Prism-based Surface Plasmon Resonance Research Articles

An Open-Source Simulator Applied to Prism Coupling Sensors Based on Kretschmann's Configuration

In this letter, we present an open-source simulator applied to design and to analyze prism coupling sensors considering surface plasmon resonance (SPR) effect based on Kretschmann's configuration. The open-source simulator is called Sim-SPR and takes into account principles of software engineering. For comparison purposes and to validate our results, we considered two simulation tools already consolidated in the literature and performed an experimental setup for detecting resonant angle in a prism-based SPR sensor. The sensor design was based on optical prism (BK7 glass) as well as Au thin film. The results show that Sim-SPR provides reflectance curves that present a minimum in the resonance condition, resulting in a good agreement when compared with simulation and experimental data. Sim-SPR provides new insights and it has great promise for possible applications in the field of biosensors.

Simultaneous measurement of refractive index and temperature for prism-based surface plasmon resonance sensors.

A detailed theoretical model is provided to analyze the effects of temperature on prism-based surface plasmon resonance (SPR) sensors, including temperature dependence of the metal and prism. A complete sensitivity matrix simultaneously measures variations in refractive index (RI) and temperatures using measurements at two wavelengths for the angular-interrogation mode, or at two angles of incidence for the wavelength-interrogation mode. Correction of matrix coefficients improves accuracy of the two modes. Validation is performed using a self-designed wavelength SPR system with an adjustable incident angle perform. This method provides a new way to detect the RI and may lead to the better design and fabrication of prism-based SPR sensors.

Theoretical study on negative permittivity of the material producing sharp surface plasmon resonance dips

Using theoretical simulations for optical fiber surface plasmon resonance (SPR) sensors and prism-based SPR sensors coated with negative permittivity material (NPM), we investigated the effect of the permittivity of NPM on the transmitted spectrum of optical fiber SPR sensors and the reflected spectrum of prism-based SPR sensors and then obtained optimum permittivity of the NPM, which can excite the sharpest SPR spectrum in the white light region (400–900 nm).

Early detection of bacteria using SPR imaging and event counting: experiments with Listeria monocytogenes and Listeria innocua.

Foodborne pathogens are of significant concern in the agrifood industry and the development of associated rapid detection and identification methods are of major importance. This paper describes the novel use of resolution-optimized prism-based surface plasmon resonance imaging (RO-SPRI) and data processing for the detection of the foodborne pathogens Listeria monocytogenes and Listeria innocua. With an imaging spatial resolution on the order of individual bacteria (2.7 ± 0.5 μm × 7.9 ± 0.6 μm) over a field of view 1.5 mm2, the RO-SPRI system enabled accurate counting of individual bacteria on the sensor surface. Using this system, we demonstrate the detection of two species of Listeria at an initial concentration of 2 × 102 CFU mL−1 in less than 7 hours. The surface density of bacteria at the point of positive detection was 15 ± 4 bacteria per mm2. Our approach offers great potential for the development of fast specific detection systems based on affinity monitoring.

Reduced Graphene Oxide/Maghemite Nanocomposite for Detection of Lead Ions in Water Using Surface Plasmon Resonance

A prism-based surface plasmon resonance (SPR) sensor deposited with reduced graphene oxide/maghemite is presented for the detection of lead ions (Pb2+) in water. The SPR setup proposed followed the Kretschmann configuration with the installment of the nanocomposite integrated bilayer sensor chip onto the prism. For protection, the nanocomposite active layer was coated with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimidehydrochloride/N-hydroxysuccinimide. When the sensor was tested with different concentrations of Pb2+ in static water, the limit of detection was achieved at 0.001 ppm with a resonance angle shift of 0.184°. As an improvisation, a sample circulation design was adapted into the setup in order to increase the interaction rate between the sample and the sensing layer. This managed to improve the detection limit to 0.3 ppb.

Prism-Based Surface Plasmon Resonance for Dual-Parameter Sensing

A simple method to construct a dual-channel in a prism-based surface plasmon resonance sensor for dual-parameter monitoring is proposed. The metal layer (sensing area), attached to the prism, is half-covered with a polymer in order to generate two individual sensing sections. In this paper, eight different sensor structures (prism/metal/polymer) were analyzed. The prisms are made of NSK16 or SF10 glass and coated with gold or silver films. Half section of the metal films is covered with Polydimethylsiloxane (PDMS) or Poly-methyl methacrylate. The sensor is based on angle interrogation, the laser beam is aligned to be incident upon the interface of the bare and polymer sections. The resonance conditions are different at each pad, due to the refractive index (RI) mismatch, thus the intensity of the reflected signal presents a pair of well-defined resonance dips in series. The sensitivity of these dips to RI and temperature (T) changes was numerically analyzed. Finally, to demonstrate the feasibility to monitor RI and T, simultaneously, a surface plasmon resonance sensor was constructed using a NSK16 glass prism coated with a thin gold film, which was half-covered with PDMS.

Nanoscale patterning of gold-coated optical fibers for improved plasmonic sensing

Merging surface plasmon resonance (SPR) to fiber optic (FO) technology has brought remarkable achievements in the field by offering attractive advantages over the conventional prism-based SPR platforms, such as simplicity, cost-effectiveness and miniaturization. However, the performance of the existing FO-SPR instruments mainly depends on the device surface condition and in particular on the structural aspect of the thin gold (Au) plasmonic film deposited on the FO substrate. In this work, a simple cost-effective colloidal lithography technique (CLT) was adapted and applied for the first time to the micrometer-sized FO substrate, to design end reflection-type FO-SPR sensors with periodic arrays of Au triangularly-shaped nanostructures on the Au mirror FO tip distal end. The nanopatterned FO-SPR sensor tips were afterwards subjected to refractometric measurements in a sucrose dilution series and subsequently compared with their non-patterned counterparts. It was observed that the spectral dips of the nanopatterned FO-SPR sensor tips were shifted towards longer wavelengths after CLT patterning. Moreover, the sensor sensitivity was improved with up to 25% compared to the conventional non-patterned FO-SPR devices. The obtained results represent important steps in the development of a new generation of FO-SPR sensors with improved performance, which can ultimately be used in various applications, ranging from food analysis and environmental monitoring, to health control and medical diagnosis.

Enhancing angular sensitivity of plasmonic nanostructures using mode transition in hexagonal gold nanohole arrays

We presented a surface plasmon resonance (SPR) sensor with an angular sensitivity up to 440 deg/RIU by using (±1,∓1) mode on a hexagonal gold nanohole array. The large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method with 180-nm-hole diameter and 600-nm period. A flat dispersion curve deviated from Bragg condition for (±1,∓1) mode occurred when incident angle was larger than 20°. The finite-difference time-domain calculations verified that plasmonic mode changed from surface plasmon mode to cavity mode in nanoholes. Such mode transition resulted in the large change of dispersion curve. The angular sensitivity of the (±1,∓1) mode near the transition band was 6.2 times higher than surface plasmon mode under Bragg condition and 4.5 times higher than prism-based SPR sensors at 850nm wavelength. Biosensing experiments for antigen-antibody interactions verified the surface binding sensitivity was higher than prism-based SPR machine.

Enhancing the Surface Sensitivity of Metallic Nanostructures Using Oblique-Angle-Induced Fano Resonances.

Surface sensitivity is an important factor that determines the minimum amount of biomolecules detected by surface plasmon resonance (SPR) sensors. We propose the use of oblique-angle-induced Fano resonances caused by two-mode coupling or three-mode coupling between the localized SPR mode and long-range surface plasmon polariton modes to increase the surface sensitivities of silver capped nanoslits. The results indicate that the coupled resonance between the split SPR (−kSPR) and cavity modes (two-mode coupling) has a high wavelength sensitivity for small-angle incidence (2°) due to its short decay length. Additionally, three-mode coupling between the split SPR (−kSPR), substrate (+kSub) and cavity modes has a high intensity sensitivity for large-angle incidence due to its short decay length, large resonance slope and enhanced transmission intensity. Compared to the wavelength measurement, the intensity measurement has a lower detectable (surface) concentration below 1 ng/ml (0.14 pg/mm2) and is reduced by at least 3 orders of magnitude. In addition, based on the calibration curve and current system noise, a theoretical detection limit of 2.73 pg/ml (0.38 fg/mm2) can be achieved. Such a surface concentration is close to that of prism-based SPR with phase measurement (0.1–0.2 fg/mm2 under a phase shift of 5 mdeg).

Sensitivity improvement of graphene based surface plasmon resonance biosensors with chaclogenide prism

Graphene and chalcogenide prism based surface plasmon resonance (SPR) biosensor used for the detection of Pseudomonas and Pseudomonas-like bacteria is presented in this paper. Angular responses, sensitivity, detection accuracy and quality parameter of SPR biosensor is investigated. This biosensor comprises of chalcogenide prism which is coated with gold layer and graphene layers. The proposed biosensor uses Kretschmann configuration to detect the change in refractive index near the sensor surface. By comparing these results with the conventional surface plasmon resonance biosensor coated with gold layer and chalcogenide prism, it is observed that the proposed SPR biosensor has sensitivity 6.47 times greater than that of chalcogenide prism based conventional SPR sensor. Also, the dependence of sensitivity, detection accuracy and quality parameter on the number of graphene layers for the proposed sensor is plotted and analyzed.

An SPR-based sensor with an extremely large dynamic range of refractive index measurements in the visible region

A promising GaP prism-based surface plasmon resonance sensor in the Kretschmann configuration with an extremely large dynamic range of refractive index detection is proposed. The prism base is coated with a gold layer and then a thin layer of silicon. The sensor is studied theoretically in terms of sensitivity and detection accuracy. The proposed sensor shows the potential of sensing media with a refractive index varying from gaseous to very dense liquid with appreciably high sensitivity.

Improved surface plasmon resonance biosensing using silanized optical fibers

Coupling surface plasmon resonance (SPR) to optical fiber (FO) technology has brought tremendous advancements in the field by offering attractive advantages over the traditional prism-based SPR platforms, such as simplicity, cost-effectiveness and miniaturization. However, the performance of the existing FO-SPR sensors widely depends on the adhesion of the gold (Au) layer to the FO silica core, thereby often representing a major limiting factor in achieving the properties of the benchmark SPR systems. In this paper, we used (3-marcaptopropyl)trimethoxysilane (MPTMS) as an adhesion promoter for developing robust Au surfaces on the three-dimensional (3D) FO-SPR sensing probe. Carefully prepared FO substrates were first silanized using a wet chemistry approach, with MPTMS concentrations ranging from 2.5 to 24mM, and subsequently exposed to a drying treatment at room temperature (RT) or at 100°C, before coating them with a ∼50nm Au plasmonic film. Differently prepared silanized FOs were next used for evaluating their sensitivities, by performing refractive index (RI) measurements in sucrose dilutions. Advanced statistical analysis of the obtained data indicated that using 8mM MPTMS solution coupled with a RT post-drying treatment is an efficient way of producing FOs with dramatically improved Au adhesion properties. The role of the MPTMS underlayer was further investigated by exposing the reference and silanized FOs to stress conditions, such as strong mechanical (adhesion tape tests), chemical (piranha solution treatments) and thermal variations. Although additional studies using scanning electron microscopy (SEM) revealed changes in the Au film morphology after these endurance tests, the silanized FOs exhibited an enhanced robustness while retaining the overall sensor's capabilities. In contrast, the reference FOs consistently failed the mechanical and chemical tests, while only resisting under thermal variations. Moreover, the improved resistance of the silanized FO-SPR probes allowed them to be reused up to three times with no significant loss in the sensor performance, while implementing bioassays based on two types of bioreceptors (a DNA aptamer against thrombin protein and a polyclonal antibody against human immunoglobulin E – hIgE). All these results might represent a step forward in the fabrication of more robust and reusable FO-SPR biosensors, featuring great potential for developing highly-sensitive biochemical assays.

Rapid and highly sensitive detection using Fano resonances in ultrathin plasmonic nanogratings

We developed a nanoplasmonic sensor platform employing the extraordinary optical properties of one-dimensional nanogratings patterned on 30 nm-thick ultrathin Ag films. Excitation of Fano resonances in the ultrathin Ag nanogratings results in transmission spectra with high amplitude, large contrast, and narrow bandwidth, making them well-suited for rapid and highly sensitive sensing applications. The ultrathin nanoplasmonic sensor chip was integrated with a polydimethylsiloxane microfluidic channel, and the measured refractive index resolution was found to be 1.46 × 10−6 refractive index units with a high temporal resolution of 1 s. This compares favorably with commercial prism-based surface plasmon resonance sensors, but is achieved using a more convenient collinear transmission geometry and a significantly smaller sensor footprint of 50 × 50 μm2. In addition, an order-of-magnitude improvement in the temporal and spatial resolutions was achieved relative to state-of-the-art nanoplasmonic sensors, for comparable detection resolutions.

Spatial resolution in prism-based surface plasmon resonance microscopy.

Several optical surface sensing techniques, such as Surface Plasmon Resonance (SPR), work by imaging the base of a prism by one of its faces. However, such a fundamental optical concern has not been fully analyzed and understood so far, and spatial resolution remains a critical and controversial issue. In SPR, the propagation length L(x) of the surface plasmon waves has been considered as the limiting factor. Here, we demonstrate that for unoptimized systems geometrical aberrations caused by the prism can be more limiting than the propagation length. By combining line-scan imaging mode with optimized prisms, we access the ultimate lateral resolution which is diffraction-limited by the object light diffusion. We describe several optimized configurations in water and discuss the trade-off between L(x) and sensitivity. The improvement of resolution is confirmed by imaging micro-structured PDMS stamps and individual living eukaryote cells and bacteria on field-of-view from 0.1 to 20 mm(2).

Theoretical analysis of highly sensitive prism based surface plasmon resonance sensor with indium tin oxide

An extremely sensitive silica glass prism based SPR sensor with indium tin oxide (ITO) layer is presented and theoretically analyzed. The sensitivity of the sensor enhances with the increase in the thickness of ITO layer. With optimized values of thickness of ITO layer and incident wavelength to be 50nm and 1600nm, respectively, the proposed sensor offers high sensitivity of 164°/RIU.

Low-cost, high performance surface plasmon resonance-compatible films characterized by the surface plasmon resonance technique

A new analytical method based on the surface plasmon resonance (SPR) technique is presented, with which SPR curves for both wavelength and angular modulations can be obtained simultaneously via only a single scan of the incident angle. Using this method, the SPR responses of TiO2-coated Cu films are characterized in the wavelength range from 600 nm to 900 nm. For the first time, we determine the effective optical constants and the thicknesses of TiO2-coated Cu films using the SPR curves of wavelength modulation. The sensitivities of prism-based SPR refractive index sensors using TiO2-coated Cu films are investigated theoretically for both wavelength and angular modulations, the results show that in the case of sensitivity with wavelength modulation, TiO2-coated Cu films are not as good as the Au film, however, they are more suitable than the Au film for SPR refractive index sensors with angular modulation because a higher sensitivity can be achieved.

Plasmonic interferometric sensor arrays for high-performance label-free biomolecular detection

A plasmonic interferometric biosensor that consists of arrays of circular aperture-groove nanostructures patterned on a gold film for phase-sensitive biomolecular detection is demonstrated. The phase and amplitude of interfering surface plasmon polaritons (SPPs) in the proposed device can be effectively engineered by structural tuning, providing flexible and efficient control over the plasmon line shape observed through SPP interference. Spectral fringes with high contrast, narrow linewidth, and large amplitude have been experimentally measured and permit the sensitive detection of protein surface coverage as low as 0.4 pg mm(-2). This sensor resolution compares favorably with commercial prism-based surface plasmon resonance systems (0.1 pg mm(-2)) but is achieved here using a significantly simpler collinear transmission geometry, a miniaturized sensor footprint, and a low-cost compact spectrometer. Furthermore, we also demonstrate superior sensor performance using the intensity interrogation method, which can be combined with CCD imaging to upscale our platform to high-throughput array sensing. A novel low-background interferometric sensing scheme yields a high sensing figure of merit (FOM*) of 146 in the visible region, surpassing that of previous plasmonic biosensors and facilitating ultrasensitive high-throughput detection.

Ultrasmooth metallic films with buried nanostructures for backside reflection-mode plasmonic biosensing.

We present a new plasmonic device architecture based on ultrasmooth metallic surfaces with buried plasmonic nanostructures. Using template-stripping techniques, ultrathin gold films with less than 5 Å surface roughness are optically coupled to an arbitrary arrangement of buried metallic gratings, rings, and nanodots. As a prototypical example, we present linear plasmonic gratings buried under an ultrasmooth 20 nm thick gold surface for biosensing. The optical illumination and collection are completely decoupled from the microfluidic delivery of liquid samples due to the backside, reflection-mode geometry. This allows for sensing with opaque or highly scattering liquids. With the buried nanostructure design, we maintain high sensitivity and decoupled backside (reflective) optical access as with traditional prism-based surface plasmon resonance (SPR) sensors. In addition, we also gain the benefits offered by nanoplasmonic sensors such as spectral tunability and high-resolution, wide-field SPR imaging with normal-incidence epi-illumination that is simple to construct and align. Beyond sensing, our buried plasmonic nanostructures with ultrasmooth metallic surfaces can benefit nanophotonic waveguides, surface-enhanced spectroscopy, nanolithography, and optical trapping.

Optical method to differentiate tequilas based on angular modulation surface plasmon resonance

We report the use of the prism-based surface plasmon resonance (SPR) technique to differentiate between three types of tequilas white or silver, aged, and extra-aged. We used the angular interrogation method in which the structure is based on prism fabricated with BK7 glass coated with a gold layer as the SPR active layer. Our study was centered in the analysis of the resonant angle of the SPR generated by the three types of tequilas produced by the three major tequila-producing firms. We observed that each tequila sample produced a well-differentiated SPR curve. We found that resonant angle of the SPR curve produced by silver tequilas is larger than that produced by the aged and extra-aged tequilas of the same producer firm. We found that the position of the SPR curve is not exclusively determined by the alcohol contents; we believe that there are other parameters derived from the aging process that should be considered. The refractive index of the tequilas used in this study was estimated using the measured resonant angle.

Chalcogenide glass prism based SPR sensor with Ag–Au bimetallic nanoparticle alloy in infrared wavelength region

A chalcogenide prism based surface plasmon resonance sensor with Ag–Au bimetallic alloy nanoparticles is proposed. The plasmonic structure based on (chalcogenide) sulfide glass Ge20Ga5Sb10S65, commonly known as 2S2G, allows for a wide range of sensing applications in the infrared wavelength region. Theoretical calculations are carried out to design a device providing an accurate sensing in the infrared range by exploiting the unique optical properties of 2S2G chalcogenide glass. The angular interrogation method is used to analyze the sensor's performance in terms of its intrinsic sensitivity. The intrinsic sensitivity takes both angular shift as well as the angular width of the SPR curve into account. The adequate values of crucial design parameters are predicted in order to achieve the best possible sensing performance. The proposed sensor can be very useful for chemical and bio-sensing applications in the infrared due to the large operating window of chalcogenide materials.