Electrochemical Surface Plasmon Resonance Research Articles

Detection of Adrenaline on Poly(3-aminobenzylamine) Ultrathin Film by Electrochemical-Surface Plasmon Resonance Spectroscopy

In this Article, we present a novel method to detect adrenaline on poly(3-aminobenzylamine) (PABA) ultrathin films by electrochemical-surface plasmon resonance (EC-SPR) spectroscopy. We prepared a PABA film, which specifically reacts with adrenaline, on a gold electrode by electropolymerization of 3-aminobenzylamine. The specific reaction of benzylamine within the PABA structure with adrenaline was studied by XPS, UV-vis spectroscopy, and EC-SPR techniques. Adrenaline was detected in real time by EC-SPR spectroscopy, which provides simultaneous monitoring of both optical SPR reflectivity and electrochemical current responses upon injecting adrenaline into the PABA thin film. The number of changes in both current and SPR reflectivity on the injection of adrenaline exhibited the linear relation to the concentration, and the detection limit was 100 pM. The responses were distinctive to those for uric acid and ascorbic acid, which are major interferences of adrenaline.

Electrochemical Surface Plasmon Resonance and Field‐Enhanced Light Scattering: Monomer Copolymerization with a Polysiloxane‐Conjugated Polythiophene Network Precursor

AbstractThe in situ electrochemical and dielectric film properties of monomer co‐electropolymerization with a CPN precursor was investigated. A polysiloxane/polythiophene precursor was electropolymerized with thiophene monomer at different composition ratios using cyclic voltammetry. This was investigated in situ by EC‐SPR spectroscopy and EC‐SPFELS. The characteristic oscillations corresponded to distinct transitions in film deposition. The resonance coupling of the SPR decreased with higher thiophene monomer content. Increasing the amount of thiophene monomer increased the RMS roughness of the film as observed by AFM, which corresponded to an increase in scattered light intensity with EC‐SPFELS. magnified image

One-chip biosensor for simultaneous disease marker/calibration substance measurement in human urine by electrochemical surface plasmon resonance method

We have developed a miniaturized electrochemical surface plasmon resonance biosensor for measuring two biomolecules that have very different molecular sizes, one is transferrin (MW = 75 kDa) as a disease marker protein, the other is creatinine (MW = 113) as a calibration marker for the accurate measurement of human urinary samples. The sensor has a PDMS based microchannel that is 2 mm wide and 20 μm deep. Two gold films were integrated in the microchannel; one was modified with anti-transferrin antibody for immuno-reaction, and the other was modified with osmium-poly-vinylpyridine wired horseradish peroxidase (Os-gel-HRP). We further immobilized a tri-enzyme layer of creatininase, creatinase and sarcosine oxidase in order to measure creatinine by converting it to hydrogen peroxide in the upstream channel. We measured the transferrin concentration from the refractive index change involved in an immuno-complex formation, and we were simultaneously able to measure creatinine by employing the refractive index change in the Os-gel-HRP caused by oxidation with the hydrogen peroxide produced from creatinine by the tri-enzyme. The effects of ascorbic acid and uric acid in urine samples were sufficiently eliminated by adding ascorbate oxidase and uricase to the urine samples during sampling. We were able to measure two analyte concentrations within 15 min by one simple injection of 50 μL of diluted human urine into our sensor. The detectable transferrin and creatinine ranges were 20 ng/mL to 10 μg/mL, and 10 μM to 10 mM, respectively, which are sufficient levels for clinical tests. Finally, we compared the results obtained using our sensor with those obtained with a conventional immunoassay and the Jaffe method. We obtained a similar trend that can reduce the fluctuation in the urinary transferrin concentration from three different samples by calibrating the creatinine concentration.

Electrochemical surface plasmon resonance and waveguide-enhanced glucose biosensing with N-alkylaminated polypyrrole/glucose oxidase multilayers.

In this work, we report an electrochemical surface plasmon resonance/waveguide (EC-SPR/waveguide) glucose biosensor that could detect enzymatic reactions in a conducting polymer/glucose oxidase (GO(x)) multilayer thin film. In order to achieve a controlled enzyme electrode and waveguide mode, GO(x) (negatively charged) was immobilized with a water-soluble, conducting N-alkylaminated polypyrrole (positively charged) using the layer-by-layer (LbL) electrostatic self-assembly technique. The electrochemical and optical signals were simultaneously obtained from the composite LbL enzyme electrode upon the addition of glucose as mediated by the electroactivity and electrochromic property of the polypyrrole layers. Signal enhancement in EC-SPR detection is obtained by monitoring the doping-dedoping events on the polypyrrole. The real-time optical signal could be distinguished between the change in the dielectric constant of the enzyme layer and other nonenzymatic reaction events such as adsorption of glucose and the change of the refractive index of the solution. This was possible by correlation of both the SPR mode and the m = 0 and 1 modes of the waveguide in an SPR/waveguide spectroscopy experiment.

Immunosensor Incorporating Anti-His (C-term) IgG F(ab’) Fragments Attached to Gold Nanorods for Detection of His-Tagged Proteins in Culture Medium

Immunosensors based on gold electrodes (electrochemical) or gold discs (optical) modified with 1,6-hexanedithiol, gold nanorods and Anti-His (C-term) monoclonal antibody F(ab’) fragment are described. The antigen detected by the sensing platform is a recombinant histidine-tagged silk proteinase inhibitor (rSPI2-His6). Electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) techniques were used as methods for detection of the antigen. This approach allows to detect the antigen protein in concentration of 10 pg per mL (0.13 pM) of culture medium. The immunosensor shows good reproducibility due to covalent immobilization of F(ab’) fragments to gold nanorods layer.

Application of polypyrrole/GOx film to glucose biosensor based on electrochemical-surface plasmon resonance technique

A surface plasmon resonance (SPR) based biosensor for glucose is presented in which a thin gold film modified with polypyrrole and glucose oxidase (PPy-GOx) acts as the sensor chip. It is based on SPR response to the change of refractive index of PPy-GOx film by the enzymatic catalytic reaction. The co-electropolymerization of pyrrole and GOx was carried out under cyclic voltammetric conditions, and simultaneously monitored by in-situ SPR. It has been revealed that the enzymatic reaction between GOx and PPy in the presence of glucose can lead to distinct changes in the SPR signal. From the experiments, a linear relationship was obtained in the range 1–100 μmol L−1 between glucose concentration and the rate of redox transformation of PPy. The detection limit was 0.5 μmol L−1 (S/N = 3) and recoveries were 95.2–102.7%.

Large-Scale Synthesis of Micrometer-Sized Silver Nanosheets

In this paper, we report on a facile and environmentally friendly large-scale synthesis of micrometer-sized silver nanosheets without the introduction of any seeds, polymers, surfactants, or sacrificial substrates. Through the addition of a small quantity of H2PdCl4, AgNO3 can easily be reduced by H2O2 in basic aqueous solution at room temperature and under normal pressure. The edge length of the silver nanosheets obtained may reach lateral dimensions of up to 10−15 μm in size and about 28 nm in thickness. Due to their large surface area, these micrometer-sized silver nanosheets may find potential applications as substrates for surface-enhanced Raman scattering, electrochemical surface plasmon resonance, metal-enhanced fluorescence, and scanning tunneling microscopy.

Electrochemically controlled surface plasmon resonance immunosensor for the detection of human immunoglobulin G on poly(3-aminobenzoic acid) ultrathin films

An electrochemically controlled surface plasmon resonance (SPR) immunosensor based on carboxylated polyaniline was constructed for detecting human immunoglobulin G (IgG) without using further labeled molecules. The carboxylated polyaniline, poly(3-aminobenzoic acid) (PABA), was prepared by electropolymerization of its monomer, 3-aminobenzoic acid (ABA), on a gold-coated high-refractive-index glass slide that was also used as a working electrode for the electrochemical system. The kinetic properties during electropolymerization were monitored in situ with electrochemical-surface plasmon resonance (EC-SPR) spectroscopy. The obtained PABA film, which was used to construct the immunosensor, showed electroactivity in neutral phosphate-buffered saline solution. The carboxylic acid surface of the PABA film was then activated to immobilize anti-human IgG. Finally, the immunosensor electrode was used to probe the binding reaction of anti-human/human IgG with various concentrations of human IgG at different constant applied potentials. The immobilization and binding reaction processes were controlled and also studied in situ by EC-SPR spectroscopy. The binding process at different applied potentials was studied and fitted using the Freundlich model. The surface morphology of the films after the immobilization of anti-human IgG was studied by atomic force microscopy.

Unobstructed electron transfer on porous polyelectrolyte nanostructures and its characterization by electrochemical surface plasmon resonance

Thin organic films with desirable redox properties have long been sought in biosensor research. We report here the development of a polymer thin film interface with well-defined hierarchical nanostructure and electrochemical behavior, and its characterization by electrochemical surface plasmon resonance (ESPR) spectroscopy. The nano-architecture build-up is monitored in real time with SPR, while the redox response is characterized by cyclic voltammetry in the same flow cell. The multilayer assembly is built on a self-assembled monolayer (SAM) of 1:1 (molar ratio) 11-ferrocenyl-1-undecanethiolate (FUT) and mercaptoundecanoic acid (MUA), and constructed using a layer-by-layer deposition of cationic poly(allylamine hydrochloride) (PAH) and anionic poly(sodium 4-styrenesulfonate) (PSS). Electron transfer (ET) on the mixed surface and the effect of the layer structures on ET are systematically studied. Under careful control, multiple layers can be deposited onto the 1:1 FUT/MUA SAM that presents unobstructed redox chemistry, indicating a highly ordered, extensively porous structure obtained under this condition. The use of SPR to trace the minute change during the electrochemical process offers neat characterization of local environment at the interface, in particular double layer region, allowing for better control over the redox functionality of the multilayers. The 1:1 SAM has a surface coverage of 4.1 ± 0.3 × 10 −10 mol cm −2 for ferrocene molecules and demonstrates unperturbed electrochemistry activity even in the presence of a 13 nm polymer film adhered to the electrode surface. This thin layer possesses some desirable properties similar to those on a SAM while presenting ∼15 nm exceedingly porous structure for high loading capacity. The high porosity allows perchlorate to freely partition into the film, leading to high current density that is useful for sensitive electrochemical measurements.

Flow-through Electrochemical Surface Plasmon Resonance: Detection of intermediate reaction products

The electrochemical reaction of hydroquinone–benzoquinone (HQ–BQ) system in acetonitrile was studied by a flow-through Electrochemical Surface Plasmon Resonance (EC-SPR) technique. The semiquinone radical anion (BQ •−) was detected as a large negative SPR shift for the first time by the hyphenated technique. The real time SPR signal shows the entire reaction process of the BQ •− including generation, transformation and disappearance. The lifetime of the BQ •− in the reaction was extracted by comparing the SPR signals along the flow stream. The study demonstrates that the flow-through EC-SPR is a powerful tool for monitoring not only surface bindings, but also solution phase chemical reactions. In addition, it is especially suitable for detecting unstable intermediate reaction products, which are difficult to measure using conventional analytical methods.

Electrochemical Surface Plasmon Resonance: Basic Formalism and Experimental Validation

A quantitative formalism of electrochemical surface plasmon resonance (EC-SPR) was developed for studying electrochemical reactions. The EC-SPR signal from the reactions was found to be a convolution function of electrochemical current, and therefore, EC-SPR is a powerful tool that can provide information similar to the conventional current-based electrochemical techniques. As an example, potential-sweep EC-SPR was analyzed in details and was found to provide a new way to measure convolution voltammetry without the need of numerical integration. In addition to the benefits provided by the conventional convolution voltammetry, the EC-SPR has several unique advantages, including (1) spatial resolution that is particularly attractive for studying heterogeneous reactions, (2) optical properties of the reactions species that may assist identification of reaction mechanisms, and (3) high surface sensitivity for studying surface binding of the reaction species. Experiments and numerical simulations were carried out for a model system, hexaammineruthenium(III) chloride. The simultaneously measured electrochemical current and SPR response confirmed the relationship between the two quantities, and the numerical simulations were in excellent agreement with the measurements.

Ferrocenyl Alkanethiols−Thio β-Cyclodextrin Mixed Self-Assembled Monolayers: Evidence of Ferrocene Electron Shuttling Through the β-Cyclodextrin Cavity

This paper reports the preparation and characterization of an Au electrode modified with self-assembled alkane ferrocenes, in the absence and in the presence of beta-cyclodextrins (betaCD). Electrode modification with ferrocene derivatives was achieved through a self-assembled monolayer (SAM) approach, using ferrocenyl hexane thiol (FcC6) and ferrocenyl undecane thiol (FcC11); the same was also done using per-6-thio-beta-cyclodextrin. The different SAMs prepared were characterized by both cyclic voltammetry and electrochemical surface plasmon resonance (EC-SPR). The behavior of both single and binary monolayers including their interfacial reorganization was investigated and critically discussed, according to the nature of the SAM used. Cyclic voltammetry combined with SPR measurements revealed the reorientation of the SAM concomitant with the oxidation of ferrocene moieties. In particular, the electron shuttling of FcC11 through the betaCD cavity (mixed SAM) was also evidenced by both SPR and the electrocatalytic oxidation of ferro(II)cyanide.

Ultrasensitive detection of mercury (II) ions using electrochemical surface plasmon resonance with magnetohydrodynamic convection

A high-precision technique that can detect mercury (II) ions down to 1 fM concentration in aqueous solutions is introduced. The technique combines the conventional electrochemical method, surface plasmon resonance (SPR), and magnetohydrodynamic (MHD) convection. Mercury ions are electroplated onto a gold SPR sensing surface, and then detected quantitatively by applying a potential scan with cyclic voltammetry. Both the SPR angular shift and the electrochemical current signal are recorded for identification and quantification of the mercury ions. The detection sensitivity is further enhanced by applying an MHD convection in the presence of a magnetic field, which does not require any moving parts intruding into the aqueous solution. The technique thus has a great advantage for small detection volume. In the presence of supporting electrolytes, 1 mM nitric acid and 10 mM potassium nitrate, Hg 2+ ionic solutions with concentrations ranging from 1 fM to 1 μM are tested under different magnetic flux densities of B = 0 , 0.27, 0.53, and 0.71 T. The experimental results demonstrate that the stripping signals of the 1 fM to 1 μM Hg 2+ ions are enhanced by 10–60% with the flux density B = 0.71 T .

Selective electrodissolution of inorganic ions/DNA multilayer film for tunable DNA release

In this contribution we illustrate a simple layer-by-layer assembly strategy to immobilize DNA on the surface of gold thin film and to trigger the selective release of DNA upon the exclusive control of external electric potential. The assembly of DNA-containing multilayer films is driven by coordination/electrostatic interactions between inorganic zirconium ion (Zr4+) and phosphate groups in the backbone of the DNA chain. The selective electrodissolution of the film is might attributable to the migration of ions in the multilayer film and the electrodeposition of ions on the gold surface, as demonstrated by X-Ray photoelectron spectroscopy (XPS) and atomic emission spectroscopy (AES). Further electrochemical surface plasmon resonance (EC-SPR) results demonstrate that the selective electrodissolution profiles of the film are depended on both of the applied potential and the ionic strength of electrolyte. The electrodissolution process can be switched off by removing the external electric potential and reactivated by reapplying the external electric potential under physiological pH condition. By incorporating plasmid DNA (pDNA) in to this system, the multilayer films can sustain the consecutive release of pDNA with its integrity and transcriptional activity retained. Given the non-specific nature of the electrostatic interactions the approach presented herein may, in principle, also be extended from polynucleotides to other negatively charged biomolecules, making this selective electrodissolution appealing model system for biomedical applications where spatiotemporal control of biological material is required.

Electrochemical quartz crystal microbalance study of covalent tethering of carboxylated thiol to polyaniline for electrocatalyzed oxidation of ascorbic acid in neutral aqueous solution

The electrochemical quartz crystal microbalance (EQCM) was used to study the electrosyntheses and electrochemical properties of two kinds of polyaniline (PANI)-thiol composite films in aqueous solutions, which were prepared by covalent binding of a thiol to the oxidized forms of PANI (PANI(post)-thiol, protocol A), and electropolymerization of aniline in the presence of a thiol (PANI(poly)-thiol, protocol B), respectively. The thiols involved were mercaptosuccinic acid (MSA), thioglycolic acid (TGA) and beta-mercaptoethanol (ME). The PANI(post)-thiol binding processes were monitored in situ with the EQCM, giving molar binding ratios (r, thiol vs. aniline unit of the polymer) of ca. 0.50 at saturation for these thiols. Both PANI(post)-thiol and PANI(poly)-thiol composite films from the carboxylated thiols showed a controllable electroactivity of the PANI moiety in neutral even weakly alkaline phosphate buffer solutions (PBS), with maximum electroactivity roughly at r = 0.11 for PANI(post)-MSA or at r = 0.21 for PANI(post)-TGA. The PANI-thiol interaction was also supported by experiments of scanning electron microscopy, electrochemical surface plasmon resonance, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy, and the interaction mechanism is briefly discussed. The PANI(post)-thiol and PANI(poly)-thiol composite films from the carboxylated thiols effectively electrocatalyzed the oxidation of ascorbic acid in pH = 7.3 PBS, and the PANI(post)-thiol exhibited electrocatalytic activity higher than the relevant PANI(poly)-thiol under our experimental conditions. The covalent anchoring of anionic thiol groups on the PANI backbone to prepare electroactive PANI in neutral solutions is conceptually new and may be extended to the development of new functional materials from many other conducting polymers and thiols for wide applications in catalysis, biosensing, molecular electronics, and so on.

Investigation of interfacial processes at tetraruthenated zinc porphyrin films using electrochemical surface plasmon resonance and electrochemical quartz crystal microbalance

In the present work we describe the investigation of interfacial and superficial processes on tetraruthenated zinc porphyrin (ZnTRP) films immobilized on gold electrode surface. In situ and real time measurements employing electrochemical surface plasmon resonance (ESPR) and electrochemical quartz crystal microbalance (EQCM) have given new insights into the electrochemical oxidation of ferrocyanide and phenolic compounds (acetaminophen, dopamine, and catechol) on ZnTRP modified electrodes. The decrease of diode like behavior in the presence of such phenolic species in contrast with ferrocyanide was clearly assigned to the inclusion of those species in the porphyrin film, creating new conduction pathways connecting the gold electrode surface with the film/solution interface. In fact, there are evidences that they can intercalate in the film (catechol > dopamine > acetaminophen), whereas ferrocyanide is completely excluded. Accordingly, the molecular size may play a fundamental role in such a process.

Studies into the interaction of a ferrocene-conjugates of Gly-Gly-Arg-Tyr with papain: AC voltammetry, impedance spectroscopy and surface plasmon resonance studies

The interaction of papain with peptide immobilized on the Au surface altered the interfacial electron transfer resistant, charge transfer resistance ( R CT), by preventing the redox species approaching the electrode was characterized by electrochemical impedance spectroscopy (EIS), AC voltammetry, cyclic voltammetry and surface plasmon resonance techniques (SPR). From cyclic voltammetry a potential shift of 25–30 mV was observed after the addition of papain, with decrease in current and the impedance results showed that R CT increased with increasing concentration of papain indicating the interaction of papain with the immobilized film. This change in kinetics was also observed in SPR. The interaction was further confirmed by reflection-absorption infrared spectroscopy (RAIR).

Electrocatalytic Oxidation Properties of Ascorbic Acid at Poly(3,4-ethylenedioxythiophene) Films Studied by Electrochemical-Surface Plasmon Resonance Spectroscopy

In this report, we demonstrate electrocatalytic oxidation properties of ascorbic acid at poly(3, 4-ethylenedioxythiophene) (PEDOT) thin films in view of their potential application for bio-sensing devices. PEDOT thin films were deposited on gold thin films by electropolymerization of EDOT monomer in acetonitrile solvent. In-situ electrochemical-surface plasmon resonance spectroscopy (EC-SPR) was used to detect both electrochemical and optical signals upon an injection of ascorbic acid.

Comparison of Electrochemical and Surface Plasmon Resonance Immunosensor Responses on Single Thin Film

AbstractThis paper reports results obtained when comparing an electrochemical enzyme immunosensor and a surface plasmon resonance (SPR) based immunosensor on the same gold surface installed in an electrochemical SPR flow cell. Simultaneous electrochemical and SPR measurements were performed on a gold surface modified with multilayers of poly‐L‐lysine and poly‐styrenesulfonate assembled with the layer‐by‐layer method. First, we obtained the SPR response induced by the formation of an immunocomplex from the shift in the SPR angle by injecting an anti tumor necrosis factor‐α antibody solution labeled with alkaline phosphatase into the flow cell containing the multilayer modified with tumor necrosis factor‐α. Then we compared this SPR result with that obtained for the electrochemical oxidation current of p‐aminophenol catalyzed by alkaline phosphatase from p‐aminophenolphosphate on the same gold film. We compared the two immunosensor responses obtained using the different measurement principles and found that there was a high correlation efficient of 0.973 between them. This was because we were able to immobilize the immunoreagents with good stability and without losing the transport of the enzyme product in the multilayer whose thickness we easily controlled with nanometer scale accuracy. We also report that the detection limit of our electrochemical immunosensor after optimization was around 100 pg/mL (0.4 pM), which is one of the lowest values yet reported for an electrochemical immunosensor.

Electrodissolution of Inorganic Ions/DNA Multilayer Film for Tunable DNA Release

A layer-by-layer film composed of DNA and inorganic zirconium ion (Zr(4+)) was fabricated on the surface of gold thin film, and an electric field triggered disintegration of the multilayer film was studied by using electrochemical surface plasmon resonance (EC-SPR). EC-SPR results demonstrated that the film was disassembled upon the application of an electric field and the disassembly rate varied with the applied potential, leading to the controlled release of DNA. The electrodissolution could be switched off by removing the electric potential and reactivated by reapplying the potential. By incorporating plasmid DNA (pDNA) in to this controlled release system, the multilayer film could sustain the consecutive release of pDNA electrochemically. The released pDNA retained its integrity and transfection activity, and expressed enhanced green fluorescent protein (EGFP) after being transfected into HEK 293 cells. The electrochemical systems, with advantages of miniaturization, surface-tailoring, safety, simplicity, convenience, automation, low-cost, and free of immune reactions, made the electrical route a very attractive gene-delivery alternative.