Gene expression analysis using single molecule detection

Recent developments of single molecule detection techniques and in particular the introduction of fluorescence correlation spectroscopy (FCS) led to a number of important applications in biological research. We present a unique approach for the gene expression analysis using dual‐color cross‐correlation. The expression assay is based on gene‐specific hybridization of two dye‐labeled DNA probes to a selected target gene. The counting of the dual‐labeled molecules within the solution allows the quantification of the expressed gene copies in absolute numbers. As detection and analysis by FCS can be performed at the level of single molecules, there is no need for any type of amplification. We describe the gene expression assay and present data demonstrating the capacity of this novel technology. In order to prove the gene specificity, we performed experiments with gene‐depleted total cDNA. The biological application was demonstrated by quantifying selected high, medium and low abundant genes in cDNA prepared from HL‐60 cell

Enhanced generation of VUV radiation by four-wave mixing in mercury using pulsed laser vaporization

The efficiency of a coherent VUV source at 125 nm, based on 2-photon resonant four-wave mixing in mercury vapor, has been enhanced by up to 2 orders of magnitude. This enhancement was obtained by locally heating a liquid Hg surface with a pulsed excimer laser, resulting in a high density vapor plume in which the nonlinear interaction occurred. Energies up to 5 μJ (1 kW peak power) have been achieved while keeping the overall Hg cell at room temperature, avoiding the use of a complex heat pipe. We have observed a strong saturation of the VUV yield when peak power densities of the fundamental beams exceed the GW/cm2 range, as well as a large intensity-dependant broadening (up to ~30 cm-1) of the two-photon resonance. The source has potential applications for high resolution interference lithography and photochemistry

Untersuchungen zu Biokompatibilität, Resorptionsverhalten und Knochenheilung nach Implantation poröser Knochenersatzmaterialien auf Basis von β-Tricalziumphosphat und DCP

In dieser Studie wurden acht verschiedene Knochenersatzmaterialien aus β-Tricalziumphosphat und Monetit in einem Bohrlochmodell in die langen Röhrenknochen von Schafen implantiert. Für die Implantation lagen die Materialien als zylinderförmige poröse Blöcke oder als Granulat vor. Zusätzlich unterschieden sich die einzelnen Implantate bezüglich ihrer Mikroporosität, Korngröße und chemischen Zusammensetzung. Nach Ablauf der Beobachtungszeiträume von zwei, vier und acht Wochen wurden die Implantate, in dem sie umgebenden Knochengewebe, zurückgewonnen und auf ihre Biokompatibilität, Resorbierbarkeit und die induzierte Rate der Knochenneubildung untersucht. Die Auswertung erfolgte histologisch sowie histomorphometrisch. Alle Implantate waren biokompatibel, resorbierbar und führten zu guten Knochenneubildungsraten. Die β-TCP Implantate waren nach acht Wochen nahezu vollständig resorbiert und die Defekte waren teilweise bereits mit neuem Knochengewebe ausgefüllt. Es konnte gezeigt werden, dass eine Erhöhung der Mikroporosität tendenziell die Implantatresorption beschleunigt und, dass auch die Korngröße die Resorptionsrate von Calziumorthophosphatkeramiken in vivo beeinflusst. Löslichkeitsunterschiede zwischen verschiedenen Werkstoffen konnten durch Variation der Makroporosität ausgeglichen werden. Summary Eight types of bone graft substitutes composed of β-Tricalciumphosphate and Monetite were implanted into drill hole defects in cancellous bone of sheep either as porous blocks or as β-TCP granules. The implants differed mainly in their form of application, microporosity, grain size and chemical composition. Biocompatibility, resorbability and bone formation of the samples were assessed after two, four and eight weeks. Histology and histomorphometry were chosen for sample analysis. All of the eight bioceramics were biocompatible, resorbable and generally induced adequate bone formation in the defects. After an eight week period, resorption of the implants was nearly complete and, depending on the implanted material, the drillholes were filled with new bone structures to different extends. Differences in resorption rates between particulary fast resorbable ceramics were bufferd in vivo and were therefore less evident then expected. An increase in microporosity accelerated implant resorption by trend, whereas the impact of grain size on the resorption rate was hardly detectable. Differences in the solubility behaviour between the raw materials were compensated by a variation of macroporosity