Controllable synthesis of tetrapod gold nanocrystals with precisely tunable near-infrared plasmon resonance towards highly efficient surface enhanced Raman spectroscopy bioimaging.

Tetrapod gold nanocrystals, to be the core of surface-enhanced Raman spectroscopy (SERS) nanoprobes, with tunable localized surface plasmon resonance (LSPR) from 650 nm to 785 nm in the Vis-NIR region have been successfully prepared by a facile seeded growth approach. The local electromagnetic field distribution and the huge extinction cross section of the tetrapod gold nanocrystals were simulated by a finite-difference time-domain method. Both the calculated and experimental results reveal that the LSPR property of the tetrapod gold nanocrystals is closely dependent on the morphology features of their tips, where a strong field enhancement appears. These tetrapod nanocrystals have exhibited a good capability not only for Raman signal enhancement but also when successfully utilized as NIR SERS bioimaging nanoprobes. In vitro SERS imaging of stained breast cancer cells has also been demonstrated. The tetrapod gold nanocrystals developed here with a precisely tunable LSPR offer advantages of enhanced signal quality, good stability and better biocompatibility in SERS imaging, which has great potential for various biomedical applications.