Atmospheric pressure atomic layer deposition for in-channel surface modification of PDMS microfluidic chips

In this paper, we designed a new concept where we deposited PDMS microfluidics devices with nano-layers. Using atmospheric pressure atomic layer deposition, we obtained a high coverage, even at a complex geometry and high aspect ratios. The nano-layers can be used for various purposes, as demonstrated with three case studies in our papers. For example, an increase of the organic solvent resistance (and their wetting property), which enables PDMS microfluidics devices to produce oil-in-water droplets often employed in emerging drug productions. Other positive properties include modifying PDMS devices' surface to evaluate unique responses of cancer cells, and decorate PDMS devices with arrays of functional nanoparticles to elucidate various catalysis in micro-level.

Abstract

Polydimethylsiloxane (PDMS) is one of the materials of choice for the fabrication of microfluidic chips. However, its broad application is constrained by its incompatibility with common organic solvents and the absence of surface anchoring groups for surface functionalization. Current solutions involving bulk-, ex-situ surface-, and in-situ liquid phase modifications are limited and practically demanding. In this work, we present a simple, novel strategy to deposit a metal oxide nano-layer on the inside of bonded PDMS microfluidic channels using atmospheric pressure atomic layer deposition (AP-ALD). Using three important classes of microfluidic experiments, i.e., (i) the production of micron-sized particles, (ii) the cultivation of biological cells, and (iii) the photocatalytic degradation in continuous flow chemistry, we demonstrate that the metal oxide nano-layer offers a higher resistance against organic solvent swelling, higher hydrophilicity, and a higher degree of further functionalization of the wall. We demonstrate the versatility of the approach by not only depositing SiO_x nano-layers, but also TiO_x  nano-layers, which in the case of the flow chemistry experiment were further functionalized with gold nanoparticles through the use of AP-ALD. This study demonstrates AP-ALD as a tool to broaden the applicability of PDMS devices.

Albert Santoso, M. Kristen David, Pouyan E. Boukany, Volkert van Steijn, J. Ruud van Ommen