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.     

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 Behavior and Determination of L‐Tyrosine at Single‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

Based on single‐walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE/SWCNTs), a novel method was presented for the determination of L ‐tyrosine. The GCE/SWCNTs exhibited remarkable catalytic and enhanced effects on the oxidation of L ‐tyrosine. In 0.10 mol/L citric acid‐sodium citrate buffer solution, the oxidation potential of L ‐tyrosine shifted negatively from +1.23 V at bare GCE to +0.76 V at GCE/SWCNTs. Under the optimized experimental conditions, the linear range of the modified electrode to the concentration of L ‐tyrosine was 5.0×10^?6–2.0×10^?5 mol/L (R₁=0.9952) and 2.7×10^?5–2.6×10^?4 mol/L (R₂=0.9998) with a detection limit of 9.3×10^?8 mol/L. The kinetic parameters such as α (charge transfer coefficient) and D (diffusion coefficient) were evaluated to be 0.66, 9.82×10^?5 cm² s^?1, respectively. And the electrochemical mechanism of L ‐tyrosine was also discussed.     

A Sensitive Electrochemical Approach for Melamine Detection Using a Disposable Screen Printed Carbon Electrode

We report here a simple and easy electrochemical approach for sensitive detection of non‐electroactive melamine using a disposable screen printed carbon electrode (SPCE) with uric acid as the recognition element. It is based on the competitive adsorptive behavior of melamine at the preanodized SPCE causing suppression in the oxidation current of uric acid. A linear range up to 126 ppb with a detection limit of 1.6 ppb (S/N=3) is achieved at the preanodized SPCE by differential pulse voltammetry. The electrochemical method is successfully applied to detect the melamine content in tainted milk powder and dog food.     

Screen Printed Carbon Electrode Modified with Poly(L‐Lactide) Stabilized Gold Nanoparticles for Sensitive As(III) Detection

Poly(L ‐lactide) stabilized gold nanoparticles (designated as PLA–Au^NP) with an average particle size of ca. 10 nm were used to modify a disposable screen‐printed carbon electrode (SPE) for the detection of As(III) by differential pulse anodic stripping voltammetry. Gold modification was evaluated by cyclic voltammetry, whereas scanning electron microscopy and transmission electron microscopy revealed the size and distribution of gold nanoparticles. The PLA–Au^NP/SPE was applied effectively to detect toxic As(III) in HCl medium. Under the optimal experimental conditions, a linear calibration curve up to 4 ppm with a detection limit (S/N=3) of 0.09 ppb was obtained. The sensitivity was good enough to detect As(III) at levels lower than the current EPA standard (10 ppb). Most importantly, the PLA–Au^NP/SPE can be tolerable from the interference of Cu, Cd, Fe, Zn, Mn, and Ni and hence provides a direct and selective detection method for As(III) in natural waters. Practical utility of the PLA–Au^NP/SPE was demonstrated to detect As(III) in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei‐Men).     

Electrocatalytic Reduction and Determination of Dissolved Oxygen at a Preanodized Screen‐Printed Carbon Electrode Modified with Palladium Nanoparticles

Efficient and stable electrocatalytic activity for the reduction of O₂ at activated screen‐printed carbon electrodes modified with palladium nanoparticles (SPE*‐Pd) was demonstrated in this study. X‐ray photoelectron spectroscopy confirmed the formation of >C?O functional group on electrode surface during the preanodization procedure at 2.0 V (vs. Ag/AgCl). The existence of chloride moieties was also identified possibly from the organic binder of carbon ink used in SPE fabrication. Both >C?O and chloride functional groups were essential for the excellent stability of the SPE*‐Pd. Electrochemical impedance spectroscopy verified the enhanced kinetic rate of oxygen reduction reaction at the as‐prepared Pd nanoparticles. The SPE*‐Pd showed ca. 250 mV positive shift in peak potential together with twice increase in peak current compared to those observed at a SPE‐Pt. The calibration plot was linear up to 8 ppm of DO with sensitivity and regression coefficient of 4.49 μA/ppm and 0.9936, respectively. The variation coefficient of i_pc for 7 DO determinations with O₂‐saturated pH 7.4 PBS was 2.1%. Real sample assays for ground and tap waters gave consistent values to those measured by a commercial dissolved oxygen meter.     

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.     

Voltammetric Determination of L‐Dopa on Poly(3,4‐ethylenedioxythiophene)‐Single‐Walled Carbon Nanotube Composite Modified Microelectrodes

In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4‐)ethylenedioxythiophene and single‐walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4‐dihydroxy‐L ‐phenylalaines (L ‐dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film‐coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10 V s^?1, also gave rise to two well‐resolved oxidation peaks for L ‐dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L ‐dopa in the concentration range between 0.1 to 20 μM with a detection limit of 100 nM.     

Electroanalytical Sensor Based on Unmodified Screen‐Printed Carbon Electrode for the Determination of Levo‐Thyroxine

The electrochemical behaviour of thyroxine (T₄) is analysed using the disposable screen‐printed carbon electrode (SPCE) in the neutral phosphate buffer solution with cyclic voltammetric technique. The Differential Pulse Voltammetry and Chronoamperometry were employed for sensing of T₄. The lowest detection limit of 3 nM was obtained from the differential pulse voltammetric method without preconditioning. The Density Functional Theoretical study of T₄ was performed to elucidate the mechanism of oxidation. The analysis of the commercial pharmaceutical samples indicates the validity of the proposed method.     

Fast Electrochemical Characterization of Historical Glasses Using Carbon Screen‐Printed Electrodes and Ultrasonic Assisted Sampling

A new method for lead oxide (PbO) analysis in glasses, using a carbon screen printed electrode (SPE) is proposed. A suspension of the powdered glass sample in nitric acid is prepared using an ultrasonic probe, 100 µL of slurry are deposited on the SPE and the voltammetric measurement is carried out. Structural information of PbO in the glass matrix is obtained by CV. Lead quantification is performed by DPV. In the best conditions a LOD of 2.30 wt% of PbO was obtained. The method has been applied with good results in the analysis of historical glasses samples.     

Label‐Free Electrochemical Aptasensor for Determination of Chloramphenicol Based on Gold Nanocubes‐Modified Screen‐Printed Gold Electrode

An ultrasensitive label‐free electrochemical aptasensor was developed for selective detection of chloramphenicol (CAP). The aptasensor was made using screen‐printed gold electrode modified with synthesized gold nanocube/cysteine. The interactions of CAP with aptamer were studied by cyclic voltammetry, square wave voltammetry (SWV) and electrochemical impedance spectroscopy. Under optimized conditions, two linear calibration curves were obtained for CAP determination using SWV technique, from 0.03 to 0.10 µM and 0.25–6.0 µM with a detection limit of 4.0 nM. The aptasensor has the advantages of good selectivity and stability and applied to the determination of CAP in human blood serum sample.     

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.     

Nanochannel Array on Electrochemically Polarized Screen Printed Carbon Electrode for Rapid and Sensitive Electrochemical Determination of Clozapine in Human Whole Blood

Rapid and highly sensitive determination of clozapine (CLZ), a psychotropic drug for the treatment of refractory schizophrenia, in patients is of great significance to reduce the risk of disease recurrence. However, direct electroanalysis of CLZ in human whole blood remains a great challenge owing to the remarkable fouling that occurs in a complex matrix. In this work, a miniaturized, integrated, disposable electrochemical sensing platform based on the integration of nanochannel arrays on the surface of screen-printed carbon electrodes (SPCE) is demonstrated. The device achieves high determination sensitivity while also offering the electrode anti-fouling and anti-interference capabilities. To enhance the electrochemical performance of SPCE, simple electrochemical polarization including anodic oxidation and cathodic reduction is applied to pretreat SPCE. The electrochemically polarized SPCE (p-SPCE) exhibits an enhanced electrochemical peak signal toward CLZ compared with bare SPCE. An electrochemically assisted self-assembly method (EASA) is utilized to conveniently electrodeposit a vertically ordered mesoporous silica nanomembrane film (VMSF) on the p-SPCE, which could further enrich CLZ through electrostatic interactions. Owing to the dual signal amplification based on the p-SPCE and VMSF nanochannels, the developed VMSF/SPCE sensor enables determination of CLZ in the range from 50 nM to 20 μM with a low limit of detection (LOD) of 28 nM (S/N = 3). Combined with the excellent anti-fouling and anti-interference abilities of VMSF, direct and sensitive determination of CLZ in human blood is also achieved.     

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.     

Determination of Total PSA Using Magnetic Beads and a Re‐usable Screen Printed Carbon Electrode Array

A total PSA (tPSA) assay using magnetic beads (1 µm) and a re‐usable 8‐channel screen printed electrochemical array is here reported. The reaction scheme is based on a one step sandwich assay. The linear range obtained is comprised between 5 and 100 ng/mL of tPSA and have a limit of detection of 1.86 ng/mL. This methodology was validated, performing determination of tPSA in serum and the results were compared with a commercial ELISA kit.     

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.     

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.     

Electrochemical Determination of Pyrogallol at Conducting Poly(3,4‐ethylenedioxythiophene) Film‐Modified Screen‐Printed Carbon Electrodes

The electrochemical oxidation of pyrogallol at electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film‐modified screen‐printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow‐injection amperometry, was obtained for 1–1000 µM pyrogallol, and a slope of 0.030 µA/µM was obtained. The detection limit (S/N=3) was 0.63 µM.     

Sensitive Determination of Nitrofurantoin by Flow Injection Analysis Using Carbon Nanofiber Screen Printed Electrodes

In this work, a new method to quantify nitrofurantoin in aqueous media using a flow injection system connected to commercially available screen‐printed carbon nanofibers was developed. A pretreatment of the screen‐printed carbon nanofibers electrode with Britton? Robinson buffer/N,N‐dimethylformamide was applied to enhance the nitrofurantoin peak current signal in one step. The developed method was demonstrated to be sensible, reproducible, easy, and inexpensive. With a low detection limit, it is applicable to real samples. The results indicate that it is highly applicable for the detection of nitrofurantoin in several matrices. When urine samples without any pretreatment were analyzed, the method proved reproducible and sensible and had a low detection limit. The use of screen‐printed electrodes has advantages over other modified electrodes as a glassy carbon due to its versatility.     

Determination of Iodide and Idoxuridine at a Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Modified Glassy Carbon Electrode

The detection limit (about 0.017 μg mL^?1) for voltammetric determination of iodide (peak at +0.87 V vs. Ag/AgCl at pH 2) at a glutaraldehyde‐cross‐linked poly‐L ‐lysine modified glassy carbon electrode involving oxidation to iodine was found to be several orders of magnitude lower than that for the voltammetric determination on a bare glassy carbon electrode. This method was applied successfully to the determination of iodide in two medicinal formulations. Idoxuridine was determined indirectly at the same electrode by accumulating it first at ?0.8 V vs. Ag/AgCl. At this potential the C? I bond in the adsorbed idoxuridine is reduced giving iodide, which is then determined at the modified electrode. The method was successfully applied to the determination of idoxuridine in a urine sample.