Photobleach of Au-nanorod under two photon excitation X.Wu Department of Physics, Fudan University, Shanghai 200433, China Gold nanoparticles and its optical properties Au-nanorod The extinction spectra(left red) and two photon excitation(TPE) emission spectra(right green) of gold nanorods in aqueous solution with the concentration of 0.1 nM Some in vitro and in vivo TPE image have been reported Photobleach of Au-nanorods In water As a fluorescence probe, the photostability is important The PL decay curve of Au nanorods in water (0.1 nM) under the irradiation of an 800nm fs laser with power of 5 mW (yellow line) and 10 mW(purple line). In cells In vivo imaging of single gold nanorods in mouse ear blood vessels. (PNAS, 2005, 102, 15752) The mechanism Compare to Au-nanorods, sphere-like Au-nanoparticles have relatively low PL quantum yield and TPACS. Thus its TPL will be much dimmer than Au-nanorods. (left up row): PL imgae of gold-nanorods in QGY cells under TPE of an 800nm fs laser. Left, PL image; middle, DIC image; right, merged image. The scale bar is 20 μm. (left low row): Photobleaching of gold-nanorods in QGY cells. Forty consecutive PL images were made under TPE and 1st (left), 10th (middle), and 40th (right) PL images were depicted as the respective images. (right chart):The PL decay curve of image photobleaching with scan times for three cell groups with different incubation concertration. Each scan costed 2 seconds. HRTEM image of gold nanorods after exposure to femtosecond laser pulses with a fluence of 1 mJ cm-2 (0.5 μJ per pulse).<J. Phys. Chem. B 2000, 104, 7867> Conclusions PL images of cellular Au nanorods were found to be photobleached with a fast rate as the image brightness has lost about 50 % after 10 scans, which is probably due to the melting effect of Au nanorods photothermally induced by TPE. The photostability of cellular Au-nanorods under TPE is so bad that the TPE is not adequate for long-term cell imaging. References [1] Haifeng Wang, Terry B. Huff, etc. PNAS, 2005, 102, 15752-15756. [2] Stephan Link, Zhong L. Wang, and Mostafa A. El-Sayed. J. Phys. Chem. B 2000, 104, 7867-7870. [3] A. Bouhelier, R. Bachelot, etc. Phys. Rev. Lett. 2005, 95, 267405. [4] Xi Wu, Tian Ming, etc. ACS Nano, 2010, 4, 113.