Incorporation of isophthalate ion derivatives into octacalcium phosphate for enhanced diagnostic bioimaging...

Octacalcium phosphate (OCP) with incorporated aromatic dicarboxylate ions exhibits visible-light and near-infrared (NIR) fluorescence, making it a promising platform for the development of diagnostic materials for bone repair and bioimaging. In this study, isophthalate ion (IP) derivatives, i.e., 5-methylisophthalate ions (MeIP), 5-aminoisophthalate ions (AmIP), 5-hydroxyisophthalate ions (HyIP), and 5-sulfoisophthalate ions (SuIP), were incorporated with OCP via a wet chemical method, and the effects of different functional groups in IP on the fluorescence properties were explored. MeIP, AmIP, and HyIP were successfully incorporated into the OCP crystal structure, whereas SuIP remained adsorbed onto the surface of the OCP, as confirmed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and UV-VIS diffuse reflectance spectroscopy (DRS). Thermal analysis revealed that SuIP-OCP exhibited the highest thermal stability, surpassing that of pure OCP, while MeIP-OCP demonstrated the lowest thermal stability. AmIP-OCP and HyIP-OCP emitted visible fluorescence when excited with UV light. Interestingly, MeIP-OCP exhibited broad fluorescence, with strong emission in the UV region and continuous emission extending into the visible range, indicating its potential as an advanced material for applications requiring fluorescence across both the UV and visible regions. This study offers an approach for designing fluorescent OCP that provides fluorescence for diagnostic applications in bioimaging.