본 연구에서는 유리(glass)와 석영(quartz)을 재질로 사용하여 MEMS(micro-electro mechanical systems) 공정을 통해 전기영동(electrophoresis)을 위한 microchip을 제작하였다. UV 광이 실리콘(silicon)을 투과하지 못하는 점에 착안하여, 다결정 실리콘(polycrystalline Si, poly-Si) 층을 채널 이외의 부분에 증착시킨 광 차단판(optical slit)에 의해 채널에만 집중된 UV 광의 신호/잡음비(signal-to-noise ratio: S/N ratio)를 크게 향상시켰다. Glass chip에서는 증착된 poly-Si 층 이 식각 마스크(etch mask)의 역할을 하는 동시에 접합표면을 적절히 형성하여 양극 접합(anodic bonding)을 가능케 하였다. Quartz 웨이퍼에 비해 불순물을 많이 포함하는 glass 웨이퍼에서는 표면이 거친 채널 내부를 형성하게 되어 시료용액의 미세한 흐름에 영향을 미치게 된다. 이에 따라, HF와 NH4F 용액에 의한 혼합 식각액(etchant)을 도입하여 표면 거칠기를 감소시켰다. 두 종류의 재질로 제작된 채널의 형태와 크기를 관찰하였고, microchip electrophoresis에 적용한 결과, quartz과 glass chip의 전기삼투 흐름속도(electroosmotic flow velocity)가 0.5와 0.36 mm/s로 측정되었다. Poly-Si 층에 의한 광 차단판의 존재에 의해, peak의 S/N ratio는 quartz chip이 약 2배 수준, glass chip이 약 3배 수준으로 향상되었고, UV 최대흡광 감도는 각각 약 1.6배 및 1.7배 정도 증가하였다.

We developed two kinds of the microchip for application to electrophoresis based on both glass and quartz employing the MEMS fabrications. The poly-Si layer deposited onto the bonding interface apart from channel regions can play a role as the optical slit cutting off the stray light in order to concentrate the UV ray, from which it is possible to improve the signal-to-noise (S/N) ratio of the detection on a chip. In the glass chip, the deposited poly-Si layer had an important function of the etch mask and provided the bonding surface properly enabling the anodic bonding. The glass wafer including more impurities than quartz one results in the higher surface roughness of the channel wall, which affects subsequently on the microflow behavior of the sample solutions. In order to solve this problem, we prepared here the mixed etchant consisting HF and NH4F solutions, by which the surface roughness was reduced. Both the shape and the dimension of each channel were observed, and the electroosmotic flow velocities were measured as 0.5 mm/s for quartz and 0.36 mm/s for glass channel by implementing the microchip electrophoresis. Applying the optical slit with poly-Si layer provides that_x000D_ the S/N ratio of the peak is increased as ca. 2 times for quartz chip and ca. 3 times for glass chip. The maximum UV absorbance is also enhanced with ca. 1.6 and 1.7 times, respectively.

MEMS Fabrication Microchip Electrophoresis Quartz Glass Poly-Silicon Etching

Harrison DJ, Manz A, Fan Z, Ludi H, Widmer HM, Anal. Chem., 64, 1926 (1992) 
Dolnik V, Liu S, Javanovich S, Electroanalysis, 21, 41 (2000)
Reyes DR, Iosssifidis D, Auroux PA, Manz A, Anal. Chem., 74, 2623 (2002) 
Nguyen NT, Wereley ST, Fundamentals and Applications of Microfluidics, Artech House, Boston (2002)
Zhang L, Dang F, Baba Y, J. Pharm. Biomed. Anal., 30, 1645 (2003) 
Nakanishi H, Nishimoto T, Arai A, Abe H, Kanai M, Fujiyama Y, Yoshida T, Electrophoresis, 22, 230 (2001) 
Nakanishi H, Nishimoto T, Nakamura R, Yotsumoto A, Yoshida T, Shoji S, Sens. Actuators A-Phys., 79, 237 (2000) 
Kroschwitz JI, Howe-Grant M, Encyclopedia of Chemical Technology: Vol. 22. Silicon Compounds to Succinic Acid and Succinic Anhydride, 4th ed., John Wiley & Sons, New York (1997)
Faust JW, Palik ED, J. Electrochem. Soc., 130, 1413 (1983) 
Madou MJ, Fundamentals of Microfabrication: The Science of Miniaturization, 2nd ed., CRC Press, New York (2002)
Lin CH, Lee GB, Lin YH, Chang GL, J. Micromech. Microeng., 11, 726 (2001) 
Schwartz B, Robbins H, J. Electrochem. Soc., 108, 365 (1961)
Chun MS, Shim MS, Choi NW, Lab Chip, 6, 302 (2006) 
Diepold T, Obermeier E, J. Micromech. Microeng., 6, 29 (1996) 
Anthony TR, J. Appl. Phys., 58, 1240 (1985) 
Kim MS, Cho SI, Lee KN, Kim YK, Sens. Actuators B-Chem., 107, 818 (2005) 
Sayah A, Solignac D, Cueni T, Gijs MAM, Sens. Actuators A-Phys., 84, 103 (2000) 
Nakanishi H, Nishimoto T, Kanai M, Saitoh T, Nakamura R, Yoshida T, Shoji S, Sens. Actuators A-Phys., 83, 136 (2000)