Reda Hassanien

Preparation and Characterization of Conductive and Photoluminescent DNA-Templated Polyindole Nanowires

Polyindole (PIn) nanowires were formed on a lambda-DNA template by chemical oxidation of indole using aqueous FeCl3. The resulting nanowires are smooth, regular, conductive and had diameters in the range of 5-30 nm. These features allow them to be aligned by molecular combing and studied by scanned conductance microscopy, conductive AFM, and two-terminal I-V measurements. Using this combination of measurements, we find that the conductivity of PIn/DNA nanowires is between 2.5 and 40 S cm(-1) at room temperature, which is substantially greater than that in previous reports on the bulk polyindole conductivity (typically 10(-2)-10(-1) S cm(-1)). The conductance at zero bias shows an Arrhenius-type of dependence on temperature over the range of 233 to 373 K, and the values observed upon heating and cooling are repeatable within 5%; this behavior is consistent with a hopping mechanism of conductivity.

Smooth and conductive DNA-templated Cu2O nanowires: growth morphology, spectroscopic and electrical characterization

DNA strands have been used as templates for the self-assembly of smooth and conductive cuprous oxide (Cu₂O) nanowires of diameter 12-23 nm and whose length is determined by the template (16 μm for λ-DNA). A combination of spectroscopic, diffraction and probe microscopy techniques showed that these nanowires comprise single crystallites of Cu₂O bound to the DNA molecules which fused together over time in a process analogous to Ostwald ripening, but driven by the free energy of interaction with the template as well as the surface tension. Electrical characterization of the nanowires by a non-contact method, scanned conductance microscopy and by contact mode conductive AFM showed the wires are electrically conductive. The conductivity estimated from the AFM cross section and the zero-bias conductance in conductive AFM experiments was 2.2-3.3 S cm⁻¹. These Cu₂O nanowires are amongst the thinnest reported and show evidence of strong quantum confinement in electronic spectra.

Networks of DNA-templated palladium nanowires : structural and electrical characterisation and their use as hydrogen gas sensors

Electroless templating on DNA is established as a means to prepare high aspect ratio nanowires via aqueous reactions at room temperature. In this report we show how Pd nanowires with extremely small grain sizes (< 2 nm) can be prepared by reduction of PdCl4(2-) in the presence of lambda-DNA. In AFM images the wires are smooth and uniform in appearance, but the grain size estimated by the Scherrer treatment of line broadening in X-ray diffraction is less than the diameter of the wires from AFM (of order 10 nm). Electrical characterisation of single nanowires by conductive AFM shows ohmic behaviour, but with high contact resistances and a resistivity (-10(-2) omega cm) much higher than the bulk value for Pd metal (-10(-5) cm @ 20 degrees C). These observations can be accounted for by a model of the nanowire growth mechanism which naturally leads to the formation of a granular metal. Using a simple combing technique with control of the surface hydrophilicity, DNA-templated Pd nanowires have also been prepared as networks on an Si/SiO2 substrate. These networks are highly convenient for the preparation of two-terminal electronic sensors for the detection of hydrogen gas. The response of these hydrogen sensors is presented and a model of the sensor response in terms of the diffusion of hydrogen into the nanowires is described. The granular structure of the nanowires makes them relatively poor conductors, but they retain a useful sensitivity to hydrogen gas.

Preparation and electrical properties of a copper-conductive polymer hybrid nanostructure

N-(3-Pyrrol-1-yl-propyl)-4,4′-bipyridinium hexafluorophosphate (NPPBH) has been synthesized and polymerized in the presence of DNA to produce DNA-templated polymer nanowires (polyNPPBH/DNA). The pyridine group serves as a ligand for Cu(II) and to direct the subsequent electroless deposition of Cu to form Cu/polyNPPBH/DNA nanowires. UV-vis absorption spectra of the hybrid materials show an absorption peak corresponding to the plasmon resonance of Cu0 particles at about 550 nm. AFM observations show that the Cu/polyNPPBH/DNA nanowires have a wide range of diameters, 10–30 nm, but individual nanowires exhibit a uniform and continuous morphology. The electrical properties of the wires were examined by scanned conductance microscopy and conductive AFM. The nanowire conductivity was estimated using the diameter and width of the as-prepared nanowires to calculate the cross-section area (assumed elliptical). We estimate 0.42 ± 0.019 S cm−1 for the Cu/polyNPPBH/DNA nanowire conductivity. This is substantially greater than the polyNPPBH/DNA conductivity (2.1 ± 0.26 × 10−2 S cm−1) which indicates that the current pathway is via the copper metallization, however the value is much lower than bulk Cu. Although the AFM images show relatively regular metal coverage of the polymer/DNA wires, the presence of discontinuities or voids along the length of the nanostructure is likely. Such gaps in the metal structure may introduce significant tunneling barriers and a granular metal model is a more appropriate description of the Cu/polyNPPBH/DNA nanowires than a simple metallic nanowire.

Metal-conductive polymer hybrid nanostructures: preparation and electrical properties of palladium–polyimidazole nanowires

A simple, convenient method for the formation of hybrid metal/conductive polymer nanostructures is described. Polyimidazole (PIm) has been templated on λ-DNA via oxidative polymerisation of imidazole using FeCl3 to produce conductive PIm/DNA nanowires. The PIm/DNA nanowires were decorated with Pd (Pd/PIm/DNA) by electroless reduction of PdCl4(-2) with NaBH4 in the presence of PIm/DNA; the choice of imidazole was motivated by the potential Pd(II) binding site at the pyridinic N atom. The formation of PIm/DNA and the presence of metallic Pd on Pd/PIm/DNA nanowires were verified by FTIR, UV-vis and XPS spectroscopy techniques. AFM studies show that the nanowires have diameters in the range 5-45 nm with a slightly greater mean diameter (17.1 ± 0.75 nm) for the Pd-decorated nanowires than the PIm/DNA nanowires (14.5 ± 0.89 nm). After incubation for 24 h in the polymerisation solution, the PIm/DNA nanowires show a smooth, uniform morphology, which is retained after decoration with Pd. Using a combination of scanned conductance microscopy, conductive AFM and two-terminal measurements we show that both types of nanowire are conductive and that it is possible to discriminate different possible mechanisms of transport. The conductivity of the Pd/PIm/DNA nanowires, (0.1-1.4 S cm(-1)), is comparable to the PIm/DNA nanowires (0.37 ± 0.029 S cm(-1)). In addition, the conductance of Pd/PIm/DNA nanowires exhibits Arrhenius behaviour (E(a )= 0.43 ± 0.02 eV) as a function of temperature in contrast to simple Pd/DNA nanowires. These results indicate that although the Pd crystallites on Pd/PIm/DNA nanowires decorate the PIm polymer, the major current pathway is through the polymer rather than the Pd.

Ultra-sensitive hydrogen gas sensing using DNA-templated palladium nanowires

This paper focuses on an ultra-sensitive H<inf>2</inf> sensor fabricated using a time and cost-effective method. The sensor is comprised of Pd nanowires fabricated using λ-DNA templates. The morphology and the electrical characterisation of the metalized DNA nanowires (diameter = 5–45nm) were investigated by AFM and conductive AFM (cAFM). The conductivity of a single Pd-DNA nanowire, 127 Scm⁻¹ was substantially lower than that of bulk Pd (9.5×10⁴ Scm⁻¹). However, the sensor shows high sensitivity towards hydrogen evaluated by recording the change in the resistance on exposure to cycles of different concentrations of H<inf>2</inf> in N<inf>2</inf> flow at 330K. The sensor showed a reversible response to H<inf>2</inf> concentrations between 2300 – 12500 ppm and a response time of ∼85 s. These results indicate that using DNA as a template is a promising method for the fabrication of low cost and rapid response sensors.

Synthesis of some heterocyclic compounds derived from indole as antimicrobial agents

ABSTRACT Recently, indoles are considered interesting heterocyclic compounds due to their wide range of biological activities such as antimicrobial activity. Herein, some new indole derivatives containing heterocyclic moieties were synthesized using 3-chloro-1H-Indole-2-carbaldehyde (1) as a starting material, then allowed to react with compounds containing active methylene under Knoevenagel condensation and afforded the corresponding compounds (2, 3, 9). Also, the compound (1) when allowed to react with hydrazine derivatives gave the corresponding thiosemiccarbazone, semicarbazone, and hydrazone derivatives (4, 5, 6). Reaction of thiosemicarbazone derivatives with α-halognated carbonyl compounds gave the thiazolyl indole derivatives (10, 12a–b). Cyclic chalcones (11a–c) were obtained when compound (10) reacted with different aromatic aldehydes. The structures of all new synthesized compounds were confirmed on the basis of spectral analysis, IR, 1H NMR, 13C NMR, and MS spectroscopy. All synthesized compounds were evaluated for their antimicrobial activity. Compounds (2, 5, 7, 8, 11a, 12a) showed high antibacterial activity and compounds (3, 6, 9, 10, 11a, 12a) showed high antifungal activity. GRAPHICAL ABSTRACT

Preparation of 1D nanostructures using biomolecules

In this paper we have shown that one-dimensional (1D) particle arrays can be obtained using biomolecules, like DNA or amino-acids. Nano-arrays of silver and gold were prepared in a single-step synthesis, by exploiting the binding abilities of λ-DNA and L-Arginine. The morphology and optical properties of these nanostructures were investigated using AFM, TEM and UV-Vis absorption spectroscopy.