Surface Modification of Pillar Array Systems for Chromatography and Fluorescence Enhancement

Thin-layer chromatography offers many advantages in the world of chemical separations due to its ease of use, high sensitivity, range of applicability, and multiplex capability. However, this technique is succeptible to band broadening effects that limit its efficiency. Attempting to resolve these effects by decreasing particle size causes a decrease in mobile phase velocity which creates its own band broadening via longitudinal diffusion. However, pillar array systems on the micro- and nanoscale have been shown as useful analogues to thin-layer chromatography which mitigate the efficiency concerns associated with the method.

The work within this dissertation is concerned with the modification of pillar array surfaces for both chromatographic and spectroscopic purposes. The first aim is to increase the surface area of the pillars for chromatography by depositing porous phases such as petal-like carbon and porous silicon oxide. The usefulness of pillar arrays as separations systems is moderated by their limited native surface area. Increasing the surface area of a stationary phase can increase the retention of analyte by the system without negatively affecting its efficiency. While we found that petal-like carbon has several properties that made it unsuitable for these pillar array systems in their current form, porous silicon oxide showed great promise as a porous phase which increased the surface area of the pillars and the retention of analytes within them.

The second aim was to immobilize fluorescent molecules at the pillar surface for signal enhancement. Pillars in the nanoscale have been shown to exhibit a field effect which amplifies fluorescence signal. To this end, we developed wet chemistry methods to functionalize the pillar surface with two different immobilizing resins, one using a uranium-capturing compound, and the other a biotin-avidin complex to sequester DNA. In both cases, we created high-throughput methods which retained high sensitivity while using only minimal amounts of sample.