Conclusions

1. Gold nanorods: photothermal therapy of cancer and living cell imaging Xi Wu, Tian Ming, Fei Yang, Ronglin Xiongand Jiyao Chen Phys. Dept., Fudan Univ., Shanghai, People’s Republic of China Two Photon Excitation (TPE) Fluorescence Bleach • High two-photo absorption cross-section (TPACS of AuNRs ≈ 2000GM compare to Rhodamine B ≈ 15GM) promise Au-nanorods use as TPL imaging agency • However, it photo bleach quickly. (a) TPE PL images of the 1st, 10th, and 40th scans from the forty consecutive scans are shown from left to right in respectively. Each scan took 2 s. (b) Photobleaching curves of the intracellular Au nanorods at the three different incubation concentrations. Each curve was averaged from six independent measurements. Photothermal Therapy (PTT) TPE Photoluminescence Bleach of Au-Nanorods • When tissue heat up to 41~47℃ for tens of minutes, tumors are selectively destroyed, while normal tissue can endure better than tumor, because poor blood supply and rapid division of cancer cell. • However, to achieve rapid and effective heating the tumor and reduce nonspecific injury of adjacent health tissue, especially tissue on the optical path of laser, some photoabsorber such as Indocyanine green (ICG) must be introduced • While gold nanorods (red line) is a much better photoabsorber than conventional ICG (green line) because its high absorption bring by local field enhancement • From TEM image of Au-Nanorods after irradiation of 800nm fs laser (figure above), we can get a figure of mechanism of the photobleach • The fs pulse induced heat and melt of gold nanorods turn nanorods to sphrere-like particles, and reduce its PL yield and TPACS, which caused photobleach. PTT using gold nanorods Confocal Reflectance imaging with Au-Nanorods • Reflectance imaging only needs microwatt cw laser, which will prevent photobleach of Au-nanorods. Cell damaging detection with PI in nanorod-loaded cells. (a) Nanorod-loaded QGY cells have been irradiated by the 800 nm laser for 15 min with a power density of 4 W/cm2. (b) Nanorod-loaded QGY cells without irradiation. QGY cell was incubated with 0.01nM Au nanorods for 50min (a)The 1st (left), 20th (middle), and 80th (right) scans from the 80 consecutive scans of confocal reflectance images of Au nanorods in QGY cells are demonstrated to show the photostability under the irradiation of a 405-nm laser. (b)Photostability comparison of the intracellular Au nanorods under the irradiation at 800 nm for TPE (red line) and at 405 nm for reflectance imaging (black dash) • Conclusions • Gold nanorods have a extra high and tunable absorption (SPR band) in the red and NIR area • Which make gold nanorods a promising material for photothermal therapy. • Gold nanorods can be used for TPE imaging, but its quick photobleach caused by strong fs laser induced melting of gold limited its usage. • While reflectance image of gold nanorods can prevent photobleach and suitable for long time trace. Publications: [1]XiWu, Fei Yang et al.Appl. Phys. Lett. 2011, accepted. [2] Xi Wu, Tian Ming et al. ACS Nano 4:113-120, 2010. [3] Yu Zhou, Xi Wu et. al.J. Microscopy 237:200-207, 2010. [4] Xiaohua Huang, Prashant K. Jain et. al. Lasers Med. Sci. 23:217–228, 2008. [5] E. Dulkeith, T. Niedereichholz, et. al. Phys. Rev. B 70:205424, 2004.