Ultrasensitive PCR and real-time detection from human genomic samples using a bidirectional flow microreactor

In this paper we present a reliable bidirectional flow DNA amplification microreactor for processing real-world genomic samples. This system shares the low-power thermal responsiveness of a continuous flow reactor with the low surface area to volume ratio character of stationary reactors for reducing surface inhibitory effects. Silanization with dimethyldichlorosilane in combination with dynamic surface passivation was used to enhance PCR compatibility and enable efficient amplification. For real-time fragment amplification monitoring we have implemented an epimodal fluorescent detection capability. The passivated bidirectional flow system was ultrasensitive, achieving an RNase P gene detection limit of 24 human genome copies with a reaction efficiency of 77%. This starts to rival the performance of a conventional real-time PCR instrument with a reaction efficiency of 93% and revitalizes flow-through PCR as a viable component of lab on a chip DNA analysis formats.     

Investigation of the polarization-dependent diffraction of deep dielectric rectangular transmission gratings illuminated in Littrow mounting

Dielectric transmission gratings with a similar period as the wavelength of the incident light can exhibit strong polarization dependence. By optimizing the groove width of a negative first-order Littrow transmission grating it can be achieved that light is transmitted to the zeroth order for one polarization, regardless of the groove depth, while it is efficiently diffracted for the other polarization. An investigation of this remarkable effect, based on a modal field representation inside the grating, as well as experimental results are presented.     

Tunable diffraction-limited light at 488 nm by single-pass frequency doubling of a broad area diode laser

A laser system that is based on second-harmonic generation of a broad area laser diode and provides 23.2 mW of diffraction-limited light with narrow bandwidth is described. It is tunable from 487.4 to 489 nm. The broad area laser diode is frequency stabilized in an external cavity that yields 800 mW of diffraction-limited light. This infrared light is converted into the visible by use of a 1 cm periodically poled MgO:LiNbO(3) bulk crystal with a measured single-pass conversion efficiency of up to 3.6%/W x cm.     

SAR distribution in human beings when using body-worn RF transmitters

This study analyzes the exposure of the human torso to electromagnetic fields caused by wireless body-mounted or handheld devices. Because of the frequency and distance ranges from 30-5800 MHz and 10 to 200 mm, respectively, both near-field and far-field effects are considered. A generic body model and simulations of anatomical models are used to evaluate the worst case tissue composition with respect to the absorption of electromagnetic energy. Both standing wave effects and enhanced coupling of reactive near-field components can lead to a specific absorption rate (SAR) increase in comparison to homogeneous tissue. In addition, the exposure and temperature increase of different inner organs is assessed. With respect to compliance testing, the observed SAR enhancement may require the introduction of a multiplication factor for the spatial peak SAR measured in the liquid-filled phantom in order to obtain a conservative exposure assessment. The observed tissue heating at the body surface under adiabatic conditions can be significant, whereas the temperature increase in the inner organs turned out to be negligible for the cases investigated.     

Evaluation of in vitro enzymatic degradation of various thiomers and cross-linked thiomers

The aim of this study was to examine the biodegradability of thiomers and cross-linked thiomers in comparison with unmodified polymers. Disulfide-cross-linked conjugates were prepared by air oxidation at room temperature. Thiomers were investigated by viscosity measurements and spectrophotometric assays. The influence of different factors on the hydrolysis rate, such as the degree of modification of thiomers, structure of the conjugates, pH value of the reaction medium, and the impact of the process of cross-linking were evaluated. Due to the modification, thiolated chitosans degraded 12.9-24.7% less than unmodified chitosan in the framework of viscosity measurements. In addition, the hydrolysis degree of thiolated alginates and modified carboxymethylcelluloses was 25.6-32.4% and 18.4-27.0% lower, respectively, in comparison to the corresponding unmodified polymers. Conjugates with higher coupling rate of thiol groups were degraded even more slowly. Moreover, the cross-linking process via disulfide bonds additionally reduced the rate of thiomer degradation. The range of degradation rates achieved in vitro could be modified by alterations of the contents of thiol and disulfide groups, as well as by suitable design of the polymer structure and ligands used.

These results represent helpful basic information for the development of mucoadhesive drug delivery systems, implantable delivery systems and tissue engineering constructs.     

Design and evaluation of a new gastrointestinal mucoadhesive patch system containing chitosan-glutathione

Within this study, a novel gastrointestinal patch system was developed and investigated regarding water-absorbing capacity, adhesive properties, in vitro release, unidirectional release and permeation enhancing effect. Water uptake studies revealed that the weight of patch systems with Ch-GSH increased about 44.5 ± 2.3 mg (127%) after 90 min. This patch system remained even after 180 h on the mucosa and released 49.7 ± 0.7% of FD₄ within 8 h. A 2.5-fold higher transport of FD₄ can be obtained in contrast to control. In conclusion this patch system could be an interesting possibility for the transport through the intestinal mucosa of macromolecules which will normally be degraded in the intestinal tract.     

Development and in vitro evaluation of surface modified poly(lactide-co-glycolide) nanoparticles with chitosan-4-thiobutylamidine

The objective of this study was to develop a nanoparticulate drug delivery system based on the surface modification of poly(lactide-co-glycolide) (PLGA) nanoparticles with a thiolated chitosan. PLGA nanoparticles were prepared by the emulsification-solvent evaporation method. Immobilization of chitosan to the surface of PLGA nanoparticles via amide bonds was mediated by a carbodiimide. Thiol groups were covalently bound to the chitosan surface of particles by reaction with 2-iminothiolane. Obtained nanoparticles were characterized in vitro regarding size, zeta potential, thiol group content, stability at different pH values, mucoadhesion, and drug release. Results demonstrated that the surface modification of PLGA nanoparticles with thiolated chitosan (chitosan-TBA) leads to nanoparticles of a mean diameter of 889.5 ± 72 nm and positive zeta potential of + 24.74 mV. The modified nanoparticles contained 7.32 ± 0.24 μmol thiol groups per gram nanoparticles. The size of nanoparticles was strongly influenced by the pH of the surrounding medium, being 925.0 ± 76.3 nm at pH 2 and 577.8 ± 66.7 nm at pH 7.4. Thiolated nanoparticles showed a 3.3-fold prolonged residence time on the mucosa and an unchanged release profile in comparison to unmodified PLGA nanoparticles. These data suggest that surface modified chitosan-TBA conjugate PLGA nanoparticles have the potential to be used as mucoadhesive drug delivery system.     

Assessment of anisotropic tissue elasticity of cortical bone from high-resolution, angular acoustic measurements

Assessment of anisotropic elastic properties at the tissue level is still one of the major challenges in bone research. In previous studies, bone sections were cut in different directions relative to a principle axis of symmetry. This causes a high preparation and measurement effort. We have developed a new acoustic scanning procedure that allows one to measure the angular dependence of the acoustic impedance of cylindrically shaped samples (diameter: 4.4 mm) with a single measurement. Our scanning acoustic microscope was equipped with a rotational stage, and a scanning procedure was developed that measures the surface reflection of the rotating cylinder. It was shown in a previous study that the acoustic impedance derived from the reflection coefficient is highly correlated with the elastic coefficient in the probing direction. From the angular reflection, the independent elastic coefficients were derived using assumptions of transverse isotropy and continuum micromechanical model constraints. This method was applied to the inspection of human femoral bone samples. Four cylinders were prepared from the anterior, posterior, medial, and lateral regions. The measurements were performed with a 50 MHz transducer, providing a lateral resolution of 23 microm. Remarkable structural and elastic variations were observed between the four samples. The means and standard deviations of the derived elastic coefficients were: c33 = 29.9 +/- 5.0 GPa, c11 = 21.9 +/- 2.1 GPa, c12 = 9.2 +/- 1.5 GPa, c13 = 9.7 +/- 1.6 GPa, and c44 = 6.7 +/- 1.2 GPa. The results demonstrate that microstructural and anisotropic elastic tissue parameters can be assessed by ultrasound in very small bone samples.