 2 was 4 with the sensitivity of 2793.36 nm/RIU and FOM of 37.24 RIU -1 . At last, immunization experiments were carried out using Goat-anti-Rabbit IgG and a detection limit of 0.33 μg/mL was achieved. The rapid response and the high bioaffinity showed a strong applicability of the proposed MoSe 2 -Au SPR immune-sensor in specific interactions and immunization therapy.

Design and analysis of surface plasmon resonance optical sensor for determining cobalt ion based on chitosan-graphene oxide decorated quantum dots-modified gold active layer.

In this study, the incorporation of surface plasmon resonance (SPR) spectroscopy with novel chitosan-graphene oxide/cadmium sulphide quantum dots (CdS QDs) active layer for cobalt ion (Co2+) detection has been developed. The interaction of different Co2+ concentrations with the novel modified active layer was monitored using the SPR technique. From the SPR results, detection range, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analysed. The results showed the detection range of this optical sensor was 0.01 to 10 ppm, and it was saturated for higher concentration of Co2+. The sensitivity obtained was 0.1188 ppm-1 for low concentration of Co2+ ranged from 0.01 to 1 ppm. The FWHM and DA were consistent for all concentration of Co2+, while the SNR of the SPR signal increased with the Co2+ concentration. The SPR angle shifts were also fitted using Langmuir, Freundlich and Sips (Langmuir-Freundlich) isotherm models, where Sips model fitted the best with the binding affinity of 0.939 ppm-1. The results proved that the novel chitosan-graphene oxide/CdS QDs modified gold thin film can detect Co2+ via SPR spectroscopy.

V-shaped micro-structure optical fiber surface plasmon resonance sensor for the simultaneous measurement of the refractive index and temperature.

We propose and demonstrate a novel and compact optical fiber surface plasmon resonance (SPR) sensor for the simultaneous measurement of the refractive index (RI) and temperature. The sensor is fabricated by employing the eccentric-core fiber (ECF), which is polished to a V-shaped micro-structure optical fiber (MOF). One side of the MOF is used as the RI sensing channel, and the other side is used as the temperature sensing channel. Two sensing channels are independent without crosstalk. The sensor has high RI sensitivity up to the maximum of 3376nm/RIU from 1.333 to 1.385RIU, and high-temperature sensitivity up to -2.65 nm/°C from 20°C to 60°C. In addition, owing to the few-mode light in the ECF, the full width at half-maximum is smaller than other SPR sensors based on multimode fiber. This sensor will be extremely helpful to improve the RI measurement uncertainty caused by temperature disturbance.

Mechanistic understanding of excitation of surface plasmons in a fiber-optic SPR sensor utilizing Al/Cu bimetallic configuration: mode field approach

This work reports on a novel approach of incorporating effective refractive indices of the guided modes obtained through wave optics to optimize the thickness of plasmonic metal in a fiber–optic surface plasmon resonance (SPR) sensor based on Kretschmann–Raether configuration. Using optical fibers with significantly smaller dimensions than used in conventional fiber–optic SPR sensors, a rigorous mathematical analysis has been carried out to conclude the existence of a single guided mode propagating in multi–layered fiber–optic sensing structure responsible for the excitation of SP mode. The effective refractive indices of the guided modes and modal attenuation for different thickness combinations of Al and Cu used in bimetallic layer configuration have been determined using wave optics. The optimized thickness of Al/Cu bimetallic layer, thus obtained, is subsequently used to simulate a fiber–optic SPR refractive index sensor. Operating in a refractive index range of 1.330–1.380 with sensitivity 3.16 μm/RIU, key attributes of the designed sensor include larger shift in resonance wavelength supplemented with simultaneous narrowing of SPR spectrum culminating in enhancing figure of merit. First and unique of its kind, this work is an attempt at the visualization of SP excitation in fiber–optic SPR sensor using wave optics, and thus, brings innovative insights towards exploration of fiber–optic SPR sensors using modal field approach.

Temperature Sensor Based on Side-Polished Fiber SPR Device Coated with Polymer.

A highly sensitive temperature sensor based on surface plasmon resonance (SPR) of a side-polished single mode fiber is demonstrated. The sensor consists of a gold film coated side-polished fiber covered by a layer of UV-curable adhesive. Before introducing the UV-curable adhesive, the gold-coated fiber exhibits refractive index (RI) sensitivity of 1691.6 nm/RIU to 8800 nm/RIU in the range of 1.32 to 1.43. The resonant wavelength of the SPR sensor shifts to 650 nm when the adhesive is coated on the gold film, and is fixed at about 725 nm when the adhesive is cured. Due to the high thermo-optic and thermal expansion coefficient of the adhesive, the sensor structure achieves a temperature sensitivity of −0.978 nm/°C between 25 °C and 100 °C. The proposed optical fiber SPR sensor is simple, highly sensitive and cost effective, which may find potential applications for temperature measurements in the biomedical and environmental industries.

Fiber optic surface plasmon resonance sensor based on a silver-coated large-core suspended-core fiber.

A fiber optic surface plasmon resonance (SPR) sensor based on a silver-coated large-core suspended-core fiber was proposed. A dynamic chemical liquid phase deposition method was adopted to fabricate a set of proposed sensors with different silver layer thicknesses. A stable fully spiced all-fiber sensing system was established to evaluate the performance of the fabricated sensors. The results show that the proposed sensor with a thicker silver layer exhibits higher sensitivity and figure of merit. The performance of the proposed sensor is comparable to those of the conventional solid-core fiber and hollow fiber SPR sensors and much higher than that of the metal nanoparticle functionalized suspended-core fiber sensors.