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The formation of porous silica microstructures (frits) in capillaries with an internal diameter of 500 mm has been examined for inducing electroosmotic flow (EOF). Capillaries with this internal diameter are normally considered too large to support efficient EOF, but the discrete pumping devices reported here are able to overcome this limitation. The formation of these structures in the capillaries has been examined, with particular emphasis on identifying parameters within the preparation stage that might give rise to variation in the porosity of the frit. The initial results showed that the induced electroosmotic flow rate increased with frit length (to an optimum of 50 mm) with an applied potential of 700 V. The work offers an opportunity to extend electroosmotic pumping to capillaries of larger internal diameter than was previously thought ideal. It offers a number of potential advantages in the area of fluid propulsion, including the electric control of flow rates, the plug like nature of the flow, and the absence of moving parts. When this technology is applied to micro-reactors, the silica structures offer the dual advantages of providing a pumping mechanism while also retaining the catalyst in the micro-reactor.

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We have developed a method for the quantitative 3-dimensional profiling of micron sized channel networks within optically transparent "lab-on-a-chip" microreactor devices. The method involves capturing digitised microscope images of the channel network filled with an optically absorbing dye. The microscope is operated in transmission mode using light filtered through a narrow bandpass filter with a maximum transmission wavelength matching the wavelength of the absorbance maximum of the dye solution. Digitised images of a chip filled with solvent and dye solution are analysed pixel by pixel to yield a spatially resolved array of absorbance values. This array is then converted to optical path length values using the Beer-Lambert law, thereby providing the 3D profile of the channel network. The method is capable of measuring channel depths from 10 to 500 microm (and probably even smaller depths) with an accuracy of a few percent. Lateral spatial resolution of less than 1 microm is achievable. It has been established that distortion of the measured profiles resulting from a mismatch in refractive index between the dye solution and the glass of the microreactors is insignificant. The method has been successfully used here to investigate the effects of thermal bonding and etch time on channel profiles. The technique provides a convenient, accurate and non-destructive method required to determine channel profiles; information which is essential to enable optimisation of the operating characteristics of microreactor devices for particular applications.