Synergism between particle-based multiplexing and microfluidics technologies may bring diagnostics closer to the patient

In the field of medical diagnostics there is a growing need for inexpensive, accurate, and quick high-throughput assays. On the one hand, recent progress in microfluidics technologies is expected to strongly support the development of miniaturized analytical devices, which will speed up (bio)analytical assays. On the other hand, a higher throughput can be obtained by the simultaneous screening of one sample for multiple targets (multiplexing) by means of encoded particle-based assays. Multiplexing at the macro level is now common in research labs and is expected to become part of clinical diagnostics. This review aims to debate on the “added value” we can expect from (bio)analysis with particles in microfluidic devices. Technologies to (a) decode, (b) analyze, and (c) manipulate the particles are described. Special emphasis is placed on the challenges of integrating currently existing detection platforms for encoded microparticles into microdevices and on promising microtechnologies that could be used to down-scale the detection units in order to obtain compact miniaturized particle-based multiplexing platforms. S. Derveaux and B. G. Stubbe contributed equally to this work.     

Study of the adsorption of organic molecules on transition metal exchanged zeolites via solid state NMR. Part 2: adsorption of organic molecules on zeolite NaX, CaX, and CaCoX

Literature [Denayer et al. Microporous Mesoporous Mater. 2007, 103, 1 and Denayer et al. Microporous Mesoporous Mater. 2007, 103, 11] shows that zeolite NaX exchanged with Ca(2+) and Co(2+) ions is able to remove cyclopentadiene (CPD) impurities from a 1-octene feed with high selectivity. In the present work, the adsorption of dicyclopentadiene (DCPD), CPD, 1-octene, and n-octane on zeolite X, exchanged with Ca(2+) and/or Co(2+) ions, has been investigated via (1)H magic-angle spinning (MAS) NMR spectroscopy. The liquid adsorbate was dosed under inert atmosphere in an MAS rotor filled with dry adsorbent, at a pore filling degree of 70%. Next, the evolution in time was recorded of the (1)H MAS NMR spectrum and the (1)H spin-lattice and spin-spin relaxation times of the adsorbed components. For the various adsorbate-adsorbent systems, a plot is made of the signal intensity versus the square root of the contact time. It is found that, over the considered time interval, Fickian diffusion takes place. On the basis of the change in time of the spin-lattice relaxation time, a transport diffusion coefficient ranging between 1 and 2 x 10(-15) m(2) x s(-1) is calculated. Moreover, there appear to be two sorption regimes, with different diffusivities. A comparison is made between the (1)H spin-lattice relaxation behavior of DCPD, 1-octene, and n-octane, indicating that 1-octene and n-octane are located closer to the paramagnetic ions than DCPD. The average distance between the adsorbate molecules and the paramagnetic ions is derived from relaxometric data. By analyzing the chemical shifts of the resonance lines, it is found that the pi-interaction of CPD and 1-octene is stronger than that of DCPD.     

Study of the adsorption of organic molecules on transition metal exchanged zeolites via solid state NMR. Part 1: theoretical aspects

A theoretical study is performed of the (1)H relaxation behavior of an organic molecule that is adsorbed in a zeolite exchanged with transition metal ions. An expression is derived for the spin-lattice and spin-spin relaxation rate constant of a uniform proton ensemble, while the occurrence of molecular exchange is taken into account. The influence is analyzed of an approach of a uniform proton ensemble toward the nearest neighboring paramagnetic ion system. It is shown that there exists a signal extinction effect, for which the critical distance was estimated.     

Release mechanisms for polyelectrolyte capsules

Polyelectrolyte capsules have recently been introduced as new microscopic vehicles which could have high potential in the biomedical field. In this critical review we give an introduction to the layer-by-layer (LbL) technique which is used to fabricate these polyelectrolyte capsules as well as to the different triggers that have been exploited to obtain drug release from these capsules. Furthermore, other types of triggered delivery systems are compared and critically discussed with regard to their clinical relevance. (171 references.).     

Time-dependent density functional theory/discrete reaction field spectra of open shell systems: The visual spectrum of [FeIII(PyPepS)2]- in aqueous solution

We report the calculated visible spectrum of [FeIII(PyPepS)2]- in aqueous solution. From all-classical molecular dynamics simulations on the solute and 200 water molecules with a polarizable force field, 25 solute/solvent configurations were chosen at random from a 50 ps production run and subjected the systems to calculations using time-dependent density functional theory (TD-DFT) for the solute, combined with a solvation model in which the water molecules carry charges and polarizabilities. In each calculation the first 60 excited states were collected in order to span the experimental spectrum. Since the solute has a doublet ground state several excitations to states are of type "three electrons in three orbitals," each of which gives rise to a manifold of a quartet and two doublet states which cannot properly be represented by single Slater determinants. We applied a tentative scheme to analyze this type of spin contamination in terms of Delta and Delta transitions between the same orbital pairs. Assuming the associated states as pure single determinants obtained from restricted calculations, we construct conformation state functions (CFSs), i.e., eigenfunctions of the Hamiltonian Sz and S2, for the two doublets and the quartet for each Delta,Delta pair, the necessary parameters coming from regular and spin-flip calculations. It appears that the lower final states remain where they were originally calculated, while the higher states move up by some tenths of an eV. In this case filtering out these higher states gives a spectrum that compares very well with experiment, but nevertheless we suggest investigating a possible (re)formulation of TD-DFT in terms of CFSs rather than determinants.