Capillary Forces Drived Microfluidic Chips And Its Application In POCT

POCT(point-of-care testing)has attracted broad attention recently.One of the restrictions of POCT developing is high instruments cost.Costly instruments or customized devices were often used during POCT.Microfluidic chip is one of the most potential strategy to realize POCT.However high instruments cost,especially the instruments need for pump aqueous solution restricted the Microfluidic chip apply in POCT,Capillary forces based microfluidic pump lies great poteincial in solving this problem,recently there emerged many Capillary forces based microfluidic chips(paper chips et.al),Recently traditional paper chips presenced insignificance as unable to quantify,low sensitivity.In this dissertation,we fabricated four micfluidic chips based on capillary forces,the detailed research content as follows:(1)2D channel regulation:We fabricated the vertical paper microfluidic devices(vPADs)using the principle of quilling and kirigami.What differentiates the vPADs from conventional paper microfluidic devices is that the paper substrate used to fabricate the device is vertical to the device plane.The fabrication of vPADs with high precision is instrument-free,requiring no photolithography,printing or heating.Two-and three-dimensional vPADs are fabricated for multiplex colorimetric assays of four biochemical indicators and automated enzyme-linked immunosorbent assay of human myoglobin,respectively.(2)3D channel regulation(micro scale):We introduced a bottom-up method for high-resolution fabrication of microfluidic paper analytical devices(μPADs).An aqueous suspension of cellulose microfibers is used as the starting material,and it is filled into hollow channel template that is fabricated by inkjet-printing of wax on a polypropylene substrate.After water evaporation,the cellulose microfibers form a porous,hydrophilic,paper microchannel in the template which wicks aqueous solution by capillary action.This method enables simple,fast,inexpensive fabrication of μPADs with mininum channel width of 10 μm,using this method,μPADs for multiplexed,colorimetric detection of glucose and BSA are fabricated,and only 0.30 μL of sample is required for the assay due to the small volume of the microchannel.(3)3D channel regulation(nano scale):We fabricated a pseudo-paper microfluidic chip based on patterned photonic nitrocellulose.The photonic nitrocellulose is fabricated using self-assembled monodisperse SiO2 nanoparticles as template.The SiO2 nanoparticles form a photonic crystal having close-packed hexagonal structure in the microchannels,so the resulted nitrocellulose has complementary inverse-opal structure.After lamination,a hollow channel is obtained which is partially filled with the photonic nitrocellulose.Owing to the highly-ordered photonic structure of the pseudo-paper chip,the flow profile of aqueous solution wicking through the channel is more uniform than conventional paper mierofluidic chip.It is also found that the wicking rate of aqueous solution can be easily manipulated by changing the diameter of the self-assembled monodisperse SiO2 nanoparticles which determines the pore size of the photonic nitrocellulose.The fluorescent enhancement property of the photonic nitrocellulose is used to increase the fluorescent intensity for multiplex detection of two cancer biomarkers.Label-free detection of human immunoglobin G based on the structure color of the photonic nitrocellulose is also demonstrated.(4)Instrument optimization:We introduced a method for quantitative point-of-care sensing using a forehead thermometer as the readout.The method is based on a fluidic chip having a capillary channel that directs an aqueous sample into an exothermic reservoir.NaOH powders are preloaded in the reservoir as the exothermic reagent.At the inlet of the capillary channel,a microvalve is fabricated using aptamer-modified hydrogel which is responsive to a specific analyte.When the aqueous sample comes in contact with the hydrogel valve,the hydrogel shrinks due to the selective analyte-hydrogel interaction.The volume reduction of the hydrogel increases the capillary flow rate,and thus increases the heat produced by the NaOH dissolution.A forehead thermometer is used to measure the temperature increment which is correlated to the analyte concentration.Using this method,mercury ions(Hg2+,Pb2+)in different real samples are quantified.