Scientia Iranica
Volume:19 Issue: 3, 2012

This paper describes an electrochemical hybridization biosensor that investigates DNA hybridization on the modified Glassy Carbon Electrode (GCE). GCE was modified by a mixture of Au nanoparticles (AuNPs) and calf thymus DNA (ctDNA). SH-ssDNA was self-assembled on a modified electrode, which is a segment of the sex determining region of the Y (SRY) gene. This electrode can detect the complementary and non-complementary strand of SRY gene, by Methylene Blue (MB), as an electroactive label, and the Differential Pulse Voltammetry (DPV) technique. The modified GCE for the complementary DNA had a linear dynamic range of 0.5–30.0 ppm. This is the first report of sex determination by the electrochemical biosensor of a Polymerase Chain Reaction (PCR) product. Also, this biosensor showed stability on thermal denaturation for five sequential denaturation processes.

Based on the nonlocal Bernoulli–Euler and Timoshenko beam theories, the dynamic stability of embedded single-walled carbon nanotubes (SWCNTs) under axial compression is studied in a thermal environment. The developed nonlocal models have the capability to interpret small scale effects. A Winkler-type elastic foundation is employed to represent the interaction of the SWCNT and the surrounding elastic medium. The free vibration and axial buckling of SWCNTs are discussed as subset problems. A parametric study is conducted to investigate the influences of the static load factor, temperature change, nonlocal elastic parameter, slenderness ratio and spring constant of the elastic medium on the dynamic stability characteristics of the SWCNTs, with simply-supported boundary conditions. It is found that the difference between instability regions predicted by local and nonlocal beam theories is significant for nanotubes with lower aspect ratios. Moreover, it is observed that in contrast to high temperature environments, at low temperatures, increasing the temperature change moves the origins of the instability regions to higher excitation frequencies and leads to further stability of the system at lower excitation frequencies.

Crystallized silver nanoparticles (SNPs) have been biosynthesized by Spirulina platensis in an aqueous system. An aqueous solution of silver ions was treated with a live biomass of Spirulina platensis for the formation of SNPs. These nanoparticles showed an absorption peak at 430 nm in the UV-visible spectrum, corresponding to the plasmon resonance of SNPs. The transmission electron micrographs of nanoparticles in an aqueous solution showed the production of SNPs (average size of most particles: ∼12 nm) by Spirulina platensis. The X-Ray Diffraction (XRD) spectrum of the nanoparticles confirmed the formation of metallic silver, and the average size of the crystallite was estimated from the peak profile by the Scherrer method. The synthesized SNPs had an average size of 11.6 nm.

In this research work, we have used a microwave combustion method to synthesize three nanocrystalline ferrites including MnFe2O4, ZnFe2O4 and Mn0.5Zn0.5Fe2O4. For synthesis of these ferrites, a mixture of iron (III) nitrate, zinc and/or manganese nitrate, along with glycine, as fuel, was heated in a microwave oven for a few minutes to afford the required ferrite in pure and quantitative yield. The obtained ferrites were characterized by X-ray powder Diffraction (XRD), and their mean grain size and morphology were determined by the Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM) studies. The magnetic properties of the synthesized ferrites were investigated with Vibrating Sample Magnetometry (VSM), and their hysteresis loops were obtained. The specific surface area and pore size distributions of the samples were also obtained using Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods, respectively.

By using a Radio Frequency (RF) sputtering technique, Zn and ZnO nanostructures were fabricated on different substrates. ZnO nonorganics were synthesized on glass substrates, and Zn nanowires, ZnO nanoparticles and ZnO nanorods were synthesized on silicon substrates. The obtained ZnO nanograins ranging from 30 to 100 nm in size showed an almost single-crystalline structure. The agglomerated ZnO nanoparticles and ZnO nanorods exhibited a polycrystalline structure. The size of agglomerated nanoparticles is in the range of 40–150 nm, and the nanorods have a diameter of about 60 nm and a length of about 650 nm. There are four peaks in the range of 400–570 nm of the photoluminescence (PL) spectra, at room temperature. The strong peaks in PL of these samples are related to green and violet emissions. The PL spectra of the grown samples indicate that the nanorods fabricated by reactive sputtering can be a good choice for use in optoelectronic devices, such as diode lasers and LEDs.

Various aqueous solutions of silver and silver/cobalt nanoparticles (Ag and Ag/Co NPs) were obtained, and their fluorescence emission spectra have been studied. First, colloidal Ag NPs were prepared by an electrochemical method under different time intervals and at different rotation speeds of rotating electrode. Next, in a reduction method, Ag/Co core–shell NPs were prepared, using Ag NPs as a core. The core–shell structure of Ag/Co NPs has been demonstrated by the Transmission Electron Micrograph (TEM) and X-Ray Diffraction (XRD) pattern. The fluorescence emission spectra of Ag and Ag/Co NPs, at different ranges of excitation wavelength, were investigated, which revealed two kinds of fluorescence emission peak. The shorter emission peak was fixed at about 485 (for Ag NPs) and 538 nm (for Ag/Co NPs). For both NPs, with an increase in excitation wavelength, the latter emission peak becomes red-shifted. The effect of duration time and rotation speed of the rotating electrode, in the electrochemical preparation of Ag NPs, on its fluorescence emission spectra, has also been investigated.

In this study, surface modification of titanium oxide nanocrystals has been considered. PEG was employed to make bio-conjugated TiO2 nanopowders (TNPs). On the basis of the modification process, the effect of PEG on the size and morphology of prepared samples has been evaluated. It was found that the addition stage of PEG plays a critical role in the characteristics of TiO2 nanopowders. It was shown that PEG affects sol–gel reactions and the crystallization process of the prepared titanium oxide nanoparticles. PEG must be added before starting the synthesis to get well-defined size distribution, compared to post-synthesis. However, TiO2/PEG nanoparticles synthesized by the second approach have good photocatalytic performance, and the photodecomposition test of methylene blue proves that the addition of PEG after the synthesis of TiO2 improves the photocatalytic properties of prepared TiO2 nanoparticles. This phenomenon will affect TiO2 functionality, as well.

Several pigments and vat dyes were used for investigating changes in the reflective behavior of printed brown and khaki cotton/polyester (65/35) fabrics in Vis/near IR (NIR) bands. Reflectance, light, rubbing, washing fastness, and colorimetric values of treated samples with TiO2 nanoparticles and carbon black powder were evaluated. The results show that NIR reflectance of brown and khaki printed fabrics was reduced by presence of TiO2 in printing formulations. Carbon black particles significantly change the visible appearance of the printed samples, rather than TiO2 nanoparticles, even at low concentration.

We report herein the development of a highly sensitive colorimetric method for the determination of cysteine and glutathione, based on aggregation of the citrate capped gold nanoparticles (Au NPs). This was exploited from high affinity of low-molecular-weight aminothiols towards the Au NPs surface, which could induce displacement of the citrate shell by the thiolate shell of target molecules, resulting in aggregation of the NPs through intermolecular electrostatic interaction or hydrogen-bonding. As a result of aggregation, which can be affected by the ionic strength, pH and concentration of Au NPs, the plasmon band at around 521 nm decreases gradually, along with formation of a new red shifted band. The calibration curves, which are derived from the intensity ratios of absorbance at-640 nm and 650 nm for cysteine and glutathione, respectively, to the original wavelength of 521 nm, display a linear relation in the range of 1×10−6–100×10−6 M cysteine and 5×10−6–200×10−6 M glutathione. The obtained detection limits (3σ) were 2.1×10−6 M and 3.3×10−6 M for determination of cysteine and glutathione, respectively.

Current chemical methods of synthesis have shown limited success in the fabrication of nanomaterials, which involves environmentally malignant chemicals. Environmental friendly synthesis requires alternative solvents, and it is expected that the use of soft options of green approaches may overcome these obstacles. Water, which is regarded as a benign solvent, has been used in the present work for the preparation of platinum nanoparticles. The average particle diameter is in the range of ∼13±5 nm and particles are largely agglomerated. The advantages of preparing nanoparticles with this method include ease, flexibility and cost effectiveness. The prospects of the process are bright, and the technique could be extended to prepare many other important metal and metal oxide nanostructures.