Migration Behavior of Low-Density Particles in Lab-on-a-Disc Devices: Effect of Walls.

The effect of the lateral walls of a Lab-On-a-Disc device on the dynamics of a model system of particles with a density lower than that of the solvent (modelling parasites eggs) is analyzed theoretically and experimentally. In the absence of lateral walls, a particle always moves in the direction of the centrifugal force, while its trajectory is deflected in the tangential direction by the inertial Coriolis and Euler forces. Lateral walls, depending on the angle forming with the radial direction, can guide the particle either in the same or in the opposite direction to the centrifugal force, thus resulting in unusual particle trajectories including zig-zag or backwards particle motion. The effect is pronounced in the case of short operation times when the acceleration of the angular rotation, and thus the Euler force, is considerable. The predicted unusual motion is demonstrated by numerically solving the equation of motion in the presence of lateral walls and verified in the experiment with particles of density lower than that of the solvent. Our analysis is useful for design and operational considerations of Lab-On-a-Disc devices aiming for or involving (bio)particle handling.

Performance of laterally elongated pillar array columns in capillary electrochromatography mode.

In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 and 1.46 µm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated, aspect ratio 4) pillar array columns, respectively. By comparing dispersion at the entire channel width to that at the central zone only, it appears that sidewall related dispersion significantly contributes to overall dispersion. A 40% reduction of the plate height was observed by taking into account only the central channel zone. A kinetic plot analysis was performed to evaluate the potential of the studied geometries by considering a maximum operating voltage of 20 kV as limiting parameter. It was demonstrated that rectangular radially elongated pillars produce a higher efficiency than cylindrical pillars and other microfabricated column structures for microchip capillary electrochromatography previously studied.

Development of a Lab-on-a-Disk Platform with Digital Imaging for Identification and Counting of Parasite Eggs in Human and Animal Stool.

We present a lab-on-a-disk technology for fast identification and quantification of parasite eggs in stool. We introduce a separation and packing method of eggs contained in 1 g of stool, allowing for removal of commonly present solid particles, fat droplets and air bubbles. The separation is based on a combined gravitational and centrifugal flotation, with the eggs guided to a packed monolayer, enabling quantitation and identification of subtypes of the eggs present in a single field of view (FOV). The prototype was tested with stool samples from pigs and humans infected with intestinal parasites (soil-transmitted helminths eggs). The quality of the images created by this platform was appropriate for identification and quantification of egg types present in the sample.