Guided-wave Surface Plasmon Resonance Research Articles

Advancing Sensitivity in Guided-Wave Surface Plasmon Resonance Sensor through Integration of 2D BlueP/MoS2 Hybrid Layers.

The surface plasmon resonance (SPR) signal, generated from the Kretschmann configuration, has been developed as an effective detection technology in chemical and biological sensors. The sensitivity of SPR signals to changes in the surrounding media makes it a valuable tool, as even a slight variation in refractive index can cause a significant change in SPR signals, such as phase, intensity, and resonance angle. However, the detection of ultralow changes in refractive index, which occur in chemical reactions or biological actions, remains a challenge for conventional SPR sensors due to their limited sensitivity. To overcome this limitation, we theoretically propose a novel guided-wave SPR (GWSPR) configuration coated with a few-layer blue phosphorene (blueP)/MoS2 hybrid structure. This configuration aims to enhance the electric field and subsequently achieve a significant improvement in sensitivity. The results of our study demonstrate that the proposed blueP/MoS2-based GWSPR sensor exhibits a high sensitivity of 290°/RIU, which represents an impressive enhancement of approximately 82.4% compared to the conventional Au-based SPR sensor. This advancement addresses the challenge of detecting ultralow changes in refractive index and offers significant potential for enhancing the performance of chemical and biological sensors.

Beam shifts controlled by orbital angular momentum in a guided-surface plasmon resonance structure with a four-level atomic medium.

We proposed a scheme to realize tunable giant Goos-Hänchen (GH) and Imbert Fedorov (IF) shifts of the Laguerre-Gauss (LG) beam on a guided-wave surface plasmon resonance (GWSPR) structure backed by a coherent atomic medium with the spontaneously generated coherence (SGC) effect. The orbital angular momentum carried by the incident LG beam can be applied to enhance and control IF shifts but is not beneficial to GH shifts. However, in the presence of SGC effect in the atomic medium, both GH and IF shifts can be simultaneously enhanced and well controlled. With the SGC effect, the linear absorption of the atomic medium vanishes, while the nonlinear absorption of that can be significantly enhanced and controlled by the trigger field, which contributes to controlling of the beam shifts. In particular, the direction of GH shifts can be switched by the Rabi frequency of the trigger field, which can be interpreted as the result of a competition between the inherent damping and the radiative damping corresponding to the nontrivial change in the loci of the reflection coefficients. This scheme provides an effective method to flexibly control and enhance the beam shifts, so it has potential applications in integrated optics, optical sensors, etc.

Violet phosphorus-enhanced plug-and-play double-lane fiber optic surface plasmon resonance refractometer

The fiber optic surface plasmon resonance (SPR) technologies can directly detect the change of the refractive index on the surface of the sensor, caused by the interaction of biochemical molecules. Fiber optic SPR technologies have advantages of small size, low cost, no labeling, high sensitivity, and are easy to realize the miniaturization, multi-parameter, real-time and <i>in-situ</i> detection. Two types of probe-type fiber optic SPR refractometers are constructed based on the novel two-dimensional nanomaterial, i.e., violet phosphorus (VP), the mature fabrication and characterization technologies. The fabrication processes of the fiber optic SPR refractometers are first introduced, and then the feasibility of the fabrication processes is verified via multiple characterization methods. In terms of the signal demodulation, the noise of the resonance spectrum is suppressed by the variational mode decomposition algorithm, and the resonance wavelength is interrogated and monitored in real time by the centroid method. The refractive index sensing performances of the near-field enhanced fiber optic SPR refractometers coated with different layers of VP are investigated. With the increase of the VP layer number, the resonance spectrum exhibits redshift and broadening and the sensitivity is enhanced. The refractive index sensing performance of the nearly guided wave fiber optic SPR refractometer is also investigated. In the low refractive index range of 1.33－1.34 corresponding to the refractive index of the low-concentration biological solution, the sensitivity and the figure of merit of the near-field enhanced fiber optic SPR refractometer with the sensing structure of fiber core/VP dielectric layer/Au layer/sample layer reach to 2335.64 nm/RIU and 24.15 RIU<sup>–1</sup>, respectively, which are 1.31 times and 1.25 times higher than the counterparts of the single Au layer fiber optic SPR refractometer, respectively. The sensitivity and the figure of merit of the nearly guided wave fiber optic SPR refractometer with the sensing structure of fiber core/Au layer/VP dielectric layer/sample layer can reach to 2802.06 nm/RIU and 22.53 RIU<sup>–1</sup>, respectively, which are 1.57 times and 1.16 times higher than the counterparts of the single Au layer fiber optic SPR refractometer. Finally, the near-field enhanced SPR and the nearly guided wave SPR are integrated into a single fiber probe to achieve the double-lane sensing. The fiber optic SPR refractometers developed in this study can realize the high-sensitivity, plug-and-play and double-lane detection of the combination of surface refractive index and volume refractive index. The probe-type refractometer also provides a new idea for detecting multi-type protein molecules and heavy metal ions in the biochemical field.

Sensitivity improvement of aluminum-based far-ultraviolet nearly guided-wave surface plasmon resonance sensor

An aluminum (Al) based nearly guided-wave surface plasmon resonance (NGWSPR) sensor is investigated in the far-ultraviolet (FUV) region. By simultaneously optimizing the thickness of Al and dielectric films, the sensitivity of the optimized Al-based FUV-NGWSPR sensor increases from 183°/RIU to 309°/RIU, and its figure of merit rises from 26.47 RIU−1 to 32.59 RIU−1 when the refractive index of dielectric increases from 2 to 5. Compared with a traditional FUV-SPR sensor without dielectric, the optimized FUV-NGWSPR sensor can realize simultaneous improvement of sensitivity and figure of merit. In addition, the FUV-NGWSPR sensor with realistic materials (diamond, Ta2O5, and GaN) is also investigated, and 137.84%, 52.70%, and 41.89% sensitivity improvements are achieved respectively. This work proposes a method for performance improvement of FUV-SPR sensors by exciting nearly guided-wave, and could be helpful for the high-performance SPR sensor in the short-wavelength region.

Comparative study on sensitivity enhancement of a graphene based nearly guided-wave surface plasmon resonance biosensor optimized using genetic algorithm in the visible region

Comparative study on sensitivity enhancement of a graphene based nearly guided-wave surface plasmon resonance biosensor optimized using genetic algorithm in the visible region

CH3NH3PbBr3 Thin Film Served as Guided-Wave Layer for Enhancing the Angular Sensitivity of Plasmon Biosensor.

CH3NH3PbBr3 perovskite thin film is used as a guided-wave layer and coated on the surface of an Au film to form the Au-perovskite hybrid structure. Using the hybrid structure, a perovskite-based guided-wave surface plasmon resonance (GWSPR) biosensor is proposed with high angular sensitivity. First, it is found that the electric field at the sensing interface is improved by the CH3NH3PbBr3 perovskite thin film, thereby enhancing the sensitivity. The result demonstrates that the angular sensitivity of the Au-perovskite-based GWSPR biosensor is as high as 278.5°/RIU, which is 110.2% higher than that of a conventional Au-based surface plasmon resonance (SPR) biosensor. Second, the selection of the coupling prism in the configuration of the GWSPR biosensor is also analyzed, and it indicates that a low refractive index (RI) prism can generate greater sensitivity. Therefore, the low-RI BK7 prism is served as the coupling prism for the proposed GWSPR biosensor. Finally, the proposed GWSPR sensing structure can not only be used for liquid sensing, but also for gas sensing, and it has also been demonstrated that the GWSPR gas sensor is 2.8 times more sensitive than the Au-based SPR gas sensor.

Engineering the penetration depth of nearly guided wave surface plasmon resonance towards application in bacterial cells monitoring

Photonic techniques based on evanescent waves sensing (such as the surface plasmon resonance (SPR) method) using plasmonic and nanostructured metallic/semiconductor materials hold huge potential in biosensing and associated analysis of biomolecular interactions. However, conventional SPR suffers from low penetration depths (<300 nm), limiting the applications for the surface interactions and analysis of larger biomolecules, such as for bacteria cells with a typical size of ∼1 μm. These cases result in the measured signal being non-monotonic with concentration, making the technique unreliable for high concentrations. Infrared wavelengths can be used, but then signal contrast suffers, and the instruments required for mid-infrared or longer wavelengths are prohibitively expensive. With this in mind, we developed a “nearly” guided SPR (NGWSPR) structure to enhance the performance of these sensors by increasing penetration depth and figure of merit using wavelengths in the optical telecommunication window where off-the-shelf instruments are available at low cost. The use of this technique for monotonic detection of cultured live Escherichia coli bacterial cells is demonstrated, thus opening a pathway to utilize and promote the approach for biosensing, biomedical research and industrial applications.

Coherent control of Goos-Hänchen shift in a guided-wave surface plasmon resonance structure with Rydberg atoms

We proposed an effective and flexible scheme to achieve tunable giant Goos-Hänchen (GH) shift of reflected light in the configuration of guided-wave surface plasmon resonance with Rydberg atoms. With the super atom model of Rydberg atom due to the dipole blocking effect, we investigated the influence of Rydberg state population on GH displacement. By adjusting the external driving field on Rydberg atoms without changing the structure geometry, not only can GH shift be enhanced significantly to the magnitude of millimeter, but also the transition between positive and negative GH shift can be controlled at the same resonant angles. Furthermore, the resonant angle position of the maximum GH shift is also tunable via detuning the field. Our scheme may offer promising prospects for the optical switches and nano-sensors with high precision.

Black phosphorus (BP)–graphene guided-wave surface plasmon resonance (GWSPR) biosensor

Abstract Due to lower out-of-plane electrical conductance, black phosphorus (BP) provides a suitable host material for improving the sensitivity of biosensors. However, BP oxidizes easily, which limits practical applications. In this article, we propose a sensitivity-enhanced guided-wave surface plasmon resonance (GWSPR) biosensor based on a BP–graphene hybrid structure. This BP–graphene hybrid structure exhibits strong antioxidation properties and exceptional biomolecule-trapping capability, which improve the stability and sensitivity of GWSPR biosensors, respectively. We show that the proposed GWSPR biosensor can distinguish refractive indices in the range of 1.33–1.78 RIU (RIU is the unit of RI), and the sensitivity reaches a maximum of 148.2°/RIU when the refractive index of sensing target is 1.33 RIU. The high sensitivity and broad detection range indicate that the proposed biosensor could significantly impact fields such as biological and chemical detection.

Electrically Control Lateral Shift Owning to Guided-Wave Surface Plasmon Resonance with a Lithium Niobate Prism

Electrically controlled lateral shift by an electro-optic crystal prism is studied theoretically. The resonance point of excitation of guided-wave surface plasmon resonance (GWSPR) can be controlled by altering the refractive index of the prism. That is to say, the positions corresponding to the least reflectivity and the largest lateral shift could be conveniently modulated while the lithium niobate prism is operated in an external electric field. The maximal lateral shift is obtained at the excitation of GWSPR when the thickness of the silver film is optimized. The results of numerical simulations confirm theoretical calculation.

Design of highly sensitive guided-wave surface plasmon resonance biosensor with deep dip using genetic algorithm

In this paper, we presented a genetic algorithm (GA) based design method of highly sensitive guided-wave surface plasmon resonance (GWSPR) biosensor with deep dip. A constraint condition of reflectivity at resonance angle was used in a sensitivity based merit function (MF) of GA to achieve simultaneous optimization of sensitivity and depth of dip of GWSPR biosensor. Using the proposed method, we designed a GWSPR biosensor with Ag–TiO2 –graphene hybrid structure at first, and compared its performance with a same structure based SPR biosensor but designed by conventional method (CM). The results indicated that the sensitivity of the GA designed GWSPR biosensor was nearly the same as the one of CM designed biosensor, but its reflectivity at resonance angle was much lower. In addition, GWSPR biosensors with different layers of graphene were also designed and analyzed. It was found that the optimal sensitivity of the proposed GWSPR biosensor decreased with increasing layers of graphene. Furthermore, the effect of target reflectivity at resonance angle on the design of GWSPR biosensor was also investigated. The proposed design method based on GA can be further applied to SPR biosensors with arbitrary multilayer structures, making it helpful for high-performance SPR sensors development.

Sensitivity comparison of graphene-based nearly guided-wave surface plasmon resonance biosensors with Au, Ag, Cu, and Al

A comparative study of sensitivity of guided-wave surface plasmon resonance (NGWSPR) biosensors with Au, Ag, Cu, and Al is presented. The thicknesses of metal films in NGWSPR biosensors were optimized first to realize minimal reflectivity at resonance angle. Then, the sensitivities of NGWSPR biosensors were optimized by optimizing the thickness of dielectric film, and the peak sensitivities for different metals are determined. By comparing peak sensitivities of different metals, we find that the Ag-based NGWSPR biosensor always exhibits largest peak sensitivity for different dielectrics, followed by Cu-, Au-, and Al-based ones. When using PbS as the dielectric in the NGWSPR biosensor, the largest peak sensitivity of Ag-based NGWSPR biosensor is up to 232.48 deg / RIU at 632.8 nm wavelength, which is 45.72%, 31.58%, or 271.49% higher than the sensitivity of Au-, Cu-, or Al-based ones. In addition, the reflectance curves and electric field intensity distributions of optimized NGWSPR biosensors with different metals are studied to analyze the origin of high sensitivity achieved by Ag. Furthermore, the effect of the number of graphene layers on the peak sensitivity of an NGWSPR biosensor is also investigated. It is believed that the sensitivity comparison of graphene-based NGWSPR biosensors with Au, Ag, Cu, and Al could be helpful for highly sensitive biosensors development.

Large Tunable Lateral Shift from Guided Wave Surface Plasmon Resonance

Large tunable lateral shift from guided wave surface plasmon resonance (GWSPR) is theoretically predicted. The dip of reflectivity and magnitude of the lateral shift can be controlled by the thickness of silver layer. The position of minimum reflection and maximum Goos-Hanchen (GH) shift can be conveniently adjusted by guided layer. The largest GH shifts at the optimal thickness of silver film can be hundreds of wavelengths when GWSPR is excited. The numerical calculation results from the Gaussian beam are in accordance with theoretical results.

Enhanced spin Hall effect of reflected light with guided-wave surface plasmon resonance

The photonic spin Hall effect (SHE) has been intensively studied and widely applied, especially in spin photonics. However, the SHE is weak and is difficult to detect directly. In this paper, we propose a method to enhance SHE with the guided-wave surface-plasmon resonance (SPR). By covering a dielectric with high refractive index on the surface of silver film, the photonic SHE can be greatly enhanced, and a giant transverse shift of horizontal polarization state is observed due to the evanescent field enhancement near the interface at the top dielectric layer and air. The maximum transverse shift of the horizontal polarization state with 11.5 μm is obtained when the thickness of Si film is optimum. There is at least an order of magnitude enhancement in contrast with the transverse shift in the conventional SPR configuration. Our research is important for providing an effective way to improve the photonic SHE and may offer the opportunity to characterize the parameters of the dielectric layer with the help of weak measurements and development of sensors based on the photonic SHE.

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%.

Sensitivity Enhanced by MoS2–Graphene Hybrid Structure in Guided-Wave Surface Plasmon Resonance Biosensor

Compared with surface plasmon resonance (SPR) biosensor, guided-wave surface plasmon resonance (GWSPR) biosensor has a higher sensitivity. In order to further enhance the sensitivity of the GWSPR biosensor, the MoS2–graphene hybrid structure is proposed to cover on the surface of the thin silicon film. It is demonstrated that the sensitivity of the proposed biosensor configuration can be doubled by using optimized MoS2–graphene hybrid structure. By analyzing the electric field distributions with the proposed GWSPR biosensor, it is shown that the electric field intensity has a dramatic change with a slight change in refractive index of sensing medium, and it also means that the biosensor is sensitive to detect the analytes. Moreover, the proposed GWSPR biosensor has a wide detection range of refractive index of sensing medium, and the sensitivity is increased with the refractive index of sensing medium increasing.