Morphology-Controlled Coating of Colloidal Particles with Silica: Influence of Particle Surface Functionalization.

We present a general, convenient, and efficient synthetic concept for the coating of colloidal particles with a silica (SiO2) shell of well-defined and precisely controlled morphology and porosity. Monodisperse submicroscopic polystyrene (PS) particles were synthesized via two-stage emulsifier-free emulsion polymerization and subsequent swelling polymerization, enabling selective particle surface modification by the incorporation of ionic (methacrylic acid, MAA) or nonionic (hydroxyethyl methacrylate, HEMA or methacrylamide, MAAm) comonomers, which could be proven by zeta potential measurements as well as by determining the three-phase contact angle of the colloidal particles adsorbed at the air-water and n-decane-water interface. The functionalized particles could be directly coated with silica shells of variable thickness, porosity, and controlled surface roughness in a seeded sol-gel process from tetraethoxysilane (TEOS), leading to hybrid PS@silica particles with morphologies ranging from core-shell (CS) to raspberry-type architectures. The experimental results demonstrated that the silica coating could be precisely tailored by the type of surface functionalization, which strongly influences the surface properties of the colloidal particles and thus the morphology of the final silica shell. Furthermore, the PS cores could be easily removed by thermal treatment, yielding extremely uniform hollow silica particles, while maintaining their initial shell architecture. These particles are highly stable against irreversible aggregation and could be readily dried, purified, and redispersed in various solvents. Herein we show a first example of coating semiconducting CdSe/ZnS nanocrystals with smooth and spherical silica shells by applying the presented method that are expected to be suitable systems for applications as markers in biology and life science by using fluorescence microscopy methods, which are also briefly discussed.

Large-scale ordering of nanoparticles using viscoelastic shear processing.

Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.

Free-space optical communications research and demonstrations at the U.S. Naval Research Laboratory.

Free-space optical communication can allow high-bandwidth data links that are hard to detect, intercept, or jam. This makes them attractive for many applications. However, these links also require very accurate pointing, and their availability is affected by weather. These challenges have limited the deployment of free-space optical systems. The U.S. Naval Research Laboratory has, for the last 15 years, engaged in research into atmospheric propagation and photonic components with a goal of characterizing and overcoming these limitations. In addition several demonstrations of free-space optical links in real-world Navy applications have been conducted. This paper reviews this work and the principles guiding it.

Reduction of scintillation in optical modulating retro-reflector links.

Optical modulating retro-reflectors enable free-space optical links that have greatly reduced pointing requirements and do not require a laser at one end of the link. However, these types of links can exhibit very high optical scintillation due to the double passage of the beam through the atmosphere. This high scintillation causes fades and surges that can lead to packet errors in the link. It is shown that scintillation can be greatly reduced through a combination of techniques including retro-reflector diversity, aperture averaging and bistatic optical interrogation. Improvements of 20 dB in link performance are demonstrated.

Thermo-cross-linked elastomeric opal films.

An efficient and convenient thermal cross-linking protocol in elastomeric opal films leading to fully reversible and stretch-tunable optical materials is reported. In this study, functional monodisperse core-shell particles were arranged in a face-centered cubic (fcc) lattice structure by a melt flow process. A problem up to now was that un-cross-linked films could not be drawn fully reversibly and hence lost their optical and mechanical performance. After thermal cross-linking reaction, the obtained films can be drawn like rubbers and the color of their Bragg reflection changes because of controlled lattice deformation, which makes the cross-linked films mechanochromic sensors. Different techniques were developed for the cross-linking of the films a posteriori, after their preparation in the melt flow process. A photo-cross-linking approach was reported earlier. This study now deals with a very efficient thermo-cross-linking approach based on the chemistry of hydroxyl- and isocyanate-functionalities that form urethane bridges. The focus of the present work is the mechanism and efficiency of this cross-linking process for elastomeric opal films with excellent mechanical and optical properties.

Fully reversible shape transition of soft spheres in elastomeric polymer opal films.

Core-interlayer-shell (CIS) beads featuring noncross-linked hard cores were used to prepare large and well-defined elastomeric opal films with remarkably distinct iridescent reflection colors. The matrix of the opal films was cross-linked by UV-irradiation after compression molding of the CIS beads mixed with a bifunctional monomer. Stress-induced deformation of the embedded PS cores lead to hexagonally arranged spheroid oblates with an aspect ratio of 2.5. Optical characterization shows that bead deformation provokes a tremendous photonic band gap shift of about 160 nm. Fully reversible shape transition from the spheroid oblates back to the spherical beads and hence full recovery of the original photonic band gap can be achieved.

One year failure rate for de-novo ventriculo-peritoneal shunts in children from a small volume paediatric neurosurgical unit.

It is the belief of some that results of shunt surgery for the treatment of hydrocephalus in children are improved if the surgery is performed in high-volume centres. Currently in the UK paediatric neurosurgery is undergoing a service review. As part of this review a set of standards of care are being drafted which state that 1-year failure rates and infection rates for de-novo ventriculo-peritoneal shunts in children should be less than 40% and 10%, respectively. Our de-novo shunt infection rate (4.3%) and our 1-year failure rate (28.6%) are well within the standards set by this process and comparable to published literature from much higher volume centres.

Monitoring nanoparticles in the presence of larger particles in liquids using acoustics and electron microscopy.

Monitoring the presence of nanoparticles in dispersions having broad particle size distributions can be a problem for many measurement techniques because large particles or even aggregates of the smaller particles can mask the presence of the sought after nanoparticles. The ability of many existing techniques to detect the nanoparticles when present in broad polydisperse systems is largely unknown, yet it is critical for proper selection of the measuring technique for characterizing a particular nanodispersion. Acoustic spectroscopy is already a known and proven tool for studying nanoparticles in systems with a narrow size distribution. The purpose of this paper is to evaluate the sensitivity of acoustic spectroscopy for determining the nanoparticle content of very polydisperse systems. We used eight different ZnO powders from different manufacturers to prepare 5wt.% dispersions, each dispersed in water. The stability of each dispersion was optimized by pH adjustment and addition of sodium hexametaphosphate as determined by maximizing the measured zeta-potential. According to the acoustic measurement, the median size of these different ZnO dispersions varied from 200nm to 700nm. Independent TEM photographs in general confirmed the size variation between the samples. Independent DLS measurements failed to provide particle size data correlating with TEM. The acoustic measurements further showed that each dispersion contained a different relative content in the nanoparticle fraction. The precision with which the nanoparticle fraction could be determined was better than 2% of the total solid loading for all samples. In order to verify consistency of this measurement we performed a mixing study by adding dispersion with the largest nanoparticle content to the dispersion with the smallest nanoparticle content, in small increments. This test confirms that the acoustic sensitivity threshold is about 2% of nanoparticles in the broad polydisperse dispersions of dense metal oxide particles.

Gravity as a factor of aggregative stability and coagulation.

Gravity is a potential factor of aggregative stability and/or coagulation for any heterogeneous system having a density contrast between the dispersed phase and its dispersion medium. However, gravity becomes comparable to other stability factors only when the particle size becomes large enough. Since the particle size may grow in time due to various other instabilities, even nano-systems may eventually become susceptible to gravity. There have been many attempts in the last century to incorporate gravity in the overall theory of aggregative stability, but the relevant papers are scattered over a wide variety of journals, some of which are very obscure. Reviews on this subject in modern handbooks are scarce and inadequate. No review describes the role of gravity at all three levels introduced by DLVO theory for characterizing aggregative stability, namely: particle pair interaction, collision frequency and population balance equation. Furthermore, the modern tendency towards numerical solutions overshadows existing analytical solutions. We present a consistent review at each DLVO level. First we describe the role of gravity in particle pair interactions, including both available analytical solutions as well as numerical stability diagrams. Next we discuss a number of works on collision frequency, including works for both charged and non-charged particles. Finally, we present analytical solutions of the population balance equation that takes gravity into account and then compare these analytical solutions with numerical solutions. In addition to the traditional aggregate model we also discuss work on a fractal model and its relevance to gravity controlled stability. Finally, we discuss many experimental works and their relationship to particular theoretical predictions.

Characterization of fractal particles using acoustics, electroacoustics, light scattering, image analysis, and conductivity.

Fractals are aggregates of primary particles organized with a certain symmetry defined essentially by one parameter-a fractal dimension. We have developed a model for the interpretation of acoustic data with respect to particle structure in aggregated fractal particles. We apply this model to the characterization of various properties of a fumed silica, being but one example of a fractal structure. Importantly, our model assumes that there is no liquid flow within the aggregates (no advection). For fractal dimensions of less than 2.5, we find that the size and density of aggregates, computed from the measured acoustic attenuation spectra, are quite independent of the assumed fractal dimension. This aggregate size agrees well with light-scattering measurements. We applied this model to the interpretation of electroacoustic data as well. A combination of electroacoustic and conductivity measurements yields sufficient data for comparing the fractal model of the particle organization with a simple model of the separate primary particles. Conductivity measurements provide information on particle surface conductivity reflected in terms of the Dukhin number (Du). Supporting information for the zeta potential and Du can also be provided by electroacoustic measurements assuming thin double-layer theory. In comparing values of Du from these two measurements, we find that the model of separate solid particles provides much more consistent results than a fractal model with zero advection. To explain this, we first need to explain an apparent contradiction in the acoustic and electroacoustic data for porous particles. Although not important for interpreting acoustic data, advection within the aggregate does turn out to be essential for interpreting electrokinetic and electroacoustic phenomena in dispersions of porous particles.

Polymorphisms of dopamine-beta-hydroxylase in ADHD children.

ADHD is a multifactorial disorder clinically characterized by inattentiveness, impulsivity and hyperactivity. The occurrence of this disorder varies between 3 and 6% of the child population, with boys predominating over girls at a ratio of 3 : 1 or more. Dysfunction or imbalance between the dopaminergic and noradrenergic systems of neurotransmitters can play a key role in the ADHD pathophysiology. Alteration of the dopamine/noradrenaline levels can result in hyperactivity. DBH is an enzyme responsible for the conversion of dopamine into noradrenaline. The DBH protein is released in response to stimulation. DBH activity, derived largely from sympathetic nerves, can be measured in human plasma. Patients with ADHD showed decreased activities of DBH in serum and urine. Low DBH levels correlate indirectly with the seriousness of the hyperkinetic syndrome in children (Galvin et al., 1995, 1997). In the DBH gene, the G444A, G910T, C1603T, C1912T, C-1021T, 5'-ins/del and TaqI polymorphisms occur frequently and may affect the function of gene products or modify gene expression and thus influence the progression of ADHD. This article reviews the DBH itself and polymorphisms in the DBH gene that influence the DBH activity in the serum and the CSF level of DBH. All those are evaluated in connection with ADHD.

[History of medical genetics in the Czech Republic]. / Historie lékarské genetiky v Ceské republice.

History of the medical genetics in Bohemia since the period of Mendel is described. Effects of the abuse of genetics in Germany before and during the Second Word War as well as consequences of the liquidation of genetics in the postwar Russia on the development of genetics and the activity of geneticist in the Czech countries are documented. The paper gives information on the progress of modern Czech medical genetics, the role of the Society of Medical Genetics of the Czech Medical Association and the credit the eminent geneticist achieved in the organization and advancement of this specialization. The network of genetic laboratories and the list of available services in the Czech Republic are described in the context of model health care in contemporary Europe.

[Expression of PAX2 and PAX8 genes in conventional type of renal carcinoma and their role in the tumor prognosis]. / Exprese genu PAX2 a PAX8 v konvencním typu renálního karcinomu a jejich role v prognostice tohoto onemocnení.

BACKGROUND: Sporadic renal cell carcinoma is one of the most common kidney malignancies in adults (85%). According to the IARC (The International Agency of Research on Cancer) Czech Republic has the first world position in the incidence and mortality for RCC. The prognosis of RCC is very poor because of high mortality around 70 to 50% and unpredictable progression after tumor removal. More precise molecular prognostic markers are required. Genes PAX2 and PAX8 control cell division during embryonic development and plays crucial role in tumor development because of stimulation of cell proliferation and/or inhibition of apoptotic program. METHODS AND RESULTS: Our RCC sample collection contains 64 tumor samples and 10 "normal" renal samples extracted from the affected kidney. mRNA was isolated from all samples and converted into cDNA. Expression of PAX genes was analyzed by using relative quantification real-time PCR with TaqMan labelled probe and GAPDH gene as an endogenous control. CONCLUSIONS: Expression of PAX2 gene was found in 97% and expression of PAX8 gene was found in 89% of analyzed tumor samples. The expression of both target genes was found in all "normal" renal samples. The level of expression of both PAX genes was very variable with the range from hundred times lower to forty times higher in comparison with the expression of chosen endogenous control. There were found no correlations between the expression of target genes and clinical-histological markers. These results do not have prognostic value yet because of short duration of patient observation. Follow-up clinical data are essential for completion of this research.

Absence of spinocerebellar ataxia type 3/Machado-Joseph disease within ataxic patients in the Czech population.

Although spinocerebellar ataxia type 3 (SCA3)/Machado-Joseph disease is the most common type of SCA worldwide, we did not identify any cases of the disease amongst SCA patients in the Czech population. It has been proposed that the prevalence of large normal alleles correlates with the frequency of various types of SCA. We have therefore attempted to resolve the absence of SCA3 in our population by investigating, within 204 normal chromosomes, the frequency and nature of CAG repeats as well as two intragenic polymorphisms. We found that large normal alleles with more than 33 CAG repeats were observed at a frequency of only 0.49%. Whereas most of the expanded alleles worldwide have the CA haplotype, this was the least common (5.4%) variant observed in our study, although it was associated with a larger mean CAG repeat length (26.9). We postulate that the absence of SCA3 in the Czech population might be explained by the lack of large normal alleles and consequently a relatively small reservoir for aberrant CAG expansions at the SCA3 locus.

Electrokinetics at high ionic strength and hypothesis of the double layer with zero surface charge.

A growing number of publications in the last two decades have suggested that the structure and other properties of the interfacial water layer can significantly affect the double layer (DL) because of changes in ion solvatation energy. Most interesting is the possibility that a double layer might in fact exist, even when there is no electric surface charge at all, solely because of the difference in cation and anion concentrations within this interfacial water layer. Dukhin, Derjaguin, and Yaroschuk suggested this possibility 20 years ago and developed a phenomenological theory. Recently, Mancui and Ruckenstein created more sophisticated microscopic model. In this article, we present our first experimental result regarding the verification of this "zero surface charge" DL model. The electroacoustic technique allows testing at high ionic strength (up to 2 M). As a first step, we confirm the surprising result of Johnson, Scales, and Healy regarding large zeta potential of alumina (8 +/- 1 mV) in 1 M KCl. As a second step, we suggest using nonionic surfactant Tween 80 for probing and modifying the structure of the interfacial layer at high ionic strength. The application of surfactant at moderate ionic strength (i.e., <0.1 mol/dm3), as might be expected, reduces the zeta potential simply by shifting the slipping plane. However, there is no influence of surfactant on the zeta potential observed at high ionic strength. It turns out that a high concentration of KCl simply eliminates surfactant adsorption. We develop a new technique for characterizing the adsorption of nonionic surfactant using an acoustic attenuation measurement. We hope that these methods in combination with a proper surfactant and electrolyte selection would allow us to gain more detailed information on the interface structure at high ionic strength.

Fluorescent multiplex PCR--fast method for autosomal dominant spinocerebellar ataxias screening.

Expansion of CAG trinucleotide repeats has been shown to cause a number of autosomal dominant spinocerebellar ataxias such as SCA1, SCA2, SCA3/MJD, SCA6 and SCA7. These disorders are characterized by a wide inter- and intrafamiliar variation in clinical features. The same mutation can result in different phenotypes and the very similar phenotypes can be caused by different mutations. Therefore it is necessary to investigate more SCA genes (according to prevalence) to identify the causal elongation. We developed a fast and efficient screening method based on touchdown multiplex PCR with fluorescent labelled primers for the most common types of SCAs (SCA 1, 2, 3 and 7). It has been reliable in 113 probands tested. Fragment analysis was performed by using 6% denaturing polyacrylamide gel and employing the automated DNA sequencer. This method considerably shortens the process of molecular genetic screening of SCAs and might be used as a tip for designing other SCA screening sets.

Use of ultrasound for characterizing dairy products.

It has been known for a long time that acoustic measurements offer some unique features for characterizing liquid food products in their intact state, without any preparation or destruction of the product sample. Acoustic characterization can yield information about fat content, droplet size distribution, and kinetics of product variation with time. Furthermore, acoustic methods are very attractive for on-line process control. This paper addresses several questions: Why does ultrasound attenuate when propagating through a heterogeneous system? What properties of dairy products can be extracted from such ultrasound measurements? Which measurement is better for product characterization: attenuation or sound speed? What measurement precision is required to adequately characterize product properties? What frequency range is of most value for determining these product properties?It is possible to provide answers to many of these questions using experimental data, thereby avoiding, for the moment, any complex mathematical analysis. We present several applications of acoustic spectroscopy for characterizing dairy products, including characterization of the fat content in a wide variety of dairy products; calculation of the fat droplet size distribution in milk without dilution; and calculation of water droplet size in butter, without dilution or melting.

[Case reports of patients with a marker chromosome]. / Kazuistiky pacientu s marker chromozómy.

Small, usually supernumerary chromosomes, denoted as marker chromosomes or markers, can be represented by various phenotypic expression, that depends on their origin and extent. Our article presents results of molecular cytogenetic analysis (FISH) of 34 patients with identified marker chromosome. In 21 cases a marker derived from acrocentric chromosome was identified, in 9 cases markers of gonosomal origin [der(X), der(Y)], and in 4 patients markers of some other chromosomes (5, 17, 18) were proved. The most frequent marker was that originating from chromosome 15 (8 cases). Two patients with different phenotype, markedly influenced by the extent of pseudoizodicentric chromosome 15 are described. In accordance with hitherto presented data, presence of supernumerary copies of the critical region PWACR (it is the partial trisomy, resp. tetrasomy 15q11-q13) in majority of cases brings about serious affection described as syndrome of the inverted duplication of chromosome 15. The most typical symptoms are psychomotoric retardation, hypotony, neurological symptoms and autistic features. The article stresses the importance of FISH method in the prenatal examination of marker chromosomes.