Masoud Ghaani

A Novel Electrochemical Biosensor Based on a Modified Gold Electrode for Hydrogen Peroxide Determination in Different Beverage Samples

In the present work, an electrochemical biosensor is constructed based on a Nafion nano composite polymer, toluidine blue (TB) and catalase enzyme-modified gold electrode (AuE). The TB molecules were strongly adsorbed on the Nafion/AuE. The electrochemical properties of this biosensor were examined. Cyclic voltammetry was used at various scan rates to investigate the redox properties of the Nafion and TB-modified AuE (Nafion/TB/AuE). The electron transfer coefficient, α, and the electron transfer rate constant, ks, were found to be 0.48 and 12.1u2009±u20090.3xa0s−1 in pH 7.0, respectively. The Nafion, TB, and catalase-modified AuE (Nafion/TB/catalase/AuE) exhibited excellent electrocatalytic response to the reduction of hydrogen peroxide (H2O2). Using cyclic voltammetry, kinetic parameters such as electron transfer coefficient, α, and heterogeneous rate constant, k’, were determined for the reduction of H2O2 at this biosensor surface. Differential pulse voltammetry exhibited two linear dynamic ranges and a detection limit of 0.25xa0μM for H2O2.

Development of an electrochemical nanosensor for the determination of gallic acid in food

In the present work, a silver nanoparticle/delphinidin modified glassy carbon electrode (AgNP/Delph/GCE) was fabricated as a highly sensitive electrochemical sensor for gallic acid (GA) determination. Cyclic voltammetry experiments indicated a higher sensitivity and better selectivity for gallic acid when using the AgNP/Delph/GCE as compared with the bare GCE surface, which were attributed to AgNPs and delphinidin, respectively. Moreover, the calculated surface electron transfer rate constant (ks), and the electron transfer coefficient (α) between the GCE and the electrodeposited delphinidin demonstrated that delphinidin is an excellent electron transfer mediator for the electrocatalytic process. The average catalytic rate constant (k′) of the overall process was also estimated to be 7.40 × 10−4 cm s−1 for the AgNP/Delph/GCE in the presence of 1.50 mmol L−1 of GA. Amperometry experiments were used to determine the limit of detection of the AgNP/Delph/GCE electrochemical sensor, which was 0.28 μmol L−1 of GA. Finally, two linear ranges were found, i.e. 0.60–8.68 μmol L−1 and 8.68–625.80 μmol L−1 for GA. The activity of the modified electrode was eventually investigated to assess the potential quantification of GA in real foods.

Mechanical behavior of biopolymer composite coatings on plastic films by depth-sensing indentation – A nanoscale study

Fundamental physical behaviors of materials at the nanoscale level are crucial when local aspects govern the macroscale performance of nanocomposites, e.g., interface and surface phenomena. Because of the increasing interest in biopolymer nanocomposite coatings for many different applications (e.g., optical devices, displays/screens, and packaging), this work investigates the potential of nanoindentation as a method for clarifying the interplay between distinct phases (i.e., organic and inorganic) at local level in thin biopolymer films loaded with nanoparticles. The nanomechanical features of pullulan nanocomposite coatings laid on polyethylene terephthalate (PET) were quantified in terms of elastic modulus (E), hardness (H), and creep (C) through an instrumented indentation test composed of a loading-holding-unloading cycle. Colloidal silica (CS) and cellulose nanocrystals (CNCs) were used as spherical and rod-like nanoparticles, respectively. An overall reinforcing effect was shown for all nanocomposite coatings over the pristine (unfilled) pullulan coating. A size effect was also disclosed for the CS-loaded surfaces, with the highest E value recorded for the largest particles (8.19u202f±u202f0.35u202fGPa) and the highest H value belonging to the smallest ones (395.41u202f±u202f25.22u202fMPa). Comparing CS and CNCs, the addition of spherical nanoparticles had a greater effect on the surface hardness than cellulose nanowhiskers (353.50u202f±u202f83.52u202fMPa and 321.36u202f±u202f43.26u202fMPa, respectively). As for the elastic modulus, the addition of CS did not provide any improvement over both the bare and CNC-loaded pullulan coatings, whereas the coating including CNCs exhibited higher E values (pu202f<u202f.05). Finally, CS-loaded pullulan coatings were the best performing in terms of C properties, with an average indentation depth of 16.5u202f±u202f1.85u202fnm under a load of ∼190u202fμN. These results are discussed in terms of local distribution gradients, surface chemistry of nanoparticles, and how nanoparticle aggregation occurred in the dry nanocomposite coatings.

Novel Non Enzymatic TBHQ Modified Electrochemical Sensor for Hydrogen Peroxide Determination in Different Beverage Samples

A nanosensor was developed for hydrogen peroxide determination based on nafion/graphene oxide/silver nanoparticles/tertiary butylhydroquinone (TBHQ) modified glassy carbon electrode (N-GO/AgNPs/TBHQ/GCE). Cyclic voltammetry was used to investigate the electrochemical behavior of this modified electrode and differential pulse voltammetry was used for the reduction of H2O2. The limit of detection was 0.46 µmol L-1 and three linear calibration ranges were obtained for H2O2 determination from 1.52-9.79 µmol L-1 for first linear segment, 9.79-231.0 µmol L-1 for second linear segment and 231.0-8330.0 µmol L-1 for third linear segment. Finally, the reliability of the nanosensor was confirmed in the real sample analysis in different beverages with satisfactory results.

Graphene Oxide Bionanocomposite Coatings with High Oxygen Barrier Properties

In this work, we present the development of bionanocomposite coatings on poly(ethylene terephthalate) (PET) with outstanding oxygen barrier properties. Pullulan and graphene oxide (GO) were used as main polymer phase and nanobuilding block (NBB), respectively. The oxygen barrier performance was investigated at different filler volume fractions (ϕ) and as a function of different relative humidity (RH) values. Noticeably, the impermeable nature of GO was reflected under dry conditions, in which an oxygen transmission rate (OTR, mL·m−2·24 h−1) value below the detection limit of the instrument (0.01 mL·m−2·24 h−1) was recorded, even for ϕ as low as 0.0004. A dramatic increase of the OTR values occurred in humid conditions, such that the barrier performance was totally lost at 90% RH (the OTR of coated PET films was equal to the OTR of bare PET films). Modelling of the experimental OTR data by Cussler’s model suggested that the spatial ordering of GO sheets within the main pullulan phase was perturbed because of RH fluctuations. In spite of the presence of the filler, all the formulations allowed the obtainment of final materials with haze values below 3%, the only exception being the formulation with the highest loading of GO (ϕ ≈ 0.03). The mechanisms underlying the experimental observations are discussed.

Simultaneous Determination of Ascorbic Acid, L-Dopa, Uric Acid, Insulin, and Acetylsalicylic Acid on Reactive Blue 19 and Multi-Wall Carbon Nanotube Modified Glassy Carbon Electrode

A trifunctional electrochemical sensor was fabricated for simultaneous determination of ascorbic acid (AA), levodopa (LD), and insulin. This was done by modifying a glassy carbon electrode (GCE) with multi-walled carbon nanotubes and reactive blue 19 (RB-MWCNT-GCE). Cyclic voltammetry was used to investigate the redox properties of this modified electrode. The electro-catalytic activity of the modified electrode was studied for the oxidation of AA, LD, and insulin. By differential pulse voltammetry (DPV), the detection limits of AA, LD, and insulin were estimated to be 0.45 µmol L -1, 0.37 µmol L-1, and 0.25xa0µmolxa0L-1, respectively. In DPV measurements, the RB-MWCNT-GCE could separate the oxidation peak potentials of AA, LD, uric acid (UA), insulin, and acetylsalicylic acid (ASA) in a mixture. The practical utility of this modified electrode was demonstrated by detecting AA, LD, UA, insulin, and ASA in real samples.

A bionanocomposite-modified glassy carbon electrode for the determination of 4,4′-methylene diphenyl diamine

A nanosensor based on a glassy carbon electrode modified with the biopolymer chitosan, multi-wall carbon nanotubes, and gold nanoparticles (MWCNTs–CS–AuNPs/GCE) was developed for the determination of 4,4′-diaminodiphenyl diamine (MDA). Cyclic voltammetry (CV) was used to investigate the electrochemical behavior of the sensor in the presence of MDA. MDA displayed a well-expressed oxidation peak at 0.54 V (versus Ag/AgCl) in Britton–Robinson (B–R) universal buffer solution (pH = 10). The transfer coefficient, α, and the overall number of electrons (n) involved in the catalytic oxidation of MDA at the MWCNTs–CS–AuNPs/GCE surface were also determined by CV. The reactivity of spiked MDA was strongly dependent on the pH of the supporting electrolyte, with the pH dependence of the MDA oxidation quantified as 27.576 mV pH−1. Through chronoamperometry, the diffusion coefficient (D) of MDA was calculated to be 9.49 × 10−5 cm2 s−1. The limit of detection of MDA was estimated to be ∼20 nM through amperometry experiments, while three linear ranges were found for MDA, i.e., 0.49–10.14 μM, 10.14–94.9 μM, and 94.9–261.18 μM. Real sample tests enabled us to emphasize the potential of this nanocomposite-modified electrode as a new analytical tool for the determination of MDA.