Nanodiamond conjugated fluorescein through ethylenediamine linker for cellular biomarking

Nanodiamond (DND) has a wide range of applications in the field of biomedicine owing to its outstanding biocompatibility and low toxicity as well as optical properties. In this work, DND-fluorescein composite nanoparticles were obtained by using a novel and green strategy that is mechanochemistry approach to achieve surface functionalization of DND with fluorescein using ethylenediamine as a linker. Particularly, our prepared DND-fluorescein composite can be dispersed stably in aqueous solution with a particle size that is about 138 nm. Moreover, the determined skin penetration property shows that, unlike free fluorescein, the fluorescent DND-fluorescein nanoparticles can only remain on the stratum corneum with no diffusion into dermal layer, and it can be easily washed off with water. DND-fluorescein particles will not affect the body and are basically non-toxic to human hepatocellular carcinoma cell line (HepG2) and human normal hepatocyte cell line (LO2) cell lines. These results suggested that DND-fluorescein can be used as long-term labelling agent with excellent properties that can be exploited for various applications such as in biolabeling and bioimaging.