Alternating Layers of Iron(III) Tetra(N‐methyl‐4‐pyridyl)‐porphyrin and Copper Tetrasulfonated Phthalocyanine for Amperometric Detection of 4‐Nitrophenol in Nanomolar Levels

The present work describes the development of a highly sensitive amperometric sensor for 4‐NP in nanomolar levels using a glassy carbon electrode modified with alternating layers of CuTSPc and FeT4MPyP. After optimizing the operational conditions, the sensor provided a linear response range for 4‐NP from 5 up to 100 nmol L^?1 with sensitivity, detection, and quantification limits of 14 nA L nmol^?1, 1.9 nmol L^?1, and 5.4 nmol L^?1, respectively. The proposed sensor showed a stable response for at least 200 successive determinations. This modified electrode can be used to the determination of 4‐NP in water samples.     

Poly(Taurine‐Glutathione)/Carbon Nanotube Modified Glassy Carbon Electrode as a New Levofloxacin Sensor

A new highly sensitive and selective electrochemical levofloxacin sensor based on co‐polymer‐carbon nanotube composite electrode was developed. Taurine and Glutathione were electrochemically co‐polymerized on multiwalled carbon nanotubes modified glassy carbon electrode (Poly(TAU‐GSH)/CNT/GCE) and used as a levofloxacin sensor in pH 6 phosphate buffer solution. The new composite electrode surfaces were characterized by scanning electron microscopy, atomic force microscopy and electrochemical impedance spectroscopy. Under the optimized conditions, two linear segments were obtained for increasing LEV concentrations between 20 nmol L^?1‐1 μmol L^?1 and 1.5 μmol L^?1‐55 μmol L^?1 LEV with a detection limit of 9 nmol L^?1 using amperometry. Poly(TAU‐GSH)/CNT/GCE exhibited high sensitivity, selectivity with good stability. The new sensor was employed for real samples of LEV tablets and urine. Promising results were obtained with good accuracy which were also in accordance with LC‐MS/MS analysis.     

Electrochemical Sensing Platform Based on Nano‐Perovskite/Glycine/Carbon Composite for Amlodipine and Ascorbic Acid Drugs

People suffered from essential hypertension have increased oxidative stress. Thus, adding vitamin C to their medical therapy resulted in decreasing the oxidative stress and increasing the antioxidant status. This may prevent further vascular damage due to the oxidative stress, leading to a better diagnosis in critical hypertension patients. A novel sensor was fabricated based on NdFeO₃ nano‐perovskite/glycine/carbon nanotubes modified carbon paste electrode in presence of sodium dodecyl sulfate; GLNFCNTCP‐SDS for electrochemical sensing and simultaneous determination of antihypertensive and antioxidant drugs, Amlodipine (AML) and ascorbic acid. The developed nanocomposite showed interactive characteristics of all the modifiers as high conductivity, enhanced surface area, surface fouling resistance and stability. This leads to accelerated electron transfer rate and increased current response of electro‐oxidation of AML by 8.3 folds compared to unmodified electrode. The method validity was investigated successfully by the quantitative analysis of AML in human urine samples and Norvasc tablets with acceptable recovery results. The featured merits of the proposed composite in the analysis of AML in human urine samples were; wide concentration range of 0.003 μmol L^?1 to 200 μmol L^?1, sensitivity of 113.2 μA/μmol L^?1, detection limit of 0.704 nmol L^?1, and quantification limit of 2.35 nmol L^?1.     

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.     

Analysis of short‐chain aliphatic amines in food and water samples using a near infrared cyanine 1‐(ε‐succinimydyl‐hexanoate)‐1′‐methyl‐3,3,3′,3′‐tetramethyl‐indocarbocyanine‐5,5′‐disulfonate potassium with CE–LIF detection

Precolumn derivatization of six short‐chain aliphatic amines by a near‐infrared dye, 1‐(ε‐succinimydyl‐hexanoate)‐1′‐methyl‐3,3,3′,3′‐tetramethyl‐indocarbocyanine‐5,5′‐ disulfonate potassium (MeCy5‐OSu), followed by MEKC–CE–LIF detection has been developed as a method for the determination of aliphatic amines in environmental water and food. Optimum derivatization was operated nicely in pH 9.0 borate buffer at 20°C for 30 min. Well separated peaks were observed with a pH 9.5 BGE containing 10 mmol L^?1 phosphoric acid, 20 mmol L^?1 SDS, and 7% methanol buffered with 1.0 mol L^?1 NaOH. The separation procedure was rapidly achieved within 11 min and the matrix interferences could be effectively eliminated. A linear calibration graph was obtained for 5–200 nmol L^?1 analytes with a correlation coefficient in the range 0.9933–0.9995 for amines. This method was successfully utilized to determine aliphatic amines in lake, sewage water, and red wine with recoveries ranging from 96.4 to 105% and the RSDs ranging from 0.9 to 2.9%. Near‐infrared, LIF‐detector‐compatible MeCy5‐OSu was proved suitable for the accurate, sensitive, and rapid separation and determination of aliphatic amines in water and food samples.     

Molecularly imprinted nanoparticles-based electrochemical sensor for determination of ultratrace parathion in real samples

Molecularly imprinted polymer nanoparticles (nano-MIP), containing parathion selective sites, were synthesized by using suspension polymerization in silicon oil and then used for carbon paste electrode preparation. The obtained electrode was applied as an electrochemical sensor for parathion determination in different fruit and vegetable samples. Different factors including electrode composition, conditions of parathion extraction in the electrode and electrochemical measurement conditions were evaluated and then optimized by using various techniques of screening and response surface experimental designs. Electrode response to parathion (Res₁) and its selectivity for parathion (Res₂) were the desired responses. These responses were optimized simultaneously. After optimization, a sensor with high selectivity and picomolar detection limit were obtained. It was shown that the sensor response to parathion concentration was linear in the concentration range of 0.05 to 150?nmol?L^?1. The detection limit of designed sensor was calculated equal to 0.02?nmol?L^?1. The developed determination method was properly used for ultra-trace level assay of parathion in different fruit and cabbage samples.     

Sensitive Voltammetric Determination of Bisphenol A Based on a Glassy Carbon Electrode Modified with Copper Oxide‐Zinc Oxide Decorated on Graphene Oxide

A highly sensitive and selective chemical sensor was prepared based on metallic copper‐copper oxides and zinc oxide decorated graphene oxide modified glassy carbon electrode (Cu?Zn/GO/GCE) through an easily electrochemical method for the quantification of bisphenol A (BPA). The composite electrode was characterized via scanning electron microscopy (SEM), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of BPA in Britton‐Robinson (BR) buffer solution (pH 7.1) was examined using cyclic voltammetry (CV). Under optimized conditions, the square wave voltammetry (SWV) response of Cu?Zn/GO/GCE towards BPA indicates two linear relationships within concentrations (3.0 nmol L^?1?0.1 μmol L^?1 and 0.35 μmol L^?1?20.0 μmol L^?) and has a low detection limit (0.88 nmol L^?1). The proposed electrochemical sensor based on Cu?Zn/GO/GCE is both time and cost effective, has good reproducibility, high selectivity as well as stability for BPA determination. The developed composite electrode was used to detect BPA in various samples including baby feeding bottle, pacifier, water bottle and food storage container and satisfactory results were obtained with high recoveries.     

Amplified Electrochemical Response of Phenol by Oxygenation of Tyrosinase Coupling with Electrochemical‐chemical‐chemical Redox Cycle

In this work, an novel electrochemical‐chemical‐chemical (ECC) redox cycle was designed in an enzyme‐based sensor for acquiring additional signal amplification. The tyrosinase (Tyr) was entrapped in a sulfonated polyaniline?chitosan (SPAN?CS) composite which was used as a redox capacitor on a glass carbon electrode. Firstly, the substrate, phenol was catalyzed to catechol and further catalyzed to o‐benzoquinone by Tyr. Next, in the presence of Ru(NH₃)₆Cl₂, the reduced state of SPAN(SPAN_red) was reacted with o‐benzoquinone to form it's oxidized state (SPAN_ox) and catechol, then SPAN_ox was reduced back to SPAN_red by Ru(II) in the solution. Finally, the amplified anodic current of catechol was obtained on electrode through above ECC redox cycle system. In addition, the ECC redox cycling led to a high signal‐to‐background ratio. The voltammetric response showed excellent analytical performance to phenol over two linear range of 3.5 to 200.0 nmol L^?1 and 200.0 to 2000.0 nmol L^?1 with a high sensitivity of 2204 μA mM^?1. The detection limit was obtained to be 0.8 nmol L^?1 (S/N=3). Furthermore, the proposed approach exhibited good repeatability, stability and specificity, and could offer practicality in the detection of phenol in tap water.     

Trace Level Determination of Hydrogen Peroxide at a Carbon Ceramic Electrode Modified with Copper Oxide Nanostructures

An electrochemical sensor was developed for determination of hydrogen peroxide based on nanocopper oxides modified carbon sol‐gel or carbon ceramic electrode (CCE). The modified electrode was prepared by electrodeposition of metallic copper on the CCE surface and derivatized in situ to copper oxides nanostructures and characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The modified electrode responded linearly to the hydrogen peroxide (H₂O₂) concentration over the range 0.78–193.98 µmol L^?1 with a detection limit of 71 nmol L^?1 (S/N=3) and the sensitivity of 0.697 A mol^?1 L cm^?2. This electrode was used as selective amperometric sensor for determination of H₂O₂ contents in hair coloring creams.     

Electrochemical Detection of Nitrite in Meat and Water Samples Using a Mesoporous Carbon Ceramic SiO2/C Electrode Modified with In Situ Generated Manganese(II) Phthalocyanine

Mesoporous carbon ceramic SiO₂/50 wt % C (S_BET=170 m² g^?1), where C is graphite, were prepared by the sol‐gel method. The materials were characterized using N₂ sorption isotherms, scanning electron microscopy, and conductivity measurements. The matrix was used as support for the in situ immobilization of Mn(II) phthalocyanine (MnPc) on their surface. XPS was used to determine the Mn/Si atomic ratios of the MnPc‐modified materials. Pressed disk electrodes were prepared with the MnPc‐modified matrix, and tested as an electrochemical sensor for nitrite oxidation. The linear response range, sensitivity, detection limit and quantification limit were 0.79–15.74 µmol L^?1, 17.31 µA L µmol^?1, 0.02 µmol L^?1 and 0.79 µmol L^?1, respectively, obtained using cyclic voltammetry. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 1.7 % for 10 measurements of a solution of 12.63 µmol L^?1 nitrite. The sensor employed to determine nitrite in sausage meat, river and lake water samples showed to be a promising tool for this purpose.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.     

Graphene Quantum Dots Modified Screen‐printed Electrodes as Electroanalytical Sensing Platform for Diethylstilbestrol

In present work a simple methodology for electroanalytical sensing of diethylstilbestrol (DES) using graphene quantum dots (GQD) surface modified screen‐printed electrodes (SPE) is reported. GQD was synthesized by simple bottom‐up method based on citric acid pyrolysis at 200 °C and electrodeposited directly at electrode surface under cyclic voltammetric conditions. The obtained GQD presented an average diameter of 7 nm and was characterized by techniques such as transmission and scanning electron microscopy, and electrochemical impedance spectroscopy. The proposed sensor exhibits a linear response from 0.05 to 7.5 μmol L^?1, with limit of detection and quantification of 8.8 nmol L^?1 and 29.0 nmol L^?1, respectively. The repeatability study presented RSD=3.6 % for 6 consecutive measurements using the same electrode surface and the reproducibility study showed RSD=6.6 % for measurements with 6 different electrode surfaces. The proposed sensor was successfully applied for DES determination in synthetic urine and tap water spiked samples and good recoveries were obtained without any sample pre‐treatment, showing its promising analytical performance.     

Voltammetric Determination of 4‐Nitrophenol and 5‐Nitrobenzimidazole Using Different Types of Silver Solid Amalgam Electrodes – A Comparative Study

The voltammetric behavior of two genotoxic nitro compounds (4‐nitrophenol and 5‐nitrobenzimidazole) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p‐AgSAE), a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and a mercury film modified silver solid amalgam electrode (MF‐AgSAE). The optimum conditions have been evaluated for their determination in Britton‐Robinson buffer solutions. The limit of quantification (L_Q) for 5‐nitrobenzimidazole at p‐AgSAE was 0.77 µmol L^?1 (DCV) and 0.47 µmol L^?1 (DPV), at m‐AgSAE it was 0.32 µmol L^?1 (DCV) and 0.16 µmol L^?1 (DPV), and at MF‐AgSAE it was 0.97 µmol L^?1 (DCV) and 0.70 µmol L^?1 (DPV). For 4‐nitrophenol at p‐AgSAE, L_Q was 0.37 µmol L^?1 (DCV) and 0.32 µmol L^?1 (DPV), at m‐AgSAE it was 0.14 µmol L^?1 (DCV) and 0.1 µmol L^?1 (DPV), and at MF‐AgSAE, it was 0.87 µmol L^?1 (DCV) and 0.37 µmol L^?1 (DPV). Thorough comparative studies have shown that m‐AgSAE is the best sensor for voltammetric determination of the two model genotoxic compounds because it gives the lowest L_Q, is easier to prepare, and its surface can be easily renewed both chemically (by new amalgamation) and/or electrochemically (by imposition of cleaning pulses). The practical applicability of the newly developed methods was verified on model samples of drinking water.     

Sensitive Nonenzymatic Electrochemiluminescence Determination of Hydrogen Peroxide in Dental Products using a Polypyrrole/Polyluminol/Titanium Dioxide Nanocomposite

A layer-by-layer assembled of a polypyrrole and polyluminol was synthesized through the electrodeposition of pyrrole and luminol in acidic medium on a graphite electrode. The electrode was then modified by casting titanium dioxide (TiO₂) nanoparticles on its surface for enhancing electrochemiluminescence of luminol. The properties of this electrochemiluminescence sensor were studied by cyclic voltammetry, electrochemical impedance spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. The results demonstrated that the modification of this electrochemiluminescence sensor shows sensitive response for the determination of hydrogen peroxide. Figures of merit include broad linearity from 1?pmol L^?1 to 4?µmol L^?1 (R²?=?0.996) with a limit of detection as low as 0.40?pmol L^?1 at a signal-to-noise ratio of three and good reproducibility with relative standard deviation of 4% for the determination of a 400?nmol L^?1 hydrogen peroxide solution (n?=?4), along with favorable long-term stability. The presence of glucose, citric acid, uric acid, dopamine, and ascorbic acid at concentrations as high as 100?nmol L^?1 of H₂O₂ did not produce any electrochemiluminescence signals, which demonstrates the selective nature of this modified electrode. The sensor was also used for the determination of H₂O₂ in mouthwash formulations and dental whitelight gels.     

Modified Carbon Paste Electrode for Kinetic Investigation and Simultaneous Determination of Ascorbic and Uric Acids

The present work explores, for the first time, the electrocatalytic oxidation of ascorbic acid (AscH₂) and its determination in the presence of uric acid (UA) on the in situ activated 4‐nitrophthalonitrile modified carbon paste electrode. The kinetic constant κ for the catalytic reaction for the electrocatalytic oxidation of ascorbic acid, evaluated by cyclic voltammetry, chronoamperometry and RDE voltammetry provided values around 10⁶ L mol^?1 s^?1. The sensor provided a linear response range for AscH₂ and UA from 5.0 up to 120.0 μmol L^?1 with detection limits of 1.6 μmol L^?1and 1.3 μmol L^?1, respectively. The sensor was applied for the simultaneous determination of AscH₂ and UA in urine samples and the average recoveries for these samples were 99.8 (±3.1)% and 99.9 (±2.1)%, respectively .     

Electrochemical Determination of Vitamin B12 Based on Cu2+‐Involved Fenton‐like Reaction

Poly(thionine) (PTH) film was generated on the electrochemically activated glassy carbon electrode (GCE(ea)) by using the two‐step cyclic voltammetric scan. Scanning electron microscopy, infrared spectral analysis and electrochemical measurement were employed to characterize the modified electrode surface. Hydroxyl radicals, which were produced by the Fenton‐like reaction, could induce the effective oxidization of PTH under near‐neutral condition and cause the notable enhancement of the cathodic peak current (I_pc) during the potential cycling process. Due to the binding of copper ions with the ligands liberated from V_B12 and the inferior catalytic ability of Co²⁺ for the generation of hydroxyl radicals, the addition of V_B12 into the Cu²⁺?H₂O₂ system inhibited the oxidization of PTH and resulted in the decrease of the I_pc value. The cathodic peak current change was linear with the logarithm of the V_B12 concentration in the range of 10 nmol L^?1–100 μmol L^?1 with a detection limit of 2 nmol L^?1 under optimal conditions. The developed sensor displayed excellent analytical performance including high sensitivity, good selectivity, acceptable reproducibility and satisfactory stability. The V_B12 content in the injection sample was measured and the recovery values were in the range of 92.0 %–102 %.     

Label‐Free,Non‐Derivatization CRET Detection Platform for 6‐Mercaptopurine Based on the Distance‐Dependent Optical Properties of Gold Nanoparticles

A label‐free, non‐derivatization chemiluminescence resonance energy transfer (CRET) detection platform has been developed for the detection of the non‐fluorescent small molecule 6‐mercaptopurine. This CRET process arose from a chemiluminescent (CL) donor–acceptor system in which the reaction of bis(2,4,6‐trichlorophenyl)oxalate (TCPO)–H₂O₂–fluorescein (maximum emission at 521.6 nm) served as the donor and gold nanoparticles (AuNPs, maximum absorption at 520.0 nm) served as the acceptor. This process caused a significant decrease in the CL signal of the TCPO–H₂O₂–fluorescein reaction. The presence of 6‐mercaptopurine induced an aggregation of AuNPs with the assistance of Cu²⁺ ions through cooperative metal–ligand interactions that was accompanied by a distinct change in color and optical properties. The maximum absorption band of the AuNPs was red‐shifted to 721.0 nm and no longer overlapped with the CL spectrum of the reaction; as a result, the CL signal was restored. This CRET system exhibited a wide linear range, from 9.0 nmol L^?1 to 18.0 μmol L^?1, and a low detection limit (0.62 nmol L^?1) for 6‐mercaptopurine. The applicability of the proposed CRET system was evaluated by analysis of 6‐mercaptopurine in spiked human plasma samples.     

Direct Determination of Phosphite in Fertilizers by Flow‐Injection Amperometry

A sensor based on graphite electrode modified with palladium‐platinum‐palladium film is proposed for phosphite determination by flow‐injection amperometry. The modified electrode was prepared by a sequential cathodic deposition of Pd, Pt and Pd on a graphite electrode from 0.5% m/v PdCl₂+28% m/v NH₄OH and 2% m/v H₂PtCl₆+10% v/v H₂SO₄ solutions. After suitable conditioning, the electrode showed catalytic activity for phosphite oxidation when 0.15 V was applied. The proposed system handles approximately 50 samples per hour (0.01–0.05 mol L^?1 Na₂HPO₃; R²=0.9997), consuming ca. 70 μL of sample per determination. The limit of detection and amperometric sensibility were 5×10^?4 mol L^?1 and 1.5 mA L mol^?1, respectively. The proposed method was applied to analysis of fertilizer samples without pre‐treatment. Results are in agreement with those obtained by spectrophotometry and titrimetry at 95% confidence level and good recoveries (96–109%) of spiked samples were found. Relative standard deviation (n= 12) of a 0.01 mol L^?1 Na₂HPO₃ sample was 2%. The useful lifetime of modified electrode was around 220 determinations. For routine purposes it means that this electrode can be continuously used for 5 hours.     

Electrochemical Determination of Neurotransmitters at Crown Ether Modified Carbon Nanotube Composite: Application for Sub‐nano‐sensing of Serotonin in Human Serum

We propose an electrochemical sensor based on applying two successive thin layers from a mixture of multiwalled carbon nanotubes‐ionic liquid crystal and crown ether at glassy carbon electrode surface (GC/(CNTs‐ILC)/Crown). The sensor was used for sensitive determination of neurotransmitters based on effective synergism between its components. The compact conducting surface of (CNTs ‐ ILC) with large surface area allowed the assembling of stable host‐guest inclusion complexes between crown ethers and neurotransmitters. The GC/(CNTs‐ILC)/Crown exhibited excellent electro‐catalytic activity toward the determination of serotonin (ST) in a wide linear dynamic range: 0.005 μmol L^?1 to 100 μmol L^?1. In the concentration range 0.005 μmol L^?1 to 1 μmol L^?1, the detection limit is 2.03×10^?10 mol L^?1 and quantification limit is 6.78×10^?10 mol L^?1 with correlation coefficient 0.999. The sensor was successfully applied for ST detection in human serum samples with satisfied recovery results. The sensor showed excellent analytical performance for the determination of ST in terms of low detection limit, good sensitivity and reproducibility. Furthermore excellent anti‐interference ability and simultaneous determination of ST in presence of other compounds as ascorbic acid, dopamine and antidepressant drug were achieved.     

Ruthenium Oxide Hexacyanoferrate Modified Electrode for Hydrogen Peroxide Detection

A sensor for H₂O₂ amperometric detection based on a Prussian blue (PB) analogue was developed. The electrocatalytic process allows the determination of hydrogen peroxide at 0.0 V with a limit of detection of 1.3 μmol L^?1 in a flow injection analysis (FIA) configuration. Studies on the optimization of the FIA parameters were performed and under optimal FIA operational conditions the linear response of the method was extended up to 500 μmol L^?1 hydrogen peroxide with good stability. The possibility of using the developed sensor in medium containing sodium ions and the increased operational stability constitute advantages in comparison with PB‐based amperometric sensors. The usefulness of the methodology was demonstrated by addition‐recovery experiments with rainwater samples and values were in the 98.8 to 103% range.