
264 Nanosensors: Physical, Chemical, and Biological
nanotube is deformed, the tube length and tube diameter are changed,
and its resonant frequency changes accordingly. There exists a relationship
between the shift of resonant frequency of a nanotube resonator and the
force the nanotube is subjected to. This is the underlying principle for car-
bon nanotube–based force sensors. Thus, the key issue of study is to estab-
lish the relationship between the resonant frequency shift and the applied
force.
How is force applied on the nanotube? An AFM tip can be used to simultane-
ously vary the force on CNT and to electrostatically gate the