A Simple Microfluidic Chip Design for Fundamental Bioseparation

Hindawi Publishing Corporation Journal of Analytical Methods in Chemistry Volume 2014, Article ID 175457, 6 pages http://dx.doi.org/10.1155/2014/175457 Research Article A Simple Microfluidic Chip Design for Fundamental Bioseparation Alan S. Chan,1,2 Michael K. Danquah,2,3 Dominic Agyei,2 Patrick G. Hartley,1 and Yonggang Zhu1 1 CSIRO Materials Science and Engineering, Highett, VIC 3190, Australia Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia 3 Department of Chemical Engineering, Curtin University of Technology, Sarawak 98009, Malaysia 2 Correspondence should be addressed to Michael K. Danquah; and Yonggang Zhu; Received 23 October 2013; Accepted 12 December 2013; Published 8 January 2014 Academic Editor: Ravichandra Potumarthi Copyright © 2014 Alan S. Chan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A microchip pressure-driven liquid chromatographic system with a packed column has been designed and fabricated by using poly(dimethylsiloxane) (PDMS). The liquid chromatographic column was packed with mesoporous silica beads of Ia3d space group. Separation of dyes and biopolymers was carried out to verify the performance of the chip. A mixture of dyes (fluorescein and rhodamine B) and a biopolymer mixture (10 kDa Dextran and 66 kDa BSA) were separated and the fluorescence technique was employed to detect the movement of the molecules. Fluorescein molecule was a nonretained species and rhodamine B was attached onto silica surface when dye mixture in deionized water was injected into the microchannel. The retention times for dextran molecule and BSA molecule in biopolymer separation experiment were 45 s and 120 s, respectively. Retention factor was estimated to be 3.3 for dextran and 10.4 for BSA. The selectivity was 3.2 and resolution was 10.7. Good separation of dyes and biopolymers was achieved and the chip design was verified. 1. Introduction High-performance liquid chromatography (HPLC) is a widely used separation technique with numerous implementations in both preparative and analytical systems [1–4]. A wide variety of chromatography media available provides different requirements for various molecular separation modes. The miniaturized HPLC system would offer the advantage of smaller sample size, reduction of dead volume, lower solvent consumption, faster, higher-throughput analysis, and portability of the analytical system, enabling on-site and remote analysis [5, 6]. Despite these advantages, miniaturization of chromatographic systems needs to address some technical issues such as fabrication of chip-based chromatographic systems without compromising separation efficiency [6]. One such challenge is the introduction of stationary phase materials into a microfabricated microchannel [7]. Numerous examples of chip-based chromatographic systems in pharmaceutical and biomedical applications have been reviewed extensively [6, 8–10]. Open-tubular liquid chromatography microchips integrated with a sample injector and electrode demonstrated low chromatographic efficiency [11]. The low efficiency could be attributed to small surface area and relatively large injection volume of the system. A microfabricated device with C18 coated channels was used to demonstrate on-chip phase extraction [12]. However, using a separation column packed with beads may yield better separation efficiency because of higher available surface area per unit volume and reduced diffusion distances through the narrow fluid paths between neighbouring particles [13]. Several microchips with porous polymer monoliths formed in channels via photoinitiated polymerization have been reported [14–18]. Reversed-phase silica particles are also widely used as the stationary phase in HPLC and solid-phase 2 Journal of Analytical Methods in Chemistry UV light Microchannel Detection point Mask Substrate Photoresist Flow path Substrate PE membrane Substrate Substrate extraction for preconcentration and separation of analytes or to remove unwanted components from samples [19– 24]. Monolithic silica prepared by sol-gel process has been used as a stationary phase in separation columns by several researchers [25–28]. Wolfe et al. [29] also reported that silica beads packing provides higher extraction efficiency than a silica network synthesized via sol-gel chemistry. The chip preparation technique generally reported in the literature requires a chemical/thermal process and etching on chip for pattern design. The deep reactive ion etching on quartz chips has made the technology too labor intensive and expensive [30]. A number of approaches for particles trapping inside a microchannel have been reported. These are based on magnetic susceptibility [31], flow profile [32], and chemical treatments [33]. However, the easiest integrated method is the use of mechanical barriers that hinder the flow of particles and this could be a dam (horizontal) or pillar (vertical) structure [34]. Dam structure is simple to fabricate, but it limits the flow of liquid dramatically and results in nonuniform flow profiles. Pillar-type bead filters allow uniform liquid flow with smaller flow resistance [35], but microfabrication of pillartype bead reservoirs is very difficult compared to dam type. An additional step in the fabrication process is required to cater for the internal structure inside the channel. Also, in the microfabrication, high precision micromachining must be obtained. In this paper, the fabrication of a cost-effective and easy structured multilayered pressure-driven microchip for reversed-phase liquid chromatography in poly(dimethylsiloxane) (PDMS) is presented. Poly(dimethylsiloxane) (PDMS) is the most dominant polymeric material for microfluidics. This is due to its unique properties such as elastomeric properties, biocompatibility, optical transparency down to A thin layer of nickel A thick layer of nickel Nickel shim Channel pack with mesoporous silica Figure 1: Schematic design of a poly(dimethylsiloxane) microfluidic chip with integrated HPLC column using mesoporous silica. The dimension of the channel cross-section is 70 𝜇m depth and 100 𝜇m width. The diameter of reservoirs and PE membrane port is 2 mm. The silica column dimension was 5 mm long, 70 𝜇m deep, and 100 𝜇m wide. Developed photoresist PDMS PDMS capping layer PDMS Microchannel Figure 2: Schematic drawing of fabrication of nickel shim for microfluidic chip manufacturing. 280 nm, hydrophobic surface chemistry, pliability and ease of molding into micron size, and low manufacturing costs [10]. Reversed-phase mesoporous silica was used as a stationary phase in the bottom layer of the microchip liquid chromatographic system. The silica was trapped in between two polyethylene membranes acting as porous frits. Injection chamber and s (...truncated)