Electroosmotic Flow in “Click” Surface Modified Microfluidic Channels

A rapid, facile, and modular surface modification scheme for the covalent attachment of pre-formed polymer moieties to self-assembled monolayers via ‘click’ chemistry within glass microfluidic channels (3 cm long, 110 μm wide and 15 μm deep) is described. The effect that different moieties have on the electroosmotic flow (EOF) within the microchannels is evaluated. The application of linear polymers such as poly(ethylene glycol) (PEG) generates hydrophilic surfaces that reduce the analyte-wall interactions, thereby increasing separation efficiency and improving resolution, especially in bio-separations. Dendritic polymers such as poly(amido amine) (PAMAM) on channel walls can provide high-surface area structures with tunable surface charge depending on the generation of the dendrimer coating. Modified surfaces are characterized by X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared-Attenuated Total Reflection spectroscopy (FTIR-ATR), and contact angle measurements. EOF measurements in modified and unmodified channels provide information about wall-analyte interactions. A PAMAM dendrimer coated channel presents an amine terminated surface with a positive charge in contrast to a negatively charged bare-glass surface. Use of surface coatings can lead to an increase of the EOF by 15% as is the case for an azide terminated surface or reverse the direction of EOF as is the case for the PAMAM coatings by changing the surface charge polarity.