Silica colloidal crystal

We have shown a new concept for selective chemical sensing based on composite core/shell polymer/silica colloidal crystal films. The vapor response selectivity is provided via the multivariate spectral analysis of the fundamental diffraction peak from the colloidal crystal film. Of course, as with any other analytical device, care should be taken not to irreversibly poison this sensor. For example, a prolonged exposure to high concentrations of nonpolar vapors will likely to irreversibly destroy the composite colloidal crystal film. Nevertheless, sensor materials based on the colloidal crystal films promise to have an improved long-term stability over the sensor materials based on organic colorimetric reagents incorporated into polymer films due to the elimination of photobleaching effects. In the experiments... 

In addition to recent advances in block co-polymer templating of periodic mesoporous silica and silica colloidal crystal templating of periodic mesopo-rous polymers [79], SAMs have been used for polymer patterning [80]. Mixtures of two strongly incompatible polymers, a polystyrene (PS)-polyvinylpyridine (PVP) blend, were found to phase separate when placed on a... 

The purpose of this chapter is to provide an overview of ceramic materials used for photonic crystals, their synthesis, and macroscopic structures and architectures. Particularly close attention is given to the fabrication of silica colloidal crystals, since these forms are the most commonly studied. Initial efforts into devices are discussed, as are newer ceramic photonic crystal structures, including an overview of work in photonic crystal optical fibers. For completeness, nonoxide and organic photonic crystals also are included briefly. 

Kuai, S., Zhang, Y., Truong, V. et al.. Improvement of optical properties of silica colloidal crystals by sintering, Appl. Phys. A, 74, 89, 2002. 

Zheng, S., Ross, E., Legg, M. A., and Wirth, M. J. High-speed electroseparations inside silica colloidal crystals. J. Am. Chem. Soc. 128, 9016, 2006. 

Wirth et al. [22] prepared a silica colloidal crystal-packed fused-silica capillary column, and 2 cm-long of which was mounted onto a PDMS chip for evaluation of efficiency of capillary electrochromatography. Three fluorophore-labeled proteins, ribonuclease A, cytochrome C, and lysozyme, were well separated over a distance of 1 cm by isocratic electromigration, using acetonitrile/water (40/60) with 0.1 % formic acid. The plate height for lysozyme was... 

Wei BC, Malkin DS, Wirth MJ (2010) Plate heights below 50 nm for protein electrochromatography using silica colloidal crystals. Anal Chem 82 10216-10221... 

By carbonization of a thin layer of phenolic resin on the suitable templates, Gierszal et al. [108] reported the synthesis of one kind of uniform carbon film with large pore volumes (6 cm g for 24 mn silica colloids), uniform pore sizes, and controlled thickness. This synthetic route involves the formation of a uniform polymeric film on the silica pore walls of silica colloidal crystals or colloidal aggregates and its carbonization and tanplate removal. After proper pre-treatment of the sihca... 

Silica colloid crystals Polymer encapsulation Ordered polymeric structure... 

Silica colloidal crystals comprise a close-packed face-centered cubic (fee) lattice of silica spheres of a sub-micrometer diameter (Fig. 8.1) with ordered arrays of nanoscale interconnected voids that constitute three-dimensional nanopores [15],... 

FIGURE 8.1 SEM images of the cross sections of the silica colloidal crystal films produced using (a) and (c) 635 nm, (b) 850 nm, and (d) 1.0 xm spheres. Reproduced with permission from Reference 15. Copyright 2003 American Chemical Society. 

All of the above features make silica colloidal crystals ideal candidates for highly selective responsive nanoporous membranes. However, until 2005, there were no publications describing transport through surface-modified colloidal membranes. In 2005, Zharov group introduced, for the first time, the concept of permselective colloidal nanoporous membranes by describing pH-responsive amine-modified colloidal membranes with controlled transport of positively charged species [26]. Later, they reported a detailed study of transport through amine-modified colloidal membranes [27], as well as membranes modified with sulfonic acids [28,29], Methods to modify the colloidal nanopores with polymers were developed [30], which allowed us to introduce temperature-responsive poly(A-isopropylacrylamide) (PNIPAAM) [31], pH- and ion-responsive poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA [32], and pH- and temperature-responsive poly(L-alanine) [33], and to study the molecular transport in these polymer-modified nanoporous coUoidal membranes as a function of the environmental conditions. In this chapter we summarize these results. 

SILICA COLLOIDAL CRYSTAL SURFACE MODIFIED WITH CHARGEABLE ORGANIC MOLECULES... 

Silica colloidal crystals with reversible permselectivity controlled by the presence of a small molecule can be prepared by surface modification of the nanopores with a responsive DNA aptamer [69]. Aptamer oligonucleotides exhibiting selective and specific binding properties toward molecules [70] have been developed for uses in medicine, analytical chemistry, and materials science [71,72], These aptamers may provide the ability to control the molecular transport through a nanoporous colloidal film by utilizing conformational changes in a biopolymer in response to small molecule binding. 

The aptamer described above was attached to the surface of the silica colloidal crystal comprising 290 nm silica spheres (resulting in 22.5 nm radius nanopores) via maleimide-activated support. The transport rate of a redox-active probe molecule (ferrocene dimethanol) through the resulting nanoporous films was measured as a function of cocaine concentration using cyclic voltammetry. A neutral redox probe, Fc(CH20H)2, was used to exclude the possibility that the observed changes in the molecular transport would result from electrostatic effects [26,27]. 

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