Portable 24-analyte surface plasmon resonance instruments for rapid, versatile biodetection

Field use of surface plasmon resonance (SPR) biosensors for environmental and defense applications such as detection and identification of biological warfare agents has been hampered by lack of rugged, portable, high-performance instrumentation. To meet this need, we have developed compact multi-analyte SPR instruments based on Texas Instruments' Spreeta sensing chips. The instruments weigh 3 kg and are built into clamshell enclosures measuring 28 cm x 22 cm x 13 cm. Functions are divided between an electronics unit in the base of the box and a fluidics assembly in the lid. Automated valves and pumps implement an injection loop flow system that allows sensors to be exposed to sample, rinsed, and treated with additional reagents (such as secondary antibodies) under computer control. Injected samples flow over the surfaces of eight sensor chips fastened into a temperature-controlled silicone flowcell. Each chip has 3 sensing regions, for a total detection of 24 areas that can be simultaneously monitored by SPR. Coating these areas with appropriate antibodies or other receptors allows a sample to be screened for up to 24 different substances simultaneously. The instruments report refractive index (RI) values every second, with a typical noise level of 1-3 x 10(-6) RI units. The design of the device is described, and performance is illustrated with detection of six distinct analytes ranging from small molecules to whole microbes during the course of a single experiment.     

Collection mode surface plasmon fibre sensors: a new biosensing platform

Sensors based on surface plasmon resonance (SPR) allow rapid, label-free, highly sensitive detection, and indeed this phenomenon underpins the only label-free optical biosensing technology that is available commercially. In these sensors, the existence of surface plasmons is inferred indirectly from absorption features that correspond to the coupling of light into a thin metallic film. Although SPR is not intrinsically a radiative process, when the metallic coating which support the plasmonic wave exhibits a significant surface roughness, the surface plasmon can itself couple to the local photon states, and emit light. Here we show that using silver coated optical fibres, this novel SPR transducing mechanism offers significant advantages compare to traditional reflectance based measurements such as lower dependency on the metallic thickness and higher signal to noise ratio. Furthermore, we show that more complex sensor architectures with multiple sensing regions scattered along a single optical fibre enable multiplexed detection and dynamic self referencing of the sensing signal. Moreover, this alternative approach allows to combine two different sensing technologies, SPR and fluorescence sensing within the same device, which has never been demonstrated previously. As a preliminary proof of concept of potential application, this approach has been used to demonstrate the detection of the seasonal influenza A virus.     

A miniature fiber optic surface plasmon resonance sensor for fast detection of Staphylococcal enterotoxin B

A fiber optic surface plasmon resonance (SPR) biosensor for detection of Staphylococcal enterotoxin B (SEB) is reported. The sensor is based on spectral interrogation of surface plasmons in a miniature sensing element based on a side-polished single-mode optical fiber with a thin metal overlayer. For specific detection of SEB, the SPR sensor is functionalized with a covalently crosslinked double-layer of antibodies against SEB. The SPR biosensor is demonstrated to be able to detect ng/ml concentrations of SEB in less than 10 min.     

A new surface plasmon resonance sensor for high-throughput screening applications

We report a new high-throughput surface plasmon resonance (SPR) sensor based on combination of SPR imaging with polarization contrast and a spatially patterned multilayer SPR structure. We demonstrate that this approach offers numerous advantageous features including high-contrast SPR images suitable for automated computer analysis, minimum crosstalk between neighboring sensing channels and inherent compensation for light level fluctuations. Applications of a laboratory prototype of the high-throughput SPR sensor with 108 sensing channels for refractometry and biosensing are described. In refractometric experiments, the noise-limited refractive index resolution of the system has been established to be 3 x 10(-6) refractive index unit (RIU). Experimental data on detection of human choriogonadotropin (hCG) suggest that in conjunction with monoclonal antibodies against hCG, the reported SPR imaging sensor is capable of detecting hCG at concentrations lower than 500 ng/ml.     

Multichannel,Line-Monitoring Sensing Approach Based on Long-Range Surface Plasmons

The refractive index resolution of a surface plasmon resonance (SPR) sensor has been significantly improved these years; however, higher sensing performance is always desired. In this work, we propose a line-monitoring, long-range SPR sensor whose resolution is much better than conventional SPR sensors. Also, in contrast to mono-channel detection, multichannel detection, using line-monitoring technique, can detect multiple channels concurrently. In this way, this system achieves a refractive index resolution of 4.0?×?10^??7 refractive index units and can monitor multiple molecular interactions simultaneously. Finally, a model experiment detecting the Escherichia coli bacteria has demonstrated the potential for biomedical applications of this system.     

Analysis of native proteins from biological fluids by biomolecular interaction analysis mass spectrometry (BIA/MS): exploring the limit of detection, identification of non-specific binding and detection of multi-protein complexes

Biomolecular interaction analysis mass spectrometry (BIA/MS) is a two-dimensional analytical technique that quantitatively and qualitatively detects analytes of interests. In the first dimension, surface plasmon resonance (SPR) is utilized for detection of biomolecules in their native environment. Because SPR detection is non-destructive, analyte(s) retained on the SPR-active sensor surface can be analyzed in a second dimension using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The qualitative nature of the MALDI-TOF MS analysis complements the quantitative character of SPR sensing and overcomes the shortcomings of the SPR detection stemming from the inability to differentiate and characterize multi-protein complexes and non-specific binding. In this work, the benefit of performing MS analysis following SPR sensing is established. Retrieval and detection of four markers present in biological fluids (cystatin C, beta-2-microglobulin, urinary protein 1 and retinol binding protein) was explored to demonstrate the effectiveness of BIA/MS in simultaneous detection of clinically related biomarkers and delineation of non-specific binding. Furthermore, the BIA/MS limit of detection at very low SPR responses was investigated. Finally, detection of in-vivo assembled protein complexes was achieved for the first time using BIA/MS.     

Surface Plasmon Resonance Imaging Sensors: A Review

Surface plasmon resonance (SPR) imaging sensors realize label-free, real-time, highly sensitive, quantitative, high-throughput biological interaction monitoring and the binding profiles from multi-analytes further provide the binding kinetic parameters between different biomolecules. In the past two decades, SPR imaging sensors found rapid increasing applications in fundamental biological studies, medical diagnostics, drug discovery, food safety, precision measurement, and environmental monitoring. In this paper, we review the recent advances of SPR imaging sensor technology towards high-throughput multi-analyte screening. Finally, we describe our multiplex spectral-phase SPR imaging biosensor for high-throughput biosensing applications.     

The light-addressable potentiometric sensor for multi-ion sensing and imaging

The light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor with an electrolyte-insulator-semiconductor structure. The LAPS can have many measuring points integrated on the sensing surface, which are individually accessed by a light beam. By modifying the measuring points with different materials, a single sensor plate can be used as a multi-analyte sensor. In this paper, instrumentation and application of LAPS to multi-ion sensing and imaging are described. As a new application of LAPS, potentiometric imaging of a microfluidic channel is proposed.     

Transmitive Spectral SPR Droplet Biosensing: Principle,Sensor Design,and Experimental Demonstration

Surface plasmons resonance (SPR) architectures based on grating coupler/disperser combination is an attractive alternative for spectral-based biochemical sensing. In this paper, we investigate theoretically and experimentally a new concept where the plasmon coupling occurs through a thin film grating and sensing occurs via the first evanescent diffraction order in transmitive mode. The surface plasmon wave excitation induces a peak in the wavelength as well as in the angular spectra of the detected first transmitted diffraction order. Accordingly, a change in SPR spectrum of the detected diffraction order can be used to quantify the amount of the target molecules immobilized on the sensor surface, and therefore, the concentration of these molecules in the analyte solution. The developed sensor architecture is dedicated to droplet biochemical sensing and appears to be especially suitable for biosensor integration and miniaturization. The presented sensor concept is perfectly suited for mass production of low-cost and reproducible SPR sensor chip for biochemical analysis. The implemented setup gives access to multichannel biosensing with the potential for efficient internal referencing essential to achieve sufficiently high reproducibility and accuracy of the measurements.     

Graphene/Au-Enhanced Plastic Clad Silica Fiber Optic Surface Plasmon Resonance Sensor

Owing to its large surface-to-volume ratio and good biocompatibility, graphene has been identified as a highly promising candidate as the sensing layer for fiber optic sensors. In this paper, a graphene/Au-enhanced plastic clad silica (PCS) fiber optic surface plasmon resonance (SPR) sensor is presented. A sheet of graphene is employed as a sensing layer coated around the Au film on the PCS fiber surface. The PCS fiber is chosen to overcome the shortcomings of the structured microfibers and construct a more stable and reliable device. It is demonstrated that the introduction of graphene can enhance the intensity of the confined electric field surrounding the sensing layer, which results in a stronger light-matter interaction and thereby the improved sensitivity. The sensitivity of graphene-based fiber optic SPR sensor exhibits more than two times larger than that of the conventional gold film SPR fiber optic sensor. Furthermore, the dynamic response analyses reveal that the graphene/Au fiber optic SPR sensor exhibits a fast response (5 s response time) and excellent reusability (3.5% fluctuation) to the protein biomolecules. Such a graphene/Au fiber optic SPR sensor with high sensitivity and fast response shows a great promise for the future biochemical application.     

Comparison of Gold and Silver/Gold Bimetallic Surface for Highly Sensitive Near-infrared SPR Sensor at 1550 nm

A large majority of surface plasmon resonance (SPR) sensors reported in the literature are designed to operate in the visible electromagnetic spectrum. However, the near-infrared, particularly at the telecommunications wavelength of 1550 nm, is also especially attractive for SPR sensing applications. In fact, SPR sensors operating in this region benefit from narrower resonance and deeper field penetration. In this paper, we report a theoretical and experimental study of an SPR sensor operating at a fixed wavelength of 1550 nm. The influence of the choice of metals and the interrogation methods on the sensitivity of the resulting SPR sensor is investigated. Two types of sensor chips (simple gold (Au) and bimetallic silver/Au structure) and three interrogation methods (monitoring of the position of the reflectivity minimum, the position of the centroid, and the intensity evolution of the reflectivity) are examined. We show that a refractive index resolution of 2.7?×?10^?6 refractive index unit can be easily obtained, and with further optimization of the measurement system, the ultimate limit of detection is expected to be even lowered. Therefore, the approach discussed here already shows a promising potential for highly sensitive SPR sensors.     

SPR Label-Free Biosensor with Oxide-Metal-Oxide-Coated D-Typed Optical Fiber: a Theoretical Study

In this article, a surface plasmon resonance (SPR) biosensor based on D-typed optical fiber coated by Al₂O₃/Ag/Al₂O₃ film is investigated numerically. Resonance in near infrared with an optimized architecture is achieved. Refractive index sensitivity of 6558 nm/RIU (refractive index unit) and detection limit of 1.5 × 10⁻⁶ RIU, corresponding to 0.4357 nm/μM and detection limit of 23 nM in BSA (bovine serum albumin) concentration sensing, are obtained. The analysis of the performance of the sensor in gaseous sensing indicates that this proposed SPR sensor is much suitable for label-free biosensing in aqueous media.

     

Colloidal Au replacement assay for highly sensitive quantification of low molecular weight analytes by surface plasmon resonance

A novel sensing method based on surface plasmon resonance (SPR) was developed for the highly sensitive quantification of low molecular weight (LMW) analytes (colloidal Au replacement assay). Gold nanoparticles (diameter = 20 nm) functionalized with lactosyl-poly(ethylene glycol) (PEG) were prepared and were specifically adsorbed onto a Ricinus communis agglutinin (RCA120)-immobilized SPR sensor chip surface. Subsequent injection of free d-galactose elicited the elution of the preadsorbed lactosyl-PEGylated gold nanoparticles in a manner proportional to the galactose concentration, achieving a substantial and quantitative analysis over a wide range of galactose concentrations (0.1-50 ppm). This method of d-galactose sensing through the substituted elution of preadsorbed nanoparticles from the sensor chip surface would be applicable for the highly sensitive SPR quantification of various LMW analytes, which are known to be difficult to detect by the conventional SPR sensing regime.     

High Sensitivity in Ni-Based SPR Sensor of Blue Phosphorene/Transition Metal Dichalcogenides Hybrid Nanostructure

In the present work, a novel surface plasmon resonance (SPR) sensor consisting of the nickel (Ni) film with hybrid structure of blue phosphorene (BlueP)/transition metal dichalcogenides (TMDCs) is reported. By optimizing the thickness of Ni layer and BlueP/TMDCs, the maximum sensitivity with 270°/RIU for the Ni-BlueP/WS₂ is achieved. Use of BlueP/TMDCs layer facilitates the sensitivity due to its high electron concentration, high mobility, optical, and electronic properties. Compared with the conventional Ni-based SPR sensor, the sensitivity of the proposed one is enhanced up to ~ 60.7%. We hope that the SPR sensor has potential application prospects in chemical detection, medical diagnostic, optical sensing, etc. due to its high sensitivity.

     

Optimization of Surface Plasmon Resonance Biosensor with Ag/Au Multilayer Structure and Fiber-Optic Miniaturization

In this paper, we report a novel wavelength interrogation-based surface plasmon resonance (SPR) system, in which a film of three Ag layers and three Au layers are alternately deposited on a Kretschmann configuration as sensing element. This multilayer film shows higher sensitivity for refractive index (RI) measurement by comparing with single Au layer structure, which is consistent with its theoretical calculation. A sensitivity range of 2056–5893 nm/RIU can be achieved, which is comparable to RI sensitivities of other wavelength-modulated SPR sensors. Compared with Ag film, this Ag/Au multilayer arrangement offers anti-oxidant protection. This SPR biosensor based on a cost-effective Ag/Au multilayer structure is applicable to the real-time detection of specific interactions and dissociation of low protein concentrations. To extend the application of this highly-sensitive metal film device, we integrated this concept on an optical fiber. The range of RI sensitivities with Ag/Au multilayer was 1847–3309 nm/RIU. This miniaturized Ag/Au multilayer-based fiber optic sensor has a broad application in chemical and biological sensing.     

Integrated Terahertz Surface Plasmon Resonance on Polyvinylidene Fluoride Layer for the Profiling of Fluid Reflectance Spectra

We design terahertz (THz) surface-plasmon-resonance (SPR) sensors using a ferroelectric polyvinylidene fluoride (PVDF) thin layer for biological sensing. The reflectivity properties based on SPR are described using transfer matrix method (TMM) and numerically simulated using finite-difference time domain (FDTD) method. The sensing characteristics of the structure are systematically analyzed through the examination of the reflectivity spectrum. The results reveal that the pronounced SPR resonance peak has quasi-linear relationship with the refractive index variation of the material under investigation. Through analyzing and optimizing the structural parameters of the THz SPR sensor, we achieved the theoretical value of the refractive index detection sensitivity as high as 0.393 THz/unit change of refractive index (RIU) for a 20-μm-thick liquid sample with a 10-μm PVDF layer. This work shows great promise toward realizing a THz SPR sensor with high sensitivity for identifying the signatures of biological fluid sample.     

Surface plasmon resonance protein sensor using Vroman effect

We report a new surface plasmon resonance (SPR) protein sensor using the Vroman effect for real-time, sensitive and selective detection of protein. The sensor relies on the competitive nature of protein adsorption onto the surface, directly depending upon protein's molecular weight. The sensor uses SPR for highly sensitive biomolecular interactions detection and the Vroman effect for highly selective detection. By using the Vroman effect we bypass having to rely on bio-receptors and their attachment to transducers, a process known to be complex and time-consuming. The protein sensor is microfabricated to perform real-time protein detection using four different proteins including aprotinin (0.65kDa), lysozyme (14.7kDa), streptavidine (53kDa), and isolectin (114kDa) on three different surfaces, namely a bare-gold surface and two others modified by OH- and COOH-terminated self-assembled monolayer (SAM). The real-time adsorption and displacement of the proteins are observed by SPR and evaluated using an atomic force microscope (AFM). The sensor can distinguish proteins of at least 14.05kDa in molecular weight and demonstrate a very low false positive rate. The protein detector can be integrated with microfluidic systems to provide extremely sensitive and selective analytical capability.     

Surface plasmon resonance immunosensor for highly sensitive detection of 2,4,6-trinitrotoluene

We have examined the sensing characteristics of a surface plasmon resonance (SPR) immunoassay for the detection of 2,4,6-trinitrotoluene (TNT) using an immunoreaction between 2,4,6-trinitrophenol-ovalbumin (TNP-OVA) conjugate and anti-2,4,6-trinitrophenol antibody (anti-TNP antibody). TNP-OVA conjugate was attached to a SPR-gold sensing surface by means of physical immobilization, which undergoes binding interaction with anti-TNP antibody. Both the immobilization and binding processes were studied from a change in the SPR-resonance angle. The quantification of TNT is based on the principle of indirect competitive immunoassay, in which the immunoreaction between the TNP-OVA conjugate and anti-TNP antibody was inhibited in the presence of free TNT in solution. The decrease in the resonance angle shift is proportional to an increase in concentration of TNT used for incubation. The immunoassay exhibited excellent sensitivity for the detection of TNT in the concentration range from 0.09 to 1000 ng/ml with good stability and reproducibility. The immunosensor developed could detect TNT as low as 0.09 ng/ml, within a response time of approximately 22 min. The sensor surface was regenerated by a brief flow of pepsin solution, which disrupts the antigen-antibody complex without destroying the conjugate biofilm. Cross-reactivity of the SPR sensor to some structurally related nitroaromatic derivative and the detection of TNT in the presence of these nitroaromatic compounds were investigated. The cross-reactivity of the SPR sensor to 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene (1,3-DNB), 2-amino-4,6-dinitrotoluene (2A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) were very low (< or =1.1%). The analytical characteristics of the proposed immunosensor are highly promising for the development of new field-portable sensors for on-site detection of landmines.     

Deposition of functionalized polymer layers in surface plasmon resonance immunosensors by in-situ polymerization in the evanescent wave field

Traditionally, the integration of sensing gel layers in surface plasmon resonance (SPR) is achieved via "bulk" methods, such as precipitation, spin-coating or in-situ polymerization onto the total surface of the sensor chip, combined with covalent attachment of the antibody or receptor to the gel surface. This is wasteful in terms of materials as the sensing only occurs at the point of resonance interrogated by the laser. By isolating the sensing materials (antibodies, enzymes, aptamers, polymers, MIPs, etc.) to this exact spot a more efficient use of these recognition elements will be achieved. Here we present a method for the in-situ formation of polymers, using the energy of the evanescent wave field on the surface of an SPR device, specifically localized at the point of interrogation. Using the photo-initiator couple of methylene blue (sensitizing dye) and sodium p-toluenesulfinate (reducing agent) we polymerized a mixture of N,N-methylene-bis-acrylamide and methacrylic acid in water at the focal point of SPR. No polymerization was seen in solution or at any other sites on the sensor surface. Varying parameters such as monomer concentration and exposure time allowed precise control over the polymer thickness (from 20-200 nm). Standard coupling with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide was used for the immobilization of protein G which was used to bind IgG in a typical biosensor format. This model system demonstrated the characteristic performance for this type of immunosensor, validating our deposition method.     

Improving the Sensitivity of Fiber Surface Plasmon Resonance Sensor by Filling Liquid in a Hollow Core Photonic Crystal Fiber

Inspired by the classic theory, we suggest that the performance of a D-shaped fiber optical surface plasmon resonance (SPR) sensor can be improved by manipulating the fiber core mode. To demonstrate this, we propose a novel fiber SPR sensor based on a hollow core photonic crystal fiber with liquid mixture filled in the core. The fiber sensor design involves a side-polished fiber with gold film deposited on the polished plane and liquid filling. Numerical simulation results suggest that by tuning the refractive index of the liquid mixture, the predicted sensitivity will be over 6,430 nm/refractive index unit for an aqueous environment, which is competitive for fiber chemical sensing. This optimization method may lead to an ultrahigh sensitivityfiber optical biosensor.