Metallic nanostructures
Metallic nanostructures excite electrons close to their surface upon incidence of light at a particular frequency. The collective movement of electrons, or resonance, in the metal converts the light energy into heat. The wavelength at which the resonance occurs is strongly dependent on the size and shape of the nanostructures.
Metallic nanocross
Nanocross is a unique cross-shaped nano structure having arms located at an angle. In metallic nanocross spectral tunability can be achieved by changing the cross arm length and the angle between the arms. The degree of rotational symmetry of the nanocross can be varied by adding extra arms, changing the arm angle and shifting the arm intersection point. The symmetry of the particles has a crucial influence on the plasmon coupling to incident radiation. Pronounced dipole, quadrupole, octupole and Fano resonances can be observed in individual cross structures. Furthermore, the nanocross geometry proves to be a useful building block for coherently coupled plasmonic dimers and trimers where the reduced symmetry results in hybridized sub radiant and super radiant modes and multiple Fano interferences.
Gold nanocross
Researchers at ASTAR Institute of materials and Engineering have developed gold plasmonic nanocrosses that are particularly suited to eliminating cancer cells in cancer therapy and used to kill human lung cancer cells.
Chemical synthesis of well-defined gold nanocrosses can be done through anisotropic growth along both 110 and 001 , whereas gold nanorods can be grown only along either 110 or 001 . The multiple branching is achieved by breaking the face-centered-cubic lattice symmetry of gold through copper-induced formation of single or double twins to result in gold nanocrosses.
The nanocrosses exhibit pronounced near-IR absorption with a great extension to the mid-IR region and get excited even when one of the branches is exposed to incident light. The unique cross-shaped gold structure enables multi-directional excitation to achieve a strong plasmonic resonance in the near- and mid-infrared region. This greatly lowers the laser power required for photo thermal cancer therapy compared to nanorods.
The gold nanocrosses useful as octopus antennas for capturing near-IR light for effective photo thermal destruction of cells, photo thermal destruction of super bugs on biofilms, two-photon luminescence imaging, IR sensing, thermal imaging and telecommunications.