Modulated photoluminescence and photodynamic efficiency of hydroxyapatite-methylene blue@carbon-ions by ion-π coupling interactions

Abstract As a noninvasive methodology, image-guided photodynamic therapy is promising to treat diseases without inducing drug resistance with chemotherpy in clinical applications. The photo-related properties of methylene blue (MB) as flurophore/photosensitizer are closely related with energy and charge transformations in multifunctional drug delivery systems. Herein, MB monomers are combined by citrate- and β-cyclodexin-modified hydroxyapatite (HAp) with ions-doped carbon shells prepared by hydrothermal carbonization of glucose. Photoluminescence and photodynamic efficiency are tuned by ion-π coupling interactions between ions (M) and MB molecules in HAp-MB@C-M. With increased addition of Zn2+ ions during carbonization, narrowed absorbance peaks to low excitonic band without additional decay channels are observed for HAp-MB@C-Zn with increased emission intensities. As energy decay pathways, ring vibrations of MB are quite weak with small infrared peaks for these fluorochromes with increased luminescence emissions. High oscillate strength contributes to the increased generation efficiency of singlet oxygen for MB released from HAp-MB@C-Zn. The present studies would shed light on the modulations of aggregation states of photosensitizers and their photo-related properties of luminescence emission and therapy efficiency to meet the simultaneous requirements of image-guided photodynamic therapy.