Development of Electrochemical Biosensor Based on Nanostructured Carbon Materials for Paracetamol Determination

This work describes the development of a biosensor for paracetamol (PAR) determination based on a glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT) and laccase enzyme (LAC), which was immobilized by means of covalent crosslinking using glutaraldehyde. Voltammetric investigations were carried out by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). The biosensor was characterized by Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FT‐IR). The results showed that the use of MWCNT/LAC composite increased the sensor sensitivity, compared to bare glassy carbon electrode. Factors affecting the voltammetric signals such as pH, ionic strength, scan rate and interferents were assessed. Linear range, limit of detection (LOD) and limit of quantitation (LOQ) obtained were 10–320 μmol L^?1, 7 μmol L^?1 and 10 μmol L^{? 1}, respectively. The developed biosensor was successfully applied to PAR determination in urine and pharmaceutical formulations samples, with recovery varying from 99.96 to 106.20 % in urine samples and a relative standard deviation less than 1.04 % for PAR determination in pharmaceutical formulations. Therefore, the MWCNT‐LAC/GCE exhibits excellent sensitivity and can be used to PAR determination as a viable alternative in clinical analyzes and quality control of pharmaceutical formulations, through a simple, fast and inexpensive methodology.     

Functionalised multi-walled carbon nanotubes-modified electrode for sensitive determination of Diuron in seawater samples

ABSTRACT

This work was focused in to develop an electroanalytical method based on a direct modification of a glassy carbon electrode (GCE) by the deposition of successive aliquots of diluted dispersions of functionalised carbon nanotubes (MWCNT-COOH) in ethanol (0.1 mg.mL^?1) aiming the determination of Diuron into seawater samples, a common antifouling substance, using differential pulse voltammetry as electroanalytical technique. The GCE/MWCNT-COOH showed a sensitivity of 2.20 μA/μmol L^?1 about 10 times higher than the unmodified counterpart (GCE) which showed a sensitivity of 0.192 μA/μmol L^?1. The limits of detection and quantificationwere 6.88 × 10^?8 and 2.29 × 10^?7 mol L^?1 for GCE/MWCNT-COOH while for GCE were 7.87 × 10^?7 and 2.62 × 10^?6 mol L^?1, respectively. The applicability was evaluated with spiked detectable amounts of Diuron into seawater samples. The recovery results were between 76% and 119%.     

Stripping Voltammetric Determination of Methyl Parathion at Activated Carbon Nanopowder Modified Electrode

An activated carbon nanopowder modified glassy carbon electrode (AC-GCE) was constructed for the sensitive determination of methyl parathion by adsorptive differential pulse anodic stripping voltammetry. The simple and rapid modification procedure included only drop-coating the electrode surface with a laponite stabilized activated carbon nanopowder suspension and drying. The modifier high adsorption ability, combined with its large electroactive surface area allowed a 30-fold signal increase to be achieved, compared to bare GCE. Under optimized experimental conditions (activated carbon to laponite ratio, pH and accumulation time), the AC-GCE exhibited a linear response to methyl parathion in two concentration ranges: from 0.01 μmol L⁻¹ to 1 μmol L⁻¹ and from 1 μmol L⁻¹ to 6 μmol L⁻¹. The LOD of 2.5 nmol L⁻¹ (S/N=3) achieved fitted with regulatory norms. It was demonstrated that the as-prepared AC-GCE is suitable for routine real samples analysis.     

Over‐Oxidized Poly (Phenol Red) Film Modified Glassy Carbon Electrode for Anodic Stripping Voltammetric Determination of Ultra‐Trace Antimony (III)

In this study, we introduce a very sensitive and selective method for the differential pulse anodic stripping determination of Sb(III) ion on the over‐oxidized poly(phenol red) modified glassy carbon electrode (PPhRed_ox/GCE) in 0.1 mol L^‐1 HCl medium. The formation of both poly(phenol red) and over‐oxidized poly(phenol red) film on the electrode surfaces were characterized by electrochemical impedance spectroscopy, X‐ray photoelectron spectroscopy and scanning electron microscopy techniques. An anodic stripping peak of Sb(III) was observed at 0.015 V on the PPhRed_ox/GCE. Higher anodic stripping peak current of Sb(III) was obtained at PPhRed_ox/GCE compared with both bare GCE and poly(phenol red) film modified GCE (PPhRed/GCE). The calibration graph consisted of two linear segments of 0.044 ‐ 1.218 μg L⁻¹ and 3.40 – 18.26 μg L⁻¹ with a detection limit of 0.0075 μg L⁻¹. The proposed over‐oxidized polymer film modified electrode was applied successfully for the analysis of antimony in different spiked water samples. Spiked recoveries for water samples were obtained in the range of 93.0–103.0%. The accuracy of the method was also verified through the analysis of standard reference materials (SCP SCIENCE‐EnviroMAT™ EP−L‐2).     

Simultaneous Electrochemical Determination of Hydroquinone and Bisphenol A using a Carbon Paste Electrode Modified with Silver Nanoparticles

In this paper, a rapid and sensitive modified electrode for the simultaneous determination of hydroquinone (HQ) and bisphenol A (BPA) is proposed. The simultaneous determination of these two compounds is extremely important since they can coexist in the same sample and are very harmful to plants, animals and the environment in general. A carbon paste electrode (CPE) was modified with silver nanoparticles (nAg) and polyvinylpyrrolidone (PVP). The PVP was used as a reducing and stabilizing agent of nAg from silver nitrate in aqueous media. The nAg‐PVP composite obtained was characterized by transmission electron microscopy and UV‐vis spectroscopy. The electrochemical behavior of HQ and BPA at the nAg‐PVP/CPE was investigated in 0.1 mol L⁻¹ B−R buffer (pH 6.0) using cyclic voltammetry (CV) and square wave voltammetry (SWV). The results indicate that the electrochemical responses are improved significantly with the use of the modified electrode. The calibration curves obtained by SWV, under the optimized conditions, showed linear ranges of 0.09–2.00 μmol L⁻¹ for HQ (limit of detection 0.088 μmol L⁻¹) and 0.04–1.00 μmol L⁻¹ for BPA (limit of detection 0.025 μmol L⁻¹). The modified electrode was successfully applied in the analysis of water samples and the results were comparable to those obtained using UV‐vis spectroscopy.     

Development of a New Voltammetric Methodology for the Determination of Ciprofloxacin in Beef Samples Using a Carbon Paste Electrode Modified with Nafion and Fullerenes

A sensitive, selective, and low cost electrochemical new methodology was developed for the quantification of ciprofloxacin (Cip) in beef samples by cyclic voltammetry and differential pulse voltammetry, using a CPE electrode modified with Nafion and Fullerenes (N−F/CPE). The optimum parameters for the composition of the N−F/CPE electrode are 0.19 g mineral oil, 0.01 g Nafion, 50 μL fullerene, and graphite powder 0.3 g. The electrochemical characterization was carried out by obtaining maximum anodic peak current associated with the oxidation of ciprofloxacin at 1.1 V, where the electrochemical process resulted to be irreversible and diffusion-controlled. The analytical characterization of the proposed methodology was carried out resulting in a LOD of 1.0 μmol L⁻¹, a LOQ of 3.0 μmol L⁻¹, a sensitivity of 0.37±0.006 μA/μmolL⁻¹, and repeatability of 5.38 %.     

A novel amperometric sensor and chromatographic detector for determination of parathion

A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0×10^–9–2.0×10^–5 mol L^–1. The detection limit was 1.0×10^–9 mol L^–1 (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC–ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0×10^–9 mol L^–1. Application of the method for determination of parathion in rice was satisfactory.     

Voltammetric Determination of Phenoxybenzyl‐Type Insecticides at Chemically Modified Conducting Polymer‐Carbon Nanotubes Coated Electrodes

The electrochemical reduction of three common insecticides such as cypermethrin (CYP), deltamethrin (DEL) and fenvalerate (FEN) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNT‐GCE), polyaniline (herein called as modifier M₁) and polypyrrole (herein called as modifier M₂) deposited MWCNT/GCE using cyclic voltammetry. Influences of pH, scan rate, and concentration were studied. The surface morphology of the modified film was characterized by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD). A systematic study of the experimental parameters that affect differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived at. The calibration plots were linear over the insecticide's concentration range 0.1–100 mg L^?1 and 0.05–100 mg L^?1 for all the three insecticides at MWCNT‐GCE and MWCNT(M₁)‐GCE respectively. The MWCNT(M₂)‐GCE performed well among the three electrode systems and the determination range obtained was 0.01–100 mg L^?1 for CYP, DEL and FEN. The limit of detection (LOD) was 0.35 μg L^?1, 0.9 μg L^?1 and 0.1 μg L^?1 for CYP, DEL and FEN respectively on MWCNT(M₂)‐GCE modified system. Suitability of this method for the trace determination of insecticide in spiked soil sample was also determined.     

Simple and rapid determination of clonidine in pharmaceutical samples by voltammetry using a bare glassy carbon electrode

This work presents, for the first time, the voltammetric behavior of clonidine (CLO) drug and its determination, using an unmodified glassy carbon electrode (GCE). CLO exhibited only an irreversible oxidation process on the GCE, with peak potential at +0.85 V in pH 12 (vs Ag/AgCl). CLO oxidation process is pH-dependent and the electrochemical mechanisms on the GCE were proposed in acidic and basic medium. The determination of CLO was optimized in 0.1 mol L⁻¹ phosphate buffer solution at pH 12.0 using differential pulse voltammetry (DPV), which provides a good linear range (0.65 to 106.00 μmol L⁻¹) and low theoretical limit of detection (0.14 μmol L⁻¹) for the quality control of this drug in pharmaceutical samples. In addition, stable responses of CLO at the GCE were obtained in the same day (RSD = 3.4 %; n = 5) and different days (RSD = 2.0 %; n = 3). Moreover, the determination of CLO in a pharmaceutical formulation using the proposed GCE-DPV method presented good accuracy, since the recovery was close to 100 % and the dosing result was in agreement with an official method (HPLC-UV). The proposed method demonstrates a good analytical performance for CLO determination in pharmaceutical samples, providing a faster, simpler and lower-cost alternative for quality control of CLO than other reported methods.     

Voltammetric Determination of an Anti-rheumatoid Drug Acemetacin on Graphite Flake Paste Electrode and Glassy Carbon Electrode

In this study, a simple and sensitive square wave voltammetric procedure has been developed for the determination of acemetacin (ACM) at graphite flake paste electrode (GFPE) and glassy carbon electrode (GCE). Under optimized conditions, the dependence of ACM peak current on its concentration showed wide linear range: 0.03–1.0 μmol L⁻¹ and 0.7–15.0 μmol L⁻¹ at GFPE and GCE, respectively. The developed method was successfully applied for the determination of ACM in pharmaceuticals and spiked urine with satisfying recoveries. The electrochemical oxidation of ACM is an irreversible process controlled by mixed nature of the mass transfer process.     

Development of Electrochemical Platform Based on Molecularly Imprinted Poly(methacrylic acid) Grafted on Iniferter-modified Carbon Nanotubes for 17β-Estradiol Determination in Water Samples

This paper describes the development of a new electrochemical sensor for 17β-estradiol (E2) determination based on glassy carbon electrode (GCE) modified with molecularly imprinted polymer grafted onto iniferter-multiwall carbon nanotubes surface (MIP-MWCNT) and dihexadecyl-hydrogen-phosphate (DHP). The electrochemical method was based on closed-circuit preconcentration of E2 in 0.1 mol L⁻¹ phosphate buffer (pH 7.0) during 500 s. Upon preconcentration, E2 was determined by differential pulse voltammetry (DPV) exhibiting a limit of detection of 0.01 μmol L⁻¹. The sensor exhibited higher selectivity toward E2 and it was applied for E2 determination in natural water samples, with accuracy attested by HPLC-DAD.     

Electrochemical Sensor Based on Multi‐walled Carbon Nanotube/Gold Nanoparticle Modified Glassy Carbon Electrode for Detection of Estradiol in Environmental Samples

We report a rapid and simple method for sensing estradiol by electro‐oxidation on a multi‐walled carbon nanotube (MWCNT) and gold nanoparticle (AuNP) modified glassy carbon electrode (GCE). Compared with a bare GCE, AuNP/GCE and MWCNT/GCE, the composite modified GCE shows an enhanced response to estradiol in 0.1 M phosphate buffer solution. Experimental parameters, including pH and accumulation time for estradiol determination were optimised at AuNP/MWCNT/GCE. A pH of 7.0 was found to be optimum pH with an accumulation time of 5 minutes. Estradiol was determined by linear sweep voltammetry over a dynamic range up to 20 %mol L^?1 and the limit of detection was estimated to be 7.0×10^?8 mol L^?1. The sensor was successfully applied to estradiol determination in tap water and waste water.     

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT−GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, α, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4 ± 0.5 s⁻¹ and 0.51, respectively at pH = 7.0. The obtained results indicate that hydrazine peak potential at OMWCNT−GCE shifted for 14, 109, and 136 mV to negative values as compared with oxadiazole-modified GCE, MWCNT−GCE, and activated GCE surface, respectively. The electron transfer coefficient, α, and the heterogeneous rate constant, k′, for the oxidation of hydrazine at OMWCNT−GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0 μM and 10.0 to 400.0 μM and detection limit of 0.17 μM for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT−GCE was shown to be successfully applied to determine hydrazine in various water samples.

     

Voltammetric Detection of Captopril in a Commercial Drug Using a Gold-Copper Metal-organic Framework Nanocomposite Modified Electrode

We report the application of an electrochemical sensor based on gold-copper metal-organic framework immobilized on the surface of a glassy carbon electrode to the detection of captopril (CAP), an angiotensin-converting enzyme inhibitor. Cyclic voltammetric studies showed that the joint action of gold nanoparticles and copper-1,3,5-benzenetricarboxylate (Cu−BTC) enhanced the electrochemical response to the Cu-captopril complex that is adsorbed onto the surface of the electrode. Release of gold nanoparticles from Au@Cu−BTC not only increased the conductivity of the electrode but also provided a more favorable environment for the deposition of reduced Cu that is catalytically renewed on the electrode surface. The anodic current of the Cu^(II)−CAP oxidation peak varied linearly within two concentration ranges, namely 0.5 to 7.0 μmol L⁻¹ and 10 to 2500 μmol L⁻¹, with a limit of detection of 0.047 μmol L⁻¹. The mean recovery for the determination of captopril in commercial tablets was 100.3 % suggesting that the method has considerable potential for future industrial applications.     

Preparation of Fe−Co−LDH/MXene modified electrode for sensitive determination of arsenic (III) in aquatic system

3-dimensional (3D) Fe−Co−LDH/MXene composite was synthesized by in-situ synthesis and assembly of Fe−Co−LDH rod around MXene under hydrothermal condition. Due to the unique 3D configuration and good conductivity, the obtained Fe−Co−LDH/MXene modified glassy carbon electrode (Fe−Co−LDH/MXene/GCE) showed excellent electrochemical activity for As(III) detection. Via square-wave anodic stripping voltammetry, the response current on Fe−Co−LDH/MXene/GCE had good linear relationship with As(III) concentrations (1∼1000 ppt) with superior sensitivity (0.22 μA ppt⁻¹ cm⁻²) and low detection limit (0.9 ppt). The mechanism of As(III) adsorption was demonstrated. The electrode showed excellent anti-interference ability. Real water sample analysis demonstrated the Fe−Co−LDH/MXene/GCE was deployable in aqua-system.     

Electrochemical Determination of Fenitrothion Organophosphorus Pesticide Using Polyzincon Modified‐glassy Carbon Electrode

In this paper, a glassy carbon electrode (GCE) was modified with polyzincon. The modified electrode was used as a simple, inexpensive and highly sensitive electrochemical sensor for the determination of organophosphorus pesticide fenitrothion. To fabricate the electrochemical sensor, GCE was immersed in 0.10 mmol L⁻¹ zincon solutions at pH 7.0 and then successively scanned between −1.00 to 2.20 V (vs . Ag/AgCl) at a scan rate of 70 mV s⁻¹ for six cycles. The morphology and structure of the polyzincon were studied with atomic force microscopy and scanning electron microscopy. A comparison of the electrochemical behavior of fenitrothion on the unmodified and polyzincon modified‐GCE showed that in the modified electrode not only the oxidation peak current increased, but also the overpotential shifted to lower one. The experimental conditions such as sample solution pH, accumulation potential, and time were optimized. The differential pulse voltammetric responses of fenitrothion at potential about −0.60 V was used for the determination of fenitrothion. The peak current increased with increasing the concentration of fenitrothion in the range of 5 to 8600 nmol L⁻¹ with a detection limit of 1.5 nmol L⁻¹. Finally, the electrochemical sensor was used for the analysis of fenitrothion in water and fruit samples.     

Glassy Carbon Electrode Modified with Layering of Carbon Black/Poly(Allylamine Hydrochloride) Composite for Multianalyte Determination

An electrochemical sensor using glassy carbon electrode modified with carbon black within a poly(allylamine hydrochloride) film is proposed in this work. The novel sensor was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry using the redox probe Fe(CN)6^3−/4−. The sensor was applied for the simultaneous determination of dopamine (DA), paracetamol (PAR), amlodipine (AML), and rosuvastatin (RSV). The quantification of all four analytes was carried out by linear sweep voltammetry and presented a linear concentration range for all analytes from 1.0 to 90 μmol L⁻¹, with limit of detection of 0.55, 1.3, 5.7, and 3.0 μmol L⁻¹ for DA, PAR, AML, and RSV, respectively. This sensor was successfully applied in the simultaneous determination of these analytes in environmental, pharmaceutical, and biological samples.     

Gold Nanoparticles-electrochemically Reduced Graphene Oxide/Poly(indole-5-carboxylic acid) Nanocomposite for Electrochemical Non-enzymatic Sensing of Hydrogen Peroxide

Herein, co-electrodeposition of AuNPs and ERGO onto GCE was conducted to prepare the modified electrode, GCE/AuNPs-ERGO. The poly(indole-5-carboxylic acid) (P(In-5-COOH) was then coated onto the GCE/AuNPs-ERGO with the help of electropolymerization. FT-IR, FE-SEM and EDX, and XRD techniques were employed to characterize the prepared nanocomposite. The nanocomposite modified electrode (GCE/AuNPs-ERGO/P(In-5-COOH)) was examined for the electrochemical reduction of H₂O₂ using chronoamperometry. A high reduction current for H₂O₂ was observed due to the synergistic effect between AuNPs-ERGO and P(In-5-COOH). The proposed sensor demonstrated a wide linear range of 0.025–750 μmol L⁻¹, with a LOD of 0.008 μmol L⁻¹ at −0.4 V. Furthermore, the developed sensor was applied for the detection of H₂O₂ in fetal bovine serum and urine samples.     

Time Resolved Direct Determination of Arsenate in the Presence of Arsenite on Pencil Graphite Electrode Modified by Graphene Oxide and Zirconium

Trace amount of arsenate in the presence of arsenite was determined directly on pencil graphite electrode modified by graphene oxide and zirconium (Zr−G−PGE). The layer‐by‐layer modification of PGE was characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Key point of the developed method was quick adsorption of arsenate than arsenite on the Zr−G−PGE. In optimal conditions, the Zr−G−PGE was applied for determination of arsenate using differential pulse voltammetry in a linear range 0.10–40.0 μg L⁻¹ with a limit of determination of 0.12±0.01 μg L⁻¹. The sensitivity of the electrode was 1.36±0.07 μA/μg L⁻¹. The modified electrode was used to measure the concentration of arsenate in the river water. A recovery test was performed by introducing 10 μg L⁻¹ arsenate into the rivers water in order and acceptable data of average recovery of 101.2 % was obtained. From the experimental results, the as‐prepared electrode can provide a satisfactory method for direct determination of arsenate in real samples.     

Fabrication of Co3O4 particles-modified multi-walled carbon nanotube and poly(phenosafranine) composite electrode for selective and sensitive rutin detection

The preparation and characterisation of a new composite electrode with Co₃O₄ particles-modified multi-walled carbon nanotube (MWCNT) and poly(phenosafranine), as well as its novel application for the voltammetric detection of rutin was described. The resulting composite electrode was characterised using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). In the optimised experimental conditions, the oxidation peak current (I_pa) of rutin showed a linear increase in concentration, between 0.008–0.6 and 0.80–6.0 μmol L⁻¹, with a detection limit of 0.00379 μmol L⁻¹. Due to its good selectivity and stability, the composite electrode was successfully applied in detecting rutin in pharmaceutical formulations.