Singlet oxygen photo-production by perylene bisimide derivative Langmuir-Schaefer films for photodynamic therapy applications

A perylene bisimide (PBI) derivative, chosen for its strong efficiency at generating singlet oxygen upon photoexcitation, was employed as a photosensitizer for photodynamic therapy (PDT). The dye was immobilized on a hydrophobized solid support using the Langmuir-Schaefer (LS) technique in order to build a preliminary medical device capable of killing cancer cells in vitro. Two PBI solution concentrations ($4.2 times 10^{-5}$ and $1.5 times 10^{-4}$ M) were selected on the basis of differing aggregation behaviour and spread onto a water subphase in a Langmuir trough; the floating films were then characterized physico-chemically and morphologically before transfer onto quartz substrates. Spectroscopic measurements of the resulting multilayer LS films confirmed that the photochemical properties of the PBI derivative were essentially preserved upon immobilization. The LS film with the highest singlet-oxygen photo-production efficiency was tested on the human cervical carcinoma C13 cell line: it showed no dark cytotoxicity and pronounced photo-cytotoxicity, indicating a promising photoactive device.