One-step-process composite colloidal monolayers and further processing aiming at porous membranes.

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly (in which a silica precursor, tetraethyl orthosilicate (TEOS), is added to the base colloid) with confined growth in a wedge-shaped cell, while profiting from the advantages of both techniques. Using this method, it is possible to fabricate the composite monolayer in a single growth step. A systematic study of the influence of TEOS concentration in the initial colloid was performed in order to improve the quality of the two-dimensional crystals produced. Thus, it was demonstrated that the two methods are compatible. Furthermore, the composites were then subjected to thermal treatment so that the polymer is removed to reveal the inverse structure. After the calcination the membranes still present very good quality and so the proposed approach is effective for the fabrication of porous membranes. A comparison of reflectance spectra, between composite monolayers fabricated using this method and composites achieved by infiltrating polystyrene bare opals with silica chemical vapor deposition, is also established. The procedure presented is expected to establish the route for an easier and quicker fabrication of inverse monolayers of high refractive index materials with applications in light control.

Qualitative and quantitative analysis of crystallographic defects present in 2D colloidal sphere arrays.

In this work, we present a study of the typical spontaneous defects present in self-assembled colloidal monolayers grown from polystyrene and silica microspheres. The quality of two-dimensional crystals from different colloidal suspensions of beads around 1 µm in diameter has been studied qualitatively and quantitatively, evaluated in 2D hexagonal arrays at different scales through Fourier analysis of SEM images and optical characterization. The crystallographic defects are identified to better understand their origin and their effects on the crystal quality, as well as to find the best conditions colloidal suspensions must fulfill to achieve optimal quality samples.

Self-assembled photonic structures.

Photonic crystals have proven their potential and are nowadays a familiar concept. They have been approached from many scientific and technological flanks. Among the many techniques devised to implement this technology self-assembly has always been one of great popularity surely due to its ease of access and the richness of results offered. Self-assembly is also probably the approach entailing more materials aspects owing to the fact that they lend themselves to be fabricated by a great many, very different methods on a vast variety of materials and to multiple purposes. To these well-known material systems a new sibling has been born (photonic glass) expanding the paradigm of optical materials inspired by solid state physics crystal concept. It is expected that they may become an important player in the near future not only because they complement the properties of photonic crystals but because they entice the researchers' curiosity. In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self-assembly.

Optical gain in DNA-DCM for lasing in photonic materials.

We present a detailed study of the gain length in an active medium obtained by doping of DNA strands with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye molecules. The superior thermal stability of the composite and its low quenching permit one to obtain an optical gain coefficient larger than 300 cm(-1). We also demonstrate that such an active material is feasible for the infiltration into photonic nanostructures, allowing one to obtain fluorescent photonic crystals and promising lasing properties.

Synthesis and evaluation of superparamagnetic silica particles for extraction of glycopeptides in the microtiter plate format.

Solid-phase extraction of glycopeptides (SPEG) coupled with quantitative proteomic analysis using mass spectrometry has shown great potential for investigating glycoproteins in an effort to discover new diagnostic biomarkers or therapeutic targets. As a solid-phase approach, SPEG can be performed with a microtiter plate to provide a high-throughput platform for large-scale screening of clinical samples. Here we describe the synthesis of superparamagnetic silica particles with hydrazide groups on the surface and further evaluate their use as the solid support for SPEG. We produced nonspherical silica particles containing superparamagnetic iron oxide cores using a modified Stöber method and then derivatized their surface with hydrazide-terminated silane. Such composite particles displayed a strong response to the external magnetic field, and this feature enabled us to capture and release the particles easily for automated, high-throughput sample preparation of glycopeptides. When measured with standard glycoproteins, the adsorption capacity of these particles was >36 mg of glycoproteins per g of nanoparticles. The nanoparticles were used in a microtiter plate format for glycopeptide capture using a liquid handler. The captured glycopeptides were then analyzed by LC-MS and LC-MS/MS to determine the specificity and reproducibility of glycopeptide isolation. Our results demonstrate the potential of these superparamagnetic colloidal particles for high-throughput analysis of glycoproteins.