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.     

SiO2-modified carbon paste electrode for electrochemical determination of pyrogallol

A silica gel-modified carbon paste electrode (Si-CPE) was fabricated and used for determination of pyrogallol. Cyclic and differential pulse voltammetric studies show that Si-CPE lowers oxidation potential remarkably increases its oxidation peak current and improves electrochemical behavior of pyrogallol, compared to unmodified CPE. The effects of pH value, amount of silica, accumulation potential and time on the oxidation peak current of pyrogallol were examined. As a result, a sensitive, rapid and convenient electroanalytical method was developed for pyrogallol. The linear range is from 2 to 300 μM, and the limit of detection is 0.7 μM after 4.0 min accumulation. Interferences from some inorganic salts and organic compounds were studied. Finally, the method was successfully used to determine pyrogallol in tap water, green tea and artificial urine samples     

Treated Screen Printed Electrodes Based on Electrochemically Reduced Graphene Nanoribbons for the Sensitive Voltammetric Determination of Dopamine in the Presence of Uric Acid

In this research, the graphene oxide nanoribbons (GONRs) were substantially synthesized by the oxidative longitudinal unzipping of the multi‐walled carbon nanotubes (MWCNTs). Then, a direct electrochemical technique was employed for reducing GONRs adsorbed on the screen printed carbon electrode (SPCE). Electrochemical reduction effectively eliminated the oxygen‐containing groups in the GONRs and produced the electrochemically reduced graphene nanoribbons (ERGNRs). Field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were employed to characterize the materials. The modified SPCE with ERGNRs (ERGNRs/SPCE) displayed acceptable electrocatalytic characteristics towards the oxidation of dopamine (DA) and uric acid (UA) and applied to the simultaneous determination of these two analytes. ERGNRs/SPCE has a peak potential difference of 245 mV between DA and UA. The anodic peak currents of DA and UA were linear within the concentration ranges between 0.5 and 300.0 μM and 1.0 to 400.0 μM in phosphate buffer (pH=7.0) respectively. The detection limit of the technique for DA is 0.15 μM (S/N=3) and for UA is 0.3 μM (S/N=3). The proposed approach has been applied to the determination of DA and UA in real samples and generated acceptable outputs.     

Amperometric Biosensors for Tyramine Determination Based on Graphene Oxide and Polyvinylferrocene Modified Screen‐printed Electrodes

A comparison of the analytical characteristics of two tyramine biosensors, based on graphene oxide (GRO) and polyvinylferrocene (PVF) modified screen‐printed carbon electrodes (SPCE), is reported. Diamine oxidase (DAOx) or monoamine oxidase (MAOx) was immobilized onto the PVF/GRO modified SPCE to fabricate the biosensors. Surface characteristics and electrochemical behaviour of the modified SPCEs were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and cyclic voltammetry (CV). Electrode surface composition and experimental variables such as pH and working potential were optimized in order to ensure a high performance. Under optimum experimental conditions, both DAOx/PVF/GRO/SPCE and MAOx/PVF/GRO/SPCE biosensors exhibited wide linear dynamic ranges for tyramine from 9.9×10^?7 to 1.2×10^?4 M and from 9.9×10^?7 to 1.1×10^?4 M, respectively. MAOx/PVF/GRO/SPCE biosensor showed higher sensitivity (11.98 μA mM^?1) for tyramine determination than the DAOx/PVF/GRO/SPCE biosensor (7.99 μA mM^?1). The substrate specifity of the biosensors to other biogenic amines namely histamine, putrescine, spermine, spermidine, tryptamine, β‐phenylethylamine and cadaverine was also investigated. The developed biosensors were successfully used for tyramine determination in cheese sample.     

Electrochemical Characteristics and Electrosensing of an Antiviral Drug,Entecavir via Synergic Effect of Graphene Oxide Nanoribbons and Ceria Nanorods

A sensitive electrochemical sensor was fabricated based on ceria‐graphene oxide nanoribbons composite (CeO₂‐GONRs) for an antiviral drug, entecavir (ETV). It was characterized by SEM, EDAX, AFM, IR and Raman spectroscopic techniques. The electrochemical behaviour of ETV was investigated by cyclic voltammetric, differential pulse voltammetric (DPV), linear sweep voltammetric (LSV) and square wave voltammetric (SWV) methods at CeO₂‐GONRs modified glassy carbon electrode. Good linearity was observed between the peak current and concentration of ETV in the range of 0.51 ‐ 100 μM with a detection limit of 0.042 μM in DPV method, 2.1 – 61.1 μM with a detection limit of 0.7 μM in LSV method and 0.1 ‐ 80 μM with a detection limit of 68.1 nM in SWV method. The proposed sensitive DPV method was successfully applied for the determination ETV in tablets and biological samples.     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

Selective Voltammetric Detection of Uric Acid in the Presence of Ascorbic Acid at Well‐Aligned Carbon Nanotube Electrode

The voltammetric behaviors of uric acid (UA) and L ‐ascorbic acid (L ‐AA) were studied at well‐aligned carbon nanotube electrode. Compared to glassy carbon, carbon nanotube electrode catalyzes oxidation of UA and L ‐AA, reducing the overpotentials by about 0.028 V and 0.416 V, respectively. Based on its differential catalytic function toward the oxidation of UA and L ‐AA, the carbon nanotube electrode resolved the overlapping voltammetric response of UA and L ‐AA into two well‐defined voltammetric peaks in applying both cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which can be used for a selective determination of UA in the presence of L ‐AA. The peak current obtained from DPV was linearly dependent on the UA concentration in the range of 0.2 μM to 80 μM with a correlation coefficient of 0.997. The detection limit (3δ) for UA was found to be 0.1 μM. Finally, the carbon nanotube electrode was successfully demonstrated as a electrochemical sensor to the determination of UA in human urine samples by simple dilution without further pretreatment.     

Development of an Aluminium Doped TiO2 Nanoparticles‐modified Screen Printed Carbon Electrode for Electrochemical Sensing of Vanillin in Food Samples

A new chemically modified electrode based on titanium dioxide nanoparticles (TiO₂‐NPs) has been developed. Aluminium was incorporated into the TiO₂‐NPs to prepare aluminium doped TiO₂ nanoparticles (Al‐TiO₂‐NPs). Aluminium doped TiO₂ nanoparticles‐modified screen printed carbon electrode (Al‐TiO₂‐NPs/SPCE) was employed as easy, efficient and rapid sensor for electrochemical detection of vanillin in various types of food samples. Al‐TiO₂‐NPs were characterized by energy‐dispersive X‐ray (EDX), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) and analyses showing that the average particle sizes varied for the Al‐NPs (7.63 nm) and Al‐TiO₂‐NPs (7.47 nm) with spherical crystal. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to optimize the analytical procedure. A detection limit of vanillin was 0.02 μM, and the relative standard deviation (RSD) was 3.50 %, obtained for a 5.0 μM concentration of vanillin. The electrochemical behaviour of several compounds, such as vanillic acid, vanillic alcohol, p‐hydroxybenzaldehyde and p‐hydroxybenzoic, etc., generally present in natural vanilla samples, were also studied to check the interferences with respect to vanillin voltammetric signal. The applicability was demonstrated by analysing food samples. The obtained results were compared with those provided by a previous method based on liquid chromatography for determination of vanillin.     

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S‐Functionalized Self‐Assembled Layers in Aqueous Solution

Gold nanoparticles (Au‐NPs), cystamine (CA) and 3,3′‐dithiodipropionic acid (DTDPA) modified gold bare electrodes were applied in voltammetric sensors for simultaneous detection of norepinephrine (NEP), ascorbic (AA) and uric (UA) acids. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1 μM to 600 μM M with the detection limit ≤0.091 μM for the electrodes modified at 2D template and in the range of 0.1 μM to 700 μM M with the detection limit ≤0.087 μM for the electrodes modified at 3D template The results have shown that using modified electrodes it is possible to perform electrochemical analysis of norepinephrine without interference of ascorbic and uric acids, whose presence is the major limitation in norepinephrine determination at a bare gold electrode. The modified SAMs electrodes show good selectivity, sensitivity, reproducibility and high stability.     

Voltammetric Determination of Urinary 1‐Hydroxypyrene Using Molecularly Imprinted Polymer‐Modified Screen‐Printed Carbon Electrodes

A two step non‐competitive affinity method for the trace determination of 1‐hydroxypyrene (1‐OHP) using a disposable molecularly imprinted polymer (MIP) modified screen‐printed carbon electrode (MIP‐SPCE) has been developed. The MIP was synthesized according to a novel strategy, which is described, and is capable of rebinding the phenolic analyte, 1‐hydroxypyrene (1‐OHP), from high pH aqueous organic media, via ionic interactions. In the first step of our method 1‐OHP was accumulated at the MIP‐SPCE from 35% aqueous methanol containing 0.014 M NaOH and 0.14 M NaCl, at open circuit. In the second step, the resulting SPCE with accumulated 1‐OHP was then transferred to fresh, clean phosphate buffered aqueous methanol, and subjected to cyclic voltammetry (CV) or differential pulse voltammetry (DPV). The latter technique proved to be more sensitive at detecting 1‐OHP, with a limit of detection of 182 nM and a linear range to 125 μM on unmodified electrodes. The possible effects of interference by related phenolic compounds in the MIP‐SPCE of 1‐OHP were investigated. Finally the method was evaluated by carrying out 1‐OHP determinations on spiked human urine samples; the recovery of 1‐OHP was 79.4% and the coefficient of variation was found to be 7.7% (n= 4) using a separate MIP‐SPCE for each determination. Therefore, the performance data suggests that the method is reliable at the concentrations examined in this study. The method was found to be superior to the direct determination of 1‐OHP in human urine by DPV alone, which was greatly affected by interference from uric acid.     

Rapid Determination of Phenolic Compounds in Water Samples: Development of a Paper‐based Nanobiosensor Modified with Functionalized Silica Nanoparticles and Potato Tissue

In this study, we present a fast, simple, low‐cost and disposable method for determination of phenolic content in water samples, using a paper based polyphenol oxidase biosensor. The propylamine functionalized silica nanoparticles was dropped onto a paper sheet. After drying at room temperature, the potato tissue extract including polyphenol oxidase was immobilized on the paper via physical and chemical adsorption. The modified paper was placed on the top of the graphite screen printed electrode. To construct of an electrochemical nanobiosensor, the electrochemical behavior of the modified electrode in different steps was investigated by cyclic voltammetry and electrochemical impedance spectroscopy methods. After being optimized the effective parameters, the changes in the biosensor electrochemical response vs. to the different concentrations of the substrate (phenol solution) were monitored by differential pulse voltammetry and amperometry methods. The linear relationships for phenol detection were obtained in the concentration ranges of 0.01–160 μM and 0.1–300 μM with a detection limit of 0.007 μM and 0.042 μM with DPV and amperometry methods, respectively. This method was successfully used in the voltammetric determination of the phenol content in the real samples, like the river water and the wastewater of wood factory.     

Highly Sensitive and Selective Adsorptive Stripping Voltammetric Method Employing a Lead Film Screen‐printed Electrode for Determination of Cobalt as its Nioximate Complex

A carbon screen‐printed electrode modified in‐situ with lead film (PbF‐SPCE) was applied for the adsorptive stripping voltammetric determination of Co(II) in the form of a complex with 1,2‐cyclohexanedione dioxime. Lead film was electrochemically deposited in situ on SPCE from a 0.2 M ammonia buffer solution (pH 8.7) containing 5 ? 10^?5 M Pb(NO₃)₂ and 5 ? 10^?5 M nioxime. Due to the very low LOD (0.003 µgL^?1, i.e., 0.05 nmol L^?1 Co(II); t_acc=120s), the developed procedure could be rated among the most sensitive methods employing SPEs. The Ni(II) signal was significantly lower than the Co(II) one and the separation of Ni(II) and Co(II) peaks was even better at the PbF‐SPCE than at the hanging mercury drop electrode.     

Voltammetric Determination of 4‐Nitrophenol Using a Novel Type of Silver Amalgam Paste Electrode

A differential pulse voltammetric (DPV) method was developed for the determination of 4‐nitrophenol (4‐NP) at a newly developed silver amalgam paste electrode (AgA‐PE) in Britton–Robinson buffer pH 3.0. The electrode is based on a disposable plastic pipette tip filled with paste amalgam based on a mixture of mercury and fine silver powder (9 : 1, w/w). The experimental parameters, such as pH of Britton–Robinson buffer and activation and regeneration potential of the electrode surface were optimized. The reduction peak current dependences were linear for the concentration of 4‐NP from 0.2 to 100 μM. The method showed reproducible results with RSD (n=45) of 1.7%. The limit of determination (LOD) was 0.3 μM. The method was successfully applied for the direct determination of 4‐NP in drinking water.     

Amperometric Detection of 4‐Chlorophenol on Two Types of Expanded Graphite Based Composite Electrodes

The assessment of an expanded graphite‐Ag‐zeolite‐epoxy composite (EG‐Z‐Ag‐Epoxy) electrode for the determination of 4‐chlorophenol (4‐CP) is described and compared to the corresponding expanded graphite‐epoxy composite (EG‐Epoxy) electrode. Cyclic voltammetry was used to characterize the electrochemical behavior and determination of 4‐CP at both electrodes in 0.1 M Na₂SO₄ and 0.1 M NaOH supporting electrolytes. A substantial enhancement of sensitivity for the determination of 4‐CP at the EG‐Z‐Ag‐Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric quantification. Also, under these last conditions the lowest limit of detection of 1 μM illustrates the analytical versatility of this electrode in a concentration range where aquatic 4‐chlorophenol pollution is known to occur.     

Polyaniline Sheathed Black Phosphorous: A Novel,Advanced Platform for Electrochemical Sensing Applications

Despite its excellent properties, the inherent unstable nature of black phosphorus (BP) in ambient atmosphere has severely restricted its use in electrochemical sensing applications. In this work, polyaniline (PANI) sheathed BP was prepared via the electrochemical polymerisation of aniline on BP coated screen printed carbon electrode (i. e., SPCE/BP) which resulted in an efficient, stable electrochemical platform (i. e., SPCE/BP@PANI) with improved properties which was evaluated for electrochemical detection of two model bioanalytes namely, ascorbic acid (AA) and Hydrazine (Hy). The formation of PANI on the SPCE/BP exhibited a pair of stable and well‐defined redox peaks indicating the better adsorption energy and fast electron transfer nature of BP as compared to other 2D materials like graphene and transitional metal dichalcogenides. FESEM and XPS studies revealed the formation and uniform growth of PANI on BP surface without any aggregation. Electrochemical impedance spectroscopy analyses revealed that SPCE/BP@PANI can act as a suitable electrocatalyst material for the sensing of AA and Hy. Thus, SPCE/BP@PANI electrode exhibited low limit of detection (D_L; 1.69 μM), excellent reproducibility and better selectivity towards AA oxidation over glucose, sucrose, urea, citric acid, sodium, nitrate, nitrite and magnesium with a sensitivity of 3.38 A M^?1 cm^?2 (R²=0.98) in the dynamic range of 10–1100 μM. The excellent analytical performance of the BP@PANI is plausible due to better adsorption energy and fast electron transfer of BP. Further, SPCE/BP@PANI was also used for successful detection of AA in processed fruit juice with good recovery. Under the optimal DPV conditions, the modified electrode was extended for detection of Hy in a linear range of 100–1500 μM with sensitivity of 0.09 A M^?1 cm^?2 (R²=0.99) and D_L=89 μM validating the potential of BP based composites in wide range of electrochemical applications.     

Fabrication of Conductive Polypyrrole Doped Chitosan Thin Film for Sensitive Detection of Sulfite in Real Food and Biological Samples

In this study, we reported electrochemical synthesis of conductive polypyrrole‐chitosan (PPY‐CHI) thin film for sensitive detection of sulfite in real samples. The synthesized PPY‐CHI film was characterized in terms of surface morphology, optical property, binding energy, conductivity and electrochemical properties. The synthesized copolymeric PPY‐CHI film displayed good electrocatalytic behaviour towards oxidation of sulfite. The synthesized PPY‐CHI film was used for sulfite detection using differential pulse voltammetric technique with detection limit, sensitivity and linearity of 0.21 μM (S/N=3), 15.28 μA μM cm^?2 and 50–1100 μM respectively. In addition, the current responses of PPY‐CHI film towards sulfite were repeatable, reproducible response and unaffected by selected electroactive interferents. Finally, the synthesized PPY‐CHI was successfully and satisfactorily applied for determination of sulfite in real food and biological samples. The results obtained from this study highly placed PPY‐CHI film as a promising sensor for sensitive and accurate detection of sulfite in food and biological samples for human health protection.     

An Electrochemical Sensor Based on Nitrogen‐doped Carbon Nanofiber for Bisphenol A Determination

In this paper, bisphenol A was determined by electrochemical method at a nitrogen‐doped carbon nanofiber modified carbon paste electrode (NCNF/CPE) with high sensitivity and good selectivity. NCNF was obtained by a simple electrospinning followed by carbonization procedure, in which polyacrylonitrile (PAN) as precursor and nitrogen doping was realized by re‐utilizing the tail gas that produced in the thermal pretreatment process. Good reproducibility and high stability were obtained for BPA detection at NCNF modified CPE. Current response plotted with BPA concentration was linear in the range of 0.1–60 μM with LOD of 0.05 μM. The proposed electrochemical sensor was employed for BPA determination with satisfactory recoveries for real water samples, indicating the practical applicability of NCNF/CPE.     

Selective Electroanalytical Assay for Cysteine at a Boron Doped Diamond Electrode

The electrochemical oxidation of the cysteine‐quinone adduct has been examined as a means of providing an electroanalytical cysteine specific detection protocol. The appliance of square‐wave voltammetry allowed 0.5 μM as a limit of detection. The effects of various biologically relevant interferences including other thiols were studied and found to present no change in the voltammetric profile. The practical applicability and efficiency of the methodology was probed through the determination of cysteine concentration in growth tissue medium.     

Voltammetric Determination of Boric Acid Using the Ternary Complexation System with Salicylaldehyde and H‐Acid

A square‐wave voltammetric method for the determination of boric acid in water has been described based on the new understanding of the electrochemical behavior of boric acid‐Azomethine H complexation. Salicylaldehyde and H‐acid were used as the starting materials of boric acid‐Azomethine H complex and their concentrations were optimized for boric acid determination in water. A glassy carbon electrode, instead of a conventional mercury electrode, was used in the measurement. The detection limit of the proposed method was 0.10 mg B dm^?3. The proposed method was successfully used for boric acid determination in the water from a seawater desalination RO plant.     

Cobalt nanoparticles anchored to porous silicon as a novel modifier for the construction of enzyme‐free hydrogen peroxide screen‐printed sensor

In this work, a screen‐printed carbon electrode (SPCE) was modified with a cobalt/porous silicon (Co@PSi) nanocomposite powder to develop a nonenzymatic sensor for the detection of hydrogen peroxide. The Co@PSi nanocomposite was synthesized through the chemical reaction between silicon powder in a HF/HNO₃ solution and cobalt cations. In this process, cobalt nanoparticles were anchored on the porous silicon. The structure and morphology of the synthesized nanocomposite were investigated by X‐ray diffraction, Fourier transform infrared spectroscopy, X‐ray photoemission spectroscopy, energy dispersive X‐ray spectroscopy, and field‐emission scanning electron microscopy. The constructed nonenzymatic, screen‐printed sensors based on the Co@PSi nanocomposite showed perfect electrocatalytic oxidation response to hydrogen peroxide over the range 1–170 and 170–3,770 μmol/L with the limit of detection of 0.8 μmol/L. In addition, the Co@PSi‐SPCE sensor exhibited good selectivity for the determination of H₂O₂ in the presence of common interfering species including glucose, ascorbic acid, uric acid, dopamine, nitrate, and nitrite ions. The constructed electrochemical sensor was successfully used for the determination of H₂O₂ in real samples.