Integrated Nano Liquid Chromatography System On-a-Chip

Citation

He, Qing (2006) Integrated Nano Liquid Chromatography System On-a-Chip. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/NQVA-F827. https://resolver.caltech.edu/CaltechETD:etd-07142005-013255

Abstract

Integrated liquid chromatography (LC) chips are valued because of their significant advantages over conventional systems. However, they are very challenging to build due to the high complexity of LC systems and the need for high-level integration of many discrete microfluidic devices.

The goal of this thesis is to develop technologies and devices towards a totally integrated LC system on-a-chip. Using parylene microfluidics technology, all of the devices are integrated on silicon wafers with CMOS-compatible batch processes. Due to the small size of the on-chip LC columns, the chips all perform nano LC, which means that the flow rates are on the scale of nano liters per minute.

The thesis starts with the solution of the problem of bead integration, since most LC columns are packed with micro-beads. A wafer-scale batch process is developed to integrate beads into micromachined devices. The technology is applied to make an LC-ESI (Electro-Spray Ionization) chip with an integrated bead column packed with 5 µm diameter C18 silica beads. The integrated ESI nozzle allows direct coupling to a mass spectrometer (MS).

Due to the high-pressure nature of LC operations, a complete LC chip must be able to both withstand and generate high pressures on-chip. Therefore, an anchoring technique is developed to dramatically increase the pressure rating of parylene devices from about 30 psi to 1000 psi. In addition, on-chip high-pressure generation is achieved with electrolysis-based micro-actuators.

An integrated ion liquid chromatography chip is demonstrated, which has on-chip column, filters, injection structure, and conductivity detector. The column is packed with 7 µm anion-exchange beads with a slurry packing technique. On-chip sample injection, separation, and detection of seven common anions are successfully demonstrated with a sensitivity of 1 ppm.

Finally, a microchip that demonstrates high-pressure LC with integrated ESI coupling to MS is presented. The capacity of the column, which is 6.5 cm long and packed with 5 µm C18 silica beads, is the highest of all the devices in the thesis. Gradient separation at a pressure of 450 psi and on-line MS detection of digested cytochrome c protein is successfully performed.

Thesis Files