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There are two main challenges in integrating microelectrodes on polymer microfluidic chips.One of the primary challenges is the incompatibility of polymers and photolithographic techniques.While photolithography is most widely used to fabricate microelectrodes on silicon or glass substrates,it is not compatible with thermoplastic polymers in chemical and thermal properties.We developed a method based on modified photolithography and wet etching for fabricating corrosible metal electrodes on poly(methyl methacrylate) (PMMA) substrates,such as Cu or Ag electrodes,and another method based on modified lift-off processes for fabricating inert metal electrodes,such as Pt or Au electrodes.Moreover,monolithic integration of three-material microelectrodes for electrochemical detection on PMMA substrates was also presented.Au-Ag-Pt and C-Ag-Pt three-electrode systems were demonstrated (Fig.1).Another major challenge is the chip bonding.Fracture of integrated microelectrodes likely happens during the thermal bonding process of polymer microfluidic chips.The fracture behavior and mechanism were studied,and a plasma assisted thermal bonding method was evaluated and first used to eliminate the fracture of microelectrodes.Based on the methods for fabricating microelectrodes and bonding chips,two kinds of microchips were fabricated.A PMMA electrophoresis microchip integrated with Pt microelectrodes for contactless conductivity detection was constructed (Fig.2),and a low limit of detection and high separation efficiencies were obtained.Another PMMA/poly(dimethylsiloxane) electrochemical sensing microchip with Au-Ag-Pt three-electrode systems was made.The characteristics of the three-electrode system and the performance of the microchip were evaluated.