Electrochemical Surface Plasmon Resonance Measurements Research Articles

Quantitative Evaluation of DNA Probe Density by Electrochemical Surface Plasmon Resonance Measurement

Quantitative Evaluation of DNA Probe Density by Electrochemical Surface Plasmon Resonance Measurement

In-situ electrochemical SPR study of gold surface smoothing by repetitive cathodic deposition and anodic dissolution of copper in an ionic liquid

Abstract We performed in-situ analysis of the initial process of copper electrodeposition in an ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (C4mimTFSA), using electrochemical surface plasmon resonance (ESPR), where the SPR resonance angle (Δθ) was recorded simultaneously with cyclic voltammograms (CVs) at the gold interface of C4mimTFSA. Δθ shifted at the potentials where faradaic current appears in the CVs, indicating that SPR probes the redox processes of copper between Cu2+, Cu+, and Cu metal. In stark contrast to the fact that the CVs are not cycle dependent, the amount of the Δθ shift due to the copper electrodeposition decreased with increasing the CV cycle. A model reflectivity analysis using the Bruggeman effective medium approximation predicted that this decrease in Δθ is due to the decrease in the roughness of the gold surface, and it was actually confirmed by ex-situ atomic force microscopy observation. Since the dissolution of gold was found to be negligible from the atomic absorption measurement of IL after the ESPR measurements, the roughness decrease of the gold surface is likely due to the surface diffusion of gold atoms promoted during copper electrodeposition and dissolution processes. It was found that ESPR can track the surface roughness change of the gold electrode in an in-situ manner in the order of A.

Electrochemical surface plasmon resonance measurements of camel-shaped static capacitance and slow dynamics of electric double layer structure at the ionic liquid/electrode interface.

Electrochemical surface plasmon resonance (ESPR) is applied to evaluate the relative static differential capacitance at the interface between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid (IL) and a gold electrode, based on the relationship between the SPR angle and surface charge density on the electrode. Potential-step and potential-scan ESPR measurements are used to probe the dynamics of the electric double layer (EDL) structure that exhibit anomalously slow and asymmetrical characteristics depending on the direction of potential perturbation. EDL dynamics respond at least 30 times more slowly to changes of potential in the positive direction than in the negative direction. ESPR experiments with the positive-going potential scan are significantly affected by the slow dynamics even at a slow scan. The surface charge density that reflects the relative static capacitance is obtained from the negative-going potential scans. The evaluated quasi-static differential capacitance exhibits a camel-shaped potential dependence, thereby agreeing with the prediction of the mean-field lattice gas model of the EDL in ILs. ESPR is shown to be an effective experimental method for determining relative values of the static differential capacitance.

Electrochemical surface plasmon resonance as a probe of redox reactions at the ionic liquid|gold interface

Electrochemical surface plasmon resonance (ESPR) has been employed as a probe of redox reactions at the interface between gold (Au) and ionic liquid (IL). Two redox couples, ferrocene (Fc)/Fc+ and (ferrocenylmethyl)trimethylammonium (FTA+)/FTA2+, and two ILs, trioctylmethylammonium bis(trifluoromethanesulfonyl)amide ([TOMA+][C1C1N−]) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim+][C1C1N−]) have been studied. In the ESPR measurements, the shift of the SPR angle has been recorded simultaneously with cyclic voltammogram (CV). It has been revealed that the SPR angle shift reproduces CV when the former is semi-differentiated or the latter is semi-integrated, and, therefore, that the ESPR response probes the surface concentration of redox couples at the IL|Au interface. Among the four combination of the two redox couples and the two ILs, the case for Fc/Fc+ in [TOMA+][C1C1N−] shows significantly greater ESPR response than the other three cases. A model has been established for the relationship between the SPR angle shift and the surface concentration of redox species. The model predicts that the SPR angle shift becomes pronounced with increasing DR/DO, the diffusion coefficient ratio of the reduced (R) and oxidized (O) species when the reduced species is initially dissolved in the IL as is the case for the present study. Significantly greater DR/DO for Fc/Fc+ in [TOMA+][C1C1N−] than the three other cases has been confirmed from the DR and DO measurements by CV with a microdisk electrode. The trend of the measured DR and DO values agrees with recent findings by researchers that small neutral solutes in ILs composed of large ions diffuse fast beyond the prediction of the Stokes-Einstein relation.

Surface plasmon resonance biomolecular recognition nanosystem: influence of the interfacial electrical potential.

It is shown that the response of a surface plasmon resonance nanosystem designed according to Kretschmann geometry on the application of an external electric potential to the gold-electrolyte interface is well described by the proposed mathematical model, which takes into account the geometric surface imperfection and dependence of optical constants of the surface layer of gold film and capacitance of the electrical double layer on applied voltage. This model allows the appropriate correction for results of electrochemical surface plasmon resonance measurements. The dependence of a value of biomolecules adsorption in a surface plasmon resonance nanosystem on applied electric potential is shown for the first time. It is found that a shift of surface plasmon resonance angular position (Δθ(SPR)) and a change of capacitance of electrical double layer on the surface of gold (ΔC(dl)) for the adsorption of proteins under applied voltage are related to the nonlinear dependence Δθ(SPR) = (a + b x ΔC(dl))(-1). This phenomenon can be exploited in biochemical analysis to monitor the interaction of biomolecules, enhance response of biosensors, block unwanted adsorption, etc.

Ultraslow relaxation of the structure at the ionic liquid|gold electrode interface to a potential step probed by electrochemical surface plasmon resonance measurements: asymmetry of the relaxation time to the potential-step direction

The relaxation of the structure in the electrical double layer at the ionic liquid|gold interface to the steps of the electrode potential has been studied using surface plasmon resonance (SPR) measurements. The relaxation of the SPR resonance angle occurs on the order of 100 s, which is distinctively slower than the RC time constant of the cell, about 0.1 s. A relaxation model considering the distribution of the time constants well reproduces the SPR curves. The potential steps to the positive direction lead to two orders of magnitude slower relaxation of the SPR resonance angle than those to the negative direction. The ultraslow relaxation and its asymmetry to the potential-step directions are likely to be caused by slow inter-layer dynamics of ions in the ionic multilayers and interaction of ions with gold, respectively.

Electrochemical Surface Plasmon Resonance Measurement Based on Gold Nanohole Array Fabricated by Nanoimprinting Technique

In this paper, we describe our development of an electrochemical surface plasmon resonance (EC-SPR) measurement device based on a bottom-filled gold nanohole array. The polymer based gold nanohole array was fabricated with a UV nanoimprint technique and electron beam gold deposition. Direct reflection mode measurement was used to monitor the SPR dip in the reflection spectra. A cyclic voltammogram was also operated by using the standard three electrodes containing working electrode having a gold nanohole array and counter and reference electrodes. The gold nanohole array was modified with an osmium-poly(vinylpyridine)-wired horseradish peroxidase (Os-gel-HRP) film, and its redox state induced by the change in potential was monitored simultaneously. The redox state of the local film was obtained simply by scanning the sample substrate stage. The substrate modified with Os-gel-HRP film was incorporated in a microfluidic chip, and then the hydrogen peroxide was determined in terms of the redox change in the Os complex mediator from the slope of the SPR dip shift. The linear relation of hydrogen peroxide from 10 to 250 μM was successfully monitored, and a high conversion efficiency was realized.

An in situ electrochemical surface plasmon resonance immunosensor with polypyrrole propylic acid film: Comparison between SPR and electrochemical responses from polymer formation to protein immunosensing

A novel in situ electrochemical surface plasmon resonance (EC-SPR) immunosensor is presented in this paper. The EC-SPR measurement can be used to in situ monitor the polymer formation, probe immobilization, antigen–antibody interaction and protein immunosensing process. A sandwich immunosensor based on permeable polypyrrole propylic acid (PPA) film is constructed using mouse IgG as a model analyte. The results show that the introduction of capture antibody conjugated enzyme not only enhances the current responses but also increases the SPR angle shift. The calibration curves of electrochemical (EC) and surface plasmon resonance (SPR) measurement exhibit a similar dependence on the bulk concentration of antigen. An approximate linear relationship can be obtained by plotting the data in semi-logarithmic reference frame. Compared with SPR, EC shows higher sensitivity with prolonged time. The in situ EC-SPR immunosensor described herein could have important potentials for diagnostics and medicine applications.

Electrochemical Surface Plasmon Resonance Measurement in a Microliter Volume Flow Cell for Evaluating the Affinity and Catalytic Activity of Biomolecules

We developed an electrochemical surface plasmon resonance flow cell for the simultaneous measurement of the binding affinity and catalytic activity of bifunctional biomolecules. These measurements will be useful for evaluating the performance of such biomolecules as ribozyme and abzyme. The simultaneous measurements were performed on a gold surface modified with a multilayer consisting of poly-l-lysine and poly(styrene sulfonate) assembled with the layer-by-layer method using an enzyme-labeled monoclonal antibody as a model compound. We obtained the amount of immunocomplex formation from the surface plasmon resonance angle shift value by injecting the compound into the flow cell containing the multilayer modified with tumor necrosis factor-alpha. Then we compared this surface plasmon resonance result with that for the in situ electrochemical oxidation of p-aminophenol formed by the catalytic reaction of labeled enzyme on the same gold film. We were able to obtain a high correlation coefficient of 0.999 between the two responses. This is because the compound could be captured with high stability with a less than 3% coulometric response decrease in the catalyzed product in the multilayer whose thickness was easily controllable. In addition, we were able to measure the catalytic activity by coulometry and thus avoid the effect of peak broadening. We also report that the dephosphorylation activity of a bound compound could be estimated from the measurement results and an equation.

Optical Properties of Ultrathin Poly(3,4-ethylenedioxythiophene) Films at Several Doping Levels Studied by In Situ Electrochemical Surface Plasmon Resonance Spectroscopy

In this paper, we report on in situ optical/electrochemical investigations using a combination of surface plasmon resonance spectroscopy and electrochemistry in order to determine the complex dielectric constants of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. The PEDOT films were deposited by in situ electropolymerization. The film thickness was monitored by a quartz crystal microbalance. In the electrochemical surface plasmon resonance (EC-SPR) measurements, three wavelengths corresponding to interband and intraband electronic transition regions were used in order to investigate electrochromic properties. The optical conductivity was also determined by EC-SPR measurement with a near-infrared laser wavelength which corresponds to the region outside the anomalous dispersion.

A novel biosensor using electrochemical surface plasmon resonance measurements

Surface plasmon resonance measurements have been conducted to construct a unique electrochemical enzyme sensor which detected the reversible change in the refractive index of a redox film containing an enzyme.

Analysis of electrochemical processes using surface plasmon resonance

We simultaneously employed voltammetry and surface plasmon resonance (SPR) measurements and monitored electrochemical processes on gold electrode. SPR is sensitive not only to the adsorbed layer on the gold electrode, but also to the dielectric properties of the solution phase. Therefore, an electrochemically modulated diffusion layer can be detected by SPR. We tested the relationship between the time differential SPR data and the electrode current for two electrochemical processes and confirmed the possibility of using electrochemical SPR measurement.