Abstract
Sample preconcentration is an important step that increases the accuracy of subsequent detection, especially for samples with extremely low concentrations. Due to the overlapping of electrical double layers in the nanofluidic channel, the concentration polarization effect can be generated by applying an electric field. Therefore, a nonlinear electrokinetic flow is induced, which results in the fast accumulation of proteins in front of the induced ionic depletion zone, the so-called exclusion-enrichment effect. Nanofractures were created in this work to preconcentrate proteins via the exclusion-enrichment effect. The protein sample was driven by electroosmotic flow and accumulated at a specific location. The preconcentration chip for proteins was fabricated using simple standard soft lithography with a polydimethylsiloxane replica. Nanofractures were formed by utilizing nanoparticle-assisted electric breakdown. The proposed method for nanofracture formation that utilizes nanoparticle deposition at the junction gap between microchannels greatly decreases the required electric breakdown voltage. The experimental results indicate that a protein sample with an extremely low concentration of 1 nM was concentrated to 1.5×104-fold in 60 min using the proposed chip.
Highlights
The development of microfluidic platforms for analyzing chemical and biological samples has increased dramatically in the past decade
A PDMS microfluidic chip bonded on the top of a glass substrate with a surface-pattern printed on a submicronthick Nafion film has been proposed for multiplexed proteomic sample preconcentration, achieving a concentration factor of as high as 104 in 5 min [8]
After nanofractures between microchannels were created after junction gap breakdown under various applied voltages for 5 min, an LCR meter was employed to measure the resistance spectrum under a relative low concentration of Phosphate-buffered saline (PBS) (1 mM) to confirm the formation of nanofractures only
Summary
The development of microfluidic platforms for analyzing chemical and biological samples has increased dramatically in the past decade. A PDMS microfluidic chip bonded on the top of a glass substrate with a surface-pattern printed on a submicronthick Nafion film has been proposed for multiplexed proteomic sample preconcentration, achieving a concentration factor of as high as 104 in 5 min [8].
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