Integrating Carbon Nanotubes into Microfluidic Chips for Separating Biochemical Compounds
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Integrating Carbon Nanotubes into Microfluidic Chips for Separating Biochemical Compounds Miaoxiang Chen1,2, Klaus B. Mogensen1, Peter Boggild1 and Jörg P. Kutter1 1
Department of Micro and Nanotechnology, Technical University of Denmark,
2800 Kgs. Lyngby, Denmark. 2
International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga, 4715-310 Braga,
Portugal. E-mail: [email protected] Keywords: Carbon Nanotubes, Stationary Phase, Microfluidics ABSTRACT We present a new type of device to separate biochemical compounds wherein carbon nanotubes (CNTs) are integrated as chromatographic stationary phase. The CNTs were directly grown on the bottom of microfluidic channels on Si/SiO2 substrate by chemical vapor deposition (CVD). Acetylene was used as carbon source and Ni was employed as catalyst. For electrokinetic separations, higher electrical field strength is usually required; therefore, the CNTs were constructed in pillar-array-form by patterning Ni catalyst layer. Electrical field strength of 2.0 kV/cm has been realized, which is more than one order of magnitude higher than the one reported so far. The microfluidic chips integrated with CNTs were successfully used to separate a compound containing two Coumarin dyes, 240 mM C460 and 270 mM C480. INTRODUCTION Over the past decade, the integration and miniaturization of chip-based analytical systems have been enormously developed [1]. Microchip electrophoresis combining with liquid chromatography is emerging as a promising separation technique to analyze biochemical compounds [2]. The mechanism of the separation technique is to employ a stationary phase to interact with solutes with different degrees for different molecules. In the research, main challenge presently is to discover more robust and powerful stationary phases which can be technologically integrated into microfluidic channels. CNTs are very promising as a new stationary phase owing to their high hydrophobicity, surface-to-volume ratio, chemical stability and outstanding mechanical strength. Additionally, their growth processes are compatible with micro fabrication techniques. Carbon-based materials have been employed as stationary phase in capillary electrophoretic and microfluidic devices for separation [3]. In these studies, the CNTs were typically incorporated in a porous rod [4], immobilized on the inner channel wall [5] or deposited on the surface of beads that subsequently were packed [6]. Recently, a few research works on growing CNTs in microfluidic channels for electrokinetic separations have been reported [7,8]. To date the main challenge to employ CNTs
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as stationary phase is the limitation of the electrical field strength (E) before bubble formation from electrolysis due to the metallic characterization of CNTs. The maximum E reported so far is around 150 V/cm, which puts a severe limitation on the fluid velocity that can be used. The low fluid velocities result in larger plate heights than optimal ones due to peak broadening from diffusion. In our work presented here, the maxi
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