Research On Mixing Characteristics Of A 3D-printed Micromixer And Its Application In Biochemical Sensing

Microfluidics is a technique that allows for the manipulation of fluids at the micro-scale.Complex experiments can be carried out on a microfluidic chip within a size of several square centimeters.Reagents or biological samples can be rapidly mixed,separated,reacted,and detected on the microfluidic chip.Micromixers,a crucial part of microfluidic chips,can effectively mix different reagents and promote biochemical reactions,widely applied in the biochemical sensing field.The mixing performance of micromixers is related to the rate and degree of biochemical reactions,often determining the overall performance of the microfluidic chip.With the development of microfluidic chips towards miniaturization,integration,and high throughput,higher requirements have been put forward for the mixing performance of micromixers.To meet the mixing needs in multi-application scenarios,the micromixer should achieve efficient mixing over a wide working range.Based on the above background,this dissertation presents a high-performance 3D micromixer featuring with helical elements.Utilizing 3D printing technology,the 3D micromixer was fabricated in a low-cost way,and its mixing mechanism and performance were investigated through numerical and experimental methods over an ultra-wide range of Reynolds numbers.The 3D micromixer was then integrated into a microfluidic synthesis platform for high-throughput,tunable,and continuous synthesis of nanocomposites.Furthermore,the performance optimization of nanocomposites was also conducted based on the synthesis platform.Moreover,a microfluidic detection chip was developed with the integration of the 3D micromixer and screen-printed carbon electrodes（SPCE）modified with nanocomposites.Finally,the microfluidic detection chip based on the micromixing technology was applied for the detection of multiple biomarkers and biological samples.The main research contents of the dissertation are as follows:（1）A novel 3D micromixer with a helical microstructure was developed and fabricated using a low-cost 3D printing method.The mixing mechanism and characteristics of the 3D micromixer were investigated through numerical and experimental methods.The mixing performance of the 3D micromixer was studied over an ultra-wide range of flow rates(0.3～70,000μL min^-1,across five orders of magnitude),and the micromixer demonstrated excellent mixing performance with a mixing efficiency of more than 96%for water and more than 85%for high-viscosity solutions（90%v/v ethylene glycol）.Furthermore,the 3D micromixer achieved rapid mixing for aqueous solutions in a short time as low as 2.1 ms.As a result,the3D micromixer can improve the difference in residence time of reagents and greatly enhance homogenous reactions.This work can solve the problem of low throughput and high-cost fabrication for 3D micromixers,greatly broadening the application range of micromixers and shedding new light on the development of high-performance micromixers.（2）A microfluidic synthesis platform for the nanocomposites assisted with micromixing has been developed,innovatively achieving a high-throughput,continuous and controllable synthesis of nanocomposites and significantly improving their electrocatalytic performance.The developed microfluidic synthesis platform can prepare the nanocomposites with a flow rate of up to 15 m L min^-1.The mean size of nanoparticles for the nanocomposites could be readily controlled within the range of 2.4～9.3 nm.Meanwhile,the synthesized nanocomposites exhibit excellent electrocatalytic performance for hydrogen peroxide detection with a wide detection range（1～12,000μM）,high detection sensitivity(304.16μA·m M^-1·cm^-2)and low detection limit（0.3μM）,far superior to those prepared by traditional methods.This work provides a new idea for the synthesis of functional nanocomposites and solves the problem of low-throughput synthesis for nanocomposites,effectively promoting the large-scale production and application of functional nanocomposites.（3）A versatile microfluidic chip for the detection of multiple biomarkers assisted with micromixing has been developed in this work.The developed multiplex microfluidic chip can quantitatively drive the fluid without a pump,just using the method of negative pressure.By integrating a high-performance 3D micromixer and a low-cost SPCE modified with nanocomposites,the microfluidic chip can detect multiple biomarkers in a low-cost,portable and rapid way.The developed multiplex microfluidic chip can simultaneously detect three biomarkers（glucose,lactate and uric acid）.The microfluidic detection chip shows excellent electrochemical performance,with good reproducibility,consistency,long-term stability and selectivity,enabling efficient detection of a wide range of biomarkers.Moreover,the microfluidic detection chip exhibits excellent anti-interference and accuracy for the detection of multiple biomarkers in various biological samples（plasma,saliva and sweat）,demonstrating the feasibility of the microfluidic detection chip for the practical detection of biological samples.This work provides a meaningful reference for the detection of multiple biomarkers based on microfluidic chips and promotes the wide application of microfluidic detection chips in point-of-care testing.