INTEGRATED ZNO SURFACE ACOUSTIC WAVE MICROFLUIDIC COMPONENTS for BIOSENSOR D.-S.Lee1, Y

INTEGRATED ZNO SURFACE ACOUSTIC WAVE MICROFLUIDIC COMPONENTS FOR BIOSENSOR D.-S.Lee1, Y. Fu2, S. Maeng1, J. Luo2, W. I. Milne2, J.H. Lee3, M.Y. Jung1, S.H. Park1, and H. C. Yoon3 1 Electronics and Telecommunications Research institute (ETRI), KOREA, 2 Centre for Advanced Photonics and Electronics (CAPE), University of Cambridge, UK, and, 3Department of Molecular Science & Technology, Ajou University, KOREA

ABSTRACT This paper describes the novel nanocrystalline film ZnO surface acoustic wave devices, which demonstrate their great potential for the portable dis- ease diagnostic system with integrated functions of microfluidic transport, mixing and biosensing. The devices can be easily integrated with electronic control circuitry and fabricated with low temperature process on Si, glass or even polymer substrates. The liquid convection and internal streaming patterns was easily induced by acoustic wave at signal voltages. With further increase in applied voltage to above 20V, the liquid droplet was pushed for- ward. Immunoreaction-based bio-detection PSA/ACT, all based on SAW devices on thin film piezoelectric ZnO on Si substrate was demonstrated.

KEYWORDS: Nanocrystalline ZnO, Surface acoustic wave, Microfluidic actuation, PSA/ACT detection

INTRODUCTION Surface acoustic wave (SAW) devices have found many commercial applications in communications [1]. Recently, there has been an increased interest in SAW based biosensors and microfluidic systems using high performance piezoelectric materials, such as LiNbO3, because they offer the opportunity to establish a low-cost system [2]. ZnO has good piezoelectric properties, a high electro-mechanical coupling coefficient, high sensitivity and reliability [3]. ZnO thin film growth with c-axis oriented wurtzite crystalline structure is quite challenging. However, using an RF magnetron sputtering, ZnO thin film can be grown on various substrates, like silicon, glass or even polymer substrates, making it the most promising material integratable with CMOS IC technology.

EXPERIMENTAL ZnO films with thicknesses up to 6 µm were deposited on Si (100) wafers using a zinc metal target. Optimization of deposition parameters has been performed in order to obtain the preferred stoichiometry and orientation, thereby maximizing the coupling coefficient and minimizing intrinsic stress.[4] Using the IC technology, the SAW devices are microfabricated. The bio-affinity surface for capturing the PSA/ACT were designed and fabricated too.

Thirteenth International Conference on Miniaturized Systems for Chemistry and Life Sciences November 1 - 5, 2009, Jeju, Korea

978-0-9798064-2-1/µTAS2009/$20ⓒ2009CBMS RESULTS AND DISCUSSION C-axis ZnO structures are preferential structures for SAW devices used for mi- crofluidics which normally require a wave displacement perpendicular to the surface. ZnO/Si SAW devices were microfabricated and frequency properties as a function of film thickness are shown in Fig. 1. When the source SAW voltage is above 2 V, the liquid convection and internal streaming patterns can be clearly observed [3]. From the top-view, the flow initiates near the center of the droplet. From the cross- sectional view, the flow starts near the top of the droplet, where the propagating acoustic wave pushes the liquid to move. The liquid is pushed along the acoustic wave propagation direction, until the wave reaches the boundary of the droplet. The interaction between the liquid and liquid surface boundary induces a reverse flow at the two sides of the droplet as well as along the bottom layer of the droplet as shown in Fig. 2 (a) to (c). The time to reach the stable SAW streaming patterns is a few seconds. The fluidic velocity induced by Sezawa wave is much higher than that induced by Rayleigh wave as shown in Fig. 2(d).

(a) (b) Figure 1. Measured reflection frequencies from the ZnO devices with varied film thickness (a), and reflection and transmission signal at ZnO (5.5 ห)/Si devices (b).

(a) (b) (c) (d) Figure 2. Fluidic streaming inside droplets on the ZnO; SAW principle (a), top view (b), cross-section view (c) and streaming speed (d) as a function of voltage applied.

Silanization has been performed on ZnO film surface in order to form a hydrophobic surface. With an increase in applied voltage to above 20V, the liquid droplet has deformed and overcome the surface energy barrier to move freely. The droplet on the surface shows a much larger contact angle (115q) comparing to that on the untreated ZnO film (81q), indicating the formation of a hydrophobic surface.(Fig. 3(a)) With an applied voltage of 20V and above, the SAW energy coupled into the liquid was sufficient to move water droplets with volume between ~100 nl to ~10 ȝl. There are significant deformation of the water droplet and movement of the droplet

Thirteenth International Conference on Miniaturized Systems for Chemistry and Life Sciences November 1 - 5, 2009, Jeju, Korea

978-0-9798064-2-1/µTAS2009/$20ⓒ2009CBMS (see Fig. 3(b), (c)).[3]. Finally, its biosensing potential of SAW was successfully evaluated using biospecific recognition between a PSA/ACT and its antibody, in the range of 1 – 20,000 ng/ml. (see Fig. 4) The system is targeted at self-diagnosis and the real-time diagnosis in a hospital and clinic environment.

(a) (b) (c) Figure 3. Superhydrophobic formation (a), deformation of large water droplet (10 ȝl) under the pressure of SAW (b) and pumping of the droplet at a speed of 22 mm/s under the SAW pressure (c).

160

140 Sezawa mode Rayleigh mode 120

100

Frequency shift (KHz) shift Frequency 20

0 1 10 100 1000 10000 100000 PSA concentration (ng/ml) (a) (b) (c)

Figure 4. PSAs sensing procedure using the droplet-based microfluidic SAW devices (a) and working principle of the SAW biosensors (b), and frequency changes of SAW biosensors as a function of PSA/ACT concentration when the PSA/ACT complex concentrations bound on gold electrodes (error bar represents ± SD for 3 replicates).

ACKNOWLEDGEMENTS This work was supported by the Ministry of Information and Communication, Republic of Korea, under project no. 2005-s-605-02.

REFERENCES [1] M.J. Vellekoop, Acoustic wave sensors and their technology, Ultrasonics, 36, pp. 7-20, (1998). [2] Z. Guttenberg, H. Muller, H. Habermuller, A. Geisbaurer, J. Pipper, J. Felbel, M. Kielpinski, J. Scriba, A. Wixforth, Planar chip device for PCR and hybridiza- tion with surface acoustic wave pump, Lab chip, 5, pp.308-313, (2005). [3] D.S. Lee, Y. Q. Fu et al. IEEE International Electronic Devices Meeting (IEDM) Washington D.C. December 10-12, pp. 851-854, (2007). [4] D.S. Lee et al., Nanocrystalline ZnO film layer on silicon and its application to surface acoustic wave-based streaming, J. Nanosci. Nanotech., 8, pp.4626- 4628, (2008).

Thirteenth International Conference on Miniaturized Systems for Chemistry and Life Sciences November 1 - 5, 2009, Jeju, Korea