Electrochemical Surface Plasmon Resonance Research Articles

Detection methods for antibiotics in wastewater: a review.

Antibiotics are widely used as fungicides because of their antibacterial and bactericidal effects. However, it is necessary to control their dosage. If the amount of antbiotics is too much, it cannot be completely metabolized and absorbed, will pollute the environment, and have a great impact on human health. Many antibiotics usually left in factory or aquaculture wastewater pollute the environment, so it is vital to detect the content of antibiotics in wastewater. This article summarizes several common methods of antibiotic detection and pretreatment steps. The detection methods of antibiotics in wastewater mainly include immunoassay, instrumental analysis method, and sensor. Studies have shown that immunoassay can detect deficient concentrations of antibiotics, but it is affected by external factors leading to errors. The detection speed of the instrumental analysis method is fast, but the repeatability is poor, the price is high, and the operation is complicated. The sensor is a method that is currently increasingly studied, including electrochemical sensors, optical sensors, biosensors, photoelectrochemical sensors, and surface plasmon resonance sensors. It has the advantages of fast detection speed, high accuracy, and strong sensitivity. However, the reproducibility and stability of the sensor are poor. At present, there is no method that can comprehensively integrate the advantages. This paper aims to review the enrichment and detection methods of antibiotics in wastewater from 2020 to the present. It also aims to provide some ideas for future research directions in this field.

Surface plasmon resonance (EC-SPR) sensor based on molecularly imprinted strategy for the determination of stimulant modafinil in saliva samples

A highly sensitive and selective molecularly imprinted polymer-based electrochemical-surface plasmon resonance (MIP-based EC-SPR) sensor was developed for the determination of modafinil in saliva samples. The optimal MIPpy film was synthesized using a modafinil concentration of 1 mM and a constant potential electropolymerization method. The fabricated sensor exhibited a wide linear range (0.1 μM to 10 μM), low detection limits (LOD: 50 nM, LOQ: 170 nM), and high selectivity towards modafinil, with selectivity coefficients of 8.5, 6.2, and 12.7 for adrafinil, armodafinil, and caffeine, respectively. The sensor also demonstrated excellent reproducibility (RSD: 4.2 %) and long-term stability (92 % response after one month). Furthermore, the applicability of the sensor in real samples was validated using spiked saliva samples, with recovery values ranging from 94.7 % to 103.5 %. These results highlight the potential of the MIP-based EC-SPR sensor as a powerful tool for the rapid, sensitive, and selective detection of modafinil in complex biological matrices.

In situ monitoring of thin alumina passive film growth by surface plasmon resonance (SPR) during an electrochemical process

This article presents a sensing technique to characterize the growth of an alumina passive film on an aluminum micro structured layer in situ. The technique uses surface plasmon resonance (SPR) on aluminum coated gratings with spectroscopic measurements during electrochemical polarization in 0.02M Na2SO4. The structure of the sensor was first simulated and then fabricated by photolithography. The grating was then replicated by nanoimprint (NIL) in Sol–Gel before pure aluminum layer was deposited by RF magnetron sputtering to produce the samples used in this study. Coupled plasmonic and electrochemical measurements confirmed the feasibility of in situ characterization (thickness) of alumina passive film on aluminum-based gratings in neutral aqueous media. Combining both measurements with an appropriated SPR spectrum fitting lead to alumina thickness monitoring within a few nanometers’ accuracy. The objectives and challenges of this study are to better characterize the alumina growth during electrochemical process combining in situ electrochemical process and SPR spectra in order to determine thin passive layer characteristics.

Reagent-Free Lactate Detection Using Prussian Blue and Electropolymerized-Molecularly Imprinted Polymers-Based Electrochemical Biosensors.

Sweat lactate, a promising biomarker for assessing physical performance and health conditions, calls for noninvasive, convenient, and affordable detection methods. This study leverages molecularly imprinted polymers (MIPs) as a synthetic biorecognition element for lactate detection due to their affordability and high stability. Traditional MIPs-based electrochemical sensors often require external redox probes such as ferricyanide/ferrocyanide in the solution to signal the binding between analytes and MIPs, which restricts their applicability. To address this, our study introduces an innovative approach utilizing a layer of Prussian blue (PB) nanoparticles as the internal redox probe on screen-printed carbon electrodes (SPCE), followed by a layer of electropolymerized MIP (eMIP) for molecular recognition, enabling reagent-free lactate detection. The real-time growth of eMIP and the processes of template elution and lactate rebinding were examined and validated using electrochemical surface plasmon resonance (EC-SPR) spectroscopy. The sensor's performance was thoroughly investigated using Differential Pulsed Voltammetry (DPV) and Electrochemical Impedance Spectroscopy (EIS) with samples spiked in 0.1 M KCl solution and artificial sweat. The developed sensors demonstrated a fast and selective response to lactate, detecting concentrations from 1 to 35 mM with a Limit of Detection (LOD) of 0.20 mM, defined by a signal-to-noise ratio of 3 in the DPV measurements. They also exhibited excellent reproducibility, reusability, and a shelf life of up to 10 months under ambient conditions. These eMIP/PB/SPCE-based lactate sensors show considerable potential as point-of-care (POC) devices for sweat lactate detection, and the technology could be adapted for reagent-free detection of a broad spectrum of molecules.

A Guide for the Electrochemical Stability of Thiolate Self-Assembled Monolayers on Gold in Various Electrolytes

Self-assembled monolayers (SAMs) are widely used in surface chemistry to modify surfaces for various applications such as biosensing1, electronics2, and electrocatalysis3. SAMs are attractive due to their high surface coverage and stability. Although studies have been conducted to test the effects of temperature, air exposure, and solvent degradation on SAMs stability 4,5, the electrochemical stability of SAMs has not been as extensively studied. Existing literature on this topic mainly focuses on the reductive desorption limits of thiolate SAMs in alkaline conditions6,7. Recent work by Ramos et al. demonstrated pH-dependent stable potential windows in which SAMs remained intact on electrode surfaces of different metals8. However, there is still a need to verify and expand on this work.To address this need, we aim to create a comprehensive guide on the electrochemical stability of thiolate SAMs on gold electrodes. We will use cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and electrochemical surface plasmon resonance (EC-SPR) to probe and verify the stable electrochemical potential windows in both aqueous and non-aqueous electrolytes. We have conducted studies on three aqueous solutions at three distinct pH, perchloric acid, potassium hydroxide, and sodium chloride. For non-aqueous solvents we tested a wide range of different organic solvents including acetonitrile, dimethylformamide, propylene carbonate, and various alcohols. Our findings demonstrate that the main factor for SAM stability in aqueous and non-aqueous electrolytes is the pH and solubility of the SAM, respectively. Our poster will present our current work and outlook on this topic.(1) Dauphin-Ducharme, P.; Ploense, K. L.; Arroyo-Currás, N.; Kippin, T. E.; Plaxco, K. W. Electrochemical Aptamer-Based Sensors: A Platform Approach to High-Frequency Molecular Monitoring In Situ in the Living Body. In Biomedical Engineering Technologies: Volume 1; Ossandon, M. R., Baker, H., Rasooly, A., Eds.; Methods in Molecular Biology; Springer US: New York, NY, 2022; pp 479–492. https://doi.org/10.1007/978-1-0716-1803-5_25.(2) Hatton, R. A.; Willis, M. R.; Chesters, M. A.; Rutten, F. J. M.; Briggs, D. Enhanced Hole Injection in Organic Light-Emitting Diodes Using a SAM-Derivatised Ultra-Thin Gold Anode Supported on ITO Glass. J. Mater. Chem. 2003, 13 (1), 38–43. https://doi.org/10.1039/B208169P.(3) Shang, H.; Wallentine, S. K.; Hofmann, D. M.; Zhu, Q.; Murphy, C. J.; Baker, L. R. Effect of Surface Ligands on Gold Nanocatalysts for CO2 Reduction. Chem. Sci. 2020, 11 (45), 12298–12306. https://doi.org/10.1039/D0SC05089J.(4) Schlenoff, J. B.; Li, M.; Ly, H. Stability and Self-Exchange in Alkanethiol Monolayers. J. Am. Chem. Soc. 1995, 117 (50), 12528–12536. https://doi.org/10.1021/ja00155a016.(5) Laibinis, P. E.; Whitesides, G. M. Self-Assembled Monolayers of n-Alkanethiolates on Copper Are Barrier Films That Protect the Metal against Oxidation by Air. J. Am. Chem. Soc. 1992, 114 (23), 9022–9028. https://doi.org/10.1021/ja00049a038.(6) Salvarezza, R. C.; Carro, P. The Electrochemical Stability of Thiols on Gold Surfaces. J. Electroanal. Chem. 2018, 819, 234–239. https://doi.org/10.1016/j.jelechem.2017.10.046.(7) Beulen, M. W. J.; Kastenberg, M. I.; van Veggel, F. C. J. M.; Reinhoudt, D. N. Electrochemical Stability of Self-Assembled Monolayers on Gold. Langmuir 1998, 14 (26), 7463–7467. https://doi.org/10.1021/la981031z.(8) Ramos, N.; Medlin, J. W.; Holewinski, A. Electrochemical Stability of Thiolate Self-Assembled Monolayers on Au, Pt, and Cu; preprint; Chemistry, 2022. https://doi.org/10.26434/chemrxiv-2022-dt7dk. Figure 1

Comparison of electrochemical lithium and sodium metal deposition: A surface plasmon resonance spectroscopy investigation

Electrochemical deposition of alkali metals on the electrode surface is important for the development of metal-based batteries with high-energy density. Here, we investigate using electrochemical surface plasmon resonance spectroscopy (EC-SPR) to compare the deposition mechanisms of lithium and sodium metal. The SPR spectrum of the Cu film electrode was clearly observed for both LiPF6 and NaPF6 based organic electrolytes. The corresponding SPR spectra for both Li and Na system were dramatically red-shifted at 1st metal deposition process, indicated direct metal deposition on Cu surface. The Li system repeatedly showed similar red shift until at least the 2nd cycle, while similar red shift was not observed at all in the Na system. This indicated that direct Na-metal deposition on the Cu electrode surface was prevented by some passivation film, formed at 1st deposition process. The complex nature of Na-metal deposition, including the surface film phenomena, is responsible for the instability at the interface between the negative electrode and electrolyte in a Na-based battery system. This suggests that Na-based systems need to be more carefully designed and managed than Li-based systems.

Electrochemical surface plasmon resonance approach to probe redox interactions between microbial extracellular polymeric substances and p-nitrophenol

Microbial extracellular polymeric substances with redox functional groups play a crucial role in the bio-conversion of pollutants, which can affect their reactivity toward diverse pollutants. However, the redox interactions between microbial EPS and pollutants have not addressed in depth due to the absence of essential analytical methodologies. In this study, we have developed an electrochemical-surface plasmon resonance (EC-SPR) system to investigate the interactions between EPS and p-nitrophenol (PNP) by simultaneously monitoring the electrochemical reaction and the binding kinetics. Moreover, in vitro PNP degradation experiments were performed in the presence of EPS across varying redox states to provide further verification of PNP reduction by EPS. The results indicated that direct electrochemical treatment successfully converted raw EPS (EPSraw) into reductive EPS (EPSred) and oxidized EPS (EPSox), respectively. The EC-SPR system served as a powerful tool for probing redox interactions between EPS at distinct redox states and PNP. The binding affinity of EPS to PNP was related to the redox states of EPS, following the order of EPSred > EPSraw > EPSox. EPS exhibited the capability to reduce PNP to p-aminophenol by donating electrons, and the reductive process highly depended on the redox states of EPS, primarily determined by their electron donating capacity. Importantly, direct electrochemical reduction treatment of EPS leads to a substantial improvement in the PNP removal efficiency from 33.8% (EPSraw) to 56.9% (EPSred). This work contributes to a comprehensive understanding of the critical role of EPS redox property in the conversion of refractory pollutants in aquatic environments.

Nanobiosensing Based on Electro-Optically Modulated Technology.

At the nanoscale, metals exhibit special electrochemical and optical properties, which play an important role in nanobiosensing. In particular, surface plasmon resonance (SPR) based on precious metal nanoparticles, as a kind of tag-free biosensor technology, has brought high sensitivity, high reliability, and convenient operation to sensor detection. By applying an electrochemical excitation signal to the nanoplasma device, modulating its surface electron density, and realizing electrochemical coupling SPR, it can effectively complete the joint transmission of electrical and optical signals, increase the resonance shift of the spectrum, and further improve the sensitivity of the designed biosensor. In addition, smartphones are playing an increasingly important role in portable mobile sensor detection systems. These systems typically connect sensing devices to smartphones to perceive different types of information, from optical signals to electrochemical signals, providing ideas for the portability and low-cost design of these sensing systems. Among them, electrochemiluminescence (ECL), as a special electrochemically coupled optical technology, has good application prospects in mobile sensing detection due to its strong anti-interference ability, which is not affected by background light. In this review, the SPR is introduced using nanoparticles, and its response process is analyzed theoretically. Then, the mechanism and sensing application of electrochemistry coupled with SPR and ECL are emphatically introduced. Finally, it extends to the relevant research on electrochemically coupled optical sensing on mobile detection platforms.

Hybrid Electrochemical-Surface Plasmon Resonance Microfiber Sensor for Pb2+ Detection

High-sensitivity detection of heavy metal ions in solution is critical for environmental monitoring. In this paper, a dual-mode method namely hybrid electrochemical-surface plasmon resonance (SPR) microfiber sensor, is proposed for the detection of Pb2+. Gold-coated indium tin oxide (ITO) is used as a working electrode, and a gold nanofilm-coated microfiber is attached to the ITO electrode to monitor the electrochemical reaction process in real time. The microfiber-based SPR sensor is sensitive to slight refractive index changes on the surface and can monitor the electrochemical deposition process and striping process on the electrode. It is shown that a broad dynamic detection range changing from 10-12 to 10-6 M can be achieved, and the limit of detection can reach to the order of pM. The proposed dual-modal detection can provide voltage, current, and optical information simultaneously, making the detection of heavy metal ions more accurate and intuitive. Additionally, the proposed hybrid electrochemical-SPR detection method has the advantages of small size, flexible shape, and cost-effectiveness, which can be potentially used for hazard and hard-to-reach environments.

Ability of Li4Ti5O12 to suppress Li metal deposition under overpotential conditions confirmed by electrochemical surface plasmon resonance spectroscopy

Undesirable Li metal deposition on the negative electrode increases the risks associated with the use of Li-ion batteries. Generally, spinel-type lithium-titanium oxide Li4Ti5O12 (LTO)-based negative electrodes are well known as safe dendrite-free options, due to their higher working potential. However, the ability of LTO-based materials to prevent Li metal deposition has not been well confirmed under sudden overpotential application. This study examines the behavior of Li metal electrodeposition under various overpotential conditions for unloaded and LTO-loaded Cu electrodes. Electrochemical surface plasmon resonance spectroscopy (EC-SPR) is used as the optical diagnostic technique, owing to its sensitivity in detecting Li metal deposition. Li metal deposition is easily detected for the unloaded Cu electrode at overpotential of − 0.2 V (voltage) versus Li counter electrode (LiCE), whereas no Li metal deposition occurs for the LTO-loaded Cu electrode under the same overpotential. The safety of LTO is investigated by analyzing the reaction kinetics.

Interfacial nanobubbles’ growth at the initial stage of electrocatalytic hydrogen evolution

The growth process of interfacial nanobubbles during the initial stage of the hydrogen evolution reaction, and their influence on the overpotential were revealed byin situelectrochemical surface plasmon resonance imaging combined with atomic force microscopy.

The high sensitive and selective detection of dopamine based on its electropolymerization by electrochemical surface plasmon resonance

Dopamine (DA) plays vital role in diagnosis and treatment of neurodegenerative disease. It is of high clinical relevance for developing simple, sensitive and selective DA detection method. But the electrochemical detection of DA still faces the problem of insufficient sensitivity, and generally need the complex material synthesis process to realize the selective detection of DA. In this work, we established a simple electrochemical surface plasmon resonance sensor for DA detection based on its electropolymerization property. The main interfering molecules of uric acid and ascorbic acid cannot undergo electropolymerization, while DA can produce polydopamine precipitation on the surface of Au film. The formation of polydopamine precipitation could amplify the SPR signal, and ensures the high selectivity and sensitivity of DA detection. The linear range is 0.01–1000 nM and the detection limit is as low as 1.4 pM. At the same time, this sensor has high selectivity for DA detection even in the presence of 50000-fold higher concentration of ascorbic acid and uric acid. Finally, the sensor was successfully applied to determine DA content in urine samples and DA released from PC12 cells under the stimulation of K+, demonstrating great potential in clinical applications.

Data Processing of SPR Curve Data to Maximize the Extraction of Changes in Electrochemical SPR Measurements.

We developed a novel measuring and data-processing method for performing electrochemical surface plasmon resonance (EC-SPR) on sensor surfaces for which detecting a specific SPR angle is difficult, such as a polymer having a non-uniform thickness with coloration. SPR measurements are used in medicine and basic research as an analytical method capable of molecular detection without labeling. However, SPR is not good for detecting small molecules with small refractive index changes. The proposed EC-SPR, which combines SPR measurements with an electrochemical reaction, makes it possible to measure small molecules without increasing the number of measurement steps. A drawback of EC-SPR is that it is difficult to detect a specific SPR angle on electron mediators, and it was found that it may not be possible to capture all the features produced. The novel method we describe here is different from the conventional one in which a specific SPR angle is obtained from an SPR curve; rather, it processes the SPR curve itself and can efficiently aggregate the feature displacements in the SPR curves that are dispersed through multiple angles. As an application, we used our method to detect small concentrations of H2O2 (LOD 0.7 μM) and glutamate (LOD 5 μM).

Novel electrochemical-surface plasmon resonance (EC-SPR) sensor for amphetamine-type stimulants detection based on molecularly imprinted strategy

The abuse of amphetamine-type stimulants (ATS) has always been a worldwide problem and the law enforcement agencies are tasked and demanded with identifying them on-site rapidly and reliably in unknown samples. In the present study, an efficient electrochemical-surface plasmon resonance (EC-SPR) sensor, coupled with molecularly imprinted strategy, for adsorption and quantitative measurement of ATS in the human urine and serum samples was demonstrated. The molecular imprinted recognition system on SPR chip was synthesized by a convenient one-step electrochemical polymerization with 3,4-methylenedioxyphenethylamine (MDEA) as the template molecule and dopamine (DA) as the functional monomer. In particular, the molecularly imprinted process was regulated and controlled through synchronous measurement of the SPR signals. This proposed method showed lower detection limit with 57 nM and 59 nM for 3,4-methylenedioxeamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA) in broad linearity, respectively and could be resistant to the interferences from various illicit drugs and other substances. Moreover, this EC-SPR sensor could be employed for detection the spiked MDMA in real urine and serum samples, significantly exhibiting attractive application prospect in forensic analysis.

Optical Study of the Surface Film Formed during Li-Metal Deposition and Dissolution Investigated by Surface Plasmon Resonance Spectroscopy.

The features of the electrode surface film during Li-metal deposition and dissolution cycles are essential for understanding the mechanism of the negative electrode reaction in Li-metal battery cells. The physical and chemical property changes of the interface during the initial stages of the reaction should be investigated under operando conditions. In this study, we focused on the changes in the optical properties of the electrode surface film of the negative electrode of a Li-metal battery. Cu-based electrochemical surface plasmon resonance spectroscopy (EC-SPR) was applied because of its high sensitivity to optical phenomena on the electrode surface and its stability against Li-metal deposition. The feature of SPR reflectance dip depends on the optical properties of the electrode surface; namely, the wavelength and depth of the reflectance dip directly connected the refractive index and extinction coefficient (color of electrode surface film), which was confirmed by reflectance simulation. In the operando EC-SPR experiment, various changes in optical properties were clearly observed during the cycles. In particular, the change in the extinction coefficient was more remarkable at the second process than the first process of Li-metal deposition. By electrochemical quartz-crystal microbalance (EQCM) measurements, surface film formation was confirmed during the first Li-metal deposition process. The remarkable change in the extinction coefficient is based on the color change of the surface film, which is caused by the chemical condition change during Li-metal deposition cycles.

Slow and Fast Dynamics at the Ionic Liquid/Gold Electrode Interface Separately Probed by Electrochemical Surface Plasmon Resonance Combined with Sequential Potential Pulse Techniques

To investigate the potential dependence of the dynamics of the interface structure of an ionic liquid (IL), electrochemical surface plasmon resonance (ESPR) has been combined with normal pulse and differential pulse techniques at the gold electrode interface of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. The fast response of SPR angle in 0.1 ∼ 0.2 s, originating from the orientation, distortion, and electronic polarization of ions in the first ionic layer, has been clearly observed, which is opposite to both the direction of the change in potential and of the slow response. This separate detection of the fast and slow responses has been realized based on the fact that the ionic rearrangement, which results in the slow response, does not proceed in a short potential pulse, especially for the positive pulse. The fast response, which reflects the interfacial dielectric constant, exhibits the potential-dependent dielectric saturation, i.e., a bell shape (or camel shape) potential dependence with a maximum around the potential of zero charge (PZC) and steep decrease at the potentials far from PZC. Molecular dynamics simulation explains that the decrease is caused by the strong electric field and ionic crowding in the first ionic layer which hinders the orientation and distortion of ions.

Interfacial viscosity and ionic reorientation probed using electrochemical surface plasmon resonance at the gold electrode interface of ionic liquids

• Interfacial dielectric relaxation of ionic liquids has been studied by ESPR. • Interfacial viscosity of ionic liquids is demonstrated to be extremely high. • Smaller ions tend to form the electric double layer with more solid-like structure. • Imidazolium ring has weak reorientation response to the potential steps. The interfacial dielectric relaxation of ionic liquids (ILs) at the gold electrode interface has been investigated using electrochemical surface plasmon resonance (SPR), by analyzing the SPR response to the potential step for four ILs with the two cations, trioctylmethylammonium and 1-butyl-3-methylimidazolium, and three amide anions, bis(fluorosulfonyl)amide, bis(trifluoromethanesulfonyl)amide, and bis(nonafluorobutanesulfonyl)amide. For all the four ILs, the SPR response to the potential step exhibits a fast relaxation process mainly ascribable to the ionic reorientation, followed by an ultraslow relaxation process ascribable to the ionic translation, with the opposite directions of SPR shift to each other. The ultraslow relaxations by the positive potential steps are always significantly slower than those by the negative steps. The average time constants of the ultraslow relaxation process and the amplitudes of the fast relaxation process are evaluated by the fitting with a multiple exponential function and are compared with the measured bulk viscosity and the dipole moments of each ion. The interfacial viscosity, estimated from the time constants of the ultraslow relaxation process, is several orders of magnitude higher than the bulk viscosity, and the viscosity increase is larger for the ILs composed of smaller ions. The amplitude of the fast relaxation, reflecting the ionic reorientation, is moderately correlated with the dipole moments of counter-ions on the electrode at the pre-step potential.

Towards electrochemical surface plasmon resonance sensor based on the molecularly imprinted polypyrrole for glyphosate sensing.

In this research the molecular imprinting technology was applied for the formation of glyphosate-sensitive layer. The glyphosate imprinted conducting polymer polypyrrole (MIPpy) was deposited on a gold chip/electrode and used as an electrochemical surface plasmon resonance (ESPR) sensor. The results described in this study disclose some restrictions and challenges, which arise during the development of glyphosate ESPR sensor based on the molecularly imprinted polymer development stage. It was demonstrated, that glyphosate could significantly affect the electrochemical deposition process of molecularly imprinted polymer on the electrode. The results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR) have demonstrated that glyphosate molecules tend to interact with bare gold electrode and thus hinder the polypyrrole deposition. As a possible solution, the formation of a self-assembled monolayer (SAM) of 11-(1H-Pyrrol-1-yl)undecane-1-thiol (PUT) before electrochemical deposition of MIPpy and NIPpy was applied. Dissociation constant (KD) and free energy of Gibbs (ΔG0) values of glyphosate on MIPpy and Ppy without glyphosate imprints (NIPpy) were calculated. For the interaction of glyphosate with MIPpy the KD was determined as 38.18±2.33⋅10-5 and ΔG0 as -19.51±0.15kJ/mol.

Self-Assembled Monolayer of Monomercaptoundecahydro-closo-dodecaborate on a Polycrystalline Gold Surface.

In this work, we present an electrochemical study of the boron cage monomercaptoundecahydro-closo-dodecaborate [B12H11SH]2− in solution and in a self-assembled monolayer over a polycrystalline gold electrode. Cyclic voltammetry of the anion [B12H11SH]2− in solution showed a shift in the peak potentials related to the redox processes of gold hydroxides, which evidences the interaction between the boron cage and the gold surface. For an Au electrode modified with the anion [B12H11SH]2−, cyclic voltammetry response of the probe Fe(CN)63−/Fe(CN)64− showed a ΔEp value typical for a surface modification. Electrochemical impedance spectroscopy presented Rtc and Cdl values related to the formation of a self-assembled monolayer (SAM). A comparison of electrochemical responses of a modified electrode with thioglycolic acid (TGA) reveals that the boron cage [B12H11SH]2− diminishes the actives sites over the Au surface due to the steric effects. Differential capacitance measurements for bare gold electrode and those modified with [B12H11SH]2− and (TGA), indicate that bulky thiols enhance charge accumulation at the electrode–solution interface. In addition to electrochemical experiments, DFT calculations and surface plasmon resonance measurements (SPR) were carried out to obtain quantum chemical descriptors and to evaluate the molecular length and the dielectric constant of the Boron cage. From SPR experiments, the adsorption kinetics of [B12H11SH]2− were studied. The data fit for a Langmuir kinetic equation, typical for the formation of a monolayer.

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

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