A three-layer PMMA electrophoresis microchip with Pt microelectrodes insulated by a thin film for contactless conductivity detection

• Published in: Lab on a chip 2011-03, Vol.11 (5), p.969-973
• Main Authors: Liu, Junshan, Wang, Junyao, Chen, Zuanguang, Yu, Yong, Yang, Xiujuan, Zhang, Xianbin, Xu, Zheng, Liu, Chong
• Format: Article
• Language: English
• Subjects: Channels; Electric Conductivity; Electrophoresis; Electrophoresis, Microchip - instrumentation; Insulating layers; Microelectrodes; Plates (structural members); Platinum; Platinum - chemistry; Polymethyl Methacrylate - chemistry; Polymethyl methacrylates; Systems Integration; Thin films
• ISSN: 1473-0197; 1473-0189
• DOI: 10.1039/c0lc00341g

A three-layer poly (methyl methacrylate) (PMMA) electrophoresis microchip integrated with Pt microelectrodes for contactless conductivity detection is presented. A 50 μm-thick PMMA film is used as the insulating layer and placed between the channel plate (containing the microchannel) and the electrode plate (containing the microelectrode). The three-layer structure facilitates the achievement of a thin insulating layer, obviates the difficulty of integrating microelectrodes on a thin film, and does not compromise the integration of microchips. To overcome the thermal and chemical incompatibilities of polymers and photolithographic techniques, a modified lift-off process was developed to integrate Pt microelectrodes onto the PMMA substrate. A novel two-step bonding method was created to assemble the complete PMMA microchip. A low limit of detection of 1.25 μg ml(-1) for Na(+) and high separation efficiency of 77,000 and 48,000 plates/m for Na(+) and K(+) were obtained when operating the detector at a low excitation frequency of 60 kHz.