Fabrication of Eu-doped Gd(OH)3 Nanorods with Enhanced Magnetic- Resonance and Luminescence Imaging

Background: Multimodal bio-imaging is a new technique with more than one imaging modality. Eu3+ doping can tailor the multi-functions of Gd-based nanorods (NRs) to obtain the resolution the imaging at the cellular level. Silk fibroin with His and Lys can induce to fabricate metal compounds particles. However, one-step preparation of SFP-linked Eu-Gd(OH)3 NRs with cyto-compatibility is very challenging. Methods: Eu-doped Gd(OH)3 nanorods with silk fibroin peptides (SFP-NRs) are synthesized via a simple and feasible biomimetic method in the assistance of SFPs. Results: The measurement results showed that these hexagonal crystal NRs possessed 300 nm of the length. Compared with pure NRs, SFP-NRs exhibited better in vitro T1 signal-enhancement of magnetic resonance (MR) imaging due to their higher ratio of Eu and Gd and SFP coating on their surface, and the longitudinal relaxivity r1 value is 2.57 (Gd mM·s)–1 under a 7.0 T MR imaging system. Furthermore, a series of in vivo T1-weighted MR images between pre- and post-injection in tumor regions for 9 h indicated that average intensity of post-injection of SF-NRs was enhanced to 68%, higher the increased value of pure NRs (19.6%), but also SFP-NRs showed the good luminescence labeling of viable cell in the fluorescence observation. Conclusion: These results indicate that Eu-doped SFP-NRs have potential as T1 MR imaging contrast agents and optical imaging probe in tumor–detection field. Keywords: Contrast enhancement, Eu–doped Gd(OH)3 nanorods, luminescent imaging, magnetic resonance imaging, mineralization, silk-fibroin.