Fabrication And Application Of Micro-nanofluidic Device Based On Microscale Photopolymerization

Nanofluid-based electrokinetic enrichment is a high efficient technology, which can be used to concentrate trace charged samples locally in microfluidic chips, and the premise of this technology is to realize the integration manufacturing of micro-nano structures in a same chip. In this paper, a simple method for fabricating micro-nanofluidic chips based on microscale photopolymerization has been developed, and electrokinetic enrichment experiments of trace samples have been conducted utilizing the made chips. The main contents are as follows:A theoretical model describing photopolymerization reaction, including photo initiator decomposition, radical consumption, polymerization, etc., was established and COMSOL software was utilized to calculate and analyze the gel photopolymerization process in microscale. The influences of exposure time and light intensity on gel nanosieve width were investigated.With an inverted fluorescence microscope, a pore density and overall size both controllable gel nanosieve was fabricated and integrated into a specific area of the microchannel through the photopolymerization of polyacrylamide gel, forming a micro-nanofluidic chip. In addition, the gels were characterized to verify the influence of the gel precursor composition on the nanopore density. And the effects of factors such as channel geometry size, exposure time, shading mask, surrounding light source, etc., on the fabrication of gel nanosieves were discussed.Performance tests of the made micro-nanofluidic chips were carried out, and nanofluid-based electrokinetic enrichment experiments of trace fluorescein isothiocyanate (FITC) small molecules and bovine serum albumin (BSA) macromolecules were conducted respectively to test the enrichment effects of the chips for different diameters of charged molecules. For FITC, when the mass ratio of the monomer acrylamide to the crosslinker N,N’-methylene bisacrylamide in the gel precursor was19:1, the fluorescence intensity in the enrichment zone changed unobviously, and when the mass ratios of the monomer to the crosslinker were14:1and9:1respectively, the maximum fluorescence intensity of the latter was significantly higher than that of the former. The largest enrichment ratio of FITC could reach600-fod as the mass ratio of the monomer to the crosslinker was9:1. In addition, electrokinetic enrichment experiment of BSA was conducted utilizing the made micro-nanofluidic chip and a high enrichment ratio of a hundred million fold was achieved.To further explore the relationship between the flow characteristics of micro-nanofluid and the nanostructure feature sizes, I-V curves and AC impedance spectroscopies of gel. nanosieves with different mass ratios of the monomer to the crosslinker were measured. Within the I-V curves, the relationship between currents and voltages was nonlinear, and the peak currents were proportional to the gel nanopore densities. Smaller the nanopore density, bigger the peak current. Within the AC impedance spectroscopies, the impedances were also proportional to the gel nanopore densities for low frequencies, and smaller the nanopore density, smaller the impedance value.