Design and structural investigations of Yb3+ substituted β-Ca3(PO4)2 contrast agents for bimodal NIR luminescence and X-ray CT imaging

Abstract

The quest for the development of bone substitutes with contrast agents for diagnostic imaging subsists to distinguish synthetic bone from native human tissue. To this aim, ytterbium (Yb3+) substitutions in β-tricalcium phosphate (β-Ca3(PO4)2, β-TCP) as contrast agents has been developed to differentiate implant materials thereby, facilitating as host for bimodal imaging application by means of NIR luminescence and X-ray computed tomography techniques. A facile aqueous chemical precipitation route with the aid of surfactant is used for the synthesis of Yb3+ substitutions in β-Ca3(PO4)2. The characterization results affirms the ability of β-Ca3(PO4)2 to host 4.36 mol% of Yb3+ while the excess Yb3+ crystallizes as YbPO4. The structure refinement results favour the occupancy of Yb3+ at the Ca2+(5) site of β-Ca3(PO4)2. The absorption and photoluminescence spectra in the near infrared region with emission intensity ~1024 nm in the second biological window correspond to 2F5/2 → 2F7/2 transitions of Yb3+. The designed Yb3+ substituted β-Ca3(PO4)2 does not exhibit any toxicity in human osteosarcoma cell lines and delivers an excellent in vitro CT contrast ability allied by the enhanced signal intensity and high X-ray absorption coefficient.