Development An Amperometric Microbial-enzyme Hybrid Cholesterol Biosensor Based On Ionic Liquid MWCNT Carbon Paste Electrode

In this study we report the development of an amperometric cholesterol biosensor based on cholesterol oxidase from Pseudomonas sp. and catalase immobilized in carbon paste electrode (CPE) modified with multiwall carbon nanotubes (MWCNT) and ionic liquid (IL). The working electrode (CPE/MWCNT-IL/Microorganism (MO)-Catalase) was characterized by impedance spectroscopy and cyclic voltammetry at different stages of its construction. This proposed cholesterol biosensor performed linear relationship in the range of 5–600 μM with a low detection limit of 1.52 μM. The biosensor showed good sensitivity and high selectivity and it was successfully applied for the measurement of cholesterol levels in lyophilized serum samples.     

Determination of Azidothymidine – an Antiproliferative and Virostatic Drug by Square‐Wave Voltammetry

The 3′‐azido‐3′‐deoxythymidine (AZT, Zidovudine) is an antiproliferative and virostatic drug widely used in human immunodeficiency virus type 1 (HIV‐1) infection treatment. With respect to side effects of high doses and a short half‐life of AZT, a fast and simple detection method for this agent could be helpful. The aim of our study was to determine AZT levels in natural samples (urine, serum, whole blood, and cell cultures, such as the HaCaT line of keratinocytes) without their mineralization and/or purification, by means of electrochemical methods using hanging mercury drop electrode (HMDE). On this electrode, AZT undergoes irreversible reduction at the peak potential near E_p?1.1 V (vs. Ag/AgCl/3 M KCl). Reduction AZT signals were measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV), square‐wave voltammetry (SWV), and constant current chronopotentiometric stripping analysis (CPSA). In phosphate buffer (pH 8) the SWV yielded the best AZT signal with the detection limit of 1 nM. The determination of AZT concentration in biological materials is affected by electroactive components, such as proteins and DNA. For monitoring the influence of these compounds, AZT reduction was performed in the presence of 10 μg/mL calf thymus ssDNA and/or 100 μg/mL bovine serum albumin. In these cases, the detection limit increased to 0.25 μM. Also studied was the AZT concentration in keratinocyte cells (HaCaT line) during cell cultivation. It has been shown that the SWV may be considered as a useful tool for the determination of AZT concentration in cell cultures, and for monitoring AZT pharmacokinetics.     

A novel electrosynthesized polymer applied to molecular imprinting technology

Poly(2-macaptobenzimidazole) (PMBI) films are prepared at the gold electrode surface by electropolymerization using imprinting technology and the target analyte cholesterol is used as the template. A cholesterol-selective sensor based on PMBI film was employed in conjunction with differential pulse voltammetry (DPV) and ferricyanide as mediator. Concentration of cholesterol up to 100 μM could be detected with a linear determination range up to 20 μM and a detection limit of 0.7 μM. The molecular imprinting approach offers a relatively nice selectivity for the sensor toward cholesterol with respect to common coexisting substances. The method is simple and the stability of the electrode prepared is satisfactory. The results of this research show the feasibility of using molecular imprinting methodology for preparing sensing devices for analytes that are electrochemically inactive.     

Electrochemical Behavior and Determination of Hyoscine‐N‐Butylbromide from Pharmaceutical Preparations

The electrooxidation of hyoscine N‐butylbromide (HBB) was investigated by rotating disk electrode voltammetry, cyclic voltammetry and controlled potential coulometry in 0.1 M HNO₃ and in 0.1 M tetrabutylammonium perchlorate (TBAP) solutions of acetonitrile at a platinum (Pt) electrode. Based on the results obtained, it is suggested that a bromide ion of HBB was oxidized in one reversible step in aqueous solutions and in two reversible steps in acetonitrile. A differential pulse voltammetric (DPV) method at a Pt electrode was developed for the determination of HBB in the concentration range of 1.0 × 10^?6‐1.0 × 10^?3 M. The procedure was applied to the determination of HBB in its formulations as well as its recovery from blood serum and urine samples.     

Immobilization of CoII-(N,N′-bis(salicylidene)-2-aminobenzylamine) on Poly(pyrrole-co-o-anisidine)/Chitosan Composite Films: Application to Electrocatalytic Oxidation of Catechol

In this study, poly (pyrrole-co-o-anisidine)/chitosan composite (Cs) films were prepared by cyclic voltammetry technique on platinum electrode using different pyrrole and o-anisidine mole ratios. Immobilization process was accomplished in Co^II-(N,N′-bis(salicylidene)-2-aminobenzylamine)(CoL) dissolved 0.15 M acetonitrile-LiClO₄ solution by cyclic voltammetry technique at 0.2–2.0 V potential range. Three electrode methods were applied in all electrochemical studies. After immobilization process, the characterizations of the electro catalytic surfaces (Cs−CoL−Pt) were carried out by cyclic voltammetry and SEM images. The SEM images clearly indicated that the [CoL] complex is immobilized onto composite films. The electrocatalytic activity of the modified electrodes on the catechol was investigated using buffer solutions of different pH values. The results of catalytic studies revealed that, pH=10 buffer solution was the optimal solution and 1 : 1 Cs−CoL−Pt electrode was the best electrode for catechol oxidation. In square wave voltammetry measurements using this electrode, two linear working ranges were determined. The linear response ranges for catechol determination were found as 3.0 μM–6.0 μM and 16 μM–80 μM for the first and the second linear working ranges, respectively, with 1.1 μM detection limit.     

A novel approach for the determination of paracetamol based on the reduction of N-acetyl-p-benzoquinoneimine formed on the electrochemically treated pencil graphite electrode

A novel approach was proposed for the simple and rapid electrochemical determination of paracetamol (PC) in the presence of uric acid in body fluids. The voltammetric determination of PC is based on the electrochemical reduction of N-acetyl-p-benzoquinoneimine formed simultaneously on the electrochemically treated pencil graphite (ETPG) electrode during the measurement. ETPG electrodes were prepared by the potential cycling between −0.3 V and +2.0 V in 0.1 M H₃PO₄ solution. The electrochemical performance of the ETPG electrode was evaluated by adsorptive transfer stripping differential pulse voltammetry (ATSDPV). The resulting sensor showed good performance for the determination of PC in human blood serum samples with a linear range of 0.05–2.5 μM and a highly reproducible response (RSD of 3.1%). The calculated detection limit was 2.5 nM (S/N = 3). The proposed method does not require any sample pretreatment, prevents the interference of uric acid and allows the determination of PC directly in blood serum samples.     

Single step modification of copper electrode for the highly sensitive and selective non-enzymatic determination of glucose

A non-enzymatic sensor was developed for the determination of glucose in alkaline medium by anodisation of copper in sodium potassium tartrate solution. The morphology of the modified copper electrode was studied by scanning electron microscopy, and its electrochemical behavior by cyclic voltammetry and electrochemical impedance spectroscopy. The electrode enables direct electrocatalytic oxidation of glucose on a CuO/Cu electrode at 0.7 V in 0.1 M sodium hydroxide. At this potential, the sensor is highly selective to glucose even in the presence of ascorbic acid, uric acid, or dopamine which are common interfering species. The sensor displays a sensitivity of 761.9 μA mM^?1 cm^?2, a linear detection range from 2 μM to 20 mM, a response time of <1 s, and a detection limit of 1 μM (S/N = 3). It was tested for determination of glucose level in blood serum.     

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.     

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.     

Electroanalytical Investigation and Simultaneous Determination of Etodolac and Thiocolchicoside at a Non-modified Glassy Carbon Electrode in Anionic Surfactant Media

In this study, a differential pulse voltammetry method was designed for the simultaneous determination of etodolac and thiocolchicoside in a tablet dosage form. This method is a sensitive, costless and reproducible one initially designed for the simultaneous determination of etodolac and thiocolchicoside using bare/unmodified glassy carbon electrode in the presence of sodium dodecyl sulfate. At optimized conditions, the method showed linear responses with etodolac and thiocolchicoside concentration in the range of 1 μM to 80 μM. The limits of detection and quantification were calculated as 0.11 μM and 0.38 μM for etodolac and 0.20 μM and 0.67 μM for thiocolchicoside, respectively.     

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.     

Fabrication and characterization of poly 2-napthol orange film modified electrode and its application to selective detection of dopamine

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between ?0.6 and 0.8 V at scan rate of 50 mV s^?1 for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory.     

Rapid and Selective Determination of Vanillin in the Presence of Caffeine,its Electrochemical Behavior on an Au Electrode Electropolymerized with 3‐Amino‐1,2,4‐triazole‐5‐thiol

Electrochemical oxidation of vanillin (VAN) in the presence of caffeine (CAF) was studied on a gold (Au) electrode modified with 3‐amino‐1,2,4‐triazole‐5‐thiol (ATT) film by using differential pulse voltammetry (DPV) and cyclic voltammetry (CV) method. The formation of the ATT film on the Au electrode surface was characterized by the CV, fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy (EIS) methods. A single irreversible oxidation peak of the VAN was obtained by using the CV method. The determination of VAN in the presence of CAF was carried out at pH 4 in Britton Robinson buffer (BR) by the DPV method. Under the optimal conditions, the oxidation peak current was proportional to the concentration of VAN in the range of 1.1 μM to 76.4 μM in the presence of CAF with the correlation coefficient of 0.997 and the detection limit of 0.19 μM (S/N=3). The selective determination of VAN in a commercial coffee sample was carried out with satisfactory results on the ATT‐Au modified electrode.     

Biocentri-voltammetric biosensor for acetylcholine and choline

We report on the determination of choline and acetylcholine via biocentrivoltammetry. This method combines centrifugation and voltammetry and is based on a carbon paste electrode modified with acetylcholinesterase and choline oxidase. The electrode was placed at the bottom of a biocentrivoltammetric cell. Acetylcholine and choline are accumulated on the enzyme electrode via centrifugative forces, upon which a direct voltammetric scan is applied. Reaction time, pH values, quantities of enzyme and centrifugation parameters were optimized. A linear response is obtained in the 0.07 to 10?μM concentration range of acetylcholine, and a limit of detection as low as 0.5?μM. The linear range is between 0.1 and 500?μM for choline. The method was applied to the determination of acetylcholine and choline in spiked serum samples.

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.     

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.     

Rapid and accurate amperometric determination of acetaminophen in pharmaceutical preparations and spiked human blood serum samples at cadmium pentacyanonitrosylferrate modified glassy carbon electrode

The present work describes a rapid and accurate amperometric technique for the determination of acetaminophen (ACT) in pharmaceutical preparations and human blood serum, based on electrocatalytic oxidation of ACT at a glassy carbon electrode modified by cadmium pentacyanonitrosylferrate (CdPCNF) film. The electrocatalytic response of the modified GC electrode was linear over the concentration of 1.64-52.90 μM. The limit of detection was found to be 2.04 μM by amperometric technique. The method was successfully utilized for the determination of ACT in various pharmaceutical preparations and the results have been statistically compared with those obtained by the official method. The interference of some pharmaceutical and biological compounds was investigated. The results of interference study showed that the Nafion-coated CdPCNF|GC electrode can be utilized as a selective amperometric sensor for acetaminophen determination in human blood serum. The mean value of rate constant k for catalytic reaction, and the diffusion coefficient of ACT (D) in the phosphate buffer solution of pH 7.2 were found to be 4.27 × 10² M?¹ s?¹, and (4.25 ± 0.33) × 10^?6 cm² s^?1, respectively.     

Determination of selenium(IV) by anodic stripping voltammetry with an in situ gold-plated rotating glassy carbon disk electrode

The application of an in situ gold-plated glassy carbon disk electrode to the determination of selenium(IV) by anodic stripping voltammetry is described. A single anodic stripping peak is obtained for solutions containing less than 1 × 10^-6 M Se(IV). The minimum concentration detected was 2 × 10^-9 M Se(IV). The determination of selenium in NBS SRM 1577 (Bovine Liver) by anodic stripping voltammetry with an in situ goldplated rotating glassy carbon electrode yielded a value of 1.14 ± 0.07 μg Se g^-1 compared with a certificate value of 1.1 ± 0.1 μg Se g^-1.     

Simultaneous Determination of Ranitidine and Metronidazole at Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

Single‐walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs‐film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10^?8 mol L^?1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10^?8 mol L^?1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.     

Controlled Electrodeposition of Au‐Copper Oxide Nanocomposite on a Renewable Carbon Ceramic Electrode for Sensitive Determination of NADH in Serum Samples

In this study, a sensitive nicotinamide adenine dinucleotide (NADH) biosensor based on Au‐Copper oxide nanocomposite modified carbon ceramic electrode (Au?CuO/CCE) was introduced. The developed NADH biosensor was prepared by controlled electrodeposition of copper and Au nanoparticles on the surface of a renewable CCE and was turned to Au?CuO/CCE by cycling the potential in alkaline media. The prepared electrode was carefully characterized with scanning electron microscopy, X‐ray diffraction, atomic force microscopy and cyclic voltammetry techniques. According to scan rate study, surface coverage (Γ) of the fabricated Au?CuO/CCE was calculated to be 1.54×10^?8 mol cm^?2 which was 3 time more than CuO/CCE. The fabricated electrode is well stable which could be reliably utilized for the determination of NADH with amperometry technique over the concentration range of 1–29 μM with sensitivity and detection limit (S/N=3) of 0.1025 μA μM^?1 and 0.09 μM respectively. The prepared biosensor was used for NADH determination in serum samples with fast response time and satisfactory analytical results.