外文翻译-- A Novel Application of Ferrofluid Actuation with PDMS Microchannel.pdf

A Novel Application of Ferrofluid Actuation with PDMS Microchannel Yaw-Jen Chang1,*, Chih-Yu Hu2, and Chu-Hsuan Lin1 1Department of Mechanical Engineering, Chung Yuan Christian University, Taiwan, R.O.C. 2Department of Biological Science and Technology, Chung Hwa University of Medical Technology, Taiwan, R.O.C. e-mail: justin@cycu.edu.tw Abstract—Ferrofluid is usually used as actuation medium in micropump or microvalve where most microchannels were fabricated with PMMA or silicon. The manufacturing is time-consuming and costly. In this paper, we present a novel microchip design based on the magnetic actuation of ferrofluid. The device contains plugs and pistons formed by a ferrofluid which is actuated by an external NdFeB permanent magnet. The ferrofluid used for this application is a colloidal suspension of nanosize Fe3O4 particles in a carrier fluid that is mixed with silicone oil and hexane. The microchannel was fabricated by Poly (dimethylsiloxane) (PDMS) with four reaction zones. The experimental result shows that the ferrofluidic actuation of fluid in the PDMS microchannel was feasible. However, leakage and swelling in the PDMS microchannel might lead to fluid actuation problems. The result also reveals that it has potential application in biochip. Keywords- ferrofluid; microchip; protein chip; PDMS channel; micropump. I. INTRODUCTION A completely miniaturized and integrated system is expected to achieve the function of micro total analysis, low cost, reduced operation error, and higher throughput. Recently, the development of lab-on-a-chip (LOC) for medical researches, biochemical analyses, and clinical diagnoses has evoked great research interests. Both micropump and microvalve play important roles on LOC. They drive and control fluid to reaction zones on chip and profit measurement or inspection. For the sake of taking the cost and convenience into account, ferrofluid has more applications in the recent years. The use of ferrofluid is an innovative actuation method for fluid handling. There are some relative papers that described the applications of ferrofluid for microvalve. Pérez-Castillejos et al. [1] reported the magnetic valving action of a ferrofluidic plug in a microfluidic system. Menz [2] presented microfluidic systems containing ferrofluids displaced with mobile magnets. Herb [3] designed many different types of microchannels with microvalve and micropump of ferrofluid to control the fluid. On the aspect of micropump, Hatch et al. [4, 5] reported a micropumps based on the pumping and valving action of a rotary plug of the ferrofluid in the circular channel. Yamahata [6] presented a micropump based on ferrofluid in a various layers of polymethylmethacrylate(PMMA) channel. Kim [7] designed a new microfluidic system to pump and control fluid by ferrofluid without any contamination by means of the diaphragm structure. Sun [8] presented a close-loop circular ferrofluid driven micropump for rapid PCR. Atzlesberger [9] reported the use of ferrofluid in a centrifugal micropump that was fabricated in LTCC technology. Ferrofluid were also used in other applications. Greivell [10] realized an electromagnetically actuated ferrofluid micropipette. Tsai [11] reported the mixing phenomena between ferro-nanofluid and water in a Y-type semi-active micromixer. Mao [12] presented a novel mixing device based on water-based ferrofluids to be a biosensor. According to the aforementioned applications of ferrofluid, most microchannels were fabricated with PMMA or silicon wafer. The manufacturing is time-consuming and costly. In this paper, we present a novel microchip design with PDMS microchannel adhered to glass substrate to form four reaction zones. The advantages of using PDMS channel include simple fabrication process, lower cost, and rapid replication. In addition, it has good biological compatibility, nontoxic feature, low surface tension, and no surface shear viscosity. Ferrofluid was injected inside the circular PDMS microchannel and an external magnet was used to drive a small ferrofluid plug for pumping the microfluid (reagent) to the reaction zones. The pumping principle is shown in Fig. 1 [1]. The number of pumping cycles can be controlled by the rotation of magnet which is manipulated by stepper motor. The microchip does not require any complicated moving parts. The fabrication process is simple. It can be used as protein chip for performing immunoreactions. However, PDMS usually has leakage problem. Except the PDMS’s innate self-adhesion, additional mechanical jigs are proper tools to solve this problem [13]. The motivation of this paper is to investigate the feasibility of PDMS microchannel incorporating with the ferrofluidic actuation. The experimental setup and results are discussed below. 978-1-4244-4713-8/10/$25.00 ©2010 IEEE Fig. 1 Pumping principle [1] II. MATERIALS AND FABRICATION PROCESS Ferrofluids are colloidal suspensions of nanosize magnetic particles in an organic or aqueous medium. The magnetic particles are coated with a surfactant layer to prevent agglomeration due to the short-range van der Waals force between individual particles. These suspensions are stable and preserve their properties at extreme temperatures and over a long period of time. In this paper, the carrier liquid of ferrofluid is the mixture of silicone oil and hexane, which is immiscible with the water. The PDMS microchannel consists of one circular channel, four reaction zones, as illustrated in Fig. 2. The width and depth of circular channel are 2 mm and 500 μm, respectively, with inner radius of 7.5 mm. Thus, the volume of the circular channel is 53.4 μl. The dimension of each reaction zone is 14 mm × 7 mm. Fig. 2 The top view of the PDMS channel. The material of PDMS was chosen due to its aforementioned properties. The microchannel was fabricated by casting PDMS in a bakelite mold. The fabrication steps are elaborated as follows. Fig. 3 shows the procedure. Fig. 3 The fabrication procedure of PDMS microchannel 2.1. The fabrication procedure of PDMS microchannel PDMS elastomer consists of base and curing agent. The two components must be thoroughly mixed using a volume ratio of 8:1. The channel mold is spread with the mixture of silicone oil and toluene before PDMS mixture is poured. Then, the mold is put in vacuum chamber of oven for de-airing such that there are no bubbles in PDMS mixture. Finally, the PDMS mixture is cured at 50°C in an oven for 4 hours. Once cured, the PDMS microchannel is carefully peeled off from the channel mold. The channel mold is reusable to fabricate more PDMS microchannels. 2.2. Bonding of PDMS microchannel and chip The leakage in bonding of PDMS microchannel and glass substrate is an important problem that we have to solve. If PDMS microchannel cannot adhere to substrate tightly, the fluid (reagent) may outflow. It might significantly influence the result of analysis. In this study, the PDMS microchannel can adhere to the surface of substrate by physical absorption. However, we also covered an additional glass template on it and used nonstaple-stapler to make PDMS microchannel and glass substrate adhering more tightly. Fig. 4 shows the microchip. 2.3. Setup of motor platform Permanent NdFeB magnet was used to act as the stationary magnet (diameter: 3 mm, thickness: 7 mm) and the revolving magnet (diameter: 3.9 mm, thickness: 12.5 mm). The revolving magnet was affixed to a PMMA rotor, which was attached to a stepper motor that was powered with a 5V external power supply. The assembly of the revolving magnet was visually aligned with the circular channel of the chip. A stepper motor is installed under the PMMA platform to drive the magnet of Reactive zone Circular channel the rotor. Finally, we used LABVIEW software to control the rotating speed of stepper motor. Fig. 4 The final bonding of PDMS microchannel and chip III. EXPERIMENTAL RESULTS AND DISCUSSIONS To test the performance of PDMS micropump, red dye was used for experiments. First of all, water was injected into the circular microchannel and filled with the entire channel. Next, the ferrofluid was injected into the circular microchannel whose volume was about 8.901 μl and attracted by permanent magnet. Then, red dye was injected into the microchannel. All the materials were injected into the microchannel with syringes. Finally, we powered on the voltage supply and supported 5 V with 8 rpm to stepper motor to drive the ferrofluid. About 44.506 μl of water was transported in the microchannel. The red dye started to move passing through the four reaction zones and flowed back to the straight microchannel to complete a cycle of transportation. The experimental setup is showed in Fig. 5 and the experimental process is showed in Fig. 6. Fig. 5 The final experimental setup Fig. 6 The experimental process of transporting red dye Fig. 7 The phenomenon of swelling of PDMS microchannel Although the ferrofluidic actuation of fluid in the PDMS microchannel was feasible, there are some phenomena deserving to be discussed. If there are gas bubbles inside the PDMS microchannel, it is difficult to transport fluid, and it may cause ferrofluid to dry in the microchannel. Because the ferrofluid is made up of hexane and silicone oil, it has the problem of volatilization when the PDMS microchannel is not tightly bonded to the substrate or water is not filled with the entire channel. These phenomena may affect the efficiency of driving. On the other hand, hexane may lead to PDMS microchannel swelling, as shown in Fig. 6. Adequate ingredients and properties of ferrofluid is the solution. Nonvolatilizable ferrofluid can prevent the dryness of ferrofluid in the microchannel and, in addition, cannot result in swelling problem in PDMS microchannel. IV. CONCLUSIONS In this study, we presented a novel microchannel design with four reaction zones. The experiment result showed that it has potential application in biochip. Some important results and barriers are summarized as follows: The advantages of this proposed design on the microchannel include: (1) disposable; (2) low cost; (3) simple fabrication process; and (4) mass-production available. Additional mechanical jigs are needed to improve the PDMS’s innate self-adhesion on the glass substrate so as to avoid leakage. However, adequate ferrofluid is also needed as pumping actuation to prevent dryness of ferrofluid and swelling of PDMS microchannel. 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