491Nanobiosensors
binding; the greater the binding energy, the greater the bending. A
ligand is an ion or molecule that binds to a central metal atom to
form a coordination complex. The bending causes movement of the
cantilever tip of the order of 1–100 nm.
2. Also, the resonance frequency of a microcantilever varies sensitively
with molecular adsorption. In the dynamic or resonance mode,
cantilevers are excited close to their resonance frequency, which is
typically in the kHz or even MHz range. When an additional mass
is attached to the oscillating cantilever, its resonance frequency
changes (adding a mass lowers the resonance frequency). This is not
surprising since at a rst approximation, cantilevers behave like a
harmonic oscillator