Surface plasmon resonance

During last decade there has been significant progress in the development of analytical techniques for evaluation of receptor-ligand iteraction. Surface plasmon resonance (SPR)-based optical biosensors are now being used extensively to defined the kinetics of wide variety of macromolecular interactions and high- and low-affinity small molecule interactions. The experimental design data analysis methods are evolving along with widespread applications in ligand fishing, microbiology, virology, host-pathogen interaction, epitope mapping and protein-, cell-, membrane-, nucleic acid-protein interactions. SPR based biosensors have strong impact on basic and applied research significantly. This brief review describes the SPR technology and few of its applications in relation to receptor-ligand interaction that has brought significant change in the methodology, analysis, interpretation, and application of the SPR technology.     

Surface plasmon resonance spectroscopy study of electrostatically adsorbed layers

The use of 4-(dimethylamino)pyridine to form an adhesion layer for the adsorption of anionic polyelectrolytes on gold surfaces is investigated. In situ surface plasmon resonance spectroscopy is used to monitor the changes in thickness of the adsorbed layers as a function of pH changes. Weak (poly(acrylate)) and strong (poly(styrenesulfonate)) polyelectrolytes have been studied. Although 4-(dimethylamino)pyridine is weakly bound to gold, it is not displaced by these polyelectrolytes and acts as an adhesion layer. The relationship of the interaction of anionic polyelectrolytes with 4-(dimethylamino)pyridine-modified planar gold and gold nanoparticles is discussed.     

Surface plasmon resonance in doping analysis

Doping analysis relies on the determination of prohibited substances that should not be present in the body of an athlete or that should be below a threshold value. In the case of xenobiotics their mere presence is sufficient to establish a doping offence. However, in the case of human biotics the analytical method faces the difficulty of distinguishing between endogenous and exogenous origin. For this purpose ingenious strategies have been implemented, often aided by state-of-the-art technological advancements such as mass spectrometry in all its possible forms. For larger molecules, i.e. protein hormones, the innate structural complexity, the heterogeneous nature, and the extremely low levels in biological fluids have rendered the analytical procedures heavily dependent of immunological approaches. Although approaches these confer specificity and sensitivity to the applications, most rely on the use of two, or even three, antibody incubations with the consequent increment in assay variability. Moreover, the requirement for different antibodies that separately recognise different epitopes in screening and confirmation assays further contributes to differences encountered in either measurement. The development of analytical techniques to measure interactions directly, such as atomic force microscopy, quartz crystal microbalance or surface plasmon resonance, have greatly contributed to the accurate evaluation of molecular interactions in all fields of biology, and expectations are that this will only increase. Here, an overview is provided of surface plasmon resonance, and its particular value in application to the field of doping analysis.     

Surface plasmon resonance biosensor for determination of tetrodotoxin: prevalidation study

A label-free surface plasmon resonance biosensor method was applied to determine tetrodotoxin (TTX) in pufferfish matrixes using an antibody inhibition assay format. A prevalidation study was conducted to demonstrate the assay performance characteristics, such as selectivity, LOD, LOQ, repeatability, reproducibility, and accuracy. Three participating laboratories reported standard curves in buffer and pufferfish matrix. A set of blind samples with TTX spiked into buffer as well as in 10% pufferfish extract were analyzed. Additionally, three blind naturally contaminated samples were analyzed, and the results were compared to those obtained using a reference method (HPLC/electrospray ionization-selected reaction monitoring-MS). The developed method was demonstrated to be capable of detecting TTX in pufferfish matrix standard samples in a broad concentration range (2-9000 ng/mL) with an LOD of 1.5 ng/mL. Between-laboratory recovery values were in the range of 51-190% with a mean of 107%, and 64-180% with a mean of 103% for TTX-spiked samples in buffer and pufferfish matrix, respectively. Between-laboratory recoveries were in the satisfactory range of 101-119% for naturally contaminated samples. This robust, rapid, and noninvasive method may serve as an attractive alternative to established methods for detection of TTX in pufferfish extracts.     

Surface plasmon resonance of electrochemically deposited Au-black

Au-black, a kind of gold nanostructure, was electrochemically deposited on a Au-vapor-deposited glass plate, and its optical properties were evaluated with a surface plasmon resonance (SPR) measurement system. The Au-black was found to exhibit an extraordinary high resonance angle (minimum reflectance angle) compared to that of the Au-vapor-deposited glass plate. We proposed a five-layer model, which consists of glass, Cr, Au, Au-black, and solution layers, to explain the high resonance angle of the Au-black plate. The calculation was based on the Fresnel formulas extended for multilayers. When the Bruggeman formula was used to obtain a refractive index of the Au-black layer, the numerical simulation could qualitatively explain the experimental observations. The curve fitting method by the five-layer model enabled us to simultaneously estimate the thickness of the Au-black layer and the volume fraction of Au in Au-black.     

Surface plasmon resonance study on HIV-1 integrase strand transfer activity

Understanding the molecular mechanism of HIV-1 integrase (IN) activity is critical to find functional inhibitors for an effective AIDS therapy. A robust, fast, and sensitive method for studying IN activity is required. In this work, an assay for real-time label-free monitoring of the IN activity based on surface plasmon resonance was developed. This assay enabled direct monitoring of the integration of a viral doubled-stranded (ds) DNA into the host genome. The strand transfer reaction was detected by using two different DNA targets: supercoiled plasmid (pUC 19) and short palindrome oligonucleotide. The effect of the length of the DNA target on the possibility to monitor the actual process of the strand transfer reaction is discussed. The surface density of integrated ds-DNA was determined. IN binding to the oligonucleotide complexes and model DNA triplexes in the presence of various divalent ions as metal cofactors was investigated as well. The assay developed can serve as an important analytical tool to search for potential strand transfer reaction inhibitors as well as for the study of compounds interfering with the binding of ds long terminal repeats–IN complexes with the host DNA. HIV-1 integrase strand transfer activity was monitored in real time using a multichannel surface plasmon resonance biosensor. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Surface plasmon resonance applications in clinical analysis

In the last 20 years, surface plasmon resonance (SPR) and its advancement with imaging (SPRi) emerged as a suitable and reliable platform in clinical analysis for label-free, sensitive, and real-time monitoring of biomolecular interactions. Thus, we report in this review the state of the art of clinical target detection with SPR-based biosensors in complex matrices (e.g., serum, saliva, blood, and urine) as well as in standard solution when innovative approaches or advanced instrumentations were employed for improved detection. The principles of SPR-based biosensors are summarized first, focusing on the physical properties of the transducer, on the assays design, on the immobilization chemistry, and on new trends for implementing system analytical performances (e.g., coupling with nanoparticles (NPs). Then we critically review the detection of analytes of interest in molecular diagnostics, such as hormones (relevant also for anti-doping control) and biomarkers of interest in inflammatory, cancer, and heart failure diseases. Antibody detection is reported in relation to immune disorder diagnostics. Subsequently, nucleic acid targets are considered for revealing genetic diseases (e.g., point mutation and single nucleotides polymorphism, SNPs) as well as new emerging clinical markers (microRNA) and for pathogen detection. Finally, examples of pathogen detection by immunosensing were also analyzed. A parallel comparison with the reference methods was duly made, indicating the progress brought about by SPR technologies in clinical routine analysis.     

Surface plasmon resonance immunosensor for bacteria detection

This work describes an approach for the development of two bacteria biosensors based on surface plasmon resonance (SPR) technique. The first biosensor was based on functionalized gold substrate and the second one on immobilized gold nanoparticles. For the first biosensor, the gold substrate was functionalized with acid-thiol using the self-assembled monolayer technique, while the second one was functionalized with gold nanoparticles immobilized on modified gold substrate. A polyclonal anti-Escherichia coli antibody was immobilized for specific (E. coli) and non-specific (Lactobacillus) bacteria detection. Detection limit with a good reproducibility of 10⁴ and 10³ cfu mL⁻¹ of E. coli bacteria has been obtained for the first biosensor and for the second one respectively. A refractive index variation below 5 × 10⁻³ due to bacteria adsorption is able to be detected. The refractive index of the multilayer structure and of the E. coli bacteria layer was estimated with a modeling software.     

Surface plasmon resonance immunosensors: sensitivity considerations

Some aspects of improving surface plasmon resonance response in immunosensing applications are considered. Both from calculations and experiments, it was found that maximum sensitivity is obtained for a silver layer about 55 nm thick in direct contact with the species to be quantified. Application of an intermediate layer with high permittivity can be useful in suppressing background responses. Experimentally, a protein surface-coverage fraction of ca. 0.1 could be measured, corresponding to ca. 10^?10 mol1^?1 antibody.     

Surface plasmon resonance imaging studies of protein-carbohydrate interactions

Carbohydrate arrays fabricated on gold films were used to study carbohydrate-protein interactions with surface plasmon resonance (SPR) imaging. An immobilization scheme consisting of the formation of a surface disulfide bond was used to attach thiol-modified carbohydrates onto gold films and to fabricate carbohydrate arrays. The carbohydrate attachment steps were characterized using polarization modulation Fourier transform infrared reflection absorption spectroscopy; and poly(dimethylsiloxane) microchannels were used to immobilize probe compounds at discrete locations on a gold film. The binding of the carbohydrate-binding proteins concanavalin A (ConA) and jacalin to arrays composed of the monosaccharides mannose and galactose was monitored with SPR imaging. SPR imaging measurements were employed to accomplish the following: (i) construct adsorption isotherms for the interactions of ConA and jacalin to the carbohydrate surfaces, (ii) monitor protein binding to surfaces presenting different compositions of the immobilized carbohydrates, and (iii) measure the solution equilibrium dissociation constants for ConA and jacalin toward mannose and galactose, respectively. Adsorption coefficients (K(ADS)) of 2.2 +/- 0.8 x 10(7) M(-)(1) and 5.6 +/- 1.7 x 10(6) M(-)(1) were obtained for jacalin adsorbing to a galactose surface and ConA adsorbing to a mannose surface, respectively. The solution equilibrium dissociation (K(D)) constant for the interaction of jacalin and galactose was found to be 16 +/- 5 microM, and for ConA and mannose was found to be 200 +/- 50 microM.     

Surface plasmon resonance imaging of limited glycoprotein samples

A surface plasmon resonance imaging method has been developed for high throughput recognition and determination of low level glycoproteins with limited sample volume at least down to 50 nL. Chicken ovalbumin and immunoglobulin G were chosen as model compounds while bovine serum albumin and lysozyme were used as control. Each protein, at a concentration of 0.0080-1.0 mg mL(-1), was printed on one gold sensing film, and the films were simultaneously reacted with a probe solution and viewed using a laboratory-built surface plasmon resonance imaging system. The imaging signals were dependent on the concentration and the type of analyte, with a limit of detection down to at least 0.5 ng. The glycoproteins dotted at either 1.0 mg mL(-1) or 0.010 mg mL(-1) were easily differentiated from the non-glycoproteins by reaction with 200 nM concanavalin A (con A), giving a limit of recognition down also to 0.5 ng glycoprotein. This imaging method was hence considered a new tool for analyzing glycoproteins.     

Surface plasmon resonance within ion implanted silver clusters

Surface plasmon resonance (SPR) belongs to the most sensitive indicators for changes in analyte concentrations or other sample properties, which depend on the refractive index in the medium. Surface plasmons represent collective electron oscillations in metal cluster or metal layers of diameter or thickness in the nanometer range. Such layers or clusters are used in many optical sensors in order to enhance the interaction between electromagnetic radiation and analyte. Clusters are preferred to enhance Raman scattering and IR absorption, whereas layers are used for SPR in the visible range. We tested the applicability of ion implanted clusters in order to enhance the stability of the metal coatings of the SPR sensor elements. A model based on the effective media theory was developed in order to enhance the sensor capabilities. The potential of the SPR with ion implanted metal clusters consists in durable resonance layers for biochemical sensors. Received: 21 December 1997 / Revised: 6 March 1998 / Accepted: 12 March 1998     

Surface plasmon resonance within ion implanted silver clusters

Surface plasmon resonance (SPR) belongs to the most sensitive indicators for changes in analyte concentrations or other sample properties, which depend on the refractive index in the medium. Surface plasmons represent collective electron oscillations in metal cluster or metal layers of diameter or thickness in the nanometer range. Such layers or clusters are used in many optical sensors in order to enhance the interaction between electromagnetic radiation and analyte. Clusters are preferred to enhance Raman scattering and IR absorption, whereas layers are used for SPR in the visible range. We tested the applicability of ion implanted clusters in order to enhance the stability of the metal coatings of the SPR sensor elements. A model based on the effective media theory was developed in order to enhance the sensor capabilities. The potential of the SPR with ion implanted metal clusters consists in durable resonance layers for biochemical sensors. Received: 21 December 1997 / Revised: 6 March 1998 / Accepted: 12 March 1998     

Surface plasmon resonance spectroscopy study of interfacial binding of thrombin to antithrombin DNA aptamers

We have applied surface plasmon resonance (SPR) spectroscopy, in combination with one-step direct binding, competition, and sandwiched assay schemes, to study thrombin binding to its DNA aptamers, with the aim to further the understanding of their interfacial binding characteristics. Using a 15-mer aptamer that binds thrombin primarily at the fibrinogen-recognition exosite as a model, we have demonstrated that introducing a DNA spacer in the aptamer enhances thrombin-binding capacity and stability, as similarly reported for hydrocarbon linkers. The bindings are aptamer surface coverage and salt concentration dependent. When free aptamers or DNA sequences complementary to the immobilized aptamer are applied after the formation of thrombin/aptamer complexes, bound thrombin is displaced to a certain extent, depending on the stability of the complexes formed under different conditions. When the 29-mer aptamer (specific to thrombin's heparin-binding exosite) is immobilized on the surface, its affinity to thrombin appears to be lower than the immobilized 15-mer aptamer, although the 29-mer aptamer is known to have a higher affinity in the solution phase. These findings underline the importance of aptamers' ability to fold into intermolecular structures and their accessibility for target capture. Using a sandwiched assay scheme followed by an additional signaling step involving biotin-streptavidin chemistry, we have observed the simultaneous binding of the 15- and 29-mer aptamers to thrombin protein at different exosites and have found that one aptamer depletes thrombin's affinity to the other when they bind together. We believe that these findings are invaluable for developing DNA aptamer-based biochips and biosensors.     

Surface plasmon resonance of silver nanoparticles on vanadium dioxide

The localized surface plasmon resonance (SPR) spectrum of silver nanoparticles fabricated on a thermochromatic film, vanadium dioxide (VO2), is studied in this paper. Owing to the temperature-dependent dielectric function of VO2, the SPR band dramatically exhibits temperature dependence in the range of 30-80 degrees C. The peak extinction wavelength, lambda(SPR), blueshifts as temperature increases and reversibly redshifts as temperature decreases. The shift magnitude (DeltalambdaSPR) is strongly dependent on the silver mass thickness, dm; a value of 50 nm of DeltalambdaSPR is achieved for particles (mean diameter 51 nm) with dm=2 nm while a value of 250 nm is achieved for particles (mean diameter 133 nm) with dm=10 nm. Beyond the SPR band, it is interesting to find that the spectral line shape of silver particles is dominated by the imaginary part of the dielectric function of VO2. These results can be interpreted based on dynamical Maxwell-Garnett theory.     

Surface plasmon resonance study on binding interactions of multivalent cyclophane hosts with immobilized guests

Guest‐binding affinities of water‐soluble cyclophane heptadecamer (1) and pentamer (2) with immobilized guests such as 1‐pyrenylmethylamine (PMA) and 2‐(1‐ naphthyl)ethylamine (NEA) were investigated by surface plasmon resonance (SPR) measurements. As a typical example, the binding constants (K) for 1 and 2 with the immobilized PMA as a guest were evaluated to be 2.5 × 10⁷ and 2.7 × 10⁶ M^?1, respectively, and were much larger than that of a monocyclic reference cyclophane (K, 2.5 × 10⁴ M^?1). Interestingly, in the complexation of 1 and 2 with the immobilized guests, more favorable association and dissociation rate constant values (k_a and k_d, respectively) were observed in comparison with those for the monocyclic cyclophane, reflecting multivalent effects in macrocycles. The multivalent effects in macrocycles as well as molecular recognition abilities of the cyclophane oligomers were confirmed even when the guest molecules were immobilized on SPR sensor chip surfaces. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface plasmon resonance application in prostate cancer biomarker research

Prostate cancer (PCa) diagnostics can be effectively addressed using sensor-based approaches. Proper selection of biomarkers to be included in biosensors for accurate detection becomes the need of the hour. Such biosensor and biochip technologies enable fast and efficient determination of proteins and provide a remarkable insight into the changes in the protein structure, such as aberrant glycosylation, which can increase the performance, sensitivity and specificity of clinic assays. However, for a thorough comprehension of such complex protein modifications, it is crucial to understand their biospecific interactions. Surface plasmon resonance (SPR), one of the most rapidly developing techniques for measuring real-time quantitative binding affinities and kinetics of the interactions of antigens and antibodies, was chosen as an appropriate tool for this purpose. Herein, experiments on the interactions of antibodies specific against different epitopes of free and complexed prostate-specific antigen (PSA), a prominent PCa biomarker, are presented with two main aims: (i) to continue as lectin glycoprofiling studies and; (ii) to be used in microfluidic immunoassay-based platforms for point-of-care devices. Various PSA-specific antibodies were covalently immobilized on the biochip surface via amine coupling, and free or complexed PSA was injected into the dual-flow channels of the SPR device. Kinetic parameters and affinity constants of these interactions, as well as cross-reactivities of the used antibodies were determined. The sandwich assay for PSA determination was developed employing both primary and secondary anti-PSA antibodies. Sensitivity of the assay was 3.63 nM^?1, the detection limit was 0.27 nM and the SPR biosensor response towards free PSA was linear up to 25 nM. All these findings are essential for proper design of a selective, sensitive, and highly reliable biosensor for PCa diagnosis as a lab-on-chip device.     

Surface plasmon resonance biosensor for genetically modified organisms detection

The development of a surface plasmon resonance (SPR) affinity biosensor based on DNA hybridisation is described. This biosensor has been applied to genetically modified organisms (GMOs) detection. Single stranded DNA (ssDNA) probes were immobilised on the sensor chip of an SPR device and the hybridisation between the immobilised probe and the complementary sequence (target) was monitored. The probe sequences were internal to the sequence of 35S promoter and NOS terminator which are inserted sequences in the genome of GMO regulating the transgene expression. The system has been optimised using synthetic oligonucleotides, then applied to real samples analysis. Samples, containing the transgenic target sequences, were amplified by polymerase chain reaction (PCR) and then detected with the SPR biosensor.