Improved photodynamic efficiency for methylene blue from silica-methylene blue@tannic acid-Fe(III) ions complexes in aqueous solutions

Abstract To avoid multidrug resistance and tumour recurrence, photodynamic therapy (PDT) was emerging as an alternative therapy and its efficiency was related to photosensitizer (PS) efficiency, oxygen concentration and light characteristic. Methylene blue (MB) molecules as PSs were loaded in silica (silica-MB) and followed by encapsulation by coordination complexes of tannic acid (TA) and Fe(III) ions. In comparison with those of silica-MB, decreased condensation of Si-O-Si, shifted infrared absorbance frequencies of chemical bands, delayed thermal degradation and modulated release behavior of MB were observed for silica-MB@TA with a core–shell structure. Although MB dimers were dominantly released from silica-MB, release of MB monomers from silica-MB@TA was significantly promoted, which was described by the Higuchi model. The promotion of release of MB monomers from silica-MB@TA indicated the well control of aggregate states of MB by the encapsulation of TA and Fe(III) ions complexes. Through monitoring the oxidation of uric acid, generation efficiency of singlet oxygen ( 1 O 2 ) by MB released from silica-MB@TA was fairly higher than that from silica-MB. A facile method to encapsulate silica-MB with complexes of TA and Fe(III) ions was herein demonstrated to raise the generation efficiency of singlet oxygen.