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.     

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.     

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.     

Development of a Sensor Based on Modified Carbon Paste with Com Iron(III) Protoporphyrin Immobilized on SiNbZn Silica Matrix for L‐tryptophan Determination

In this work, SiO₂/Nb₂O₅/ZnO prepared by the sol‐gel processing method was used as substrate base for immobilization of the protoporphyrin‐IX ion. Iron(III) ion was inserted into the porphyrin ring (SiNbZn‐PPFe). A simple square wave voltammetry method based on a composite sensor carbon paste electrode of this material,designed as EPC‐SiNbZn‐PPFe, was developed and validated successfully for the determination of L‐tryptophan (Trp). The optimum conditions were obtained by using sensor modified with 18.00 mg SiNbZn‐PPFe material, 12.00 mg graphite powder and 6.0 μL mineral oil and phosphate buffer 0.3 mol L⁻¹ pH 7.0. The sensitivity of the sensor was found to be 0.523 AL mol ⁻¹, linear range from 10 to 70 μmol L⁻¹ and limit of detection of 3.28 μmol L⁻¹. Therefore, the developed method was successfully applied for the Trp determination in real samples of pharmaceutical formulation and can be used for routine quality control pharmaceutical formulations containing Trp.     

Simultaneous Determination of Lipophilic Vitamin Esters Using Square-wave Voltammetry at the Glassy Carbon Electrode

Simple and rapid voltammetric method for simultaneous determination of all-trans-retinyl acetate (RAc) or all-trans-retinyl palmitate (RPa) and α-tocopheryl acetate (α-TOAc) has been proposed. The respective method was based on the anodic oxidation of the compounds of interest by square-wave voltammetry in acetone with 0.1 mol L⁻¹ LiClO₄ at the glassy carbon electrode. The procedure was also beneficial with respect to simple dissolution of sample directly in the supporting electrolyte. The all-trans-retinyl acetate could be quantified in two linear ranges (3.1–140 μmol L⁻¹ and 140–400 μmol L⁻¹) and α-tocopheryl acetate in linear range 5.3–400 μmol L⁻¹ with detection limits of 0.9 μmol L⁻¹ RAc (or 0.8 μmol L⁻¹ RPa) and of 1.6 μmol L⁻¹ α-TOAc. Selected commercial cosmetic products were analysed achieving satisfactory recoveries.     

Disposable Pencil Graphite Electrode for Ciprofloxacin Determination in Pharmaceutical Formulations by Square Wave Voltammetry

In this work, a new electrochemical sensor based on pencil graphite with interesting features, such as low cost (US$ 0.01 per electrode), ease manufacture, and portability was developed. The sensor showed an adequate manufacturing reproducibility with RSD <5.3 %. Under this electrochemical platform, ciprofloxacin underwent an irreversible oxidation process at 1.03 V, characterized by the diffusion of electroactive species. A simple method by square wave voltammetry (SWV) has been optimized for the determination of ciprofloxacin in pharmaceutical formulations using a pencil graphite electrode (PGE). The method showed satisfactory analytical performance, with a wide linear range (12 to 55 μmol L⁻¹), low detection limit (5.6 μmol L⁻¹), adequate precision (RSD <3.2 %), and accuracy with an average recovery of (102±15)%. Samples of pharmaceutical formulations were evaluated, obtaining levels of ciprofloxacin close to those established by the manufacturers. In addition, the samples were analyzed by liquid chromatography and there was no significant difference between the methods at the 95 % confidence level. In this sense, the method developed proved to be reliable and promising for the quality control of pharmaceutical formulations.     

Electrochemical Sensor Based on Gold Nanoparticles Stabilized in Poly(Allylamine hydrochloride) for Determination of Vanillin

Gold nanoparticles stabilized in poly(allylamine hydrochloride) (AuNP‐PAH) were synthesized, characterized and applied in the development of a new sensor for the determination of vanillin by square‐wave voltammetry. Under optimized conditions, the calibration curve showed a linear range for vanillin of 0.90 to 15.0 µmol L^?1, with a limit of detection of 55 nmol L^?1. The sensor demonstrated acceptable selectivity and stability, as well as good intra‐day and inter‐day repeatability and electrode‐to‐electrode repeatability (with relative standard deviations of 3.5, 4.5 and 3.9 %, respectively). The sensor was successfully applied in the determination of vanillin in different commercial samples.     

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.     

A Novel Electrochemical Glassy Carbon Electrode Modified with Carbon Black and Glyceline Deep Eutectic Solvent within a Crosslinked Chitosan Film for Simultaneous Determination of Acetaminophen and Diclofenac

Glyceline, reline, or ethaline deep eutectic solvents and carbon black nanoparticles within a crosslinked chitosan film are investigated as glassy carbon electrode modifiers for the first time. The selected 5 mg mL⁻¹ glyceline modified GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Simultaneous determination of acetaminophen and diclofenac by differential pulse adsorptive stripping voltammetry (DPAdSV) presented limits of detection of 2.6×10⁻⁸ and 5.2×10⁻⁸ mol L⁻¹ for acetaminophen and diclofenac, respectively, in pharmaceutical and biological samples. The obtained results were compared with those obtained by HPLC at a confidence level of 95 %.     

Square-wave Anodic Stripping Voltammetric Method for Novelty Detection of Bismuth Extracted by Aqueous Two-phase Systems

In this work, a voltammetric sensor was used to monitor the concentration of bismuth extracted from an eutectic alloy of BiSn by aqueous two-phase system. This strategy is a sustainable and economically viable way of recovering bismuth from secondary sources. In the aqueous two-phase system (ATPS), biodegradable and non-toxic constituents dispersed in water (major constituent) are used. For monitoring the extraction, bismuth was determined in the upper phase of the aqueous two-phase system, which is rich in L35 copolymer, that causes attenuation of the electrochemical signal (anodic peak current). The electrode and operational parameters of the square-wave anodic stripping voltammetry (SWASV) were evaluated according to the deposition and stripping processes of the bismuth on the surface of the carbon paste electrode (CPE). It was observed a similarity between the electrochemical response of the bismuth extracted by ATPS and with the standard solution of bismuth. The proposed method shows a linear range of 1.29–8.94 μmol L⁻¹, limit of detection (1.07 μmol L⁻¹) and limit of quantification (3.57 μmol L⁻¹) and good precision (RSD%=2.27 %). This method was validated by comparing the results with Flame Atomic Absorption Spectroscopy (FAAS), using statistical tests to verify precision and accuracy. In conclusion, using a voltammetric sensor to monitor the concentration of bismuth extracted by ATPS proved to be an efficient method, in agreement with the concentrations of the referenced method.     

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.     

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.     

Metal Organic Framework-235 (MOF-235) Modified Carbon Paste Electrode for Catechol Determination in Water

MOF-235 is presented as an orange powder, with crystals of the octahedral formation. It was already used as adsorbent to remove different compounds from water; however, no attempts have been published about the exploration of the MOF-235 application as electrochemical sensor for organic compounds yet. MOF-235 was synthetized and after that, it was characterized by SEM, XRD and FTIR. Graphite electrodes (GEs) were modified with different MOF-235 ratio (5 %, 7 %, 10 %, 12 % and 14 %) and these modified GEs were characterized by cyclic voltammetry (CV) measurements in order to determine the effect of MOF-235 concentration on the current response. Results indicated that, a significant improvement on the current response was attained at MOF-235(10 %)/GE respect to unmodified GE. This behavior is related to the pore structure and multiple active sites on the MOF surface. The performance of the MOF-235(10 %)/GE as electrochemical sensor for detecting catechol was assessed by differential pulse voltammetry (DPV). Catechol detection response of MOF-based sensor provided a detection limit of about 12.79 μmol L⁻¹ with a correlation coefficient (R²) of about 0.9928 ranging from 12 to 514 μmol L⁻¹. Finally, MOF-235(10 %)/GE was used to determine catechol in real water matrixes.     

Electroanalytical Determination of Estrone in Seawater Samples Using Functionalized Multiwalled Carbon Nanotubes

In this work, a glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes functionalized with carboxylic groups (MWCNT−COOH) was used to determine the hormone estrone in seawater samples. Modification of the electrode was optimized using three successive 10-μL aliquots of the MWCNT−COOH dispersion in ethanol (1 : 5 mL). The cyclic voltammetry results showed an oxidation peak at 0.59 V with characteristics of an irreversible process, pH dependent and controlled by adsorption of species. The results of square-wave voltammetry showed that the intensities of peak currents for the MWCNT−COOH/GCE were about 2.5 times higher than for GCE. The calibration curve showed a linearity of 0.9981 and a sensitivity of 0.1521 μA/mol L⁻¹. The limits of detection and quantification were 0.117 and 0.392 μmol L⁻¹, respectively. The recovery obtained using seawater samples was 91%, indicating the applicability of the method in marine environments.     

Bismuth Nanoparticles@Porous Silicon Nanostructure,Application as a Selective and Sensitive Electrochemical Sensor for the Determination of Thioridazine

A bismuth@porous silicon (Bi/PSi) nanostructure is fabricated and used as a new highly sensitive electrochemical sensor for measurement of thioridazine. For this purpose, commercial silicon powder is converted to porous silicon using metal‐assisted chemical etching method. Then, bismuth nanoparticles are deposited on the surface of the porous silicon that synthesized in the previous step. The effects of pH and instrumental parameters are studied on the sensor response. After optimization of the parameters, differential pulse voltammetry is used to determine sub‐micro molar amounts of thioridazine. The Linear region of the electrochemical sensor is in the range of 0.1 to 260 μmol L⁻¹ thioridazine with a detection limit of 0.03 μmol L⁻¹, when Bi/PSi/CNTPE is used as an electrochemical sensor. The precision and accuracy of the sensor is evaluated. The Bi/PSi/CNTPE is used as an appropriated tool for accurate measurement of low amounts of thioridazine in real samples with satisfactory results.     

Tapioca Biofilm Containing Nitrogen‐doped Titanium Dioxide Nanoparticles for Electrochemical Detection of 17‐β Estradiol

A novel sensor architecture based on thin film of tapioca decorated within nitrogen‐doped titanium dioxide (N‐TiO₂) nanoparticles is reported. The nanostructures were characterized by scanning electron microscope, transmission electron microscope, X‐rays diffraction and voltammetric techniques. The proposed electrode was used for detection of low concentrations of 17‐β estradiol in without purification step, which was investigated by using linear sweep adsorptive stripping voltammetry. Under optimal conditions, the analytical curve was linear over a 17β‐estradiol concentration range of 9.9×10⁻⁶ to 1.4×10⁻⁵ mol L⁻¹, with a detection limit of 1.7×10⁻⁷ mol L⁻¹. The tapioca and N‐TiO₂ nanoparticles homogeneous film was applied for detection of 17‐β‐estradiol in tap water and synthetic urine samples, which presented satisfactory results.     

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.     

Photoelectrochemical Sensor for Isoniazid: Application in Drugs Used in the Treatment of Tuberculosis

The present work describes the development of a photoelectrochemical sensor based on titanium dioxide, cadmium telluride quantum dots and the tris (2,2′-bipyridyl) ruthenium(II) chloride complex for detection of Isoniazid (INH). The Ru(bpy)₃²⁺/CdTe-QDs/TiO₂/FTO photoelectrochemical platform was characterized by scanning electrochemical microscopy, electrochemical impedance spectroscopy and amperometry. The photoelectrochemical sensor presented two linear ranges for INH concentrations ranging from 0.5 to 150 μmol L⁻¹ and 150 to 1270 μmol L⁻¹, with a theoretical detection limit of 0.02 μmol L⁻¹. The sensor was successfully applied for the determination of INH in drugs samples used in the treatment of tuberculosis.     

A Comparison of Edge-plane and Basal-plane Pyrolytic Graphite Electrodes towards Sensitive Determination of the Fungicide Mandipropamid

A sensitive square-wave voltammetry (SWV) method based on basal-plane pyrolytic graphite electrode (BPPGE) and edge-plane pyrolytic graphite electrode (EPPGE) was developed to determine the concentration of the pesticide mandipropamid (MAN) in spiked river water and grape juice samples. Under optimal experimental conditions, the SWV response of EPPGE and BPPGE was linear over the concentration ranges of 0.7 to 9.0 μmol L⁻¹ and 0.5 to 10.0 μmol L⁻¹, respectively. The method was successfully used to determine MAN in spiked samples with good recovery. Cyclic voltammetry (CV) was conducted to understand the mechanism underlying the electrode process of MAN.     

A new Approach for the Voltammetric Sensing of the Phytoestrogen Genistein at a Non-modified Boron-doped Diamond Electrode

An effective electrochemical sensor was constructed using an unmodified boron-doped diamond electrode for determination of genistein by square-wave voltammetry. Cyclic voltammetric investigations of genistein with HClO₄ solution indicated that irreversible behavior, adsorption-controlled and well-defined two oxidation peaks at about +0.92 (P_A1) & +1.27 V (P_A2). pH, as well as supporting electrolytes, are important in genistein oxidations. Quantification analyses of genistein were conducted using its two oxidation peaks. Using optimized experiments as well as instrumental conditions, the current response with genistein was proportionately linear in the concentrations range of 0.1 to 50.0 μg mL⁻¹ (3.7×10⁻⁷−1.9×10⁻⁴ mol L⁻¹), by the detection limit of 0.023 μg mL⁻¹ (8.5×10⁻⁸ mol L⁻¹) for P_A1 and 0.028 μg mL⁻¹ (1.1×10⁻⁷ mol L⁻¹) for P_A2 in 0.1 mol L⁻¹ HClO₄ solution (in the open circuit condition at 30 s accumulation time). Ultimately, the developed method was effectively applied to detect genistein in model human urine samples by using its second oxidation peak (P_A2).