Development of a surface plasmon resonance immunosensor and ELISA for 3-nitrotyrosine in human urine

3-Nitrotyrosine (3-NT) is thought to be a relevant biomarker of nitrosative stress which is associated with many inflammatory and chronic diseases. It is necessary to develop confidential method for specific and sensitive 3-NT detection. In this paper, on the basis of anti-3-NT specific antibody, we developed a label-free indirect competitive surface plasmon resonance (SPR) immunosensor and ELISA for the detection of 3-NT. Under the optimized conditions, the SPR immunosensor can obtain a linear range of 0.17-6.07 μg/mL and a limit of detection (LOD) of 0.12 μg/mL while the ELISA can reach 0.33-9.94 μg/mL and a LOD of 0.24 μg/mL.The selectivity of 3-NT was also testified by six kinds of amino acid analogues. Besides, the developed SPR immunosensor was compared thoroughly with a conventional ELISA in spiked analysis of urine samples. Good recoveries and correlation between these two methods were observed (R² = 0.964). Therefore, it is concluded that the automated SPR platform can be applied to quantify 3-NT in biological samples with its sensitivity, accuracy, and real-timing.

Rapid detection of Escherichia coli using fiber optic surface plasmon resonance immunosensor based on biofunctionalized Molybdenum disulfide (MoS2) nanosheets

The molybdenum disulfide (MoS₂) nanosheets functionalized fiber optic surface plasmon resonance (SPR) immunosensor has been reported for the sensitive detection of Escherichia coli (E. coli). The MoS₂ nanosheets were prepared by chemical exfoliation method. The synthesised nanostructures were characterized for their structural, morphological and optical properties. The E. coli monoclonal antibodies were successfully immobilized on the MoS₂ functionalized sensing platform via hydrophobic interactions. An alternative method simplifying the antibodies immobilization process by functionalization of 2D nanomaterial (MoS₂ nanosheets) for rapid (~15 mins) bacterial quantification is presented in this study. The immunosensor uses wavelength interrogation method and a strong linear relationship (R² = 0.994) was observed between spectral response of immunosensor and different concentration of E. coli. The nonspecificity and cross-reactivity studies of the developed immunosensor were investigated with detection of Salmonella Typhimurium and Staphylococcus aureus. To demonstrate the practical application, spiked samples of water and orange juice were analysed with acceptable recovery results. The label-free immunosensor exhibits better performance, detection limit (94 CFU/mL), high sensitivity (2.9 nm/1000 CFU mL^-1; 3135 nm/RIU) and profound specificity as compared to conventional fiber optic SPR sensor (detection limit: 391 CFU/mL, sensitivity: 0.6 nm/1000 CFU mL^-1; 1646 nm/RIU). This sensing platform shows promising applications in regular water and food quality monitoring for various pathogenic microorganisms.

Label-free cell signaling pathway deconvolution of angiotensin type 1 receptor reveals time-resolved G-protein activity and distinct AngII and AngIIIIV responses

Angiotensin II (AngII) type 1 receptor (AT₁R) is a G protein-coupled receptor known for its role in numerous physiological processes and its implication in many vascular diseases. Its functions are mediated through G protein dependent and independent signaling pathways. AT₁R has several endogenous peptidic agonists, all derived from angiotensinogen, as well as several synthetic ligands known to elicit biased signaling responses. Here, surface plasmon resonance (SPR) was used as a cell-based and label-free technique to quantify, in real time, the response of HEK293 cells stably expressing the human AT₁R. The goal was to take advantage of the integrative nature of this assay to identify specific signaling pathways in the features of the response profiles generated by numerous endogenous and synthetic ligands of AT₁R. First, we assessed the contributions of Gq, G12/13, Gi, Gβγ, ERK1/2 and β-arrestins pathways in the cellular responses measured by SPR where Gq, G12/Rho/ROCK together with β-arrestins and ERK1/2 were found to play significant roles. More specifically, we established a major role for G12 in the early events of the AT₁R-dependent response, which was followed by a robust ERK1/2 component associated to the later phase of the signal. Interestingly, endogenous AT₁R ligands (AngII, AngIII and AngIV) exhibited distinct responses signatures with a significant increase of the ERK1/2-like components for both AngIII and AngIV, which points toward possibly distinct physiological roles for the later. We also tested AT₁R biased ligands, all of which affected both the early and later events. Our results support SPR-based integrative cellular assays as a powerful approach to delineate the contribution of specific signaling pathways for a given cell response and reveal response differences associated with ligands with distinct pharmacological properties.

Exploring the biological functional mechanism of the HMGB1/TLR4/MD-2 complex by surface plasmon resonance

BACKGROUND

High Mobility Group Box 1 (HMGB1) was first identified as a nonhistone chromatin-binding protein that functions as a pro-inflammatory cytokine and a Damage-Associated Molecular Pattern molecule when released from necrotic cells or activated leukocytes. HMGB1 consists of two structurally similar HMG boxes that comprise the pro-inflammatory (B-box) and the anti-inflammatory (A-box) domains. Paradoxically, the A-box also contains the epitope for the well-characterized anti-HMGB1 monoclonal antibody "2G7", which also potently inhibits HMGB1-mediated inflammation in a wide variety of in vivo models. The molecular mechanisms through which the A-box domain inhibits the inflammatory activity of HMGB1 and 2G7 exerts anti-inflammatory activity after binding the A-box domain have been a mystery. Recently, we demonstrated that: 1) the TLR4/MD-2 receptor is required for HMGB1-mediated cytokine production and 2) the HMGB1-TLR4/MD-2 interaction is controlled by the redox state of HMGB1 isoforms.

METHODS

We investigated the interactions of HMGB1 isoforms (redox state) or HMGB1 fragments (A- and B-box) with TLR4/MD-2 complex using Surface Plasmon Resonance (SPR) studies.

RESULTS

Our results demonstrate that: 1) intact HMGB1 binds to TLR4 via the A-box domain with high affinity but an appreciable dissociation rate; 2) intact HMGB1 binds to MD-2 via the B-box domain with low affinity but a very slow dissociation rate; and 3) HMGB1 A-box domain alone binds to TLR4 more stably than the intact protein and thereby antagonizes HMGB1 by blocking HMGB1 from interacting with the TLR4/MD-2 complex.

CONCLUSIONS

These findings not only suggest a model whereby HMGB1 interacts with TLR4/MD-2 in a two-stage process but also explain how the A-box domain and 2G7 inhibit HMGB1.

Affinity capture surface carboxyl-functionalized MoS2 sheets to enhance the sensitivity of surface plasmon resonance immunosensors

The development of functionalized molybdenum disulfide (MoS₂) has led to a new trend in the biosensing field, owing to its high sensitivity and bio-affinity characteristics with regards to the simple synthesis of carboxyl-functionalized MoS₂ nanocomposites. In this study, we used monochloroacetic acid (MCA) to successfully modify carboxyl-MoS₂. The efficiency of this MCA modification method showed a higher -COOH group content of 30.1%, mainly due to chlorine atoms occupying the MoS2 sulfur vacancy to allow for the formation of a strong bonding effect. This then enhanced the surface area of -COOH and improved the formation of covalent bonds between proteins. We demonstrated that MoS₂-COOH-based surface plasmon resonance (SPR) chips can provide excellent sensitivity and high affinity for immunoassay biomolecules detected in a low sample volume of 20 μl. With respect to the shifts of the SPR angles of the chips, the high binding affinity at a BSA concentration of 14.5 nM for a MoS₂-COOH chip, a MoS₂ chip and a traditional SPR chip are 4.69 m°, 2.49 m° and 1.53 m°, respectively. In addition, the MoS₂-COOH chip could amplify the SPR angle response by 3.1 folds and enhance the high association rate of ka by 212 folds compared to MoS₂ and traditional SPR chips. The results thus obtained revealed that the overall affinity binding value, K_A, of the MoS₂-COOH chip can be significantly enhanced by up to ∼ 6.5 folds that of the MoS₂ chip. In summary, the excellent binding affinity, biocompatible and high sensitivity suggest the potential of the clinical application of this MoS₂-COOH-based SPR chip detection method for in vitro diagnostic and point-of-care testing devices.

Nanomaterials and phase sensitive based signal enhancment in surface plasmon resonance

Measurement of small molecules in extremely dilute concentrations of analyte play an important role in different issues ranging from food industry to biological, pharmaceutical and therapeutical applications. Surface plasmon resonance (SPR) sensors can be a suitable choice for detection of small molecules based on interactions with biomolecules. However, sensitivity of the system for detection of these molecules is very low. Improving sensitivity has been a challenge for years. Therefore, different methods have been used to enhance SPR signals. The SPR signal enhancement using numerous nanomaterials has provided exciting results. Among various nanomaterials, metal nanoparticles (for instance gold, silver and magnetic nanoparticles), quantum dots, nanorads, and carbon-based nanostructures have got much attention due to ease in fabrication, appropriate size and shape. In addition to the advantages provided by using nanomaterials, signal enhancement provided by the appropriate use of phase information of the reflected light could be also important to improve SPR sensitivity. Phase-sensitive SPR sensors are able to detect infinitesimal changes in external properties of target while traditional type of SPR cannot demonstrate these changes. This article provides an overview on signal enhancment in SPR using nanomaterials and properties of light. We also discuss on recent progresses of the field, describing basic concepts concerning nanostructures as well as phase-sensitive sensors as platform for enhancement of signal in SPR.

A combination of 19F NMR and surface plasmon resonance for site-specific hit selection and validation of fragment molecules that bind to the ATP-binding site of a kinase

¹⁹F NMR has recently emerged as an efficient, sensitive tool for analyzing protein binding to small molecules, and surface plasmon resonance (SPR) is also a popular tool for this purpose. Herein a combination of ¹⁹F NMR and SPR was used to find novel binders to the ATP-binding pocket of MAP kinase extracellular regulated kinase 2 (ERK2) by fragment screening with an original fluorinated-fragment library. The ¹⁹F NMR screening yielded a high primary hit rate of binders to the ERK2 ATP-binding pocket compared with the rate for the SPR screening. Hit compounds were evaluated and categorized according to their ability to bind to different binding sites in the ATP-binding pocket. The binding manner was characterized by using isothermal titration calorimetry and docking simulation. Combining ¹⁹F NMR with other biophysical methods allows the identification of multiple types of hit compounds, thereby increasing opportunities for drug design using preferred fragments.

Label-Free Immuno-Sensors for the Fast Detection of Listeria in Food

Foodborne diseases are a major concern for both food industry and health organizations due to the economic costs and potential threats for human lives. For these reasons, specific regulations impose the research of pathogenic bacteria in food products. Nevertheless, current methods, references and alternatives, take up to several days and require many handling steps. In order to improve pathogen detection in food, we developed an immune-sensor, based on Surface Plasmon Resonance imaging (SPRi) and bacterial growth which allows the detection of a very low number of Listeria monocytogenes in food sample in one day. Adequate sensitivity is achieved by the deposition of several antibodies in a micro-array format allowing real-time detection. This label-free method thus reduces handling and time to result compared with current methods.

Calculation extinction cross sections and molar attenuation coefficient of small gold nanoparticles and experimental observation of their UV-vis spectral properties

Gold nanoparticles (AuNPs) have been researched extensively, such as applied in various biosensors, biomedical imaging and diagnosis, catalysis and physico-chemical analysis. These applications usually required to know the nanoparticle size or concentration. Researchers have been studying a simply and quick way to estimate the concentration or size of nanoparticles from their optical spectra and SPR feature for several years. The extinction cross-sections and the molar attenuation coefficient were one of the key parameters. In this study, we calculated the extinction cross-sections and molar attenuation coefficient (decadic molar extinction coefficient) of small gold nanoparticles by dipole approximation method and modified Beer-Lambert law. The theoretical result showed that the surface plasmon resonance peak of small gold nanoparticles was blueshift with an increase size. Moreover, small AuNPs (sub-10nm) were prepared by using of dextran or trisodium citrate as reducing agent and capping agent. The experimental synthesized AuNPs was also shows a blueshift as increasing particle size in a certain range. And the concentration of AuNPs was calculated based on the obtained molar attenuation coefficient. For small nanoparticles, the size of nanoparticles and surface plasmon resonance property was not showed a positive correlation compared to larger nanoparticles. These results suggested that SPR peak depended not only on the nanoparticle size and shape but also on the nanoparticles environment.

High level expression and immunochemical characterization of botulinum neurotoxin type F light chain

Botulinum neurotoxins (BoNTs) are the most toxic biological substances known. Their potential use as biological warfare agent results in their classification as category A biowarfare agent by Centers for Disease Control and Prevention (CDC), USA. Presently, there are no approved detection system and pharmacological treatments for BoNT intoxication. Although a toxoid vaccine is available for immuno-prophylaxis, vaccines cannot reverse the effect of pre-translocated toxin. Direct handling of the live BoNTs for developing detection and therapeutics may pose fatal danger. This concern was addressed by purifying the recombinant catalytically active light chain of BoNT/F. BoNT/F-LC gene was amplified from the genomic DNA using specifically designed primers and expressed in Escherichia coli. Expression and purification profile were optimized under different conditions for biologically active light chain production. Specific polyclonal antibodies generated against type F illustrates in vivo neutralization in mice and rabbit. These antibodies play key role in conceiving the development of high throughput SPR based detection system which is a highly precise label free technique for protein interaction analysis. The presented work is first of its kind, signifying the production of highly stable and active rBoNT/F-LC and its immunochemical characterization. The study aids in paving the path towards developing a persistent detection system as well as in presenting comprehended scheme for in vitro small molecule therapeutics analysis.

Core-size regulated aggregation/disaggregation of citrate-coated gold nanoparticles (5-50nm) and dissolved organic matter: Extinction, emission, and scattering evidence

Knowledge of the interactions between gold nanoparticles (GNPs) and dissolved organic matter (DOM) is significant in the development of detection devices for environmental sensing, studies of environmental fate and transport, and advances in antifouling water treatment membranes. The specific objective of this research was to spectroscopically investigate the fundamental interactions between citrate-stabilized gold nanoparticles (CT-GNPs) and DOM. Studies indicated that 30 and 50nm diameter GNPs promoted disaggregation of the DOM. This result-disaggregation of an environmentally important polyelectrolyte-will be quite useful regarding antifouling properties in water treatment and water-based sensing applications. Furthermore, resonance Rayleigh scattering results showed significant enhancement in the UV range which can be useful to characterize DOM and can be exploited as an analytical tool to better sense and improve our comprehension of nanomaterial interactions with environmental systems. CT-GNPs having core size diameters of 5, 10, 30, and 50nm were studied in the absence and presence of added DOM at 2 and 8 ppm at low ionic strength and near neutral pH (6.0-6.5) approximating surface water conditions. Interactions were monitored by cross-interpretation among ultraviolet (UV)-visible extinction spectroscopy, excitation-emission matrix (EEM) spectroscopy (emission and Rayleigh scattering), and dynamic light scattering (DLS). This comprehensive combination of spectroscopic analyses lends new insights into the antifouling behavior of GNPs. The CT-GNP-5 and -10 controls emitted light and aggregated. In contrast, the CT-GNP-30 and CT-GNP-50 controls scattered light intensely, but did not aggregate and did not emit light. The presence of any CT-GNP did not affect the extinction spectra of DOM, and the presence of DOM did not affect the extinction spectra of the CT-GNPs. The emission spectra (visible range) differed only slightly between calculated and actual mixtures of CT-GNP-5 or -10 with DOM, whereas emissions for mixtures of CT-GNP-30 or -50 with DOM were enhanced at the surface plasmon resonance (SPR) wavelength. The emission spectra (ultraviolet range) for protein-like constituents of DOM were quenched. Resonance Rayleigh scattering (RRS) was more intense for the CT-GNP-30 and -50 than for the CT-GNP-5 and -10 controls. Intensity-based DLS particle size distributions (PSDs) of DOM controls, CT-GNP-5 and -10nm controls, and 5- and 10nm GNP-DOM mixtures exhibited multimodal aggregation. Analyses of CT-GNP-5 and CT-GNP-10nm mixtures with DOM indicated overcoating of DOM molecules occurred in close proximity (<10nm) to GNPs, whereas similar overcoating was not supported for the CT-GNP-30 or -50 mixtures with DOM. These fundamental observations can be exploited to improve our comprehension of nanomaterial interactions with environmental systems.

Enlarge the biologic coating-induced absorbance enhancement of Au-Ag bimetallic nanoshells by tuning the metal composition

Surface plasmon resonance (SPR) absorption properties of biologic layer-coated Au-Ag core-shell nanoparticle have been studied theoretically. By comparing with pure Au and Ag nanoparticles, the absorption peak intensity of Au-Ag bimetallic nanoparticle is more dependent on the dielectric coating, and the longer wavelength peak corresponding to the Au-Ag interface is more sensitive to the coating thickness. As the Au-Ag composition ratio is increased, the dielectric coating-dependent peak intensity change is always non-monotonous, and the critical Au-Ag composition ratio corresponding to the greatest peak intensity increase could be further tuned by changing the dielectric constant of the coated dielectric layer. The physical mechanism of the non-monotonous sensitivity change has been attributed to the Au-Ag composition ratio-dependent separation and overlap of the two SPR peaks from Au-Ag interface and outer Ag surface. These results indicate that the plasmonic absorption intensity of Au-Ag core-shell nanoparticle could be used in refractive index sensing and biologic detection.

Measuring Antibody-Antigen Binding Kinetics Using Surface Plasmon Resonance

Surface plasmon resonance (SPR) is now widely embraced as a technology for monitoring a diverse range of protein-protein interactions and is considered almost de rigueur for characterizing antibody-antigen interactions. The technique obviates the need to label either of the interacting species, and the binding event is visualized in real time. Thus, it is ideally suited for screening crude, unpurified antibody samples that dominate early candidate panels following antibody selection campaigns. SPR returns not only concentration and affinity data but when used correctly can resolve the discrete component kinetic parameters (association and dissociation rate constants) of the affinity interaction. Herein, we outline some SPR-based generic antibody screening configurations and methodologies in the context of expediting data-rich ranking of candidate antibody panels and ensuring that antibodies with the optimal kinetic binding characteristics are reliably identified.

Direct regulation of IL-2 by curcumin

Interleukin-2 (IL-2) is a crucial growth factor for both regulatory and effector T cells. Thus, IL-2 plays a critical role in the stimulation and suppression of immune responses. Recently, anti-IL-2 antibodies (Abs) have been shown to possess strong IL-2 modulatory activities by affecting the interaction between IL-2 and IL-2 receptors. In this study, we screened an herbal library to identify a compound that regulates IL-2, which resulted in the identification of curcumin as a direct binder and inhibitor of IL-2. Curcumin is a phytochemical with well-known anti-cancer properties. In this study, curcumin mimicked or altered the binding pattern of anti-IL-2 Abs against IL-2 and remarkably inhibited the interaction of recombinant IL-2 with the IL-2 receptor α, CD25. Interestingly, curcumin neutralized the biological activities of IL-2 both in vitro and in vivo. In this report, we elucidated the unsolved mechanism of the anti-cancer effect of curcumin by identifying IL-2 as a direct molecular target. Curcumin, as a small molecule IL-2 modulator, has the potential to be used to treat IL-2 related pathologic conditions.

The role of human monoacylglycerol lipase (hMAGL) binding pocket in breakup of unsaturated phospholipid membranes

Human monoacylglycerol lipase (hMAGL) plays a key role in homeostatic tuning of the endocannabinoid signaling system and supports aggressive tumorogenesis, making this enzyme a promising therapeutic target. hMAGL features a membrane-associated lid domain that regulates entry of endocannabinoid lipid substrates into the hydrophobic channel accessing the active site, likely from the membrane bilayer. The present work applied simultaneous surface plasmon resonance and electrochemical impedance spectroscopy measurements to show that, in absence of the substrate, hMAGL can remove phospholipid molecules from the membrane and, thereby, disintegrate pre-formed, intact, tethered phospholipid bilayer membrane mimetics (tBLMs) composed of unsaturated phosphatidylcholines. To probe the mechanism of hMAGL-induced on tBLMs compromise, we investigated the effect of wild type and mutant hMAGLs and hMAGL rendered catalytically inactive, as a function of concentration and in the presence of chemically distinct active-site inhibitors. Our data show that hMAGL's lid domain and hydrophobic substrate-binding pocket play important roles in hMAGL-induced bilayer lipid mobilization, whereas hydrolytic activity of the enzyme does not appear to be a factor.

Soluble polymorphic bank vole prion proteins induced by co-expression of quiescin sulfhydryl oxidase in E. coli and their aggregation behaviors

Background

The infectious prion protein (PrP^Sc or prion) is derived from its cellular form (PrP^C) through a conformational transition in animal and human prion diseases. Studies have shown that the interspecies conversion of PrP^C to PrP^Sc is largely swayed by species barriers, which is mainly deciphered by the sequence and conformation of the proteins among species. However, the bank vole PrP^C (BVPrP) is highly susceptible to PrP^Sc from different species. Transgenic mice expressing BVPrP with the polymorphic isoleucine (109I) but methionine (109M) at residue 109 spontaneously develop prion disease.

Results

To explore the mechanism underlying the unique susceptibility and convertibility, we generated soluble BVPrP by co-expression of BVPrP with Quiescin sulfhydryl oxidase (QSOX) in Escherichia coli. Interestingly, rBVPrP-109M and rBVPrP-109I exhibited distinct seeded aggregation pathways and aggregate morphologies upon seeding of mouse recombinant PrP fibrils, as monitored by thioflavin T fluorescence and electron microscopy. Moreover, they displayed different aggregation behaviors induced by seeding of hamster and mouse prion strains under real-time quaking-induced conversion.

Conclusions

Our results suggest that QSOX facilitates the formation of soluble prion protein and provide further evidence that the polymorphism at residue 109 of QSOX-induced BVPrP may be a determinant in mediating its distinct convertibility and susceptibility.

Glycan profiling of proteins using lectin binding by Surface Plasmon Resonance

Glycan profiling of proteins was studied through their lectin binding activity by Surface Plasmon Resonance (SPR). To validate the method, we monitored specific lectin binding with sequential removal of sugar moieties from human transferrin using specific glycosidases. The results clearly indicated that glycans on the protein can be identified by their selective binding activity to various lectins. Using this method, we characterized Fc glycosylation profiles of therapeutic peptibodies and antibodies expressed in mammalian cells (CHO and HEK 293 6E cells), with E. coli expressed proteins as the negative controls. We observed that antibodies expressed in CHO cells did not contain any sialic acid, while antibodies expressed in 293 6E cells contained sialic acid. CHO cell expressed antibodies were also more heavily fucosylated than the ones expressed by 293 6E cells. We further applied this method to measure the fucose composition of glycan engineered mouse antibodies, as well as to determine mannose composition of human antibody variants with depletion or enrichment of high mannose. The glycan profiles generated using this method were comparable to results from 2-AB labeled glycan analysis of normal-phase separated glycans, and Fc gamma receptor binding activity of the glycan engineered antibodies were consistent with their glycan profiles. Hence, we demonstrated that SPR lectin binding analysis can be a quick alternative method to profile protein glycosylation.

Antiproliferative factor (APF) binds specifically to sites within the cytoskeleton-associated protein 4 (CKAP4) extracellular domain

Background

Antiproliferative factor (APF) is a sialoglycopeptide elevated in the urine of patients with interstitial cystitis—a chronic, painful bladder disease. APF inhibits the proliferation of normal bladder epithelial cells and cancer cells in vitro, presumably by binding to its cellular receptor, cytoskeleton associated-protein 4 (CKAP4); however, the biophysical interaction of APF with CKAP4 has not been characterized previously. In this study, we used surface plasmon resonance (SPR) to explore the binding kinetics of the interaction of APF and as-APF (a desialylated APF analogue with full activity) to CKAP4.

Results

We immobilized non-glycosylated APF (TVPAAVVVA) to the Fc1 channel as the control and as-APF to Fc2 channel as the ligand in order to measure the binding of CKAP4 recombinant proteins encompassing only the extracellular domain (Aa 127–602) or the extracellular domain plus the transmembrane domain (Aa 106–602). Positive binding was detected to both CKAP4_126–602 and CKAP4_106–602, suggesting that as-APF can bind specifically to CKAP4 and that the potential binding site(s) are located within the extracellular domain. To identify the primary APF binding site(s) within the CKAP4 extracellular domain, deletion mutants were designed according to structural predictions, and the purified recombinant proteins were immobilized on a CM5 chip through amine-coupling to measure as-APF binding activity. Importantly, both CKAP4_127–360 and CKAP4_361–524 exhibited a fast association rate (k_on) and a slow dissociation rate (k_off), thus generating high binding affinity and suggesting that both regions contribute relatively equally to overall as-APF binding. Therefore, two or more as-APF binding sites may exist within the Aa 127–524 region of the CKAP4 extracellular domain.

Conclusions

We determined that the CKAP4_127–360 and CKAP4_361–524 mutants exhibit improved binding activity to as-APF as compared to the full-length extracellular domain, making it possible to detect low concentrations of as-APF in urine, thereby establishing a foundation for a non-invasive diagnostic assay for IC. Further, these data have revealed novel APF binding site(s) suggesting that targeting this region of CKAP4 to inhibit APF binding may be a useful strategy for treating IC-related bladder pathology.

Effect of repeat unit structure and molecular mass of lactic acid bacteria hetero-exopolysaccharides on binding to milk proteins

Interactions of exopolysaccharides and proteins are of great importance in food science, but complicated to analyze and quantify at the molecular level. A surface plasmon resonance procedure was established to characterize binding of seven structure-determined, branched hetero-exopolysaccharides (HePSs) of 0.14-4.9MDa from lactic acid bacteria to different milk proteins (β-casein, κ-casein, native and heat-treated β-lactoglobulin) at pH 4.0-5.0. Maximum binding capacity (RU_max) and apparent affinity (K_A,app) were HePS- and protein-dependent and varied for example 10- and 600-fold, respectively, in the complexation with native β-lactoglobulin at pH 4.0. Highest RU_max and K_A,app were obtained with heat-treated β-lactoglobulin and β-casein, respectively. Overall, RU_max and K_A,app decreased 6- and 20-fold, respectively, with increasing pH from 4.0 to 5.0. K_A,app was influenced by ionic strength and temperature, indicating that polar interactions stabilize HePS-protein complexes. HePS size as well as oligosaccharide repeat structure, conferring chain flexibility and hydrogen bonding potential, influence the K_A,app.

Photochemical formation of chitosan-stabilized near-infrared-absorbing silver Nanoworms: A "Green" synthetic strategy and activity on Gram-negative pathogenic bacteria

A facile, single-step, non-seeded photochemical protocol for producing a new type of anisotropic silver nanostructure, "nanoworms", with curved longer dimensions and smooth, rounded edges. The nanoworms exhibit surface plasmon resonance (SPR) absorption in the near-infrared window (NIRW) region and are stabilized using biocompatible polymer chitosan, rendering biocompatibility and amplified safety for biological utility of the composition. Both NIRW-absorbing nanoworms and visible-absorbing nanospheres herein are attained exclusively by employing green chemistry principles. Contrary to seed-mediated or polyol techniques, the protocol demonstrates the feasibility to selectively synthesize NIRW-absorbing silver nanostructures in a single step and in complete absence of any known reducing agent. The effect of irradiation, pH, and concentration of starting materials on the formation of nanoworms vs nanospheres is investigated in detail and analyzed by optical spectroscopy and electron microscopy. The dominant SPR obtained in the NIRW region of the nanoworms results from anisotropic AgNPs, as opposed to agglomeration. From TEM images, it is also very clear that a strong correlation exists between the SPR peak maximum and the size distribution of the anisotropic nanoworm structures, with SPR peak maximum exhibiting red shift with the increase in the size of the nanoworm population. Although there is significant size variation of different nanoworms of a given population, all samples exhibit remarkable stability. The nanoworms retained their NIRW-absorbing features even at physiological pH and at a constant ionic strength. The nanodispersions also retained their SPR features in King's B medium. Antipathogenic assays reveal that the anisotropic NIRW-absorbing nanoworms exhibit the highest growth inhibition compared to other spherical nanosilver and molecular silver forms on Gram-negative pathogenic bacteria, Pseudomonas syringae pv. maculicola ES4326 and P. syringae pv. tomato DC3000. These results underscore shape effects of AgNPs and suggest that nanoworms favor the adhesion to (curved) rod-shaped Gram-negative bacteria, resulting in the highest inhibition compared to isotropic AgNPs (smaller spheres), sulfa antibiotics (silver sulfadiazine), and silver ions (AgNO₃).

Discovery of selective ATP-competitive eIF4A3 inhibitors

Eukaryotic initiation factor 4A3 (eIF4A3), an ATP-dependent RNA helicase, is a core component of exon junction complex (EJC). EJC has a variety of roles in RNA metabolism such as translation, surveillance, and localization of spliced RNA. It is worthwhile to identify selective eIF4A3 inhibitors with a view to investigating the functions of eIF4A3 and EJC further to clarify the roles of the ATPase and helicase activities in cells. Our chemical optimization of hit compound 2 culminated in the discovery of ATP-competitive eIF4A3 inhibitor 18 with submicromolar ATPase inhibitory activity and excellent selectivity over other helicases. Hence, compound 18 could be a valuable chemical probe to elucidate the detailed functions of eIF4A3 and EJC.

High-sensitive surface plasmon resonance microRNA biosensor based on streptavidin functionalized gold nanorods-assisted signal amplification

Herein, a facile and sensitive microRNA (miRNA) biosensor was designed by using interfacial biotinylated thiolated DNA molecular beacon (MB) as probe and streptavidin functionalized gold nanorods (Stre-GNRs) as tag for the enhanced surface plasmon resonance (SPR) signal. The MB probe with two terminals labeled with biotin and thiol groups, respectively, was modified on the gold film via thiol-gold interaction. Upon hybridization with the target, the biotinylated group became accessible to the Stre-GNRs. The introduction of the Stre-GNRs tag to the gold film produced strong SPR signal for detection. Our work has illustrated that the plasmonic field extension generated from the gold film to GNRs and the mass increase due to the GNRs have led to drastic sensitivity enhancement. Under optimal conditions, this proposed approach allowed detection of miRNA with the limit of detection (LOD) down to 0.045 pM. The results have shown that the MB probe functionalized sensing film, together with streptavidin-conjugated GNRs, was readily served as a plasmonic coupling partner that can be used as a powerful ultrasensitive sandwich assay for miRNA detection, and GNRs were readily served as promising amplification labels in SPR sensing technology.

An interaction domain in human SAMD9 is essential for myxoma virus host-range determinant M062 antagonism of host anti-viral function

In humans, deleterious mutations in the sterile α motif domain protein 9 (SAMD9) gene are associated with cancer, inflammation, weakening of the immune response, and developmental arrest. However, the biological function of SAMD9 and its sequence-structure relationships remain to be characterized. Previously, we found that an essential host range factor, M062 protein from myxoma virus (MYXV), antagonized the function of human SAMD9. In this study, we examine the interaction between M062 and human SAMD9 to identify regions that are critical to SAMD9 function. We also characterize the in vitro kinetics of the interaction. In an infection assay, exogenous expression of SAMD9 N-terminus leads to a potent inhibition of wild-type MYXV infection. We reason that this effect is due to the sequestration of viral M062 by the exogenously expressed N-terminal SAMD9 region. Our studies reveal the first molecular insight into viral M062-dependent mechanisms that suppress human SAMD9-associated antiviral function.

Label-Free Sensing on Microarrays

Microarrays of biological molecules such as DNAs, proteins, carbohydrates, and small molecules provide a high-throughput platform for screening tens of thousands of biomolecular interactions simultaneously, facilitating the functional characterization of these biomolecules in areas of genomics, proteomics, glycomics, and cytomics. Routinely, analysis of binding reactions between solution-phased probes and surface-immobilized targets involves some kinds of fluorescence-based detection methods. Even though these methods have advantages of high sensitivity and wide dynamic range, labeling probes and/or targets inevitably changes their innate properties and in turn affects probe-target interactions in often uncharacterized ways. Therefore, in recent years, various label-free sensing technologies have been developed for characterizing biomolecular interactions in microarray format. These biosensors, to a certain extent, take the place of fluorescent methods by providing a comparable sensitivity as well as retaining the conformational and functional integrality of biomolecules to be investigated. More importantly, some of these biosensors are capable of real-time monitoring probe-target interactions, providing the binding affinities of these reactions. Using label-free biosensors in microarrays has become a current trend in developing high-throughput screening platforms for drug discoveries and applications in all areas of "-omics." This article is aimed to provide principles and recent developments in label-free sensing technologies applicable to microarrays, with special attentions being paid to surface plasmon resonance microscopy and oblique-incidence reflectivity difference microscopy.

Assaying Auxin Receptor Activity Using SPR Assays with F-Box Proteins and Aux/IAA Degrons

The identification of TIR1 as an auxin receptor combined with advanced biophysical instrumentation has led to the development of real-time activity assays for auxins. Traditionally, molecules have been assessed for auxinic activity using bioassays, and agrochemical compound discovery continues to be based on "spray and pray" technologies. Here, we describe the methodology behind an SPR-based assay that uses TIR1 and related F-box proteins with surface plasmon resonance spectrometry for rapid compound screening. In addition, methods for collecting kinetic binding data and data processing are given so that they may support programs for rational design of novel auxin ligands.

Quantification and simultaneous evaluation of the bioactivity of antibody produced in CHO cell culture-The use of the ectodomain of FcγRI and surface plasmon resonance-based biosensor

A surface plasmon resonance (SPR)-based assay has been developed in order to quantify the monoclonal antibody (Mab) Trastuzumab within the supernatant of a mammalian cell culture using the ectodomain of FcγRI (CD64) and confirm Mab bioactivity, i.e. binding to its antigen Her2, in a single biosensing experiment. Under partial mass transport limitation, we were able to quantify Mab present in unpurified samples taken throughout the cell culture. While Mab capture on the biosensor surface confirmed the ability of its Fc region to bind to FcγRI, the binding activity of its Fab region was also tested by injecting increasing concentrations of the Mab antigen (Her2). The kinetics of the interactions we recorded from 48h post transfection until the end of the culture, were superimposable, which highly suggested that the quality attributes of the antibody were conserved throughout the process. This SPR methodology is thus of great interest for atline quality control analysis during Mab production campaign.

Sub-monolayer silver loss from large gold nanospheres detected by surface plasmon resonance in the sigmoidal region

Nanosilver becomes labile upon entering the human body or the environment. This lability creates silver species with antimicrobial properties that make nanosilver attractive as active components in many consumer products, wound dressings, and agricultural applications. Because lability depends strongly on morphology, it is imperative to use a material with constant lability throughout kinetic studies so that accurate lability data can be acquired with efficient detection. Here 2.5nm thick silver was coated onto 90-nm diameter gold nanosphere cores and this surface silver layer was gradually removed by either chemical or X-ray radiation etching. The most sensitive region of a sigmoidal surface plasmon resonance (SPR) response as a function of silver thickness was found for the first time between 0.9- and 1.6-nm thick silver, revealing a new nanosilver standard for lability studies. The SPR peak position detection sensitivity is 8nm (SPR peak shift)/nm (silver thickness change) within this steepest region of the plasmon response curve whereas outside, sensitivity drops to 1nm/nm. Since the centroid of SPR profiles can be discerned with 0.25nm precision, the 8-nm/nm sensitivity means it is possible to detect a 0.3-angstrom or sub-monolayer change in silver thickness. The SPR response simulated by discrete dipole approximation (DDA) was an identical sigmoidal function between 0 and 2nm of silver coating. These findings were supported by several other analytical measurements, which confirmed no silver recoating during these etching processes.

Ca-asp bound X-ray structure and inhibition of Bacillus anthracis dihydroorotase (DHOase)

Dihydroorotase (DHOase) is the third enzyme in the de novo pyrimidine synthesis pathway and is responsible for the reversible cyclization of carbamyl-aspartate (Ca-asp) to dihydroorotate (DHO). DHOase is further divided into two classes based on several structural characteristics, one of which is the length of the flexible catalytic loop that interacts with the substrate, Ca-asp, regulating the enzyme activity. Here, we present the crystal structure of Class I Bacillus anthracis DHOase with Ca-asp in the active site, which shows the peptide backbone of glycine in the shorter loop forming the necessary hydrogen bonds with the substrate, in place of the two threonines found in Class II DHOases. Despite the differences in the catalytic loop, the structure confirms that the key interactions between the substrate and active site residues are similar between Class I and Class II DHOase enzymes, which we further validated by mutagenesis studies. B. anthracis DHOase is also a potential antibacterial drug target. In order to identify prospective inhibitors, we performed high-throughput screening against several libraries using a colorimetric enzymatic assay and an orthogonal fluorescence thermal binding assay. Surface plasmon resonance was used for determining binding affinity (KD) and competition analysis with Ca-asp. Our results highlight that the primary difference between Class I and Class II DHOase is the catalytic loop. We also identify several compounds that can potentially be further optimized as potential B. anthracis inhibitors.

Non-specific binding and steric hindrance thresholds for penetration of particulate drug carriers within tumor tissue

Therapeutic nanoparticles (NPs) approved for clinical use in solid tumor therapy provide only modest improvements in patient survival, in part due to physiological barriers that limit delivery of the particles throughout the entire tumor. Here, we explore the thresholds for NP size and surface poly(ethylene glycol) (PEG) density for penetration within tumor tissue extracellular matrix (ECM). We found that NPs as large as 62nm, but less than 110nm in diameter, diffused rapidly within a tumor ECM preparation (Matrigel) and breast tumor xenograft slices ex vivo. Studies of PEG-density revealed that increasing PEG density enhanced NP diffusion and that PEG density below a critical value led to adhesion of NP to ECM. Non-specific binding of NPs to tumor ECM components was assessed by surface plasmon resonance (SPR), which revealed excellent correlation with the particle diffusion results. Intravital microscopy of NP spread in breast tumor tissue confirmed a significant difference in tumor tissue penetration between the 62 and 110nm PEG-coated NPs, as well as between PEG-coated and uncoated NPs. SPR assays also revealed that Abraxane, an FDA-approved non-PEGylated NP formulation used for cancer therapy, binds to tumor ECM. Our results establish limitations on the size and surface PEG density parameters required to achieve uniform and broad dispersion within tumor tissue and highlight the utility of SPR as a high throughput method to screen NPs for tumor penetration.

Carboxyl-functionalized graphene oxide composites as SPR biosensors with enhanced sensitivity for immunoaffinity detection

This work demonstrates the excellent potential of carboxyl-functionalized graphene oxide (GO-COOH) composites to form biocompatible surfaces on sensing films for use in surface plasmon resonance (SPR)-based immunoaffinity biosensors. Carboxyl-functionalization of graphene carbon can modulate its visible spectrum, and can therefore be used to improve and control the plasmonic coupling mechanism. The binding properties of the molecules between a sensing film and a protein were elucidated at various flow rates of those molecules. The bio-specific binding interaction among the molecules was investigated by performing an antigen and antibody affinity immunoassay. The results thus obtained revealed that the overall affinity binding value, K_A, of the Au/GO-COOH chip can be significantly enhanced by up to ∼5.15 times that of the Au/GO chip. With respect to the shifts of the SPR angles of the chips, the affinity immunoassay interaction at a BSA concentration of 1μg/ml for an Au/GO-COOH chip, an Au/GO chip and a traditional SPR chip are 35.5m°, 9.128m° and 8.816m°, respectively. The enhancement of the antigen-antibody interaction of the Au/GO-COOH chip cause this chip to become four times as sensitive to the SPR angle shift and to have the lowest antibody detection limit of 0.01pg/ml. These results indicate the potential of the chip in detecting specific proteins, and the development of real-time in vivo blood analysis and diagnosis based on cancer tumor markers.

A reliable aptamer array prepared by repeating inkjet-spotting toward on-site measurement

A preparation protocol is proposed for a reliable aptamer array utilizing an ink-jet spotter. We accumulated streptavidin and biotinylated-aptamer in this order on a biotinylated-polyethylene glycol-coated gold substrate to prepare an aptamer array. The aptamer array was prepared with an alternate spotting structure where each aptamer spot was placed between reference spots formed with blocking solution thus suppressing contamination from neighboring spots during the blocking and washing processes. Four aptamer spots were prepared in a small area of 1×4.8mm(2) with five reference spots made of blocking solution. We evaluated the thrombin binding ability of the spotted aptamer array using a multi-analysis surface plasmon resonance sensor. We prepared a disposable capillary-driven flow chip designed for on-site measurement (Miura et al., 2010) with our aptamer array and detected thrombin from phosphate-buffered saline at concentrations of 50ngmL(-1) and 1μgmL(-1) (equivalent to 1.35 and 27nM, respectively). A correlation was observed between the refractive index shift and thrombin concentration. This implies that our array preparation protocol meets the requirement for the preparation of a one-time-use chip for on-site measurement.

Sialylation of vitronectin regulates stress fiber formation and cell spreading of dermal fibroblasts via a heparin-binding site

Vitronectin (VN) plays an important role in tissue regeneration. We previously reported that VN from partial hepatectomized (PH) rats results in a decrease of sialylation of VN and de-sialylation of VN decreases the cell spreading of hepatic stellate cells. In this study, we analyzed the mechanism how sialylation of VN regulates the properties of mouse primary cultured dermal fibroblasts (MDF) and a dermal fibroblast cell line, Swiss 3T3 cells. At first, we confirmed that VN from PH rats or de-sialylated VN also decreased cell spreading in MDF and Swiss 3T3 cells. The de-sialylation suppressed stress fiber formation in Swiss 3T3 cells. Next, we analyzed the effect of the de-sialylation of VN on stress fiber formation in Swiss 3T3 cells. RGD peptide, an inhibitor for a cell binding site of VN, did not affect the cell attachment of Swiss 3T3 cells on untreated VN but significantly decreased it on de-sialylated VN, suggesting that the de-sialylation attenuates the binding activity of an RGD-independent binding site in VN. To analyze a candidate RGD-independent binding site, an inhibition experiment of stress fiber formation for a heparin binding site was performed. The addition of heparin and treatment of cells with heparinase decreased stress fiber formation in Swiss 3T3 cells. Furthermore, de-sialylation increased the binding activity of VN to heparin, as detected by surface plasmon resonance (SPR). These results demonstrate that sialylation of VN glycans regulates stress fiber formation and cell spreading of dermal fibroblast cells via a heparin binding site.

Noble metal-based bimetallic nanoparticles: the effect of the structure on the optical, catalytic and photocatalytic properties

Nanoparticles composed of two different metal elements show novel electronic, optical, catalytic or photocatalytic properties from monometallic nanoparticles. Bimetallic nanoparticles could show not only the combination of the properties related to the presence of two individual metals, but also new properties due to a synergy between two metals. The structure of bimetallic nanoparticles can be oriented in random alloy, alloy with an intermetallic compound, cluster-in-cluster or core-shell structures and is strictly dependent on the relative strengths of metal-metal bond, surface energies of bulk elements, relative atomic sizes, preparation method and conditions, etc. In this review, selected properties, such as structure, optical, catalytic and photocatalytic of noble metals-based bimetallic nanoparticles, are discussed together with preparation routes. The effects of preparation method conditions as well as metal properties on the final structure of bimetallic nanoparticles (from alloy to core-shell structure) are followed. The role of bimetallic nanoparticles in heterogeneous catalysis and photocatalysis are discussed. Furthermore, structure and optical characteristics of bimetallic nanoparticles are described in relation to the some features of monometallic NPs. Such a complex approach allows to systematize knowledge and to identify the future direction of research.

Kinetics and thermodynamics of interaction between sulfonamide antibiotics and humic acids: Surface plasmon resonance and isothermal titration microcalorimetry analysis

The presence of sulfonamide antibiotics in the environments has been recognized as a crucial issue. Their migration and transformation in the environment is determined by natural organic matters that widely exist in natural water and soil. In this study, the kinetics and thermodynamics of interactions between humic acids (HA) and sulfamethazine (SMZ) were investigated by employing surface plasmon resonance (SPR) combined with isothermal titration microcalorimetry (ITC) technologies. Results show that SMZ could be effectively bound with HA. The binding strength could be enhanced by increasing ionic strength and decreasing temperature. High pH was not favorable for the interaction. Hydrogen bond and electrostatic interaction may play important roles in driving the binding process, with auxiliary contribution from hydrophobic interaction. The results implied that HA existed in the environment may have a significant influence on the migration and transformation of organic pollutants through the binding process.

Surface Plasmon Resonance (SPR) Analysis of Binding Interactions of Inner-Ear Proteins

Surface plasmon resonance is an optical technique that is utilized for detecting molecular interactions. Binding of a mobile molecule (analyte) to a molecule immobilized on a thin metal film (ligand) changes the refractive index of the film. The angle of extinction of light that is completely reflected after polarized light impinges upon the film, is altered, and monitored as a change in detector position for a dip in reflected intensity (the surface plasmon resonance phenomenon). Because the method strictly detects mass, there is no need to label the interacting components, thus eliminating possible changes of their molecular properties. We have utilized surface plasmon resonance to study interaction of proteins of inner-ear sensory epithelia.

Surface plasmon resonance as a high throughput method to evaluate specific and non-specific binding of nanotherapeutics

Surface plasmon resonance (SPR) is a powerful analytical technique used to quantitatively examine the interactions between various biomolecules, such as proteins and nucleic acids. The technique has been particularly useful in screening and evaluating binding affinity of novel small molecule and biomolecule-derived therapeutics for various diseases and applications including lupus medications, thrombin inhibitors, HIV protease inhibitors, DNA gyrase inhibitors and many others. Recently, there has been increasing interest in nanotherapeutics (nanoRx), due to their unique properties and potential for controlled release of encapsulated drugs and structure-specific targeting to diseased tissues. NanoRx offer the potential to solve many drug delivery challenges by enabling, specific interactions between molecules on the surface of the nanoparticle and molecules in the diseased tissue, while minimizing off-target interactions toward non-diseased tissues. These properties are largely dependent upon careful control and balance of nanoRx interactions and binding properties with tissues in vivo. Given the great promise of nanoRx with regard to engineering specific molecular interactions, SPR can rapidly quantify small aliquots of nanoRx formulations for desired and undesired molecular interactions. Moving forward, we believe that utilization of SPR in the screening and design of nanoRx has the potential to greatly improve the development of targeted nanoRx formulations and eventually lead to improved therapeutic efficacy. In this review, we discuss (1) the fundamental principles of SPR and basic quantitative analysis of SPR data, (2) previous applications of SPR in the study of non-particulate therapeutics and nanoRx, and (3) future opportunities for the use of SPR in the evaluation of nanoRx.

In Situ Regeneration of Si-based ARROW-B Surface Plasmon Resonance Biosensors

Si-based antiresonant reflecting optical waveguide type B (ARROW-B) surface plasmon resonance (SPR) biosensors allow label-free high-sensitivity detection of biomolecular interactions in real time. The ARROW-B waveguide, which has a thick guiding layer, provides efficient coupling with a single-mode fiber. The Si-based ARROW-B SPR biosensors were fabricated by using the standard semiconductor fabrication processes with a single-step lithography. A fluid flow system was designed to transport samples or analytes. The waveguide consists of propagation and SPR sensing regions. The propagation regions in the front and rear of the SPR sensing region have a symmetric cladding structure to isolate them from environmental changes. A high-index O-ring is used to seal the liquid flow channel. The intensity interrogation method was used to characterize the sensors. The sensitivity of the biosensors was 3.0 × 10³ µW/RIU (refractive index unit) with a resolution of 6.2 × 10⁻⁵ RIU. An in situ regeneration process was designed to make the sensors reusable and eliminate re-alignment of the optical measurement system. The regeneration was realized using ammonia-hydrogen peroxide mixture solutions to remove molecules bound on the sensor surface, such as self-assembled 11-mercapto-1undecanoic acid and bovine serum albumin. SPR was used to monitor the regeneration processes. The experimental results show that the sensing response did not significantly change after the sensor was reused more than 10 times. In situ regenerations of the sensors were achieved.

Detection of 17β-estradiol in water samples by a novel double-layer molecularly imprinted film-based biosensor

This study reports a novel double-layer molecularly imprinted film (MIF)-based biosensor for rapid, sensitive and highly selective detection of small molecule 17β-estradiol (E2) that is frequently detected in environmental water samples. In this system, the modification of gold surface of SPR chip was performed by 1-dodecanethiol. Then double-layer MIF was generated on the 1-dodecanethiol modified gold surface. The non-modified and imprinted surfaces were characterized by atomic force microscopy (AFM), scanning electron microscope (SEM) and contact angle measurements. Analysis of surface plasmon resonance (SPR) spectroscopy showed that the imprinted sensing film displayed good selectivity for E2 compared to other analog molecules and NIF. A good linear relationship was obtained between the SPR angle and E2 concentrations over a range of 2.50×10(-13)-2.50×10(-)(9)mol/L (R(2)=0.993) with the lowest measurable concentration of 2.50×10(-13)mol/L. The sensor can be regenerated with the mixture of acetic acid and PBS buffer (v/v=1:9) as a desorption agent over tens of times without significant deterioration of the sensor performance. Potential interference of real environmental sample matrix was assessed by spiked samples in several waste seawater effluents. This portable sensor system can be successfully applied for on-site real-time inexpensive and easy-to-use monitoring of E2 or other small molecule pollutants in environmental samples such as effluents or water bodies.

Detection of urinary creatinine using gold nanoparticles after solid phase extraction

Label-free gold nanoparticles (AuNPs) were utilized in the detection of creatinine in human urine after a sample preparation by extraction of creatinine on sulfonic acid functionalized silica gel. With the proposed sample preparation method, the interfering effects of the urine matrix on creatinine detection by AuNPs were eliminated. Parameters affecting creatinine extraction were investigated. The aggregation of AuNPs induced by creatinine resulted in a change in the surface plasmon resonance signal with a concomitant color change that could be observed by the naked eye and quantified spectrometrically. The effect of AuNP concentration and reaction time on AuNP aggregation was investigated. The method described herein provides a determination of creatinine in a range of 15-40mgL(-1) with a detection limit of 13.7mgL(-1) and it was successfully used in the detection of creatinine in human urine samples.

Surface Plasmon Resonance Method to Evaluate Anti-citrullinated Protein/Peptide Antibody Affinity to Citrullinated Peptides

Surface plasmon resonance (SPR) technique is extremely interesting in immunology because it has the potential to directly visualize biomolecular interactions in real-time monitoring antibody affinity, one of the parameters affecting pathogenicity in autoimmune diseases. Herein we describe the affinity evaluation of anti-citrullinated peptide antibodies (ACPA) to a peptide-based biosensor by SPR. The method describes the purification of ACPA isolated from rheumatoid arthritis (RA) patients using affinity columns, the strategy employed for the immobilization of citrullinated peptides onto a sensor chip, and the evaluation of the specific binding of purified ACPA to immobilized peptides.

Minimizing the non-specific binding of nanoparticles to the brain enables active targeting of Fn14-positive glioblastoma cells

A major limitation in the treatment of glioblastoma (GBM), the most common and deadly primary brain cancer, is delivery of therapeutics to invading tumor cells outside of the area that is safe for surgical removal. A promising way to target invading GBM cells is via drug-loaded nanoparticles that bind to fibroblast growth factor-inducible 14 (Fn14), thereby potentially improving efficacy and reducing toxicity. However, achieving broad particle distribution and nanoparticle targeting within the brain remains a significant challenge due to the adhesive extracellular matrix (ECM) and clearance mechanisms in the brain. In this work, we developed Fn14 monoclonal antibody-decorated nanoparticles that can efficiently penetrate brain tissue. We show these Fn14-targeted brain tissue penetrating nanoparticles are able to (i) selectively bind to recombinant Fn14 but not brain ECM proteins, (ii) associate with and be internalized by Fn14-positive GBM cells, and (iii) diffuse within brain tissue in a manner similar to non-targeted brain penetrating nanoparticles. In addition, when administered intracranially, Fn14-targeted nanoparticles showed improved tumor cell co-localization in mice bearing human GBM xenografts compared to non-targeted nanoparticles. Minimizing non-specific binding of targeted nanoparticles in the brain may greatly improve the access of particulate delivery systems to remote brain tumor cells and other brain targets.

Graphene oxide-based SPR biosensor chip for immunoassay applications

This work develops a highly sensitive immunoassay sensor for use in graphene oxide sheet (GOS)-based surface plasmon resonance (SPR) chips. This sensing film, which is formed by chemically modifying a GOS surface, has covalent bonds that strongly interact with the bovine serum albumin (BSA), explaining why it has a higher sensitivity. This GOS film-based SPR chip has a BSA concentration detection limit that is 100 times higher than that of the conventional Au-film-based sensor. The affinity constants (K A) on the GOS film-based SPR chip and the conventional SPR chip for 100 μg/ml BSA are 80.82 × 10(6) M(-1) and 15.67 × 10(6) M(-1), respectively. Therefore, the affinity constant of the GOS film-based SPR chip is 5.2 times higher than that of the conventional chip. With respect to the protein-protein interaction, the SPR sensor capability to detect angle changes at a low concentration anti-BSA of 75.75 nM on the GOS film-based SPR chip and the conventional SPR chip is 36.1867 and 26.1759 mdeg, respectively. At a high concentration, anti-BSA of 378.78 nM on the GOS film-based SPR chip and the conventional SPR chip reveals two times increases in the SPR angle shift. Above results demonstrate that the GOS film is promising for highly sensitive clinical diagnostic applications.

Surface plasmon resonance sensor for femtomolar detection of testosterone with water-compatible macroporous molecularly imprinted film

A novel water-compatible macroporous molecularly imprinted film (MIF) has been developed for rapid, sensitive, and label-free detection of small molecule testosterone in urine. The MIF was synthesized by photo copolymerization of monomers (methacrylic acid [MAA] and 2-hydroxyethyl methacrylate [HEMA]), cross-linker (ethylene glycol dimethacrylate, EGDMA), and polystyrene nanoparticles (PS NPs) in combination with template testosterone molecules. The PS NPs and template molecules were subsequently removed to form an MIF with macroporous structures and the specific recognition sites of testosterone. Incubation of artificial urine and human urine on the MIF and the non-imprinted film (NIF), respectively, indicated undetectable nonspecific adsorption. Accordingly, the MIF was applied on a surface plasmon resonance (SPR) sensor for the detection of testosterone in phosphate-buffered saline (PBS) and artificial urine with a limit of detection (LOD) down to 10(-15)g/ml. To the best of our knowledge, the LOD is considered as one of the lowest among the SPR sensors for the detection of small molecules. The control experiments performed with analogue molecules such as progesterone and estradiol demonstrated the good selectivity of this MIF for sensing testosterone. Furthermore, this MIF-based SPR sensor shows high stability and reproducibility over 8months of storage at room temperature, which is more robust than protein-based biosensors.

Interaction of protein phosphatase inhibitors with membrane lipids assessed by surface plasmon resonance based binding technique

The interaction of okadaic acid (OA), tautomycin (TM), microcystin-LR (MC-LR), cantharidin (CA), epigallocatechin-gallate (EGCG) and cyclosporin A (CsA), inhibitors of protein phosphatases, with liposome covered surfaces prepared from the lipid extracts of bovine brain, heart and liver was investigated by surface plasmon resonance (SPR) based binding technique. The SPR sensorgrams indicated reversible association or partial intercalation of the inhibitors with liposomes at 20°C or 37°C, respectively. Distinct lipid composition specificities were reflected in different saturation values of inhibitor binding in a decreasing order of liver>heart>>brain lipids. Assaying the effect of OA, TM, MC-LR, CA and EGCG on the activity of protein phosphatases in neuroblastoma B50, cardiomyoblast H9C2 and hepatocarcinoma HepG2 cells implied that the cell type specific association of phosphatase inhibitors with membrane lipids may influence their inhibitory potencies exerted on intact cells.

Towards the development of a surface plasmon resonance assay to evaluate the glycosylation pattern of monoclonal antibodies using the extracellular domains of CD16a and CD64

We here report the production and purification of the extracellular domains of two Fcγ receptors, namely CD16a and CD64, by transient transfection in mammalian cells. The use of these two receptor ectodomains for the development of quantitative assays aiming at controlling the quality of monoclonal antibody production lots is then discussed. More specifically, the development of surface plasmon resonance-based biosensor assays for the evaluation of the glycosylation pattern and the aggregation state of monoclonal antibodies is presented. Our biosensor approach allows discriminating between antibodies harboring different galactosylation profiles as well as to detect low levels (i.e., less than 2%) of monoclonal antibody aggregates.

The effect of acidic pH on the inhibitory efficacy of peptides against the interaction ICAM-1/LFA-1 studied by surface plasmon resonance (SPR)

Synthetic peptides have been developed for therapeutic applications for decades. The therapeutic efficacy often depends not only on the stabilization of the peptides but also on their binding specificity and affinity to the target molecules to interfere with designated molecular interaction. In this study, the binding affinity of human intercellular adhesion molecule 1 (ICAM-1) chimera and leukocyte function-associated antigen-1 (LFA-1) derived peptides was measured by surface plasmon resonance (SPR) detection, and the results were compared with that of the interaction (of ICAM-1) with the LFA-1 whole protein. To mimic diverse pathological situations in vivo where a low pH has been reported, we studied pH regulated binding affinity of ICAM-1/LFA-1 at pH 7.4, 6.5, and 4.0 without and with magnesium ion. We have found that the binding affinity of LFA-1 whole protein and ICAM-1 increases significantly as the environmental pH decreases, regardless of the absence or the presence of magnesium ion. The affinity of different (LFA-1) derived peptides also depends on the pH, although in all cases the peptides retain its ability to inhibit ICAM-1/LFA-1 interaction. The biomedical relevance of these data has been confirmed using a cell aggregation assay, suggesting that LFA-1 derived peptides show great potential for peptide drug development with a wide functional window of pH range for potential applications in LFA-1 related tumor therapy and autoimmune disease treatment.

Surface plasmon resonance measurements of plasma antibody avidity during primary and secondary responses to anthrax protective antigen

Establishment of humoral immunity against pathogens is dependent on events that occur in the germinal center and the subsequent induction of high-affinity neutralizing antibodies. Quantitative assays that allow monitoring of affinity maturation and duration of antibody responses can provide useful information regarding the efficacy of vaccines and adjuvants. Using an anthrax protective antigen (rPA) and alum model antigen/adjuvant system, we describe a methodology for monitoring antigen-specific serum antibody concentration and avidity by surface plasmon resonance during primary and secondary immune responses. Our analyses showed that following a priming dose in mice, rPA-specific antibody concentration and avidity increases over time and reaches a maximal response in about six weeks, but gradually declines in the absence of antigenic boost. Germinal center reactions were observed early with maximal development achieved during the primary response, which coincided with peak antibody avidity responses to primary immunization. Boosting with antigen resulted in a rapid increase in rPA-specific antibody concentration and five-fold increase in avidity, which was not dependent on sustained GC development. The described methodology couples surface plasmon resonance-based plasma avidity measurements with germinal center analysis and provides a novel way to monitor humoral responses that can play a role in facilitating vaccine and adjuvant development.

Surface plasmon resonance immunoassay for the detection of the TNFα biomarker in human serum

A simple method for the detection of TNF-alpha protein biomarker in human serum with great sensitivity has been developed using a surface plasmon resonance biosensor. Signal amplification based on a sandwich immunoassay including gold nanoparticles was used. Detection in serum proved to be challenging due to high undesirable non-specific binding to the sensor surface stemming from the matrix nature of the sample. After optimization of the assay parameters and, in the case of serum, of a sample dilution buffer to minimize the non-specific binding, very low limits of detection were achieved: 11.6 pg/mL (211 fM) and 54.4 pg/mL (989 fM) for spiked buffer and human serum respectively. The amplification steps with high affinity biotinylated antibodies and streptavidin-fuctionalized nanoparticles greatly enhanced the signal with the advantage of additional specificity. Due to its simplicity and sensitivity, the immunoassay has proved feasible to be used for detection of low concentration biomarkers in real samples.

Flavodoxin cofactor binding induces structural changes that are required for protein-protein interactions with NADP(+) oxidoreductase and pyruvate formate-lyase activating enzyme

Flavodoxin (Fld) conformational changes, thermal stability, and cofactor binding were studied using circular dichroism (CD), isothermal titration calorimetry (ITC), and limited proteolysis. Thermodynamics of apo and holo-Fld folding were examined to discern the features of this important electron transfer protein and to provide data on apo-Fld. With the exception of fluorescence and UV-vis binding experiments with its cofactor flavin mononucleotide (FMN), apo-Fld is almost completely uncharacterized in Escherichia coli. Fld is more structured when the FMN cofactor is bound; the association is tight and driven by enthalpy of binding. Surface plasmon resonance binding experiments were carried out under anaerobic conditions for both apo- and holo-Fld and demonstrate the importance of structure and conformation for the interaction with binding partners. Holo-Fld is capable of associating with NADP(+)-dependent flavodoxin oxidoreductase (FNR) and pyruvate formate-lyase activating enzyme (PFL-AE) whereas there is no detectable interaction between apo-Fld and either protein. Limited proteolysis experiments were analyzed by LC-MS to identify the regions in Fld that are involved in conformation changes upon cofactor binding. Docking software was used to model the Fld/PFL-AE complex to understand the interactions between these two proteins and gain insight into electron transfer reactions from Fld to PFL-AE.

Non-labeled monitoring of targeted liposome interactions with a model receptor surface: effect of flow rate and water content

In this study, we present a novel in vitro approach that utilizes two surface-sensitive and label-free techniques, i.e. surface plasmon resonance (SPR) and quartz crystal microbalance (QCM), to study the interfacial events during liposome-target surface interactions. The flow channels of SPR and QCM devices were first synchronized via hydrodynamic modeling. Biotin-streptavidin was used as a model pair and self-assembled monolayers (SAMs) were utilized as model surfaces for targeted liposome-surface interaction studies. The interactions between biotin-liposomes and the streptavidin-biotin-SAM surfaces were investigated under controlled shear flows using the synchronized SPR and QCM devices. The response of the liposome interaction was monitored as a function of the flow rate. The affinity and the amount of bound liposome indicated that the increased flow rate improved the binding of the targeted liposomes to the model membrane surfaces. The combined use of the synchronized SPR and QCM devices for nanoparticle interaction studies clearly demonstrates the effect of the flow rate (or the shear stress) on the liposome binding. Our results suggest that the binding of liposomes to the model membranes is flow rate and shear stress regulated. Thus, the flow rate (or the shear stress), which is usually neglected, should be taken into account during the development and optimization of targeted liposome formulations. In addition, the water content within the liposome layer (including the water inside the liposomes and the water between the liposomes) had a significant influence on the visco-elasticity and the binding kinetics to the SAM surfaces.