The basic principle of PDT is that photosensitizers can be selectively taken up and retained in tumor tissues; thus, the excitation of these photosensitizers by exposure to specific wavelengths of light can generate signaling pathway cytotoxic singlet oxygen atoms and/or oxygen-free OSI 906 radicals that achieve the therapeutic objectives of killing tumor cells, disrupting tumor blood vessels, stimulating immunomodulatory effects in the body, and causing necrosis and shedding among tumor cells [18]. PDT involves lasers and photosensitive drugs (photosensitizers). In particular, the

photosensitizers (or their metabolites) under excitation at appropriate wavelengths of light produce photodynamic effects, which can destroy the targeted

cells. The introduction, development, and application of PDT have been accompanied by gradual improvement of photosensitizers. However, most photosensitizers discussed in available reports exhibit certain shortcomings mainly related to hydrophobicity or limited solubility in aqueous solutions. This issue causes various deleterious effects that impair the therapeutic value of these photosensitizers, including accumulation in bodily fluids see more (such as blood), alteration of photosensitizer photochemical properties, and reduction of singlet oxygen production. Recent progress in nano-pharmaceutical research has proposed a few methods to tackle these problems [8]. Silica nanoparticles have drawn increasing attention due to several advantages, including extremely controllable shape and size, good water solubility, stability, and high biocompatibility. More importantly, silica nanoparticles are permeable to small molecules such as singlet oxygen [19, 20], the key impact factor in PDT, and the small size of these nanoparticles allows them to permeate through cell membranes [21, 22]. Therefore, the use of silica nanoparticles provides clear advantages to overcome conventional nanocarriers

see more that require photosensitizer release processes to occur [23]. Therefore, silica nanoparticles constitute an ideal nanocarrier that can enhance the photodynamic effects of photosensitizers, as shown elsewhere [15]. In in vitro experiments, we first used MTT assays to confirm that both conventional Photosan- and nanoscale Photosan-mediated PDT resulted in HepG2 hepatoma cell cytotoxicity. We found that relative to conventional Photosan, nanoscale Photosan was more cytotoxic, required shorter photosensitizer incubation times, and enhanced PDT efficacy. In addition, experiments revealed that nanoscale photosensitizers did not exhibit cytotoxicity. These findings provide a basis for promoting the use of photosensitizers. These findings regarding the relatively higher cytotoxic effects of nanoscale Photosan-mediated PDT were further confirmed by flow cytometry.