Comparison of Insulin Determination on NiNPs/chitosan‐ MWCNTs and NiONPs/chitosan‐MWCNTs Modified Pencil Graphite Electrode

The rising amount of patients suffering for diabetes mellitus increases the requirements for effective insulin sensors. Carbon materials are a suitable choice for the development of insulin sensors due to their electrochemical characteristics. Pencil graphite electrodes (PGE) represent the trade‐off between price and excellent conductive properties. The modification of PGE by NiO and Ni nanoparticles fixed by chitosan results in surface area enlargement and improved electrocatalytic properties. This paper is focused on the comparison of different properties of Ni and NiO nanoparticles and their effect on redox reaction mechanism of insulin and detection characteristics. The electrode modified by Ni nanoparticles displays linear range of 1 μM–5 μM (R² 0.80), limit of detection (LOD) of 4.34 μM and sensitivity of 0.12 μA/μM. On the other hand, the electrode modified by NiO nanoparticles displays enhanced electrochemical characteristics such as linear range of 0.05 μM–5 μM (R² 0.99), limit of detection of 260 nM and sensitivity of 0.64 μA/μM. These properties make the NiO nanoparticles modified PGE the appropriate candidate for insulin determination.     

Development of Simple Electrochemical Sensor for Selective Determination of Methadone in Biological Samples Using Multi‐walled Carbon Nanotubes Modified Pencil Graphite Electrode

The electrochemical sensor was developed for determination of methadone (MTD) using multi‐walled carbon nanotubes (MWCNT) modified pencil graphite electrode (MWCNT‐PGE). It was found that the oxidation peak current of MTD at the MWCNT‐PGE was greatly improved compared with that of the bare‐PGE. At the MWCNT‐PGE, well‐defined anodic peak of MTD was observed at about 0.7 V (in pH 7 solution). The influence of several parameters on the determination of MTD was investigated. At optimum experimental conditions, differential pulse voltammetry (DPV) was used for determination of MTD, which exhibited a linear calibration graph of Ip versus MTD concentration in the range of 0.1–15 µM with a correlation coefficient of 0.9992. The calculated detection limit for S/N = 3 was 87 nM. It has been shown that the peaks obtained for oxidation of ascorbic acid (AA), uric acid (UA) and MTD in their mixture could be well resolved by differential pulse voltammetry, permitting us to develop a sensitive and selective electrochemical sensor for determination of MTD in the presence of AA and UA. Finally, MWCNT‐PGE was used for determination of MTD in biological samples, such as human serum and urine, using the standard addition procedure and the results were quite promising.     

Amperometric sensor based on carbon nanotubes and electropolymerized vanillic acid for simultaneous determination of ascorbic acid,dopamine, and uric acid

This paper describes the development of a simple and efficient nanostructured platform based on multi-walled carbon nanotubes (MWCNT) functionalized with an in situ generated vanillic acid (VA) polymer. It was used as an analytical sensor for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electropolymerization process of VA, performed on MWCNT-modified glassy carbon electrode, produces three redox systems based on quinone/hydroquinone functionality, as observed by cyclic voltammetry. The amperometric sensor has as figures of merit for the simultaneous determination of AA, DA, and UA the following values: for AA, a linear range of 5–120 μM and detection limit of 3.5 μM; for DA, a linear range of 5–120 μM and detection limit of 4.5 μM; and for UA, a linear range of 5–120 μM and a detection limit of 1.5 μM. From the obtained performance, the development of the platform based on MWCNT/poly-VA is justified for the simultaneous determination of AA, DA, and UA.     

Simultaneous,Selective and Highly Sensitive Voltammetric Determination of Lead,Cadmium, and Zinc via Modified Pencil Graphite Electrodes

Pencil graphite electrode (PGE) modified with MWCNT and Bi³⁺ (MWCNT/Bi/PGE) was utilized in simultaneous analysis of Pb²⁺, Cd²⁺, and Zn²⁺. Surface and electrochemical characteristics of MWCNT/Bi/PGE were investigated via SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and FTIR measurements. Even though modification with MWCNT did not improve the electroactive surface area, it significantly decreased the charge transfer resistance. Furthermore, modification with Bi³⁺ significantly increased the sensitivity. Finally, MWCNT/Bi/PGE exhibited the highest sensitivity and reproducibility compared to PGE and PGE modified with only MWCNT. MWCNT/Bi/PGE provided LOD values of 0.27, 0.43, and 1.63 μg L⁻¹, and linear ranges of 1–80, 5–80, and 10–80 μg L⁻¹ for Pb²⁺, Cd²⁺, and Zn²⁺, respectively. Proposed modification method offers effective electroanalytical performance with low time consumption and cost for the analyst.     

Electrochemical Sensor Based on Multi‐walled Carbon Nanotubes and Cobalt Phthalocyanine Composite for Pyridoxine Determination

In this work, an electrochemical sensor based on pyrolytic graphite electrode (PGE), cobalt phthalocyanine (CoPc) and multiwalled carbon nanotube (MWCNT) composite designed as PGE‐MWCNT/CoPc was developed and validated for pyridoxine (vitamin B6) determination employing Differential Pulse Voltammetry (DPV). The electrochemical behaviour of pyridoxine at the PGE‐MWCNT/CoPc has been evaluated and the charge transfer coefficient, α, and the charge transfer rate constant, κ, were calculated as 0.30 and 11.67±0.43 s^?1, respectively, which indicates that, although this system is irreversible, it is viable kinetically to be used as a sensor. The optimized experimental conditions were pH 5.5 in 0.30 mol L^?1 phosphate buffer. The linear range found was 10 to 400 μmol L^?1 of pyridoxine, with r=0.9987. The limits of detection and quantification were 0.50 and 1.67 μmol L^?1, respectively, showing the good sensitivity of the method. The method was successfully applied for the pyridoxine determination in real samples of pharmaceutical formulation with RSD% lower than 5 % indicating that it can be used for routine quality control pharmaceutical formulations containing pyridoxine. Furthermore, it has the advantages of a fast response, a low detection limit and low cost.     

Pt‐doped NiO Nanoparticle‐Ionic Liquid Modified Electrochemical Sensor: A Powerful Approach for Determination of Epinine in the Presence of Phenylephrine as two Blood Pressure Raising Drugs

A new and progressive electroanalytical sensor was made by the incorporation of Pt‐doped NiO nanoparticle (Pt‐NiO‐NPs) into carbon paste electrode (CPE) amplified with 1‐hexyl‐3‐methylimidazolium tetrafluoroborate (1H3MTFB) as a conductive binder. The Pt‐NiO‐NPs/1H3MTFB/CPE caused an extraordinary rise in the oxidation peak current of epinine (～4.6 times) and simultaneous reduction in the oxidation over‐potential of catecholamine drug (～120 mV). SWV method was employed to investigate the ability of Pt‐NiO‐NPs/1H3MTFB/CPE as an electroanalytical sensor in the determination of epinine in the presence of phenylephrine as two blood pressure raising drugs with ΔE=280 mV for the first time. Experimental results pertinent to SW voltammetric investigation reveal a linear relation between epinine and phenylephrine currents and drugs concentration in the rages 0.004–450 and 0.02–350 μM, respectively.     

Anodic stripping voltammetry of sulphide at a nickel film: towards the development of a reagentless sensor

The determination of sulphide at an electrochemically generated nickel oxide layer at glassy carbon and screen-printed electrodes in acidic media has been examined and appraised. The NiO layer was found to produce a stripping-like signal to sulphide and gave a linear peak current response from 20 to 90 μM. The response was further enhanced by repetitive cycling allowing accumulation of nickel sulphide at the electrode surface such that lower micromolar levels of sulphide (i.e. 5 μM) can be determined. The response at the NiO layer to sulphide is shown to be reproducible over a period of 24 h, thereby offering the development of a disposable amperometric sensor for sulphide.     

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.     

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.     

Facile Green Synthesis of NiO/NiCo2O4 Nanocomposite as an Efficient Electrochemical Platform for Determination of Dopamine

The synthesis of NiO/NiCo₂O₄ nanoparticles by an eco-friendly, fast, simple and cost-effective approach employing Urtica extract is reported in this study. The NiO/NiCo₂O₄ nanocomposite were characterized using VSM, FTIR, XRD, and SEM techniques. Moreover, to construct a modified carbon paste electrode, NiO/NiCo₂O₄ were employed and this sensor was used for dopamine (DA) detection. Using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques, the electrochemical behavior of dopamine at the NiO/NiCo₂O₄/CPE was investigated. Analysis of dopamine, with a limit of detection (LOD) equal to 0.04 μM, in the concentration range of 0.1–100.0 μM, was facilitated by NiO/NiCo₂O₄/CPE. Moreover, the satisfactory selectivity for DA determination in the presence of uric acid (UA) and ascorbic acid (AA), was obtained. The suggested new sensor displayed a good reproducibility, sensitivity, and stability for determination of DA in drug and biological samples.     

Electrochemical Investigation of Glucose on a Highly Sensitive Nickel‐Copper Modified Pencil Graphite Electrode

Novel nickel‐copper modified pencil graphite electrode (Ni?Cu/PGE) was fabricated and used as non‐enzymatic sensor for glucose determination. Ni and copper were electrodeposited on PGE using cyclic voltammetry. Morphology and composition of the modified PGE electrode were characterized by field‐emission gun scanning electron microscopy (FEG‐SEM), energy‐dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT‐IR). Electrochemical oxidation of glucose was evaluated by cyclic voltammetry as well as by amperometry. Electrochemical measurements indicate that the Ni?Cu/PGE exhibits a high sensitivity of 2951 μA mM^?1 cm^?2, and a low detection limit of 0.99 μM which are, respectively, three times higher and twice lower than that on Ni/PGE prepared in the same conditions. Moreover, Ni?Cu/PGE exhibits a wider linear range from 1 to 10000 μM with a rapid response time within 2 s. Moreover, Ni?Cu/PGE showed a remarkable stability. The electrode was successfully applied for determination of glucose concentration in human blood without significant interference from potential endogenic interferents. The good applicability of the elaborated sensor made Ni?Cu/PGE promising for the development of effective and inexpensive non‐enzymatic glucose sensor.     

Ag ion irradiated based sensor for the electrochemical determination of epinephrine and 5-hydroxytryptamine in human biological fluids

A promising and highly sensitive voltammetric method has been developed for the first time for the determination of epinephrine (EP) and 5-hydroxytryptamine (5-HT) using 120 MeV Ag ion irradiated multi-walled carbon nano tube (MWCNT) based sensor. The MWCNT were irradiated at various fluences of 1e12, 3e12 and 1e13 ions cm⁻² using palletron accelerator. The simultaneous determination of EP and 5-HT has been carried out in phosphate buffer solution of pH 7.20 using square wave voltammetry and cyclic voltammetry. Experimental results suggested that irradiation of MWCNT by Ag ions enhanced the electrocatalytic activity due to increase in effective surface area and insertion of Ag ions, leading to a remarkable enhancement in peak currents and shift of peak potentials to less positive values as compared to the unirradiated MWCNT (pristine). The developed sensor exhibited a linear relationship between peak current and concentration of EP and 5-HT in the range 0.1–105 μM with detection limit (3σ/b) of 2 nM and 0.75 nM, respectively. The practical utility of irradiation based MWCNT sensor has been demonstrated for the determination of EP and 5-HT in human urine and blood samples.     

Ultra‐sensitive Amperometric Hydrazine Sensing via Dimethyl Glyoxomat Derived NiO Nanostructures

Here we report the synthesis of NiO nanostructures via glyoxomat assisted precipitation protocol using hydrothermal route under the influence of ammonia followed by annealing at 450 ^oC. These nanostructures were characterized via Scanning Electron Microscopy (SEM) and X‐ray Diffraction (XRD) method. The morphological investigation of the finally prepared NiO revealed foam‐like porous nanostructures. These NiO nanostructures were immobilized onto glassy carbon electrode (GCE) with nafion as binding material and used as highly sensitive and selective sensor for determining hydrazine in the range of 100–500 nM and 600–1600 nM with a calculated limit of detection (LOD) equal to 5 nM. The as prepared sensor was tested for the presence of various interfering species such as Na⁺, Cu²⁺, uric acid, hydrogen peroxide and glucose in the presence of equimolar concentration of hydrazine and negligible interference was noticed. The sensor was further tested for hydrazine detection using square wave voltammetry (SWV) however it only worked in the range of 50–1200 μM. Finally the sensor was successfully implemented for hydrazine determination in real water samples using amperometric protocol.     

Simultaneous electrochemical determination of hydrazine and nitrite based on Au nanoparticles decorated on the poly(Nile Blue) modified carbon nanotube

In this study, simultaneous determination of toxic hydrazine and nitrite was performed on composite electrodes of poly(Nile blue)(NB), carbon nanotube(CNT) and gold nanoparticles(AuNPs). The prepared AuNPs/CNT/poly(NB)/GCE was used for as a sensor platform for individual and simultaneous determination of hydrazine and nitrite. Electrodes were characterized by HRTEM, SEM, XPS, EIS. The LOD for nitrite and hydrazine was 5.0 μM and 3.1 μM at AuNP/CNT/poly(NB)/GCE, respectively. Also, sensitive amperometric determinations of hydrazine and nitrite were performed and LOD were calculated as 0.33 μM and 0.68 μM, respectively. The method was applied to sausage and river water samples and recovery results were obtained in the range 85–115 %.     

Fabrication of Cu−CeO2 Coated Multiwall Carbon Nanotube Composite Electrode for Simultaneous Determination of Guanine and Adenine

A copper nano particles and cerium (IV) oxide modified carbon nanotube based composite on glassy carbon electrode (Cu−CeO₂/MWCNT/GCE) was fabricated for simultaneous determination of guanine and adenine. The surface morphology, chemistry and conductance of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy dispersion X‐ray (EDX), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The Cu−CeO₂/MWCNT/GCE improved electrochemical behaviour of guanine and adenine compared to other electrodes. The modified electrode was also used for individual and simultaneous determination of guanine and adenine. Under optimized conditions, the calibration curves were obtained linearly in the range of 0.20 to 6.00 μM for the guanine and 0.10 to 8.0 μM for the adenine by differential pulse voltammetry. The limits of detection of guanine and adenine were calculated as 0.128 and 0.062 μM, respectively. Interferences studies were also performed in the presence of inorganic and organic compounds. Moreover, the determination of guanine and adenine contents were carried out in a calf thymus DNA sample by the developed method with satisfactory results.     

A Comparison of Four Different Electrode Matrices on the Performance of Amperometric Hydrogen Peroxide (Bio)Sensors

A comparison of the analytical performances of four different (bio)sensor designs in H₂O₂ determination is discussed. The (bio)sensor designs developed were based on the use of (i) multiwalled carbon nanotubes (MWCNT), zinc oxide nanoparticles (ZnONP), prussian blue (PB); (ii) MWCNT, ZnONP, PB and ionic liquid (IL); (iii) MWCNT, ZnONP and horseradish peroxidase (HRP) and (iv) MWCNT, ZnONP, HRP and IL modified glassy carbon electrode (GCE). A performance comparison of (bio)sensors showed that the one based on HRP/IL-MWCNT-ZnONP/GCE showed the best analytical characteristics with a linear dynamic range of 9.99×10⁻⁸–7.55×10⁻⁴ M, detection limit of 1.37×10⁻⁸ M and sensitivity of 17.00 μA mM⁻¹.     

Two-layered Au@Ag Bimetallic Nanocomposites-poly (L-Met) Platform for Highly Sensitive Chlorpheniramine Maleate Detection

The two-layered bimetallic Au@Ag and poly(L-methionine) (Au@Ag/p-L-met) sensor was newly developed for the electrochemical determination of chlorpheniramine maleate (CPM). After electropolymerization of L-met, bimetallic surfaces were prepared by electrodeposition of Au@Ag nanoparticles on the p-L-met/PGE. The surface characterization was carried out by scanning electron microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), Cyclic Voltammetry (CV) and Electrochemical impedance spectroscopy (EIS). The sensor shows good electrocatalytic activity, high sensitivity, wide linear range (0.87–600.0 μM) and a low detection limit (0.26 μM) by using Differential pulse voltammetry (DPV). The sensor was used to determine CPM in pharmaceutical samples with satisfactory results.     

Electrochemical Detection of Epinephrine Based on a Screen-printed Electrode Modified with NiO−ERGO Nanocomposite Film

This study presents a new electrochemical sensor (NiO−ERGO/SPE) for sensitive and selective detection of epinephrine (EPI) on the screen-printed electrode (SPE) which is modified with a nanocomposite film consisting of electrochemically reduced graphene oxide and NiO nanoparticles. After surface functionalization, structural and electrochemical characterization of NiO−ERGO film, DPV signals of NiO−ERGO/SPE towards the oxidation of EPI exhibited a linear correlation in the concentration range of 0.025 μM to 175 μM with a detection limit of 0.015 μM, which reveals NiO−ERGO film is manifested a good electrocatalytic activity for EPI detection compared with the previous reports. The selectivity of NiO−ERGO film was also tested on a very wide scale of possible interferents (ascorbic acid, uric acid, dopamine, lactic acid, phenylalanine, tyrosine, tryptophan, Li⁺, Na⁺, K⁺, Ca²⁺, and Zn²⁺). Moreover, to evaluate the applicability of the proposed sensor for real sample analysis, NiO−ERGO/SPE was successfully utilized for the determination of EPI in pharmaceutical samples.     

Selective Detection of Dopamine in the Presence of Uric Acid Using NiO Nanoparticles Decorated on Graphene Nanosheets Modified Screen‐printed Electrodes

A convenient, low cost, and sensitive electrochemical method, based on a disposable graphene nanosheets (GR) and NiO nanoparticles modified carbon screen printed electrode (NiO/GR/SPE), is described for the simultaneous determination of dopamine (DA) and uric acid (UA). The modified electrode exhibited good electrocatalytic properties toward the oxidation of DA and UA. A peak potential difference of 150 mV between DA and UA was large enough to determine DA and UA individually and simultaneously. The anodic peak currents of DA were found to be linear in the concentration range of 1.0–500.0 μM with the detection limit of 3.14×10^?7 M.     

A non-enzymatic sensor for hydrogen peroxide based on polyaniline, multiwalled carbon nanotubes and gold nanoparticles modified Au electrode

We describe the construction of a polyaniline (PANI), multiwalled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs) modified Au electrode for determination of hydrogen peroxide without using peroxidase (HRP). The AuNPs/MWCNT/PANI composite film deposited on Au electrode was characterized by Scanning Electron Microscopy (SEM) and electrochemical methods. Cyclic voltammetric (CV) studies of the electrode at different stages of construction demonstrated that the modified electrode had enhanced electrochemical oxidation of H(2)O(2), which offers a number of attractive features to develop amperometric sensors based on split of H(2)O(2). The amperometric response to H(2)O(2) showed a linear relationship in the range from 3.0 μM to 600.0 μM with a detection limit of 0.3 μM (S/N = 3) and with high sensitivity of 3.3 mA μM(-1). The sensor gave accurate and satisfactory results, when employed for determination of H(2)O(2) in milk and urine.