High-efficiency Fabrication Of Multifunctional Glass Microfluidic Devices Using Ultrafast Laser-assisted Chemical Etching

Microfluidics provides an effective approach for multi-functional and precise manipulation of small volumes of fluids in a micron-scale confined environment.As one of the representative processing substrates in microfluidics,glass has good chemical stability,optical transparency,and biocompatibility.At present,the controllable fabrication of two-dimensional glass microfluidic structures can be well prepared by conventional planar photolithographic methods.However,the fabrication of the glass microchannel structures with three-dimensional(3D)configurations using above-mentioned methods often requires multi-step bonding of the patterned substrate,which increases the complexity and cost of the fabrication procedure.As a nonlinear optical processing method,femtosecond(fs)laser micromachining has unique advantages such as 3D volume processing of transparent materials,beyond the diffraction limit processing,and multi-functional integration.For glass microstructuring,fs laser-assisted chemical etching allows the bonding-free fabrication of 3D hollow microstructures with flexible configurations.However,the etching rate of the conventional fs laser-modified tracks usually exhibits a significant dependence on laser polarization,which is difficult to directly realize the microchannel fabrication with 3D uniform etching.Although currently some methods such as temporal pulse shaping,dynamic polarization control,and circular polarization have been proposed to achieve isotropic etching in microchannel fabrication,some limitations still exist in terms of the complexity,flexibility of the related fabrication procedures,as well as fabrication efficiency in practical application.To this end,this thesis has explored the highefficiency microfabrication technique for multi-functional glass microfluidic devices using polarization-insensitive high-rate spatially selective etching in the specific picosecond pulse range.Moreover,a 3D glass high-efficiency micro-mixer was fabricated,and the multi-functional temperature-controlled glass microfluidic device was fabricated based on the ultrafast laser-assisted chemical etching combined with chemical metal plating and mechanical polishing.The innovative results obtained in this thesis are as follows:1.Polarization-insensitive high-rate spatially selective etching has been achieved using picosecond(ps)laser.By adjusting the time-domain pulse width to the specific ps,the periodic nanogratings induced by conventional fs laser pulses in the laser irradiation area can be transformed into nanocracks that preferentially extend along the direct laser writing direction,thereby achieving polarization-insensitive high rate nearly isotropic etching.At the same time,the special multi-pulse incubation mechanism induced by time-domain controlled ultrafast laser was studied by lateral pump-probe microscopy.The proposed approach is beneficial for the high-performance manufacturing of large-scale glass microfluidic structures and 3D glass high-precision printing.2.Through the combination of polarization-insensitive spatial selective etching and extra-access ports enhanced etching,a 3D microchannel mixer based on Baker's transformation principle is fabricated inside the fused silica glass.Numerical simulation and experimental results confirm that the fabricated mixer has a high mixing efficiency.The introduction of extra-access port enhanced the fabrication efficiency of the micromixer and ensured the uniformity of the size of the mixing unit.The online and efficient synthesis of gold nanoparticles by using the fabricated micromixer is demonstrated.Compared with the existing fabrication methods for 3D glass microfluidic devices,this method allow the customized manufacture of microfluidic devices with highly controllable size and configuration inside the glass without multi-step bonding or special porous glass materials.3.By combining ultrafast laser-assisted chemical etching with continuous flow chemical plating and mechanical polishing,multifunctional embedded microthermal microcomponents have been fabricated on the glass surface and the monolithic integration of temperature-controlled microfluidic devices has been realized.Firstly,continuous flow electroless plating and mechanical polishing can be used to realize the fabrication of embedded conductive metal microstructures in the grooves on the glass surface,and then micro-heaters of different sizes and configurations can be fabricated to achieve efficient and controllable heating in small areas.Flexible fabrication of microheaters arrays,customized temperature control,and on-chip sensing integration have been demonstrated.Further,by integrating microfluidic elements on the same substrate,precise temperature control of microfluidic channels and acceleration of chemical reactions have been achieved.Compared with planar microthermal components prepared by traditional technology,thermal control components based on embedded metal microstructures have superior advantages in terms of their capabilities for long-term operation,spatial temperature control,and multi-functional integration.