Electrochemical Characterization of Screen‐Printed Carbon Electrodes by Modification with Chitosan Oligomers

The kinetics on the current amplification of the disposable screen‐printed carbon electrodes (SPCEs) by modification with chitosan oligomers (COs), coupled with the Fe(CN) redox system, were characterized with the variation of electron‐transfer rate constant (k°) and the electroactive area (A_ea) at electrode surface. The nonlinear response characteristics of peak currents with increase in Fe(CN) bulk concentrations complicated the estimation of A_ea in cyclic voltammetric analysis. Upon the modification with COs, the rate constant of SPCEs was not much influenced and the current amplification was characterized with the increase of a better estimated A_ea, obtained from electrochemical impedance measurements and verified with the reciprocal of electron‐transfer resistances linearly proportional to the Fe(CN) bulk concentrations. It is hereby provided for an evaluation of the carbon based electrodes with modification.     

Electrochemical Analysis of Acrylamide Using Screen‐Printed Carboxylated Single‐Walled Carbon Nanotube Electrodes

Acrylamide (AA) was electrochemically detected and quantified by means of its voltammetric response on carboxylic modified Single‐Walled Carbon Nanotube Screen Printed Electrodes (COOH‐SWCNT‐SPEs). The electroreduction signal of AA was proportional to AA concentration at low values (below 300 µM) and the observed sensitivity was explained in terms of AA adsorption on the COOH‐SWCNT‐SPEs that was demonstrated using the electrochemical response of [Fe(CN)₆]^3? and [Fe(CN)₆]^4? and Raman spectroscopy experiments. In order to test the suggested analytic approach (LOD of 0.03 µM, LOQ of 0.04 µM), detection and quantification of AA in fried potatoes was carried out using the proposed electrochemical method and HPLC. Both techniques showed similar contents of AA.     

Facile Fabrication of Zirconia Modified Screen‐Printed Carbon Electrodes for Electrochemical Sensing of Phosphate

We report here a facile method to immobilize zirconia nanoparticles on a disposable screen‐printed carbon electrode (designated as ZrO₂‐SPCE) for phosphate sensor application. Simply by ultrasonicating a bare SPCE in a ZrO₂ slurry, ZrO₂ nanoparticles can be immobilized effectively on the electrode surface as verified by surface characterization evidences. Using ferricyanide as a redox probe, an increase in the charge transfer resistance (R_ct) of ferricyanide upon adsorption of phosphate on ZrO₂ is used for the determination of phosphate. This ZrO₂‐SPCE phosphate sensor shows a wide linear range up to 1 mM and a detection limit of 1.69 µM (S/N=3). Practical applicability of the ZrO₂‐SPCE is demonstrated by detecting phosphate content in human blood samples.     

Electrochemical Oxidation and Sensitive Determination of Acetaminophen in Pharmaceuticals at Poly(3,4‐ethylenedioxythiophene)‐Modified Screen‐Printed Electrodes

The current study reports electrocatalytic oxidation of acetaminophen at screen‐printed electrode (SPE) modified with electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film. Cyclic voltammetric studies show that the SPE/PEDOT electrode lowers overpotentials and improves electrochemical behavior of acetaminophen (ACAP) in aqueous buffer solutions, compared to the bare SPE. Excellent analytical features are achieved, including high sensitivity, low detection limit and satisfactory dynamic range, by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and flow‐injection amperometry (FIA) under optimized conditions. The proposed methods obtain satisfactory results in detection of acetaminophen in two commercial tablets.     

A Capillary Electrophoresis End‐Column Amperometric Detection System Incorporating Disposable Copper‐Plated Screen‐Printed Carbon Electrodes

We report here the development of copper‐plated screen‐printed carbon electrodes (designated as Cu‐SPE) to employ as electrochemical detectors for the determination of sugars by capillary electrophoresis (CE). A simple end‐column amperometric detection system with easily exchangeable (or even disposable) electrode and capillary in CE is described in this study. A complex alignment procedure was not required in this system based on the end‐column electrode arrangement using an 85 cm length and 20 μm (i.d.) capillary. The optimized separation voltage and applied potential were 9 KV and 0.4 V (vs. Ag/AgCl), respectively, for the detection of sugars using the Cu‐SPE. Good resolution was obtained by this proposed system with migration times of 28.8, 29.5, 29.9, 30.7, 31.2, and 32.0 min for galactose, glucose, arabinose, fructose, xylose, and ribose, respectively.     

Lead Sensor Using Gold Nanostructured Screen‐Printed Carbon Electrodes as Transducers

Gold nanostructured screen‐printed carbon electrodes are demonstrated to be suitable transducers for the determination of lead using square‐wave voltammetry. Reproducible gold nanostructures have been obtained by direct electrochemical deposition. A calibration plot from 2.5 to 250 μg/L was obtained in acidic solutions of Pb(II) with a reproducibility of 4% (n=10). The detection limit was 0.09 μg/L of lead. The method is then applied to perform a blood lead analysis by adjusting square‐wave parameters in capillary or venous blood with a minimum sample pretreatment and excellent accuracy and reproducibility.     

Anodic Stripping Voltammetric Determination of Aurothiomalate in Urine Using a Screen‐Printed Carbon Electrode

This work describes an electroanalytical method for determining gold(I) thiomalate, aurothiomalate, widely used for treatment of reumatoid arthiritis, using a screen‐printed carbon electrode (SPCE). Aurothiomalate (AuTM) was determined indirectly at the same electrode by accumulating it first at ?1.5 V vs. printed carbon. At this potential in the adsorbed state, the AuTM is reduced to Au(0), which is then oxidized at two steps at ?0.22 V and +0.54 V on SPCE. Using optimized conditions of 60 s deposition time, ?1.5 V (vs. printed carbon) accumulation potential, 100 mV s^?1 scan rate, linear calibration graphs can be obtained by monitoring the peak at +0.54 V for AuTM in HCl 0.1 mol L^?1 from 1.43×10^?6 to 1.55×10^?4 mol L^?1. A limit of detection obtained was 6.50×10^?7 mol L^?1, and the relative standard deviation from five measurements of 3.0×10^?5 mol L^?1 AuTM is 4.5%. The method was successfully applied for AuTM determination in human urine sample.     

A Facile and Cost‐effective Electroanalytical Strategy for the Quantification of Deoxyguanosine and Deoxyadenosine in Oligonucleotides Using Screen‐printed Graphite Electrodes

The development of electroanalytical methods for the detection and quantification of nucleotides in DNA offers vital implications in assessing the degree of oxidation or epigenetic modification in DNA. Unfortunately, the electrochemical response of oligonucleotides is strongly influenced by the size, composition and nucleic base sequence. In this article, an optimized analytical procedure for the enzymatically breakdown of the oligonucleotides to their corresponding nucleotides for the evaluation of the electrochemical response through the use of square wave voltammetry (SWV) is presented. Enzymatic digestion of oligonucleotides has been optimized in terms of buffer composition, digestion time, strategy for stopping the enzymatic reaction and filtration requirement for enzyme removal, and then compared to an established protocol. Under the optimized protocol SWV response of a number of untreated and enzymatically digested six‐mer oligonucleotides, namely 5′‐GGGGGG‐3′, 5′‐AAAAAA‐3′, 5′‐CGCGCG‐3′ and 5′‐AAACGC‐3′ have been analysed, providing a higher sensitivity for the determination of guanosine and adenosine monophosphate species under digestion conditions with a more facile and cost effective procedure. The novel strategy for the enzymatically treated oligonucleotides in combination with the SWV response provides a proof of principle for feasible applications in the diagnosis of methylated guanosine in DNA as a potential biomarker due to its relation with cancer.     

Screen‐Printed Electrodes for Amperometric Determination of Iodide

An amperometric method for the determination of iodide ions has been developed using disposable, screen‐printed electrodes. The used sensors have a gold, graphite and platinum working electrodes with an area of about 7 mm². Calibration curves exhibit a linear relationship between the electrode response and the iodide concentration up to 3.00 mM. The correlation coefficients for all calibration curves varied from 0.988 to 0.998. The relative standard deviations were equal to or less than 5.26 % (n=5). The lowest iodide concentration measured was 100 µM.     

A Microbial Sensor Based on Direct Electron Transfer at Shewanella Sp. Drop‐Coated Screen‐Printed Carbon Electrodes

Aerobically grown Shewanella sp. bacterial suspension drop‐coated on a disposable screen‐printed carbon electrode was found to possess electroactivity without the aid of redox mediator. Cyclic voltammetric studies revealed the characteristics of a mixed diffusion adsorption‐controlled electrochemical process for direct electron transfer at the bacteria‐modified electrode. Both FE‐SEM and ATR FT‐IR experiments were carried out to investigate the surface characteristics. The electroanalytical applicability was further demonstrated for electrocatalytic reduction of arsenite, hydrogen peroxide and nitrite. Low cost and very simple manufacturing procedure allow for the proposed bacterial sensor to be applied as disposable devices.     

Sensitive Electrochemical Detection of Horseradish Peroxidase at Disposable Screen‐Printed Carbon Electrode

A rapid, simple and sensitive electrochemical assay of horseradish peroxidase (HRP) performed on disposable screen‐printed carbon electrode was developed. HRP activities were monitored by square‐wave voltammetric (SWV) measuring the electroactive enzymatic product in the presence of o‐aminophenol and hydrogen peroxide substrate solution. SWV analysis demonstrated a greater sensitivity and shorter analysis time than the widely used amperometric and differential‐pulsed voltammetric methods. The voltammetric characteristics of substrate and enzymatic product as well as the parameters of SWV analysis were optimized. Under optimized conditions, a linear response for HRP from 0.003 to 0.1 U/mL and a detection limit of 0.002 U/mL (1.25×10^?15 mol in 25 μL) were obtained with a good precision (RSD=8%; n=6). This rapid and sensitive HRP assay with microliter‐assay volume could be readily integrated to portable devices and point‐of‐care (POC) diagnosis applications.     

Electrochemical Behaviour and Rapid Determination of L‐Dopa at Electrochemically Pretreated Screen Printed Carbon Electrode

A simple and rapid voltammetric method based on a disposable electrochemically pretreated screen‐printed carbon electrode is proposed for the determination of L ‐dopa. Under optimum differential pulse voltammetry conditions a limit of detection of 3.6×10^?7 M for L ‐dopa was obtained. The method was successfully applied to the determination of L ‐dopa in a commercial pharmaceutical formulation.     

Incorporation of Disposable Screen‐Printed Electrodes for Use in Capillary Electrophoresis End‐Column Amperometric Detection System

The development and performance of an end‐column amperometric detection system integrated with disposable screen‐printed electrodes for capillary electrophoresis is presented. In this system, the electrode and capillary can be easily replaced and the capillary/electrode alignment procedure is straightforward. The use of easily replaceable screen‐printed electrodes offers a tremendous benefit for capillary electrophoresis applications requiring frequent replacement of the working electrode due to fouling. This simple and convenient system is very attractive for routine analyses by capillary electrophoresis with electrochemical detection. The separation and determination of uric acid in human urine is presented.     

Voltammetric Determination of 5‐Aminoquinoline at Carbon Film Electrode and Carbon and Gold Screen Printed Electrodes – A Comparative Study

Aminoquinolines are widely used as antimalarial drugs and thus there is an ever increasing demand for their determination. In this paper, non‐traditional carbon film electrode developed in our laboratory (CFE) with easily replaceable carbon film was used for the determination of 5‐aminoquinoline (5‐AQ) and compared with well‐established commercially available carbon screen printed electrode (CSPE) and gold screen printed electrode (AuSPE). Electrochemical behavior of 5‐AQ was characterized by cyclic and differential pulse voltammetry. Differences in electrochemical behavior of 5‐AQ at different electrodes were evaluated. Determination of 5‐AQ was carried out by differential pulse, square wave, and direct current voltammetry. Practical applicability of the method was verified by direct determination of 5‐AQ in model samples of drinking and river water. Achieved limits of quantitation were in submicromolar concentrations. It was found out that novel CFE in terms of overall performance is in most aspects superior to routinely used commercially available CSPE and AuSPE.     

Determination of Free Metal Ion Concentrations Using Screen‐Printed Electrodes and AGNES with the Charge as Response Function

AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) has been implemented with screen‐printed electrodes (SPE) for the determination of the free concentration of Zn²⁺, Cd²⁺ and Pb²⁺. For SPE, the stripped charge is a suitable response function which does not require the second stage of AGNES to be under diffusion limited conditions. This property can be used in the avoiding of the interference of Pb on [Cd²⁺] determination. The proportionality factor between stripped charge and concentration of amalgamated metal depends on the volume of mercury and opens the way to a future calibrationless strategy. Zn and Cd complexation with oxalate at various pH‐values confirms the suitability of the developed methodology, which compares favourable with the standard one based on the Hanging Mercury Drop Electrode.     

Novel Preparation and Photoelectrochemical Properties of γ‐CuI Semiconductor Nanocrystallites on Screen‐Printed Carbon Electrodes

Cuprous iodide (γ‐CuI) is an important semiconductor material having a bang gap of 3.1 eV often used for visible light assisted photoelectrochemical and solar energy conservation systems. We report the first and unique preparation of fine and precisely controlled γ‐CuI semiconductor nanocrystallites on the surface of a screen‐printed carbon electrode using a photoelectrochemical copper nanoparticle deposition method with tris(hydroxymethyl)aminomethane (Tris) buffer solution as a control medium. Tris buffer helps to split Cu O and Cu^IIO oxidation states through specific complexation mechanism and in turn to selective iodination of Cu O to the formation of γ‐CuI on the electrode. Stable and linear photoelectrochemical response was further demonstrated against variable light intensity up to 400 Klux using the γ‐CuI modified system.     

A Multiple Evaluation Approach of Commercially Available Screen‐Printed Nanostructured Carbon Electrodes

Commercially available carbon‐based screen‐printed electrodes were studied by cyclic voltammetry and electrochemical impedance spectroscopy in their behavior towards electron transfer to the soluble fast redox probes hexacyanoferrate(III), hexaammineruthenium(III) and methyl‐viologen. Semi‐infinite linear diffusion was observed for hexacyanoferrate(III) probe, with heterogeneous electron transfer rate constants significantly favored on nanotubes‐modified surfaces. Finite diffusion was observed for methyl‐viologen on graphene electrodes, which was reflected in the enhancement of the faradic currents by 4‐folds. Hexaammineruthenium(III) showed mixed diffusion behavior. These characteristics are reflected in the voltammetric behavior of lead(II) and cadmium(II) stripping from in‐situ deposited bismuth layer.     

Homogeneous Platinum‐Deposited Screen‐Printed Edge Band Ultramicroelectrodes for Amperometric Sensing of Carbon Monoxide

We report here the fabrication and application of an electrochemical carbon monoxide (CO) gas sensor based on the deposition of Pt nanoparticles on a screen‐printed edge band ultramicroelectrode (SPUME) with Nafion as the solid polymer electrolyte. Homogeneous size and distribution of Pt nanoparticles is stably deposited on the SPUME without either protective or capped agents. The edge diffusion effect at the SPUME, to even out the generation rate of hydrogen and to speed up the mass transfer of Pt solution, is believed to play a key role in achieving the deposition result. The obvious advantage of the proposed ultramicroelectrode system is that no supporting electrolyte (i.e., internal electrolyte) is required in the sensor scheme. The current–time curve recorded under conditions of +0.45 V vs. pseudo Ag reference electrode and various CO concentrations suggests that current response depends linearly on CO concentration up to 1000 ppm (correlation coefficient=0.994) with a sensitivity of 3.76 nA/(ppm?cm²). This report demonstrates potential application of the disposable CO gas sensor.     

Electrochemical Oxidation and Sensitive Determination of Pyrogallol at Preanodized Screen‐Printed Carbon Electrodes

In this study, we report a simple, low‐cost and rapid electrochemical sensor based on the anodically pretreated screen‐printed carbon electrodes (SPCE*) for the determination of pyrogallol in pH 7.0 buffer solutions. Cyclic voltammetric studies show that SPCE* lowers overpotentials and improve electrochemical behaviour of pyrogallol, compared to untreated SPCE. All experimental parameters were optimized to improve voltammetric responses; excellent analytical features were achieved by flow‐injection amperometric methods. A linear calibration plot was obtained for 10‐1000 μM pyrogallol with a slope of 0.0562 μA/μM. The detection limit (S/N = 3) was 0.33 μM. Interferences from some inorganic salts and organic compounds were studied. The assay was applied to the determination of pyrogallol in tap water and lake water, respectively.     

Voltammetric Behaviour of 7‐Methylguanine Using Screen‐printed Graphite Electrodes: towards a Guanine Methylation Electrochemical Sensor

The determination of 7‐methylguanine (7mG) is an interesting analytical target since its quantification can be correlated with the methylation of cytosine which is one of the most relevant epigenetic modification of DNA. In this work, screen‐printed graphite electrodes were used to study the electrochemical characterization of 7mG by cyclic and square wave voltammetry. 7mG concentration and pH were examined, as well as the repeatability of the measurements. The electrochemical response of 7mG in the presence of guanine and adenine was also investigated. Results aim to the future development of an electrochemical sensor for the methylation degree in DNA.