Combination Of Surface Plasmon Resonance Research Articles

Understanding the interaction of concanavalin a with mannosyl glycoliposomes: A surface plasmon resonance and fluorescence study

The specificity of carbohydrate-protein interaction is a key factor in many biological processes and it is the foundation of technologies using glycoliposomes in drug delivery. The incorporation of glycolipids in vesicles is expected to increase their specificity toward particular targets such as lectins; however, the degree of exposure of the carbohydrate moiety at the liposome surface is a crucial parameter to be considered in the interaction. Herein we report the synthesis of mannose derivatives with one or two hydrophobic chains of different length, designed with the purpose of modifying the degree of exposure of the mannose when they were incorporated into liposomes.The interaction of glycovesicles with Con A was studied using: (i) agglutination assays; measured by dynamic laser light scattering (DLS); (ii) time resolved fluorescence methods and (iii) surface plasmon resonance (SPR) kinetic measurements. DLS data showed that an increase in hydrophobic chain length promotes a decrease of liposomes hydrodynamic radius. A longer hydrocarbon chain favors a deeper insertion into the bilayer and mannose moiety results less exposed at the surface to interact with lectin. Fluorescence experiments showed changes in the structure of glycovesicles due to the interaction with the protein. From SPR measurements the kinetic and equilibrium constants associated to the interaction of ConA with the different glycolipid synthetized were determined.The combination of SPR and fluorescence techniques allowed to study the interaction of Con A with mannosyl glycovesicles at three levels: at the surface, at the interface and deeper into the bilayer.

Tubulin on Biomimetic Mitochondrial Membranes: Structural Features and Lipid Discrimination

Dimeric tubulin, an abundant cytosolic water-soluble protein, has emerged as an important regulatory factor of the permeability of the voltage-dependent anion channel (VDAC) in the mitochondrial outer membrane, with implications for mitochondrial energetics as well as the Warburg effect observed in cancer cells. A wealth of recent in vitro and in vivo evidence points to a mechanism of this regulation, in which a charged C-terminal tail of tubulin inserts into the water-filled VDAC pore, thus blocking metabolite fluxes through this passive transport channel. The membrane-binding properties of tubulin have proven difficult to ascertain, as early work generated contradictory results regarding the tubulin-membrane association, including whether it was integral or peripheral in nature. Here we report on a comprehensive biophysical study of tubulin binding to lipid membranes with compositions that mimic the mitochondrial outer membrane. A combination of surface plasmon resonance, bilayer overtone (second harmonics) analysis, and single-channel recordings show that tubulin distinguishes between lamellar and non-lamellar lipid components of the membrane. To obtain the structural features of the tubulin heterodimer on the membrane surface, we have employed neutron reflectometry (NR) of tubulin on a tethered bilayer lipid membrane platform. The NR results definitively show that tubulin binds peripherally, and in combination with molecular dynamics (MD) simulations suggest the binding domain to be a highly conserved amphipathic α-helix on α-tubulin. Thus tubulin joins a short but growing list of amphitropic proteins that target cell and organelle membranes by sensing lipid packing defects via amphipathic α-helices, suggesting a pathway by which lipid homeostasis regulates mitochondrial function.

Effect of Probe-Probe Distance on the Stability of DNA Hybrids on Surfaces.

We have used temperature gradient surface plasmon resonance (SPR) measurements to quantitatively evaluate how the stability of different types of hybrids formed with DNA probes on surfaces is affected by probe spacing. SPR sensors with different average surface densities of probes were prepared by coadsorbing probes with lateral spacers strands comprised of phosphorothioated adenine nucleotides (A15*). Increasing the fraction of A15* spacers in the immobilization solution results in larger distances between probes on the sensor, determined here using a combination of SPR and X-ray photoelectron spectroscopy (XPS) measurements. The hybridization activities of probes were simultaneously measured over a temperature range that spanned the denaturation temperature (Tm) of hybrids by applying a spatial temperature gradient across the sensor surface. The resulting temperature profiles of hybridization activity show how the stability of hybrids increases as either the distance between probes or the ionic strength of the hybridization buffer increase. Additionally, hybridization activity profiles sharpen as the spacing between probes increases, indicating more homogeneous hybridization behavior of probes. The results provide quantitative experimental data for testing theoretical models of stability, supporting models that account for both repulsive interactions between DNA strands and local variability in probe surface density.

A highly sensitive and distinctly selective d-sorbitol biosensor using SDH enzyme entrapped Ta2O5 nanoflowers assembly coupled with fiber optic SPR

The current work introduces a novel platform for detection of d-sorbitol in aqueous samples employing surface plasmon resonance (SPR) as the cardinal sensing principle. The sensing probe encompasses an assembly of sorbitol dehydrogenase enzyme entrapped tantalum pentaoxide nanoflowers decorated onto the plasmonic metal silver coated unclad core of an optical fiber. When the sensing probe is brought in vicinity of d-sorbitol solutions of varying concentration, the formation and subsequently decomposition of enzyme-analyte complex is entailed, which, in turn, alters the dielectric function of the sensing layer. This tailoring of dielectric function within the premises of sensing probe is manifested in terms of the shift in resonance wavelength. The concentration range 0.1–1.1μg/ml of d-sorbitol defines the limit of operation of the sensor, for which a blue shift of 55nm in resonance wavelength has been observed. The sensitivity and the limit of detection are obtained as, 92.16nm/μg/ml and 3.6ng/ml, respectively, which excel the previously reported results. Influence of pH over the performance and selectivity/specificity of the sensor are also investigated. The sensor showcases immense scope of usage in medical, pharmaceutical and food industry on grounds of myriad advantages provided by combination of SPR and fiber optics.

A dielectric barrier discharge ionization based interface for online coupling surface plasmon resonance with mass spectrometry.

The online combination of surface plasmon resonance (SPR) with mass spectrometry (MS) could be beneficial for accurately acquiring molecular interaction data simultaneously with their structural information at high throughputs. In this work, a novel SPR-MS interface was developed using a dielectric barrier discharge ionization (DBDI) source. The DBDI source was placed in front of the MS inlet, generating an ionization plasma jet. A spray tip was set between the DBDI source outlet and the MS inlet, nebulizing the SPR sample solution. Using this interface, samples could first be studied by SPR, then sprayed and ionized, finally analyzed by MS. By analyzing model samples containing small-molecule drugs dissolved in salt containing solutions, the practicability of this SPR-DBDI-MS interface was proved, observing the consistent change of SPR and MS signals. Compared with our previously developed direct analysis in real time (DART) based SPR-MS interface, this new interface exhibited a higher and better tolerance to non-volatile salts, and different ionization capabilities for various samples. These results indicated that the interface could find further utilization in SPR-MS studies especially when physiological conditions were needed.

Real-Time Evaluation of Live Cancer Cells by an in Situ Surface Plasmon Resonance and Electrochemical Study.

This work presents a new strategy of the combination of surface plasmon resonance (SPR) and electrochemical study for real-time evaluation of live cancer cells treated with daunorubicin (DNR) at the interface of the SPR chip and living cancer cells. The observations demonstrate that the SPR signal changes could be closely related to the morphology and mass changes of adsorbed cancer cells and the variation of the refractive index of the medium solution. The results of light microscopy images and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide studies also illustrate the release or desorption of HepG2 cancer cells, which were due to their apoptosis after treatment with DNR. It is evident that the extracellular concentration of DNR residue can be readily determined through electrochemical measurements. The decreases in the magnitudes of SPR signals were linearly related to cell survival rates, and the combination of SPR with electrochemical study could be utilized to evaluate the potential therapeutic efficiency of bioactive agents to cells. Thus, this label-free, real-time SPR-electrochemical detection technique has great promise in bioanalysis or monitoring of relevant treatment processes in clinical applications.

Characterization of the direct interaction between KcsA-Kv1.3 and its inhibitors

Integral membrane proteins (IMPs) are of therapeutic interest and are targeted by a majority of approved drugs. It's difficult to express, purify, and maintain the functional conformation of IMPs. Nanodisc presents a reliable method to solubilize and stabilize IMPs in detergent-free condition. In this study, we demonstrate the assembly and purification of a chimeric ion channel, KcsA-Kv1.3 Nanodisc. We further detail biophysical analysis of the assembled Nanodisc using analytical ultracentrifugation (AUC), surface plasmon resonance (SPR), and back scattering interferometry (BSI). AUC is employed to determine the molecular composition of the empty and KcsA-Kv1.3 Nanodisc. Combination of SPR and BSI overcomes each other's limitation and provides insight of equilibrium binding properties of peptide and small molecule ligands to KcsA-Kv1.3.

Gremlin1 preferentially binds to bone morphogenetic protein-2 (BMP-2) and BMP-4 over BMP-7.

Gremlin (Grem1) is a member of the DAN family of secreted bone morphogenetic protein (BMP) antagonists. Bone morphogenetic protein-7 (BMP-7) mediates protective effects during renal fibrosis associated with diabetes and other renal diseases. The pathogenic mechanism of Grem1 during diabetic nephropathy (DN) has been suggested to be binding and inhibition of BMP-7. However, the precise interactions between Grem1, BMP-7 and other BMPs have not been accurately defined. In the present study, we show the affinity of Grem1 for BMP-7 is lower than that of BMP-2 and BMP-4, using a combination of surface plasmon resonance and cell culture techniques. Using kidney proximal tubule cells and HEK (human embryonic kidney)-293 cell Smad1/5/8 phosphorylation and BMP-dependent gene expression as readouts, Grem1 consistently demonstrated a higher affinity for BMP-2>BMP-4>BMP-7. Cell-associated Grem1 did not inhibit BMP-2- or BMP-4-mediated signalling, suggesting that Grem1-BMP-2 binding occurred in solution, preventing BMP receptor activation. These data suggest that Grem1 preferentially binds to BMP-2 and this may be the dominant complex in a disease situation where levels of Grem1 and BMPs are elevated.

Deciphering the stepwise binding mode of HRG1β to HER3 by surface plasmon resonance and interaction map.

For the development of efficient anti-cancer therapeutics against the HER receptor family it is indispensable to understand the mechanistic model of the HER receptor activation upon ligand binding. Due to its high complexity the binding mode of Heregulin 1 beta (HRG1β) with its receptor HER3 is so far not understood. Analysis of the interaction of HRG1β with surface immobilized HER3 extracellular domain by time-resolved Surface Plasmon Resonance (SPR) was so far not interpretable using any regular analysis method as the interaction was highly complex. Here, we show that Interaction Map (IM) made it possible to shed light on this interaction. IM allowed deciphering the rate limiting kinetic contributions from complex SPR sensorgrams and thereby enabling the extraction of discrete kinetic rate components from the apparently heterogeneous interactions. We could resolve details from the complex avidity-driven binding mode of HRG1β with HER3 by using a combination of SPR and IM data. Our findings contribute to the general understanding that a major conformational change of HER3 during its activation is induced by a complex sequential HRG1β docking mode.

Evaluation of β-Amyloid Peptides Fibrillation Induced by Nanomaterials Based on Molecular Dynamics and Surface Plasmon Resonance.

This report investigated the effect of carbon nanomaterials, single-wall carbon nanotube (SWCNT) and graphene oxide, on fibrillation of β-amyloid 40 (Aβ40) based on surface plasmon resonance (SPR) and molecular dynamics (MD). MD simulations are carried out in order to reveal the molecular mechanisms of the interaction between nanomaterials and Aβ40. The strong interaction between Aβ40 and nanomaterials is related to Van der Waals forces and the Coulomb force, inducing delicate manipulation of the main bonding energy for fibrillation of Aβ40. The interaction energy between the Aβ peptide and graphene is higher than that of SWCNT. Experimental results show both carbon nanomaterials enhance the appearance of a critical nucleus for nucleation of peptide fibrils. Graphene is more beneficial to assist the nucleation process than SWCNT. Combination of SPR and molecular dynamics could be a high-throughput method to screen protein fibrillation.

Determination of Bisphenol A using a Molecularly Imprinted Polymer Surface Plasmon Resonance Sensor

A novel sensor was prepared for the determination of bisphenol A by molecular imprinting combined with surface plasmon resonance (SPR). The molecular interaction of the functional monomer 4-vinyl pyridine with the template bisphenol A was characterized by spectrophotometry. A bisphenol A imprinted membrane was assembled on the surface of the surface plasmon resonance chip using 4-vinyl pyridine as the functional monomer, ethylene glycol dimethacrylate as the cross-linking agent, and azodiisobutyronitrile as the initiator. The adsorptivity and selectivity of the imprinted film to bisphenol A were evaluated at the optimum pH. The imprinted sensor had higher selectivity for bisphenol A than the nonimprinted device. The linear dynamic range of the imprinted sensor for bisphenol A was from 1.0 × 10−8 to 1.0 × 10−6 mole per liter. Based on a signal-to-noise ratio of three, the detection limits of bisphenol A were 6.15 × 10−9 moles per liter for bottled water and 6.84 × 10−9 moles per liter for polycarbonate, demonstrating good sensitivity. The combination of surface plasmon resonance with an imprinted film is a promising method for the determination of bisphenol A.

Unravelling nonspecific adsorption of complex protein mixture on surfaces with SPR and MS.

Characterization of protein adsorption to surfaces has implications from biosensing to protective biocoatings. While research studies have principally focused on determining the magnitude of protein adsorption to surfaces, the proteins involved in the process remains only broadly identified and has not been investigated on several surfaces. To further elucidate the nonspecific adsorption process of serum to surfaces, surface plasmon resonance (SPR) and matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) were used in combination to obtain quantitative and qualitative information about the process of protein adsorption to surfaces. To validate the technique, crude serum was nonspecifically adsorbed on four self-assembled monolayer (SAM) on gold: 16-mercaptohexadecanoic acid (16-MHA), 11-mercaptoundecane(ethylene glycol)3-COOH (PEG), 3-MPA-LHDLHD-OH, and 3-MPA-HHHDD-OH. Direct MS analysis of the nonspecifically adsorbed proteins suggested the presence of a variety of protein (BSA, IgG, and apolipoprotein A-1). Performing a trypsin digestion of the nonspecifically adsorbed proteins confirmed the presence of BSA and apolipoprotein A-1 and further revealed the complexity of the process by detecting the presence of complement C3, SHC-transforming protein 1, and kininogen 2. The level of nonspecific adsorption on different surfaces measured by SPR sensing directly correlated with the intensity of the serum protein and indirectly with the tryptic peptides measured by MS. Detailed analysis of the BSA peptides digested on 16-MHA and for BSA digested in solution was used to investigate the orientation of BSA on this surface. The combination of SPR and MS allows the quantitative and qualitative understanding of protein adsorption processes to surfaces.

Rapid surface plasmon resonance immunoassays for the determination of mycotoxins in cereals and cereal-based food products

In recent times surface plasmon resonance has demonstrated its applicability to the detection of a wide range of contaminants in food and feed including mycotoxins in cereals and cereal-based food products. Commercially available, laboratory-based systems have exploited high affinity polyclonal, monoclonal and recombinant antibodies and robust sensing surfaces to provide rapid, accurate and sensitive means of determining these toxins. In addition many custom-built, prototype devices have shown a great deal of potential for this particular application and have included the combination of surface plasmon resonance with enzyme-derivatised sensors, molecularly imprinted polymers, fluorescence spectroscopy and the use of gold nanoparticles for signal enhancement. Of note is the lack of available devices that allow the detection of multiple mycotoxins simultaneously and portable devices that could be used in the field, therefore future research and development should focus on these areas to deliver cost-effective miniaturised devices with multiplexing capabilities.

Enhanced Polar Magneto-optical Kerr Rotation in Cobalt Thin Film Incorporating Ag Nanoparticles

We report an experimental study on the effect of Ag nanoparticles on the polar magneto-optical Kerr effect in cobalt thin film. The magneto-optical cobalt thin film was prepared by electron beam deposition method onto the Ag nanoparticles which were synthesized by laser ablation in liquid technique. Our results indicate that we have sufficient enhancement of polar magneto-optical Kerr effect of cobalt thin film around the surface plasmon resonance of Ag nanoparticles. Moreover, combination of surface plasmon resonance of the Ag nanoparticles and very thin Au layer can be attained the enhancement factor in all of visible spectral region.

Surface plasmon resonance-based real-time bioaerosol detection

Rapid and precise bioaerosol detection in different environments has become an important research and technological issue over last decades. Previously, we employed a real-time PCR protocol in conjunction with personal bioaerosol sampler for rapid detection of airborne viruses. The approach has been proved to be specific and sensitive. However, a period of time required for entire procedure was in manner of hours. Some new developments are required to decrease the detection time down to real-time protocols. Presently, a surface plasmon resonance (SPR)-based immunosensor that coupled with a specific antigen-antibody reaction could offer sensitive, specific, rapid and label-free detection. This study describes the possibility of combining the personal sampler with SPR technology for qualitative and extremely rapid detection of airborne micro-organisms. Common viral surrogate MS2 bacteriophage, frequently used in bioaerosol studies, was employed as a model organism. The results of the sensor functionalizing procedure with monoclonal anti-MS2 antibody and optimization of the chip performance are presented. The SPR-based detection of the airborne virus was found to be very fast; the viral presence was detected in less than 2min, and the entire procedure (sampling and analysis) was undertaken in 6min, which could be considered as real-time detection for this type of measurements. The combination of SPR with the personal sampler targeted towards bioaerosol detection was proven to be feasible. The SPR sensor was found to be highly stable and suitable for multiple utilizations without significant decrease in response. The suggested approach opens new possibilities for the development of portable and rapid (almost real time) bioaerosol monitors. This technology is the first in the world real-time bioaerosol monitor. This outcome would be of strong interest to individuals representing public health, biosecurity, defence forces, environmental sciences and many others.

Surface plasmon resonance based fiber optic hydrogen peroxide sensor using polymer embedded nanoparticles

A fiber optic sensor utilizing combination of surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) for the detection of hydrogen peroxide has been fabricated and characterized using polyvinyl alcohol (PVA) embedded silver nanoparticles over the silver coated core of the optical fiber. Wavelength interrogation mode of operation has been used to characterize the sensor. The detection of hydrogen peroxide has been carried out by measuring the shift in the resonance wavelength for the concentration range 10−8 to 10−1M. Experiments show a large shift in the resonance wavelength with the increase in the concentration of hydrogen peroxide. This is due to the fact that silver nanoparticles have the catalytic efficiency to decompose hydrogen peroxide. The decomposition of hydrogen peroxide results in the degradation of silver nanoparticles which changes the refractive index of the nanocomposite layer and causes shift in resonance wavelength. This reason has been further supported by the X-ray diffraction (XRD) results. The sensor possesses very fast response time, high sensitivity. Being the fiber optic probe the sensor is compact, cheap and can be used for online and remote sensing. It will find applications in medical, clinical and environmental sciences.

Contribution of Au nanoparticles to the longitudinal magneto-optical Kerr effect of Bragg reflector based magneto-plasmonicmultilayers

In this paper, we investigate a significant enhancement of the longitudinal magneto-optical Kerr effect when a magneto-optical thin film is covered by the Bragg reflector mirror and Au nanoparticles on its right and left side respectively. Our results indicate the sufficient longitudinal magneto-optical Kerr effect enhancement in this new structure by the aid of combination of surface plasmon resonance and light localization in magneto-optical garnet layer at one practical communication wavelength in the middle of the visible spectrum. These results confirmed by the aid of Finite difference frequency domain simulation method.

Optical fiber sensor for the detection of tetracycline using surface plasmon resonance and molecular imprinting

We present a simple and highly selective optical fiber sensor for the detection of tetracycline in foodstuffs by using the combination of surface plasmon resonance (SPR) and a molecular imprinted polymer (MIP) matrix. The sensor is fabricated first by coating a thin film of silver metal over the unclad portion of an optical fiber, and then preparing a molecular imprinting of the target molecules over the metal coated region. The MIP creates several binding sites/nano-cavities which have the complementary shape and functional groups of the target molecules on its surface. The sensor works on the wavelength modulation scheme in which the shift in resonance wavelength is measured with respect to the change in tetracycline concentration. Two kinds of tetracycline, tetracycline hydrochloride (TC) and oxy-tetracycline hydrochloride (OTC) have been selected as the imprinting molecules because these possess similar structures. The presence of tetracycline samples in the vicinity of the sensing region causes the interaction between binding sites and target molecules which results in the change in the dielectric properties of the sensing surface, causing the shift in the SPR spectrum towards the red region. The selectivity of the sensor for dissimilar compounds, and cross-selectivity between TC and OTC, has been tested. The reusability of the sensor has also been checked. The present sensor is suitable for commercialization for the detection of tetracycline in food as it has several advantageous features such as low cost, ease of handling, a miniaturized probe, fast response, high selectivity, reusability and the possibility of online monitoring and remote sensing.

Towards Pharmacological Modulation of ETS-Dependent Transcription

Specific inhibition or activation of enzymes and other proteins with small molecules is a widely exploited approach to modulating cellular pathways. Targeting the expression of these proteins at the level of transcription has remained relatively unexplored, however, and may offer significant biotechnological and therapeutic potential. We are interested in pharmacological modulation of genes controlled by members of the ETS family of transcription factors. ETS proteins are widely distributed among metazoan phyla and regulate a functionally diverse array of genes. As a model system, we have characterized the inhibition of sequence-specific binding of the ETS domain of PU.1 (Spi-1) to a natural high-affinity site by distamycin. Using previously established thermodynamic data on this protein-DNA system, we have refined the experimental conditions for surface-plasmon resonance (SPR) overcome mass transfer and other issues that have limited the use of SPR in protein-DNA interactions under physiologically relevant conditions. We found that distamycin potently inhibits PU.1 ETS binding with an IC50 of 2.5 nM under physiologic conditions. Since distamycin binds in the minor groove and ETS domains recognize their consensus motif in the major groove, this is an example of allosteric inhibition of a DNA-binding protein. We are now extending our studies to explore the potential of inhibiting the ptgs2 promoter, a native ETS-dependent promoter sequence, in live cells. We have engineered a reporter system based on a bright but destabilized green fluorescent protein (GFP) with a 2-hour biological half-life. We are characterizing this system in various cell lines that respond to various stimuli by inducing expression of the ptgs2 gene. We expect the combination of SPR and GFP reporter to serve as a useful platform for screening and developing ETS-targeting drug candidates.

Longitudinal Magneto-Optical Kerr Effect in Magneto-Plasmonic Heterostructures

In this paper, the effect of Au nanoparticles and a Bragg reflector mirror on the optical and longitudinal magneto-optical Kerr effect of a new magneto-plasmonic structure has been investigated. The new magneto-plasmonic heterostructure consists of a Bragg reflector mirror beside a crystalline Ce:YIG thin film incorporating gold nanoparticles. Our results indicate sufficient broad band longitudinal magneto-optical Kerr effect enhancement in this new structure using the combination of surface plasmon resonance and Bragg reflector mirror.