Enhanced mass sensitivity of ZnO nanorod-grown quartz crystal microbalances

ZnO nanorods were directly grown on the surface of a quartz crystal in zinc nitrate hexahydrate solution. The nanorod dimensions were controlled by varying the growth time, from 0.6 μm for a growth time of 1 h to 2.0 μm after 3 h of growth. After sequentially coating the nanorod-grown quartz crystals with thin layers of titanium and gold by thermal evaporation, the crystals were exposed to mercaptohexanol solution and the frequency change due to mercaptohexanol adsorption was determined. The frequency change for the nanorod-grown quartz crystal was about 60 times greater than that of the corresponding plain gold-coated quartz crystal due to the increase in surface area afforded by the nanorods. A similar enhancement of mass sensitivity was observed for the immobilization and hybridization of oligonucleotides on the nanorod-grown crystals. Although for larger molecules the enhancement of mass sensitivity was degraded by steric hindrance, the results demonstrate the potential of ZnO nanorod-grown quartz crystals for use in DNA-based biosensor applications.