Enhanced cellular photodamage of femtosecond laser by gold nanoparticles

The enhanced cellular photodamage is studied by using gold nanoparticles (Au NPs) under the irradiation of a femtosecond laser. For our experiment, macrophage cell line of rat (RAW264.7) was incubated with Au NPs medium for 30 min. After that, these cells were irradiated by a pulsed Ti: Sapphire laser, and observed by a laser scanning confocal microscopy. The duration of each pulse is 100 femtoseconds with a repetition rate of 80 MHz, and five different wavelengths (700 nm, 765 nm, 800 nm, 850 nm, and 900 nm) were used. Our results show that the necrosis speed of cells caused by the photodamage depends on the uptake amount of Au NPs and the power of laser. Moreover, the morphology and speed of necrosis are dependent of the wavelengths at the same power. If the wavelength is less than 800 nm, the blebbings of cells are observed almost at the beginning, and then a giant plasma membrane vesicle (GPMV) is formed. If the wavelength is longer than 850 nm, the cells still survive nearly without any damage after 2-hours exposure. The wavelength-dependent damage is attributed to the two-photon effect. When the femtosecond laser irradiates Au NPs, a broadband scattered light is induced; e.g. for the irradiation of 700 nm, the scattering spectrum from Au NPs covers 350 to 700 nm. The UV-A (320 to 400 nm) components might induce the depolymerization of actin filament to make the cortical actin loose, so as to cause the GPMV. In contrast, the fluence of laser at the focal spot is so low that the photothermal effect is not severe.