Novel hybrid nanorod carriers of fluorescent hydroxyapatite shelled with mesoporous silica effective for drug delivery and cell imaging

Development of biocompatible multifunctional nanocarriers is necessary for the success of theranostics. Here, we report a novel hybrid nanorod with self-fluorescent property, high drug loading capacity, and good biocompatibility. Fluorescent hydroxyapatite (fHA) nanorod was ensheathed with mesoporous silica (mSi). The mSi shell was uniformly layered and was tunable in thickness (10-30 nm) over the fHA nanorod. Highly mesoporous structure of mSi shell facilitated the loading of a large quantity of biological molecules, as confirmed with fluorescein isothiocynate; ∼1% loading for fHA increased to ∼10% loading for fHA@mSi. The self-fluorescent property of the fHA resulting from CO₂^.- radicals was well preserved in the fHA@mSi hybrid, as analyzed by photoluminescence and electron paramagnetic resonance property. Cellular toxicity of the fHA@mSi hybrid nanorod showed favorable cell viability (>90% viability of control) up to a concentration of ∼40lg/mL. Intracellular uptake rate of the hybrid nanorod was as high as 80-90%, as analyzed by fluorescent-assisted cell sorter. Results demonstrate the newly developed fHA@mSi nanocarriers have great potential for the effective loading of therapeutic molecules and delivery within intracellular compartments in concert with a capacity for in situ imaging.