Microbubbles-overlapping mode for laser killing of cancer cells with absorbing nanoparticle clusters

Laser-induced bubble formation around nanoparticles may play a crucial role in selective laser nanophotothermolysis of cancer cells targeted with nanoparticles. In this paper, we propose theoretically, and confirm experimentally, a new dynamic mode for selective cancer treatment that involves the overlapping of bubbles inside the cell volume. This bubbles-overlapping mode (BOM) can dramatically increase the efficiency of cancer treatment by laser-heated nanoparticles as a result of the large damage range. On the basis of nanoparticle optics below the diffraction limit and the kinetic model of bubble dynamics, we found the criteria and conditions (interparticle distance and particle size and concentration) for BOM initiation in cancer cells by laser radiation. Using MDA-MB-231 breast cancer cells, we showed that the optimal size range of the gold nanoparticles for effective laser initiation of BOM is 30-40 nm and the lower concentration limit is n approximate to 2.44 x 10(11) cm(-3) (i.e. the absolute number of particles homogeneously distributed inside a tumour cell is n 430). It was demonstrated that the formation of nanoclusters on the cell surface with sizes larger than the sizes of individual nanoparticles, may further increase the efficiency of the laser treatment of cancer.