Research On The Fabrication Of Functional Devices In Microfluidic Chips

In1990, Manz and Widmer in Swiss proposed a concept of Miniaturized TotalAnalysis Systems （μTAS） firstly, in order to develop sample analysis and teston the integrated microregion. At the same time, the microfluidic chip becamethe research hotspot for μTAS. With the rapid development ofμTAS, thisadvanced technology has attracted much attention, especially for academia andindustry. Microfluidic systems, which have a lot of distinct advantages, havebeen intensively investigated due to their broad applications in chemistry,physics, biology and medicine. Thus it shows a significant impact on thedevelopment of science and technology progress. Recently, triggered by thematerial science and micronanofabrication techniques, microfluidic chips withhigh performance, bio-compatibility, high flux, high integrated, and evencomplex three dimensional interconnected structures are desired. Generally,two-dimensional （2D） microfluidic chips are readily created by technologiessuch as e-beam, X-ray lithographies, soft lithography and LIGA. However, thefabrication of three-dimensional （3D） microchip is still difficult despitesome success examples.With the development of micro electro-mechanical system,the size of2Dmicrofluidic channel has reached micron range, however, it seems to belimitation. It’s still changing to obtain higher dimensional precision andmore complex three dimensional structures. Femtosecond laser micro-nanofabrication shows the capability to solve this problem. Especially,femtosecond laser direct writing technique holds great perspective for on-chipintegration of designable3D microstructures towards chip functionalization,such as3D microchannel. We call this fabrication progress “the second fabrication”. Here, we present the fabrication of functional devices to endowgeneral microfluidic chips with newly integrated multifunctions.Experimentally, a glass microfluidic chip with a cross shaped channel wasfabricated by traditional wet etching technology. Then it was coated withnegative resin SU-82075for further fabrication of flow divider. The bufferHF-NH₄F-H2O （BHF） solution was prepared by dissolving2g of ammonium fluoridein Hydrofluoric acid2.6%（pH=6.0）. We get a cross shaped microchannel witha depth of20μm, and a width of80μm using metal film pattern, thereforewe have mastered the principle of wet-eching. As the experimental resultsproved, anneal was the critical procedure in the whole fabrication process.After that, we fabricated polymer flow divider by two-photon absorptionreaction--focusing femtosecond laser on the resin over the cross shapedchannel. The process was pre-programmed to scan point by point on the coverglasses and it was recorded by a CCD camera. In the flow tests, two kinds ofliquids including Rhodamine B and Methylene blue solution can flowrespectively in the cross shaped microchannel without any interference,indicating the3D microchannel flowing capability.Notably, femtosecond laser micro-nano machining technology shows greatpotential for on-chip integration of designable3D microstructures towardschip functionalization. With the help of femtosecond laser direct writing,various microdevices could be embellished inside microfluidic channels.Femtosecond laser fabrication holds great perspective for chipfunctionalization and integration in the future.