Combination Of Surface Plasmon Resonance Research Articles

A Biochemical and Biophysical Analysis of the Interaction of nsp9 with nsp12 from SARS-CoV-2-Implications for Future Drug Discovery Efforts.

The ongoing global pandemic of the coronavirus 2019 (COVID-19) disease is caused by the virus SARS-CoV-2, with very few highly effective antiviral treatments currently available. The machinery responsible for the replication and transcription of viral RNA during infection is made up of several important proteins. Two of these are nsp12, the catalytic subunit of the viral polymerase, and nsp9, a cofactor of nsp12 involved in the capping and priming of viral RNA. While several recent studies have determined the structural details of the interaction of nsp9 with nsp12 in the context of RNA capping, very few biochemical or biophysical details are currently available. In this study, we have used a combination of surface plasmon resonance (SPR) experiments, size exclusion chromatography (SEC) experiments, and biochemical assays to identify specific nsp9 residues that are critical for nsp12 binding as well as RNAylation, both of which are essential for the RNA capping process. Our data indicate that nsp9 dimerization is unlikely to play a significant functional role in the virus. We confirm that a set of recently discovered antiviral peptides inhibit nsp9-nsp12 interaction by specifically binding to nsp9; however, we find that these peptides do not impact RNAylation. In summary, our results have important implications for future drug discovery efforts to combat SARS-CoV-2 and any newly emerging coronaviruses.

Study of cell and drug interactions based on dual-mode detection using SPR and fluorescence imaging

The investigation of the interactions between cells and drugs forms a crucial aspect of biological and clinical medical studies. Generally, single-cell or local-cellular studies require a microscopic imaging system with high magnifications, which suffers from low detection throughputs and poor time responses. The study presented in this paper combined SPR and fluorescence to achieve cell localization, real-time monitoring of cell images and quantitative analysis of drugs. In order to obtain more comprehensive, accurate and real-time data, a dual-mode system based on surface plasmon resonance (SPR) and fluorescence was constructed based on a 4× magnification lens. This enables simultaneous studies of an entire cell and a specific region of the cell membrane. An adaptive adjustment algorithm was established for distorted SPR images, achieving temporal and spatial matching of the dual-mode detection. The combination of SPR and fluorescence not only achieved micro-detection but also complemented the qualitative or quantitative limitations of SPR or fluorescence method alone. In system characterization, the response signal of SPR was noticed to increase with the increasing concentration of EGF in stimulated cells. It indicated that this platform could be employed for quantitative detection of the cell membrane region. Upon addition of EGF, a peak in the SPR curve was observed, and the cells in the corresponding SPR image turned whiter. This indicated that the platform can simultaneously monitor the SPR response signal and image changes. The response time of fluorescence in EGF testing was several seconds earlier than SPR, revealing that signal transduction first occurred in the whole cell and then propagated to the cell membrane region. The inhibitory ability of Gefitinib on cells was verified in a fast and real-time manner within 20 min. The results indicated that the detection limit of this method was 20 IU/mL for EGF and 10 µg/mL for Gefitinib. In conclusion, this study demonstrates the advantages of SPR and fluorescence dual-mode techniques in the analysis of cell-drug interactions, as well as their strong potential in drug screening.

Biosensing empowered by molecular identification: Advances in surface plasmon resonance techniques coupled with mass spectrometry and Raman spectroscopy

Surface plasmon resonance (SPR) has been utilized extensively in bioanalysis since the early 90s due to its unique combination of label-free, highly sensitive, and robust detection. In recent years, SPR has been coupled with and complimented by several other techniques that provide the qualitative and molecular information that SPR lacks. In this paper, advances in studies that present molecular identification to quantitative measurements by SPR are reviewed. In particular, coupling of SPR measurements and MALDI mass spectrometry (MALDI-MS) has been broadly explored where plasmon-assisted ionization upon gold substrates appears to demonstrate many added benefits. Imaging SPR analysis, upon coupling, has contributed to new analytical capability that proves to be powerful with elevated throughput. The combination of SPR and Raman spectroscopy has also found a wide range of applications in providing molecular information that promotes quantitative analysis. Similar to MALDI, the plasmonic thin-film metal substrates provide a desired surface structure and property for Raman enhancement, improving subsequent molecular recognition. Instrumentation advancements and improvements in coupling efficiency has facilitated a series of SPR sensor developments where the plasmonic properties of the surface contribute uniquely to the performance of the coupled technique.

Directional screening and identification of potential cytotoxic components from Achnatherum inebrians by a combination of surface palsmon resonance and chromatography

ObjectiveTo establish a method for directional screening of the cytotoxic components from the medicinal herb of Achnatherum inebrians by a combination of surface plasmon resonance (SPR) biosensor and chromatographic isolation technology. MethodsUnder the guidance of bioactive assessment based on binding abilities between objects and the α-Mannosidase (α-Man) target, the active components from different solvents extracts, different polar extraction parts and fractions were screened orderly and directionally using SPR. Components with a high binding ability to α-Man can be precisely oriented in a narrower fractions range and are easy to isolate. Three human cancer cells were used to evaluate the cytotoxic activity of component with the highest affinity to α-Man. ResultsEight compounds were isolated and identificated from A. inebrians for the first time. Deoxyvasicinone possessed the highest affinity to α-Man among them. Moreover, deoxyvasicinone showed good effects on inhibited proliferation of human hepatoma cells HepG2 (IC50 = 5.7 μmol/L), human breast cancer cells MCF7 (IC50 = 7.21 μmol/L) and human lung cancer cells HCC827 (IC50 = 0.75 μmol/L), respectively. In particular, its inhibitory effect on HCC827 was stronger than the positive drug gefitinib (IC50 = 1.65 μmol/L). ConclusionA comprehensive strategy of directional screening potential cytotoxic components from herb based on biomolecular interaction and chromatography was established. Deoxyvasicinone as an effective anti-cancer component was initially isolated from A. inebrians. It is expected that this screening strategy could provide new perspectives for rapid screening and identification of active components from natural plants with the complex matrix.

Au and Co3O4 anchored Bi2WO6 with enhanced electron paramagnetic resonance, surface plasmon resonance, nonlinear and magnetic properties

AbstractThe combination of surface plasmon resonance (SPR) effect with hetero‐p–n structure shows promising benefits to optical linear and nonlinear properties. In this study, Au nanoparticles (NPs) decorated p–n hetero‐structured Co3O4/Bi2WO6 composite was synthesized and characterized in terms of the optical linear and nonlinear and magnetic properties, morphology, electron transition, charge transfer, energy band gap, polarizability, SPR effect, and oxygen vacancies using scanning electron microscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Z‐scan, ultraviolet–visible spectra, and vibrating sample magnetometer. The combination of Co3O4 provided active 3d electrons transition and charge transfer which increased carriers’ concentration and reduced the energy band gap. Au SPR enhanced the internal polarization and strengthened the built‐in electric field, yielding strong nonlinear behavior. In addition, magnetic Co3O4 endowed sample with room‐temperature ferromagnetism which was obviously strengthened by Au NPs. The obtained sample is promising for laser and photonics applications.

DFT, EPR and SPR insight to the relation between photocatalytic activity and nonlinearity and anisotropy ferromagnetism of Au/Co3O4/Bi2MoO6 composites

The combination of Surface Plasmon Resonance (SPR) effect with hetero-p-n structure has shown promising benefits to photocatalytic activity of catalysts. In this study, Au nanoparticles doped p-n hetero-structured Co3O4/Bi2MoO6 composites were synthesized and subjected to photocatalytic and photocurrent tests using visible light irradiation. The synthesized Au/Co3O4/Bi2MoO6 efficiently removed 97.2% of Methyl orange within 60 min, showing very good photocatalytic stability through leaching test. Colorless pollutant phenol degradation test verified the excellent photocatalytic activity of Au/Co3O4/Bi2MoO6. Possible influential factors such as electron transition, charge transfer, energy band gap, DOS, polarizability, SPR effect, oxygen vacancies and anisotropy permittivity were investigated through DFT, XPS, EPR, Z-scan, UV–visible spectra, ellipsometer spectroscopy and Mott-Schottky analysis. A reasonable degradation mechanism and possible pathway for Methyl orange were proposed based on the experimental results and DFT calculations. The doped Co3O4 provided active 3d electrons transition and charge transfer which increased carriers’ concentration and reduced the energy band gap, while the Au SPR enhanced internal polarization and strengthened the built-in electric field, yielding strong driving force for photo-generated electrons-holes pairs separation and consumption. In addition, magnetic Co3O4 endowed sample with room-temperature ferromagnetism which was obviously strengthened by Au NPs. The magnetism of sample was beneficial for separation and recovery in photocatalytic practical applications.

A Small Ligand That Selectively Binds to the G-quadruplex at the Human Vascular Endothelial Growth Factor Internal Ribosomal Entry Site and Represses the Translation.

G-quadruplexes are believed to have important biological functions, so many small molecules have been screened or developed for targeting G-quadruplexes. However, it is still a major challenge to find molecules that recognize specific G-quadruplexes. Here, by using a combination of surface plasmon resonance, electrospray ionization mass spectrometry, circular dichroism, Western blot, luciferase assay, and reverse transcriptase stop assay, we observed a small molecule, namely, oxymatrine (OMT) that could selectively bind to the RNA G-quadruplex in 5′-untranslated regions (UTRs) of human vascular endothelial growth factor (hVEGF), but could not bind to other G-quadruplexes. OMT could selectively repress the translation of VEGF in cervical cancer cells. Furthermore, it could recognize VEGF RNA G-quadruplexes in special conformations. The results indicate that OMT may serve as a potentially special tool for studying the VEGF RNA G-quadruplex in cells and as a valuable scaffold for the design of ligands that recognize different G-quadruplexes.

High-performance refractive index sensing system based on multiple Fano resonances in polarization-insensitive metasurface with nanorings.

An optical refractive index sensor is a detection device that can convert changes in the refractive index into detectable optical information. The combination of surface plasmon resonance (SPR) and Fano resonance can improve some key indicators, i. e., sensing sensitivity, figure of merit (FOM), band number, and polarization sensitivity, which are all related to the comprehensive performance for high-precision and multi-band sensing. In our manuscript, we proposed a refractive index sensor composed of a nanoring array and a Fabry-Pérot (F-P) resonant cavity. The coupling of the localized surface plasmon resonances (LSPR) of the nanoring array and the cavity mode of the F-P resonant cavity can produce double Fano resonances. The corresponding sensing sensitivities can reach 621.5 nm/RIU and 906.9 nm/RIU, and the corresponding FOMs can reach 119.7 and 119.0. Then we studied the influence of the structure parameters on the sensitivity and FOM of the sensor through simulation calculation and theoretical analysis and verified the insensitivity of the structure to the polarization of incident light. Our structure has high comprehensive performance, not only polarization insensitivity but also high sensing sensitivity and FOM in both bands, which is more suitable for practical applications.

Thin-Film Polyisocyanide-Based Hydrogels for Affinity Biosensors

A new type of hydrogel thin film that can be post-modified with biofunctional molecules is investigated for possible applications in evanescent wave optical affinity biosensors. This material is based on a polyisocyanide (PIC) copolymer that self-assembles into a fibrous polymer network. It is covalently tethered to a solid transducer surface, and its swelling gives rise to a hydrogel layer with a thickness up to several micrometers, as characterized by a combination of surface plasmon resonance and optical waveguide spectroscopy. Thin PIC-based hydrogel films with pendant functional biomolecules can be used in label-free affinity sensing strategies. In this work, we demonstrate the PIC-based affinity binding matrix through an avidin coupling of functional biomolecules and immunoassay-based detection, which can be readily expanded to other types of assays and target analytes. In addition, the stable PIC matrix proves to be resistant to fouling, even in the presence of complex biological fluids such as blood plasma or serum.

Asymmetric flow field-flow fractionation coupled to surface plasmon resonance detection for analysis of therapeutic proteins in blood serum

Coupling of surface plasmon resonance (SPR) detection to asymmetric flow field-flow fractionation (AF4) offers the possibility to study active fractions of bio-separations on real samples, such as serum and saliva, including the assessment of activity of possibly aggregated species. The coupling of SPR with AF4 requires the possibility to select fractions from a fractogram and redirect them to the SPR. The combination of SPR with chromatography-like methods also requires a mechanism for regeneration of the receptor immobilised onto the SPR sensor surface. In recent work, the combination of size exclusion chromatography (SEC) with SPR was pioneered as a successful methodology for identification, characterisation and quantification of active biocomponents in biological samples. In this study, the approach using AF4 is evaluated for the antibody trastuzumab in buffer and serum. The particular object of this study was to test the feasibility of using AF4 in combination with SPR to detect and quantify proteins and aggregates in complex samples such as blood serum. Also, in the investigation, three different immobilisation methods for the receptor HER-2 were compared, which involved (1) direct binding via EDC/NHS, the standard approach; (2) immobilisation via NTA-Ni-Histag complexation; and (3) biotin/avidin-linked chemistry using a regenerable form of avidin. The highest specific activity was obtained for the biotin-avidin method, while the lowest specific activity was observed for the NTA-Ni-Histag linkage. The data show that AF4 can separate trastuzumab monomers and aggregates in blood serum and that SPR has the ability to selectively monitor the elution. This is an encouraging result for automated analysis of complex biological samples using AF4-SPR.

Measurement of Chiral Molecular Parameters Based on a Combination of Surface Plasmon Resonance and Weak Value Amplification.

A novel combination of surface plasmon resonance (SPR) and weak value amplification (WVA) is employed to measure the optical rotation angle and refractive index of chiral enantiomers such as sugars and amino acids. An extremely low optical rotation change (2.73 × 10-4 rad) is readily measurable, with a resolution of 6.75 × 10-7 rad, 1 order of magnitude higher than that obtained using weak value amplification with intensity modulation, and a refractive index change of 1.13 × 10-6 RIU is also detected, with a resolution of 1.99 × 10-9 RIU, a nearly 1-order-of-magnitude increase in sensitivity over weak measurement based on a Mach-Zehnder interferometer. The optical activity and refractive index changes of chiral molecules are determined in real time by measurements of the output light intensity variation, whereby the absolute configuration of the chiral molecule is identified through the relation between intensity and molecular orientation. The SPR-WVA combination sensing scheme fills the gap of capability for detecting the optical activity of a molecular solution, which has not been possible with conventional SPR alone.

Combination of surface plasmon resonance and differential Mueller matrix formalism for noninvasive glucose sensing

A novel technique is proposed for circular birefringence (CB) sensing using a surface plasmon resonance (SPR) prism coupler and differential Mueller matrix polarimetry. In the proposed system, the SPR prism coupler is placed in front of the sample in order to generate a weak-scattering medium model and enhance the sensitivity of the measurement process. The CB properties of the sample are then extracted using a dynamic Stokes-Mueller matrix polarimetry measurement system in the reflectance mode. The practical feasibility of the system is demonstrated by measuring the CB properties of aqueous glucose solutions and glucose phantom solutions containing 2% lipofundin. The oral glucose tolerance tests pilot study was performed on four healthy human volunteers aged between 20 and 25 years old. The experimental results show that the proposed method has a resolution of just 10 mg/dL. In general, the results confirm that the proposed polarimetry-SPR system provides a fastand reliable approach for CB detection and has significant potential for noninvasive glucose monitoring device (NIGMD) applications.

Dietary flavonoid fisetin binds human SUMO1 and blocks sumoylation of p53.

Flavonoids are plant-derived compounds that occur abundantly in fruits and vegetables and have been shown to possess potent anti-cancer, antioxidant, and anti-inflammatory properties. However, their direct targets and molecular mechanism of action are not well characterized, hampering exploitation of the beneficial properties of flavonoids for drug development. Small ubiquitin-related modifier 1 (SUMO1) is attached to target proteins as part of a post-translational modification system implicated in a myriad of cellular processes from nuclear trafficking to transcriptional regulation. Using a combination of surface plasmon resonance, differential scanning fluorimetry and fluorescence quenching studies, we provide evidence for direct binding of the dietary flavonoid fisetin to human SUMO1. Our NMR chemical shift perturbation analyses reveal that binding to fisetin involves four conserved amino acid residues (L65, F66, E67, M82) previously shown to be important for conjugation of SUMO1 to target proteins. In vitro sumoylation experiments indicate that fisetin blocks sumoylation of tumor suppressor p53, consistent with fisetin negatively affecting post-translational modification and thus the biological activity of p53. A series of differential scanning fluorimetry experiments suggest that high concentrations of fisetin result in destabilization and unfolding of SUMO1, presenting a molecular mechanism by which flavonoid binding affects its activity. Overall, our data establish a novel direct interaction between fisetin and SUMO1, providing a mechanistic explanation for the ability of fisetin to modulate multiple key signaling pathways inside cells.

Protein secondary structure detection based on surface plasmon resonance of graphene nanowires

Surface plasmon resonance (SPR) can generate a high intensity electrical field on the metal surface, which is widely used in the field of biosensor technology. The combination of SPR and mid-infrared spectroscopy has unique advantages in protein structure detection and analysis. Protein plays an important role in the identification and analysis of diseases. The change of protein conformation information is also the cause of some major diseases. In this paper, a grating SPR sensor based on graphene is proposed. SPR is excited by mid-infrared light, and a lot of energy is localized at both ends of graphene nanowires. Finite-Difference Time-Domain (FDTD) method is used to simulate the performance of the sensor. The parameters of the sensor are adjusted to satisfy the detection of protein secondary structure in amide I. The conformational information of protein in dry and water environments are calculated respectively. Graphene is used as sensing materials instead of metal. On the one hand, it is to avoid chemical reaction and prolong the life of the sensor. On the other hand, for protein biomolecules, graphene has stronger adsorption and field localization characteristics than metal. This sensor provides a new idea for protein detection.

Epitope Identification and Affinity Determination of an Inhibiting Human Antibody to Interleukin IL8 (CXCL8) by SPR- Biosensor-Mass Spectrometry Combination.

The polypeptide chemokine Interleukin-8 (IL8) plays a crucial role in inflammatory processes in humans. IL8 is involved in chronic inflammatory lung diseases, rheumatoid arthritis, and cancer. Previous studies have shown that the interaction of IL8 with its natural receptors CXCR1 and CXCR2 is critical in these diseases. Antibodies have been used to study the receptor interaction of IL8; however, the binding epitopes were hitherto unknown. Identification of the antibody epitope(s) could lead to a molecular understanding of the inhibiting mechanism and development of improved inhibitors. Here, we report the epitope identification and the affinity characterization of IL8 to a monoclonal anti-human IL8 antibody inhibiting the receptor binding by a combination of surface plasmon resonance (SPR) biosensor analysis and MALDI-mass spectrometry. SPR determination of IL8 with the immobilized antibody revealed high affinity (KD, 82.2 nM). Epitope identification of IL-8 was obtained by proteolytic epitope-extraction mass spectrometry of the peptide fragments upon high pressure trypsin digestion, using an affinity microcolumn with immobilized anti-IL-8 antibody. MALDI-MS of the affinity-bound peptide elution fraction revealed an assembled (discontinuous) epitope comprising two specific peptides, IL8 [12-20] and IL8 [55-60]. Identical epitope peptides were identified by direct MALDI-MS of the eluted epitope fraction from the immobilized anti-IL8 antibody on the SPR chip. SPR determination of the synthetic epitope peptides provided high affinities confirming their binding specificity. The previously reported finding that the anti-Il8 antibody is inhibiting the IL8-CXCR1 interaction is well consistent with the overlapping region of epitope interactions identified in the present study.

Morphological analysis of Apolipoprotein E binding to A\u03b2 Amyloid using a combination of Surface Plasmon Resonance, Immunogold Labeling and Scanning Electron Microscopy

BackgroundImmunogold labeling in combination with transmission electron microscopy analysis is a technique frequently used to correlate high-resolution morphology studies with detailed information regarding localization of specific antigens. Although powerful, the methodology has limitations and it is frequently difficult to acquire a stringent system where unspecific low-affinity interactions are removed prior to analysis.ResultsWe here describe a combinatorial strategy where surface plasmon resonance and immunogold labeling are used followed by a direct analysis of the sensor-chip surface by scanning electron microscopy. Using this approach, we have probed the interaction between amyloid-β fibrils, associated to Alzheimer’s disease, and apolipoprotein E, a well-known ligand frequently found co-deposited to the fibrillar form of Aβ in vivo. The results display a lateral binding of ApoE along the amyloid fibrils and illustrates how the gold-beads represent a good reporter of the binding.ConclusionsThis approach exposes a technique with generic features which enables both a quantitative and a morphological evaluation of a ligand-receptor based system. The methodology mediates an advantage compared to traditional immunogold labeling since all washing steps can be monitored and where a high stringency can be maintained throughout the experiment.

Dually Cross‐Linked Supramolecular Hydrogel as Surface Plasmon Resonance Sensor for Small Molecule Detection

Dually cross-linked supramolecular hydrogels (DCSH) are designed to show responsive properties while maintaining the gel structure by introducing two different kinds of cross-links. This is realized by utilizing a photo-cross-linker for permanent cross-linking and β-cyclodextrin (β-CD) and ferrocene (Fc) as host-guest recognition pair. The DCSH shows increased swelling in the presence of the small target molecule adamantane amine (Ada). Ada can break the non-covalent bonding between β-CD and Fc through competitive molecular guest interaction with β-CD. By using a combination of surface plasmon resonance and optical waveguide spectroscopy, it is possible to use this behavior to construct a reversible sensor for specific small molecule detection.

Probing the Effect of Bulky Lesion-Induced Replication Fork Conformational Heterogeneity Using 4-Aminobiphenyl-Modified DNA.

Bulky organic carcinogens are activated in vivo and subsequently react with nucleobases of cellular DNA to produce adducts. Some of these DNA adducts exist in multiple conformations that are slowly interconverted to one another. Different conformations have been implicated in different mutagenic and repair outcomes. However, studies on the conformation-specific inhibition of replication, which is more relevant to cell survival, are scarce, presumably due to the structural dynamics of DNA lesions at the replication fork. It is difficult to capture the exact nature of replication inhibition by existing end-point assays, which usually detect either the ensemble of consequences of all the conformers or the culmination of all cellular behaviors, such as mutagenicity or survival rate. We previously reported very unusual sequence-dependent conformational heterogeneities involving FABP-modified DNA under different sequence contexts (TG1*G2T [67%B:33%S] and TG1G2*T [100%B], G*, N-(2′-deoxyguanosin-8-yl)-4′-fluoro-4-aminobiphenyl) (Cai et al. Nucleic Acids Research, 46, 6356–6370 (2018)). In the present study, we attempted to correlate the in vitro inhibition of polymerase activity to different conformations from a single FABP-modified DNA lesion. We utilized a combination of surface plasmon resonance (SPR) and HPLC-based steady-state kinetics to reveal the differences in terms of binding affinity and inhibition with polymerase between these two conformers (67%B:33%S and 100%B).

Magneto-plasmonic biosensing platform for detection of glucose concentration

A magneto-optical sensor consisting of [Glass/Au/Co/Au/GS] has been simulated for detection of glucose concentration using a combination of surface plasmon resonance and magneto optical Kerr effect. In this optical sensor, plasmon excitation occurs in the Au thin film and Co plays the role of a magnetic layer. Under optimal conditions of Au and Co thicknesses and incident angle, the magneto-optical transverse Kerr signal is amplified, resulting in an increase in optical sensor sensitivity. In fact, the SPR based sensor evaluates changes in refractive index (RI) of GS. The sensor performance is designed based on two approaches: I) angle shift in the minimum of reflection curve and maximum of transverse Kerr signal in the variable incident angle; II) variation of transverse Kerr signal intensity in a fixed incident angle. Our simulations show that the second approach provides a higher sensitivity, being more applicable due to the performance at a fixed incident angle. This simulated sensor has resolution of 0.003 in the RI value which is equivalent to 0.02 g/ml of glucose concentration. These findings can convey a new pathway to integration of surface plasmon excitation and transverse Kerr effect for sensing applications.

Plasmonic sensor based on tapered optical fibers and magnetic fluids for measuring magnetic fields

We present a new sensor based on the combination of Surface Plasmon Resonance (SPR) with magneto-refractive materials. We use doubly-deposited uniform-waist tapered optical fibers (DLUWTs), that have shown their good performance and versatility as refractometers, and magnetic fluids as transducers to measure magnetic fields in an all-optical-fiber configuration. We experimentally show the feasibility of our approach, by demonstrating the physical principle of the device and characterizing the performance of the sensors, which show very good sensitivity and resolution. In this way, we propose a new field of development for SPR optical fiber sensors to extend the field of application of the plasmonics-based technologies.