Enhanced photodynamic efficiency of methylene blue with controlled aggregation state in silica-methylene bule-acetate@tannic acid-iron(III) ions complexes

摘要

Photodynamic therapy (PDT) is a promising alternative to traditional chemotherapy for cancer treatment. The photodynamic efficiency of PDT is closely related to the generation of singlet oxygen, which is greatly dependent on the aggregation state of photosensitizer (PS). Herein, methylene blue (MB) molecules as PSs were loaded in silica-MB via electrostatic interactions, and silica-MB was subsequently incubated in acetate (Ac) buffer solution to obtain silica-MB-Ac. Silica-MB-Ac@TA with a core-shell structure was finally prepared with an assembly of coordination complexes of tannic acid (TA) and Fe(III) ions. Compared with those values for silica-MB, cumulative amount and absorbance ratio of monomer versus dimer of MB released from both silica-MB-Ac and silica-MB-Ac@TA increased remarkably as a result of significant decrease of MB self-aggregations with aromatic aromatic interactions. Sustained and pH-dependent release behaviors of monomeric MB were well simulated by the theoretical Higuchi model based on the Fickian diffusion. The generation of singlet oxygen, photodynamic efficiency and stability against in vitro reduction of monomeric MB released from silica-MB-Ac@TA were significantly higher than those for silica-MB-Ac, due to the effective control of aggregation state of MB molecules during outward diffusion through the complexes of TA and Fe(III) ions. The present investigation demonstrated a facile route to obtain high photodynamic efficiency by finely controlling the aggregation state of MB molecules.