Surface Engineered Ho³⁺ Incorporated Fluorescent Dye-Doped Bifunctional Silica Nanoparticles for Receptor Targeted Fluorescence Imaging and Potential Magnetic Resonance Imaging

The authors report Ho³⁺ ion incorporated and fluorescent dye-doped silica nanoparticles which are engineered to enable the imaging modalities of receptor targeted fluorescence imaging (FI) and magnetic resonance imaging (MRI). The silica nanoparticles synthesized through a modified Stöber method is luminomagnetic by virtue of the luminescence of organic dye fluorophore (FITC) and magnetism of Ho³⁺. The doping concentration of Ho³⁺ is estimated by inductively coupled plasma mass spectrometry (ICP-MS) as 0.97%. The presence of Ho³⁺ has a little effect on the luminescence intensity but impart strong paramagnetism of 27.217 emu/g at room temperature. The relaxivity measurements shown that the nanoparticles exhibit a longitudinal relaxivity (r₁) of 0.12 s^-1 mM^-1 and transverse relaxivity (r₂) of 26.96 s^-1 mM^-1, which makes the system potentially suitable for developing T2 MRI contrast agents based on holmium. The luminomagnetic nanoparticles were surface engineered through aminization and conjugated with folic acid (FA) to address the folate receptor targeted imaging of the cancer cells. The biocompatibility studies revealed no apparent toxicity even at higher doses of 750 μg/mL and at 48 h of incubation. The as prepared nanoparticles were demonstrated as a bioimaging probe in the in vitro receptor targeted fluorescence imaging of HeLa cells. The luminescence and magnetism together with biocompatibility enables the adaptability of the present system as a nano platform for potential bimodal imaging. Graphical Abstract ᅟ.