Carbon nanotube resonator in liquid.

To achieve mass measurement of biological molecules in viscous fluids using carbon nanotube resonators, we investigated the vibration of nanotube cantilevers in water using the optical detection technique. In vacuum, we often found a few resonance modes of nanotube vibrations. However, the nanotube lost its fundamental oscillation once immersed in water, suggesting a great viscous resistance to the nanotube vibration in water. The resonant frequency of the nanotube in water decreased with lowering the water temperature, corresponding to the natural phenomenon by which liquid viscosity tends to increase at lower temperatures.