Diamond Electrode Surface Research Articles

The effect of acetylcholine immobilization on the electrochemical properties of thiocholine on boron-doped diamond electrode for chlorpyrifos sensor

Background: The inhibition reactions of acetylcholinesterase (AChE) have been studied to develop chlorpyrifos biosensors. The performance of AChE, both as a free enzyme and when immobilized on avidin-functionalized magnetic beads (aMB), was evaluated for the hydrolysis of acetylthiocholine. Detection was conducted through the oxidation of thiocholine on a boron-doped diamond (BDD) electrode surface. Methods: The study compared the performance of free and immobilized AChE by analyzing their ability to oxidize thiocholine on the BDD electrode surface. The inhibitory effects of chlorpyrifos were assessed by determining IC10 and IC50 values for both enzyme forms. Additionally, the influence of metal ions (Fe²⁺ and Mn²⁺) on AChE activity was investigated to evaluate interference effects. Findings: Free AChE demonstrated superior performance in thiocholine oxidation compared to the immobilized enzyme. In chlorpyrifos detection, free AChE exhibited a significantly lower IC10 value (3.44 × 10⁻⁶ mM) compared to immobilized AChE (12.9 × 10⁻⁶ mM), and its IC50 value (3.8 × 10⁻⁴ mM) was approximately two orders of magnitude lower than that of the immobilized AChE (5.18 mM). Furthermore, AChE exhibited resistance to metal ion interference, with signal losses of 48.7% and 40.8% in the presence of Fe²⁺ and Mn²⁺ ions, respectively. These findings indicate that the immobilization of AChE must be carefully optimized for effective sensor application. Conclusion: The study highlights the superior performance of free AChE in chlorpyrifos detection compared to its immobilized counterpart. Immobilization significantly affects enzyme sensitivity, resulting in higher inhibitory concentration values. Additionally, AChE demonstrated notable resistance to interference from metal ions. These results emphasize the need for careful consideration when immobilizing AChE for sensor applications. Novelty/Originality or this article: This study provides a detailed comparison between free and immobilized AChE in chlorpyrifos biosensing, highlighting the impact of immobilization on enzyme sensitivity and performance. The findings contribute to the development of more efficient biosensors by emphasizing the importance of optimizing enzyme immobilization strategies.

Fluorescence and electron transfer of Limnospira indica functionalized biophotoelectrodes

Cyanobacteria play a crucial role in global carbon and nitrogen cycles through photosynthesis, making them valuable subjects for understanding the factors influencing their light utilization efficiency. Photosynthetic microorganisms offer a promising avenue for sustainable energy conversion in the field of photovoltaics. It was demonstrated before that application of an external electric field to the microbial biofilm or cell improves electron transfer kinetics and, consequently, efficiency of power generation. We have integrated live cyanobacterial cultures into photovoltaic devices by embedding Limnospira indica PCC 8005 cyanobacteria in agar and PEDOT:PSS matrices on the surface of boron-doped diamond electrodes. We have subjected them to varying external polarizations while simultaneously measuring current response and photosynthetic performance. For the latter, we employed Pulse-Amplitude-Modulation (PAM) fluorometry as a non-invasive and real-time monitoring tool. Our study demonstrates an improved light utilization efficiency for L. indica PCC 8005 when immobilized in a conductive matrix, particularly so for low-intensity light. Simultaneously, the impact of electrical polarization as an environmental factor influencing the photosynthetic apparatus diminishes as matrix conductivity increases. This results in only a slight decrease in light utilization efficiency for the illuminated sample compared to the dark-adapted state.

Highly Sensitive and Selective Detection of L-Tryptophan by ECL Using Boron-Doped Diamond Electrodes.

L-tryptophan is an amino acid that is essential to the metabolism of humans. Therefore, there is a high interest for its detection in biological fluids including blood, urine, and saliva for medical studies, but also in food products. Towards this goal, we report on a new electrochemiluminescence (ECL) method for L-tryptophan detection involving the in situ production of hydrogen peroxide at the surface of boron-doped diamond (BDD) electrodes. We demonstrate that the ECL response efficiency is directly related to H2O2 production at the electrode surface and propose a mechanism for the ECL emission of L-tryptophan. After optimizing the analytical conditions, we show that the ECL response to L-tryptophan is directly linear with concentration in the range of 0.005 to 1 µM. We achieved a limit of detection of 0.4 nM and limit of quantification of 1.4 nM in phosphate buffer saline (PBS, pH 7.4). Good selectivity against other indolic compounds (serotonin, 3-methylindole, tryptamine, indole) potentially found in biological fluids was observed, thus making this approach highly promising for quantifying L-tryptophan in a broad range of aqueous matrices of interest.

A simple and reliable electrochemical method employing an unmodified boron-doped diamond electrode for the determination of triclocarban

Since the advent of the COVID-19 pandemic, triclocarban-containing cleaning products have been increasingly consumed. As triclocarban is an emerging compound, it is necessary to develop new sensors for its monitoring. So, a simple and reliable electroanalytical method for the determination of triclocarban using an unmodified boron-doped diamond electrode was developed. The application of a cathodic pretreatment (−2.0 V, 30 min, 0.5 mol L−1 H2SO4) on the electrode surface provided higher current intensities and lower resistance to charge transfer in contrast to the non-treated surface. On the diamond electrode surface, the triclocarban showed an irreversible behavior with two oxidation peaks at +1.10 and +1.40 V vs. Ag/AgCl, KCl(sat). The hypothesis for removing hydrogens of both amide groups of the triclocarban structure was supported by computational methodology which also explained the broadened oxidation peaks and the distance between them. The calibration curve for triclocarban, obtained by using differential pulse voltammetry in a supporting electrolyte composed of McIlvaine buffer (pH 3.0) and ethanol (80:20 v/v), covered a concentration range of 1.0 to 50 μmol L−1, and it exhibited a detection limit of 0.31 μmol L−1 under optimized experimental conditions. Using an accumulation time of 120 s at open circuit potential, a calibration curve by differential pulse adsorptive stripping voltammetry was constructed in a range of 0.05 to 20 µmol L−1 of triclocarban, with a detection limit of 18 nmol L−1. Triclocarban quantification assays were carried out on samples of antibacterial soaps and river water, and data were recorded with acceptable precision and accuracy.

Utilizing an anionic surfactant aqueous media for voltammetric sensing of anti-cancer drug imiquimod in the pharmaceutical formulation and urine samples at the boron-doped diamond electrode surface

This work demonstrates an electroanalytical evaluation for voltammetric sensing of the anti-cancer drug imiquimod (IMQ) at the boron-doped diamond electrode. By using cyclic voltammetric technique, IMQ demonstrated a well-defined, adsorption-controlled, irreversible anodic peak at approximately +1.56 V (vs Ag/AgCl) in 0.1 M H2SO4 solution. A possible mechanism for the electro-oxidation of IMQ was proposed based on the pH investigation data. The voltammetric signals of IMQ were improved by adding sodium dodecyl sulfate (SDS), an anionic surfactant, to the selected supporting electrolyte. By utilizing the square wave-adsorptive stripping voltammetric technique, acceptable linearity was obtained in 0.1 M H2SO4 solution with SDS at about +1.49 V (vs Ag/AgCl). The presented approach was linear in the concentration range of 0.005 and 1.0 μg mL−1 (2.1 × 10−8-4.2 × 10−6 M), with a lower limit of detection of 0.0015 μg mL−1 (6.2 × 10−9 M). Eventually, the proposed approach's applicability was investigated by sensing IMQ in pharmaceutical formulations and urine samples.

Utilizing epicatechin voltammetric oxidation signal for the estimation of total phenolic content in the tea samples via the unmodified boron-doped diamond electrode surface

In this work, the boron-doped diamond (BDD) electrode surface was employed for the first time in conjunction with the epicatechin (EC) oxidation signal to estimate the total phenolic content of tea samples by voltammetry. During cyclic voltammetry analysis of the EC, an easily identifiable, irreversible, and adsorption-controlled oxidation peak was observed at around +1.05 V (vs. Ag/AgCl) in HNO3 solution. Our experimental setup was fine-tuned by investigating the effect of electrode pretreatment, pH of the supporting electrolyte, accumulation factors, and instrumental parameters on the oxidation peak response of EC. When measuring EC in a 0.1 mol L−1 HNO3 solution at +1.0 V, square-wave adsorptive stripping voltammetry provided a highly linear response (at open-circuit accumulation for 30 s). The dynamic range was determined to be between 1.0 and 50.0 μg mL−1 (3.4510−6–1.7210−4 mol L−1), while the detection limit was found to be 0.28 μg mL−1 (9.6510−7 mol L−1). Selectivity studies were performed with other phenolic compounds found in tea such as epigallocatechin gallate, catechin, tannic acid, and gallic acid. Finally, by assessing the total phenolic content in the black and green tea samples, the suggested approach's applicability was shown by providing an estimate of the EC equivalents present in the samples.

An anodically pretreated boron-doped diamond electrode surface for square-wave adsorptive stripping voltammetric quantification of the non-absorbable antibiotic rifaximin in the pharmaceutical formulation

An anodically pretreated boron-doped diamond electrode surface for square-wave adsorptive stripping voltammetric quantification of the non-absorbable antibiotic rifaximin in the pharmaceutical formulation

Voltammetric determination of anti-malarial drug amodiaquine at a boron-doped diamond electrode surface in an anionic surfactant media

In this study, the electrochemical determination of the amodiaquine (ADQ) drug was evaluated using an electrochemically pretreated boron-doped diamond (BDD) electrode due to the enhanced surface activity. The cyclic voltammogram results of ADQ were given as single reversible and diffusion-controlled peaks at +0.48 V for the oxidation peak and +0.05 V for the reduction peak (vs. Ag/AgCl) in Britton-Robinson (BR) buffer at pH 8.0. The peak potential and current signals of ADQ were evaluated at the surface of the BDD electrode using instrumental parameters to develop a simple method for ADQ detection. Also, the effect of an anionic surfactant, sodium dodecyl sulfate (SDS), on the adsorption applicability of the BDD electrode significantly increased the stripping voltammetric determination of ADQ. Under the optimal conditions chosen and employing square-wave adsorptive stripping voltammetry at the BDD electrode, ADQ was determined at + 0.34 V (vs. Ag/AgCl) at the open-circuit condition in BR buffer at pH 8.0 in the presence of 2·10–4 mol l–1 SDS. Furthermore, analytical parameters showed the linear relationship for ADQ determination in the concentration range of 0.1–20.0 μg ml–1 (2.2·10–7 – 4.3·10–5 mol l–1), with a detection limit of 0.03 μg ml–1 (6.5·10–8 mol l–1). The proposed approach can be applied to determine ADQ in water samples.

Detection of Aqueous Solvated Electrons Produced by Photoemission from Solids Using Transient Absorption Measurements.

Solvated electrons in water have long been of interest to chemists. While readily produced using intense multiphoton excitation of water and/or irradiation with high-energy particles, the possible role of solvated electrons in electrochemical and photoelectrochemical reactions at electrodes has been controversial. Recent studies showed that excitation of electrons to the conduction band of diamond leads to barrier-free emission of electrons into water. While these electrons can be inferred from the reactions they induce, direct detection by transient absorption measurements provides more direct evidence. Here, we present studies demonstrating direct detection of solvated electrons produced at diamond electrode surfaces and the influence of electrochemical potential and solution-phase electron scavengers. We further present a more detailed analysis of experimental conditions needed to detect solvated electrons emitted from diamond and other solid materials through transient optical absorption measurements.

Effect of plasma-assisted electrochemical treatment of the boron-doped synthetic diamond compact electrodes on the oxygen electroreduction kinetics

The effect of plasma electrochemical activation of boron-doped diamond compact electrodes on the oxygen electroreduction reaction kinetics is studied. The conducting compact electrodes are prepared via graphite-to-diamond conversion in C–B growth system at high pressure and high temperature. The diamond compact electrode surface was modified in Na2SO4 aqueous solution by exposition to cathodic–anodic electrolytic plasma produced by the application of voltage pulses with amplitude up to 300 V. The cathodic–anodic plasma alone proved to produce but negligible catalytic effect with respect to the oxygen reduction reaction. However, on the cathodic reduction of thus treated electrode, it acquired significant electrocatalytical activity manifested itself in the predominant O2-to-H2O reduction by a four-electron pathway. At the same time, the cathodic treatment of the plasma-modified electrodes has no real impact on the rate constant of electron transfer in the “fast” [Ru(NH3)6]2+/3+ and [Fe(CN)6]4–/3– redox systems. The observed electrocatalytical effect with respect to the oxygen reduction reaction is assumed to be caused by the quinone groups formation at the boron-doped diamond electrode surface under the combined action of cathodic–anodic plasma and cathodic polarization, these groups being active centers for the four-electron oxygen reduction.

Novel voltammetric strategy for determination and electrochemical evaluation of progesterone by CPT-BDD electrode

In this study, electrochemical properties of progesterone at boron doped diamond (BDD) electrode surface were examined in strongly acidic medium (HClO4 and H2SO4). A fast, sensitive, selective and simple electroanalytic method has been proposed with a cathodically pre-treated (CPT-BDD) electrode in 0.5 M H2SO4 medium. Progesterone yielded a well-defined voltammetric response in 0.5 M H2SO4 medium at +1.51 V (vs. Ag/AgCl). Using the optimal square wave-adsorptive stripping voltammetry (SW-AdSV) conditions, the oxidation peak was used to determine of progesterone in the concentration range of 0.1 to 7.1 μM. Limit of detection is 0.012 μM; the relative standard deviation value for the concentration value of 3.1 μM (n = 11) was calculated as 4.87%. The developed voltammetric method was successfully applied to serum and drug samples.

A detailed EIS study of boron doped diamond electrodes decorated with gold nanoparticles for high sensitivity mercury detection

This work compares the electrochemical impedance response of polished and unpolished boron doped diamond (BDD) electrodes, during mercury detection measurements. For each substrate type both bare electrodes and electrodes decorated with average diameter 30 nm AuNPs were used, to investigate the role of AuNPs during mercury sensing with diamond electrodes. In square wave anodic stripping voltammetry (SWASV) measurements for mercury detection, the mercury ions in the electrolyte are deposited onto, then stripped from the diamond electrode surface. To investigate the different electrode performances during these steps, the EIS measurements were made at the deposition and stripping potentials, alongside scans at open circuit potential for comparison. The performance of the electrodes is assessed in terms of their electron transfer rate (k0). The electrodes decorated with AuNPs are shown to have lower capacitance and higher reactivity than the bare pBDD and BDD electrodes, until the mercury concentration in the electrolyte is < 500 µM, when the sp2/sp3 carbon ratio at the surface of the electrodes has a greater influence on the sensitivity for mercury detection than the presence of AuNPs.

Understanding the electrochemical oxidation of dyes on platinum and boron–doped diamond electrode surfaces: experimental and computational study

Anodic oxidation (AO) approach proceeds via direct and indirect electrochemical pathways and their subsequent reactions. The interest to elucidate the mechanisms for removing dyes from water contributes to the understanding of more complex reactions involving organic pollutants towards anode surfaces. The present study was motivated by the reports that promote the use of AO for removing different organic compounds but no considerations about the influence of different functional groups in their structure have been discussed. Therefore, we have evaluated the influence of different functional groups in the dye structure (Reactive Orange 16, Reactive Violet 4, Reactive Red 228, and Reactive Black 5) by potentiodynamic measurements and by computational analyzes using density functional theory (DFT). The computational studies have allowed to carry out morphological studies on the frontier orbitals where the electrons are more energetic and then, the electron-transfer to electrode surface is achieved, which was associated to the electrochemical measurements (current-potential profiles). Also, the theoretical studies were used to understand the bulk electrolysis, in terms of mineralization. The results clearly demonstrate that organic molecules can be degraded in different way and level due to the oxidants electrochemically generated as well as the interaction of dyes with anode surface by adsorbed/non-adsorbed intermediates. Conversely, the decolorization mechanisms, which are related to the fragmentation of chromophore group, are associated to the direct AO approach, favoring different order of elimination, as already reported in our previous work. The results were discussed in light of the existing literature.

Bacteria poration on modified boron-doped diamond electrode surfaces induced by divalent cation chelation

This work showed that divalent ions from the outer membrane of bacteria can be chelated byN-propyl-2-hydroxyacetamide functional groups that were immobilized on boron-doped diamond electrodes.

Role of Near-Electrode Solution Chemistry on Bacteria Attachment and Poration at Low Applied Potentials.

This research investigated mechanisms for biofouling control at boron-doped diamond (BDD) electrode surfaces polarized at low applied potentials (e.g., -0.2 to 1.0 V vs Ag/AgCl), using Pseudomonas aeruginosa as a model organism. Results indicated that electrostatic interactions between bacteria and ionic electrode functional groups facilitated bacteria attachment at the open-circuit potential (OCP). However, under polarization, the applied potential governed these electrostatic interactions and electrochemical reactions resulted in surface bubble formation and near-surface pH modulation that decreased surface attachment under anodic conditions. The poration of the attached bacteria occurred at OCP conditions and increased with the applied potential. Scanning electrochemical microscopy (SECM) provided near-surface pH and oxidant formation measurements under anodic and cathodic polarizations. The near-surface pH was 3.1 at 1.0 V vs Ag/AgCl and 8.0 at -0.2 V vs Ag/AgCl and was possibly a contributor to bacteria poration. Interpretation of SECM data using a reactive transport model allowed for a better understanding of the near-electrode chemistry. Under cathodic conditions, the primary oxidant formed was H2O2, and under anodic conditions, a combination of H2O2, Cl•, HO2•, Cl2•-, and Cl2 formations likely contributed to bacteria poration at potentials as low as 0.5 V vs Ag/AgCl.

In-situ monitoring of electropolymerization processes at boron-doped diamond electrodes by Mach-Zehnder interferometer

In this work, the Mach-Zehnder interferometer was designed to monitor the electrochemical processes conducted at boron-doped diamond electrode surface. The diamond electrodes were synthesized via Microwave Plasma-Assisted Chemical Vapor Deposition on optical grade quartz glass. The achieved transmittance in working are of diamond electrodes reached 55 %. A cage system-based Mach-Zehnder interferometer was used which allowed the insertion of thin-layer electrochemical cells. Electrochemical studies were carried out in a thin-layer working cell. The application of such setup, allows to combine optical monitoring of surface of the working electrode during electrochemical measurements, electropolymerization or surface modification. The conducted investigation shows that during surface modification by melamine the phase shift is up to 0.0328 μm−1. The aforementioned set up can be applied for in situ monitoring of surface modifications with various compounds, and to detect organic substances whose oxidation or reduction products absorb onto the electrode surface.

Multifrequency nanoscale impedance microscopy (m-NIM): A novel approach towards detection of selective and subtle modifications on the surface of polycrystalline boron-doped diamond electrodes

In this paper, we describe the modification of Nanoscale Impedance Microscopy (NIM), namely, a combination of contact-mode atomic force microscopy with local impedance measurements. The postulated approach is based on the application of multifrequency voltage perturbation instead of standard frequency-by-frequency analysis, which among others offers more time-efficient and accurate determination of the resultant impedance spectra with high spatial resolution. Based on the impedance spectra analysis with an appropriate electric equivalent circuit, it was possible to map surface resistance and contact capacitance.Polycrystalline heavy boron-doped diamond (BDD) electrodes were the research object. Recent studies have shown that the exposure of such electrodes to oxidizing environment may result in the modification of termination type, and thus it is a key factor in describing the electric and electrochemical properties of BDD. We have successfully applied multifrequency NIM, which allowed us to prove that the modification of termination type is selective and occurs with different propensity on the grains having specific crystallographic orientation. Furthermore, our approach enabled the detection of even subtle submicroscopic surface heterogeneities, created as a result of various oxidation treatments and to distinguish them from the surface heterogeneity related to the local distribution of boron at the grain boundaries.

Electrochemical Determination of Cadmium, Lead, and Nickel Using a Polyphenol–Polyvinyl Chloride—Boron-Doped Diamond Electrode

ABSTRACTBoron-doped diamond electrode surfaces were modified by a polyphenol—polyvinyl chloride membrane. The polyphenols were extracted from the skin of acorns, the fruit of the oak tree. The polymer film was applied on the boron-doped diamond electrode surface by solvent evaporation. The resulting polyphenol–polyvinyl chloride–boron-doped diamond electrode was used as a sensor for cadmium, lead, and nickel. The synergy between the chemically modified surfaces and electrochemical performances of the boron-doped diamond microcell electrode was examined by differential pulse anodic stripping voltammetry at nanomolar concentrations of the three metal ions. The modified electrode provided a stable, sensitive, and selective response to cadmium, lead(II), and nickel(II) ions. The resulting detection limits were 0.0221, 0.25, and 0.00424 nmole L−1, respectively.

Hydroxide Ion Oxidation in Aqueous Solutions Using Boron-Doped Diamond Electrodes.

The electrochemical oxidation behavior of hydroxide ions at the surface of boron-doped diamond (BDD) electrodes is presented. The hydroxide ion oxidation behavior was found to be affected by the surface conditions of the BDD electrode. Over the NaOH concentration range of 0.5-10 mM, a well-defined voltammetric wave attributed to hydroxide ion oxidation was observed at ∼1.25 V versus a Ag/AgCl reference electrode when using an anodically oxidized BDD (AO-BDD) electrode, while it was observed at around ∼1.15 V when a cathodically reduced BDD (CR-BDD) electrode was used. Although the hydroxide ion oxidation profiles were slightly different for the AO-BDD and CR-BDD electrodes, the peak currents was each found to have linear relationships with the NaOH concentration over the same range.

Hierarchically nanostructured boron-doped diamond electrode surface

A boron-doped diamond (BDD) electrode with a large specific surface area was fabricated by formation of a hierarchical nanostructure. A BDD thin film was deposited on a silicon pillar array substrate fabricated using photolithography to obtain a BDD pillar array (BDD-PA). The BDD-PA was subjected to a two-step thermal treatment to form dense pores on the surface (P-BDD-PA). The P-BDD-PA was then treated by reactive ion etching (RIE) to form nanowhiskers on the surface (P-BDDW-PA). The combination of these structures (pillar array, pores and nanowhiskers) enabled enhanced double-layer capacitance (ca. 2800μFcm−2) based on the enlarged specific surface area without narrowing of the potential window (ca. 3V) in an aqueous electrolyte. The combination of the two-step thermal treatment and RIE treatment should be an effective post-treatment method for enhancement of the capacitance of porous BDD materials consisting of micrometer-sized structures without significant increase of the time constant.