Synthesis,Characterisation of Novel Polyaniline Nanomaterials and Application in Amperometric Biosensors

Summary: Anthracene sulfonic acid doped polyaniline nanomaterials were prepared through the chemical oxidative polymerisation process. Ammonium peroxydisulfate (APS) was employed as oxidant. Scanning electron microscopy (SEM) results show the resultant polyaniline (PANi) materials exhibited nanofibrillar morphology with diameter sizes less than 300 nm. Using the nanofibrillar PANI, amperometric biosensors for H₂O₂ and erythromycin were constructed through the drop-coating technique. Anthracene sulfonic acid (ASA) doped PANi and the test enzymes horseradish peroxidase, (HRP), or cytochrome P₄₅₀ 3A4, (CYP₄₅₀3A4) were mixed in phosphate buffer solution before drop coating onto the electrode. The resultant biosensors displayed typical Michaelis-Menten behaviour. The apparent Michaelis-Menten constant obtained was 0.18 ± 0.01 mM and 0.80 ± 0.02 µM L⁻¹ for the peroxide and erythromycin biosensor respectively. The sensitivity for the peroxide sensor was 3.3 × 10⁻³ A · cm⁻² · mM⁻¹, and the detection limit was found to be 1.2 × 10⁻² mM respectively. Similarly, the sensitivity for the erythromycin sensor was in the same order at 1.57 × 10⁻³ A · cm⁻² · mM⁻¹ and detection limit was found to be 7.58 × 10⁻² µM.     

Comparative Study on Electroanalysis of Fenthion Using Silver Amalgam Film Electrode and Glassy Carbon Electrode Modified with Reduced Graphene Oxide

Oxidation and reduction processes of the insecticide fenthion was comparatively investigated at a reduced graphene oxide modified glassy carbon electrode (RGO‐GCE) and a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) using square wave stripping voltammetry (SWSV). The influence of pH and SW parameters was investigated. The linear concentration ranges were found to be 1 × 10⁻⁶ – 2 × 10⁻⁵ and 1 × 10⁻⁷ – 2 × 10⁻⁵ mol L⁻¹ for Hg(Ag)FE and RGO‐GCE, respectively. The detection and quantification limits were calculated as 1.3 × 10⁻⁷ and 4.5 × 10⁻⁷ mol L⁻¹ for Hg(Ag)FE and 7.6 × 10⁻⁹ and 2.5 × 10⁻⁸ mol L⁻¹ for RGO‐GCE. Both of the developed electroanalytical methods offer rapid and simple detection of fenthion and were used on spiked tap and river water and apple juice samples. Scanning electron microscopy was used for RGO‐GCE surface characterization.     

Voltammetric Method for the Simultaneous Determination of Melatonin and Pyridoxine in Dietary Supplements Using a Cathodically Pretreated Boron‐doped Diamond Electrode

The simultaneous voltammetric determination of melatonin (MT) and pyridoxine (PY) has been carried out at a cathodically pretreated boron‐doped diamond electrode. By using cyclic voltammetry, a separation of the oxidation peak potentials of both compounds present in mixture was about 0.47 V in Britton‐Robinson buffer, pH 2. The results obtained by square‐wave voltammetry allowed a method to be developed for determination of MT and PY simultaneously in the ranges 1–100 μg mL⁻¹ (4.3×10⁻⁶–4.3×10⁻⁴ mol L⁻¹) and 10–175 μg mL⁻¹ (4.9×10⁻⁵–8.5×10⁻⁴ mol L⁻¹), with detection limits of 0.14 μg mL⁻¹ (6.0×10⁻⁷ mol L⁻¹) and 1.35 μg mL⁻¹ (6.6×10⁻⁶ mol L⁻¹), respectively. The proposed method was successfully to the dietary supplements samples containing these compounds for health‐caring purposes.     

Selective Electroanalysis of Ascorbic Acid Using a Nickel Hexacyanoferrate and Poly(3,4‐ethylenedioxythiophene) Hybrid Film Modified Electrode

The mixed‐valent nickel hexacyanoferrate (NiHCF) and poly(3,4‐ethylenedioxythiophene) (PEDOT) hybrid film (NiHCF‐PEDOT) was prepared on a glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. The films were characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and electrochemical impedance spectroscopy (AC impedance). The advantages of these films were demonstrated for the detection of ascorbic acid (AA) using cyclic voltammetry and amperometric techniques. The electrocatalytic oxidation of AA at different electrode surfaces, such as the bare GCE, the NiHCF/GCE, and the NiHCF‐PEDOT/GCE modified electrodes, was determined in phosphate buffer solution (pH 7). The AA electrochemical sensor exhibited a linear response from 5×10⁻⁶ to 1.5×10⁻⁴ M (R²=0.9973) and from 1.55×10⁻⁴ to 3×10⁻⁴ M (R²=0.9983), detection limit=1×10⁻⁶ M, with a fast response time (3 s) for AA determination. In addition, the NiHCF‐PEDOT/GCE was advantageous in terms of its simple preparation, specificity, stability and reproducibility.     

[JW1]Oxidation of NADH by dopamine incorporated in lipid film cast onto a glassy carbon electrode

Stable lipid film was made by casting lipid in chloroform onto a glassy carbon electrode. This model of a biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by dopamine. After this electrode had been immersed in dopamine solution for 10 h, it was found that some dopamine had been incorporated in the film. The cyclic voltammogram was obtained for the oxidation of 2.0×10⁻³ mol l⁻¹ NADH with dopamine incorporated in the films. All electrochemical experiments were performed in 0.005 mol l⁻¹ phosphate buffer (pH 7.0) containing 0.1 mol l⁻¹ NaCl without oxygen. The oxidation current increased gradually with successive sweeps and reached steady state. It was a different phenomenon from previous results. The anodic overpotential was reduced by about 130 mV compared with that obtained at a bare glassy carbon electrode. The diffusion coefficient for 2.0×10⁻³ mol l⁻¹ NADH was 6.7×10^–6 cm² s⁻¹.     

Pt‐Pd Bimetallic Nanoparticles Decorated Nanoporous Graphene as a Catalytic Amplification Platform for Electrochemical Detection of Xanthine

The nanoporous graphene papers (NGPs) was prepared by the hard‐template method. The Pt−Pd modified NGPs hybrid was prepared by the self‐assembly method. Then a glassy carbon electrode (GCE) modified with Pt−Pd bimetallic nanoparticles‐functionalized nanoporous graphene composite has been prepared for the electrochemical determination of Xanthine (XA). The Pt−Pd/NGPs hybrid was characterized by transmission electron microscopy, scanning electron microscope and X‐ray diffraction. The electrochemical behavior of XA on Pt−Pd/NGPs/GCE was investigated by cyclic voltammetry and amperometric i‐t. The Pt−Pd/NGPs modified electrode exhibited remarkably electrocatalytic activity towards the oxidation reaction of XA in phosphate buffer solution (pH=5.5). Under the optimal conditions, the determination of XA was accomplished by using amperometric i‐t, the linear response range from 1.0×10⁻⁵∼1.2×10⁻⁴ M. The detection limit was 3.0×10⁻⁶ M (S/N=3). The proposed modified electrode showed good sensitivity, selectivity, and stability with applied to determine XA in human urine.     

Newly selective electrochemical sensors for trace-level determination of Al(III) ions in drainage water,spiked tap water and pharmaceutical preparation samples

In this work, two newly sensitive and selective Al(III)-modified carbon paste electrodes (MCPEs) were developed based on diphenylcarbazone (DPC) modifier mixed with tricresyl phosphate plasticizer and either graphite powder (electrode I) or graphite powder mixed with graphene (electrode II). The potentiometric performance characteristics of the two electrodes were scrutinized and discussed. The proposed sensors showed a high electrochemical response in the linear concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹ with a good Nernstian slopes of 20.12 ± 0.30 mV decade⁻¹ and 20.63 ± 0.66 mV decade⁻¹ and limits of detection of 9.0 × 10⁻⁷ and 8.5 × 10⁻⁷ mol L⁻¹ for electrode (I) and electrode (II), respectively. Both electrodes showed a fast response time and reasonable thermal stability. The potentiometric response of the DPC-based electrodes was independent on the pH of the tested solutions in ranges of 2.5–5 and 2.5–5.5 for electrode (I) and electrode (II), respectively. The two electrodes can be also used in partially non-aqueous medium containing up to 20% (v/v) acetone or methanol with no significant changes in the working concentration ranges or the slopes. The proposed electrodes showed fairly good discriminating ability toward Al(III) ions in comparison with many other metal ions. The electrodes were applied successfully for Al(III) ions determination in drainage water, spiked tap water and pharmaceutical preparation samples. Furthermore, the electrode surfaces were characterized using energy-dispersive X-ray (EDX) and scanning electron microscopic (SEM) as surface characterization techniques and Fourier Transform Infrared (FT-IR) technique to confirm the interaction between Al(III) and DPC.

     

Screen-printed electrochemical sensors for label-free potentiometric and impedimetric detection of human serum albumin

Herein, two electrochemical methods based on potentiometric and impedimetric transductions were presented for albumin targeting, employing screen-printed platforms (SPEs) to make easy and cost-effective sensors with good detection merits. The SPEs incorporated ion-to-electron multi-walled carbon nanotubes (MWCNTs) transducer. Sensors were constructed using either tridodecyl methyl-ammonium chloride (TDMACl) (sensor I) or aliquate 336S (sensor II) in plasticized polymeric matrices of carboxylated poly (vinyl chloride) (PVC-COOH). Analytical performances of the sensors were evaluated using the above-mentioned electrochemical techniques. For potentiometric assay, constructed sensors responded to albumin with −81.7 ± 1.7 (r² = 0.9986) and −146.2 ± 2.3 mV/decade (r² = 0.9991) slopes over the linearity range 1.5 μM–1.5 mM with 0.8 and 1.0 μM detection limits for respective TDMAC- and aliquate-based sensors. Interference study showed apparent selectivity for both sensors. Impedimetric assays were performed at pH = 7.5 in 10 mM PBS buffer solution with a 0.02 M [Fe(CN)₆]^−3/−4 redox-active electrolyte. Sensors achieved detection limits of 4.3 × 10⁻⁸ and 1.8 × 10⁻⁷ M over the linear ranges of 5.2×10⁻⁸–1.0×10⁻⁴ M and 1.4×10⁻⁶–1.4×10⁻³ M, with 0.09 ± 0.004 and 0.168 ± 0.009 log Ω/decade slopes for sensors based on TDMAC and aliquate, respectively. These sensors are characterized with simple construction, high sensitivity and selectivity, fast response time, single-use, and cost-effectiveness. The methods were successfully applied to albumin assessment in different biological fluids.     

An Electrochemical Sensor Based on Silver Nanoparticles‐Benzalkonium Chloride for the Voltammetric Determination of Antiviral Drug Tenofovir

A simple voltammetric nanosensor was described for the highly sensitive determination of antiviral drug Tenofovir. The benzalkonium chloride and silver nanoparticles were associated to build a nanosensor on glassy carbon electrode. Surface characterictics were achieved using scanning electron microscopic technique. The voltammetric measurements were performed in pH range between 1.0 and 10.0 using cyclic, adsorptive stripping differential pulse and adsorptive stripping square wave voltammetry. The linear dependence of the peak current on the square root of scan rates and the slope value (0.770) demonstrated that the oxidation of tenofovir is a mix diffusion‐adsorption controlled process in pH 5.70 acetate buffer. The linearity range was found to be 6.0×10⁻⁸–1.0×10⁻⁶ M, and nanosensor displayed an excellent detection limit of 2.39×10⁻⁹ M by square wave adsorptive stripping voltammetry. The developed nanosensor was successfully applied for the determination of Tenofovir in pharmaceutical dosage form. Moreover, the voltammetric oxidation pathway of tenofovir was also investigated at bare glassy carbon electrode comparing with some possible model compounds (Adenine and Adefovir).     

Electrochemical determination of prolintane in pharmaceutical formulations and in human urine

The oxidative behavior of 1-[1-(phenylmethyl)butyl]pyrrolidine, prolintane, was studied at a glassy carbon electrode using linear-sweep and differential-pulse voltammetry. The oxidation process was shown to be irreversible using 0.04 M Britton–Robinson buffer and was diffusion-adsorption controlled. Two voltammetric methods were developed for the determination of prolintane using different techniques: linear-sweep and differential-pulse voltammetry. The peak current varied linearly with prolintane concentrations in the range of 1.0 × 10⁻⁵ −2.5 × 10⁻⁴ M, with a detection limit of 8.5 × 10⁻⁶ and 4.0 × 10⁻⁶ M, and with relative standard deviations of 2.1 % and 3.1 %, respectively. The methods were applied to commercial preparations, giving relative errors less than 3.1 % and relative standard deviations lower than 4.8 % (n = 10). Determination of prolintane (down to the 8.5 × 10⁻⁸ M level) can be performed by using a preconcentration step prior to the determination by differential-pulse voltammetry in 0.04 M Britton–Robinson buffer (pH 8.0) with preconcentration potential of 0.0 V. The detection limit was found to be 6.2 × 10⁻⁸ M (4 min preconcentration) and the relative standard deviation for 2.5 × 10⁻⁷ M prolintane (n = 5) was 4.6 %. Applicability to human urine analysis is illustrated (recovery 98 ± 2 %). Standard additions method can be used to determine prolintane in real samples of urine.     

Anodic Oxidation of α‐Lipoic Acid at a Glassy Carbon Electrode and Its Determination in Dietary Supplements

Abstract

Direct electrochemistry of alpha‐lipoic acid (ALA) was performed at a glassy carbon electrode using cyclic, differential pulse and square wave voltammetry over a wide range of pH. The oxidation of ALA is an irreversible process, pH independent, and involves the charge transfer of one electron. The diffusion coefficient of ALA was calculated from the results obtained at pH 6.9 in 0.1 M phosphate buffer and was shown to be D ₀=1.1×10^?5 cm² s^?1. The limits of detection (LOD) and quantification (LOQ) calculated from the results obtained at this pH are 1.8 and 6.1 µM, respectively.

The lipoic acid content in two dietary supplements samples, a syrup containing ALA and capsules of ALA, has been determined directly at the glassy carbon electrode by differential pulse voltammetry using the standard addition method.     

Fabrication of CeO2 Nanoparticle Modified Glassy Carbon Electrode for Ultrasensitive Determination of Trace Amounts of Uric Acid in Urine

The preparation of a glassy carbon electrode modified by CeO2 nanoparticles was described, which was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. In pH 6.0 buffer, the CeO2 nanoparticle modified electrode （CeO2 NP/GC） gave an excellent electrocatalytic activity for the oxidation of uric acid （UA）. The catalytic current of UA versus its concentration had a good linear relation in the range of 2.0 × 10^-7-5.0 × 10^- 4 mol/L, with the correlation coefficient of 0.9986 and detection limit of 1.0 ×10^-7 mol/L. The modified electrode can be used for the determination of UA in urine, which can tolerate the interference of ascorbic acid up to 1000-fold. The method was simple, quick and sensitive.     

The Electropolymerization of 2,6‐Diaminopyridine and Its Application as Mercury Ion Selective Electrode

A composite graphite (CG) electrode modified with poly(2,6‐diaminopyridine) (PDAP) was used as solid state‐ion selective electrode for determination of mercury. The electrooxidation of monomer 2, 6 diaminopyridine (DAP) onto CG was accomplished from the 30 mM DAP in 5% H₂SO₄ and 0.5 M ZnSO₄. The electrode displayed Nernstian response with slope of 28.4±1 mV decade⁻¹ in concentration range of 1×10⁻⁶ to 1×10⁻¹ M and in solution of pH 3–5. The limit of detection for electrode was 3×10⁻⁸ M with response time of 25 s. The electrode was also suitable as an indicator electrode in the potentiometric titration of Hg²⁺ with iodide.     

Highly Sensitive Electrochemical Sensor for Nitric Oxide Using the Self‐Assembled Monolayer of 1,8,15,22‐Tetraaminophthalocyanatocobalt(II) on Glassy Carbon Electrode

Glassy carbon (GC) electrode modified with a self‐assembled monolayer (SAM) of 1,8,15,22‐tetraaminophthalocyanatocobalt(II) (4α‐Co^IITAPc) was used for the selective and highly sensitive determination of nitric oxide (NO). The SAM of 4α‐Co^IITAPc was formed on GC electrode by spontaneous adsorption from DMF containing 1 mM 4α‐Co^IITAPc. The SAM showed two pairs of well‐defined redox peaks corresponding to Co^III/Co^II and Co^IIIPc^?1/Co^IIIPc^?2 in 0.2 M phosphate buffer (PB) solution (pH 2.5). The SAM modified electrode showed excellent electrocatalytic activity towards the oxidation of nitric oxide (NO) by enhancing its oxidation current with 310 mV less positive potential shift when compared to bare GC electrode. In amperometric measurements, the current response for NO oxidation was linearly increased in the concentration range of 3×10^?9 to 30×10^?9 M with a detection limit of 1.4×10^?10 M (S/N=3). The proposed method showed a better recovery for NO in human blood serum samples.     

Electrochemical properties of violuric acid and oxidase biosensor preparation

The electrochemical properties of violuric acid (VA) have been investigated at pH 4.0–10.0 by using cyclic voltammetry on a glassy carbon electrode. The peak current was proportional to the square root of the potential scan rate. The calculated diffusion coefficient was 2.0±0.7×10⁻⁶ cm² s⁻¹. The formal oxidation–reduction potential of VA was 0.63 V versus SCE at pH 7.0. The kinetics of VA interaction with reduced glucose oxidase (GO) was explored in the electrocatalytical system. A typical electrocatalytical wave was generated in the presence of the VA and glucose. An apparent k_ox calculated by using the Nicholson–Shain function was 1.85×10⁶ M⁻¹ s⁻¹ at pH 7.0 and 25 °C. Glucose and l-lactate bioelectrodes were prepared by adsorbing the GO and l-lactate oxidase (LO) onto the VA-modified graphite electrode. The electrode was poised at 0.6 V versus SCE and linear response was obtained over the range of 4–20 mM glucose and 2–12 mM l-lactate, respectively.     

A Novel Electrochemical Glassy Carbon Electrode Modified with Carbon Black and Glyceline Deep Eutectic Solvent within a Crosslinked Chitosan Film for Simultaneous Determination of Acetaminophen and Diclofenac

Glyceline, reline, or ethaline deep eutectic solvents and carbon black nanoparticles within a crosslinked chitosan film are investigated as glassy carbon electrode modifiers for the first time. The selected 5 mg mL⁻¹ glyceline modified GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Simultaneous determination of acetaminophen and diclofenac by differential pulse adsorptive stripping voltammetry (DPAdSV) presented limits of detection of 2.6×10⁻⁸ and 5.2×10⁻⁸ mol L⁻¹ for acetaminophen and diclofenac, respectively, in pharmaceutical and biological samples. The obtained results were compared with those obtained by HPLC at a confidence level of 95 %.     

A Graphene‐based Electrochemical Sensor for the Individual,Selective and Simultaneous Determination of Total Chlorogenic Acids,Vanillin and Caffeine in Food and Beverage Samples

An electrochemical sensor based on the electrocatalytic activity of graphene (GR) was prepared, and used for the individual, selective and simultaneous determination of 5‐O‐Caffeoylquinic acid (5‐CQA) that is major compound of chlorogenic acids in coffee, vanillin (VAN) and caffeine (CAF). The electrochemical behaviors of these compounds on GR modified glassy carbon electrode (GR/GCE) were investigated by cyclic voltammetry and square‐wave adsorptive stripping voltammetry. By using stripping conditions after 30 s accumulation under open‐circuit voltage, the electrochemical oxidation peaks appeared at +0.53, 0.83 and 1.39 V in phosphate buffer pH 2.5, and good linear current responses were obtained with detection limits of 4.4×10⁻⁹, 5.0×10⁻⁷, and 3.0×10⁻⁷ M for 5‐CQA, VAN and CAF, respectively. The potential applicability of the proposed method was illustrated in commercial food and beverage samples.     

Graphdiyne and Ionic Liquid Composite Modified Gold Electrode for Sensitive Voltammetric Analysis of Rutin

It is significant to develop a point-of-care testing (POCT) method for rapid detection of medicinal molecules. In this paper, a graphdiyne (GDY)-ionic liquid (IL) composite was prepared via one-step facile ultrasound preparation process and then modified on gold (Au) electrode surface by simple casting method. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of GDY-IL composite. Cyclic voltammetric results proved that GDY-IL composite on the electrode surface could effectively improve electron transfer rate, which meant that GDY-IL composite had high conductivity with big surface area. Finally, the modified electrode exhibited excellent performances for rutin detection with wider linear range (8.0×10⁻⁹ mol L⁻¹–2.0×10⁻⁶ mol L⁻¹ and 2.0×10⁻⁶ mol L⁻¹–1.5×10⁻⁴ mol L⁻¹) and lower detection limit (2.7 nmol L⁻¹, 3S₀/S). The Nafion/GDY-IL/Au electrode showed good sensitivity and high selectivity, which was satisfactory in analytical application to real samples. Therefore, the GDY-IL composite modified electrode has the potential applications in the POCT for electrochemical analysis of various medicinal molecules.     

Heterogeneous electron-transfer kinetic parameters of metalloproteins as studied by channel-flow hydrodynamic voltammetry

Channel-flow hydrodynamic voltammetry was used to study the direct electron-transfer reactions of two metalloproteins, myoglobin and cytochrome c, under steady-state conditions at methyl viologen modified (MVM) gold foil electrodes. Utilization of a dual working electrode cell with this technique permitted determination of the heterogeneous electron-transfer kinetics for both the reduction and oxidation of myoglobin. The formal heterogeneous electron-transfer rate constants in pH 7.00 phosphate buffered solutions were found to be 8.9 (±1.5)×10⁻⁵ cm s⁻¹ for the reduction, and 7.7 (±1.2)×10⁻⁵ cm s⁻¹ for the reoxidation of myoglobin. The transfer coefficient values obtained were 0.21 (±0.01) for the reductive (α) and 0.82 (±0.01) for the oxidative (1−α) electrode reactions. Ionic strength and pH dependences were observed in these direct electron-transfer reactions. Collective current efficiency measurements in the myoglobin experiments indicated that an overall simple charge-transfer process occurred at the respective electrode interfaces. A formal rate constant of 3.4 (±0.2)×10⁻⁵ cm s⁻¹ with a transfer coefficient of 0.25 (±0.01) for the reduction (α) of cytochrome c was obtained by this hydrodynamic technique. The use of channel-flow hydrodynamic voltammetry in characterizing an electrode reaction as well as an interpretation of the data presented are discussed.     

Preconcentration of tranquilizers by adsorption/extraction at a wax-impregnated graphite electrode

The tranquilizers promethiazine, diethazine, trifluoperazine, fluphenazine and clozapin adsorb at the surface and extract into the wax-impregnated graphite electrode (WIGE) as shown by chronocoulometry. Extraction/adsorption at the electrode serves as a preconcentration step which improves the limit of detection for the drugs by differential pulse voltammetry. A 15-min preconcentration gave a linear range of 10^?4–5 × 10^?8 M with a detection limit of 5 × 10^?9 M for clozapin in pH 7 phosphate buffer. The determination of tranquilizers in urine and plasma required no preliminary treatment; the detection limits were 5 × 10^?8 M in urine and 10^?7 in plasma. Plasma measurements were made at a WIGE covered with a Spectrapor membrane to prevent electrode fouling by protein adsorption.