Standard Redox Probes Research Articles

3D-Printed Microelectrodes for Biological Measurement.

Microelectrodes are useful electrochemical sensors that can provide spatial biological monitoring. Carbon fiber has been by far the most widely used microelectrode; however, a vast number of different materials and modification strategies have been developed to broaden the scope of microelectrodes. Carbon composite electrodes provide a simple approach to making microelectrodes with a wide range of materials, but manufacturing strategies are complex. 3D printing can provide the ability to make microelectrodes with high precision. We used fused filament fabrication to print single strands of carbon black/polylactic acid (CB/PLA) and multiwall carbon nanotube/polylactic acid (MWCNT/PLA), which were then made into microelectrodes. Microelectrodes ranged from 70 μm in diameter to 400 μm in diameter and were assessed using standard redox probes. MWCNT/PLA electrodes exhibited greater sensitivity, a lower limit of detection, and stability for the measurement of serotonin (5-HT). Both CB/PLA and MWCNT/PLA microelectrodes were able to monitor 5-HT overflow from the ex vivo ileum tissue. MWCNT/PLA microelectrodes were utilized to show differences in 5-HT overflow from ex vivo ileum and colon following exposure to odorants present in spices. These findings highlight that any conductive thermoplastic material can be fabricated into a microelectrode. This simple strategy can utilize a wide range of materials to make 3D-printed microelectrodes for a diverse range of applications.

Electrochemical Monitoring in Anticoagulation Therapy.

The process of blood coagulation, wherein circulating blood transforms into a clot in response to an internal or external injury, is a critical physiological mechanism. Monitoring this coagulation process is vital to ensure that blood clotting neither occurs too rapidly nor too slowly. Anticoagulants, a category of medications designed to prevent and treat blood clots, require meticulous monitoring to optimise dosage, enhance clinical outcomes, and minimise adverse effects. This review article delves into the various stages of blood coagulation, explores commonly used anticoagulants and their targets within the coagulation enzyme system, and emphasises the electrochemical methods employed in anticoagulant testing. Electrochemical sensors for anticoagulant monitoring are categorised into two types. The first type focuses on assays measuring thrombin activity via electrochemical techniques. The second type involves modified electrode surfaces that either directly measure the redox behaviours of anticoagulants or monitor the responses of standard redox probes in the presence of these drugs. This review comprehensively lists different electrode compositions and their detection and quantification limits. Additionally, it discusses the potential of employing a universal calibration plot to replace individual drug-specific calibrations. The presented insights are anticipated to significantly contribute to the sensor community's efforts in this field.

Evaluation of a same-metal PCB-based three-electrode system via impedance studies using potassium ferricyanide.

We report for the first time the successful acquisition of electrochemical impedance spectroscopy data using an unconventional same-metal PCB-based three-electrode system. Conventional three-electrode systems primarily require expensive and bulky electrodes, and a high volume of analytes to conduct electrochemical impedance spectroscopy studies. The miniaturized PCB-based three-electrode system used in this work requires only trace amounts of analytes in the order of 10-20 μL owing to the design of the electrode sensor. Prominent standard redox probe potassium ferricyanide was used for impedance spectroscopic characterization studies. The results obtained were in congruence with existing literature; additionally the PCB-based three-electrode system demonstrated significantly higher repeatability, reproducibility, and consistency across different models of electrochemical instrumentations. Interestingly, the electrochemical impedance spectroscopy data of the PCB-3T sensor exhibited a consistent semi-circular impedance curve on a Nyquist plot and two distinct phase change regions on a Bode plot indicative of a simplified Randles cell model with an excellent circuit fit. Additionally this model provides an accurate impedance model for analysing trace analytes of potassium ferricyanide. Based on the circuit fitting model, potassium ferricyanide samples of varying concentrations at 1 mM, 5 mM, 10 mM, 15 mM and 20 mM demonstrated characteristic EIS charge transfer resistance corresponding to 435, 300, 233, 72 and 55 kΩ, respectively, and solution resistance of 260, 254, 218, 169 and 157 Ω, respectively. Therefore, the proposed novel same-metal three-electrode sensor can be employed in effective analysis and detection of samples with high accuracy and high sensitivity for trace amounts of analytes.

Kinetic and thermodynamic analysis of ammonia electro-oxidation over alumina supported copper oxide (CuO/Al2O3) catalysts for direct ammonia fuel cells

In this work, ammonia electrooxidation (AEO) is studied to probe the electrochemical behavior of aqueous NH3 as direct fuel by implication of gamma alumina supported copper oxide catalysts (CuO/Al2O3). Precipitation and impregnation techniques are adapted to synthesize the substrate Al2O3, and loading of different ratios (1%, 2%, 3%, 4%) of active precursor i.e., CuO, respectively. Small average crystallite sizes (DAvg) in range of 1.46–6.76 nm and smaller particle sizes from micrographs proposed a superb activity of the catalysts. Modified GCE exhibited the excellent conductive properties towards standard redox probe K4[Fe(CN)6] and KCl, displaying a high active electrochemical surface area of up to 0.0021 cm2. Current profiles in response to increase in scan rates, concentrations of ammonia and temperature have been observed in 0.1 M KOH, thereby estimating the thermodynamic and kinetic constraints of the AEO process. Attributed to the electroactive properties towards AEO, CuO/Al2O3 is found to exhibit the desirable physiochemical properties owing to large oxidation current, large diffusion coefficient “D°” (3.6 × 10-9 cm2 s-1), large rate constant “ko” (1.2 × 10-5 cm s-1), large system entropy “ΔS” (-108 J K-1 mol-1), high change in enthalpy “ΔH” (72.3 J mol-1) and low activation energy “ΔG” (32.8 kJ mol-1). Resultingly, the oxidation of ammonia is found to be facile and robust by incorporation of CuO/Al2O3 catalysts owing to large ko, ΔH and ΔH. This study opened a gateway towards eco-benign and economical efficient energy generation and viable market entry of direct ammonia fuel cells.

Effect of the chiral blocks of functionalized fullerene on levofloxacin enantioselective voltammetric sensing

Antibiotics are one of the most important bioactive and chemotherapeutic groups of compounds. However, as a result of their excessive consumption for human treatment, veterinary and food industries, it can lead to direct toxic effects, pathogen resistance and allergic hypersensitivity in humans. The situation calls for developing sensitive and selective techniques for antibiotics analysis to monitor their appropriate use, public health, and new drugs design. In this study the glassy carbon voltammetric sensors (GCE) based on layer-by-layer deposited graphene oxide (rGO) and functionalized fullerene (C60) were proposed for the levofloxacin (Lev: S-(–)-Ofloxacin) sensing. Since Lev is an optically active substance, it can be assumed that the sensitive layer of sensor with chiral selector will selectively interact with the antibiotic through various intermolecular interactions. Therefore, a number of selectors with different optical center configurations were obtained and studied, such as S/R-2-chloro-N-(1-phenylethyl)acetamide fullerene (S/R-C60AA), and S/R-N,N'-bis(1-phenylethyl)malonamide fullerene (S/R-C60MA). The structure of obtained selectors was confirmed by NMR and IR spectroscopy, polarimetric studies were carried out. The proposed sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using standard redox probe. Morphological studies were carried out by scanning electron microscopy (SEM). Possible binding sites between Lev and selectors were revealed by computational studies. Some patterns of changes in the electrochemical behavior of Lev depending on the composition of the sensitive layer of the sensor were obtained by differential pulse voltammetry (DPV). Quantitative determination of Lev was carried out using sensor GCE/rGO/S-C60AA. Calibration plot was found to be linear in two ranges, such as 1.0·10−6–3.0·10−5 M and 3.0·10−5–5.0·10−4 M with sensitivity values of 82.14 and 58.71 μA/mM, respectively. The limits of detection and quantitation were calculated to be 3.7·10−8 M and 1.2·10−7 M, respectively (according to 3Sb/m and 10Sb/m). The developed sensor has a simple design, good analytical and operational characteristics compared to some previous reports in the literature. In addition, the sensor was successfully tested for Lev quantification in real samples of biological fluids and pharmaceutical formulations with a good recovery percentage ranged in 91.5–104.4 %.

Influence of instrument parameters on the electrochemical activity of 3D printed carbon thermoplastic electrodes

3D printing provides a reliable approach for the manufacture of carbon thermoplastic composite electrochemical sensors. Many studies have explored the impact of printing parameters on the electrochemical activity of carbon thermoplastic electrodes but limited is known about the influence of instrument parameters, which have been shown to alter the structure and mechanical strength of 3D printed thermoplastics. We explored the impact of extruder temperature, nozzle diameter and heated bed temperature on the electrochemical activity of carbon black/poly-lactic acid (CB/PLA) electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were conducted using standard redox probes. The electrode surface and cross-section of the electrode was visualised using scanning electron microscopy. We found that using extruder temperatures of 230 °C and 240 °C improved the electrochemical activity of CB/PLA electrodes, due to an increase in surface roughness and a reduction in the number of voids in-between print layers. Nozzle diameter, heated bed temperature of different 3D printers did not impact the electrochemical activity of CB/PLA electrodes. However high-end printers provide improved batch reproducibility of electrodes. These findings highlight the key instrument parameters that need to be considered when manufacturing carbon thermoplastic composite electrochemical sensors when using 3D printing.

Platform-agnostic electrochemical sensing app and companion potentiostat.

Electrochemical sensing is ubiquitous in a number of fields ranging from biosensing, to environmental monitoring through to food safety and battery or corrosion characterisation. Whereas conventional potentiostats are ideal to develop assays in laboratory settings, they are in general, not well-suited for field work due to their size and power requirements. To address this need, a number of portable battery-operated potentiostats have been proposed over the years. However, most open source solutions do not take full advantage of integrated circuit (IC) potentiostats, a rapidly evolving field. This is partly due to the constraining requirements inherent to the development of dedicated interfaces, such as apps, to address and control a set of common electrochemical sensing parameters. Here we propose the PocketEC, a universal app that has all the functionalities to interface with potentiostat ICs through a user defined property file. The versatility of PocketEC, developed with an assay developer mindset, was demonstrated by interfacing it, via Bluetooth, to the ADuCM355 evaluation board, the open-source DStat potentiostat and the Voyager board, a custom-built, small footprint potentiostat based around the LMP91000 chip. The Voyager board is presented here for the first time. Data obtained using a standard redox probe, Ferrocene Carboxylic Acid (FCA) and a silver ion assay using anodic stripping multi-step amperometry were in good agreement with analogous measurements using a bench top potentiostat. Combined with its Voyager board companion, the PocketEC app can be used directly for a number of wearable or portable electrochemical sensing applications. Importantly, the versatility of the app makes it a candidate of choice for the development of future portable potentiostats. Finally, the app is available to download on the Google Play store and the source codes and design files for the PocketEC app and the Voyager board are shared via Creative Commons license (CC BY-NC 3.0) to promote the development of novel portable or wearable applications based on electrochemical sensing.

Exploring the structural and electrochemical sensing of wide bandgap calcium phosphate/CuxFe3-xO4 core-shell nanoceramics for H2O2 detection

Calcium phosphate/Cu x- Fe 2-x O 4 core-shell nanoceramics have been synthesized using the organic sol-gel process and calcined at 600 o C. The nanoceramics were explored by X-ray powder diffractometry (XRD), transmission electron microscopy (TEM)), Fourier transforms infrared spectroscopy (FT-IR), UV–visible diffuse reflectance spectra (DRS), and electrochemical techniques including cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The FTIR results confirmed the presence of calcium phosphate (CP) and CP coated with Cu-ferrite (0-30 mol% Cu:Fe 3 O 4 ) core-shell nanoceramics. TEM analysis displayed nanospheres of calcium phosphate shielded with a porous spheres-like morphology with internal nanoparticles of about 33 nm. The reflectance spectra increase for all samples with increasing wavelength. Both direct and indirect gap transitions were detected with lower values of the direct case than the indirect type. The dielectric constant, refractive index, and optical electronegativity of all samples were calculated. When the ferricyanide was applied as the standard redox probe for the electrochemical characterization, CV and EIS results revealed a remarkable enhancement in the generated electrochemical signals. Moreover, modified screen-printed electrodes with the 20 Cu-CPF produced the highest redox current (0.198 mA) towards the direct oxidation of hydrogen peroxide. The obtained interesting features nominate the newly developed core-shell calcium phosphate/Cu x Fe 2-x O 4 nanoceramics as promising candidates for talented magneto-optical and peroxide sensor applications.

A microfluidic system for analysis of electrochemical processing using a highly sensitive optical fiber microcavity

Microfluidics provide unique possibilities to control tiny volumes of liquids and their composition. In this work we combined a microfluidic system with a microcavity in-line Mach-Zehnder interferometer (µIMZI) induced in the side surface of a single-mode optical fiber using a femtosecond laser micromachining. The µIMZI shows capability for investigating optical properties of volumes down to picoliters with an exceptionally high refractive index sensitivity. Here we report numerical analysis and experimental results that show that when the µIMZI is incorporated with the microfluidic system the measurements can be performed with sensitivity exceeding 14,000 nm/RIU which is similar to measurements done under static conditions. In a flow injection system, we show the influence of flow rate and injection volume on the response, and that the orientation of the cavity versus the flow direction has only a minor impact on the results. Finally, we have supported the system by band electrodes making it possible to induce redox reactions in the microchannel to detect the flowing products of the reactions optically. It has been found that thanks to the high sensitivity of the µIMZI the products of the reactions can be clearly detected both electrochemically and optically even when the only part of the flowing redox probe is oxidized at the band electrode. The capability for monitoring the products was shown for a standard redox probe, potassium ferricyanide, as well as for the neurotransmitter dopamine. This work shows that the proposed solution may offer highly sensitive optical measurements, even when the chemical reactions are not effective in the whole volume of the system.

Exploring carbon particle type and plasma treatment to improve electrochemical properties of stencil-printed carbon electrodes

Stencil-printing conductive carbon inks has revolutionized the development of inexpensive, disposable and portable electrochemical sensors. However, stencil-printed carbon electrodes (SPCEs) typically suffer from poor electrochemical properties. While many surface pretreatments and modifications have been tested to improve the electrochemical activity of SPCEs, the bulk composition of the inks used for printing has been largely ignored. Recent studies of other carbon composite electrode materials show significant evidence that the conductive carbon particle component is strongly related to electrochemical performance. However, such a study has not been carried out with SPCEs. In this work, we perform a systematic characterization of SPCEs made with different carbon particle types including graphite particles, glassy carbon microparticles and carbon black. The relationship between carbon particle characteristics including particle size, particle purity, and particle morphology as well as particle mass loading on the fabrication and electrochemical properties of SPCEs is studied. SPCEs were plasma treated for surface activation and the electrochemical properties of both untreated and plasma treated SPCEs are also compared. SPCEs displayed distinct analytical utilities characterized through solvent window and double layer capacitance. Cyclic voltammetry (CV) of several standard redox probes, FcTMA+, ferri/ferrocyanide, and pAP was used to establish the effects of carbon particle type and plasma treatment on electron transfer kinetics of SPCEs. CV of the biologically relevant molecules uric acid, NADH and dopamine was employed to further illustrate the differences in sensing and fouling characteristics of SPCEs fabricated with different carbon particle types. SEM imaging revealed significant differences in the SPCE surface microstructures. This systematic study demonstrates that the electrochemical properties of SPCEs can be tuned and significantly improved through careful selection of carbon particle type and plasma cleaning with a goal toward the development of better performing electrochemical point-of-need sensors.

In-situ production of Histamine-imprinted polymeric materials for electrochemical monitoring of fish

Histamine (HIS) is a major public health problem due to its toxic properties. High levels can cause a chronic toxicity as poisoning and can be used as a signal of food hygiene. Thus, a new electrochemical sensor for HIS detection in fish is presented herein, prepared by tailoring a molecularly imprinted polymer (MIP) sensing material on a gold screen-printed electrode (Au-SPEs), in which the polymeric film was generated in-situ. This film was obtained by electropolymerizing aniline under conditions that preserved the chemical structure of HIS. Raman spectroscopy followed the chemical changes occurring at each stage of the electrode modification.The device performance was assessed by evaluating the changes in electron transfer properties of a standard redox probe [Fe(CN)6]4−/[Fe(CN)6]3−, by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS was also used to calibrate the sensor, being the standard solutions prepared under different background media (electrolyte or a blank sample of fish extract). The device displayed a linear response from 500 nM to 1 mM, with a limit of detection of 210 nM, and a selective behaviour against tyramine, another amine related to fish degradation. The sensing system was further employed to monitor the HIS content in samples in different time points of storage at ambient temperature. The obtained results were in agreement with the ELISA method, while offering more reproducible data.In general, the optimized sensor allowed reproducible and accurate analysis of fish samples subject to degradation and was completely assembled in-situ, in a very simple and straightforward approach. The device is low cost and suitable for further adaptation to on-site analysis, as required in food control.

Bioinspired electro-permeable glycans on carbon: Fouling control for sensing in complex matrices

The effect of glycan adlayers on the electrochemical response of glassy carbon electrodes was studied using standard redox probes and complex aqueous matrices. Aryldiazonium cations of aryl-lactoside precursors were used to modify glassy carbon via spontaneous and electrochemically assisted covalent grafting. Contact angle and fluorescence binding using Peanut Agglutinin (PNA) as a diagnostic lectin indicate that electrografting results in adlayers with greater glycan surface density than those obtained via spontaneous reaction. X-ray photoelectron spectroscopy with a fluorinated analog confirmed that electrografting results in multilayers of cross-linked aryl-lactosides. Adsorption studies with Bovine Serum Albumin (BSA) show that aryl-lactoside adlayers minimize unspecific protein adsorption. However, no significant differences were detected between spontaneous and electrografted layers in their ability to resist protein fouling despite their differences in coverage. Voltammetry studies show that spontaneous grafting has minimal effects on the response of standard redox probes in solution, whereas electrografting results in additional charge transfer impedance arising from increased electrode passivation. Bare and lactoside-modified carbon electrodes were tested for the detection of caffeine before and after prolonged exposure to coffee solutions. Spontaneous grafting was found to result in optimal properties by imparting antifouling performance in these complex matrices while preserving fast interfacial charge transfer.

Fabrication of a label-free electrochemical immunosensor for direct detection of Candidatus Phytoplasma Aurantifolia

A novel label-free electrochemical immunosensor was fabricated for selective and sensitive detection of Candidatus Phytoplasma Aurantifolia (CPA), the main factor of witches broom diseases, in tree sap samples. CPA antibody was immobilized on a thiol terminated surface of a gold electrode modified by gold nanoparticles; the surface was then activated by mixture of N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) and N-HydroxySuccinamide (NHS). Scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed for surface characterization. All the electrochemical measurements of CPA were accomplished based on the [Fe(CN)6]3−/4− solution response as the standard redox probe. CPA detection was carried out using square wave voltammetry (SWV) technique, at frequency of 20 Hz and amplitude of 0.1 V. In order to reach the maximum efficiency in performance of the immunosensor, Anti-CPA 1 mg mL−1, pH 7.4 and the incubation time of 45 min were selected as optimized experimental conditions. According to the calibration curve data, the obtained linear range was 0.005 to 100 μg mL−1, with limit of detection (LOD) of 1.5 ng mL−1, which was lower than the value reported for ELISA method applied for CPA detection. The immunosensor demonstrated adequate selectivity and stability besides; there was no significant interference observed from other probable protein based components in the real sample matrix.

An electrochemical sensor for homocysteine detection using gold nanoparticle incorporated reduced graphene oxide.

In this work, we report a methodology for the quantification of Homocysteine (HcySH) at neutral pH (pH-7.0) using Au nanoparticles incorporated reduced graphene oxide (AuNP/rGO/GCE) modified glassy carbon electrode. The modified electrode was characterized using SEM and XRD techniques. The electrode exhibited a typical behavior against the standard redox probe [Fe(CN)6]3-/4- and resulted in 0.06 V peak to peak potential value. The modified electrode exhibited electrocatalytic activity towards electrochemical biosensing of HcySH, which is established using voltammetric studies. HcySH oxidation peak potential is observed at 0.12 V on AuNP/rGO/GCE which is 0.7 V cathodic than bare glassy carbon electrode (0.82 V). The large peak potential shift observed is reasoned as the interaction of SH group of HcySH with the gold nanoparticles and the electrocatalytic property of reduced graphene oxide that enhances the electrochemical detection at reduced overpotential. Further, successive addition of HcySH showed a linear increment in the sensitivity within the concentration range of 2-14 mM. From an amperometric protocol, the limit of detection is found as 6.9 μM with a sensitivity of 14.8 nA/μM. From a set of cyclic voltammetric measurements, it is observed that the electrode produces a linear signal on the concentration of HcySH in the presence of hydrogen peroxide. Thus it can be concluded that the matrix can detect HcySH even in the presence of hydrogen peroxide.

In-situ generated molecularly imprinted material for chloramphenicol electrochemical sensing in waters down to the nanomolar level

A novel device for monitoring chloramphenicol (CAP) on-site is described, making use of commercial carbon screen-printed electrodes (C-SPEs) modified with a suitable sensing element. This element consisted of a molecularly imprinted polymer (MIP), produced in-situ, by electro-polymerization. The monomers used herein were Eriochrome black T (EBT), and polymerization was conducted in acetonitrile. Raman spectroscopy followed the chemical changes occurring at each stage of the carbon surface modification.The device performance was assessed by evaluating the changes in electron transfer properties of a standard redox probe [Fe(CN)6]3−/[Fe(CN)6]4− by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square wave voltammetry (SWV). SWV and EIS electrochemical techniques were used to calibrate the system, having standard solutions prepared under different background media (electrolyte or water coming from a home fish tank). A wide linear range was observed, with linear responses of current/resistance against log (CAP concentration) down to 10nM.Overall, the results obtained revealed that all modifications carried out on the sensing element were effective. The final sensor provided reproducible and accurate readings and was all assembled in-situ, in a very simple and straightforward approach, most likely suitable for scaling-up, directing towards its subsequent commercial use.

Basic electrochemical properties of sputtered gold film electrodes

Gold nanolayers made by sputtering of pure gold (physical vapour deposition) are commonly used for many biophysical and material applications. However, the use of sputtering method for fabrication of working electrodes for electroanalytical purposes is less common. This paper focuses on the testing and characterization of sputtered working roughened gold nanostructured film electrodes, which fall into category of upcoming desirable new generation of nanostructured gold working electrodes. Gold nanostructured films (80nm thin) were sputtered onto 50μm thin PTFE substrates with three different types of treatment: pristine, plasma treated, and plasma treated and subsequently spontaneously grafted with biphenyl-4,4′-dithiol.The characterization of gold nanostructured film electrodes was carried out by examination of the electrode reaction of standard redox probes (ferrocyanide/ferricyanide, hydroquinone/benzoquinone) in different types of supporting electrolytes (BR buffers of various pH, KCl, KNO3, H2SO4), by exploration of the electrode surface by scanning electron microscopy, by atomic force microscopy accompanied by elementary analysis and contact angle measurements. The testing of electrodes was complemented by an attempt to calculate their real surface areas from Randles-Sevcik equation. All results were compared to conventional bulk gold electrode. The practical applicability of the nanostructured gold electrodes as sensors for the determination of environmental pollutants was verified by voltammetric determination of hydroquinone as a model electrochemically oxidisable organic environmental pollutant.

Ultra-Wide-Range Electrochemical Sensing Using Continuous Electrospun Carbon Nanofibers with High Densities of States

Carbon-based sensors for wide-range electrochemical detection of redox-active chemical and biological molecules were fabricated by the electrospinning of polyacrylonitrile fibers directly onto a polyacrylonitrile-coated substrate followed by carbonization at 1200 °C. The resulting electrospun carbon nanofibers (ECNFs) were firmly attached to the substrate with good mesh integrity and had high densities of electronic states (DOS), which was achieved without need for further modifications or the use of any additives. The mass of ECNFs deposited, and thus the electroactive surface area (ESA) of the sensor, was adjusted by varying the electrospinning deposition time, thereby enabling the systematic manipulation of the dynamic range of the sensor. A standard redox probe (Fe(CN)6(3-/4-)) was used to demonstrate that the ECNF sensor exhibits strong electrocatalytic activity without current saturation at high analyte concentrations. Dopamine was used as a model analyte to evaluate the sensor performance; we find that the ECNF device exhibits a dynamic range ∼10(5) greater than that of many existing carbon-based sensors. The ECNF sensors exhibited excellent sensitivity, selectivity, stability, and reproducibility for dopamine detection.

Electroanalytical Sensing Properties of Pristine and Functionalized Multilayer Graphene

This paper describes the heterogeneous electron transfer (ET) properties of high-quality multilayer graphene (MLG) films grown using chemical vapor deposition (CVD) on nickel and transferred to insulating poly(ethylene terephthalate) (PET) sheets. An oxygen plasma treatment is used to enhance the ET properties of the films by generating oxygenated functionalities and edge-plane sites and defects. Scanning electron microscopy (SEM), Raman, and X-ray photoelectron spectroscopy (XPS) along with voltammetry of the standard redox probes [Ru(NH3)6]3+/2+, [Fe(CN)6]3–/4–, and Fe3+/2+ are used to demonstrate this effect. The biologically relevant molecules dopamine, NADH, ascorbic acid, and uric acid are employed to show the improved sensing characteristics of the treated films. Control experiments involving commercially available edge-plane and basal-plane pyrolytic graphite (EPPG and BPPG) electrodes help to explain the different responses observed for each probe, and it is shown that, in certain cases, treated MLG provides a viable alternative to EPPG, hitherto considered to be the “best-case scenario” in carbon electrochemistry. This is the first comprehensive study of the electroanalytical properties of pristine and functionalized CVD-grown MLG, and it will serve as an important benchmark in the clarification of ET behavior at graphene surfaces, with a view to the development of novel electrochemical sensors.

Electroanalytical sensing of chromium(iii) and (vi) utilising gold screen printed macro electrodes

We report the fabrication of gold screen printed macro electrodes which are electrochemically characterised and contrasted to polycrystalline gold macroelectrodes with their potential analytical application towards the sensing of chromium(III) and (VI) critically explored. It is found that while these gold screen printed macro electrodes have electrode kinetics typically one order of magnitude lower than polycrystalline gold macroelectrodes as is measured via a standard redox probe, in terms of analytical sensing, these gold screen printed macro electrodes mimic polycrystalline gold in terms of their analytical performance towards the sensing of chromium(III) and (VI), whilst boasting additional advantages over the macro electrode due to their disposable one-shot nature and the ease of mass production. An additional advantage of these gold screen printed macro electrodes compared to polycrystalline gold is the alleviation of the requirement to potential cycle the latter to form the required gold oxide which aids in the simplification of the analytical protocol. We demonstrate that gold screen printed macro electrodes allow the low micro-molar sensing of chromium(VI) in aqueous solutions over the range 10 to 1600 μM with a limit of detection (3σ) of 4.4 μM. The feasibility of the analytical protocol is also tested through chromium(VI) detection in environmental samples.

Development of inlaid electrodes for whole column electrochemical detection in HPLC

An electrochemical microfluidic device has been fabricated on PET (polyethylene terephthalate) substrate using an imprinting method. The imprinting transfers patterns from a stamp into a substrate mechanically. However, a blanket mould imprinting process has been introduced to embed the photolithographically produced gold metal electrode lines into the PET substrate resulting in an individually addressable array flush to better than 100 nm. The device formed one wall of a packed chromatography column. The array was electrochemically characterised using standard redox probes in both stagnant conditions and under flow. Both numerical modelling and experimental data show improved sensitivity under flow and a limiting current which scaled linearly with the cube root of the volume flow rate. A chromatographic separation of the bioanalytical significant neurotransmitter dopamine (DA) and its metabolite DOPAC was achieved and electrochemically detected at multiple locations within the column. The PET device was stable and robust to leaks to pressures well in excess of those required for chromatographic separations.