Preparation And Application Of Low-cost,Impermeability Paper-based Microfluidic Chips Based On Inkjet Printing

Microfluidic chips had many significant advantages in food safety,disease screening and environmental protection due to their miniaturization,integration,and portability.Compared with other artificial synthetic substrates?such as plastic,silicon,glass,etc.?,paper was regarded as an attractive and promising substrate for the construction of pump-free microfluidic chips due to its biochemical compatibility,natural capillary effect,lightweight,sustainability,mature processability,and high chemical reactivity.So far,a series of methods such as photolithography,wax printing,etching,inkjet printing,for constructing paper-based microfluidics had been reported and successfully used in medical,food and environmental and other fields.Aiming at the scientific problems in the existing methods such as the retention of the test liquid during channel transportation,which led to low sample transport efficiency,and some hydrophobic substances were therefore difficult to form a sufficient hydrophobic barrier.Herein,we reported a straightforward method from the papermaking technique for the fabrication of paper-based microfluidic chips by the integration of surface processing technology and inkjet printing technology to make the chips truly cost-effective and prevent the test liquid from excessively penetrating the paper while further reducing the amount of test samples.The main research results were as follows:First,as-prepared cellulose paper was used as the substrate of the paper-based microfluidic chips.Based on internal and surface sizing methods,and taking the permeability and diffusion properties of the liquid in the channel as the evaluation criteria,the optimized preparation process of paper-based microfluidic chips was obtained:cellulose paper?preset basis weight of80 g/m²?was prepared from eucalyptus sulfate pulp,and the surface sizing compound was prepared by Alkyl Ketene Dimer?AKD?and modified cassava starch at an absolute dry ratio of 3:7.The mixture of AKD and cassava starch was precoated onto the cellulose substrate via a rod coating method,which endowed the paper with a hydrophobic surface?water contact angle of 128±2°?.The coated samples were dried in a hot-air dryer at 105?and calendered under a pressure of 2 MPa with a roller speed of 3.5 m/min before inkjet printing.Then,a customized ink was prepared by slowly dissolving the Bis?2-ethylhexyl?sulfosuccinate sodium salt into a diluted ethanol solution?50%?at a ratio of 1:1.A prefabricated ink based on commercial surfactant solution was applied onto the paper surface to construct the hydrophilic microchannels?water contact angle of 7±2°?by inkjet printing,which achieved the basic functions of a paper-based microfluidic chip.In this study,Scanning Electron Microscope?SEM?,Fourier Transform Infrared Spectrometer?FTIR?,and Laser Scanning Confocal Microscope?LSCM?were used to characterize the surface morphology,chemical structure of the paper,and liquid penetration in the channel.The linear fit of channel printing accuracy reached 0.9987,showing a highly smooth edge.And the results showed that the liquid transport rate increased with the increase of the channel width.The average liquid flow rate could reach 1.43 mm/s in a channel with width of 1200?m.If the designed paper-based chip was as small as possible,the minimum width channel constructed for liquid flowing by this method could reach 500?m.In addition,the formed hydrophobic barrier exhibited superior liquid-limiting properties for solutions with a surface tension greater than 40 m N/m,and the aqueous solution could be well confined to the upper surface layer of the paper?depth?93.66±3.11?m?.Meanwhile,in order to ensure a good liquid flowing effect in the channel,the lower layer(Cobb₆₀=19.1 g/m²)still showed a certain degree of impermeability to prevent the solution from completely penetrating,which was beneficial to reduce the loss of the solution.Compared with related work,surface treatment and inkjet printing methods with low-cost fabrication process,the paper-based chips showed better comprehensive advantages in terms of cost,production efficiency,resolution,diffusion resistance and degradation.To verify the practicality of the paper-based chip in nitrite detection applications,a circular detection area with a diameter of 4.5 mm was designed.When the amount of Griess reagent and test liquid was set to 2.5?L,the color display effect was best.The correlation between test results and the nitrite concentration?0.027?0.87 m M?was determined by evaluating the color density and color difference,which has been demonstrated with high correlation coefficients of R²=0.9985 and R²=0.994.According to the fitting equation,semi-quantitative analysis could be utilized in practical applications.From the trend of fitting curves,the limit of detection in nitrite was lower than 0.027 m M,which had good detection accuracy and quick response in the existing work.Moreover,to ensure the availability of the reaction results,the chips loaded Griess reagent were stored in a refrigerated room sealed at about 3?.