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.     

Determination of Ethambutol in Aqueous Medium Using an Inexpensive Gold Microelectrode Array as Amperometric Sensor

In this paper, gold microelectrode array (Au‐MEA) were employed to determination of ethambutol in aqueous medium. Au‐MEA was constructed with an electronic microchip integrated circuit. The standard curve (analytical curve) was constructed for a single microelectrode (ME) in a concentration range of 5.0×10^?5 to 2.0×10^?3 mol L^?1, allowing estimation of both the limit of detection (LOD) (4.73×10^?5 mol L^?1) and the limit of quantification (LOQ) (1.57×10^?4 mol L^?1) for ethambutol. When the MEA was utilized, the LOD and LOQ were 1.55×10^?7 and 5.18×10^?7 mol L^?1, respectively. Our results indicated that Au‐MEA can be utilized as amperometric sensors for ethambutol determination in aqueous media.     

Direct Determination of Paracetamol in Environmental Samples Using Screen‐printed Carbon/Carbon Nanofibers Sensor – Experimental and Theoretical Studies

The paper describes the first electrochemical method (differential pulse adsorptive stripping voltammetry, DPAdSV) using a screen‐printed sensor with a carbon/carbon nanofibers working electrode (SPCE/CNFs) for the direct determination of low (real) concentrations of paracetamol (PA) in environmental water samples. By applying this sensor together with DPAdSV, two linear PA concentration ranges from 2.0×10^?9 to 5.0×10^?8 mol L^?1 (r=0.9991) and 1.0×10^?7–2.0×10^?6 mol L^?1 ( r=0.9994) were obtained. For the accumulation time of 90 s, the limit of detection was 5.4×10^?10 mol L^?1. Moreover, the SPCE/CNFs sensor and the DPADSV procedure for PA determination are potentially applicable in field analysis. The process of PA adsorption at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and theoretical studies. In the theoretical study of the interaction of CNF and PA, the first species was modelled by graphene‐like clusters containing up to 37 rings. It was found that the preferable orientation of PA is parallel to the carbon surface with the binding energy of about ?68 kJ/mol calculated by symmetry‐adapted perturbation theory (SAPT). Both the selectivity and the accuracy of the developed sensor for real sample analysis were also investigated using Polish river and sea samples.     

Ionic Organic Film Sensor for Determination of Phenolic Compounds

This paper describes the development of a new sensor based on an ionic organic film. The amphiphilic molecule, 4‐[(4‐decyloxyphenyl)‐ethynyl]‐1‐methylpyridinium iodide (10PyI), which has liquid‐crystalline properties, was synthesized and applied in the construction of a GCE/10PyI sensor. Analytical parameters for caffeic acid, repeatability (4.8 %), reproducibility (2.8 %), linearity (two ranges: 9.9×10^?7 to 3.8×10^?5 mol L^?1 and 4.7×10^?5 to 9.9×10^?5 mol L^?1) and detection limits (9.0×10^?7 mol L^?1 and 8.7×10^?6 mol L^?1), were determined. The method was successfully applied in the determination of total phenolic compounds (TPC) in mate herb extracts.     

Amino‐Containing Ultrafine Organosilica‐Nanoparticle‐Modified Au Electrode for the Determination of Cu(II) Ions

Using 3‐Aminopropyltriethoxysilane(APTES) as a single silica source, an amino‐rich ultrafine organosilica‐nanoparticle‐modified Au electrode was fabricated, following the formation of (3‐mercaptopropyl)‐trimethoxysilane (MPTS) monolayer on Au surface (MPTS/Au). With cetyltrimethylammonium bromide as an additive, APTES‐based gel particles on the electrode have a narrow particle size distribution of 4–7 nm and “crystal‐like” structure. AFM and electrochemical characterization confirmed the successful grafting of APTES nanoparticles on MPTS/Au. The APTES/MPTS/Au electrode is highly sensitive for the detection of copper(II) ions with a detection limit as low as 1.6×10^?12 mol L^?1 (S/N>3) by square wave voltammetry. The current is linear to copper(II) concentration between 1.6×10^?12 and 6.25×10^?10 mol L^?1.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

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.     

Simultaneous Determination of Thallium and Lead on a Chemically Modified Electrode with Langmuir– Blodgett Film of a p‐tert‐Butylcalix[4]arene Derivative

A new voltammetric sensor, Langmuir–Blodgett (LB) film of a p‐tert‐butylcalix[4]arene derivative modified glassy carbon electrode, was designed and successfully used in simultaneous determination of Tl⁺ and Pb²⁺ by square‐wave anodic stripping voltammetry. Under the optimum experimental conditions, this newly developed sensor reveal good linear response for Tl⁺ and Pb²⁺ in the concentration range of 3×10^?8–4×10^?6 mol L^?1 and 2×10^?7–2×10^?5 mol L^?1 respectively. The detect limits are 2×10^?8 mol L^?1 for Tl⁺ and 8×10^?8 mol L^?1 for Pb²⁺. Using proposed method, Tl⁺ and Pb²⁺ in environment samples were determined with satisfactory results.     

Improvement of Selectivity and Stability of Amperometric Detection of Hydrogen Peroxide Using Prussian Blue‐PAMAM Supramolecular Complex Membrane as a Catalytic Layer

A novel hydrogen peroxide (H₂O₂) sensor was fabricated by using a submonolayer of 3‐mercaptopropionic acid (3‐MPA) adsorbed on a polycrystalline gold electrode further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) to obtain a film on which Prussian Blue (PB) was later coordinated to afford a mixed and stable electrocatalytic layer for H₂O₂ reduction. On the basis of the electrochemical behaviors, atomic force microscopy (AFM) and X‐ray photoelectron spectra (XPS), it is suggested that the PB molecules are located within the dendritic structure of the surface attached PAMAM dendrimers. It was found that the PB/PAMAM/3‐MPA/Au modified electrode showed an excellent electrocatalytic activity for H₂O₂ reduction. The effects of applied potential and pH of solution upon the response of the modified electrode were investigated for an optimum analytical performance. Even in the presence of dissolved oxygen, the sensor exhibited highly sensitive and rapid response to H₂O₂. The steady‐state cathodic current responses of the modified electrode obtained at ?0.20 V (vs. SCE) in air‐saturated 0.1 mol L^?1 phosphate buffer solution (PBS, pH 6.50) showed a linear relationship to H₂O₂ concentration ranging from 1.2×10^?6 mol L^?1 to 6.5×10^?4 mol L^?1 with a detection limit of 3.1×10^?7 mol L^?1. Performance of the electrode was evaluated with respected to possible interferences such as ascorbic acid and uric acid etc. The selectivity, stability, and reproducibility of the modified electrode were satisfactory.     

The New Application of Boron Doped Diamond Electrode Modified with Nafion and Lead Films for Simultaneous Voltammetric Determination of Dopamine and Paracetamol

A new voltammetric procedure for the simultaneous determination of dopamine (DA) and paracetamol (PA) using boron doped diamond electrode modified with Nafion and lead films (PbF/Nafion/BDDE) was investigated. The use of this electrode resolved the overlapped voltammetric waves of DA and PA into well‐defined peaks with peak to peak separation of about 320 mV. Under the optimized experimental conditions in differential pulse voltammetric technique, DA and PA gave a linear response over the ranges 2.0×10^?7–1.0×10^?4 mol L^?1*(R²=0.9996) and 5.0×10^?7–1.0×10^?3 mol L^?1 (R²=0.9979), respectively. The detection limits were found to be 5.4×10^?8 mol L^?1 for DA and 1.4×10^?7 mol L^?1 for PA. They are lower, comparable or in some cases a little bit higher than those obtained using other electrochemical sensors. However, the proposed procedure of the sensor preparation is much simpler than procedures described in the literature with a lower detection limit. The proposed procedure was successfully applied to the determination of PA in some commercial pharmaceuticals as well as to the simultaneous determination of DA and PA in human urine, whole blood and serum samples directly without any separation steps.     

Electrochemical Morphine Sensor Based on Gold Nanoparticles Metalphthalocyanine Modified Carbon Paste Electrode

Composites of gold nanoparticles (Au) electrochemically deposited and different metal phthalocyanines (Co, Ni, Cu, and Fe) were chemically prepared. The composites were used as modifiers for carbon paste electrodes and were used for the determination of morphine in presence of ascorbic acid and uric acid. Central metal atoms of phthalocyanine moiety affected the rate of electron transfer. Thus, the electroactivity of different modifiers were evaluated towards morphine oxidation. Au‐CoPcM‐CPE possessed the highest rate for charge transfer rate in all studied pH electrolytes. Limit of detection was 5.48×10^?9 mol L^?1 in the range of 4.0×10^?7 to 9.0×10^?4 mol L^?1.     

Electroanalysis of Benazepril Hydrochloride Antihypertensive Drug Using an Ionic Liquid Crystal Modified Carbon Paste Electrode

Electroanalysis of benazepril HCl was successful using a carbon paste electrode modified with an ionic liquid crystal ( 1‐butyl‐1‐methylpiperidinium hexafluorophosphate) in presence of sodium dodecyl sulfate. The electrode performance was compared to ionic liquids (1‐n‐hexyl‐3‐methyl imidazolium tetrafluoroborate and 1‐butyl‐4‐methyl pyridinium tetrafluoroborate). Electrochemical determination of benazepril HCl was in the linear dynamic range of 8.89×10^?7 to 1.77×10^?5 mol L^?1 (correlation coefficient 0.999) and LOD 7.17×10^?9 mol L^?1. benazepril HCl was determined using this sensor in presence of urine metabolites such as uric acid, ascorbic acid. Binary mixtures of dopamine/benazepril and amlodipine/benazepril were also determined successfully.     

Pattern Recognition of Sweeteners in Biological Fluids,Beverages, and Ketchup using Stochastic Sensors

Three stochastic sensors based on nanodiamond (nDP) paste modified with α, β, and γ‐cyclodextrin were designed and characterized for pattern recognition of aspartame, acesulfame K and sodium cyclamate in beverages, ketchup, and biological fluids. The linear concentration ranges obtained for acesulfame K (between 1.00×10^?10 mol L^?1and 1.00×10^?3 mol L^?1), for aspartame (between 1.00×10^?12 mol L^?1 and 1.00×10^?3 mol L^?1) and for sodium cyclamate (between 4.97×10^?12 mol L^?1 and 4.97×10^?3 mol L^?1) allow their assay in biological fluids, beverages and ketchup. The lowest limits of quantification were obtained using the stochastic sensor based on γ‐CD/nDP: for acesulfame K 1.00×10^?10 mol L^?1, for aspartame 1.00×10^?12 mol L^?1 and for sodium cyclamate 4.97×10^?12 mol L^?1. All three stochastic sensors revealed very high values of sensitivities. The proposed method was reliable for qualitative and quantitative assay of aspartame, acesulfame K and sodium cyclamate in beverages, ketchup, and in biological fluids such as urine.     

Man‐Tailored Biomimetic Sensor of Molecularly Imprinted Materials for the Potentiometric Measurement of Rivastigmine in Tablets and Biological Fluids and Employing the Taguchi Optimization Methodology to Optimize the MIP‐Based Membranes

This work proposes a novel biomimetic sensor for the potentiometric transduction of rivastigmine based on molecularly imprinted polymer (MIP). Using the Taguchi method, this study analyzed the optimum conditions for preparing the MIP‐based membranes. The rank order of each controllable factor was also determined. MIP‐based membranes exhibited a Nernstian response (30.7±1.1 mV decade^?1) in a concentration range from 1.0×10^?5 to 1.0×10^?2 mol L^?1 with a LOD of 6.3×10^?6 mol L^?1. The sensor was successfully applied to the determination of rivastigmine concentrations in human serum, plasma, urine, rat brain and tablets.     

Differential Pulse Voltammetric Determination of Selenocystine Using Selenium‐gold Film Modified Electrode

Differential pulse voltammetric determination of selenocystine (SeC) using selenium‐gold film modified glassy carbon electrode ((Se‐Au)/GC) is presented. In 0.10 mol?L^?1 KNO₃ (pH 3.20) solution, SeC yields a sensitive reduction peak at ?740 mV on (Se‐Au)/GC electrode. The peak current has a linear relationship with the concentration of SeC in the range of 5.0×10^?8–7.0×10^?4 mol?L^?1, and a 3σ detection limit of SeC is 3.0×10^?8 mol?L^?1. The relative standard deviation of the reduction current at SeC concentration of 10^?6 mol?L^?1 is 3.88% (n=8) using the same electrode, and 4.19% when using three modified electrodes prepared at different times. The content of SeC in the selenium‐enriched yeast and selenium‐enriched tea is determined. The total selenium in ordinary or selenium‐enriched tea is determined by DAN fluorescence method. The results indicate that in selenium‐enriched yeast about 20% of total selenium is present as SeC and in selenium‐enriched tea SeC is the major form of selenoamino acids. The total selenium content in selenium‐enriched tea soup is 0.09 μgSe/g accounting by 7% compared with that in selenium‐enriched tea. Hence, only a little amount of selenium is utilized by drinking tea, and most selenium still stay in tealeaf. Uncertainty are 22.4% and 16.1% for determination of SeC in selenium‐enriched yeast and selenium‐enriched tea by differential pulse voltammetry (DPV) on (Se‐Au)/GC electrode, respectively.     

Use of a Carbon Paste Electrode Modified with Spinel‐Type Manganese Oxide as a Potentiometric Sensor for Lithium Ions in Flow Injection Analysis

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel‐type manganese oxide (lambda‐MnO₂), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li⁺ against other alkali and alkaline‐earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6×10^?5–1.0×10^?2 mol L^?1 with a slope 78.9±0.3 mV dec^?1 over a wide pH range 7–10 (Tris buffer), without interference of other alkali and alkaline‐earth metals. For a flow rate of 5.0 mL min^?1 and a injection sample volume of 408.6 μL, the relative standard deviation for repeated injections of a 5.0×10^?4 mol L^?1 lithium ions was 0.3%.     

Multi‐responses Methodology Applied in the Electroanalytical Determination of Hair Dye by Using Printed Carbon Electrode Modified with Graphene

This paper describes a rapid and sensitive method for determination of the hair dye Basic Blue 41 in wastewater samples using screen‐printed carbon electrodes modified with graphene (SPCE/Gr). The method is based on the reversible reduction of azo groups of the dye at potential of ?0.23 V/?0.26 V, where both the anodic and cathodic currents increased 1,300 % when compared to screen‐printed carbon (SPCE) and glassy carbon electrodes (GCE). The optimization of a square wave voltammetric method was performed by means of 2³ factorial design, Doehlert matrix and multi‐response assays, and the best parameters were: frequency (54.8 Hz), step potential (6 mV), pulse amplitude (43.7 mV) and pH 4.5. The analytical curve was constructed from 3.00×10^?8 to 2.01×10^?6 mol L^?1, with detection and quantification limits of 5.00×10^?9 and 1.70×10^?8 mol L^?1, respectively. The repeatability of the method evaluated for 10 consecutive measurements at concentrations of 1.70×10^?7 mol L^?1 and 1.70×10^?6 mol L^?1, showed relative standard deviation of 3.56 and 0.57 %, respectively. The sensor based in SPCE/Gr was successfully applied in wastewater samples collected from a drinking water treatment plant and validated by comparison with HPLC‐DAD method with good accuracy.     

Differential Pulse Voltammetric Determination of Selenocystine and Selenomethionine Using SAM nanoSe0/Vc/SeCys‐Film Modified Au Electrode

The SAM nanoSe⁰/Vc/SeCys‐film modified Au electrode has been prepared to determine selenocystine and selenomethionine. The AFM and SEM showed the special three‐dimensional (3D) network structure of the sol‐gel films. The affinity between nanoparticles and biomolecules created special chemical characters analyzed by the XRD and fluorescence. The modified electrode was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified films partly had resistance in the charge transduction of Fe(CN) , but the less electron‐transfer resistance. Differential pulse voltammetric (DPV) determination of selenoamino acids using SAM nanoSe⁰/Vc/SeCys‐film modified Au electrode was presented. In PBS (pH 7.0)+0.1 mol L^?1 NaClO₄ solution, selenoamino acids yielded a sensitive reduction peak at about +400±50 mV. The peak current had a linear relationship with the concentration of selenoamino acids in the range of 5.0×10^?8–1.0×10^?5 mol L^?1, and a 3σ detection limit of selenoamino acids was 1.2×10^?8 mol L^?1. The relative standard deviation of DPV signals of 0.50×10^?6 mol L^?1 selenoamino acids was 3.8% (n=8) using the same electrode and was 4.4% (n=5) when using three modified electrodes prepared at different times. The content of selenoamino acids in the organo‐selenium powder were determined by DPV. The results showed 71.5 μg g^?1 of SeCys and 65.1 μg g^?1 of SeMet in the organo‐selenium powder.     

Construction and Validation of New Electrochemical Carbon Nanotubes Sensors for Determination of Acebutolol Hydrochloride in Pharmaceuticals and Biological Fluids

A simple, rapid and a highly selective method for direct electrochemical determination of acebutolol hydrochloride (AC) was developed. The developed method was based on the construction of three types of sensors conventional polymer (I), carbon paste (II) and modified carbon nanotubes (MCNTs) carbon paste (III). The fabricated sensors depend mainly on the incorporation of acebutolol hydrochloride with phosphotungstic acid (PTA) forming ion exchange acebutolol‐phosphotungstate (AC‐PT). The performance characteristics of the proposed sensors were studied. The sensors exhibited Nernstian responses (55.6 ± 0.5, 57.14 ± 0.2 and 58.6 ± 0.4 mV mol L^?1) at 25 °C over drug concentration ranges (1.0 × 10^?6‐1.0 × 10^?2, 1.0 × 10^?7‐1.0 × 10^?2 and 5.0 × 10^?8‐1.0 × 10^?2 mol L^?1 with lower detection limits of (5.0 × 10^?7, 5.0 × 10^?8 and 2.5 × 10^?8 mol L^?1 for sensors (I), (II) and (III), respectively. The influence of common and possible interfering species, pharmaceutical additives and some related pharmacological action drugs was investigated using separate solution method and no interference was found. The stability indicating using forced degradation of acebutolol hydrochloride was studied. The standard addition method was used for determination of the investigated drug in its pharmaceutical dosage forms and biological fluids. The results were validated and statistically analysed and compared with those from previously reported methods.