Electrokinetic Protein Preconcentration Using a Simple Glass/Poly(dimethylsiloxane) Microfluidic Chip

Abstract

We discovered that a protein concentration device can be constructed using a simple one-layer fabrication process. Microfluidic half-channels are molded using standard procedures in PDMS; the PDMS layer is reversibly bonded to a glass base such as a microscope slide. The microfluidic channels are chevron-shaped, in mirror image orientation, with their apexes designed to pass within approximately 20 microm of each other, forming a thin-walled section between the channels. When an electric field is applied across this thin-walled section, negatively charged proteins are observed to concentrate on the anode side of it. About 10(3)-10(6)-fold protein concentration was achieved in 30 min. Subsequent separation of two different concentrated proteins is easily achieved by switching the direction of the electric field in the direction parallel to the thin-walled section. We hypothesize that a nanoscale channel forms between the PDMS and the glass due to the weak, reversible bonding method. This hypothesis is supported by the observation that, when the PDMS and glass are irreversibly bonded, this phenomenon is not observed until a very high E-field was applied and dielectric breakdown of the PDMS is observed. We therefore suspect that the ion exclusion-enrichment effect caused by electrical double layer overlapping induces cationic selectivity of this nanochannel. This simple on-chip protein preconcentration and separation device could be a useful component in practically any PDMS-on-glass microfluidic device used for protein assays.

Increase of Reaction Rate and Sensitivity of Low-Abundance Enzyme Assay Using Micro/Nanofluidic Preconcentration Chip

“…One critical step for the nanochannel formation in PDMS chip is the generation of nanogaps, and several techniques have already been developed for this purpose. 21,22 In this work, we used Nafion film printing on the glass substrate to generate a submicron thick ion-selective membrane. 23,24 At first, SU8 photoresist (SU8-2025, MicroChem Inc., Newton, MA) was patterned on a silicon wafer to build a positive master.…”

Effect of a Low-conductivity Zone on Field-amplified Sample Stacking in Microchip Micellar Electrokinetic Chromatography

“…Therefore, various online sample preconcentration techniques have been developed to improve the sensitivity of MCE. [6][7][8][9][10] One of the successful strategies is to combine other preconcentration devices with MCE on a single microchip, e.g., solid-phase extraction, 11 filtering using a nanopore or nanochannel, 12,13 and so on. 14,15 As a typical example, Kim et al reported that the preconcentration with a nanochannel could attain a million-fold improvement of the detectability, but it required a long analysis time of over 30 min.…”

“…14,15 As a typical example, Kim et al reported that the preconcentration with a nanochannel could attain a million-fold improvement of the detectability, but it required a long analysis time of over 30 min. 13 Furthermore, the nano-fabrication schemes need an expensive apparatus and complicated procedures. Thus, it is appropriate for MCE to apply a rapid and simple preconcentration technique including field-amplified stacking (FASS), [16][17][18] sweeping, [19][20][21] transient isotachophoresis, 22,23 isoelectric focusing, 24,25 transient trapping, 26 and so on.…”

Simulation guided design of a microfluidic device for electrophoretic stretching of DNA

“…3 In general, these devices use flow or electric field to manipulate biomolecules for specific purposes, including concentration, 4,5 separation, 6 and detection. 7 Most microfluidic devices in the literatures are prototypes to demonstrate new ideas.…”