Hadi Hosseini

A novel electrochemical sensor based on metal-organic framework for electro-catalytic oxidation of L-cysteine

A novel electrochemical sensor based on Au-SH-SiO₂ nanoparticles supported on metal-organic framework (Au-SH-SiO₂@Cu-MOF) has been developed for electrocatalytic oxidation and determination of L-cysteine. The Au-SH-SiO₂@Cu-MOF was characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and cyclic voltammetry. The electrochemical behavior of L-cysteine at the Au-SH-SiO₂@Cu-MOF was investigated by cyclic voltammetry. The Au-SH-SiO₂@Cu-MOF showed a very efficient electrocatalytic activity for the oxidation of L-cysteine in 0.1 M phosphate buffer solution (pH 5.0). The oxidation overpotentials of L-cysteine decreased significantly and their oxidation peak currents increased dramatically at Au-SH-SiO₂@Cu-MOF. The potential utility of the sensor was demonstrated by applying it to the analytical determination of L-cysteine concentration. The results showed that the electrocatalytic current increased linearly with the L-cysteine concentration in the range of 0.02-300 μM and the detection limit was 0.008 μM. Finally, the sensor was applied to determine L-cysteine in water and biological samples.

ADSORPTION PROPERTIES OF TETRACYCLINE ONTO GRAPHENE OXIDE: EQUILIBRIUM, KINETIC AND THERMODYNAMIC STUDIES

Graphene oxide (GO) nanoparticle is a high potential effective absorbent. Tetracycline (TC) is a broad-spectrum antibiotic produced, indicated for use against many bacterial infections. In the present research, a systematic study of the adsorption and release process of tetracycline on GO was performed by varying pH, sorption time and temperature. The results of our studies showed that tetracycline strongly loads on the GO surface via π–π interaction and cation–π bonding. Investigation of TC adsorption kinetics showed that the equilibrium was reached within 15 min following the pseudo-second-order model with observed rate constants of k2 = 0.2742–0.5362 g/mg min (at different temperatures). The sorption data has interpreted by the Langmuir model with the maximum adsorption of 323 mg/g (298 K). The mean energy of adsorption was determined 1.83 kJ/mol (298 K) based on the Dubinin–Radushkevich (D–R) adsorption isotherm. Moreover, the thermodynamic parameters such as ΔH°, ΔS° and ΔG° values for the adsorption were estimated which indicated the endothermic and spontaneous nature of the sorption process. The electrochemistry approved an ideal reaction for the adsorption under electrodic process. Simulation of GO and TC was done by LAMMPS. Force studies in z direction showed that tetracycline comes close to GO sheet by C8 direction. Then it goes far and turns and again comes close from amine group to the GO sheet.

Ordered carbohydrate-derived porous carbons immobilized gold nanoparticles as a new electrode material for electrocatalytical oxidation and determination of nicotinamide adenine dinucleotide.

The ordered carbohydrate-derived porous carbons (OC-DPCs) were first functionalized with thiol groups (-SH) and then immobilized with gold nanoparticles (AuNPs). The Au-SH-OC-DPCs were characterized by CHN analysis, transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). The Au-SH-OC-DPCs were applied for the fabrication of a new electrochemical sensor. The electrocatalytic capabilities of the new sensor were tested by the oxidation of nicotinamide adenine dinucleotide (NADH) in a 0.1 M Robinson buffer solution (pH 7.0) using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). The Au-SH-OC-DPCs showed a good voltammetric performance in the electrochemical detection of NADH with a low detection limit (1.0 nM), high sensitivity (4.934 μA/μM), and wide linear concentration range (5.0 nM-10 µM).

A novel bioelectrochemical sensing platform based on covalently attachment of cobalt phthalocyanine to graphene oxide.

Graphene oxide-cobalt phthalocyanine (GO-PcCo) hybrid material as a new electrocatalyst was synthesized and used successfully to fabrication of new biosensor for the electrooxidation of l-cysteine (CSH) in aqueous media. Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) images revealed that cobalt phthalocyanine is covalently attachment on graphene oxide sheets as single layers GO-PcCo. Cyclic voltammetric studies showed that the GO-PcCo/glassy carbon electrode (GO-PcCo/GCE) improves electrochemical behavior of CSH oxidation, as compared to the GO and PcCo. In addition, the results indicated that GO and PcCo have a synergic effect in the electrooxidation of CSH. The catalytic oxidation responses were studied and the reaction mechanisms were discussed. The electrocatalytic behavior is further developed as a new detection scheme for CSH by chronoamperometry method and under optimized conditions, excellent analytical features, including high sensitivity and selectivity, low detection limit and satisfactory dynamic range, were achieved.

Electrochemistry of raloxifene on glassy carbon electrode and its determination in pharmaceutical formulations and human plasma

The electrochemical behavior of raloxifene (RLX) on the surface of a glassy carbon electrode (GCE) has been studied by cyclic voltammetry (CV). The CV studies were performed in various supporting electrolytes, wide range of potential scan rates, and pHs. The results showed an adsorption-controlled and quasi-reversible process for the electrochemical reaction of RLX, and a probable redox mechanism was suggested. Under the optimum conditions, differential pulse voltammetry (DPV) was applied for quantitative determination of the RLX in pharmaceutical formulations. The DPV measurements showed that the anodic peak current of the RLX was linear to its concentration in the range of 0.2-50.0μM with a detection limit of 0.0750μM, relative standard deviation (RSD %) below 3.0%, and a good sensitivity. The proposed method was successfully applied for determination of the RLX in pharmaceutical and human plasma samples with a good selectivity and suitable recovery.

Electrochemical study and differential pulse voltammetric determination of oxcarbazepine and its main metabolite at a glassy carbon electrode

In this paper, the electrochemical behavior of oxcarbazepine (OX) and its main metabolite monohydroxy carbamazepine (MHD) was studied by cyclic voltammetry (CV) at a glassy carbon electrode. The effect of factors such as type of supporting electrolytes and solvent, potential scan rates and pH on the voltammetric behaviour of OX and MHD was investigated by CV. The results indicated one irreversible anodic peak at the potential Epa = 1. 84 V for OX and two irreversible anodic peaks at potentials EA1 = +1. 64 V and EA2 = +1.84 V for MHD. The oxidation reactions for both compounds (OX and MHD) were shown to be diffusion controlled. A possible mechanism is proposed to explain the electrochemical oxidation of OX. A differential pulse voltammetric method was used for the determination of OX in tablet and MHD in plasma samples. Based on this study, the calibration plots to determine OX and MHD concentrations were linear in the range of 2–23 μM and 0.35–18 μM, respectively. The detection limits were found to be 0.81 μM for OX and 0.135 μM for MHD. The results indicate that the proposed method is sensitive, selective, fast and simple for determination of OX and MHD.