Laser-nanoparticles interactions have been widely used for several years. In biomedicine, several in vitro and in vivo experiments have shown promising results for the detection and treatment of cancer. One of the techniques of interest to us, is the nanoparticle-assisted photothermal therapy (PTT), which consists of irradiating cancer cells incubated with nanoparticles with either a pulsed or continuous (cw) laser in order to damage the cells.
However, there is still a debate over which type of laser is most effective for PTT for cancer treatment. On the one hand, cw lasers are minimally invasive and can be used for both detection and treatment of tumors. On the other hand, pulsed lasers offer great spatial precision and can deposit higher energy fluences than cw lasers, making them very efficient for inducing cavitation to damage cancer cells and tumors mechanically.
The aim of this study is to investigate whether simultaneous application of cw and pulsed laser could offer a synergetic enhancement of PTT efficacy to damage cancer cells in vitro, compared to either laser applied individually. PTT efficacy is evaluated through cell viability tests following the irradiation of prostate cancer (PC3) cells incubated with gold nanorods (5.7 X10 10 p/ml).
By irradiating the PC3-nanorod solution with the cw laser at 808 nm for ~60 seconds, the temperature increases from 37.5 to ~45°C, which damages some cancer cells via the heat shock response within the cells, and also could increase their sensitivity to the mechanical stress caused by the shock wave generated from inducing cavitation in the solution by the pulsed laser irradiation.
High-speed video imaging was used to study the dynamic behavior of cavitation bubbles induced by a continuous wave (CW) laser into highly absorbing droplets water containing copper nitrate (CuNO<sub>4</sub>). The droplet lays horizontally on a glass surface and the laser beam (λ=975 nm) propagates vertically from underneath, across the glass and into the droplet. This beam is focused ζ=400 μm above the glass-liquid interface in order to produce the largest bubble as possible (R<sub>max</sub> ~ 1mm). In our experiment the thermocavitation bubbles are always in contact with the substrate, taking a hemispherical shape, regardless of where the laser focal point is, as opposed to the other methods that involved nano and picosecond laser pulses, where bubbles may nucleate and grow within the bulk of the fluid. We focus on the liquid jet which emerges out the droplet at velocities of about 3 m/s, due to the acoustic pressure wave (APW) emitted immediately after the bubble collapse, and after it breaks up into a secondary droplet or droplets depending of the droplet’s volume, showing an alternative way of droplet generator that is simplest, light and cheaper. The dynamics of cavitation bubbles in confined geometries (drops) offers a rich hydrodynamic and the liquid jet generated after the bubble collapse could be used like acoustic waveguide, as was showed by Nicolas Bertin et. al.