Ultra-rapid separation of an angiotensin mixture in nanochannels using shear-driven chromatography.

The present paper reports on the separation of a mixture of fluorescein isothiocyanate-labeled angiotensin I and II peptides in a shear-driven nanochannel with a C18-coating and using an eluent consisting of 5% acetonitrile in 0.02 M aqueous phosphate buffer at pH 6.5. The flat-rectangular nanochannel in fused silica consisted of an etched structure in combination with a flat moving wall. The very fast separation kinetics that can be achieved in a nanochannel allowed to separate the angiotensin peptides in less then 0.2 s in a distance of only 1.8 mm. Plate heights as small as 0.4 microm were calculated after substraction of the injection effect.

Measurements of diffusion coefficients in 1-D micro- and nanochannels using shear-driven flows.

The present paper describes a method for measuring the molecular diffusion coefficient of fluorescent molecules in microfluidic systems. The proposed static shear-driven flow method allows one to perform diffusion measurements in a fast and accurate manner. The method also allows one to work in very thin (i.e. submicron) channels, hence allowing the investigation of diffusion in highly confined spaces. In the deepest investigated channels, the obtained results were comparable to the existing literature values, but when the channel size dropped below the micrometer range, a significant decrease (more than 30%) in molecular diffusivity was observed. The reduction of the diffusivity was most significant for the largest considered molecules (ssDNA oligomers with a size ranging between 25 to 100 bases), but the decrease was also observed for smaller tracer molecules (FITC). This decrease can be attributed to the interactions of the analyte molecules with the channel walls, which can no longer be neglected when the depth of the channel reaches a critical value. The change in diffusivity seems to become more explicit as the molecular weight of the analytes increases.

A novel microstep device for the size separation of cells.

We report on a series of preliminary experiments investigating the applicability of a novel method for the size separation of nano- and microsized particles and cells. The working principle is based on the application of a shear-driven flow through stepwise tapered micro- or nanochannels. Size separations of mixtures of 0.5 and 1.0 microm carboxylated polystyrene beads as well as of binary mixtures of Staphylococcus aureus and Saccharomyces cerevisiae cells and of S. cerevisiae and Escherichia coli cells are demonstrated.

High-velocity transport of nanoparticles through 1-D nanochannels at very large particle to channel diameter ratios.

We explore the possibility of generating high-velocity flows of nanoparticles through flat-rectangular nanochannels, which are only 50% deeper than the diameter of the particles. Using the shear-driven flow principle, 200-nm particles can, for example, be transported through a 300-nm-deep channel at velocities up to 35 mm/s (upper limit of our current setup). Working under high-pH conditions, the velocity of the carboxylated nanoparticles still respects the small-molecule velocity law, despite the high degree of confinement to which the particles are subjected. The high degree of confinement is also found to lead to a reduced band broadening. When injecting sharply delimited particle plugs, the plate heights observed for the flow of 0.2-microm particles through a 0.3-microm channel (with plate heights of the order of 1-2 microm) are, for example, approximately 1 order of magnitude smaller than for the flow of 1.0-microm particles through a 1.4-microm channel. It is also found that the band broadening is, within its statistical variation, independent of the fluid velocity over a large range of particle velocities (5-35 mm/s). The flow method distinguishes itself from pressure-driven field-flow fractionation and hydrodynamic chromatography in that the mean particle velocity is independent of the particle size over the entire range of possible particle to channel diameter ratios.

The stimulating effect of a harsh environment on the bacteriocin activity by Enterococcus faecium RZS C5 and dependency on the environmental stress factor used.

Bacteriocin production by Enterococcus faecium RZS C5 occurs in a growth-associated way but is generally switched off in the very early growth phase. The influence of environmental stress on the bacteriocin production kinetics by E. faecium RZS C5 was analysed at a controlled temperature of 35 degrees C and constant pH 6.5. The effect of environmental stress on bacteriocin production was depending on the type of stress applied. Oxidative stress did not interfere with cell growth or bacteriocin activity. In contrast, salt stress decreased both the cell growth and the specific bacteriocin production. Nevertheless, moderate levels of sodium chloride improved bacteriocin activity because they increased the biomass concentration at which bacteriocin production was switched off. Environmental stress due to limitations in sugar or complex nutrients did not affect the early shut-off mechanism or the specific bacteriocin production. However, bacteriocin stability decreased or increased at low levels of sugar or complex nutrients, respectively.