Conception of a new technique in cell cultivation using a lab-on-chip aided miniaturised device with calibratable electrochemical sensors

Continuous electrochemical sensing is often carried out in order to track the growth of cells as an alternative to optical monitoring. Planar sensors and multi-sensor chips are applied in case of adhered growing cells, and usually introduced into lab-on-chip systems. Repeated recalibration is necessary with most chemosensors so far and this limits the operational lifetime of such lab-on-chip systems to a few days. An assembly is presented here that eliminates this disadvantage and enables the monitoring of a long-term cultivation of tissue. Cell cultures and sensor are arranged such that they can be separated or contacted at variable times without having an impact on the growth of the cells. The use of a biocompatible nano-porous membrane is especially important. A multi-well system is described where each well is supplied with a planar multi-sensor chip below the adhered cells to determine (a) pH, (b) glucose, (c) oxygen, and—optionally—impedance, for example during the cultivation of cartilage tissue.     

Photoluminescence spectroscopy of pure pentacene, perfluoropentacene, and mixed thin films

We report detailed temperature dependent photoluminescence (PL) spectra of pentacene (PEN), perfluoropentacene (PFP), and PEN:PFP mixed thin films grown on SiO(2). PEN and PFP are particularly suitable for this study, since they are structurally compatible for good intermixing and form a model donor/acceptor system. The PL spectra of PEN are discussed in the context of existing literature and compared to the new findings for PFP. We analyze the optical transitions observed in the spectra of PEN and PFP using time-dependent density functional theory calculations. Importantly, for the mixed PEN:PFP film we observe an optical transition in PL at 1.4 eV providing evidence for coupling effects in the blend. We discuss a possible charge-transfer (CT) and provide a tentative scheme of the optical transitions in the blended films.     

Facile synthesis of potassium tetrathiooxalate – The “true” monomer for the preparation of electron-conductive poly(nickel-ethylenetetrathiolate)

Herein, aiming at optimization of the polymerization process leading to a family of hole- and electron-conducting 1,1,2,2-ethenetetrathiolate-based polymers, such as poly(nickel-1,1,2,2-ethenetetrathiolate), poly[K_x(Ni-ett)], we investigated transformations of the monomer precursor 1,3,4,6-tetrathiapentalene-2,5-dione (TPD) occurring under polymerization conditions. We found that only one ring of TPD opens upon its reaction with potassium methoxide under inert conditions at room temperature which leads to the formation of potassium 2-oxo-1,3-dithiol-4,5-dithiolate (K₂[3]). Heating of K₂[3] under reflux in methanol solution under inert conditions opens the second ring, however the resulting product is not potassium ethenetetrathiolate (K₄[2]), the product of an exhaustive methanolysis of TPD, but potassium tetrathiooxalate (K₂[4]), the product of the decarbonylation of K₂[3]. Preliminary experiments reveal that the involvement of K₂[4] in the polymerization process is beneficial for reproducible formation of high quality 1,1,2,2-ethenetetrathiolate-based polymers suitable for thermoelectric applications.     

Preparation of relativistic 7Li+ ion beams for precision experiments at storage rings

Heavy ion storage rings allow for tests of the structure of local space time via the Doppler effect. At the TSR/Heidelberg an experiment with high resolution laser spectroscopy at ⁷Li⁺ is performed. To gain the maximum resolution for saturation spectroscopy new methods of relativistic ion beam preparation and diagnostics have been developed. The laser cooling of the beam allows for precision determination of the mean velocity of the ions. A novel phase synchronous detection scheme, ultimately sensitive to single ions, gives insights into the cooling mechanism and dynamics. With an additional synchronous excitation scheme systematic uncertainties of the test experiment can be drastically reduced. After separation of the ground state ions from the triplet states of ⁷Li⁺ by the combination of laser and electron cooling, a bunched and cooled ensemble of fast moving high precision clocks with minimized perturbations by space charge effects and intra beam scattering is available. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the lattice structure of kernel operators

Consider the lattice of bounded linear operators on the space of Borel measures on a Polish space. We prove that the operators which are continuous with respect to the weak topology induced by the bounded measurable functions form a sublattice that is lattice isomorphic to the space of transition kernels. As an application we present a purely analytic proof of Doob's theorem concerning stability of transition semigroups.