Microfluidic Protein Preconcentrator Using a Microchannel-Integrated Nafion Strip: Experiment and Modeling

摘要

We propose a simple microfluidic device for proteinnpreconcentration based on the electrokinetic trappingnprinciple. It comprises a narrow Nafion strip that is simplyncut from a commercial membrane and is integrated intona molded poly(dimethylsiloxane) (PDMS) microfluidicnstructure using a guiding channel. Mechanically clampingnthe PDMS/Nafion assembly with a glass substrate resultsnin a rapid prototypable, leak-tight, and easily disposablendevice. Our device preconcentrates negatively chargednfluorescent proteins located at the anodic microfluidicncompartment side of the Nafion strip within a few minutesnand up to a concentration factor of 104. Moreover, wenpresent a numerical study of the preconcentrationneffect by solving the coupled Poisson, Nernst-Planck,nand Navier-Stokes equations for our type of device,nwhich provides microscopic insight into the mechanismnof preconcentration. The electrical field acrossnthe ion-permselective Nafion generates concentrationnpolarization, i.e., ion depletion at the anodic side andnion enrichment at the cathodic side for both types ofnions, with a local excess of mobile positive ions in thendepleted concentration polarization zone, inducing annonequilibrium electrical double layer in close proximitynto the Nafion membrane. A voltage differencenapplied over the anodic compartment is used to generatenthe electrophoretic flow velocity of the negativelyncharged tracer biomolecules. This, in combination withnthe electroosmotic flow in the opposite direction, whichnoriginates from the fixed charges on the channel wallsnand the induced space charge near the membrane,nprovides the basis for the local preconcentration of thennegative tracer biomolecules.