Laser-induced transformation of graphitic materials to two-dimensional graphene-like structures at ambient conditions.

Laser processing of carbon compounds towards the formation of graphene-based structures gains ground in view of the practicality that lasers offer against other conventional graphene preparation methods. The current work explores the viability of low-cost lasers, operating at ambient conditions, for the transformation of various graphitic materials to structures with graphene-like atomic arrangements. Starting materials are at two opposing sides. On one side stands the typical graphite crystal with Bernal stacking and strong sp 2 character, while nanocrystalline graphitic powders are also investigated. It is demonstrated that graphene-like structures can be prepared either by starting from a well-organized Bernal-stacked network or by irradiating nanocrystalline carbon. The current findings document that laser processing at minimal chamber conditions shows high potential for preparing high-quality graphene-based structures starting from low-cost materials. Apart from being scalable, the proposed method is adaptable to current technological platforms emerging as a viable and eco-friendly graphene production technology.

Facile, substrate-scale growth of mono- and few-layer homogeneous MoS2 films on Mo foils with enhanced catalytic activity as counter electrodes in DSSCs.

The growth of MoS2 films by sulfurization of Mo foils at atmospheric pressure is reported. The growth procedure provides, in a controlled way, mono- and few-layer thick MoS2 films with substrate-scale uniformity across square-centimeter area on commercial foils without any pre- or post-treatment. The prepared few-layer MoS2 films are investigated as counter electrodes for dye-sensitized solar cells (DSSCs) by assessing their ability to catalyse the reduction of I3(-) to I(-) in triiodide redox shuttles. The dependence of the MoS2 catalytic activity on the number of monolayers is explored down to the bilayer thickness, showing performance similar to that of, and stability against corrosion better than, Pt-based nanostructured film. The DSSC with the MoS2-Mo counter electrode yields a photovoltaic energy conversion efficiency of 8.4%, very close to that of the Pt-FTO-based DSSC, i.e. 8.7%. The current results disclose a facile, cost-effective and green method for the fabrication of mechanically robust and chemically stable, few-layer MoS2 on flexible Mo substrates and further demonstrate that efficient counter electrodes for DSSCs can be prepared at thicknesses down to the 1-2 nm scale.

Inhibition of Bacterial Attachment on Surfaces by Immobilization of Tobramycin-Loaded Liposomes.

Stainless steel surfaces were processed by gold deposition in order to immobilize tobramycin-loaded liposomes which were functionalized on their surface with thiol-groups (through maleimide (MAL) derivatization with thiols). After optimizing the tobramycin loading in liposomes (LIPs), and the immobilization of THIOL-MAL-functionalized LIPs on gold-sputtered surfaces, the coated surfaces were challenged with two reference Staphylococcus epidermidis strains: ATCC 35984 (slime-positive) and ATCC 12228 (slime-negative), in order to measure the degree of surface protection from biofilm formation. Moreover, the effect of the reference and two well characterized clinical S. epidermidis strains on the integrity of LIPs (composed of PC or DSPC) was evaluated, in order to investigate whether specific interactions between LIPs and bacteria occur, and if they are affected by LIP membrane composition and/or bacterial strain type. Bacteria growth on surfaces is substantially inhibited by TOBR-loaded-LIP immobilization, especially in the case of the non-biofilm forming bacterial strain. Gold sputtered surfaces were moderately (albeit significantly) protected, from both reference strains tested (compared to bare surfaces). Interestingly, LIP integrity is significantly decreased in the presence of bacteria (at specific lipid/bacteria ratios); the biofilm-forming bacteria being most potent for LIP disruption, whereas, less rigid liposomal membranes (PC) are affected more compared to rigid (DSPC) ones. The clinical strains are also reactive against LIP. This interaction indicates a potential for triggered release of LIP-encapsulated drugs in presence of biofilm-forming bacteria, therefore LIP encapsulation/immobilization may be envisioned as a potential platform technology for triggered antimicrobial therapy.

Transmission environmental scanning electron microscope with scintillation gaseous detection device.

A transmission environmental scanning electron microscope with use of a scintillation gaseous detection device has been implemented. This corresponds to a transmission scanning electron microscope but with addition of a gaseous environment acting both as environmental and detection medium. A commercial type of low vacuum machine has been employed together with appropriate modifications to the detection configuration. This involves controlled screening of various emitted signals in conjunction with a scintillation gaseous detection device already provided with the machine for regular surface imaging. Dark field and bright field imaging has been obtained along with other detection conditions. With a progressive series of modifications and tests, the theory and practice of a novel type of microscopy is briefly shown now ushering further significant improvements and developments in electron microscopy as a whole.

Inter- and intramolecular interactions in imidazolium protic ionic liquids.

The interactions of alkyl substituted imidazolium bis(trifluoromethanolsulfonyl)imide protic ionic liquids (PILs) HCnImNTf2 (n = 0-12) were studied using vibrational spectroscopy (FT-IR/ATR and FT-Raman) and differential scanning calorimetry (DSC). The effect of alkyl substituent length (n = 0-12) and temperature on the relative magnitude of the different interactions is elucidated. For short carbon alkyl chains (n < 3), the PIL structure is affected from intramolecular interaction caused from the induction effect (+I) due to the chain substituent of the imidazolium ring, while for PILs with n > 3 the van der Waals forces between the chains and π-π interaction between neighboring imidazolium rings become important. The tendency of reducing the melting point and increasing glass transition values with the lengthening of the alkyl chain was also noticed as a result the increasing contribution of the van der Waals forces to the overall interactions. Finally, we also show that the conformational isomerism of the anion (expressed by ΔHeq) is a good indicator of the relative magnitude of the interactions. When Coulombic interactions are predominant, the trans conformer is the most probable, while when other type of interactions (HB, vdW, etc.) become important the cis conformer is favored.

Laser-assisted growth of t-Te nanotubes and their controlled photo-induced unzipping to ultrathin core-Te/sheath-TeO(2) nanowires.

One dimensional (1D) nanostructures of semiconducting oxides and elemental chalcogens culminate over the last decade in nanotechnology owing to their unique properties exploitable in several applications sectors. Whereas several synthetic strategies have been established for rational design of 1D materials using solution chemistry and high temperature evaporation methods, much less attention has been given to the laser-assisted growth of hybrid nanostructures. Here, we present a laser-assisted method for the controlled fabrication of Te nanotubes. A series of light-driven phase transition is employed to controllably transform Te nanotubes to core-Te/sheath-TeO(2) and/or even neat TeO(2) nanowires. This solid-state laser-processing of semiconducting materials apart from offering new opportunities for the fast and spatially controlled fabrication of anisotropic nanostructures, provides a means of simultaneous growing and integrating these nanostructures into an optoelectronic or photonic device.

ESEM modifications to LEO SUPRA 35 VP FESEM.

A LEO SUPRA 35 VP FESEM has been modified to significantly improve image quality in the low pressure mode of operation. It is further shown that the same conversion can allow the machine to operate also as a fully fledged environmental scanning electron microscope with specimen chamber pressures in excess of 2000 Pa. This is achieved by a diamagnetic insert with a thin pressure limiting aperture at the bottom of the pole-piece. The insert allows the use of various size apertures in addition to the existing 1 mm differential diaphragm.

PLGA, chitosan or chitosan-coated PLGA microparticles for alveolar delivery? A comparative study of particle stability during nebulization.

Various types of rifampicin (RIF)-loaded microparticles were compared for their stability during nebulization. Poly(lactide-co-glycolide) (PLGA), chitosan (CHT) and PLGA/CHT microparticles (MPs) were prepared by emulsion or precipitation techniques. MPs ability to be nebulized (NE%) as well as stability during freeze-drying or/and nebulization (NEED%), were evaluated after RIF extraction from MPs and determination by light spectroscopy. MP mean diameters and zeta-potential values were measured by dynamic light scattering, morphology was assessed by SEM, cytotoxicity by MTT method and mucoadhesive properties by mucin association. In all cases, freeze-drying prior to nebulization did not affect EE%, NE or NEED%. In CHT, MPs RIF encapsulation efficiency (EE%) decreased with increasing CHT concentration (viscosity) and CHT-MP NEED% was higher when the polymer was crosslinked by glutaraldehyde. PLGA MPs, exhibited both higher RIF EE% and also higher nebulization ability and NEED%, compared to CHT ones, but also higher cytotoxicity. However, when the two polymers were combined in the PLGA/CHT MPs, EE%, NE% and NEED% increased with increasing MP CHT-content. PLGA/CHT MPs with 0.50% or 0.75% CHT exhibited highest EE% for RIF and also best nebulization ability and stability, compared to all other MP formulations studied. Additionally they had good mucoadhesive properties and comparably low cytotoxicity.