Sensitivity Of Surface Plasmon Resonance Sensor Research Articles

A Highly Sensitive SPR Sensors Based on Two Parallel PCFs for Low Refractive Index Detection

Based on two parallel photonic crystal fibers (PCFs) with D-shape structure, a novel surface plasmon resonance (SPR) sensor with low refractive index (RI) detection at near-infrared wavelengths is described. According to the coupled-mode theory, directional power transfer between the two fiber cores is enhanced by resonant coupling between the surface plasmon modes and fiber core-guided modes. In comparison with corresponding single D-shape PCF, a maximum spectral sensitivity up to 13 500 nm/RIU and resolution of 7.41 × 10 -6 RIU for RI detection range between 1.27 and 1.32 are achieved. The proposed two parallel D-shape PCFs-SPR sensor with lower RI detection range offer large potential in the fields of pharmaceutical inspection and pharmaceutical leakage monitoring.

Graphene–MoS2–metal hybrid structures for plasmonic biosensors

Abstract Surface Plasmon Resonance (SPR) biosensors are widely used for real-time label-free detection in medical diagnostics, pharmaceutical researches and food safety. Although there is a growing interest in miniaturization of biosensors for self-detection and diagnostics at out of laboratory, the performance of conventional metal SPR sensors is still limited. In this paper, we propose graphene–MoS 2 – metal hybrid structures based plasmon sensors under the best minimum light intensity approach, which represents the performance analysis in case of the lowest reflected light strength. It is demonstrated that the metal thickness can be reduced from 55 nm to 32 nm and 37 nm meanwhile the performance of the background sensor can be improved by 87% and 13% with the 4 additional MoS2 and graphene layers, respectively. We show that MoS2 based SPR devices provide much better sensitivity performance than graphene based devices. Our results reveal the another promising property of MoS2: The sensitivity of SPR sensors can be greatly increased with a few number of MoS2 within the angular SPR system while reducing the size of the device, especially for particular applications such as detecting a single molecule and biosensing at low biomolecule concentration. Furthermore, we show that the equivalent optical properties of multilayered nanostructures also depend on the layer thickness which is a novel knowledge for the next studies on 2D material based SPR plasmonic devices.

Analyte induced AuNPs aggregation enhanced surface plasmon resonance for sensitive detection of paraquat

Paraquat (PQ) residue is harmful for people's health. This work fabricated an efficient approach to determine PQ sensitively. We exploited a novel surface plasmon resonance (SPR) detection system based on the analyte induced network architecture of supermolecules modified gold nanoparticles (AuNPs) on the chip surface. para-Sulfonatocalix[4]arene (pSC4) were used as a recognition molecule for paraquat. PQ can mediate the aggregation of pSC4 capped AuNPs (pSC4-AuNPs) through the host-guest recognition, which can be used as signal amplification for PQ assay. This achievement is due to several outstanding properties of this detection system: first, local SPR and high refractive index of AuNPs can enhance the signal of SPR dramatically; second, AuNPs is more stable and biocompatible and diffusely used in colorimetric methods; third, the network AuNPs structure has unique photo characterization for enhancement of SPR. Analyte induced AuNPs aggregation amplified SPR assay shows dramatic signal enhancement ability. The detection limit for PQ was found to be 2.2 pM This strategy provides a new concept for developing sensitive SPR sensors for the highly selective detection of small molecules.

Fiber-optic surface plasmon resonance glucose sensor enhanced with phenylboronic acid modified Au nanoparticles

A highly sensitive surface plasmon resonance (SPR) sensor is reported for glucose detection using self-assembled p-mercaptophenylboronic acid (PMBA) monolayer on Au coated optical fibers. The cis-diol group of saccharides, such as for glucose, interacted with the self-assembled PMBA monolayers on the optical fibers, but the low molecular mass of glucose is insufficient for measuring a significant shift in SPR wavelength. The response for glucose was thus enhanced with Au nanoparticles (Au NPs) modified with 2-aminoethanethiol (AET) and PMBA. Selectivity was assured since glucose has the ability to capture the signal amplification tags (Au NPs/AET- PMBA) through secondary binding with another set of syn-periplanar diol groups and the PMBA on the gold surface. Accordingly, a glucose concentration-dependent sandwich structure was formed and the coupling between Au NPs and Au film results in the red shift of SPR resonance wavelength. The experimental results demonstrated that this SPR sensor responded to glucose within a range of 0.01–30 mM better than to fructose and galactose. The minimum concentration for quantify glucose is as low as 80 nM, which is lower than the physiological blood glucose level. Glucose was then accurately detected in urine sample, which indicated the potential application of the sensor for the analysis of glucose in urine. We believe that our proposed PMBA-modified single amplification tag and sensing principle can also be used for biomolecules consisting of carbohydrate structures, particularly for DNA-associated bioanalysis.

Experimental demonstration of high sensitivity for silver rectangular grating-coupled surface plasmon resonance (SPR) sensing

We experimentally demonstrated a high sensitivity of surface plasmon resonance (SPR) sensor with silver rectangular grating coupling. The reflection spectra of the silver gratings indicated that surface plasmon resonance can be excited by either positive or negative order diffraction of the grating, depending on the period of the gratings. Comparing to prism-coupled SPR sensor, the sensitivities are higher for negative order diffraction coupling in bigger coupling angle, but much smaller for positive order diffraction coupling of the gratings. High sensitivity of 254.13 degree/RIU is experimentally realized by grating-based SPR sensor in the negative diffraction excitation mode. Our work paves the way for compact and sensitive SPR sensor in the applications of biochemical and gas sensing.

An ultra-highly sensitive surface plasmon resonance sensor based on D-shaped optical fiber with a silver-graphene layer

We propose a highly sensitive surface plasmon resonance (SPR) sensor based on D-shaped with a silver-graphene layer. The sensing characteristics is numerically analyzed by the finite-element method. An ultra-high spectral sensitivity of 58650nm/refractive index unit (RIU) with high linearity is achieved in the sensing range between 1.42 and 1.44, thereby resulting in a high resolution of 2×10−6RIU as a sensor. The influence of thickness of silver and graphene layer on sensing performance have been investigated and analyzed in detail. The D-shaped structure of the fiber helps in improving the phase matching, and the graphene layer can provides enhancing its sensing performance effectively. Results have potential application for designing high-performance optical fiber SPR sensors.

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.

High sensitivity SPR sensor for liquid phase sample with Ag/PbS/Graphene hybrid nanostructure

A surface plasmon resonance (SPR) sensor with Ag/PbS/GR hybrid nanostructure has been proposed for the diagnostics of liquid phase samples. Here Ag/PbS/GR hybrid nanostructure is designed as an asymmetric MIM waveguide for surface plasmon. Due to the guided wave SPR (GWSPR) modes, the index of the liquid phase samples can be measured more accurately than the conventional SPR sensors. Numerical simulation results show that the sensitivity of the sensor is about 5 times higher than the conventional SPR sensors. The origin of the enhancement mechanism is the combination of GWSPR in the Ag/PbS/GR hybrid nanostructure which enables the surface plasmon to spread along the PbS layer. In Ag/PbS/GR hybrid nanostructure, the electric field is concentrated mostly in the PbS layer, and the enhancement of the field intensity is nearly 30%.

Surface plasmon resonance based fiber optic sensor using an additional layer of platinum: A theoretical study

Surface plasmon resonance (SPR) based fiber optic sensor with bimetallic layers of Au/Ag/Cu-Pt is theoretically studied. The outer Pt layer over Au/Ag/Cu layer is shown to enhance the sensitivity of SPR sensor. For a fixed thickness of Au/Ag/Cu layer, the sensitivity increases with increase in Pt layer thickness. Sensitivity also enhances with increase in thickness of Au/Ag/Cu layer for all thicknesses of Pt layers. Besides, Au-Pt bimetallic layers based SPR sensor possesses higher sensitivity than that of Ag-Pt and Cu-Pt bimetallic layers. 50nm Au–20nm Pt based SPR sensor exhibits maximum sensitivity of 3571nm/RIU.

Optimization of SPR signals: Monitoring the physical structures and refractive indices of prisms

Surface plasmon resonance (SPR) can only be achieved if sufficient energy is provided at the boundary between metal and dielectric. An employment of prism as a light coupler by using Kretschmann configuration is one of the alternative for the production of adequate energy to be generated as surface plasmon polaritons (SPP). This work is carried out to investigate the effect of physical structure of the prism and its refractive index to the excitation of SPPs. A 50nm gold thin metal film with dielectric constant of ɛ=-12.45i+1.3 was deposited on the hypotenuse surface of the prisms. The physical structures of the prisms were varied such as triangular, conical, hemispherical and half cylindrical. These prisms were classified into two types of refractive indices (RI), namely n=1.51(type BK7) and n=1.77(type SF11). Based on SPR curve analyses, we discovered that strong SPR signals which consist of 82.98% photons were excited as SPPs can be obtained by using type-BK7 prism with physical structures of hemispherical or half cylindrical. From the view of selectivity ability as sensors, the usage of type-SF11 prisms (half cylindrical and hemispherical) able to enhance this impressive feature in which sharp SPR curves with small FWHM values were obtained. In conclusion, apart from properties of thin film materials, the physical structure of prisms and their RI values play crucial roles to obtain optimum SPR signal. High sensitivity SPR sensor can be established with the appointment of type-BK7 prisms (hemispherical or half cylindrical shape) as light couplers.

Graphene/Graphene Oxide-Based Ultrasensitive Surface Plasmon Resonance Biosensor

Surface plasmon resonance (SPR)-based biosensing is an accurate and sensitive technique used to evaluate the biomolecular interactions in real time in a label-free environment. Several new approaches have been proposed to improve the sensitivity of SPR sensors. The development of sensing surfaces can significantly improve the performance of biosensors; graphene and graphene oxide (GO) offer several advantages due to their extraordinary optical and structural properties. In this paper, the SPR biosensor structure based on graphene and GO linking layers are suggested. For proposed configurations, the features and characteristics such as reflectivity and sensitivity using the finite element analysis (FEA) model are discussed and compared with results from N-layer model. The effect of cap layer thickness in the sensitivity of the SPR biosensor has been calculated. Computational results show that the proposed graphene and GO-based SPR biosensor have more than two and four times greater sensitivity than the conventional gold film-based SPR sensor respectively due to their better adsorption of biomolecules.

An ultra-high sensitivity surface plasmon resonance sensor based on graphene-aluminum-graphene sandwich-like structure

An ultra-high sensitivity graphene optical sensor based on the surface plasmon resonance (SPR) is proposed using the graphene-aluminum (Al)-graphene sandwich-like structure. Here, the graphene sheets are introduced for enhancing the SPR and preventing the oxidation. It is found that our proposed graphene optical sensor is 3.4 times more sensitive than the Al-based sensor without the graphene layers. We demonstrate that a higher sensitivity can be obtained at the short wavelength due to the increases of the sensitivity with the decreases of wavelength. Especially, the sensitivity can be enhanced marked by increasing the number of graphene layers, which is totally different from the previous graphene-based optical sensor where the sensitivity is often decreased with the increases of the number of graphene layers.

Highly Sensitive SPR Sensor Based on D-shaped Photonic Crystal Fiber Coated with Indium Tin Oxide at Near-Infrared Wavelength

A surface plasmon resonance (SPR) sensor based on D-shaped photonic crystal fiber (PCF) coated with indium tin oxide (ITO) film is proposed and numerically investigated. Thanks to the adjustable complex refractive index of ITO, the sensor can be operated in the near-infrared (NIR) region. The wavelength sensitivity, amplitude sensitivity, and phase sensitivity are investigated with different fiber structure parameters. Simulation results show that ∼6000 nm/refractive index unit (RIU), ∼148/RIU, and ∼1.2 × 106 deg/RIU/cm sensitivity can be achieved for wavelength interrogation, amplitude interrogation, and phase interrogation, respectively, when the environment refractive index varies between 1.30 and 1.31. It is noted that the wavelength sensitivity and phase sensitivity are more pronounced with larger refractive index. The proposed SPR sensor can be used in various applications, including medicine, environment, and large-scale targets detection.

Highly sensitive surface plasmon resonance sensor utilizing a long period grating with photosensitive cladding.

In this study, we propose and investigate a novel grating-assisted surface plasmon resonance (SPR) platform based on a silver coated long period fiber grating having a photosensitive cladding (C-LPFG). We show that the SPR mode is transited from the higher EH mode with an effective refractive index (ERI) close to that of the surrounding refractive index (SRI) and is highly sensitive to a change in the SRI. Compared with a conventional SPR sensor, a much higher sensitivity is obtained for the novel C-LPFG-based SPR sensor. The sensitivity can be further improved by reducing the fiber diameter. The numerical results show that the highest local sensitivity, which can be as high as ∼4900 nm/RIU, and the corresponding resolution of ∼2.04×10(-6) RIU are achieved for the reduced silver coated C-LPFG sensor. Moreover, the Q-factor and the figure of merit exhibit better characteristics than those of the conventional LPFG-based SPR sensor. Our findings provide insight into the C-LPFG-based SPR platform being a potentially important area to explore for biochemical sensing.

Surface plasmon resonance sensor based on a new opto-mechanical scanning mechanism

Surface plasmon resonance (SPR) is employed as one of the key phenomena in biological, chemical and gas sensors. In this paper, we report development of a Kretschmann configuration based SPR sensing instrument by adopting a unique opto-mechanical scanning mechanism. The new scanning mechanism ensures portable, very low-cost and sensitive SPR sensor. In contrary to the traditional scanning mechanism, we utilized a rotating mirror for changing angle of incidence, and a quadrant photodiode (QPD) for recording reflected intensity. In order to achieve constant spot measurement on the sensing area (gold surface) for a fixed referencing, the prism-sensor assembly is translated vertically in a highly controlled manner governed by a feedback mechanism. In the feedback mechanism, the deflection of reflected beam is quantified by the QPD, and the prism-sensor assembly is translated vertically so as to regain the original set point. The SPR spectra of different materials deposited onto the gold surface using different techniques were collected and studied. Using the developed SPR instrument with pure gold sensing surface, the lowest detectable concentration of the sucrose in aqueous medium was found to be 100femto-molar. The sensitivity of the instrument was estimated using the different concentration of aqueous solutions of sucrose with known refractive indices, and it was found to be around 52.6°/RIU. These studies indicate a high resolution and good sensitivity of the instrument.

Theoretical analysis of surface plasmon resonance based fiber optic sensor using ITO and ZnO thin films

Surface plasmon resonance (SPR) based fiber optic sensor with bi layers of ITO–ZnO is theoretically analyzed. The top ZnO layer over ITO layer has been shown to improve the sensitivity of SPR sensor. For all thicknesses of ITO layers, the sensitivity enhances with increase in ZnO layer thickness. SPR based fiber optic sensor with bi layers of 50 nm ITO-30 nm ZnO displays the highest sensitivity of 2202 nm/RIU.

Twin-core fiber SPR sensor.

We propose and demonstrate a novel surface plasmon resonance (SPR)-sensing approach by using the fundamental mode beam based on a twin-core fiber (TCF). Although normally in a fiber SPR sensor, a multimode fiber (MMF) has often been used to improve the coupling efficiency; for improving fiber SPR sensor sensitivity, single-mode beam is optimal. We provide a novel method to employ the single (fundamental)-mode beam to SPR sense based on the TCF. We grind the TCF tip to be a frustum wedge shape, and plate a 50-nm sensing gold film on the end face, and two 500-nm reflected gold films on the side faces of the wedge tip. By using this new configuration, we reduce the mode noise effectively and get a high testing sensitivity (the testing highest sensitivity reaches to 6463nm/RIU). This SPR probe can be applied in a microfluidic chip and monitors the refractive index (RI) charges of the flow liquid in the microfluidic channel in real-time. The probe successfully monitors the refractive index of liquid ranged from 1.3333 to 1.3706, and the average sensitivity reaches to 5213nm/RIU in the solution, which is much higher than most multimode SPR systems.

High Sensitive Surface Plasmon Resonance (SPR) Sensor Based on Modified Calix(4)arene Self Assembled Monolayer for Cadmium Ions Detection

In this work, a new chromogenic calix(4) arene was functionalized onto self assembled monolayer (SAM) of cysteamine for cadmium ions detection and tested by using SPR measurement. The functionalization of modified SPR sensor is based on the oxidation of calixarene-SAM alcohol group to quinone. Four interfering ions were used Cu2+, Co2+, Mg2+ and Ca2+. pH of sensor in which the sensitivity of sensor is higher was optimized for cadmium ions and detection of ions was made in basic solution. Detection limit reached for Cd2+ is lower than 10(-11) M with a dynamic response time of about 16 s when changing from 10(-6) M cadmium to 10(-5) M.

Sensitivity enhancement of a surface plasmon resonance based fiber optic sensor using ZnO thin film: a theoretical study

A surface plasmon resonance (SPR) based fiber optic sensor with bi layers of metal–ZnO is proposed and theoretically studied. Three metals: gold (Au), silver (Ag) and copper (Cu) have been exercised in the study. The top ZnO layer is shown to protect the metallic layer from oxidation and to enhance the sensitivity of the SPR sensor. Besides, increase in thickness of Au/Ag/Cu layer increases the sensitivity of SPR sensor for all thicknesses of ZnO layers. For a fixed thickness of ZnO layer, the sensitivity of sensor is larger for Au layer than that of Ag/Cu layer. Sensitivity also increases with increase in ZnO layer thickness for all thicknesses of Au/Ag/Cu layers. The SPR sensor based on bi layers of 40nm Au–15nm ZnO demonstrates the maximum sensitivity of 3161nm/RIU.

Highly sensitive SPR response of Au/chitosan/graphene oxide nanostructured thin films toward Pb (II) ions

Optical sensors based on surface plasmon resonance (SPR) are utilized for detecting toxic heavy metals in solutions. To improve the sensitivity of SPR sensors, nanostructured thin films with active layers can be synthesized. In this study, the response to Pb (II) was measured and compared for SPR sensors incorporating gold–chitosan–graphene oxide (Au/CS/GO) nanostructured thin films and Au/CS films. The characterization of Au/CS/GO using FESEM analysis revealed a film composed of nanosheets with wrinkled, rough surfaces. The results from XRD analysis confirmed the successful incorporation of GO in the prepared films. Additionally, AFM analysis determined that the Au/CS/GO films had a root mean square (rms) roughness of 28.38nm and were considerably rougher than the Au/CS films. Upon exposure to a 5ppm Pb (II) ion solution, the Au/CS/GO films exhibited higher SPR sensitivity, as much as 1.11200ppm−1, than Au/CS films, 0.77600ppm−1. This enhancement of the SPR response was attributed to strong covalent bonding between CS and GO in these films. These results indicated that the Au/CS/GO films show potential for the detection of heavy metal pollution in environmental applications.