Electroosmotic Flow in “Click” Surface Modified Microfluidic Channels

Abstract

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.

“Click” Modification of Silica Surfaces and Glass Microfluidic Channels

“…Glass microfluidic devices were made by patterning a single channel on Corning 2947 microscope slides by using AZ1518 (Clariant, Inc.) as the photoresist (PR). AP8000 (Dow Chemicals) was used as the adhesion promoter for the PR layer, which was later used as the etch mask . The patterned microscope slides were exposed to a 4:1 solution of DI water and NH 4 F/HF (BHF) for 20 min with gentle agitation.…”

“…Uniform surface charges can assist in minimizing pressure-driven flows and subsequent deviation from pluglike flows. − Thus, the ability to alter surface potential to produce desired electroosmotic flow (EOF) characteristics within a microchannel can be a powerful tool for a separations technologist. For CE systems, wall coatings can help improve electrophoretic separation reproducibility, reduce analyte−wall interactions, and provide greater control over EOF and device performance. − Different methods have been used to control EOF in CE systems, including manipulation of buffer concentrations, addition of surfactants and surface-active materials to analyte solutions, application of radial electric fields, manipulating solution pH, and chemical modification of surfaces to alter ζ potential . The common link between all these methods is an attempt to control the interaction between the solution in the channel and the double layer at the channel wall surface.…”

Developing an ultra non-fouling SU-8 and PDMS hybrid microfluidic device by poly(amidoamine) engraftment

“…In addition, we also demonstrated that the microfluidic system reduced Escherichia coli O157:H7 bacterial cell adsorption by as much as 95%, a much improved non-fouling performance comparable with other reports in the literature. In microfluidic systems, PAMAM dendrimers have been used to either provide high surface area because of their molecular structures [23] or improve the sensitivity of microfluidic biosensors due to their multi-functional end groups that allow more loading capacity of biomarkers [24]. However to our best knowledge, there is no report focusing on the non-fouling property of PAMAM dendrimers in microfluidic systems and articles reporting ways to employ PAMAM for SU-8/PDMS hybrid device fabrications, which is of significant importance for microfluidic systems for applications in diagnostic and biosensing [25].…”

Characterization of ionic transport at the nanoscale

“…The various layers are aligned manually and bonded using a commercial adhesive. The process for applying and curing the adhesive layers has been reported previously [17,28,30]. Briefly, an epoxy-based adhesive (epoxy novalacmodified resin, Dow Corning) is contact printed from a poly(dimethyl siloxane), or PDMS, stamp onto the back-side of the cavity die, which is then bonded to the front (PI side) of the electrode die at 130˚C for 10 minutes.…”

“…The surface charge on the walls can be a key parameter that influences ionic transport at the nanoscale. Recent developments of surface-modified microchannels, nanofluidic transistors, and ion-current rectifiers have shown the importance of surface charge [16][17][18][19]. It was found that, for the case of EDL overlap, the ionic conductance of nanochannels reaches a plateau at low concentrations [16].…”