Short communicationOne-stage fabrication of sub-micron hydrophilic microchannels on PDMS
Introduction
Microchannel chip technology has been employed in many fields, especially in chemical and biological analysis. The development of microchannel fabrication has received large attention. The micromation and high performance of microchannel have a higher demand for the substrate properties [1], [2].
Polymeric materials such as poly(methylmethacrylate) (PMMA), polystyrene, polycarbonate (PC), polyurethane, and poly(dimethylsiloxane) (PDMS) have been widely used as the substrate materials for microchannels. Among them, PDMS has received more attention due to its outstanding performances such as transparency, high permeability to gases, high elasticity, easy processing and seals the channel readily, etc. [3]. Nevertheless, PDMS is extremely hydrophobic, which makes it very difficult for aqueous solutions to flow inside the microchannels. In addition, the absorption function of PDMS surface may generate fouling on the surface. The hydrophobicity has long been the bottleneck to the application of PDMS as a microchannel material [3], [4]. Because of this, different approaches, such as oxygen plasmas [5], ultraviolet light (UV) [6], corona discharges [7] and so on [8] have been employed to modify PDMS to obtain a hydrophilic surface. In all these approaches, the microchannels were produced firstly, then the microchannel surfaces modified indicating a time-consuming and complicated process. What's more, the hydrophilicity of the PDMS surface thus obtained will not last long, say three weeks. In this communication, a relatively simple method, i.e., one-stage fabrication of microchannels was reported, using vacuum ultraviolet light (VUV) lithography in vacuum. As demonstrated below, the hydrophilicity on the PDMS surface can be kept for a longer term after the treatment.
Section snippets
Experimental
Sylgard 184, consisting of poly(dimethylsiloxane) and a reinforcing silica filler was prepared by carefully mixing the precursors Sylgard 184 A/B at a ratio of 10:1 by mass. The PDMS precursors were then spin-coated onto the cleaned glass coverslips at 5000 rps using the spincoater [9]. The resultant PDMS thin films were then degassed under vacuum and cured in an oven at 70 °C for 3 h to produce cross-linked PDMS. Then the PDMS films under a closely contacted photomask, which consisted of a 3-mm
Results and discussion
The topographies and properties of the irradiated PDMS surface were characterized and analyzed by atomic force microscopy (AFM) with the IC mode (Fig. 1).
As clearly shown in the AFM height image (Fig. 1, left), the height in different sub-micron areas was different. Interlaced microchannel network was clearly formed on the PDMS surface. The bright and dark regions in the AFM image correspond to the irradiated and the masked areas, respectively. The width of the microchannel was 500 nm. The etch
Conclusions
In conclusion, sub-micron hydrophilic microchannels can be fabricated by vacuum ultraviolet light (172 nm) lithography. XPS analysis showed that the chemical composition of the microchannel surface was changed, and a silicon oxide glass-like cross-linking structure may be formed, which can prevent the movement of hydrophilic groups from the surface to the bulk and thereby gives rise to the longer hydrophilicity of the microchannel surface.
Acknowledgements
This work was supported by the National Natural Science Foundation (90606013,20634030), the Ministry of Education (107080, NCET0606055) of China and the Scientific Research Foundation for the Returned Overseas Chinese Scholars (SEM).
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