In this work, a microfluidic free-flow electrophoresis device with a novel approach for preventing gas bubbles from entering the separation area is presented. This is achieved by integrating partitioning bars to reduce the channel depth between electrode channels and separation chamber in order to obtain electrical contact and simultaneously prevent bubbles from entering the separation area. The three-layer sandwich chip features a reusable carrier plate with integrated ports for fluidic connection combined with a softlithographically cast microfluidic PDMS layer and a sealing glass slide. This design allows for a straightforward and rapid chip prototyping process. The performance of the device is demonstrated by free-flow zone electrophoretic separations of fluorescent dye mixtures as well as by the separation of labeled amines and amino acids with separation voltages up to 297 V.
In this study we present a device based on surface-enhanced Raman scattering (SERS) for the detection of airborne explosives. The explosives are resublimated on a cooled nanostructured gold substrate. The explosives trinitrotoluene (TNT) and triacetone triperoxide (TATP) are used. The SERS spectrum of the explosives is analyzed. Thus, TNT is deposited from an acetonitrile solution on the gold substrate. In the case of TATP, first the bulk TATP Raman spectrum was recorded and compared with the SERS spectrum, generated by deposition out of the gas phase. The frequencies of the SERS spectrum are hardly shifted compared to the spectrum of bulk TATP. The influence of the nanostructured gold substrate temperature on the signals of TATP was studied. A decrease in temperature up to 200 K increased the intensities of the TATP bands in the SERS spectrum; below 200 K, the TATP fingerprint disappeared.
In this work we present an approach towards economic free-flow electrophoresis chips fabricated by injection molding as mass replication process. This is achieved by the development of a free-flow electrophoresis chip design suitable for one step molding fabrication. Integrated partitioning bars are incorporated as key elements for bubble segregation. A defined open gap of 20 mu m in height and 500 mu m in width was integrated between the separation chamber and the electrode channels, acting as a barrier for gas bubbles while maintaining electrical contact by the fluidic junction. Additionally, we present an approach to avoid internal electrodes in FFE microchips for a facile mass production process. The injection molded thermoplastic mu FFE chips are ready to use without subsequent labor-intensive implementation of membranes or comparable structures serving as salt bridges
The selective population of rotational, spin, and Λ-doublet states of OH(2Π,v=0,1) by inelastic collisions with H2 and D2 is investigated in two experiments. In the first experiment OH radicals are generated by photolysis inside a pulsed nozzle beam source and prepared in the ground state j=1.5, v=0, 2Π3/2 with equal amounts in both Λ-doublets by rotational cooling in the subsequent expansion. The collisional excitation of OH by the secondary beam is probed via laser-induced fluorescence selectively for the Λ-doublet states for the different rotational levels in both spin manifolds of v=0. Integral cross sections σ(j=1.5,Ω̄=1.5→j ′,Ω̄′,ε′) averaged over the Λ-doublet substates in the input channel, but Λ-doublet substate resolved in the output channel are obtained in this case. In contrast to some previous predictions the Π(A′) Λ-doublet substate is preferentially populated. This implies a population inversion in the Λ-doublets for 2Π1/2 and an anti-inversion for 2Π3/2, which rules out previously proposed pump mechanisms for astronomical OH masers. In the second experiment OH is generated also by photolysis, in this case however in a flow system. Single Λ-doublet states are prepared by infrared excitation of the thermally relaxed OH in 2Π3/2, v=1 for two rotational states (j=1.5,4.5). The redistribution in v=1 induced by collisions with H2 is probed by laser-induced fluorescence. Rate constants are obtained for transitions from the initially prepared Λ-doublet states to the other Λ-doublet of the same j and also for transitions to other rotational states.
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