Imaging with gold nanorods

The use of gold nanorods as an imaging agent for biological imaging is discussed. Unlike fluorescence, where a molecule is pumped to the excitation state, the gold nanorods pump electrons from the excited state and leave a hole in the ground state. The gold nanorods exhibit the optimal excitation wavelength for two-photon luminescence in the near-field region, where a minimal amount of light is lost by water and molecular absorption, allowing light to travel easily through tissue. The nanorods' emission is also dependent on the excitation light's polarization, which may prove useful for determining the rods' orientation in sample.