Reactive deposition of nano-films in deep polymeric microcavities.

Authors:
Asif Riaz
Asif Riaz
School of Chemistry
Berkeley | United States
Ram P Gandhiraman
Ram P Gandhiraman
NASA Ames Research Center
Ivan K Dimov
Ivan K Dimov
Dublin City University
Ireland
Lourdes Basabe-Desmonts
Lourdes Basabe-Desmonts
Biomedical Diagnostics Institute
Ireland
Dr. Jens Ducree, Dr. rer. nat. habil. Dipl. Phys.
Dr. Jens Ducree, Dr. rer. nat. habil. Dipl. Phys.
Fraunhofer Project Centre at Dublin City University
Professor (Full)
microfluidics, Lab-on-a-Chip, hydrodynanmics, business development, project management, organisational leadership
Glasnevin, Dublin 9 | Ireland
Stephen Daniels
Stephen Daniels
Cincinnati Children's Hospital Medical Center
United States
Antonio J Ricco
Antonio J Ricco
Biomedical Diagnostics Institute
Ireland
Luke P Lee
Luke P Lee
University of California
United States

Lab Chip 2012 Nov;12(22):4877-83

Biomedical Diagnostics Institute, National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin, Ireland.

We report the controlled diffusion of gas-phase high-reactivity chemical species into long polymeric microcavities to form glass-like, low-permeability barrier films on the interior surfaces of the microcavities. Reactive species created from fragmentation of O(2) and hexamethyldisiloxane (HMDSO) in a radio-frequency (RF) plasma environment are allowed to diffuse into the microcavities of polydimethylsiloxane (PDMS), where surface reactions lead to the formation of an effective, glass-like thin-film barrier. Reactive species including silicon radicals and elemental oxygen maintain their reactivity for sufficient times (up to 7000 s) and survive the random diffusional walk through the microcavities to form glass barriers as much as 65 mm from the cavity entrance. The barrier thickness and the growth length can be controlled by the reaction time and chamber operating pressure. Increasing the cross sectional area of the cavity inlet and/or decreasing the mean free path was found to increase the thickness of the barrier film. Optical emission spectroscopic analysis was used to characterize the reactive fragments formed from HMDSO, and energy-dispersive X-ray analysis revealed that the barrier composition is consistent with oxides of silicon (SiO(x)). Formed inside PDMS microcavities, the glass barrier blocks the penetration or absorption of small molecules such as rhodamine B (RhB) and biotin, and also resists permeation of organic solvents such as toluene, preventing the PDMS microfluidic structures from swelling and deforming. Moreover, formation of glass-like thin films in PDMS microcavities enhances the stability of electroosmotic flow (EOF) relative to uncoated PDMS devices, in which EOF instabilities are significant; this enables separation by electrophoresis with reproducibility (relative standard deviation 3%, n = 5) and baseline peak resolution (R:1.3) comparable to that obtained in conventional fused-silica capillaries.

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November 2012
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