Controlled protein adsorption on microfluidic channels with engineered roughness and wettability

Plasma processing is demonstrated as a generic technology not only to fabricate, roughen, and control the wetting properties of microfluidic devices but also to control the protein adsorption in microfluidic channels intended for bio-analysis. After lithography on poly(methyl methacrylate) (PMMA) substrates, deep anisotropic O2 plasma etching was utilized to pattern microchannels, at conditions where very rough bottom walls were obtained. Where desirable, the rough surfaces were hydrophobized by means of a C4F8 plasma deposition step through a stencil mask creating superhydrophobic and hydrophilic stripes. In such microchannels, protein adsorption was controlled by the surface roughness and wettability showing null adsorption on superhydrophobic stripes and greatly enhanced adsorption on rough hydrophilic stripes. Using the biotin–streptavidin system, we demonstrate application of rough microchannels in extremely sensitive detection of proteins with two orders of magnitude improvement compared to flat microchannels. Thus, such control in protein immobilization on the rough walls can be potentially applied in bio-analysis.