Laser-Stimulated Release of Methylene Blue from Porous Silicon Nanocontainers

Aqueous suspensions of nanocontainers consisting of porous silicon (PSi) nanoparticles with Methylene blue (MB) loading were investigated by means of the optical spectroscopy and infrared thermometry under laser irradiation. The photothermal conversion efficiency and kinetics of the MB release from those nanocontainers based on PSi without additional oxidation and after thermal oxidation (ox-PSi) were analyzed to establish an influence of the oxidation of PSi on MB release. The optical spectroscopical study of the loaded nanocontainers showed a strong absorption band of MB at 600−700 nm, while the absorption bands of PSi and, especially, ox-PSi were relatively weak in this spectral region, indicating a high degree of the MB loading for both types of NPs. The MB release from nanocontainers in an aqueous medium was monitored by measuring the MB photoluminescence in the spectral region of 700−800 nm when excited by a continuous wave laser at a wavelength of 660 nm. The MB release from the nanocontainer based on PSi NPs was found to be significantly promoted by nanosecond laser irradiation at 532 nm because of the laser induced heating of PSi NPs. To assess possible applications of the MB release and photoheating, in vitro experiments were carried out with unicellular organisms of Paramecium caudatum, and their results confirmed the effect of spatially localized photoheating of MB-loaded PSi NPs under pulsed laser irradiation, which enhanced the MB release. The obtained results indicate new possibilities for the controlled drug release using PSi NPs and may be useful for biomedical applications as antibacterial treatment and combination therapy of cancer.