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.     

Electrochemical determination of nitrate on Ag nanoparticles-decorated poly (direct blue 15) electrodes

In this study, for the first time, the electro-polymerization of Direct blue15 (DB15), an azo dye, was carried out on the surface of ITO. Furthermore, the poly(DB15) surface was electrochemically decorated with Ag nanoparticles (AgNPs), and the fabricated AgNPs/PDB15 electrodes were examined as nitrate sensors. Compared to unmodified ITO electrode, the AgNPs/PDB15 electrode had greatly improved electrochemical response to nitrate reduction. The nitrate determination in a linear range from 1.0×10⁻⁵ mol L⁻¹ to 2.27×10⁻³ mol L⁻¹ was performed with a detection limit of 9.66 μM. The synthesized electrode is a promising sensor for the electrochemical detection of nitrate pollutants in water.     

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 %.     

Voltammetric Determination of Captopril on a Glassy Carbon Electrode Modified with Copper Metal‐organic Framework

We report in this work, a new method for the determination of captopril by differential pulse voltammetry using a glassy carbon electrode modified with a copper metal‐organic framework (H‐Kust‐1 or Cu₃(BTC)₂ or Cu‐BTC), immobilized on the surface by a copolymer of acrylamide and sodium acrylate. This compound is detected by the formation of a copper(II)‐captopril complex that is observed in an oxidation potential at ca. +0.28 V vs . Ag/AgCl. A linear dynamic range is obtained for a captopril concentration of 0.5 μM to 7.0 μM and the voltammetric response is highly reproducible within 3.52 % error. The sensitivity of 9.71±0.37 nA μM⁻¹ and the limit of detection of 0.20±0.01 μM make this methodology highly applicable for practical applications. The determination of captopril in a commercial pharmaceutical sample showed a recovery of 93.3 %.     

Simple and Fast Determination of Warfarin in Pharmaceutical Samples Using Boron‐doped Diamond Electrode in BIA and FIA Systems with Multiple Pulse Amperometric Detection

This paper proposes the use of the boron‐doped diamond electrode (BDDE) in flow and batch injection analysis (FIA and BIA) systems with multiple‐pulse amperometric (MPA) detection for the determination of warfarin (WA) in pharmaceutical formulations. The electrochemical behavior of WA obtained by cyclic voltammetry (CV) in 0.1 mol L⁻¹ phosphate buffer shows an irreversible oxidation process at +1.0 V (vs Ag/AgCl). The MPA was based on the application of two sequential potential pulses as a function of time on BDDE: (1) for WA detection at +1.2 V/100 ms and; (2) for electrode surface cleaning at −0.2 V/200 ms. Both hydrodynamic systems (FIA‐MPA and BIA‐MPA) used for WA determination achieved high precision (with relative standard deviations around 2 %, n =10), wide linear range (2.0−400.0 μmol L⁻¹), low limits of detection (0.5 μmol L⁻¹) and good analytical frequency (94 h⁻¹ for FIA and 130 h⁻¹ for BIA). The WA determination made by the proposed methods was compared to the official spectrophotometric method. The FIA‐MPA and BIA‐MPA methods are simple and fast, being an attractive option for WA routine analysis in pharmaceutical industries.     

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

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

A MnOOH‐Polyaniline Nanocomposite Modified Gold Electrode for Electrochemical Sensing of Nitrite

A novel non‐enzymatic nitrite sensor was fabricated by immobilizing MnOOH‐PANI nanocomposites on a gold electrode (Au electrode). The morphology and composition of the nanocomposites were investigated by transmission electron microscopy (TEM ) and Fourier transform infrared spectrum (FTIR ). The electrochemical results showed that the sensor possessed excellent electrocatalytic ability for NO₂⁻ oxidation. The sensor displayed a linear range from 3.0 μmol•L⁻¹ to 76.0 mmol•L⁻¹ with a detection limit of 0.9 μmol•L⁻¹ (S/N = 3), a sensitivity of 132.2 μA •L•mol⁻¹•cm⁻² and a response time of 3 s. Furthermore, the sensor showed good reproducibility and long‐term stability. It is expected that the MnOOH‐PANI nanocomposites could be applied for more active sensors and used in practice for nitrite sensing.     

Sensitive Voltammetric Determination of Captopril Using a Carbon Paste Electrode Modified with Nano-TiO2/Ferrocene Carboxylic Acid

A carbon paste electrode (CPE) modified with ferrocene carboxylic acid (FcCA) and TiO2 nanoparticles was constructed by incorporating TiO2 nanoparticles and ferrocene carboxylic acid into the carbon paste matrix.The electrochemical behavior of captopril (CAP) at the surface of the modified electrode was investigated using electroanalytical methods.The modified electrode showed excellent electrocatalytic activity for the oxidation of CAP in aqueous solutions at physiological pH values.Cyclic voltammetric curves showed that the oxidation of CAP at the surface of the modified electrode reduced its overpotential by more than 290 mV.The modified electrode was used for detecting captopril using cyclic voltammetry and square wave voltammetry techniques.A calibration curve in the range of 0.03 to 2400μmol/L was obtained that had a detection limit of 0.0096 μmol/L (3σ) under the optimized conditions.The modified electrode was successfully used for the determination of captopril in pharmaceutical and biological samples.     

Synthesis of Silver Nanoparticle‐Graphene Composites for Electroanalysis Applications using Chemical and Electrochemical Methods

An electrochemical device was developed for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) using differential pulse voltammetry and glassy carbon (GC) electrodes modified with reduced graphene oxide (rGO) and silver nanoparticle (AgNP) composites, synthesised using both chemical and electrochemical methods. The morphology and electrochemical behaviour of the GC electrodes modified with the rGO/AgNP (chemical method) and rGO‐AgNP (electrochemical method) composites were characterised by scanning electron microscopy and cyclic voltammetry. These techniques demonstrated that, in both methods, the graphene oxide was modified by the AgNPs, and the composite synthesised by the electrochemical method showed a better dispersion of the nanoparticles, resulting in an increase in the surface area compared to the rGO/AgNP composite. The GC/rGO‐AgNP electrode was evaluated and optimised for the simultaneous determination of SMX and TMP, achieving detection limits of 0.6 μmol L⁻¹ for the SMX and 0.4 μmol L⁻¹ for the TMP. The proposed GC/rGO‐AgNP electrochemical device was successfully applied to the simultaneous determination of SMX and TMP in wastewaters samples.     

Application of a Tetraamino Cobalt(II) Phthalocyanine Modified Screen Printed Carbon Electrode for the Sensitive Electrochemical Determination of L-Dopa in Pharmaceutical and Biological Samples

A novel synthesized tetraamino cobalt(II) phthalocyanine monomer was used for the fabrication of a sensor by electrochemical polymerization. A disposable electrochemical sensor based on the use of a screen printed carbon electrode covered with an electropolymerized film of tetraamino cobalt(II) phthalocyanine for the determination of L-dopa in pharmaceutical tablets and biological samples was described. Cyclic voltammetry and electrochemical impedance spectroscopy were performed for the characterization of the bare and modified electrode. For the electrochemical detection of L-dopa differential pulse voltammetry was used. The proposed method exhibits a good response towards electrooxidation of L-dopa in the linear concentration range: from 0.1 to 1000.0 μmol L⁻¹ in BRB pH=2.0, with a detection limit of 0.03 μmol L⁻¹ and from 1 to 1000 μmol L⁻¹ in PBS pH=7.4, with a detection limit of 0.33 μmol L⁻¹. Due to the fact that the developed sensor was applied in two different types of real samples, two buffer media were used, BRB pH=2.0 for pharmaceutical and urine samples and PBS pH=7.4 for whole blood samples. The proposed pCoTAPc/SPCE was successfully applied for the determination of L-dopa in pharmaceutical tablets, urine and in whole blood samples with satisfactory results.     

Amperometric Biosensor for Detection of Phenolic Compounds Based on Tyrosinase,N‐Acetyl‐L‐cysteine‐capped Gold Nanoparticles and Chitosan Nanocomposite

A novel biosensor was fabricated based on the immobilization of tyrosinase and N ‐acetyl‐L ‐cysteine‐capped gold nanoparticles onto the surface of the glassy carbon electrode via the film forming by chitosan. The NAC‐AuNPs (N ‐acetyl‐L ‐cysteine‐capped gold nanoparticles) with the average size of 3.4 nm had much higher specific surface area and good biocompatibility, which were favorable for increasing the immobilization amount of enzyme, retaining the catalytic activity of enzyme and facilitating the fast electron transfer. The prepared biosensor exhibited suitable amperometric responses at −0.2 V for phenolic compounds vs. saturated calomel electrode. The parameters of influencing on the working electrode such as pH , temperature, working potential were investigated. Under optimum conditions, the biosensor was applied to detect catechol with a linear range of 1.0 × 10⁻⁷ to 6.0 × 10⁻⁵ mol•L⁻¹ , and the detection limit of 5.0 × 10⁻⁸ mol•L⁻¹ (S /N =3). The stability and selectivity of the proposed biosensor were also evaluated.     

AgNP-decorated SBA-15 for MWCNT Paste Modified Electrode: A Sensor for Simultaneous Voltammetric Determination of Paracetamol and Sulfamethoxazole

A new electrochemical sensor based on a carbon nanotube paste electrode modified with a Santa Barbara Amorphous material (SBA-15) decorated with silver nanoparticles, namely CNT/SBA/Ag-PE, was developed. It was successfully applied for individual and simultaneous determination of both paracetamol (PC) and sulfamethoxazole (SMZ) medicines. The electrode exhibited a linear dynamic range of 0.12–110 μmol L⁻¹ for paracetamol and 0.06–70 μmol L⁻¹ for sulfamethoxazole, and detection limits of 38 and 19 nmol L⁻¹, respectively. The proposed sensor offered high sensitivity, fast response time and the potential for detecting both drugs simultaneously. The CNT/SBA/Ag-PE enabled the simultaneous determination of PC and SMZ in urine samples with high recovery rates.     

Gold Nanoparticles Stabilized in β‐Cyclodextrin and Decorated with Laccase Applied in the Construction of a Biosensor for Rutin

This paper describes the synthesis and characterization of gold nanoparticles stabilized in β‐cyclodextrin (AuNP‐CD), which were applied as a platform in the immobilization of laccase (LAC). The AuNP‐CD‐LAC were used in the construction of a new biosensor for rutin determination by square‐wave voltammetry (SWV). Under optimized conditions, the calibration curve showed a linear range for rutin of 0.30 to 2.97 μmol L⁻¹, with a limit of detection of 0.17 μmol L⁻¹. The biosensor demonstrated satisfactory repeatability and electrode‐to‐electrode repeatability (with relative standard deviations of 5.6 and 6.0 %, respectively) and good stability. The biosensor was successfully applied in the determination of rutin in different pharmaceutical samples.     

An enhanced Nonenzymatic Electrochemical Glucose Sensor Based on Copper‐Palladium Nanoparticles Modified Glassy Carbon Electrodes

Novel copper‐palladium nanoparticles modified glassy carbon electrodes (Cu−Pd/GC) with enhanced nonenzymatic sensing for glucose were facilely prepared by one‐step electrodeposition. The structure and composition of the prepared nanoparticles were characterized by XRD, SEM, TEM and EDS, respectively. The electrode modified process was characterized by electrochemical impedance spectroscopy. Cyclic voltammetry and chronoamperometric experiments were used to evaluate the electrocatalytic activities of the electrodes toward glucose. The surface morphology and the electrocatalytic activities of Cu−Pd/GC was compared to Pd and Cu nanoparticles modified glassy carbon electrodes (Pd/GC and Cu/GC), respectively. Thanks to homogeneous distribution of Cu−Pd nanoparticles and the synergistic effect of Cu and Pd atoms, Cu−Pd/GC exhibited the highest sensitivity (298 μA mM⁻¹ cm⁻²) and the widest linear amperometric response (0.01 mM to 9.6 mM, R²=0.996) toward glucose compared to Pd/GC and Cu/GC. The detection limit of Cu−Pd/GC was 0.32 μM (S/N=3). In addition, the as‐prepared Cu−Pd/GC glucose sensor also exhibited exceptional capabilities of anti‐interference, reproducibility and long‐term stability. The as‐prepared sensor was also evaluated for determination of glucose concentration in human blood serum samples, which exhibited high reliability and accuracy, having great potential in clinical application.     

Nanostructured Hexacyanoferrate Intercalated Ni/Al Layered Double Hydroxide Modified Electrode as a Sensitive Electrochemical Sensor for Paracetamol Determination

An electrochemical sensor for paracetamol (PC) based on the hexacyanoferate(III) intercalated Ni−Al layered double hydroxide (Ni−Al−HCF) was presented. The as‐prepared LDH structurally and morphologically was characterized by scanning electron microscopy, X‐ray diffraction, and Fourier transform IR. Electrochemical studies revealed that Ni−Al−HCF film modified glassy carbon (GC) electrode exhibited remarkable electrocatalytic activity toward the oxidation of paracetamol. The electrochemical behavior of PC on the Ni−Al−HCF film was investigated in detail. Under optimum experimental conditions, the electrocatalytic response of the modified GC electrode was linear in the PC concentration range 3×10⁻⁶⁻–1.5×10⁻³ mol L⁻¹, with a detection limit of 8×10⁻⁷ mol L⁻¹ (S/N=3), using hydrodynamic amperometry. In addition, the modified electrode exhibited good reproducibility, long‐term stability and anti‐interference property. The fabricated sensor was successfully applied to determination of PC in various pharmaceutical preparations such as tablets, oral solution, and oral drops. Finally, the method was validated by the analysis of paracetamol spiked human serum samples, and good recoveries were obtained in the range of 99.2–103 %.     

Nanoporous Gold Microelectrode: A Novel Sensing Platform for Highly Sensitive and Selective Determination of Arsenic (III) using Anodic Stripping Voltammetry

A home‐made gold microelectrode (Au‐μE) was fabricated and its surface was modified with nanoporous gold structures via a facile electrochemical approach (anodization followed by electrochemical reduction method). The fabricated nanoporous Au microelectrode (NPG‐μE) was used as a sensor probe for the determination of As(III) in 1.0 mol L⁻¹ HCl solution using square wave anodic stripping voltammetry (SWASV) technique. Field emission scanning electron microscopy (FE‐SEM) and cyclic voltammetry were used to characterize the surface morphology and assess the electrochemical surface area and the roughness factor of the NPG‐μE. SWASVs recorded with the NPG‐μE in As(III) solutions indicated linear behaviour in the concentration ranges of 10–200 μg L⁻¹ and 2–30 μg L⁻¹, with regression coefficients of 0.996 and 0.999 at a deposition time of 120 s, respectively. The limit of detection (LOD) was found to be 0.62 μg L⁻¹ with high sensitivity of 29.75 μA (μg L⁻¹)⁻¹ cm⁻². Repeatability and reproducibility were also examined and values were determined as 3.2 % and 9.0 %. Negligible interference from major interfering copper ion was noticed, revealing the excellent anti‐interference property of the proposed sensing platform. The developed NPG‐μE was successfully used for As(III) determination in tap water samples.     

Sensitive immunoassay for the β-agonist ractopamine based on glassy carbon electrode modified with gold nanoparticles and multi-walled carbon nanotubes in a film of poly-arginine

We are presenting an electrochemical immunosensor for the determination of the β-agonist and food additive ractopamine. A glassy carbon electrode (GCE) was modified with gold nanoparticles and a film of a composite made from poly(arginine) and multi-walled carbon nanotubes. Antibody against ractopamine was immobilized on the surface of the modified GCE which then was blocked with bovine serum albumin. The assembly of the immunosensor was followed by electrochemical impedance spectroscopy. Results demonstrated that the semicircle diameter increases, indicating that the film formed on the surface hinders electron transfer due to formation of the antibody-antigen complex on the modified electrode. Under optimal conditions, the peak current obtained by differential pulse voltammetry decreases linearly with increasing ractopamine concentrations in the 0.1 nmol•L⁻¹ to 1 μmol•L⁻¹ concentration range. The lower detection limit is 0.1 nmol•L⁻¹. The sensor displays good stability and reproducibility. The method was applied to the analysis of spiked swine feed samples and gave satisfactory results.

Immunoassay for ractopamine based on glassy carbon electrode modified with gold nanoparticles and a film of a composite made from poly (arginine) and multi-walled carbon nanotubes was proposed. Under optimal conditions, the peak currents obtained by differential pulse voltammetry decreases linearly with increasing ractopamine concentrations in the 0.1 nmol•L⁻¹ to 1 μmol•L⁻¹ concentration range. The detection limit is 0.1 nmol•L⁻¹.

     

Sensor Modified with Gold Nanoparticles Stabilized in Dialdehyde Starch/DMSO Matrix for Methyldopa Detection

In this study, gold nanoparticles (AuNP) were synthesized using a novel stabilizer based on dialdehyde starch polymer (DAS) and dimethyl sulfoxide (DMSO) and the nanomaterial was applied to develop a sensor for methyldopa detection. The nanoparticles were characterized by transmission electron microscopy and the proposed sensor was electrochemically characterized by electrochemical impedance spectroscopy, chronocoulometry and square-wave voltammetry. Under optimized conditions (0.1 mol L⁻¹ McIlvaine buffer solution at pH 3.5 and 50 μL AuNP/DAS-DMSO), using square-wave voltammetry, the calibration curve presented a linear range of 0.99 to 19.60 μmol L⁻¹, with a detection limit of 0.50 μmol L⁻¹. The sensor showed good accuracy, with coefficients of variation of 7.8 % (inter-day; n=6) and 5.9 % (intra-day; n=3), and recovery values in the range of 95.3 to 105.2 %. The methyldopa content in a pharmaceutical sample was determined and the results show good correlation with the label value and the method recommended by the Pharmacopoeia, representing a fast and accurate alternative for detecting methyldopa in pharmaceutical products.     

Detection of DNA immobilized on bare gold electrodes and gold nanoparticle-modified electrodes via electrogenerated chemiluminescence using a ruthenium complex as a tag

Electrogenerated chemiluminescence (ECL) for DNA hybridization detection is demonstrated based on DNA that was self-assembled onto a bare gold electrode and onto a gold nanoparticles modified gold electrode. A ruthenium complex served as an ECL tag. Gold nanoparticles were self-assembled on a gold electrode associated with a 1,6-hexanedithiol monolayer. The surface density of single stranded DNA (ssDNA) on the gold nanoparticle modified gold electrode was 4.8?×?10¹⁴ molecules per square centimeter which was 12-fold higher than that on the bare gold electrode. Hybridization was induced by exposure of the target ssDNA gold electrode to the solution of ECL probe consisting of complementary ssDNA tagged with ruthenium complex. The detection limit of target ssDNA on a gold nanoparticle modified gold electrode (6.7?×?10^?12 mol L^?1) is much lower than that on a bare gold electrode (1.2?×?10^?10 mol L^?1). The method has been applied to the detection of the DNA sequence related to cystic fibrosis. This work demonstrates that employment of gold nanoparticles self-assembled on a gold electrode is a promising strategy for the enhancement of the sensitivity of ECL detection of DNA.     

Fabrication of β‐Cyclodextrin/Glycine/Carbon Nanotubes Electrochemical Neurotransmitters Sensor – Application in Ultra‐sensitive Determination of DOPAC in Human Serum

In this work, an electrochemical sensor was constructed by applying two successive thin layers of glycine‐carbon nanotubes mixture and β‐cyclodextrin (CNTs‐Gly)/CD over glassy carbon electrode surface for some neurotransmitters determination. A host‐guest interaction between CD and neurotransmitters molecules is expected and resulted in enhanced sensitivity, selectivity and stability of sensor response. Other components of the sensor are crucial for the unique electrochemical response. Carbon nanotubes allowed large surface area for glycine distribution that provided hydrogen bonding to CD moieties and contributed to facilitated charge transfer. It was possible to determine 3,4‐dihydroxy phenyl acetic acid (DOPAC) in the linear range of 0.1 μmol L⁻¹ to 80 μmol L⁻¹ with detection limit of 9.40 nmol L⁻¹, quantification limit of 31.5 nmol L⁻¹ and sensitivity of 4.16 μA/μmol L⁻¹. The proposed sensor was applied in synthetic cerebrospinal fluids samples using random standard addition method. Also, the proposed sensor was used to determine DOPAC in presence of common interferences and acceptable recovery results were achieved for its analysis in real blood serum. Figures of merit for (CNTs‐Gly)/CD composite in terms of precision, robustness, repeatability and reproducibility were reported.