Long-range Surface Plasmon Resonance Research Articles

Optimization of angle-pixel resolution for angular plasmonic biosensors

An angular plasmonic sensor based on optimized angle-pixel resolution to detect antibody-antigen binding process is presented. Owing to discrete resonance curves by the CCD pixels, the pixel sensitivity and detection noise of the plasmonic sensors need to be balanced. The angle-pixel resolution is adjusted by changing the distance between the sensor chip and the CCD to obtain the optimal refractive index (RI) resolution for three plasmonic sensors, which are surface plasmon resonance (SPR), long range surface plasmon resonance (LRSPR) and plasmon waveguide resonance (PWR) sensors. Each plasmonic sensor can achieve its optimal RI resolution at the optimal distance, and the LRSPR sensor has the best RI resolution. Attributing to the reference channel and temperature control module in the sensor system, the RI resolution can achieve 4.37 × 10−7 RIU at Normal mode and 1.13 × 10-7 RIU at a slow response Extreme mode. The Protein A-IgG binding reaction experiment indicates that the plasmonic sensor has linear response to IgG concentration in a wide range and the limit of detection (LOD) is 5.45 pM at Extreme mode. The procedure and result of this work are helpful to the optimization of other angular plasmonic sensors.

Two-dimensional transition metal dichalcogenides mediated long range surface plasmon resonance biosensors

Two-dimensional transition metal dichalcogenides (TMDCs), as promising alternative plasmon supporting materials to graphene, exhibit potential applications in sensing. Here, we propose a TMDCs-mediated long range surface plasmon resonance (LRSPR) imaging biosensor, which shows tremendous improvements in both imaging sensitivity (2) and detection accuracy (10) as compared to conventional surface plasmon resonance (cSPR) biosensors. It is found that the imaging sensitivity of the LRSPR biosensor can be enhanced by the integration of TMDC layers, which is different from the previously reported graphene-mediated cSPR imaging sensor, whose imaging sensitivity decreases with the number of graphene layers. This imaging sensitivity enhancement effect for the TMDCs-mediated LRSPR sensor originates from the propagating nature of the LRSPR at both interfaces of sensing medium/gold and gold/cytop layer (with a matching refractive index as sensing medium). By tuning the thickness of gold film and cytop layer, it is possible to achieve optimized imaging sensitivity for LRSPR sensors with any known integrated number of TMDC layers and an analyte refractive index. The proposed TMDCs-mediated LRSPR imaging sensor could provide potential applications in chemical sensing and biosensing.

Refractive Index Sensor Using Long-Range Surface Plasmon Resonance with Prism Coupler

Long-range surface plasmon resonance (LRSPR)-based sensors exhibit high sensitivity as compared to the conventional SPR sensors due to low losses. A high refractive index prism and low refractive index dielectrics are required to excite long-range surface plasmon (LRSP) mode. In this work, a symmetrical structure consisting of metal (Au) layer sandwiched between the two similar refractive index dielectrics has been utilized to excite LRSPR modes. Two dielectrics, i.e., LiF and MgF2 thin films have been chosen for glucose sensing. Theoretical simulations for optimizing the thickness of two dielectrics have been carried out. Highly sensitive refractive index sensors based on LRSPR have been developed using the two dielectric thin films and their sensitivities have been compared.

Giant Goos–Hänchen shifts of waveguide coupled long-range surface plasmon resonance mode**Project supported by the National Natural Science Foundation of China (Grant Nos. 61505111 and 11604216), the China Postdoctoral Science Foundation (Grant No. 2016M600667), the Science and Technology Planning Project of Guangdong Province, China (Grant No. 2016B050501005), the Fund from the Educational Commission of Guangdong Province, China (Grant No. 2016KCXTD006), and

A hybrid structure based on a planar waveguide (PWG) mode coupling a long-range surface plasmon resonance (LRSPR) mode is proposed to enhance the GH shift. Both the PWG mode and LRSPR mode can be in strong resonance, and these two modes can be coupled together due to the normal-mode splitting. The largest GH shift of PWG-coupled LRSPR structure is 4156 times that of the incident beam, which is 23 times and 3.6 times that of the surface plasmon resonance (SPR) structure and the LRSPR structure, respectively. As a GH shift sensor, the highest sensitivity of 4.68 × 107λ is realized in the coupled structure. Compared with the sensitivity of the traditional SPR structure, the sensitivity of our structure is increased by more than 2 orders, which theoretically indicates that the proposed configuration can be applied to the field of high-sensitivity sensors in the future.

Enhancement of spin components’ shifts of reflected beam via long range surface plasmon resonance

In this letter, we investigated the impact of long range surface plasmon resonance (LRSPR) on the spatial and angular shifts of left and right spin components of a p-polarization Gaussian beam reflected from a glass-fused silica-gold-fused silica interface, and deduced the formulas of these shifts. We found that the spatial and angular spin splitting of left and right spin components only occur in the direction perpendicular to the plane of incidence (out-of-plane), but not in the direction parallel to the plane of incidence (in-plane). The spatial and angular in-plane shifts of left and right spin components are the same, which are equal to those of the total reflected beam (i.e., angular and spatial Goos–Hänchen shifts). We found that all the in-plane and out-of-plane shifts can be greatly enhanced by LRSPR. The maximum angular and spatial in-plane shifts can be up to 1.060×10−4 rad and 249.977 μm, respectively, which are almost equal to half of the divergence angle and beam waist of the incident Gaussian beam. The maximum spatial in-plane shift (about 20.148 μm) is about 5 times larger than the previously reported enhanced value. We also found that the directions and magnitude of angular and spatial in-plane and out-of-plane shifts can be controlled by slightly adjusting the angle of incidence or the thickness of fused silica film or gold film under certain conditions, which may provide a new way for photon manipulation. Furthermore, our work may provide some help for precision measurement of physical and biological parameters and the development of SPR sensing technology.

Long-range surface plasmon excitation and photoisomerization of Azobenzene dye

ABSTRACTEnhancement of photoisomerization of Azobenzene dye Chicago Sky Blue 6B (CSB) was attempted using long-range surface plasmon resonance (LRSPR). The CSB film was prepared on a grating substrate with metal film for LRSPR, and its transmission light property was investigated before and after white light irradiation for photoisomerization. The transmission light was markedly changed by irradiation of p-polarized white light, and the change was attributed to photoisomerization of CSB induced by LRSPR which accompanies an intense electric field. Furthermore, the effect of LRSPR was significant compared to standard SPR.

A Localized Surface Plasmon Resonance Sensor Using Double-Metal-Complex Nanostructures and a Review of Recent Approaches.

From active developments and applications of various devices to acquire outside and inside information and to operate based on feedback from that information, the sensor market is growing rapidly. In accordance to this trend, the surface plasmon resonance (SPR) sensor, an optical sensor, has been actively developed for high-sensitivity real-time detection. In this study, the fundamentals of SPR sensors and recent approaches for enhancing sensing performance are reported. In the section on the fundamentals of SPR sensors, a brief description of surface plasmon phenomena, SPR, SPR-based sensing applications, and several configuration types of SPR sensors are introduced. In addition, advanced nanotechnology- and nanofabrication-based techniques for improving the sensing performance of SPR sensors are proposed: (1) localized SPR (LSPR) using nanostructures or nanoparticles; (2) long-range SPR (LRSPR); and (3) double-metal-layer SPR sensors for additional performance improvements. Consequently, a high-sensitivity, high-biocompatibility SPR sensor method is suggested. Moreover, we briefly describe issues (miniaturization and communication technology integration) for future SPR sensors.

Analysis of high-resolution electro-optical beam steering by long-range surface plasmon resonance using a ZnSe prism.

A proposal on high-resolution electro-optical beam steering is conceptualized analytically using a long-range surface plasmon resonance configuration comprising a liquid crystal layer of E44 for 1550nm wavelength. With the tuning of the refractive index of E44 through variations of applied voltage from 0 to 10V, an optical beam steering can be attained considering the composite effect of spatial and angular Goos-Hanchen and Imbert-Fedorov shifts. As compared with the existing beam shift processes in μrad by mechanical means, here, the computed angular resolution is 3.40nrad. The proposed idea finds a new avenue in the field of pulse generation, optical sensor applications, and atomic force microscopy, mitigating existing drawbacks.

Long-range surface plasmon-induced tunable ultralow threshold optical bistability using graphene sheets at terahertz frequency.

A proposal on optical bistability at ultralow switching threshold and lower Fermi-level of graphene around 2 THz is implemented analytically through the proposed long-range surface plasmon resonance configuration by employing local field enhancement effects owing to the excitation of a graphene symmetric mode within graphene sheets. Reported threshold intensity for the optical bistability to date is 1.6 kW/cm2 within the terahertz region and 1.83 MW/cm2 at near-IR range. Whereas the proposed scheme explores the possibility of reducing this threshold down to 143.68 W/cm2, this technique proffers potential applications in nanoillumination, optical memory, and all-optical switching at an ultra-low threshold.

Metal clad waveguide (MCWG) based imaging using a high numerical aperture microscope objective.

Evanescent-field based methods such as surface plasmon resonance (SPR) have been used very effectively for label-free imaging of microscopic biological material in close proximity to a sensing surface. However, the shallow probing depth of SPR (typically less than ~200 nm) can be problematic when imaging relatively thick biological objects such as cells or bacteria. In this paper, we demonstrate how metal-clad waveguides (MCWG) can be used to achieve deeper probing depth compared to SPR while maintaining good imaging spatial resolution. Comparative numerical simulations of imaging spatial resolution versus probing depth are shown for a number of common SPR, long-range SPR, and MCWG configurations, demonstrating that MCWG offer the best compromise between resolution and depth for imaging thick biological objects. Experimental results of synthetic target and live cell imaging are shown that validate the numerical simulations and demonstrate the capabilities of the method.

Long-range surface plasmon resonance and surface-enhanced Raman scattering on X-shaped gold plasmonic nanohole arrays.

A multilayered architecture including a thin Au film supporting an X-shaped nanohole array and a thick continuous Au film separated by a Cytop dielectric layer is reported in this work. Long-range surface plasmon resonance (LR-SPR) was generated at the top Au/water interface, which also resulted in a long-range surface-enhanced Raman scattering (LR-SERS) effect. LR-SPR originates from the coupling of surface plasmons (SPs) propagating along the opposite sides of the thin Au film embedded in a symmetric refractive index environment with Cytop (n = 1.34) and water (n = 1.33). The finite-difference time-domain (FDTD) simulation method was used to investigate the optimal dimensions of the substrate by studying the reflectance spectra and electric field profiles. The calculated optimal structure was then fabricated via electron beam lithography, and its LR-SERS performance was demonstrated by detecting rhodamine 6G and 4-mercaptobenzoic acid in the refractive index-matched environment. We believe that this structure as a LR-SPR or LR-SERS substrate can have broad applications in biosensing.

Enhancing photonic spin Hall effect via long-range surface plasmon resonance.

We presented the significant enhancement of the photonic spin Hall effect by taking advantage of long-range surface plasmon resonance (LRSPR). The influence of the thicknesses of metal and dielectric layers in the insulator-metal-insulator structure which supports LRSPR was investigated. Under the optimal parameter setup, the largest transverse separation with a 632.8 nm incident Gaussian beam reaches 7.85 μm, which is much larger than previous reported values.

Transmission light property due to grating-coupled long-range surface plasmon resonance

Transmission light property due to surface plasmon resonance (SPR) was investigated for glass substrate/500-nm-thick fluoropolymer (CYTOP) with a grating structure/thin metal film/mixed solution of water and glycerol system. Transmission light peaks were observed due to grating-coupled SPR, with a remarkable peak intensity when pure water exists as an ambient dielectric. CYTOP exhibits a refractive index close to that of water, and the remarkable peak intensity was attributed to long-range SPR. The monitoring of polyelectrolyte layer-by-layer film deposition using transmission light was also investigated.

Influence of Plasma Polymerized Dielectric Buffer Layer and Gold Film on the Excitation of Long-Range Surface Plasmon Resonance

Recently, long-range surface plasmon resonance (LRSPR) sensor has attracted a great deal of attention as a potentially non-destructive and label-free technique for cellular studies in real time. Thus, much effort has been placed on the fabrication and optimization of multilayered structure required for the excitation of LRSPR. In this work, a detailed study about the influence of both plasma polymerized dielectric buffer layer (DBL) and thin gold film on the excitation of LRSPR was performed. The DBLs of different thicknesses were deposited directly onto SF11 glass slides by radio frequency plasma polymerization (pp) of perfluorooctyl ethylene (PFOE). Thereafter, Au films of different thicknesses were thermally evaporated onto the ppPFOE layers. Atomic force microscopy (AFM) results suggest that the resulting SF11/ppPFOE/Au structure has a smooth surface regardless of Au film’s thickness. LRSPR measurements indicate that the excitation of LRSPR relies not only on the thickness of the ppPFOE buffer layer, but also on the thickness and optical property of thin Au film. Theoretical simulation based on Fresnel’s equation allows for the determination of both the thickness and optical constant of each layer supporting the LRSPR, and also enables us to predict the optimum combination of ppPFOE and Au film in a LRSPR sensor. The performance of various LRSPR sensors to monitor the bulk refractive index variation has also been investigated.

Long-Range Surface Plasmon With Graphene for Enhancing the Sensitivity and Detection Accuracy of Biosensor

A novel long-range surface plasmon with graphene is proposed to enhance the sensitivity and detection accuracy (DA) of the biosensor. Compared with the conventional long-range surface plasmon resonance (LRSPR) structure with Au, the coating of the metal surface with graphene is employed to increase the biomolecules adsorption, prevent oxidation, and enhance the sensitivity and DA. Furthermore, we demonstrated that the sensitivity has a nearly tenfold improvement with a huge increasing DA in the proposed LRSPR biosensor compared with the SPR biosensor. Finally, we discuss the influence of the refractive index of sensing medium on the LRSPR biosensor and find that the sensitivity is changing with the refractive index of the sensing medium and that an optimal sensitivity can be obtained at a suitable refractive index. We believe that this scheme could find potential applications in chemical examination, medical diagnosis, and biological detection.

Investigation of plasmonic signal enhancement based on long range surface plasmon resonance with gold nanoparticle tags

Gold nanoparticle (AuNP) molecular tags yield a significant signal enhancement in long range SPR-based biosensing.

Application of Long-Range Surface Plasmon Resonance for ABO Blood Typing.

In this study, we demonstrate a long-range surface plasmon resonance (LR-SPR) biosensor for the detection of whole cell by captured antigens A and B on the surface of red blood cells (RBCs) as a model. The LR-SPR sensor chip consists of high-refractive index glass, a Cytop film layer, and a thin gold (Au) film, which makes the evanescent field intensity and the penetration depth longer than conventional SPR. Therefore, the LR-SPR biosensor has improved capability for detecting large analytes, such as RBCs. The antibodies specific to blood group A and group B (Anti-A and Anti-B) are covalently immobilized on a grafting self-assembled monolayer (SAM)/Au surface on the biosensor. For blood typing, RBC samples can be detected by the LR-SPR biosensor through a change in the refractive index. We determined that the results of blood typing using the LR-SPR biosensor are consistent with the results obtained from the agglutination test. We obtained the lowest detection limits of 1.58 × 105 cells/ml for RBC-A and 3.83 × 105 cells/ml for RBC-B, indicating that the LR-SPR chip has a higher sensitivity than conventional SPR biosensors (3.3 × 108 cells/ml). The surface of the biosensor can be efficiently regenerated using 20 mM NaOH. In summary, as the LR-SPR technique is sensitive and has a simple experimental setup, it can easily be applied for ABO blood group typing.

Study on the symmetrical metal-cladding waveguide-enhanced quality factor

The quality factor (Q value) is a vital parameter for evaluating the sensitivity feature of optical sensors. A comparative study of Q values is carried out by analyzing the absorption peaks of the attenuated total reflection in the surface plasmon resonance, long-range surface plasmon resonance, metal clad leaky waveguide, and symmetrical metal-cladding waveguide. The calculation results show that the full width at half maximum of the ultrahigh-order modes, which are excited in the SMCW, can be reduced to the order of 10−2 nm, and the corresponding Q value can be enhanced to the order of 104, which is far beyond those of other sensing structures.

Long-range surface plasmon resonance sensors fabricated with plasma polymerized fluorocarbon thin films

A rapid and simple approach to prepare the dielectric buffer layers is of crucial importance for the development of long-range surface plasmon resonance (LRSPR) sensors. In this regard, we describe for the first time the use of plasma polymerized fluorocarbon thin films as the dielectric buffer layers for the construction of LRSPR sensors. The fluorocarbon films were achieved by radio frequency plasma polymerization of perfluorooctyl ethylene (PFOE) at continuous wave mode with an input power of 60 Watts. The resulting ppPFOE exhibited good adhesion with both the glass substrate and the gold superstrate, and also remained relatively stable in aqueous solutions as seen by optical waveguide spectroscopy (OWS). The obtained LRSPR sensor consisting of a SF11-ppPFOE-Au structure was employed for the detection of both the bulk refractive index variation and the protein adsorption.

Long-range surface plasmon resonance sensor based on dielectric/silver coated hollow fiber with enhanced figure of merit.

A long-range surface plasmon resonance (LRSPR) sensor based on dielectric/silver-coated hollow fiber (HF) is proposed. It can detect the refractive index (RI) of sensed liquid filled in the hollow core of the sensor. A HF LRSPR sensor with 90-nm-thick silver layer and 260-nm-thick OC300 layer is fabricated. Experiments are taken to evaluate the performance of the sensor by measuring the transmission spectra. Theoretical analysis based on a ray model is also taken, and the results agree well with the experimental results. The proposed sensor has similar sensitivity but much smaller SPR dip width than the silver-coated HF SPR sensor. Thus figure of merit of the sensor is enhanced approximately five times. The stability of the sensor is also improved because the dielectric layer acts as a protection layer for the damageable silver layer.