Green and one-step synthesis of gold nanoparticles insorporated into electrospun cyclodextrin nanofibers

Cataloged from PDF version of article.The green and one-step synthesis of gold nanoparticles (Au-NP) incorporated into electrospun cyclodextrin-nanofibers (CD-NF) without the use of a carrier polymer matrix was achieved in this study. Chemically modified CD (hydroxypropyl-β-cyclodextrin (HPβCD)) was used as both a reducing and stabilizing agent as well as a fiber matrix for the electrospinning of HPβCD/Au-NP-NF composite mats. Electrospinning of metallic NP incorporating CD-NF would have exclusive properties by combining the very large surface area of nanofibers with specific functionality of the metal NP and CD

Electrospinning of nanofibers from non-polymeric systems: polymer-free nanofibers from cyclodextrin derivatives

Cataloged from PDF version of article.High molecular weight polymers and high polymer concentrations are desirable for the electrospinning of nanofibers since polymer chain entanglements and overlapping are important for uniform fiber formation. Hence, the electrospinning of nanofibers from non-polymeric systems such as cyclodextrins (CDs) is quite a challenge since CDs are cyclic oligosaccharides. Nevertheless, in this study, we have successfully achieved the electrospinning of nanofibers from chemically modified CDs without using a carrier polymer matrix. Polymer-free nanofibers were electrospun from three different CD derivatives, hydroxypropyl-β-cyclodextrin (HPβCD), hydroxypropyl-γ-cyclodextrin (HPγCD) and methyl-β-cyclodextrin (MβCD) in three different solvent systems, water, dimethylformamide (DMF) and dimethylacetamide (DMAc). We observed that the electrospinning of these CDs is quite similar to polymeric systems in which the solvent type, the solution concentration and the solution conductivity are some of the key factors for obtaining uniform nanofibers. Dynamic light scattering (DLS) measurements indicated that the presence of considerable CD aggregates and the very high solution viscosity were playing a key role for attaining nanofibers from CD derivatives without the use of any polymeric carrier. The electrospinning of CD solutions containing urea yielded no fibers but only beads or splashes since urea caused a notable destruction of the self-associated CD aggregates in their concentrated solutions. The structural, thermal and mechanical characteristics of the CD nanofibers were also investigated. Although the CD derivatives are amorphous small molecules, interestingly, we observed that these electrospun CD nanofibers/nanowebs have shown some mechanical integrity by which they can be easily handled and folded as a free standing material

Cyclodextrin nanofibers by electrospinning

We have demonstrated that cyclodextrin (CD) (a non-polymeric system) can be electrospun into nanofibers by itself; methyl-beta-cyclodextrin (MβCD) nanofibers were electrospun and it was observed that the success of the electrospinning of the CD nanofibers strongly depends on (i) type of solvent, (ii) CD solution concentration and (iii) intermolecular interactions between the CD molecules. © 2010 The Royal Society of Chemistry

Electrospun gamma-cyclodextrin (γ-CD) nanofibers for the entrapment of volatile organic compounds

Electrospinning of gamma cyclodextrin (γ-CD) nanofibers from a DMSO-water solvent system was achieved without using a carrier polymeric matrix. The effects of viscosity and rheological properties on the electrospinnability of γ-CD solutions were examined. XRD and HR-TEM studies confirmed that the electrospun γ-CD nanofibers were amorphous without showing any particular crystalline packing. The surface area of the γ-CD nanofibrous web was three times higher than the γ-CD in powder form. As a preliminary study, we have investigated the molecular entrapment capability of γ-CD nanofibers. γ-CD nanofibers were quite successful for entrapping of VOCs (aniline and toluene) by inclusion complexation, whereas γ-CD in powder form did not show any entrapment capability. © 2013 The Royal Society of Chemistry

Electrospinning of Polymer-free Nanofibers from Cyclodextrin Inclusion Complexes

Cataloged from PDF version of article.The electrospinning of polymer-free nanofibers from highly concentrated (160%, w/v) aqueous solutions of hydroxypropyl-β-cyclodextrin (HPβCD) and its inclusion complexes with triclosan (HPβCD/triclosan-IC) was achieved successfully. The dynamic light scattering (DLS) and rheology measurements indicated that the presence of considerable HPβCD aggregates and the high solution viscosity were the key factors in obtaining electrospun HPβCD and HPβCD/triclosan-IC nanofibers without the use of any polymeric carrier. The HPβCD and HPβCD/triclosan-IC solutions containing 20% (w/w) urea yielded no fibers but only beads and splashes because of the depression of the self-aggregation of the HPβCD. The inclusion complexation of triclosan with HPβCD was studied by isothermal titration calorimetry (ITC) and turbidity measurements. The characteristics of the HPβCD and HPβCD/triclosan-IC nanofibers were investigated by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). It was found that the electrospinning of HPβCD/triclosan-IC solution having a 1:1 molar ratio was optimal for obtaining nanofibers without any uncomplexed guest molecules

Electrospun porous cellulose acetate fibers from volatile solvent mixture

Cataloged from PDF version of article.Electrospun porous cellulose acetate (CA) fibers were produced from highly volatile binary solvent system; dichloromethane(DCM)/acetone. The morphology and porous structure of CA fibers were highly dependent on DCM/acetone ratio and the concentration of the solutions. Ribbon-like porous CA fibers were obtained from 5% (w/v) to 10% (w/v) polymer solutions depending on the DCM/acetone ratio; 1/1, 2/1, 3/1 and 9/1 (v/v). Using higher DCM/acetone ratio resulted in bead-free fibers from less concentrated polymer solutions due to the high viscosity of the solutions, in addition, more porous CA fibers were obtained owing to the high volatility of DCM

Flexible and highly stabel electrospun nanofibrous membrane incorporating gold nanocluster as a efficient probe for visual colorimetric detection of Hg(II)

Cataloged from PDF version of article.Here, we describe the visual colorimetric detection of Hg2+ based on a flexible fluorescent electrospun nanofibrous membrane (NFM). It is an efficient approach, in which we have effectively integrated fluorescent gold nanoclusters (AuNC) into electrospun polyvinyl alcohol nanofibers. Interestingly, the resulting composite nanofibers (AuNC*NFM) are shown to retain the fluorescence properties of AuNC and exhibit red fluorescence under UV light, being cogent criteria for the production of a visual colorimetric sensor. Furthermore, capabilities with regard to the stability of the AuNC*NFM have been under observation for a period of six months, with conditions matching those of typical atmosphere, and the resulting outcome has thrown light on their long-term storability and usability. It is clear, from the fact that the nanofibrous membrane preserves the fluorescence ability up to a temperature of 100 °C, that temperature does not have an effect on the sensing performance in real-time application. The water-insoluble AuNC*NFM have been successfully tailored by cross-linking with glutaraldehyde vapor. Further, the contact mode approach has been taken into consideration for the visual fluorescent response to Hg2+, and the observed change of color indicates the utility of the composite nanofibers for onsite detection of Hg2+ with a detection limit of 1 ppb. The selectivity of the AuNC*NFM hybrid system has been analyzed by its response to other common toxic metal interferences (Pb2+, Mn2+, Cu2+, Ni2+, Zn2+, Cd2+) in water. Several unique features of the hybrid system have been determined, including high stability, self-standing ability, naked-eye detection, selectivity, reproducibility and easy handling – setting a new trend in membrane-based sensor systems

Real-time selective visual monitoring of Hg 2+ detection at ppt level: An approach to lighting electrospun nanofibers using gold nanoclusters

In this work, fluorescent gold nanocluster (AuNC) decorated polycaprolactone (PCL) nanofibers (AuNC∗PCL-NF) for real time visual monitoring of Hg 2+ detection at ppt level in water is demonstrated. The resultant AuNC∗PCL-NF exhibiting remarkable stability more than four months at ambient environment and facilitates increased accessibility to active sites resulting in improved sensing performance with rapid response time. The fluorescence changes of AuNC∗PCL-NF and their corresponding time dependent spectra, upon introduction of Hg 2+, led to the visual identification of the sensor performance. It is observed that the effective removal of excess ligand (bovine serum albumin (BSA) greatly enhances the surface exposure of AuNC and therefore their selective sensing performance is achieved over competent metal ions such as Cu 2+, Ni 2+, Mn 2+, Zn 2+, Cd 2+, and Pb 2+ present in the water. An exceptional interaction is observed between AuNC and Hg 2+, wherein the absence of excess interrupting ligand makes AuNC more selective towards Hg 2+. The underlying mechanism is found to be due to the formation of Au-Hg amalgam, which was further investigated with XPS, TEM and elemental mapping studies. In short, our findings may lead to develop very efficient fluorescent-based nanofibrous mercury sensor, keeping in view of its stability, simplicity, reproducibility, and low cost

Distributed Detection of DDoS Attacks During the Intermediate Phase Through Mobile Agents

A Distributed Denial of Service attack is a large-scale, coordinated attack on the availability of services of a victim system, launched indirectly through many compromised computers on the Internet. Intrusion detection systems are network security tools that process local audit data or monitor network traffic to search for specific patterns or certain deviations from expected behavior, which indicate malicious activities against the protected network. In this study, we propose distributed intrusion detection methods to detect Distributed Denial of Service attacks in a special dataset and test these methods in a simulated-real time environment, in which the mobile agents are synchronized with the timestamp stated in the dataset. All of our methods use the alarms generated by SNORT, a signature-based network intrusion detection system. We use mobile agents in our methods on the Jade platform in order to reduce network bandwidth usage and to decrease the dependency on the central unit for a higher reliability. The methods are compared based on reliability, network load and mean detection time values

Drivers of convergence/divergence of corporate governance codes of MENA countries

This study aims to fill an existing gap in the regional corporate governance research by investigating the extent of and the drivers behind the convergence/divergence of the corporate governance codes among Middle Eastern and North African (MENA) countries comparing to the globally known Organization for Economic Cooperation and Development (OECD) principles of corporate governance. The results of the study revealed that the convergence level of the codes among the countries and compared to OECD principles significantly varies among countries, ranging from 31% to 73%. The results show that the adopted governance principles in the codes are ‘decoupled’ from legitimation concerns and focus on efficiency goals. The macroeconomic factors of MENA countries do not consistently reflect the convergence score of the codes with the OECD principles. The institutional quality factors of MENA countries are not aligned with their codes. The study provides several important implications for regulators, firms and other stakeholders