Electroanalytical Applications Research Articles

A Current Averaging Strategy for Maximizing Analyte and Minimizing Redox Interference Signals with Square Wave Voltammetry.

Square wave voltammetry (SWV) is commonly used in electroanalytical applications to enhance analyte faradaic signals and minimize nonfaradaic processes. However, little attention is given as to how best use SWV to minimize faradaic interference signals that arise from redox species present in solution that have redox potentials that convolute with that of the analyte. In conventional SWV, a series of current-time (i-t) transients are collected, and i is averaged over a specified window of each transient (potentiostat dependent). This average i is reported against the electrode potential, E. As the i-t response is governed by the type of electron transfer reaction under investigation, we show how by collecting all i-t data and through judicious choice of the current averaging window, it is possible to enhance the analyte response while at the same time reducing the interferent signal. We look at three different electron transfer reactions, fast electron transfer outer sphere, metal electrodeposition/stripping, and surface-confined proton-coupled electron transfer (PCET) and demonstrate different i-t behaviors in SWV, visually aided by the use of 3D i-t-E plots. In the case of PCET quinone-based voltammetric sensing of pH in the presence of a heavy metal (here Cu2+), we show that the use of a much earlier current averaging window (2-10% of the i-t response) results in the pH signal being clearly distinguished from that of the overlapping heavy metal.

LDH-Based Voltammetric Sensors.

Layered double hydroxides (LDHs), also named hydrotalcite-like compounds, are anionic clays with a lamellar structure which have been extensively used in the last two decades as electrode modifiers for the design of electrochemical sensors. These materials can be classified into LDHs containing or not containing redox-active centers. In the former case, a transition metal cation undergoing a reversible redox reaction within a proper potential window is present in the layers, and, therefore, it can act as electron transfer mediator, and electrocatalyze the oxidation of an analyte for which the required overpotential is too high. In the latter case, a negatively charged species acting as a redox mediator can be introduced into the interlayer spaces after exchanging the anion coming from the synthesis, and, again, the material can display electrocatalytic properties. Alternatively, due to the large specific surface area of LDHs, molecules with electroactivity can be adsorbed on their surface. In this review, the most significant electroanalytical applications of LDHs as electrode modifiers for the development of voltammetric sensors are presented, grouping them based on the two types of materials.

Recent Trends in Therapeutic and Electroanalytical Applications of Boron-Doped Diamond Sensors

Abstract:: In recent years, research and development efforts have been heavily focused on conductive diamond electrodes for electrochemical applications. Such initiatives may have been spurred by their broad potential window, low background current, chemical inertness, and mechanical robustness. Compared to other carbon-based materials, conducting diamond can oxidize several analytes before the breakdown of water in aqueous electrolytes. Since the evolution of oxygen and hydrogen does not obstruct the analysis, this is significant for the detection and/or identification of species in solution. As a result, conductive diamond electrodes expand the application of electrochemical detection and make it possible to use them for analytes that are incompatible with traditional electrode materials. Fabricating boron-doped diamond films via chemical vapor deposition on different substrates is of special interest. This article highlights the therapeutic and electroanalytical applications of boron-doped diamond electrodes in various aspects in addition to the synthetic strategies to obtain Boron Doped Diamond Electrodes (BDDE), the cost-effectiveness of BDD and its in-vivo compatibility that will help the analytical researchers to learn almost everything about the previous studies done on BDDE and encourage them to work more efficiently in this research field.

Voltammetric behavior of solifenacin succinate on gold, glassy carbon and boron-doped diamond electrodes: Stability testing and determination

The anticholinergic drug, solifenacin, is frequently used for the treatment of the urological tract for urinary incontinence, and urinary frequency. The development of reliable and effective solifenacin electrochemical sensors is of great importance for the pharmaceutical industry and clinical practice. In this work, the electrochemical behavior of solifenacin succinate (SOL) was studied using three different working electrodes: gold (Au), glassy carbon (GCE) and boron-doped diamond electrode (BDDE). The cyclic voltammetric (CV) measurements performed in 0.05 M NaHCO3 indicated that the SOL oxidation process is irreversible and diffusion-controlled at all investigated working electrodes. Afterwards, the testing of SOL electrochemical stability and the possibility of its electrochemical degradation was performed at the Au electrode by the cycling of the potential during 3 h and continuously to 6 h. It was shown that the SOL was electrochemically transformed into another electroactive species and its degradation was excluded. For electroanalytical application, the anodically pretreated BDDE (+2.0 V; 30 s) was selected. Various experimental parameters were optimized, including the pH of the aqueous Britton-Robinson (B-R) buffer as a supporting electrolyte (from pH 2.0 to 11.98) and the most intensive peak of the target analyte was at pH 11.0, so this pH value was chosen as the optimum for further measurements. Based on the correlation of the SOL peak intensity and different concentrations, the developed differential pulse voltammetric (DPV) method was characterized by a linear concentration range from 0.041 to 2.50 µM, with a correlation coefficient of 0.999, and a relative standard deviation of 0.3 %. Taking into account the sensitivity of the developed DPV method towards the electrochemical oxidation of SOL, a very low detection limit of 0.012 µM in the model system was achieved. The BDDE showed adequate selectivity for SOL in the presence of the investigated interferents. The obtained results indicate that the BDDE with an optimized DPV method could be applied for the trace-level electroanalytical determination of SOL in human urine sample with excellent recovery and reproducibility.

Electroanalytical application of phenol-functionalized reduced graphene oxide produced using gallic acid in a single step

This study introduces a simple one-step approach for synthesizing phenol-functionalized reduced graphene oxide for electroanalytical purposes, just using gallic acid (GA) and graphene oxide (GO). GA serves as both a reductant for GO and a stabilizing, functionalizing agent, introducing phenolic groups to the nanomaterial. This functionalization imparts remarkable attributes to the nanomaterial, allowing complete dispersion in aqueous solutions and tuning of its electrochemical performance, making it very convenient for electrode modification. The resulting nanomaterials (GA-rGO) underwent characterization through UV–visible, Fourier-transform infrared (FTIR), and Raman spectroscopies, as well as scanning electron microscopy (SEM). Glassy carbon electrodes modified with aqueous dispersions of these nanomaterials (GA-rGO/GCE) were employed in voltammetric experiments to evaluate the optimal dispersion composition for electroanalytical application.These GA-rGO/GCE displayed high electrocatalytic activity for the electrochemical oxidation of relevant clinical and environmental analytes. The unique functionalization of GA-rGO facilitated the selective accumulation of dopamine (DA) and uric acid (UA) on the electrode surface, even in the presence of significant amounts of ascorbic acid (AA) in mixtures. Under the specified conditions, voltammetric currents display linear increments over the concentration ranges of 3.0 x 10-7 M to 2.0 x 10-5 M for DA and 7.0 x 10-6 M to 1.0 x 10-4 M for UA. The sensor demonstrated a low detection limit of 0.090 and 2.1 μM for DA and UA, respectively. The reliability of the electroanalytical performance of the proposed sensor in real samples was demonstrated by the quantification of DA in medications, as well as DA and UA in human urine samples, yielding recovery values between 82 % and 105 %, with relative standard deviation below 11 %.

Electrocatalytic Amplified Sensor For Determination of Ofloxacin Using Zn2SnO4/Reduced Graphene Oxide Composite As Surface-Modifying Agent

This study describes an electroanalytical approach for the quantification of ofloxacin (OFL) through an electrochemical sensor based on a glassy carbon electrode modified with composite material (Zn2SnO4-rGO/GCE) using square wave voltammetry. Zn2SnO4 was synthesized by hydrothermal treatment and characterized by X-ray diffraction, Fourier-transform infrared and Raman spectroscopy and scanning electron microscopy. The analysis suggests a synergistic effect between the composite material, indicating irreversible oxidation of OFL in its protonated form (OFL+), involving two electrons. The electroanalytical methodology was successfully applied to determine OFL in ophthalmic solutions samples, achieving recovery rates ranging from 98.03% to 104.91%. Furthermore, it demonstrated high stability in both repeatability (RSD = 3.20%, n = 12) and reproducibility (RSD = 4.64%, n = 7), with no observed interference when additional substances were added. These results suggest the potential electroanalytical application of Zn2SnO4 and recommend the developed methodology as an alternative tool for OFL determination in commercial pharmaceutical samples.

Synthesis and characterization of hollow dual-tube MOF hybrid nanocomposites for electroanalytical applications

This study provides a nano-synergistic engineering for the controllable assembly of hollow dual-tube MOF composite to detect dopamine, which exhibits excellent linearity range with a detection limit as low as 0.02 μmol L−1.

Solvent-activated 3D-printed electrodes and their electroanalytical potential

This work is a comprehensive study describing the optimization of the solvent-activated carbon-based 3D printed electrodes. Three different conductive filaments were used for the preparation of 3D-printed electrodes. Electrodes treatment with organic solvents, electrochemical characterization, and finally electroanalytical application was performed in a dedicated polyamide-based cell also created using 3D printing. We have investigated the effect of the used solvent (acetone, dichloromethane, dichloroethane, acetonitrile, and tetrahydrofuran), time of activation (from immersion up to 3600 s), and the type of commercially available filament (three different options were studied, each being a formulation of a polylactic acid and conductive carbon material). We have obtained and analysed a significant amount of collected data which cover the solvent-activated carbon-based electrodes surface wettability, microscopic insights into the surface topography analysed with scanning electron microscopy and atomic force microscopy, and finally voltammetric evaluation of the obtained carbon electrodes electrochemical response. All data are tabulated, discussed, and compared to finally provide the superior activation procedure. The electroanalytical performance of the chosen electrode is discussed based on the voltammetric detection of ferrocenemethanol.

Laser-induced graphene trending in biosensors: understanding electrode shelf-life of this highly porous material

Laser-induced graphene (LIG) has received much attention in recent years as a possible transducer material for electroanalytical sensors. Its simplicity of fabrication and good electrochemical performance are typically highlighted. However, we found that unmodified and untreated LIG electrodes had a limited shelf-life for certain electroanalytical applications, likely due to the adsorption of adventitious hydrocarbons from the storage environment. Electrode responses did not change immediately after exposure to ambient conditions but over longer periods of time, probably due to the immense specific surface area of the LIG material. LIG shelf-life is seldomly discussed prominently in the literature, yet overall trends for solutions to this challenge can be identified. Such findings from the literature regarding the long-term storage stability of LIG electrodes, pure and modified, are discussed here along with explanations for likely protective mechanisms. Specifically, applying a protective coating on LIG electrodes after manufacture is possibly the easiest method to preserve electrode functionality and should be identified as a trend for well-performing LIG electrodes in the future. Furthermore, suggested influences of the accompanying LIG microstructure/morphology on electrode characteristics are evaluated.

Ultrafast Electrochemical Self-Doping of Anodic Titanium Dioxide Nanotubes for Enhanced Electroanalytical and Photocatalytic Performance

This study explores an ultrarapid electrochemical self-doping procedure applied to anodic titanium dioxide (TiO2) nanotube arrays in an alkaline solution to boost their performance for electroanalytical and photocatalytic applications. The electrochemical self-doping process (i.e., the creation of surface Ti3+ states by applying a negative potential) is recently emerging as a simpler and cleaner way to improve the electronic properties of TiO2 compared to traditional chemical and high-temperature doping strategies. Here, self-doping was carried out through varying voltages and treatment times to identify the most performing materials without compromising their structural stability. Interestingly, cyclic voltammetry characterization revealed that undoped TiO2 shows negligible activity, whereas all self-doped materials demonstrate their suitability as electrode materials: an outstandingly short 10 s self-doping treatment leads to the highest electrochemical activity. The electrochemical detection of hydrogen peroxide was assessed as well, demonstrating a good sensitivity and a linear detection range of 3–200 µM. Additionally, the self-doped TiO2 nanotubes exhibited an enhanced photocatalytic activity compared to the untreated substrate: the degradation potential of methylene blue under UV light exposure increased by 25% in comparison to undoped materials. Overall, this study highlights the potential of ultrafast electrochemical self-doping to unleash and improve TiO2 nanotubes performances for electroanalytical and photocatalytic applications.

Adsorption of Model Polyfluoroalkyl Substances on Gold Electrodes for Electroanalytical Applications

AbstractElectrochemical methods can detect trace amounts of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in the environment to help their management. PFAS adsorption on electrodes is an essential step in these methods, but is poorly understood. Here, we study the adsorption of perfluorooctanoic acid (PFOA), a model PFAS molecule, on gold substrates using metadynamics and equilibrium molecular dynamics simulations. The two‐dimensional free energy landscape obtained from metadynamics reveals that a PFOA molecule can adsorb on a neutral gold surface with the lowest free energy of −83.9 kJ/mol by adopting a co‐planar orientation, indicating a strong enrichment of PFOA occurs near the electrode. Spontaneous adsorption in other configurations, e. g., only a PFOA molecule‘s head attaches to the electrode, also occurs. However, a PFOA molecule generally must overcome energy barriers to become adsorbed. We show that energetic effects, particularly those associated with van der Waals PFOA‐gold interactions, are the primary driver for PFOA adsorption, and entropic effects associated with interfacial water molecules are the secondary driver. The implications of these results for the electrochemical detection and analysis of PFAS molecules are discussed.

Surface characterization and electroanalytical applications of the newly developed copper(II)-selective potentiometric sensor.

In this work, we developed a new copper(II)-selective potentiometric sensor and investigated its surface with scanning electron microscopy (SEM). Besides the surface images of the sensors conditioned in copper(II) solutions, energy-dispersive X-ray (EDX) and mapping studies were carried out. According to the results obtained, it was determined that copper(II) ions adhered to the porous areas on the sensor surface, and that Cu2+ ions showed a wide distribution on the sensor surface in mapping studies. The new sensor had a Nernstian response of 29.3 ± 0.5mV/decade in the concentration range of 1.0 × 10-1-1.0 × 10-5M and a low detection limit of 8.56 × 10-6M. The proposed sensor had fast response time (< 10s), wide pH working range (5.0-10.0), good repeatability and stability. Finally, the sensor performed the determination of copper(II) ions in various water samples with very high recoveries (96.0-102.0%).

Biochar-based materials for electroanalytical applications: An overview

Biochar-based materials, derived from renewable biomass resources, have emerged as promising candidates for electroanalytical applications due to their unique physicochemical properties, such as high surface area, excellent biocompatibility, and good chemical stability. This review provides a comprehensive overview of recent advancements in the development and application of biochar-based materials in electrochemical devices, including sensors, energy storage, and catalysis. We discuss the synthesis and functionalization of biochar materials, focusing on the effects of feedstock and pyrolysis conditions on their properties. The applications of biochar-based materials in electrochemical devices are reviewed, with a particular emphasis on enzyme-based biosensors, DNA-based biosensors, and immunosensors. Despite their promising performance, challenges such as reproducibility, electrical conductivity, and long-term stability need to be addressed to facilitate their widespread adoption in the industry. We also discuss emerging trends, such as the development of multifunctional hybrid materials and integration into flexible devices. Finally, we highlight the importance of policy, regulatory aspects, and environmental assessments to ensure the safe and sustainable use of biochar-based materials in electroanalytical applications.

Boron-doped diamond nanosheet volume-enriched screen-printed carbon electrodes: a platform for electroanalytical and impedimetric biosensor applications

This paper focuses on the development of a novel electrode based on boron-doped diamond nanosheet full-volume-enriched screen-printed carbon electrodes (BDDPE) for use as an impedimetric biosensor. Impedimetric biosensors offer high sensitivity and selectivity for virus detection, but their use as point-of-care devices is limited by the complexity of nanomaterials’ architecture and the receptor immobilisation procedures. The study presents a two-step modification process involving the electroreduction of diazonium salt at the BDDPE and the immobilisation of antibodies using zero-length cross-linkers for a selective impedimetric biosensor of Haemophilus influenzae (Hi). The incorporation of diamond nanosheets into BDDPE leads to enhanced charge transfer and electrochemical behaviour, demonstrating greatly improved electrochemically active surface area compared with unmodified screen-printed electrodes (by 44% and 10% on average for [Ru(NH3)6]Cl2 and K3[Fe(CN)6], respectively). The presented sensing system shows high specificity towards protein D in Hi bacteria, as confirmed by negative controls against potential interference from other pathogens, with an estimated tolerance limit for interference under 12%. The Hi limit of detection by electrochemical impedance spectroscopy was 1 CFU/mL (measured at − 0.13 V vs BDDPE pseudo-reference), which was achieved in under 10 min, including 5 min sample incubation in the presence of the analyte.Graphical abstract

Nanobioengineered surface comprising carbon based materials for advanced biosensing and biomedical application

Carbon-based nanomaterials (CNMs) are at the cutting edge of materials science. Due to their distinctive architectures, substantial surface area, favourable biocompatibility, and reactivity to internal and/or external chemico-physical stimuli, carbon-based nanomaterials are becoming more and more significant in a wide range of applications. Numerous research has been conducted and still is going on to investigate the potential uses of carbon-based hybrid materials for diverse applications such as biosensing, bioimaging, smart drug delivery with the potential for theranostic or combinatorial therapies etc. This review is mainly focused on the classifications and synthesis of various types of CNMs and their electroanalytical application for development of efficient and ultra-sensitive electrochemical biosensors for the point of care diagnosis of fatal and severe diseases at their very initial stage. This review is mainly focused on the classification, synthesis and application of carbon-based material for biosensing applications. The integration of various types of CNMs with nanomaterials, enzymes, redox mediators and biomarkers have been used discussed in development of smart biosensing platform. We have also made an effort to discuss the future prospects for these CNMs in the biosensing area as well as the most recent advancements and applications which will be quite useful for the researchers working across the globe working specially in biosensors field.

Edge and Basal Plane Anisotropy of a Preanodized Pencil Graphite Electrode Surface Revealed Using Scanning Electrochemical Microscopy and Electrocatalytic Dopamine Oxidation as a Molecular Probe.

Pencil graphite (PGE), an ultralow-cost and ready-to-use disposable-type electrode, has been used for various electrochemical and electroanalytical applications after its surface anodization (PGE*, * means preanodized surface). Indeed, systematic studies on mechanistic and surface features of PGE* have not yet been explored. Herein, we report anodized pencil graphite as a model system to study molecular level insights into the surface using a scanning electrochemical microscopy (SECM) technique and dopamine (DA) electrocatalytic oxidation reaction as a molecular probe. The as-prepared PGE* showed an appreciable electronic conductivity similar to the edge-plane graphitic sites (EPPG) of the highly pyrolytic graphitic electrode (HOPG) but without any surface deterioration that occurs with HOPG due to the instability of the EPPG. Physicochemical characterizations by FESEM, FTIR, Raman, and XPS techniques revealed a flake-like exfoliated PGE* surface with higher contents of carbon-oxygen especially phenolic/alcoholic functional groups than the PGE surface. Based on the chronocoulometric experiment, the number of functional groups formed on the PGE* was calculated as 10.9 × 10-10 mol cm-2. An independent SECM technique using ferricyanide as a redox probe showed the existence of a heterogeneous surface and exhibited an improved electron transfer activity due to the flake-like graphitic island on the PGE* surface. Investigated DA electrochemical oxidation on PGE* yielded about three times enhancement in the peak current signal and about 200 mV reduction in the oxidation potential over the PGE without any serious surface fouling feature that is related to the intermediate polydopamine formation on the basal-plane graphitic surface of the underlying electrode. As an independent electroanalytical study, a prototype electrochemical sensor using PGE* as a working electrode for instant detection of DA-containing pharmaceutical samples in a 1 mL Eppendorf vial has been demonstrated.

Fabrication and Applications of Electroplated Three-Dimensional, Open-Cell, Noble Metal Electrodes

Noble metal electrodes (Au, Ag, and Pt) have found numerous applications in electroanalysis and electrocatalysis. Noble metal electrodes are typically composed entirely of a bulk noble metal so their cost is high and they have a two-dimensional geometry. This presentation describes the fabrication of inexpensive, electroplated noble metal electrodes that have an open-cell, three-dimensional complex geometry. The electroplated noble metal electrodes exhibit a defect-free layer of a noble metal (i.e., Au, Pt or Ag) deposited onto a copper substrate structure of the desired geometry. The surface roughness of the electrodeposited films was tailored by adjusting the electroplating conditions and the composition of the electroplating solution. The electrochemical performance of the electrodes was fully characterized. The electroplated three-dimensional, open-cell electrodes were used for the detection of heavy metals in aqueous samples and the decontamination of aqueous samples that contained bacteria.

Easy cleaning plus stable activation of glassy carbon electrode surface by oxygen plasma

Glassy carbon (GC) electrodes are widely used in electroanalytical applications especially in bioelectrochemistry. Their use starts with an efficient surface cleaning and activation protocol, mostly based on surface polishing steps. We studied the use of an oxygen plasma exposure of GC electrodes to replace common polishing procedures. The cyclic voltammetry (CV) responses of ferrocyanide and ferrocene-dimethanol were used to compare brand new, surface-polished and plasma-treated GC electrodes. Plasma treatment induces CV responses with improved features, close to theoretical values, as compared to other methods. The plasma effects were quasi-stable over a week when electrodes were stored in water, this being explained by increased surface energy and hydrophilicity. Furthermore, when electroreduction of diazonium was performed on GC electrodes, the surface blockade could be removed by the plasma. Thus, a short oxygen plasma treatment is prone to replace polishing protocols, that display person-dependent efficiency, in most of the experiments with GC electrodes.

Bidirectional Negative Coupling Induced Dynamical Patterns in a Branched Epoxy-Based Dual-Electrode Microchip Flow Cell

In this contribution, we investigated the spatiotemporal pattern formation of oscillatory electrodissolution of nickel in sulfuric acid with two micro-wires placed in two branches of a microfluidic flow cell. In the flow channel, the reference and counter electrodes are placed at the opposite end of the branched flow channel (contralateral placement). A theory based on modeling the potential drop in the flow channel and the interactions between the reactions showed the presence of bidirectional negative electrical coupling between the electrode potential variables. Experiments and numerical simulations with a kinetic model showed that such bidirectional negative coupling could induce complex dynamics. The experiments showed that anti-phase synchronization occurred only when electrodes were placed in the middle of the branched flow channel. When the electrodes were close to beginning or the end of the channels, where the reference and counter electrodes were placed, respectively, no phase locking was observed. The coupling is intensified in magnitude when the electrodes are in the middle of the flow channel, which maximizes the loop current which can flow towards the reference electrode. The nature of the bidirectional coupling is confirmed in independent experiments with synchrony analysis using the Hilbert transform. Additionally, to further verify the nature of the migration current coupling, a data driven approach, inferring connections of networks (ICON), was utilized. Analysis using the ICON technique showed that the synchronization patterns can be described by a phase repulsive bidirectional coupling. The findings indicate that contralateral placement should be used with great care in electroanalytical application with reactions that exhibit negative differential resistance(NDR) region, e.g., due to passivation or adsorption of an inhibitor. Ultimately, revealing connectivity is essential to characterize the dynamical structures and functions of networks, which in turn, leads to the fundamental understanding of many real-world complex systems such as the topology of the physical or functional connections of neurons in the brain.

Tailoring diamondised nanocarbon-loaded poly(lactic acid) composites for highly electroactive surfaces: extrusion and characterisation of filaments for improved 3D-printed surfaces

A new 3D-printable composite has been developed dedicated to electroanalytical applications. Two types of diamondised nanocarbons - detonation nanodiamonds (DNDs) and boron-doped carbon nanowalls (BCNWs) - were added as fillers in poly(lactic acid) (PLA)-based composites to extrude 3D filaments. Carbon black served as a primary filler to reach high composite conductivity at low diamondised nanocarbon concentrations (0.01 to 0.2 S/cm, depending on the type and amount of filler). The aim was to thoroughly describe and understand the interactions between the composite components and how they affect the rheological, mechanical and thermal properties, and electrochemical characteristics of filaments and material extrusion printouts. The electrocatalytic properties of composite-based electrodes, fabricated with a simple 3D pen, were evaluated using multiple electrochemical techniques (cyclic and differential pulse voltammetry and electrochemical impedance spectroscopy). The results showed that the addition of 5 wt% of any of the diamond-rich nanocarbons fillers significantly enhanced the redox process kinetics, leading to lower redox activation overpotentials compared with carbon black–loaded PLA. The detection of dopamine was successfully achieved through fabricated composite electrodes, exhibiting lower limits of detection (0.12 μM for DND and 0.18 μM for BCNW) compared with the reference CB-PLA electrodes (0.48 μM). The thermogravimetric results demonstrated that both DND and BCNW powders can accelerate thermal degradation. The presence of diamondised nanocarbons, regardless of their type, resulted in a decrease in the decomposition temperature of the composite. The study provides insight into the interactions between composite components and their impact on the electrochemical properties of 3D-printed surfaces, suggesting electroanalytic potential.Graphical abstract