Fourier Transform Surface Plasmon Resonance Research Articles

Expanding the Scope of an Amphoteric Condensed Tannin, Tanfloc, for Antibacterial Coatings.

Bacterial infections are a common mode of failure for medical implants. This study aims to develop antibacterial polyelectrolyte multilayer (PEM) coatings that contain a plant-derived condensed tannin polymer (Tanfloc, TAN) with inherent antimicrobial activity. Tanfloc is amphoteric, and herein we show that it can be used as either a polyanion or a polycation in PEMs, thereby expanding the possibility of its use in PEM coatings. PEMs are ordinarily formed using a polycation and a polyanion, in which the functional (ionic) groups of the two polymers are complexed to each other. However, using the amphoteric polymer Tanfloc with weakly basic amine and weakly acidic catechol and pyrogallol groups enables PEM formation using only one or the other of its functional groups, leaving the other functional group available to impart antibacterial activity. This work demonstrates Tanfloc-containing PEMs using multiple counter-polyelectrolytes including three polyanionic glycosaminoglycans of varying charge density, and the polycations N,N,N-trimethyl chitosan and polyethyleneimine. The layer-by-layer (LbL) assembly of PEMs was monitored using in situ Fourier-transform surface plasmon resonance (FT-SPR), confirming a stable LbL assembly. X-ray photoelectron spectroscopy (XPS) was used to evaluate surface chemistry, and atomic force microscopy (AFM) was used to determine the surface roughness. The LDH release levels from cells cultured on the Tanfloc-containing PEMs were not statistically different from those on the negative control (p > 0.05), confirming their non-cytotoxicity, while exhibiting remarkable antiadhesive and bactericidal properties against Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus), respectively. The antibacterial effects were attributed to electrostatic interactions and Tanfloc's polyphenolic nature. This work underscores the potential of Tanfloc as a versatile biomaterial for combating infections on surfaces.

Plasmonic-Magnetic Active Nanorheology for Intracellular Viscosity.

We demonstrate active plasmonic systems where plasmonic signals are repeatedly modulated by changing the orientation of nanoprobes under an external magnetic field, which is a prerequisite for in situ active nanorheology in intracellular viscosity measurements. Au/Ni/Au nanorods act as "nanotransmitters", which transmit the mechanical motion of nanorods to an electromagnetic radiation signal as a periodic sine function. This fluctuating optical response is transduced to frequency peaks via Fourier transform surface plasmon resonance (FTSPR). As a driving frequency of the external magnetic field applied to the Au/Ni/Au nanorods increases and reaches above a critical threshold, there is a transition from the synchronous motion of nanorods to asynchronous responses, leading to the disappearance of the FTSPR peak, which allows us to measure the local viscosity of the complex fluids. Using this ensemble-based method with plasmonic functional nanomaterials, we measure the intracellular viscosity of cancer cells and normal cells in a reliable and reproducible manner.

Polycationic condensed tannin/polysaccharide-based polyelectrolyte multilayers prevent microbial adhesion and proliferation

Bacterial adhesion and biofilm formation are significant issues associated with microbial infections in biomedical applications. It has been a challenge to prepare durable coatings with antiadhesive and antimicrobial activities. We show that a condensed tannin derivative (amino-functionalized) can be assembled with polysaccharides (pectin and iota-carrageenan) to create polyelectrolyte multilayers (PEMs). PEMs were prepared from the layer-by-layer approach by assembling polycationic-polyanionic pairs in an acetic acid-acetate buffer (pH 5.0). The tannin-based material (polycationic polymer) was characterized by X-ray photoelectron spectroscopy (XPS), while PEMs were characterized through XPS, in-situ Fourier transform surface plasmon resonance, atomic force microscopy, and water contact angle measurements. Compared to the native glass substrate, all PEMs present nanoscale surface roughness, and hydrophilic surfaces. A stability test performed in PBS for 7 days confirms that 15-layer PEMs are durable in aqueous environments. Initial adhesion and antimicrobial tests against Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) show that the PEMs exhibit antiadhesive and bactericidal activities after 6 h. The antibacterial test in-vitro indicates that PEMs can kill and prevent the attachment and proliferation of bacteria significantly, especially during initial exposure. These PEMs can be applied as coatings to avoid infections imparted by microbial adhesion in biomedical applications.

Tricomponent Multiblock Nanorods for Fourier Transform Surface Plasmon Resonance and Its Chemical Sensing.

In this study, we report a new mode of chemical sensing using Fourier transform surface plasmon resonance with tricomponent nanorods (Au, Ni, and Pt). By applying an external magnetic field, magnetically responsive multiblock nanorods fluctuate periodically, producing sigmoidal optical responses that are represented as a dominant frequency peak after Fourier transform conversion. Adding H2O2 to the solution under an external magnetic field perturbed the periodic nanorod rotation due to a catalytic reaction between the Pt segment and H2O2, which produces catalytic random fluctuation states. The target chemicals were detected by measuring the frequency domain recovery time between two competing states, the magnetic dominant state and the catalytic random state. These two states can be controlled and maximized by nanorod block design, demonstrating the effectiveness of our chemical sensing design using Fourier transform surface plasmon resonance.

Fourier Transform Surface Plasmon Resonance of Nanodisks Embedded in Magnetic Nanorods.

In this study, we demonstrate the synthesis and application of magnetic plasmonic gyro-nanodisks (GNDs) for Fourier transform surface plasmon resonance based biodetection. Plasmonically active and magnetically responsive gyro-nanodisks were synthesized using electrochemical methods with anodized aluminum templates. Due to the unique properties of GNDs (magnetic responsiveness and surface plasmon bands), periodic extinction signals were generated under an external rotating magnetic field, which is, in turn, converted into frequency domains using Fourier transformation. After the binding of a target on GNDs, an increase in the shear force causes a shift in the frequency domain, which allows us to investigate biodetection for HA1 (the influenza virus). Most importantly, by modulating the number and the location of plasmonic nanodisks (a method for controlling the hydrodynamic forces by rationally designing the nanomaterial architecture), we achieved enhanced biodetection sensitivity. We expect that our results will contribute to improved sensing module performance, as well as a better understanding of dynamic nanoparticle systems, by harnessing the perturbed periodic fluctuation of surface plasmon bands under the modulated magnetic field.

Fourier Transform Surface Plasmon Resonance (FTSPR) with Gyromagnetic Plasmonic Nanorods.

An unprecedented active and dynamic sensing platform based on a LSPR configuration that is modulated by using an external magnetic field is reported. Electrochemically synthesized Au/Fe/Au nanorods exhibited plasmonically active behavior through plasmonic coupling, and the middle ferromagnetic Fe block responded to a magnetic impetus, allowing the nanorods to be modulated. The shear force variation induced by the specific binding events between antigens and antibodies on the nanorod surface is used to enhance the sensitivity of detection of antigens in the plasmonics-based sensor application. As a proof-of-concept, influenza A virus (HA1) was used as a target protein. The limit of detection was enhanced by two orders of magnitude compared to that of traditional LSPR sensing.

Multi-block magnetic nanorods for controlled drug release modulated by Fourier transform surface plasmon resonance.

Stimuli-responsive tunable drug release using nanocarriers is an important subject in smart drug delivery systems. Specifically, magnetic-responsive nanocarriers provide a great opportunity for remote control as well as on-demand command. To effectively utilize magnetic-responsive nanocarriers in vivo and in vitro, drug release should not only be controlled in an efficient way, but also monitored in situ. To satisfy those prerequisites, a template-assisted electrochemical deposition method can be a great option for the synthesis of designer materials that are targeted for specific purposes. Here, we synthesized plasmonic-magnetic nanocarriers by template-assisted electrochemical deposition and covered their surface with a silica shell for drug loading. By appropriately designing the blocks, we synthesized nanocarriers that were plasmonically active and magnetically active with spaces for drug payload. These nanocarriers could be modulated under an external magnetic field and their rotation (or agitation) could be monitored by Fourier transform conversion. Using our nanocarriers, we systematically investigated the tunable release of the anticancer drug doxorubicin as a function of the external magnetic field. Additionally, by applying this modulation system to an in vitro system using HeLa cells we were able to not only monitor the modulation systems but also tailor the drug release in a controlled manner. We expect that our approach will contribute to understanding of nanocarriers in a simulative manner in vitro.

Interaction of Thermus thermophilus ArsC enzyme and gold nanoparticles naked-eye assays speciation between As(III) and As(V)

The thermophilic bacterium Thermus thermophilus HB27 encodes chromosomal arsenate reductase (TtArsC), the enzyme responsible for resistance to the harmful effects of arsenic. We report on adsorption of TtArsC onto gold nanoparticles for naked-eye monitoring of biomolecular interaction between the enzyme and arsenic species. Synthesis of hybrid biological–metallic nanoparticles has been characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV–vis), dynamic light scattering (DLS) and phase modulated infrared reflection absorption (PM-IRRAS) spectroscopies. Molecular interactions have been monitored by UV–vis and Fourier transform-surface plasmon resonance (FT-SPR). Due to the nanoparticles’ aggregation on exposure to metal salts, pentavalent and trivalent arsenic solutions can be clearly distinguished by naked-eye assay, even at 85 μM concentration. Moreover, the assay shows partial selectivity against other heavy metals.

Effect of Nitric Oxide on the Interaction Between Mitochondrial Malate Dehydrogenase and Citrate Synthase

Mitochondrial malate dehydrogenase (mMDH) and citrate synthase (CS) are sequential enzymes in Krebs cycle. mMDH, CS and the complex between mMDH and CS (mMDH+CS) were treated with nitric oxide solution. The roles of notric oxide (NO) on the secondary structures and the interactions between mMDH and CS were studied using circular diehroism (CD) and Fourier transform surface plasmon resonance (FT-SPR), respectivley. The effects of NO on the activities of mMDH, CS and mMDH+CS were also studied. And the regulations by NO on mMDH and CS were simulated by PyMOL software. The results of SPR confirmed that strong interaction between mMDH and CS existed and NO could significantly regulate the interaction between the two enzymes. NO reduced the mass percents of α-helix and increased that of random in mMDH, CS and mMDH+CS. NO increased the activities of CS and mMDH+CS, and inhibited the activity of mMDH. Graphic simulation indicated that covalent bond was formed between NO and Asn242 in active site of CS. However, there was no direct bond between NO and mMDH. The increase in activity of mMDH+CS complex depended mostly on the interaction between NO and CS. All the results suggested that the regulations by NO on the activity and interaction between mMDH and CS were accord with the changes in mMDH, CS and mMDH+CS caused by NO.

Determination of Subgroup J Avian Leukosis Virus by Surface Plasmon Resonance Immunosensor

Two novel Fourier transform-surface plasmon resonance immunosensors were fabricated for the determination of the subgroup J avian leukosis virus. The immunosensors were based on a functionalized gold substrate and immobilized gold–silver nanoparticles. For the first immunosensor, the gold substrate was functionalized with a dense self-assembled monolayer of 3-mercaptopropionic acid through gold–sulfur bonds, and then protein A which can combine subgroup J avian leucosis virus antibody on the antigen nonbinding site was modified on the sensor chip surface via covalent bonds formed between the amino groups and the activated carboxyl groups of 3-mercaptopropionic acid. After inactivation by ethanolamine, the sensor chip immobilized the antibody by the combination with protein A to produce a sensor. For the second immunosensor, 1,6- hexanedithiol formed a self-assembled monolayer on the sensor chip surface through gold–sulfur bonds. Then gold–silver nanoparticles were immobilized on the sensor chip by gold–sulfur and silver–sulfur bonds. The modification by various reagents and determination of the subgroup J avian leukosis virus antigen were the same as in the first immunosensor. The immunosensors determined the subgroup J avian leukosis virus antigen to analyte concentrations of 659 TCID 50 ·mL− 1 and 1054 TCID 50 ·mL− 1 , respectively. The result suggested that introducing gold–silver nanoparticles to the Fourier transform-surface plasmon resonance immunosensor is beneficial to effectively improving the sensitivity of the immunosensor. Moreover, the contrast experiment presented that the immunosensors showed high specificity for the subgroup J avian leucosis virus detection.

Analysis of benzoyl-peroxide and formaldehyde as dental allergens by FT-SPR method

In parallel with the appearance of new dental materials the number of induced allergic diseases increases. Based on this fact more sensitive detection of allergens is major importance. The Fourier-Transform Surface Plasmon Resonance (FT-SPR) is a sensitive, broadly applicable real-time method for analysing thin layers of materials on gold surfaces. FT-SPR measurement is performed at a fixed angel of incident light, and reflectivity is measured over a range of wavelength in the near infrared. In our study the formaldehyde and benzoyl-peroxide were examined as members of the most common dental allergens by FT-SPR spectroscopy. The aim of this work was the investigation of the suitability of this method for the direct detection of these materials. Different concentrations of formaldehyde and benzoyl-peroxide solutions were measured from this purpose. The individual spectra were measured for all of the solutions, and calibration curves were calculated for the materials for the possibility of the determination of an unknown concentration. In addition, series measurements were performed whereby the association and dissociation properties of formaldehyde or benzoyl-peroxide were described. The results of the experiments proved that the method capable to measure directly these materials and can provide appropriate calibration curves for determination of unknown concentrations.

Binding of leachable components of polymethyl methacrylate (PMMA) and peptide on modified SPR chip

Many types of polymers are often used in dentistry, which may cause allergic reaction, mainly methyl methacrylate allergy due to the leachable, degradable components of polymerized dental products. The aim of this study was to investigate the interaction between the leachable components of PMMA and peptides by Fourier-transform Surface Plasmon Resonance (FT SPR). In our previous work binding of oligopeptides (Ph.D.-7 and Ph.D.-12 Peptide Library Kit) was investigated to PMMA surface by phage display technique. It was found that oligopeptides bounded specifically to PMMA surface. The most common amino acids were leucine and proline inside the amino acids sequences of DNA of phages. The binding of haptens, as formaldehyde and methacrylic acid, to frequent amino acids was to investigate on the modified gold SPR chip. Self assembled monolayer (SAM) modified the surface of gold chip and ensured the specific binding between the haptens and amino acids. It was found that amino acids bounded to modified SPR gold and the haptens bounded to amino acids by creating multilayer on the chip surface. By the application of phage display and SPR modern bioanalytical methods the interaction between allergens and peptides can be investigated.

Bioconjugated gold nanorods to enhance the sensitivity of FT-SPR-based biosensors

In this paper, we report a feasible solvent-free approach for the synthesis and self-assembling of gold nanorods after bioconjugation to antibodies; scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed a remarkable shape and size narrow distribution, as well as a tendency to form linear assemblies on a clean gold surface, upon interaction with antibodies.These bioconjugated gold nanorods were in turns tested in a model Fourier Transform Surface Plasmon Resonance (FT-SPR)-based immunosensor, leading to an improvement of the detection sensitivity by a factor of 8.The results highlight the simplicity of the synthesis protocol of gold nanorods and the interest of using them as labels to enhance the sensitivity of SPR-based sensors.

Responses of Fourier Transform-Surface Plasmon Resonance Frequency to Refractive Index of the Solution in Contact with the Gold Film

By using the fourier transform-surface plasmon resonance(FT-SPR) technique,the FT-SPR responses(R) toward NaCl,KCl and ethanol with various aqueous concentrations were measured.A quantitative equation of R=1.53×105(n-1.3333) was set up for the response toward the concentration dependent solution refractive index(n).The result shows that the FT-SPR response of 15 cm-1 is obtained upon 0.0001 change in the refractive index.This equation is promising in direct measurement of refractive index of unknown media.

Responses of Fourier Transform-Surface Plasmon Resonance Frequency to Refractive Index of the Solution in Contact with the Gold Film

By using the fourier transform-surface plasmon resonance(FT-SPR) technique,the FT-SPR responses(R) toward NaCl,KCl and ethanol with various aqueous concentrations were measured.A quantitative equation of R=1.53×105(n-1.3333) was set up for the response toward the concentration dependent solution refractive index(n).The result shows that the FT-SPR response of 15 cm-1 is obtained upon 0.0001 change in the refractive index.This equation is promising in direct measurement of refractive index of unknown media.

Layer-by-Layer Assembly of Polysaccharide-Based Polyelectrolyte Multilayers: A Spectroscopic Study of Hydrophilicity, Composition, and Ion Pairing

Polyelectrolyte multilayers using the polycations chitosan and N,N,N-trimethyl chitosan and the polyanions hyaluronan, chondroitin sulfate, and heparin are studied. Chitosan and hyaluronan behave as a weak polycation and weak polyanion, respectively, whereas N,N,N-trimethyl chitosan, chondroitin sulfate, and heparin behave as strong polyelectrolytes. Hydrophilicity is determined by water contact angle measurements and by comparing wet and dry film thickness measurements. Wet thickness is obtained using Fourier transform surface plasmon resonance, whereas dry thickness is obtained through ellipsometry. For the very thin PEMs studied here, the surface hydrophilicity and swelling in water are highly correlated. The multilayer chemistry is assessed by FT-IR and X-ray photoelectron spectroscopy (XPS). FT-IR and XPS provide information about the composition, degree of ionization, and by inference, the ion pairing. We find that hydrophilicity and swelling are reduced when one polyelectrolyte is strong and the other is weak, whereas ion pairing is increased. By this combination of techniques, we are able to compose a unified description of how the PEM swelling is dictated by the ion pairing in thin polysaccharide-based PEMs.

Non-specific and specific interactions on functionalized polymer surface studied by FT-SPR

Fourier transform surface plasmon resonance (FT-SPR) was utilized to study specific and non-specific interactions between proteins and a biotinylated polymer film by monitoring adsorptions of streptavidin (SAv) and bovine serum albumin (BSA) on the polymer films. The biotinylated polymer, poly(lactide-co-2,2-dihydroxymethyl-propylene carbonate-graft-biotin) [P(LA-co-DHC/biotin)], was prepared by ring-opening copolymerization of lactide and a OH-bearing cyclic carbonate monomer, followed by biotinylation of the OH groups. The copolymer was coated onto the FT-SPR chip and vacuum-dried, hydrated at 70°C, and treated with a blocking agent respectively to achieve different surface status. The FT-SPR results showed that the vacuum-dried film had the most BSA adsorption; hydration treatment led to migration of the biotin moieties from inner film to surface and thus resulted in less BSA adsorption; blocking layer on the polymer surface saturated the active sites for physical and chemical adsorptions on the surface and thus weakened the BSA adsorption. Adsorption of SAv displayed similar polymer-surface-status dependence, i.e., more adsorption on vacuum-dried surface, less adsorption on hydrated surface and the least adsorption on blocked surface. Compared with BSA, SAv showed more enhanced adsorptions on P(LA-co-DHC/biotin) surface because of the specific interaction of biotin moieties in the polymer with SAv molecules, especially on the blocked surface. The above semi-quantified results further indicate that the FT-SPR system is suitable for investigating interactions between polymer surface and bio-molecules.

Polysaccharide-Based Polyelectrolyte Multilayer Surface Coatings can Enhance Mesenchymal Stem Cell Response to Adsorbed Growth Factors

It is generally accepted that both surface chemistry and biochemical cues affect mesenchymal stem cell (MSC) proliferation and differentiation. Several growth factors that have strong influences on MSC behavior bind to glycosaminoglycans in interactions that affect their stability and their biochemical activity. The goal of this work was to develop polysaccharide-based polyelectrolyte multilayers (PEMs) to bind and stabilize growth factors for delivery to MSCs. Using the naturally derived polysaccharides chitosan and heparin, PEMs were constructed on gold-coated glass chips, tissue-culture polystyrene (TCPS), and titanium. PEM construction and basic fibroblast growth factor (FGF-2) adsorption to PEMs were evaluated by Fourier transform surface plasmon resonance, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection absorption spectroscopy. The functional response of bone marrow-derived ovine MSCs to FGF-2 on PEM-coated TCPS and titanium was evaluated in vitro, in the presence and absence of adsorbed fibronectin. The effect of FGF-2 dose and presentation on MSC attachment and proliferation was evaluated using low-serum media, over four days. On PEM-coated TCPS, we found that FGF-2 adsorbed to heparin-terminated PEMs with adsorbed fibronectin induces greater cell density and a higher proliferation rate of MSCs than any of the other conditions tested, including delivery of the FGF-2 in solution, at an optimally mitogenic dose. Cell densities on day four were 1.8 times higher when FGF-2 was delivered by adsorption to the PEM than when FGF-2 was delivered in solution. This system represents a promising candidate for the development of surface coatings that can stabilize and potentiate the activity of growth factors for therapeutic applications. Interestingly, the same effects were not observed when FGF-2 was delivered by adsorption to PEMs on titanium. When the polysaccharide-based PEMs were formed on titanium, the proliferative response of ovine MSCs to adsorbed FGF-2 was not as strong as the response to FGF-2 delivered in solution.

Investigation of an Allergen Adsorption on Amine- and Acid-Terminated Thiol Layers: Influence on Their Affinity to Specific Antibodies

This work describes the controlled immobilization of a recognized allergen, beta-lactoglobulin, onto gold transducers with the aim of optimizing the elaboration of a biosensor directed against allergen-produced antibodies. This protein was immobilized on both amine- and acid-terminated thiol self-assembled monolayers, and the influence on its affinity to a specific IgG was investigated. For amine-terminated layers, the beta-lactoglobulin was immobilized via its surface acid functions implying an activation step with 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride/ester of N-hydroxysuccinimide (EDC-NHS). Conversely, the grafting on acid-terminated layer takes advantage of the accessible amine groups that react with the activated acidalkylthiols. The resulting layers of beta-lactoglobulin were then submitted to various concentrations of rabbit serum containing beta-lactoglobulin specific rabbit immunoglobulin (rIgG), and the antigen/antibody affinity was evaluated using modulated polarization-infrared absorption spectroscopy (PM-IRRAS) and Fourier transform surface plasmon resonance (FT-SPR). Even though for similar concentration, the amount of adsorbed beta-lactoglobulin was identical on both surfaces, atomic force microscopy (AFM) images showed a better dispersion for amine-terminated layers. Moreover, the affinity to specific IgG, estimated under static conditions by PM-IRRAS and under dynamic conditions by SPR, was different. Grafting beta-lactoglobulin via its acid groups gave an affinity constant 3 times higher than its immobilization via its amine groups despite the fact that the amount of accessible recognition sites appeared to be similar for both systems. This work underlines the importance of the involved chemical groups upon protein immobilization on their biological activity and will be essential for the construction of nondirect biosensors for detecting specific immunoglobulin E (IgE) of allergens.

Interactions between meniscal cells and a self assembled biomimetic surface composed of hyaluronic acid, chitosan and meniscal extracellular matrix molecules

Menisci are one of the most commonly injured parts of the knee with a limited healing potential. This study focuses on fabrication and characterization of biomimetic surfaces for meniscal tissue engineering. To achieve this, a combination of hyaluronic acid/chitosan (HA/CH) mutilayers with covalently immobilized major extracellular matrix (ECM) components of native meniscus, namely collagen I/II (COL.I/II) and chondroitin-6-sulfate (C6S) was employed. Adsorption of the biomolecules was monitored using a quartz crystal microbalance with dissipation (QCM-D) and fourier transform-surface plasmon resonance (FT-SPR). Immobilization of the biomolecules onto HA/CH mutilayers was achieved by sequential adsorption, with optimum binding at a molar ratio of 1.4:1 (COL.I/II: C6S). After adding COL.I/II, the layers became relatively more rigid and large aggregates were evident. The effects of the modified surfaces on cell proliferation, gene expression and proteoglycan production of rat meniscal cells were examined. Quantitative real-time reverse transcriptase polymerase chain reaction (RT-qPCR) analysis showed that primary meniscal cells dedifferentiated rapidly after one passage in monolayer culture. This process could be reversed by culturing the cells on C6S surfaces, as indicated by increases in both collagen II and aggrecan gene expression, as well as proteoglycan production. Cells with abundant lipid vacuoles were evident on all the surfaces over an extended culture period. The results demonstrate the feasibility of C6S surfaces to avoid the dedifferentiation that normally occurs during monolayer expansion of meniscal cells.