Design and implementation of injector/distributor structures for microfabricated non-porous pillar columns for capillary electrochromatography

A previously proposed foil definition is applied in the design of injector/distributor structures for solid microfabricated column structures for capillary electrochromatography. In addition to a typical bifurcated distributor, an optimized design alternative with two different configurations is experimentally evaluated. Optimized designs yielded a flat profile for the injected sample with a maximum of 3% variation from the mean width, while it went up to 18% for the typical bifurcated distributor. The implemented electrokinetic injection approach enabled controlling the volume of the injected sample accurately without sacrificing the compactness of the device design. The width of the injected sample was directly proportional to the injection time, namely 165 and 218 μm base widths were obtained for 0.6 and 0.8 s of feeding, respectively. Reducing the external porosity of the distributor by 85% compared to the typical design, optimized distributors caused a decrease in the mean flow velocity of up to 70%. However, having a flat initial plug shape enabled the separation of a mixture of Coumarin 440, 460, 480 and 540 at 1 mm downstream of the injection point in 80 s, while it was even not possible to detect the C440 signal for a typical bifurcated design

Design and implementation of injector/distributor structures for microfabricated non-porous pillar columns for capillary electrochromatography

A previously proposed foil definition is applied in the design of injector/distributor structures for solid microfabricated column structures for capillary electrochromatography. In addition to a typical bifurcated distributor, an optimized design alternative with two different configurations is experimentally evaluated. Optimized designs yielded a flat profile for the injected sample with a maximum of 3% variation from the mean width, while it went up to 18% for the typical bifurcated distributor. The implemented electrokinetic injection approach enabled controlling the volume of the injected sample accurately without sacrificing the compactness of the device design. The width of the injected sample was directly proportional to the injection time, namely 165 and 218 μm base widths were obtained for 0.6 and 0.8 s of feeding, respectively. Reducing the external porosity of the distributor by 85% compared to the typical design, optimized distributors caused a decrease in the mean flow velocity of up to 70%. However, having a flat initial plug shape enabled the separation of a mixture of Coumarin 440, 460, 480 and 540 at 1 mm downstream of the injection point in 80 s, while it was even not possible to detect the C440 signal for a typical bifurcated design

Fabrication of integrated porous glass for microfluidic applications

This paper presents a method for the fabrication of integrated porous silica layers in microfluidic channel networks by microfabrication techniques. Porous silica is obtained by anodization of silicon, followed by full conversion of the porous silicon network into porous silica by means of thermal oxidation. A series of experiments were performed with various channel layouts to determine the critical parameters, including the I–V characteristics and the optimal working potential for stable pore formation, during anodic etching. Typical test structures were anodized in 5% HF for 15 min at 1 V, yielding an average pore size of around 5.4 nm and porosity of 49%. Complete conversion of porous silicon into porous glass was accomplished with wet oxidation at 900 °C. The average pore size and porosity of porous glass network were around 3.8 nm and 34%, respectively. This decrease in both pore size and porosity is caused by the increase in molar volume when silicon oxidizes to silicon oxide. The transparency and the hydrophilicity of porous glass layers are evidenced by means of monitoring the diffusion of Rhodamine B fluorescent dye through the porous network. This fabrication method can be applied to (3-D) structured microfluidic channels and it is envisioned that the resulting porous silica layers can be employed for a wide range of application areas, such as membrane technology, catalyst supports, chromatography and electrokinetics

Microassembly using a cluster of paramagnetic microparticles

We use a cluster of paramagnetic microparticles to carry out a wireless two-dimensional microassembly operation. A magnetic-based manipulation system is used to control the motion of the cluster under the influence of the applied magnetic fields. Wireless motion control of the cluster is implemented at an average velocity and maximum position tracking error of 144 μm/s and 50 μm, respectively. This control is used to achieve point-to-point positioning of the cluster, manipulation of microobjects, and assembly of microobjects into a microstructure. The control system achieves stable positioning of the cluster, while simultaneously compensating for the planar drag forces on the cluster and the microobject. The presented magneticbased microassembly technique allows for the selective pushing and pulling of microobjects with specific geometries towards their destinations inside a microstructure in an execution time of 18 s, within a workspace of 1.8 mm × 2.4 mm

Performance Evaluation of Different Design Alternatives for Microfabricated Nonporous Fused Silica Pillar Columns for Capillary Electrochromatography

An experimental study comparing the performance of different designs for microfabricated column structures for microchip capillary electrochromatography is presented. The work is a follow-up to our previously published modeling and simulation study on the same topic. Experiments were performed using fused silica microchips with and without octadecyltrimethoxysilane coating for nonretained and retained modes of operation, respectively. Showing the same trends as the modeling results, the foil shape produces a significant decrease in plate height with an increase of around 15% in mobile phase velocity in nonretained measurements of Coumarin 480 (C480). Measured plate heights at 1 kV/cm applied electric field were 0.77, 1.33, and 1.42 μm for foil, diamond, and hexagon, respectively. Chromatographic runs of C480 yielded minimal plate height values of 1.85 and 3.28 μm for foil and diamond, respectively. The optimization of the shape and placement of the structures appeared to have a considerable impact on the achievable performanc

Novel four-point-probe design and nanorobotic dual endeffector strategy for electrical characterization of as-grown SWCNT bundles

In this paper, a novel nanorobotic strategy for non-destructive and direct electrical characterization of as-grown bundles of single-walled carbon nanotubes (SWCNTs) is presented. For this purpose, test patterns of SWCNT bundles having different diameters are grown on a silicon substrate by chemical vapor deposition. A new design of microstructured four-point-probes is proposed and fabricated allowing for direct contacting of vertically aligned bundles of SWCNTs. A nanorobotic setup is upgraded into a dual endeffector system to achieve good electrical contact between four-point-probe and SWCNT bundle and to perform electrical measurements. First experimental results of non-destructive electrical characterization are presented and discussed. ©2010 IEEE