Cytochrome c/Multi-walled Carbon Nanotubes Modified Glassy Carbon Electrode for the Detection of Streptomycin in Pharmaceutical Samples.

A novel electrochemical glassy carbon electrode modified with a multi-walled carbon nanotube, cytochrome c (Cyt c) and zinc oxide nanoparticles (ZnONPs) was fabricated to increase the sensitivity of electrode for the detection of streptomycin (STN) in certain pharmaceutical samples. Cyclic voltammetry (CV) and differential pulse voltammetry techniques were used for an electrochemical characterization of the electrode. Furthermore, the electrochemical biosensor construction phases were examined by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). Under the optimal experimental conditions, the electrode offers a high selectivity and sensitivity signaling in the co-existence method of STN with the linear concentration ranging from 0.02 to 2.2 µM. The detection limits (LOD) and limit of quantification (LOQ) were found to be 0.0028 and 0.0562 µM, respectively. The fabricated sensing electrode has good stability, reproducibility and sensitivity towards STN in the pharmaceutical samples. Preliminary determinations of binding sites within the specified grid box size, which covers both Cyt c and STN, were done by molecular docking analysis. Moreover, density functional theory (DFT) computations were performed to provide insightful information into the optimized geometry of STN.

Simultaneous detection of ethambutol and pyrazinamide with IL@CoFe2O4NPs@MWCNTs fabricated glassy carbon electrode.

For the first time, we report a novel electrochemical sensor for the simultaneous detection of ethambutol (ETB) and pyrazinamide (PZM) using 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) ionic liquid (IL) assimilated with multiwalled carbon nanotubes (MWCNTs) decorated cobalt ferrite nanoparticles (CoFe2O4NPs) on the surface of glassy carbon electrode (GCE). The surface morphological and electrochemical properties of the IL@CoFe2O4NPs@MWCNTs was characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV), differential pulse voltammetry (DPV) respectively. Moreover, the obtained results of CV demonstrated that the 9-folds enhancement in the electrochemical signals was achieved with IL@CoFe2O4NPs@MWCNTs@GCE compared to that of a bare GCE. Additionally, the simultaneous electrochemical detection of ETB and PZM was successfully accomplished using IL@CoFe2O4NPs@MWCNTs over a wide-range of concentration with good limit of detection (3S/m) of 0.0201 and 0.010 µM respectively. The findings of this study identify IL@CoFe2O4NPs@MWCNTs@GCE has promising abilities of simultaneous detection of ETB and PZM in pharmaceutical formulations.

Molecular interaction studies of binary systems comprising [C2mim] [BF4] with ethyl acetoacetate or benzaldehyde.

In this work, new data for the binary mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim] [BF4]) ionic liquid (IL) with benzaldehyde or ethyl acetoacetate were investigated under atmospheric pressure (p = 0.1 MPa) and at temperatures (293.15-313.15) K. The binary mixtures were completely miscible at all proportions. Densities ( ρ ), viscosities ( η ) as well as speeds of sound ( u ) were conducted across the entire range of mole fraction ( x i = 0 to 1). The excess properties which include excess molar volumes ( V m E ) , intermolecular free length ( L f ), deviations in viscosity ( Δ Î· ), isentropic compressibility ( k s ) , apparent molar isentropic compressibility ( K ϕ ) as well as deviation in isentropic compressibility ( Δ k s ) were determined from the experimentally found results of speed of sound, viscosity and density. The obtained derived properties have been elucidated in terms of solute-solvent interactions taking place in the systems. The investigation of thermophysical properties of organic solvents with ionic liquids is essential as they decide the transformation of ionic liquids from small laboratory scale to large industrial applications. The obtained results are important and essential as they describe the molecular interactions, and can be used in constructing the structure-property correlation as well as molecular modelling that exist between [C2mim] [BF4] with benzaldehyde or ethyl acetoacetate. Redlich-Kister polynomial equation was used to fit the excess values and a good correlation was achieved.

A lignin polymer nanocomposite based electrochemical sensor for the sensitive detection of chlorogenic acid in coffee samples.

In this study, an innovative nanocomposite of multiwalled carbon nanotubes (MWCNTs), copper oxide nanoparticles (CuONPs) and lignin (LGN) polymer were successfully synthesized and used to modify the glassy carbon electrode for the determination of chlorogenic acid (CGA). Cyclic voltammetry (CV) emphasised a quasi-reversible, adsorption controlled and pH dependent electrode procedure. In cyclic voltammetry a pair of well distinct redox peaks of CGA were observed at the LGN-MWCNTs-CuONPs-GCE in 0.1 M phosphate buffer solution (PBS), at pH 2. The synthesized nanoparticles and nanocomposites were characterized by Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses. Differential pulse voltammetry (DPV) was applied to the anodic peak and used for the quantitative detection of CGA. Under optimal conditions, the proposed sensor showed linear responses from 5 µM to 50 µM, the linear regression equation Ipa (µA) = 2.6074 C-5.1027 (R2 = 0.995), whilst the limit of detection (LOD) and limit of quantifications (LOQ) were found to be 0.0125 µM and 0.2631 µM respectively. The LGN-MWCNTs-CuONPs-GCE were applied to detect the CGA in real coffee samples with the recovery ranging from 97 to 106 %. The developed sensor was successfully applied for the analysis of CGA content in the coffee samples. In addition, electrophilic, nucleophilic reactions and chlorogenic acid docking studies were carried out to better understand the redox mechanisms and were supported by density functional theory calculations.

An Enzyme-Induced Novel Biosensor for the Sensitive Electrochemical Determination of Isoniazid.

In this present work, a glassy carbon electrode (GCE) was modified primarily with multiwalled carbon nanotubes (MWCNTs) and a composite of MWCNTs and titanium oxide nanoparticles (TiO2NPs). The enzyme horseradish peroxidase (HRP) was immobilized to enhance the sensing ability of GCE. The proposed biosensor was used for the sensitive determination of isoniazid (INZ) in various pharmaceutical samples. The electrochemical behaviour of the developed MWCNT-TiO2NPs-HRP-GCE biosensor was studied by using cyclic voltammetry (CV) and differential pulse voltammetric (DPV) techniques. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetry (TGA) and transmission electron microscopy (TEM) techniques were used to characterize the developed sensor. Phosphate buffer solution (PBS) with pH 7 was used as supporting electrolyte in the present investigation. The cyclic voltammetric results revealed that the increment of anodic peak currents for the enzyme-induced sensor was almost 8-fold greater than that of a bare GCE. The DPV technique exhibited good limit of detection and limit of quantification values, viz., 0.0335 µM and 0.1118 µM, respectively. Moreover, the developed sensor showed long-lasting stability and repeatability without any interferents. This strongly indicates that the fabricated sensor shows outstanding electrochemical performance towards INZ, with excellent selectivity and sensitivity. The developed sensor was successfully applied to pharmaceutical samples and gave good percentages of recoveries.