Conventional Surface Plasmon Resonance Sensor Research Articles

Titanium dioxide nanoparticle modified plasmonic interface for enhanced refractometric and biomolecular sensing.

A surface plasmon resonance (SPR) biosensor, which contains an overlayer of titanium dioxide nanoparticles (TDNPs) to modify the plasmonic interface, has been developed and investigated. Owing to its large surface area and high refractive index, the TDNP overlayer significantly enhances the probing electric field intensity and detection sensitivity. This sensitivity is related to the TDNP overlayer thickness, which can be engineered by changing the TiO2-ethanol dispersion's spin-coating concentration. The highest refractive index sensitivity for ethylene glycol measurement is 2567.3 nm/RIU, which is 38% higher than that of a conventional SPR sensor with an uncoated gold film. The proposed TDNP-SPR sensor also exhibits a 1.59-fold sensitivity enhancement in fetal bovine serum detection. Moreover, the proposed interface modification approach that is applied without additional biochemical amplification steps is chemical-free and contamination-free; therefore this TDNP-SPR sensor could be integrated into a sensitive, cost-effective, and biocompatible platform for rapid and label-free biochemical detection.

Rapid detection of Escherichia coli using fiber optic surface plasmon resonance immunosensor based on biofunctionalized Molybdenum disulfide (MoS2) nanosheets

The molybdenum disulfide (MoS2) nanosheets functionalized fiber optic surface plasmon resonance (SPR) immunosensor has been reported for the sensitive detection of Escherichia coli (E. coli). The MoS2 nanosheets were prepared by chemical exfoliation method. The synthesised nanostructures were characterized for their structural, morphological and optical properties. The E. coli monoclonal antibodies were successfully immobilized on the MoS2 functionalized sensing platform via hydrophobic interactions. An alternative method simplifying the antibodies immobilization process by functionalization of 2D nanomaterial (MoS2 nanosheets) for rapid (~15 mins) bacterial quantification is presented in this study. The immunosensor uses wavelength interrogation method and a strong linear relationship (R2 = 0.994) was observed between spectral response of immunosensor and different concentration of E. coli. The nonspecificity and cross-reactivity studies of the developed immunosensor were investigated with detection of Salmonella Typhimurium and Staphylococcus aureus. To demonstrate the practical application, spiked samples of water and orange juice were analysed with acceptable recovery results. The label-free immunosensor exhibits better performance, detection limit (94 CFU/mL), high sensitivity (2.9 nm/1000 CFU mL−1; 3135 nm/RIU) and profound specificity as compared to conventional fiber optic SPR sensor (detection limit: 391 CFU/mL, sensitivity: 0.6 nm/1000 CFU mL−1; 1646 nm/RIU). This sensing platform shows promising applications in regular water and food quality monitoring for various pathogenic microorganisms.

Design and Optimization of Surface Plasmon Resonance Sensor Based on Polymer-Tipped Optical Fiber

In this study, a novel surface plasmon resonance (SPR) sensor based on a single-mode polymer-tipped optical fiber (PTOF) is designed and optimized. The refractive index (RI) measurement is achieved by exciting SPR at the interface between gold film and TiO2 layer coated on the polymer-tip. Finite-difference time-domain (FDTD) method based commercial optiFDTD software is used to optimize the design of the proposed sensor for a better performance related to the materials of the metal film, the shape of polymer-tips, and the thickness of TiO2 layer. The results show that the sensitivity of optimal single-mode PTOF SPR sensor reaches 3798 nm/RIU when analyte RI is 1.333, and reaches 5708 nm/RIU when analyte RI is 1.383. Compared with conventional optical fiber SPR sensors, the single-mode PTOF SPR sensor proposed in the paper is simpler in fabrication, smaller in size, and higher in sensitivity, which has broad application prospect in biomedical sensing.

Performance Enhancement of SPR Biosensor Based on Phosphorene and Transition Metal Dichalcogenides for Sensing DNA Hybridization

Two-dimensional (2-D) materials have attracted a lot of attention for using in surface plasmon resonance (SPR) biosensors. High sensitivity and figure of merit are two desirable parameters in sensor performance analysis. Using heterostructures of phosphorene, graphene, and transition metal dichalcogenides is proposed to enhance the sensitivity of biosensor. Although the proposed biosensor can be used for detection of different analytes with a wide refractive index range, DNA hybridization is the sensing target in this paper. Sensing parameters of different biosensor configurations based on a few-layer black phosphorus (BP) and other 2-D materials are compared with the conventional Au-based SPR sensor and the highest sensitivity of 187°/RIU for the structure consists of 10-layer BP and monolayer WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is obtained. The suggested sensor structure provides the sensitivity more than two times of the conventional biosensor. This high sensor performance may have potential applications in medical diagnosis and biochemical detection.

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.

Angle-Scanning Surface Plasmon Resonance System with 3D Printed Components for Biorecognition Investigation

Surface plasmon resonance (SPR) is a real-time, label-free, and high-sensitive detection technology. SPR has been widely used in many applications such as biomolecular interaction analysis, environmental monitoring, and medical diagnostics. However, conventional SPR sensor systems usually require expensive equipment and complicated optics. In this paper, we have demonstrated a rapid prototyping of angle-scanning SPR for bioanalytical investigation. Rapid prototyping was attained by utilizing the FDM (fused deposition modeling) based 3D (three-dimensional) printing technology. Two rotating platforms were employed to drive the laser source and photodiode, respectively. A temperature regulation unit was incorporated to maintain the system temperature in order to reduce the temperature effect. The proposed SPR rapid prototyping yielded a refractive index resolution of 6.4×10−6 RIU (refractive index unit), and the biotin-avidin system validated the kinetics parameters measurement capability. The obtained results indicated that the FDM 3D printing has great potential for developing rapid-prototyping SPR system.

An Optical Fiber Refractive Index Sensor Based on the Hybrid Mode of Tamm and Surface Plasmon Polaritons.

A novel high performance optical fiber refractive index (RI) sensor based on the hybrid transverse magnetic (TM) mode of Tamm plasmon polariton (TPP) and surface plasmon polariton (SPP) is proposed. The structure of the sensor is a multi-mode optical fiber with a one dimensional photonic crystal (1 DPC)/metal multi-films outer coated on its fiber core. A simulation study of the proposed sensor is carried out with the geometrical optical model to investigate the performance of the designed sensor with respect to the center wavelength, bilayer period and the thickness of silver layer. Because the lights transmitted in the fiber sensor have much larger incident angles than those in the prism based sensors, the center wavelength of the 1 DPC should shift to longer wavelength. When the coupling between TM-TPP and SPP is stronger, the sensor exhibits better performance because the electromagnetic field of the TPP-SPP hybrid mode is enhanced more in the analyte. Compared to most conventional fiber surface plasmon resonance sensors, the figure of merit of the proposed sensor is much higher while the sensitivity is comparable. The idea of utilizing TPP-SPP hybrid mode for RI sensing in the solid-core optical fiber structure presented in this paper could contribute to the study of the fiber RI sensor based on TPP.

A Waveguide-Coupled Surface Plasmon Resonance Sensor Using an Au-MgF2-Au Structure

We describe an Au-MgF2-Au trilayered waveguide-coupled surface plasmon resonance (WCSPR) sensor in this article. The characteristics of this sensing structure are compared with those of the conventional single-layered gold surface plasmon resonance (SPR) sensor theoretically and experimentally. The experiment results show that WCSPR can provide not only seven times smaller refractive index resolution in the bulk sensing application but also more accurate measurement results for the biomolecular interaction analysis than the conventional single-layered gold SPR. What’s more, this high-resolution sensor is easy to build and not sensitive to film thickness variations. The Au-MgF2-Au trilayered WCSPR may provide a simple and convenient chip-based strategy for performance enhancement of SPR sensors without varying the hardware and software of measurement instruments.

Composite layer based plasmon waveguide resonance for label-free biosensing with high figure of merit

A plasmon waveguide resonance (PWR) sensing structure was presented based on composite waveguide layer in this article. This composite layer based PWR (CLPWR) could provide stronger evanescent electric field and sharper resonance curve than surface plasmon resonance (SPR). Owing to these, the CLPWR sensor could provide up to 20 times higher resolution than the conventional SPR technology under ideal conditions. The vacuum coating techniques and optimal optical arrangements were developed for the realization of CLPWR sensor, and the residual analysis was introduced to quantify the effect of experimental system noise on measurement accuracy. In the label free biosensing experiment, it was demonstrated that the CLPWR sensor could provide more accurate measurement results than conventional SPR sensor for label free biomolecular interaction analysis in complex media.

Refractive index sensing characteristics of carbon nanotube-deposited photonic crystal fiber SPR sensor

Abstract In this paper, the carbon nanotubes (CNTs)-deposited Au film photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor (CNTs/Au-PCF sensor) and CNTs-deposited Ag film PCF SPR sensor (CNTs/Ag-PCF sensor) were developed and utilized to conduct a series of experiments for the refractive index sensing characteristics study of the CNTs-deposited SPR sensors. The PCF, spliced between two sections of multimode fibers (MMFs), was coated with a metal (Au or Ag) film and then deposited with CNTs for further sensing. CNTs coating can enhance the confined electric field intensity surrounding the sensing layer, making the SPR sensor more sensitive to the changes in the ambient medium. Compared with conventional Au film PCF SPR sensor (Au-PCF sensor), the sensitivity of CNTs/Au-PCF sensor increases by 1016.09 nm/RIU. Compared with conventional Ag film PCF SPR sensor (Ag-PCF sensor), the sensitivity of CNTs/Ag-PCF sensor increases by 709.22 nm/RIU. Therefore, we find that CNTs have a more significant effect on the Au-PCF sensor than the Ag-PCF sensor. The experimental measurements results agreed well with the simulation results. Furthermore, CNTs have high surface-to-volume ratio and extremely excellent biocompatibility. Bovine serum albumin (BSA) was employed as the target analyte to evaluate the feasibility of the CNTs/Au-PCF sensor for the detection of biomolecules, and the sensor exhibits higher sensitivity (8.18 nm/(mg/mL)), lower limit of detection (LOD) (2.5 µg/mL), and faster response time (8 s) than the Au-PCF sensor. Such CNTs-deposited SPR sensors with high sensitivities and fast response present highly promising potential for application in the field of biochemistry.

Blue Phosphorene/MoS2Heterostructure Based SPR Sensor With Enhanced Sensitivity

Sensitivity enhancement of surface plasmon resonance (SPR) sensor is proposed utilizing two-dimensional blue phosphorene/molybdenum disulfide (i.e., BlueP/MoS2) heterostructure as an interacting layer with analyte. The analysis indicates that the proposed sensor design provides significantly higher sensitivity in comparison to conventional and graphene-based SPR sensors. The combined effect of number of heterostructure layers and light wavelength on sensitivity is also analyzed. The results will open a new way to BlueP/MoS2 heterostructure based SPR sensor for bio- and gas-sensing applications in visible and near infrared spectral regions.

High-Performance Lossy-Mode Resonance Sensor Based on Few-Layer Black Phosphorus

Surface plasmon resonance (SPR) can be excited only by the transverse magnetic (TM)-polarized light in the conventional SPR sensor, whereas the lossy-mode resonance (LMR) can be achieved with both ...

Two-Dimensional Layered Nanomaterial-Based One-Dimensional Photonic Crystal Refractive Index Sensor.

One-dimensional photonic crystal (1DPC) sensors have emerged as contenders for traditional surface plasmon resonance sensors, owing to their potential for the detection of bigger molecules and particles due to their higher interaction volume in the sensing medium. Two-dimensional layered nanomaterials, most notably graphene and dichalcogenides (e.g., MoS2, MoSe2, WS2, and WSe2), have shown higher refractive index sensitivity because of their absorption as well as adsorption property. The proposed configuration of 1DPC presented consists of alternate layers of the aforementioned nanomaterials and silicon. The performance parameters, namely the sensitivity, resolution, quality factor, and the evanescent field penetration depth, are calculated and compared with 1DPC having poly methyl methacrylate (PMMA) in place of silicon. Increased shift in resonance angle and quality factor are observed by replacing PMMA with silicon, but at the cost of decreased resolution. Further, our results show that although the sensitivity and quality factor of the 1DPC sensor is less than that of the conventional surface plasmon resonance sensor (SPR) with a gold thin film, it has much higher resolution and penetration depth to make it suitable for large molecules.

Resolution Enhancement of Plasmonic Sensors by Metal‐Insulator‐Metal Structures

AbstractOptical sensors based on surface plasmons have attracted much attention over the past decades owing to the wealth of applications in bio‐ and chemical and gas sensing. In surface plasmon resonance sensors, a single metal layer is commonly used, but its resolution is limited because of broad resonances. In this context, we have developed a sensor chip based on a stack of metals and a dielectric, e.g. a metal‐insulator‐metal structure, consisting of a thick insulator layer sandwiched by metal layers, that exhibits a sharp resonance due to the excitation of surface plasmon polaritons hybrid modes. We have performed both experiments and theoretical simulations to estimate the enhancement of the sensitivity of such a structure. By changing the refractive index of an aqueous solution of glucose on top of the sensor chip, we found that the use of a metal‐insulator‐metal structure improves the figure of merit of the sensor 7.5 times compared to that of a conventional surface plasmon resonance sensor chip.

Design Analysis of Refractive Index Sensor with High Quality Factor Using Au-Al2O3 Grating on Aluminum

We propose a surface plasmon resonance (SPR)-based refractive index sensor using gold-alumina grating over aluminum film for biosensing. Conventional SPR sensor based on gold grating exhibits broader SPR dips whereas that based on aluminum grating exhibits narrow reflection dip. A narrow reflection dip is desirable as it provides good resolution and improves the accuracy of measurement. Aluminum is less stable and generally is not preferred for an SPR-based sensor. It is more prone to being oxidized, which reduces the sensitivity and increases the width of the reflection dip of the sensor. While gold cannot provide narrow SPR reflection dips, but is used as an SPR active metal due to its more chemical stability. In order to improve the accuracy of gold grating-based sensor while taking care of oxidation problem of aluminum, in this paper, we propose a gold grating over aluminum film for SPR-based sensor and show that this configuration improves the sensitivity and the detection accuracy of the conventional sensor. Moreover, the oxidation problem is reduced to some extent as a part of aluminum is covered with gold. In order to completely avoid the oxidation of aluminum, we further propose to cover the exposed part of the aluminum with alumina and show that this configuration further improves the accuracy by reducing the width of the SPR reflection dip without affecting the sensitivity significantly. Numerical simulations show that sensitivity of proposed sensor is 270.33°/RIU with quality factor of more than 267.65 RIU−1.

Characteristics of multiple Fano resonances in waveguide-coupled surface plasmon resonance sensors based on waveguide theory

We observe and analyze multiple Fano resonances and the plasmon-induced transparency (PIT) arising from waveguidecoupled surface plasmon resonance in a metal-dielectric Kretschmann configuration. It is shown that the simulation results for designed structures agree well with those of the dispersion relation of waveguide theory. We demonstrate that the coupling between the surface plasmon polariton mode and multi-order planar waveguide modes leads to multiple Fano resonances and PIT. The obtained results show that the number of Fano resonances and the linewidth of resonances depend on two structural parameters, the Parylene C and SiO2 layers, respectively. For the sensing action of Fano resonance, the figure of merit for the sensitivity by intensity is estimated to be 44 times higher than that of conventional surface plasmon resonance sensors. Our research reveals the potential advantage of sensors with high sensitivity based on coupling between the SPP mode and multi-order PWG modes.

Spectrometer-Free Plasmonic Biosensing with Metal-Insulator-Metal Nanocup Arrays.

The development of high performing and accessible sensors is crucial to future point-of-care diagnostic sensing systems. Here, we report on a gold-titanium dioxide-gold metal-insulator-metal plasmonic nanocup array device for spectrometer-free refractometric sensing with a performance exceeding conventional surface plasmon resonance sensors. This device shows distinct spectral properties such that a superstrate refractive index increase causes a transmission intensity increase at the peak resonance wavelength. There is no spectral shift at this peak and there are spectral regions with no transmission intensity change, which can be used as internal device references. The sensing mechanism, plasmon-cavity coupling optimization, and material properties are studied using electromagnetic simulations. The optimal device structure is determined using simulation and experimental parameter sweeps to tune the cavity confinement and the resonance coupling. An experimental sensitivity of 800 ΔT%/RIU is demonstrated. Spectrometer-free, imaged-based detection is also carried out for the cancer biomarker carcinoembryonic antigen with a 10 ng/mL limit of detection. The high performance and distinct spectral features of this metal-insulator-metal plasmonic nanocup array make this device promising for future portable optical sensing systems with minimal instrumentation requirements.

Improving the performance of hollow fiber surface plasssmon resonance sensor with one dimensional photonic crystal structure.

A high performance hollow fiber (HF) surface plasmon resonance (SPR) sensor utilizing one-dimensional photonic crystal (1DPC) is proposed. The performance of the designed sensor is analyzed theoretically with respect to the center wavelength and the bilayer period. Because the light transmitted in the sensor mostly have large incident angles, the center wavelength of the 1DPC should shift to longer wavelength to ensure the band gap covers the spectrum range of the incident light. The sensor exhibits better performance when the detection spectral range is located in the band gap of 1DPC for incident angle larger than 80°. Compared to conventional HF SPR sensor, the figure of merit (FOM) of the proposed sensor is three to four times higher while the sensitivity is comparable. Moreover, within the limited spectrum range of 400 to 800nm, the proposed sensor have much wider refractive index (RI) detection range and can detect sensed medium with low RI very close to the supporting tube.

High Sensitivity Intensity-Interrogated Bloch Surface Wave Biosensor With Graphene

Bloch surface wave (BSW) is a surface state excited within the truncate defect layer at the surface of a dielectric 1-D photonic crystal (1DPC), which has been suggested as an attractive alternative to surface plasmon resonance (SPR) in chemical and biological sensors. In this paper, we propose an intensity-sensitive BSW sensor based on the truncate 1DPC with graphene. By optimizing the thickness of the defect layer and the layer number of graphene, the maximum intensity sensitivity of biosensor can surpass $3.5\times 10^{4}$ /RIU, which is greater than that for the conventional BSW or SPR sensors. With such excellent and interesting performance, we believe that the structure can be useful for many important applications in the field of chemical and biological sensors in the future.

Ultrasensitive Terahertz Biosensors Based on Fano Resonance of a Graphene/Waveguide Hybrid Structure.

Graphene terahertz (THz) surface plasmons provide hope for developing functional devices in the THz frequency. By coupling graphene surface plasmon polaritons (SPPs) and a planar waveguide (PWG) mode, Fano resonances are demonstrated to realize an ultrasensitive terahertz biosensor. By analyzing the dispersion relation of graphene SPPs and PWG, the tunable Fano resonances in the terahertz frequency are discussed. It is found that the asymmetric lineshape of Fano resonances can be manipulated by changing the Fermi level of graphene, and the influence of the thickness of coupling layer and air layer in sandwich structure on the Fano resonances is also discussed in detail. We then apply the proposed Fano resonance to realize the ultrasensitive terahertz biosensors, it is shown that the highest sensitivities of 3260 RIU−1 are realized. Our result is two orders of a conventional surface plasmon resonance sensor. Furthermore, we find that when sensing medium is in the vicinity of water in THz, the sensitivity increases with increasing refractive index of the sensing medium.