Research On Electrokinetic Nanofluid Enrichment Method In Micro-nanofluidic Chips

Characteristic dimension of nanofluid locates between study scales of quantum mechanics and microfluid dynamics, when combining nanofluid with microfluid, trace injection, high-fold enrichment, purification, rapid separation of DNA and other functions are achieved through utilizing scale-span effects generated by the transition of such physical characteristics as flow resistance and electric double layer, which is resulted from confinement change of micro-nanostructure characteristic size. Now, electrokinetic nanofluid enrichment in micro-nanofluidic chips is one of the focus, million-fold preconcentration of many protein molecules and thousand-fold or so of charged small molecules are obtained to improve system detecting sensitivity utilizing a variety of micro-nanofluidic chips. Electrokinetic nanofluid enrichment has been applied to immunoassay, enzyme reaction and many other aspects, and may be used for the detection of trace markers in cancer’s early stage. However, mechanism study of electrokinetic nanofluid enrichment is still in its infancy and fabricating process of high density nanostructures integrated with microstructures is lacking, which severely affect the performance of electrokinetic nanofluid enrichment. To counter the problems above, enrichment process based on electrokinetic nanofluid in the micro-nanochannel structure is analyzed through a numerical calculation method and the influences of the parameters related to electrokinetic nanofluid enrichment on enrichment performance are researched, then a variety of methods are employed to fabricate micro-nanofluidic chips with different substrates and electrokinetic nanofluid enrichment with high enrichment ratio and good stability is implemented, main contents are as follows:First, a model coupling Poisson-Nernst-Planck and Navier-Stokes equations is builded to describe electrokinetic nanofluid enrichment process, the relative flux of electrophoresis-electroosmotic flow as an index is employed to measure the ratio of electrokinetic ion enrichment, the influences of the viscosity, the external voltage, the charge density of micro-nano wall, the nanochannel density, the nanochannel depth on enrichment ratio are analyzed, the results show that high enrichment ratio can be obtained by improving the relative flux of electrophoresis-electroosmotic flow, the measures for improving the ralative flux include improving the fluid viscosity, increasing the external voltage, enhancing the charge density of micro-nano wall, deepening the nanochannel depth and boosting the nanochannel density. Second, a method for fabricating glass micro-nanofluidic chips with polyacrylamide gel is presented, micromachining techniques (such as photolithography, etching and thermal bonding) and photopolymerization reaction of polyacrylamide gel are utilized to fabricate a polyacrylamide gel plug integrated in glass microchannels and then gel-glass micro-nanofluidic chips are obtained. Polyacrylamide gel plugs of three proportions (the ratios of acrylamide and bisacrylamide are19:1,14:1,9:1) are developed, with the increasing of bisacrylamide proportion (19:1,14:1,9:1), pore size of polyacrylamide gel reduces, pore density increases from1.2to2.4number/100μm2. Nine array planar nanochannels are fabricated on the PMMA substrate through utilizing plasma etching methods and then PMMA micro-nanofluidic chips are obtained combining with a thermal bonding technology.Third, enrichment experiments based on electrokinetic nanofluid are developed utilizing a laser induced fluorescence method, the effects of the nanopore density and the applied voltage on enrichment performance based on electrokinetic nanofluid are considered. The results show that enlarging nanopore density and increasing the applied voltage in a certain range are contributed to improving enrichment ratio,600-fold enrichment ratio for lOnM FITC ions and higher enrichment ratio for bovine serum albumin labeled with0.002ng/ml FITC are achieved. An approach of ion enrichment driven by electrochemical potential is presented, electrochemical potential is generated utilizing reducibility difference of different electrodes, ion enrichment experiments in micro-nanofluidic chips are achieved under conditions in which no external power was provided, fluorescence intensities of ion enrichment based on Al-Pt, Fe-Pt and Cu-Pt electrodes are40.2,27.1and15.0respectively. Enrichment application experiment of electrokinetic nanofluid for antigen-antibody immunoassay is developed, the rabbit IgG FITC-labeled and sheep anti-rabbit IgG coupling with magnetic beads are adopted as the antigen and antibody of immunoassay reaction respectively. Through placing magnetic microbeads at the enrichment end of the gel, an overlapping zone for enrichment and immunoassay is achieved to improve immunoassay efficiency. Combination amount of the antigens and antibodies is improved and then fluorescence intensity of immunoassay reaction is enhanced by sixty percent through concentrating the antigens of low concentration, detection limits of antigen protein can be improved hopefully.