Fabricating a QCM Device with the Nanostructures Using the AAO Template

Abstract

Quartz Crystal Microbalance (QCM) method is one of promising approach to detect gas molecules and bio materials since it has advantages in real time measurement, high sensitivity, and portability. However, the method shows poor sensitivity to low molecular weight materials because of its measuring principle, mass change. To improve the sensitivity to the low molecular weight materials, we introduce to fabricate nano structures on the quartz crystal. As the results, the surface area derived from nano stractures to bind with analytes is greatly improved. Anodizing Aluminiun Oxide (AAO) is known as a one of attractive functional materials which has self assembled nano structure provided by anodizing highly-pure Aluminium in the acid solutions, for examples, oxalic acid and sulfuric acid. The nano structure of AAO is controllable by the anodizing condition such as voltage, anodizing time, and the acid solutions. Then, we can get the regularly arranged pores with high aspect ratio. Our nano structures on the quartz crystal were referred from the AAO nano structure. Figure 1 shows the nanowires array composed of Au. The nanowires were fabricated on a SiO2 substrate. The shape of the nanowire was evaluated by Scanning electron microscopy (SEM). Average of the height and the diameter of the nanowire was 1 μm and 70 nm, respectively. As the results, we could get the aspect ratio more than 14. In fact, large surface area was achieved on the quartz crystal. By using our process, nanowire positions would be arranged in three angles lattice. This manufacture procedure to fabricate Au nanowire arrays used electrical plating, so it enables to fabricate arbitrary nanowire arrays to suit someone’s measurement needs by changing the plating solution. To detect antigen-antibody reaction, we manufactured Au nanowires that have a high affinity with protein and the cell because of thiol linkage. Our fabricating process was written below. Ti/Au/Al (30/100/1000 nm thick, respectively) was sputtered on the SiO2 substrate by using a DC magnetron sputtering equipment. AAO was obtained by anodizing the Al thin film with Pt plate (cathode) with applied voltage of 40 V in 0.3 M oxalic acid. Then, the sample was immersed in 0.3 M phosphoric acid to expand pores size and to remove the barrier layer which was located on the AAO bottom. The sample was electrodeposited at constant current of 0.004 mA/mm2 using Au plating solutions. Finally, regularly arranged nanowires were obtained by removing AAO in 1 M phosphoric acid. By this manufacture procedure, we fabricated nanowires structure on the sensor electrode and tried to detect the antigen-antibody reaction using the QCM method which had nano structures on the quartz crystal. In the conference, we will show the result about the comparison measurement. Figure 1