Long-range Surface Plasmon Resonance Sensor Research Articles

Design of a highly sensitive and precise long-range surface plasmon resonance sensor for early detection of malaria

This manuscript presents an innovative Kretschmann configured for Long Range Surface Plasmon Resonance (LRSPR) sensor for malaria detection. It utilizes tungsten diselenide (WSe2) as a bio+molecular recognition element (BRE) layer to attach target analyte. The optimized sensor design demonstrates exceptional performance in detecting different malaria stages (Schizont with refractive index (RI) = 1.371, Trophozoite with RI = 1.381, and Ring with RI = 1.396) at a 633 nm wavelength. In comparison to conventional surface plasmon resonance (CSPR), the LRSPR biosensor exhibits a substantial improvement, a 6.67 to 10 times increase in detection accuracy (DA), an impressive 40 to 86.55 times enhancement in imaging figure of merit (IFOM), and a 6.0 to 8.66 times boost in imaging sensitivity (Simg.) for the sequential detection of different stages of malaria. COMSOL Multiphysics simulations highlight a deeper penetration depth (PD) of 258.71 nm, 276.85 nm, and 373.04 nm for the detection of Schizont, Trophozoite, and Ring stages, respectively.

A high-performance long-range surface plasmon resonance sensor based on the co-modification of carbon nanotubes and gold nanorods

In order to solve the problem that the sensitivity of the optical fiber surface plasmon resonance (SPR) sensor is limited and the full width at half maxima (FWHM) is greatly increased after modification of two-dimensional materials such as carbon nanotubes (CNTs), this paper proposes a Long-Range Surface Plasmon Resonance (LRSPR) Sensors co-modified by CNTs and gold nanorods. Gold nanorods were used to further enhance the sensitivity, and a simple and convenient method was used to excite the LRSPR by using low refractive index UV glue as a dielectric matching layer (DML). Compared with SPR sensor, the FWHM is reduced. The LRSPR sensor produced in this paper has a sensitivity of 5056.35 nm/RIU and a figure of merit (FOM) of 23.52 RIU−1, which are 150.64% and 24.38% higher than conventional SPR sensors, providing a method to achieve high sensitivity and FOM of the sensor. At the same time, the large specific surface area of CNTs and gold nanorods can also improve the biocompatibility of the sensor surface, which makes it have the potential of biosensing. In this paper, the use of UV glue as a DML to excite LRSPR is proposed for the first time.

Long-range surface plasmon resonance-based hollow fiber temperature sensor with ultrahigh sensitivity and tunable detection range.

A dielectric/Ag-coated hollow fiber (HF) temperature sensor based on long-range surface plasmon resonance (LRSPR) is proposed and experimentally demonstrated. The structural parameters, including the dielectric material and layer thicknesses, are optimized through comprehensive theoretical analysis to achieve the best performance. By filling it with a high refractive index (RI) thermosensitive liquid, the GK570/Ag-coated HF temperature sensor with optimal structural parameters is fabricated. Due to the high sensitivity of the LRSPR sensor and the optimized design, the fabricated sensor achieves a temperature sensitivity of 3.6∼20.5 nm/°C, which is almost the highest among the optical fiber temperature sensors based on surface plasmon resonance reported experimentally. Moreover, the detection range of the proposed sensor can be easily tuned up to 170°C by varying the RI of the filled thermosensitive liquid, and the sensor performance remains stable. Considering that most temperature sensors using polydimethylsiloxane have a fixed detection range, this is an outstanding advantage that could expand the application field of the optical fiber temperature sensor.

Low Dimensional Nanostructure-Assisted Long-Range Surface Plasmon Resonance Sensors With High Figure of Merit.

Long-range surface plasmon resonance (LRSPR) sensors have been extensively studied by virtue of their extremely narrow full width at half maxima (FWHM) characteristics, but their low sensitivity remains an important factor limiting the figure of merit (FOM), making the sensors have difficulties in detecting small refractive index changes accurately. To address this problem, this paper proposes and demonstrates a low dimensional nanostructure (Au nanospheres, WS2) assisted LRSPR sensor to achieve an effective enhancement of the sensor interfaced electric field and thus improve the sensitivity. The performance parameters of the two sensors are compared with the LRSPR sensor by finite element method analysis, and the results showed that the assistance of the low dimensional nanostructure has a positive effect on the sensor. The first refractive index sensing experiment of the WS2-assisted LRSPR sensor was realized with a 25.47% increase in sensitivity and a 7.13% increase in FOM simultaneously, and the Au nanospheres-assisted LRSPR sensor with a 29.23% increase in sensitivity and a 15.95% increase in FOM simultaneously. The introduction of low dimensional nanostructures provides a flexible and effective means of sensitization for LRSPR sensors, making the plasmon resonance sensors combine high sensitivity, narrow FWHM and high FOM, which have promising applications in biochemical sensing.

Black Phosphorous and Cytop Nanofilm‐Based Long‐Range SPR Sensor with Enhanced Quality Factor

This numerical work proposes two novel designs of long‐range surface plasmon resonance sensors (LRSPR) using two different coupling prisms. The performance analysis of the proposed sensor has been investigated using the performance parameters like quality factor (Q), detection accuracy (DA), sensitivity (S), and full‐width half maximum (FWHM). The transfer matrix method (TMM) has been employed to compute reflectance. The role of the basic recognition element (BRE) has been played by the popular two‐dimensional (2D) material, black phosphorus (BP), due to its many optoelectrical features. The maximum obtained values for Q, DA, and S are 3333.25 (1/RIU), 250 (degree−1), and 13.33333 degree/RIU for 2S2G coupled sensor design and 3055.5 (1/RIU), 83.33 (degree−1), and 36.66667 degree/RIU for BK7 coupled sensor design. The operating wavelength of 633 nm, followed by the principle of attenuated total reflection (ATR), has been employed to carry out the theoretical investigation.

Highly sensitive MXene-immobilized long range SPR sensor for biomolecule detection

In this article, a long-range surface plasmon resonance (LRSPR) sensor is proposed using the dielectric (Teflon)-metal (Silver)-Ti3C2Tx (MXene) layer for imaging sensitivity enhancement. MXene shows excellent properties, such as larger surface area, hydrophilic nature, high metallic conductivity, chemical stability, and strong biocompatibility for detection of biomolecules. The MXene layer is used here to improve imaging sensitivity and prevent unwanted silver oxidation. The proposed sensor takes advantage of the high adsorption efficiency of MXene for biomolecules and high resolution due to the LRSPR technique. Long-range SPPs are used to improve the imaging sensitivity, detection accuracy (DA), figure of merit (FoM) and penetration depth (PD) up to 4998/RIU, 12.5/°, 199.1/RIU and 546.65 nm, respectively, which are much higher than the present state of the art. The field intensity enhancement factor at the interface of the constituent layer of the proposed sensor and the conventional surface plasmon resonance (cSPR) sensor is also verified. The penetration depth (PD) of the field into the sensing layer for the LRSPR sensor is 2.5 times greater than that of the cSPR sensor. Thus, the proposed sensor offers potential benefits for sensing of large-sized biomolecules in the area of medical diagnostics.

Enhancement of Sensitivity with High-Reflective-Index Guided-Wave Nanomaterials for a Long-Range Surface Plasmon Resonance Sensor.

A guided−wave long−range surface plasmon resonance (GW−LRSPR) sensor was proposed in this investigation. In the proposed sensor, high−refractive−index (RI) dielectric films (i.e., CH3NH3PbBr3 perovskite, silicon) served as the guided−wave (GW) layer, which was combined with the long−range surface plasmon resonance (LRSPR) structure to form the GW−LRSPR sensing structure. The theoretical results based on the transfer matrix method (TMM) demonstrated that the LRSPR signal was enhanced by the additional high#x2212;RI GW layer, which was called the GW−LRSPR signal. The achieved GW−LRSPR signal had a strong ability to perceive the analyte. By optimizing the low− and high−RI dielectrics in the GW−LRSPR sensing structure, we obtained the highest sensitivity (S) of 1340.4 RIU−1 based on a CH3NH3PbBr3 GW layer, and the corresponding figure of merit (FOM) was 8.16 × 104 RIU−1 deg−1. Compared with the conventional LRSPR sensor (S = 688.9 RIU−1), the sensitivity of this new type of sensor was improved by nearly 94%.

Long-range surface plasmon resonance sensor based on side-polished D-shaped hexagonal structure photonic crystal fiber with the buffer layer of magnesium fluoride

In this paper, we demonstrate a long-range surface plasmon resonance (LRSPR) sensor based on D-shaped hexagonal structure photonic crystal fiber (PCF) with buffer layer of magnesium fluoride (MgF2). The theoretical analysis is first introduced to reveal surface plasmon polariton (SPP) mode excitation by the y-polarized core-guided mode. The influences exerted by different thicknesses of Au film and MgF2 buffer layer are theoretically investigated with the full vectorial finite element method for optimizing structure parameters. A novel status of electric field boundary (SEFB) technique is proposed to analyze the reciprocal sensing performance of symmetric LRSPR (sLRSPR) sensor. Theoretical simulation reveals that the LRSPR with PCF/MgF2 (100 nm)/Au (50 nm) architecture exhibits the significant performance and has an intensity sensitivity improvement of 160.13% compared with conventional SPR (cSPR) sensor. With the simulation providing the theoretical basis, a proof-of-concept experiment is performed with the D-shaped PCF fabricated by a wheel polishing system. The experimental results show good agreement with the theoretical calculations, and both of them consistently indicate that the LRSPR-based sensor has an improved intensity sensitivity (−490.625% RIU−1) and an increased penetration depth. Furthermore, focusing on the sensing principle, the proposed SEFB method can be applied in the analysis of other types of multilayer SPR sensor. The optimal LRSPR sensor with improved detection accuracy shows great promise for applications in the field of biochemical measurement.

Sensitivity Enhanced Refractive Index Fiber Sensor Based on Long-Range Surface Plasmon Resonance in SiO2-Au-TiO2 Heterostructure

Long-range surface plasmon resonance (LRSPR), generated from a coupled plasmon polariton in a thin metal slab sandwiched by two dielectrics, has attracted more and more attention due to its merits, such as longer propagation and deeper penetration than conventional single-interface surface plasmon resonance. Many useful applications related to light–medium interaction have been demonstrated based on the LRSPR effect, especially in the sensing area. Here, we propose and demonstrate an LRSPR-based refractive index sensor by using a SiO2-Au-TiO2 heterostructure, in which a D-shaped honeycomb-microstructure optical fiber (MOF) is designed as the silica substrate and then deposited with a gold film and thin-layer titanium dioxide (TiO2). By using the full-vector finite-element method (FEM), this heterostructure is numerically investigated and demonstrated to excite LRSPR without a buffer layer, which is usually necessary in previous LRSPR devices. Through comprehensive discussion about the influence of structural parameters on the resonant wavelength, the excitation of the LRSPR in the proposed heterostructure is revealed to be highly related to the effective refractive index of MOF’s fundamental core mode, which is mainly determined by the MOF’s pitch, the thicknesses of the silica web and the planar-layer silica. Moreover, the thin-layer TiO2 plays an important role in significantly enhancing the resonance and the sensitivity to analyte’s refractive index as well, when it is coated on the top of the Au film rather than between the metal and waveguide. Finally, the proposed LRSPR sensor based on SiO2-Au-TiO2 heterostructure shows an ultra-high wavelength sensitivity of 20,100 nm/RIU and the corresponding minimum resolution is as low as 4.98×10−7 RIU. Thus, the proposed LRSPR device offers considerable potential for sensing applications in biomedical and biochemical areas.

Figure of merit enhancement of Ti3C2Tx-graphene based long-range surface plasmon sensor at telecommunication wavelength

In this work, the long-range surface plasmon resonance (LRSPR) sensor based on dielectric Ti3C2Tx-graphene layers is demonstrated. Here, MXene (Ti3C2Tx) is used as a metal for strong surface plasmon’s generation at 1550 nm excitation wavelength. Graphene is used to attach the biomolecules having carbon–carbon structure with pi stacking interactions. The detection accuracy (DA) and figure of merit (FoM) for the proposed LRSPR sensor is theoretically investigated at telecommunication wavelength. The highest FoM of (559.64 RIU−1) is obtained at 3100 nm dielectric thickness and 14 nm Ti3C2Tx thickness of the proposed sensor. The maximum improvement in FoM is 273% to the traditional LRSPR sensors. Propagation depths are also evaluated for Au-graphene and proposed LRSPR sensor at 14 and 27 nm thicknesses of Ti3C2Tx We believe that the Ti3C2Tx can be used in place of metals for strong plasmon generation in future sensor designs at telecommunication wavelengths.

Rotating Angle Modulation Method for Improving the Measurement Performance of LRSPR Sensor

Long-range surface plasmon resonance (LRSPR) sensor has attracted extensive attention from research institutions and commercial companies due to its label-free detection, real-time analysis, high detection accuracy (DA) and high sensitivity. In this paper, a novel, simple, and effective rotating angle modulation (RAM) method for the metal-graphene structure LRSPR sensor is proposed. Compared with the general SPR sensor, the metal-graphene structure LRSPR sensor has a narrower full width at half maximum (FWHM) and a very high DA, especially the metal material is copper (Cu). The theoretical analysis for the Cu-graphene structure LRSPR sensor using RAM method shows that the FWHM, sensitivity and figure of merit (FOM) of the proposed sensor can be 0.74°, 320.4°/RIU and 498.24/RIU, respectively. In addition, this method enables the LRSPR sensor to obtain good measurement results even with the low-resolution rotating device and effectively reduces the dependence of the sensor on the high-resolution expensive rotating device. A preliminary comparative experiment for the SPR sensor has proved this new method. Finally, the concept of combining the RAM and general incident angle methods is proposed to provide the sensor with a large measuring range and low optical losses. We believe that this method can provide a favorable reference for solving the shortcomings of LRSPR sensors, such as complex structure, limited sensitivity and high cost, so that it can be widely promoted and applied in biological detection, medical assay, chemical investigation, etc.

Au-nanoshells modified surface field enhanced LRSPR biosensor with low LOD for highly sensitive hIgG sensing

A high sensitivity side polished fiber long-range surface plasmon resonance (LRSPR) biosensor with electronic field enhanced through surface modified with Au-nanoshells is proposed to detect human immunoglobulin G (hIgG). LRSPR which has high penetration depth and long propagation distance can effectively detect biomacromolecules. The plasmon coupling effect between the Au-nanoshells and Au-film can enhance the electric field intensity on the surface of the sensor, which makes the proposed sensor structure have a lower limit of detection (LOD) and higher sensitivity. The experimental results show that the sensitivity as well as LOD of side-polished-fiber (SPF)/dielectric-matching-layer (DML)/Au-film/Au-nanoshells sensor is 1.84 nm/(µg/mL) and 0.20 µg/mL, which indicates better responses to hIgG with a concentration range of 1–40 µg/ml compared with the SPF/DML/Au-film sensor. The LRSPR sensor modified by Au-nanoshells was used to detect chicken serum samples and the calculated recovery is 107.62%, showing good practicality and superior self-referenced function. The biosensor has the advantages of small volume, high sensitivity and long-distance detection, and has good practicability in the field of biochemical sensing.

Refractive index tuning of SiO2 for Long Range Surface Plasmon Resonance based biosensor

A novel, highly sensitive and low cost Long Range Surface Plasmon Resonance (LRSPR) biosensor for detecting uric acid, as a model analyte, has been developed in this work. Silicon dioxide (SiO2) having low and tunable refractive index has been chosen as the dielectric layer for the excitation of LRSP modes replacing the most explored Cytop and Teflon polymers. The prepared LRSPR based uric acid bio-sensor gives good response characteristics with a high sensitivity of about 21.6°/mM and low limit of detection (LOD) of 0.02 mM. The fabricated LRSPR sensor was also evaluated to detect uric acid in real serum samples. The results yield a great scope to promote the development of robust, efficient and highly selective LRSPR based biosensors with SiO2 as tunable dielectric layer.

Resolution-improved SPR sensor with a rotational modulation method.

A resolution-improved prism coupler-based surface plasmon resonance (SPR) sensor with a simple, effective rotational modulation method is proposed in this paper. For a conventional SPR sensor, the way to improve its measurement resolution is usually to use the rotating device with higher resolution. Measurement resolution depends on the modulation resolution of the incident angle; therefore, we propose a rotational modulation method that is implemented by rotating the prism horizontally to improve the modulation resolution of the incident angle, instead of using a more expensive rotating device with higher resolution. This scheme is validated both theoretically and experimentally. Furthermore, theoretical simulations show that the rotational modulation method can also be applied to long-range surface plasmon resonance sensors for better results.

Sensing self-referenced fiber optic long-range surface plasmon resonance sensor based on electronic coupling between surface plasmon polaritons.

A type of hollow gold nanoparticle (HGNP)-modified fiber optic long-range surface plasmon resonance (LRSPR) sensor with sensing self-reference is proposed and demonstrated. HGNPs have a stronger plasmonic field compared to solid GNPs because of the coupling between the inner and outer walls of HGNPs. The intense near-field electronic coupling between long-range surface plasmon polaritons associated with the LRSPR gold layer and localized surface plasmon polaritons of HGNPs leads to localized electromagnetic-field enhancement and LRSPR response signal amplification. Therefore, the HGNP-modified LRSPR sensor possesses a more excellent sensing property compared with the unmodified LRSPR sensor. The long-range resonance dip in the transmission spectrum is shown to shift in response to ambient refractivity change, and the characteristic absorption peak is fixed, allowing to regard it as a reference to improve detection accuracy of the sensors. The mode-field distribution of the sensors is simulated by using the finite element method, and the simulation results show that the electric-field intensity on the HGNP surface is significantly enhanced compared with that of the gold layer surface of the unmodified LRSPR sensor. 1874.79 nm/RIU improvement in sensitivity, 1.42 times improvement in figure of merit (FOM), and approximately 50% reduction in limit of detection (LOD) are achieved for the refractivity measurement of a low-concentration biological solution with the employment of HGNPs in LRSPR sensing experiments. The HGNP-modified LRSPR sensor proposed in this paper has high detection accuracy and FOM and low LOD, and can realize remote real-time online monitoring. Therefore, it has important research value and broad application prospects in the field of biochemical detection.

A D-Shaped Fiber Long-Range Surface Plasmon Resonance Sensor With High Q-Factor and Temperature Self-Compensation

A D-shaped fiber based long-range surface plasmon resonance (LRSPR) sensor with high quality factor ( $Q$ -factor) of 67.75 RIU−1 and temperature self-compensation was proposed and demonstrated. The multilayered architecture of the LRSPR sensor consisted of fiber/dielectric buffer layer (DBL)/Au film/analyte, and the deep penetration depth and long propagation distance of long-range surface plasmon polaritons made the LRSPR sensor possess high $Q$ -factor. The temperature-sensitive photoabsorption characteristic of the Terbium(III) complexes was utilized to provide temperature self-compensation for the refractive index (RI) measurement of the LRSPR sensor, and the LRSPR sensor realized simultaneous measurement of RI and temperature at the exact same location, which could eliminate the measurement error introduced by temperature to RI measurement. The simulation analysis, supported by finite element analysis (FEA) based on coupled-mode theory, was presented in detail. The simulation results showed that the electric field intensity on the surface of the LRSPR sensor was 2.52 times higher than that of the surface plasmon resonance (SPR) sensor and the sensitivity of the LRSPR sensor increased by 947.31 nm/RIU compared with the SPR sensor, implying the LRSPR sensor possessed more excellent sensing performance. An SPR sensor and a Terbium(III) complex-based LRSPR sensor were developed, and their RI sensing performance was systematically studied and tabulated. The experimental results showed that the $Q$ -factor of the LRSPR sensor was 2.56 times higher than that of the SPR sensor, which agreed well with the simulation results. The LRSPR sensor proposed in this paper possessed higher detection precision and presented greatly promising application prospects in the field of biochemistry.

A D-type fiber based symmetrical long-range surface plasmon resonance sensor with high quality factor

A D-type fiber based symmetrical long-range surface plasmon resonance (sLRSPR) sensor with high quality factor (Q-F) as high as 107.52 RIU−1 was proposed and experimentally demonstrated. The sensing structure of the proposed sensor consisted of fiber/dielectric buffer layer (DBL)/Au film/DBL/analyte, and the DBLs on both sides of the Au film in the sLRSPR sensor were identical, which greatly increased the permittivity matching degree between the analyte and the DBL near the D-type fiber, and reduced the loss of long-range surface plasmon polaritons. For LRSPR sensor, the closer the permittivities of DBL and analyte on both sides of metal film are, the easier the LRSPR is to stimulate, and thus the proposed sensor possessed higher sensitivity and higher detection accuracy. The transfer matrix method supported by the finite-difference beam propagation method and the finite element analysis was employed to optimize the sensor parameters for the first time. The refractive index sensing performance of the conventional SPR (cSPR) sensor, the conventional LRSPR (cLRSPR) sensor, and the sLRSPR sensor with optimal parameters were systematically researched by simulation and in-depth experiment. The results suggested that the sensing performance of the sLRSPR sensor was better than that of the other two sensors. This paper provided a meaningful advancement for designing an optical fiber SPR sensor with remarkable performance to measure biomass.

Long-range surface plasmon resonance sensor based on the GK570/Ag coated hollow fiber with an asymmetric layer structure.

A long-range surface plasmon resonance (LRSPR) sensor based on GK570/Silver coated hollow fiber (HF) with an asymmetric layer structure is proposed. A set of proposed sensors with different layer thicknesses were fabricated by the liquid phase coating method. Both theoretical and experimental analyses were carried out to evaluate the performances of the fabricated sensors, such as sensitivity, figure of merit (FOM) and detection range. The theoretical results based on the ray modal agreed well with the experimental results. The highest experimentally obtained sensitivity and FOM were over 12500 nm/RIU and 150 RIU-1, respectively. The FOM was approximately ten times that of the HF SPR sensor. Moreover, compared to the HF LRSPR sensor with a symmetric layer structure, the proposed sensor has a much larger sensitivity and an approximately double FOM without sacrificing other advantages of the HF LRSPR sensor.

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.