Detection of cadmium heavy metal ions using a nanostructured green sensor in food, biological and environmental samples.

Heavy metals are one of the most important pollutants in the environment due to their toxic properties, accumulation, and indestructibility. So that when the metals enter the body of plants from natural and artificial sources, they accumulate in the organs and tissues. Therefore, in the present study, a sensitive and selective strategy is reported for the detection of cadmium(II) ions. To achieve this purpose, first sodium aluminate nanostructures were synthesized using a sol-gel method and green route. Then, using the nanostructures, a modified nanostructured sensor was designed. The characterization of the nanostructures was performed using various techniques. Next, the electrochemical behavior of the modified nanostructured electrode was investigated. The studies show the environment-friendly sensor has an enhanced voltammetric response than the unmodified sensor for cadmium(II) ions. After confirming the performance of the modified sensor, the analysis of cadmium(II) ions at the surface of the nanostructured modified electrode was investigated. Then, by differential pulse voltammetry (DPV) technique, the detection limit of cadmium(II) ions in optimal conditions was obtained at 1.10 nM with a broad dynamic linear range of 0.02-20.00 µM and 20.00-900.00 µM. Finally, the performance of the modified nanostructure sensor was investigated in food, biological and environmental samples, and acceptable results were obtained using the proposed method.

Synthesis, characterization and electrochemical sensors application of Tb2Ti2O7 nanoparticle modified carbon paste electrode for the sensing of mefenamic acid drug in biological samples and pharmaceutical industry wastewater.

Today, in most fields, wide research has been done in the manufacture of biosensors and the detection of various types of substances, including drugs. Nevertheless, the analytical detection of drugs from a biological sample by a simple and portable method for on-site detection is still important and very challenging. This paper investigates the electrochemical determination of the mefenamic acid (MEF), with a novel carbon paste electrode modified with terbium titanate nanostructures (TTN/CPE). The effect of the capping agent on the morphology and size of terbium titanate synthesized from terbium nitrate in the presence of ethylene glycol (EG) as a stabilization agent is investigated. The as-produced nanostructures are characterized by X-ray diffraction (XRD), Fourier transforms infrared (FT-IR) spectroscopy, energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). Electrochemical studies in optimized conditions indicate MEF has two linear responses in the range of 1.0 × 10-2-4.0 × 102 µM with a detection limit of 2.4 nM at the surface of TTN/CPE. The suggested sensor reveals good sensitivity, selectivity, stability, and reproducibility and can be utilized for some important biological samples and wastewater with satisfactory results.

An eco-friendly and simple sol-gel autocombustion method for synthesis of copper hexaferrite nanostructures: characterization and photocatalytic activity for elimination of water contaminations.

In this work, copper hexaferrite (CuFe12O19) nanostructures are successfully synthesized by the sol-gel autocombustion route. Two natural reagents containing pomegranate and beetroot juices are used as green and eco-friendly fuels for synthesis of the nanostructures. The nanostructures are characterized by different techniques such as X-ray diffraction (XRD), energy-dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), and diffuse reflectance spectroscopy (DRS). The results show an appropriate amount of pomegranate juice as a fuel source creating a suitable route for synthesis of CuFe12O19 nanostructures. Therefore, the nanostructures are applied for degradation of different water contaminants containing eosin, erythrosine, rhodamin B, and methyl violet dyes. The comparison of the results shows that the nanostructures are a good photocatalyst for degradation of erythrosine. Therefore, green CuFe12O19 nanostructures can be a good candidate as UV light catalyst for removal of wastewater contaminations.

Bio-based Fe3O4/chitosan nanocomposite sensor for response surface methodology and sensitive determination of gallic acid.

In this study, preparation of a novel bio-sensor based on Fe3O4/chitosan nanocomposites reported for electrochemical studies and determination of gallic acid (GA). Combination of chitosan with Fe3O4 nanoparticles causes to improve oxidation current of the GA. Characterization of the nanocomposite is carried out by different techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, electrochemical impedance spectroscopy and cyclic voltammetry. Furthermore, multivariate optimization strategy is applied for simultaneous optimization of the chemical and instrumental parameters. Moreover, electrochemical behavior of GA at the surface of the nano-structured sensor is studied by various techniques such as chronoamperometry, chronocoulometry and linear sweep. Using these techniques, the diffusion coefficient (D = 5.05 × 10-4 cm2 s-1 and or 4.86 × 10-4 cm2 s-1), and the kinetic parameters containing the exchanging current density (j0 = 0.23 µA cm-2) and electron transfer coefficient (α = 0.1) are determined for GA, respectively. Then, the detection limit for GA is found to be 12.1 nM with a broad linear dynamic range 0.5-300.0 µM using differential pulse voltammetry DPV at the surface of the Fe3O4/chitosan sensor. Finally, the proposed method is successfully applied for the detection of the analyte in real samples.

Green synthesis and characterization of DyMnO3-ZnO ceramic nanocomposites for the electrochemical ultratrace detection of atenolol.

The present study is a first report about magnetic, optical and electrical as well as drug sensing properties of DyMnO3-ZnO green-nanocomposites that are synthesized by Pechini modified method. Three natural compounds containing Vitis vinifera, Hibiscus sabdariffa and rhus juices are used as green and eco-friendly reagents for synthesis of the nanostructures. The nanostructures are characterized by various techniques containing Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), field emission scanning electron microscopes (FESEM), high resolution transmission electron microscopy (HR-TEM), vibrating sample magnetometer (VSM) and diffuse reflectance spectroscopy (DRS). The calcination temperature, type of chelating agent and pH are optimized to achieve the best structural and smallest crystallite sizes of the systems via an eco-friendly approach. The studies show that the Vitis vinifera juice creates the best homogeneous sphere-like nanostructures. Therefore, the samples that are synthesized by Vitis vinifera juice are used for fabrication of a carbon paste electrode modified with DyMnO3-ZnO nanocomposites (DMZN/CPE). The nanostructured modified electrode exhibits an excellent electrocatalytic effect for determination of atenolol (ATN) using voltammetry techniques. The results reveal that the DyMnO3-ZnO green-nanocomposites have potential applications as a sensitive material in the drug analysis in biological samples.

Multivariate optimization methods for in-situ growth of LDH/ZIF-8 nanocrystals on anodized aluminium substrate as a nanosorbent for stir bar sorptive extraction in biological and food samples.

In-situ growth of zeolite imidazolate frameworks (ZIFs) on the surface of layered double hydroxides (LDHs) for preparation of porous nanocomposites is a favorable strategy to design potential materials in separation fields. In this research, nanoporous Zn-Al LDH/ZIF-8 composite was prepared by in-situ growth of ZIF-8 on the Zn-Al LDH surface. The nanocomposite was applied for stir bar sorptive extraction and detection of benzylpenicillin (penicillin G, PEN G). Characterizations of the nanocomposite were performed by various techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and thermogravimetric differential thermal analysis. An optimized strategy based on response surface methodology was combined with high performance liquid chromatography analysis. Under the optimized conditions, the limit of detection and quantification obtained were 0.05 and 0.15 µg l-1, respectively. The good validation criteria results allowed the method to be used in the quantification of PEN G in real samples.

Chemometrics-assisted determination of Sudan dyes using zinc oxide nanoparticle-based electrochemical sensor.

Multivariate curve resolution-alternating least squares (MCR-ALS) assisted with electrochemical techniques was applied for simultaneous determination of Sudan II and III at a surface of zinc oxide nanoparticles (ZnONPs) modified carbon paste electrode. Characterization of the ZnONPs and the nanostructured modified electrode was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Response surface methodology using central composite rotatable design was employed to design of experiments and achieving to optimum values of variables. For simultaneous determination of Sudan II and III, electrochemical second order data were obtained by changing of pulse height in differential pulse voltammetry technique. MCR-ALS was performed on the data to obtain the decomposition peaks of analytes. Then, the detection limits were obtained 1.87 and 2.62 nM for Sudan II and III, respectively. Finally, this method used for the analysis of the two analytes in real samples.

Gas chromatography-mass spectrometry analysis and antimicrobial, antioxidant and anti-cancer activities of essential oils and extracts of Stachys schtschegleevii plant as biological macromolecules.

This work reports the chemical composition and antimicrobial activity of the essential oil as well as antioxidant and anti-cancer activities of ethyl acetate and aqueous extracts from leaf and stem of Stachys schtschegleevii. The structure of volatile parts and effective phenolic compounds as biological macromolecules as well as biological activity of the Stachys schtschegleevii plant were studied using various methods. Essential oils of stem and leaf were identified by steam distillation method and characterization was performed using a gas chromatography-mass spectrometry (GC-MS) analysis. Anti-microbial activity of extracted macromolecules from essential oils of two ethyl acetate and aqueous parts of stem and leaf were analyzed by minimal inhibition concentration (MIC) method. The crude extracts exhibited no appreciable antioxidant activities, in 2,2-diphenyl-1-picrylhydrazyl (DPPH) test by IC50 317.98 and 328.09 µg/mL for aqueous and ethyl acetate fractions, respectively. But, antioxidant activities for butylated hydroxytoluene (BHT) as a standard antioxidant showed significant results (18.16 µg/mL). Also, it was confirmed that antioxidant activities with the phenolic and flavonoid content of the plant for the aqueous and ethyl acetate elements were obtained 57.73, 59.81 and 21.95, 26.124 µg/mg, respectively. Furthermore, in ß-carotene/linoleic acid assay, inhibition percentages were recorded 71.17 and 96.24 for the aqueous and ethyl acetate elements, respectively. Therefore, ethyl acetate section of the plant showed antioxidant activity more than aqueous part. Hydrogen peroxide scavenging assay evaluated antioxidant activity for aqueous and the ethyl acetate extracts sections as 565 and 560 µg/mL, respectively. Also, power determinations of iron (III) oxide antioxidants from aqueous and ethyl acetate fractions were 6113 and 2.69, respectively. Furthermore, Anti-cancer activity of aqueous and ethyl acetate components evaluated in brine shrimp lethality test with LC50 about 100 and 700 µg/mL for aqueous and ethyl acetate fractions, respectively. The results showed that aqueous section species has a much lower effect than the calculated standard, but ethyl acetate section of the plant sample shows a more favorable effect than the standard. Therefore, the plant screened good antimicrobial, antioxidant and anti-cancer activities for its essential oil and ethyl acetate extract.

Experimental and statistical analysis on a nanostructured sensor for determination of p-hydroxybenzoic acid in cosmetics.

In this research, differential pulse voltammetry (DPV) coupled with experimental design, was used for determination of p-hydroxybenzoic acid (PHB) in cosmetics. Optimization of effecting parameters was carried out based on rotatable central composite design (RCCD) and response surface methodology (RSM) at the surface of a nanostructured electrode for achieving the best sensitivity. Sol-gel process was used for synthesize of nickel titanate (NiTiO3) nanoceramics. The structural and morphological characterization of the nanoparticles was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Then the NiTiO3 nanopowders were used for surface modification of a carbon paste modified electrode (CPE). Surface characterization of the electrode was accomplished using SEM, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Under the optimized conditions, the voltammograms exhibited two linear dynamic ranges of 0.7-80.0 µM and 80.0-1000.0 µM for PHB with the detection limit of 62.0 nM (S/N = 3). Finally the NiTiO3 nanoceramics modified carbon paste electrode (NiTiO3/CPE) could be employed for the determination of PHB in real samples with satisfactory results.

A carbon paste electrode modified with a nickel titanate nanoceramic for simultaneous voltammetric determination of ortho- and para-hydroxybenzoic acids.

An electrochemical sensor is described for the simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB). The sensor consists of a carbon paste electrode modified with nickel titanate nanoceramics (NiTiO3/CPE). The NiTiO3 nanoceramics and the nanostructured modified CPE were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Differential pulse voltammetry indicates that the response to OHB (best measured at 0.90 V vs. Ag/AgCl) and PHB (measured at 0.80 V vs. Ag/AgCl) is significantly improved at the modified CPE compared to a bare CPE. The limits of detection (at S/N = 3) are 0.38 and 0.10 µM for OHB and PHB, respectively. The method was applied to the determination of the two isomers in peeling skin lotion and during the Kolbe-Schmitt reaction. Graphical abstract Nickel titanate nanoceramics (NiTiO3) were synthesized by a sol-gel method. Then, a carbon paste electrode modified with NiTiO3 (NiTiO3/CPE) was constructed. The modified electrode was applied to the interference-free and simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB).

Preparation of a manganese titanate nanosensor: Application in electrochemical studies of captopril in the presence of para-aminobenzoic acid.

This study reports the synthesis and characterization of a novel nanostructure-based electrode for electrochemical studies and determination of captopril (CP). At first manganese titanate nanoceramics were synthesized by the sol-gel method. The structural evaluations of the pure nanopowders were investigated by different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Then it was used to prepare a new nanostructured manganese titanate carbon paste electrode (MnTiO3/CPE). The characterization of the modified sensor was carried out by comprehensive techniques such as electrochemical impedance spectroscopy (EIS), SEM, and voltammetry. Subsequently, the modified electrode was used for CP catalytic oxidation in the presence of para-aminobenzoic acid (PABA) as a mediator. The results showed that PABA has high catalytic activity for CP oxidation. The electrochemical behavior of CP was studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CHA), and differential pulse voltammetry (DPV) techniques. Under the optimized conditions, the catalytic oxidation peak current of CP showed two linear dynamic concentration ranges of 1.0 × 10(-8) to 1.0 × 10(-7) and 1.0 × 10(-7) to 1.0 × 10(-6), with a detection limit of 1.6 nM (signal/noise = 3), using the DPV technique. Finally, the proposed method was successfully applied for determination of CP in pharmaceutical and biological samples.

Design and evaluation of a highly sensitive nanostructure-based surface modification of glassy carbon electrode for electrochemical studies of hydroxychloroquine in the presence of acetaminophen.

N,N'-bis[(E)-(1-pyridyl) methylidene]-1,3-propanediamine (PMPDA) self-assembled monolayer (SAM) was covalently prepared on a glassy carbon electrode (GCE). The electrode surface modification was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Then GC-PMPDA SAM modified electrode was used to investigate the electrochemical behavior of hydroxychloroquine (HQ) using CV, double potential step chronocoulometry and linear sweep voltammetry (LSV) techniques. Using these techniques, the diffusion coefficient (D), electron transfer coefficient (α) and exchanging current density (j0) for HQ were calculated. Furthermore the modified electrode was applied as a high sensitive biosensor for determination of HQ in the presence of acetaminophen (AC). The GC-PMPDA SAM modified electrode provides two linear responses for HQ in the presence of AC in the concentration ranges from 0.09 to 10.21 µM and 10.21 to 98.29 µM by differential pulse voltammetry (DPV). The detection limit (three times the signal blank/slope) was 4.65 nM. Finally the modified electrode was satisfactorily used for determining of HQ in human body fluids.

Three-dimensional voltammetry: a chemometrical analysis of electrochemical data for determination of dopamine in the presence of unexpected interference by a biosensor based on gold nanoparticles.

Multivariate curve resolution by alternating least-squares (MCR-ALS) was used for voltammetric determination of dopamine (DA) in the presence of epinephrine (EP) at a gold nanoparticles chemically modified carbon paste electrode (AuNPs/CPE). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques were applied for characterization of the nanostructure modified electrode. Central composite rotatable design (CCRD) was employed to generate an experimental program to offer data to model the effects of different parameters on voltammetric responses. Response surface methodology (RSM) was applied to show the individual and interactive effects of chemical and instrumental variables at five levels, combined according to CCRD. For determination of DA in the presence of unexpected interference, three-way data were achieved from various pulse heights in differential pulse voltammetry (DPV) technique. This type of data construction, analyzed by MCR-ALS, makes it possible to exploit the so-called "second-order advantage". The second-order advantage provided unbiased results even in the presence of electroactive interferences with highly overlapped peaks. Also, an algorithm was applied to correct the detected potential shift in the voltammetric data. The voltammograms of the samples were then deposited in an augmented data matrix (column-wise) and subsequently analyzed by MCR-ALS. The effect of rotational ambiguity associated with a particular MCR-ALS solution under a set of constraints was also studied. The proposed method could be applied for the determination of DA and EP in the presence of each other in a wide concentration range of 0.1-205.0 µM, and the detection limit of DA has been found to be 35.5 nM. Finally, the technique has been used for the reliable analysis of DA in real samples.

Sensitive and selective determination of hydroxychloroquine in the presence of uric acid using a new nanostructure self-assembled monolayer modified electrode: optimization by multivariate data analysis.

A highly sensitive electrochemical nanosensor was developed using covalent modification of a glassy carbon electrode (GCE) by self-assembly of a novel Schiff base. Scanning electron microscopy (SEM) and electrochemical techniques were used to investigate the immobilization of the self-assembled monolayer (SAM) on the GCE. The electrochemical behavior of hydroxychloroquine (HCQ) in the presence of uric acid (UA) at the surface of the modified electrode was studied using the differential pulse voltammetry (DPV) technique. Response surface methodology (RSM) is used to optimize the effects of various operating variables such as pH, immersion time, scan rate, step potential and modulation amplitude on the voltammetric response of HCQ. RSM formulates a mathematical model which correlates the independent parameters with the peak current of HCQ. The central composite rotatable design (CCRD) has been applied to conduct the experiments. Then, under the optimized conditions, HCQ was determined in the presence of UA. The electrochemical measurements demonstrated that this biosensor responded well to HCQ, confirming that the self-assembly immobilization method was effective. Also, the interference, the storage stability, and the reproducibility of the biosensor were studied and assessed. The developed nanosensor was economical and efficient, making it potentially attractive for application to real sample analysis.

Multivariate curve resolution-alternating least squares assisted by voltammetry for simultaneous determination of betaxolol and atenolol using carbon nanotube paste electrode.

In the present work differential pulse voltammetry coupled with multivariate curve resolution-alternating least squares (MCR-ALS) was applied for simultaneous determination of betaxolol (Bet) and atenolol (Ate) in 0.20 M Britton-Robinson (B-R) buffer solution at the surface of a multi-walled carbon nanotube modified carbon paste electrode (MWCNT/CPE). Characterization of the modified electrode was carried out by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A strategy based on experimental design was followed. Operating conditions were improved with central composite rotatable design (CCRD) and response surface methodology (RSM), involving several chemical and instrumental parameters. Then second order data were built from variable pulse heights of DPV and after correction in potential shift analyzed by MCR-ALS. Analytical parameters such as linearity, repeatability, and stability were also investigated and a detection limit (DL) of 0.19 and 0.29 µM for Bet and Ate was achieved, respectively. The proposed method was successfully applied in simultaneous determining the two analytes in human plasma.