Highly Sensitive Nanostructured Electrochemical Sensor Based on Carbon Nanotubes-Pt Nanoparticles Paste Electrode for Simultaneous Determination of Levodopa and Tyramine

A multicomponent electrochemical sensor, with two nanometer-scale components in sensing matrix/electrode, was used to simultaneous determination of levodopa (LD) and tyramine (TR) in pharmaceutical and diet samples. Multiwall carbon nanotubes (MWCNTs) were used as carbonaceous materials in the electrode construction. 5-amino-3',4'-dimethoxy-biphenyl-2-ol (5ADMB) was used as electron mediator and Pt nanoparticles (nPt) as a catalyst. The 5ADMB catalyzes the oxidation of LD to the corresponding catecholamine, which is electrochemically reduced back to LD. Preparation of this electrode was very simple and modified electrode showed good properties at electrocatalytic oxidization of LD and TR. Using differential pulse voltammetry (DPV), a highly selective and simultaneous determination of LD and TR has been explored at the modified electrode. Differential pulse voltammetry peak currents of LD and TR increased linearly with their concentrations at the ranges of 0.50–100.0 μM and 0.60–100.0 μM, respectively. Also, the detection limits for LD and TR were 0.31 and 0.52 μM, respectively. The electrode exhibited an efficient catalytic response with good reproducibility and stability.     

Nano composite system based on coumarin derivative–titanium dioxide nanoparticles and ionic liquid: Determination of levodopa and carbidopa in human serum and pharmaceutical formulations

The combination of coumarin derivative (7-(1,3-dithiolan-2-yl)-9,10-dihydroxy-6H-benzofuro[3,2-c]chromen-6-on), (DC)–titanium dioxide nanoparticles (TiO₂) and ionic liquid (IL) yields nanostructured electrochemical sensor, formed a novel kind of structurally uniform and electrocatalytic activity material. This new ionic liquid–TiO₂ nanoparticles modified carbon paste electrode (IL–CTP) due to its enhanced conductivity presented very large current response from electroactive substrates. The modified electrode was characterized by different methods including a scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and voltammetry. A pair of well-defined quasi reversible redox peaks of coumarin derivative was obtained at the modified carbon paste electrode (DC/IL–CTP) by direct electron transfer between the coumarin derivative and the CP electrode. Dramatically enhanced electrocatalytic activity was exemplified at the DC/IL–CTP electrode, as an electrochemical sensor to study the electro oxidation of levodopa (LD) and carbidopa (CD). Based on differential pulse voltammetry (DPV), the oxidation of LD and CD exhibited the dynamic range between 0.10– 900.0 μM and 20.0–900.0 μM respectively, and the detection limit (3σ) for LD and CD were 41 nM and 0.38 μM, respectively. DPV was used for simultaneous determination of LD and CD at the DC/IL–CTP electrode, and quantitation of LD and CD in some real samples (such as tablets of Parkin-C Fort and Madopar, Sinemet, water, urine, and human blood serum) by the standard addition method.     

Graphene sheet for improving the electrocatalytic activity of a benzofuran derivative modified electrode for determination of epinephrine in the presence of serotonin

A nanocomposite system based on coumarin derivative and graphene sheet was used to prepare a new electrochemical sensor. The objective of the mentioned nanocomposite was to investigate novel electrochemical properties enabling the quantification of epinephrine (Ep). Cyclic voltammetry was used to study the redox properties of the mentioned modified electrode at different scan rates. Henceforward, the electrocatalytic oxidation of Ep at the surface of the modified electrode was considered. The data has shown excellent catalytic activity of the modified electrode for the electrooxidation of Ep, which leads to a reduction of overpotential for more than 238 mV. According to differential pulse voltammetry (DPV), the oxidation of Ep showed a dynamic range between 0.1 and 1000.0 μM and the detection limit (3s) of 0.011 μM. Besides, DPV was used for the determination of Ep at the mentioned modified electrode in the presence of serotonin.     

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.     

Platinum Nanoparticles/Poly(isoleucine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Hydroquinone and Catechol

A new electrochemical sensor based on Poly(Isoleucine) modified glassy carbon electrode decorated with platinum nanoparticles (Pt/Poly(Isoleucine)/GCE) was developed for sensitive individual and simultaneous determination of hydroquinone (HQ) and catechol (CC). Scanning electron microscopy (SEM), Electrochemical impedance spectroscopy (EIS), Cyclic voltammetry (CV) and Differential pulse voltammetry (DPV) were performed in order to characterize the Pt/Poly(Isoleucine)/GCE nanocomposite. For simultaneous determination of HQ and CC, Pt/Poly(Isoleucine)/GCE showed wide linear range between the 0.01–100.0 μM. The detection limits were 0.006 μM for HQ and 0.005 μM for CC. The Pt/Poly(Isoleucine)/GC electrode exhibited good sensitivity and reliability in the simultaneous electroanalysis of two isomers in PBS of pH 7.5. The modified electrode was used to detect the isomers in naturel samples.     

Electrochemical Behavior and Ultrasensitive,Simple and Effective Voltammetric Determination of Acetaminophen Using Modified Glassy Carbon Electrode Based on 4-Hydroxyquinoline-3-carboxylic Acid

An electrochemical oxidation of acetaminophen (ACOP) has been successfully performed by using glassy carbon electrode covered with 4-hydroxyquinoline-3-carboxylic acid (4HQ3CA) to reinforce electrode's feature. To characterize the modified electrode (4HQ3CA/GC), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Fourier transform infrared spectroscopy (FT-IR) techniques were used. The finding optimum conditions (supporting electrolyte, pH) and the electrochemical determination studies were performed with differential pulse voltammetry (DPV). It was decided that the supporting electrolyte medium suitable for ACOP determination was Britton-Robinson (BR) buffer and the effect of pH change on the oxidation peak of ACOP in this media was investigated. The effect of changing scan rate on the oxidation peak of ACOP was examined and this study showed that the oxidation process of ACOP on the 4HQ3CA/GC modified electrode surface was diffusion and adsorption controlled process. A wide concentration range from 0.0025 μM to 141 μM with a limit of detection (LOD) of 5.98×10⁻¹⁰ M (3 s/m) was obtained. This prepared sensor was carried out for the determination of ACOP in pharmaceutical sample.     

Simultaneous Determination of Isoproterenol,Acetaminophen and Folic Acid Using a Novel Nanostructure‐Based Electrochemical Sensor

In this study, a carbon paste electrode modified with (E)‐2‐((2‐chlorophenylimino)methyl)benzene‐1,4‐diol (CD) and titanium dioxide nanoparticles (TiO₂) was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for the detection of isoproterenol (IP) in the presence of acetaminophen (AC) and folic acid (FA). Initially, cyclic voltammetry (CV) was used to investigate the redox properties of this modified electrode at various scan rates. In the following, the mediated oxidation of IP at the modified electrode was described. The results showed an efficient catalytic activity of the electrode for the electrooxidation of IP, which leads to a reduction in its overpotential by more than 235 mV. The value of the electron transfer coefficient (α), catalytic rate constant (k_h) and diffusion coefficient (D) were calculated for IP, using electrochemical approaches. Based on differential pulse voltammetry (DPV), the oxidation of IP exhibited a dynamic range between 0.5 and 1000 µM and a detection limit (3σ) of 0.47 µM. DPV was used for simultaneous determination of IP, AC and FA at the modified electrode. Finally, this method was used for the determination of IP in real samples, using standard addition method.     

Highly Sensitive Electrochemical Sensor Based on Pt Doped NiO Nanoparticles/MWCNTs Nanocomposite Modified Electrode for Simultaneous Sensing of Piroxicam and Amlodipine

In this paper, a high‐sensitivity electrochemical sensor based on platinum (Pt) doped nickel oxide (NiO) nanoparticles and multi‐walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (Pt?NiO/MWCNTs/GCE) has been developed to determine piroxicam (PIR) and amlodipine (AML) simultaneously. The electrochemical behavior of PIR and AML at the proposed sensor has been investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) methods. Pt doped NiO nanoparticles were synthesized by the sol‐gel procedure and were investigated using X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) techniques. DPV responses of PIR and AML increased linearly with their concentration in wide linear dynamic ranges of 0.6–320.0 μM and 1.0–250.0 μM, respectively. The limits of detection were 0.061 μM for PIR and 0.092 μM for AML. The excellent analytical figure of merits of the proposed modified electrode leads to application of it promising electrochemical sensor to determine PIR and AML in human serum and urine with satisfactory results.     

Copper‐based Metal‐organic Framework for Non‐enzymatic Electrochemical Detection of Glucose

A non‐enzymatic electrochemical glucose sensor based on a Cu‐based metal‐organic framework (Cu‐MOF) modified electrode was developed. The Cu‐MOF was prepared by a simple ionothermal synthesis, and the characterizations of the Cu‐MOF were studied by Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), single‐crystal X‐ray powder diffraction (SCXRD), and X‐ray powder diffraction (XRD). Electrochemical behaviors of the Cu‐MOF modified electrode to glucose were measured by differential pulse voltammetry (DPV). The electrochemical results showed that the Cu‐MOF modified electrode exhibited an excellent electro‐catalytic oxidation towards glucose in the range of 0.06 μM to 5 mM with a sensitivity of 89 μA/mM cm² and a detection limit of 10.5 nM. Moreover, the fabricated sensor showed a high selectivity to the oxidation of glucose in coexistence with other interferences. The sensor was satisfactorily applied to the determination of glucose in urine samples. With the significant electrochemical performances, MOFs may provide a suitable platform in the construction of kinds of electrochemical sensors and/or biosensors and hold a great promise for sensing applications.     

Application of Carbon Paste Electrode Modified with Carbon Nanofibres/Polyaniline/Platinum Nanoparticles as an Electrochemical Sensor for the Determination of Bezafibrate

The present study deals with the development of an electrochemical sensor for quantitative determination of Bezafibrate (BZF) based on carbon nanofibers/polyaniline/platinum nanoparticles modified carbon paste electrode (CNF/PANI/Pt/CPE). BZF is a fibric acid derivative and is used largely in the treatment of lipid disorders. The nanocomposite was synthesized by in situ polymerization of aniline using ammonium persulphate and platinum nanoparticles were uniformly decorated on the CNF/PANI surface by reducing hexachloroplatinic acid using sodium borohydride. The electrochemical response of BZF at CNF/PANI/Pt/CPE was studied using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The above study resulted into significant improvement of the electrochemical signal towards the oxidation of BZF, revealing that the oxidation process is highly favorable at the surface of modified electrode. The anodic peak current I_p (μA) is found to be linearly dependent on BZF concentration in the range of 0.025 μM to 100 μM with a detection limit of 2.46 nM. The practical analytical utilities of the sensor were investigated by performing the experiments on synthetic pharmaceutical formulations, human blood serum and urine samples which offered good recovery, suggesting the high efficacy and authenticity of CNF/PANI/Pt/CPE sensor for BZF determination.     

Application of 2-(3,4-dihydroxyphenyl)-1,3-dithialone self-assembled monolayer on gold electrode as a nanosensor for electrocatalytic determination of dopamine and uric acid

The electrooxidation of dopamine (DA), uric acid (UA) and their mixture on a gold electrode modified by a self-assembled monolayer of 2-(3,4-dihydroxyphenyl)-1,3-dithialone has been studied by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). CV was used to investigate the redox properties of the modified electrode at various scan rates and the apparent charge transfer rate constant (k(s)), and transfer coefficient (α) were calculated. The mediated oxidation of DA at the modified electrode under the optimum condition (pH = 7.0) in CV occurs at a potential about 220 mV less positive than that of the unmodified gold electrode. The values of electron transfer coefficients (α), catalytic rate constant (k) and diffusion coefficient (D) were calculated for DA, using electrochemical methods. DPV exhibited a linear dynamic range over the concentration range of 0.2-250.0 μM and a detection limit (3σ) of 0.07 μM for DA. The modified electrode was used for simultaneous determination of DA and UA by DPV. The results showed that the electrode is highly efficient for the catalytic electrooxidation of DA and UA, leading to a remarkable peak resolution (~350 mV) for two compounds. The electrode was used for the determination of DA in an injection sample.     

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.     

A Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotube/Chitosan Composite as a New Sensor for Simultaneous Determination of Acetaminophen and Mefenamic Acid in Pharmaceutical Preparations and Biological Samples

A new chemically modified electrode is constructed based on multiwalled carbon nanotube/chitosan modified glassy carbon electrode (MWCNTs‐CHT/GCE) for simultaneous determination of acetaminophen (ACT) and mefenamic acid (MEF) in aqueous buffered media. The measurements were carried out by application of differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. Application of DPV method showed that the linear relationship between oxidation peak current and concentration of ACT and MEF were 1 μM to 145 μM, and 4 μM to 200 μM, respectively. The analytical performance of this sensor has been evaluated for detection of ACT and MEF in human serum, human urine and a pharmaceutical preparation with satisfactory results.     

Selective and Sensitive Determination of Paracetamol and Levodopa with Using Electropolymerized 3,5-Diamino-1,2,4-triazole Film on Glassy Carbon Electrode

For determination of levodopa (L-DOPA) and paracetamol (PAR), selective, effective and sensitive electrochemical sensor based on 3,5-diamino-1,2,4-triazole (35DT) on glassy carbon (GC) electrode was reported. The DPV method was used to obtain the oxidation peak current of L-DOPA which increased linearly with its concentration at the range of 1–99 μM and 99–480 μM. The linear relationship between the concentration of PAR and its peak current was obtained in the range of 0.3–55 μM and 55–475 μM. The limit of detection values for PAR and L-DOPA were found to be 0.1 and 0.25 μM, respectively. Satisfactory results were obtained in pharmaceutical samples.     

Simultaneous Trace Electrochemical Determination of Xanthine Theophylline and Theobromine with a Novel Sensor Based on a Composite Including Metal Oxide Nanoparticle Multi-walled Carbon Nanotube and Nano-Na-montmorillonite Clay

We report the simultaneous determination of purine molecules with biological significance on pencil graphite electrode (PGE) modified with a composite solution including NiO nanoparticles, multi-walled carbon nanotube (MWCNT), and natural nano-Na-montmorillonite clay (NNaM) using DPV technique. The novel sensor, NiO/MWCNT/NNaM/PGE, achieved simultaneous determination of xanthine, theophylline, and theobromine at the detection limits 0.077 μM, 0.361 μM, and 0.458 μM with the linear working ranges 0.5–150 μM, 5–200 μM, and 5–250 μM in Britton-Robinson buffer at pH 2.0, respectively. The sensor revealed excellent performance for the simultaneous determination of XT, TP, and TB in three real-world samples.     

Chitosan Incorporating Cetyltrimethylammonium Bromide Modified Glassy Carbon Electrode for Simultaneous Determination of Ascorbic Acid and Dopamine

Simultaneous determination of a neurotransmitter, dopamine (DA), and ascorbic acid (AA) is achieved at neutral pH on a chitosan incorporating cetyltrimethylammonium bromide (CTAB) modified glassy carbon (GC) electrode. Differential pulse voltammetry (DPV) technique was used to investigate the electrochemical response of DA and AA at a glassy carbon electrode modified with chitosan incorporating CTAB. An optimum 6.0 mmol L^?1 of CTAB together with 0.5 wt% of chitosan was used to improve the resolution and the determination sensitivity. In 0.1 mol L^?1 aqueous phosphate buffer solution of pH 6.8, the chitosan‐CTAB modified electrode showed a good electrocatalytic response towards DA and AA. The anodic peak potential of DA shifted positively, while that of AA shifted negatively. Thus, the difference of the anodic peaks of DA and AA reached 0.23 V, which was enough to separate the two anodic peaks very well. The presented method herein could be applied to the direct simultaneous determination of DA and AA without prior treatment. The anodic peak currents (I_pa) of DPV are proportional to DA in the concentration range of 8 μM to 1000 μM, to that of AA 10 μM to 2000 μM, with correlation coefficients of 0.9930 and 0.9945, respectively. The linear range is much wider than previously reported.     

Nafion-graphene composite film modified glassy carbon electrode for voltammetric determination of p-aminophenol

A Nafion-graphene (Nafion-GR) nanocomposite film modified glassy carbon electrode was fabricated by a simple drop-casting method, and used in the electrochemical detection of p-aminophenol (4-AP). Owing to the large surface area, good conductivity of GR and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of 4-AP. The electrochemical behaviors of 4-AP on Nafion/GR film modified glassy carbon electrodes were investigated by cyclic voltammetry and differential pulse voltammetry. A calibration curve is constructed in the same matrix, urine, as the unknown samples to be analyzed. The Nafion-GR film modified electrode was linearly dependent on the 4-AP concentration and the linear analytical curve was obtained in the ranges of 0.5–200 μM with differential pulse voltammetry (DPV) and the detection limit was 0.051 μM. The Nafion-graphene nanocomposite modified electrode exhibited good reusability than pure graphene modified GCE. This procedure can be used for the determination of p-aminophenol in the presence of its degradation products and paracetamol. Finally, the proposed method was successfully used to determine p-aminophenol in local tap water samples in urine samples and pharmaceutical preparations.     

Simultaneous determination of levodopa and carbidopa by a novel nanostructure modified carbon paste electrode

The electrochemical behavior of levodopa (LD) was investigated on the surface of a carbon paste electrode modified with TiO₂ nanoparticles and 2,2??-(1,2 butanediylbis(nitriloethylidyne))-bis-hydroquinone (BNH). The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of LD, leading to a remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction. The mechanism of the electrocatalytic process on the surface of the modified electrode was analyzed by obtaining the cyclic voltammograms in various potential sweep rates. This modified electrode exhibited well-separated oxidation peaks for LD and carbidopa (CD). The differential pulse voltammetry was applied as a very sensitive analytical method for the determination of LD and CD. A linear dynamic range of 2.0?C600.0 and 20.0?C400.0???M with a detection limit of 0.2???M (with sensitivity of 0.199 ??A ??M^?1) and 10???M (with sensitivity of 0.024???A???M^?1) was obtained for LD and CD, respectively. The modified electrode was prepared quite easily and renewed on the surface by simple polishing.     

Enhanced sensing of dopamine in the present of ascorbic acid based on graphene/poly(p-aminobenzoic acid) composite film

Graphene/p-aminobenzoic acid composite film modified glassy carbon electrode (Gr/p-ABA/GCE) was first employed for the sensitive determination of dopamine (DA). The electrochemical behavior of DA at the modified electrode was investigated by cyclic voltametry (CV), differential pulse voltametry (DPV) and amperometric curve. The oxidation peak currents of DA increased dramatically at Gr/p-ABA/GCE. The modified electrode was used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA). The Gr/p-ABA composite film showed excellent electrocatalytic activity for the oxidation of DA in phosphate buffer solution (pH 6.5). The peak separation between DA and AA was large up to 220 mV. Using DPV technique, the calibration curve for DA determination was obtained in the range of 0.05-10 μM. The detection limit for DA was 20 nM. AA did not interfere with the determination of DA because of the very distinct attractive interaction between DA cations and the negatively Gr/p-ABA composite film. The proposed method exhibited good stability and reproducibility.     

A Novel Sensitive Electrochemical Sensor Based on Nickel Chloride Solution Modified Glassy Carbon Electrode for Curcumin Determination

In this research, the high conductivity of nickel chloride solution as well as the ability of nickel ions in establishing particular bonds with curcumin was benefited to fabricate a new electrochemical sensor based on nickel chloride solution modified glassy carbon electrode (NiCl₂/GCE) for detection and measurement of curcumin in human blood serum. Atomic force microscope (AFM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods indicated that using nickel chloride solution for the modification of the glassy carbon electrode (GCE) surface had a significant effect on improvement of the electrode performance. Differential pulse voltammetry (DPV) was used for quantitative measurement of curcumin, which exhibited the linear response of NiCl₂/GCE toward curcumin within the concentration range of 10–600 μM and provided the detection limit of 0.109 μM for curcumin in human blood serum.