Investigation of the behavior of serum and plasma in a microfluidics system

There are common problems with adsorption of analytes on the surfaces of microfluidic systems with physiological samples such as blood serum, plasma, and urine. The authors\u27 investigation involves the interaction of serum components with fused-silica surfaces under various flow regimes in microcapillaries. Their focus will include the individual components of serum as well as fresh whole serum. The authors studied the whole serum components in our microfluidic system to uncover the responses of proteins in capillary and microchannel surfaces when influenced by the highly variable serum constituents. They have observed the whole serum with a total protein assay by using the bicinchoninic acid assay in combination with a characterization method, such as SDS polyacrylamide gel electrophoresis, and repeated observations for any change of flow rate in fused-silica capillaries (50 mu m inside diameter) under continuous flow. The authors\u27 preliminary results contradict anecdotal evidence that proteins and other components of serum clog or prevent flow at steady low flow rates

Size-resolved and bulk activation properties of aerosols in the North China Plain

Size-resolved and bulk activation properties of aerosols were measured at a regional/suburban site in the North China Plain (NCP), which is occasionally heavily polluted by anthropogenic aerosol particles and gases. A Cloud Condensation Nuclei (CCN) closure study is conducted with bulk CCN number concentration (NCCN) and calculated CCN number concentration based on the aerosol number size distribution and size-resolved activation properties. The observed CCN number concentration (NCCN-obs) are higher than those observed in other locations than China, with average NCCN-obs of roughly 2000, 3000, 6000, 10 000 and 13 000 cm−3 at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.70%, respectively. An inferred critical dry diameter (Dm) is calculated based on the NCCN-obs and aerosol number size distribution assuming homogeneous chemical composition. The inferred cut-off diameters are in the ranges of 190–280, 160–260, 95–180, 65–120 and 50–100 nm at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.7%, with their mean values 230.1, 198.4, 128.4, 86.4 and 69.2 nm, respectively. Size-resolved activation measurements show that most of the 300 nm particles are activated at the investigated supersaturations, while almost no particles of 30 nm are activated even at the highest supersaturation of 0.72%. The activation ratio increases with increasing supersaturation and particle size. The slopes of the activation curves for ambient aerosols are not as steep as those observed in calibrations with ammonium sulfate suggesting that the observed aerosols is an external mixture of more hygroscopic and hydrophobic particles. The calculated CCN number concentrations (NCCN-calc) based on the size-resolved activation ratio and aerosol number size distribution correlate well with the NCCN-obs, and show an average overestimation of 19%. Sensitivity studies of the CCN closure show that the NCCN at each supersaturation is well predicted with the campaign average of size-resolved activation curves. These results indicate that the aerosol number size distribution is critical in the prediction of possible CCN. The CCN number concentration can be reliably estimated using time-averaged, size-resolved activation efficiencies without accounting for the temporal variations

Size-resolved and bulk activation properties of aerosols in the North China Plain

Size-resolved and bulk activation properties of aerosols were measured at a regional/suburban site in the North China Plain (NCP), which is occasionally heavily polluted by anthropogenic aerosol particles and gases. A Cloud Condensation Nuclei (CCN) closure study is conducted with bulk CCN number concentration (<i>N</i><sub>CCN</sub>) and calculated CCN number concentration based on the aerosol number size distribution and size-resolved activation properties. <br><br> The observed CCN number concentration (<i>N</i><sub>CCN-obs</sub>) are higher than those observed in other locations than China, with average <i>N</i><sub>CCN-obs</sub> of roughly 2000, 3000, 6000, 10 000 and 13 000 cm<sup>−3</sup> at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.70%, respectively. An inferred critical dry diameter (<i>D</i><sub>m</sub>) is calculated based on the <i>N</i><sub>CCN-obs</sub> and aerosol number size distribution assuming homogeneous chemical composition. The inferred cut-off diameters are in the ranges of 190–280, 160–260, 95–180, 65–120 and 50–100 nm at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.7%, with their mean values 230.1, 198.4, 128.4, 86.4 and 69.2 nm, respectively. <br><br> Size-resolved activation measurements show that most of the 300 nm particles are activated at the investigated supersaturations, while almost no particles of 30 nm are activated even at the highest supersaturation of 0.72%. The activation ratio increases with increasing supersaturation and particle size. The slopes of the activation curves for ambient aerosols are not as steep as those observed in calibrations with ammonium sulfate suggesting that the observed aerosols is an external mixture of more hygroscopic and hydrophobic particles. <br><br> The calculated CCN number concentrations (<i>N</i><sub>CCN-calc</sub>) based on the size-resolved activation ratio and aerosol number size distribution correlate well with the <i>N</i><sub>CCN-obs</sub>, and show an average overestimation of 19%. Sensitivity studies of the CCN closure show that the <i>N</i><sub>CCN</sub> at each supersaturation is well predicted with the campaign average of size-resolved activation curves. These results indicate that the aerosol number size distribution is critical in the prediction of possible CCN. The CCN number concentration can be reliably estimated using time-averaged, size-resolved activation efficiencies without accounting for the temporal variations

Chloride versus Protons Ion Currents in the Cell-Transistor Junction

The cell-transistor junction has been investigated throughout the last two decades. Equivalent electric circuits and various models were devised to reproduce measurements and thus increase an understanding of processes within the junction. In parallel, the minute geometry between an individual electrogenic cell and a field-effect transistor was characterized to fine-tune the models. Surprisingly, all past experiments were entirely based on cations, such as sodium or potassium, disregarding potential applications for anions. In this thesis, the role and influence of anions in the cell-transistor junction was investigated. According to state-of-the-art theory in the field, cations and anions have different effects on measurements, since field-effect transistors show a selective sensitivity for small cations. In order to verify the theoretical expectations, a human embryonic kidney cell line was stably transfected with ligand-gated chloride channels, which provided anion currents upon chemical stimulation. As anticipated, a comparison of recordings with field-effect transistors and inert gold electrodes showed no significant differences. Based on the results obtained from experiments with chloride currents, the recently discovered antiparallel transport of chloride and protons in some voltage-gated chloride channels was investigated. The cell-transistor junction offered the opportunity to reveal the transport of protons in chloride channels since the cation-sensitivity of field-effect transistors induces strong sensor responses upon pH changes. In order to clearly reveal the transport of even smaller amounts of protons, assays were developed to influence pH changes due to buffer concentrations. Signal modeling and simulation was employed to determine the transport stoichiometry of chloride versus protons in voltage-gated chloride channels. Even advanced models of the cell-transistor junction considered only ion currents carried by one single ion species. Therefore, a new comprehensive model of the cell-transistor junction was developed to simulate electric, electrodiffusive and ion-sensitive processes for multiple ion species. In addition, pH and buffer effects were implemented to simulate the influence of transported protons. The shape and attachment of cells was analyzed by means of membrane allocation profiling, a new method developed in the course of this thesis. The results were employed to provide accurate geometrical proportions of the junction for the comprehensive model of the cell-transistor junction. This work unites the fields of cell biology, biophysics and chemistry with microelectronics as well as computational sciences to advance the understanding of cell-transistor junctions. New detail was provided about the junction's geometry. Further, state-of-the-art theories in the field were first confirmed and then improved to develop a comprehensive model of the cell-transistor junction. Finally, the new model was employed to provide insights into the transport stoichiometry of Cl-/H+ antiporters

Suspended Nanoporous Membranes as Interfaces for Neuronal Biohybrid Systems

A biohybrid system composed of neuronal cells and silicon-supported nanoporous membranes has been designed to facilitate control of the biochemical environment of neuronal networks with cellular resolution. The membranes may exhibit variable pore sizes and interpore distances and are interfaced to a microfluidic device. Different porosity parameters give rise to changes in the transconductance of the nanopores and can therefore be used to control diffusion of molecules through the membranes. It was shown that the porous membranes are biocompatible with primary vertebrate as well as insect neurons. Our results indicate that nanoporous membranes may be used to interface with biological materials in a biohybrid system, for example as an artificial chemical synapse interface