A novel methodology for systematic study on molecular release from microscale reservoirs

We have developed a novel method to systematically investigate molecular release. A series of processes including buckling of thin polymer films, deposition of solute molecules, and transfer to other substrates enabled the fabrication of uniform and submicron-sized tunnel-like molecular reservoirs. From the release profiles, diffusivity and solubility of the solute molecules in the polymeric barriers were calculated. As a model study, we investigated the release of rhodamine B and FITC-labeled dextran polymer representing small molecules and large molecules. The degree of hydration of the polymer barrier was controlled by changing the chain end group of polystyrene (PS) by tert-butyl (PS-t-Bu) and nitrilotriacetic acid (PS-NTA). The NTA-terminated PS thin films showed 13% water uptake regardless of the film thickness while the bare PS and PS-t-Bu barriers exhibited 4% and 6% uptake. This difference in hydration affected release behavior of the molecules. The release of small molecules was dependent on the barrier polymers, while the release of large molecules was completely blocked due to the restricted chain movement of the barrier polymers. Surface treatment by CF4 plasma on the PS-NTA barriers considerably retarded the release of small molecules and blocked the release of large molecules. The release behavior could be well explained by the diffusivity and solubility calculated from the release profile.