Surface Modification of Fluorescent Nanodiamond for Biomedical Applications as Fluorescent Probe

Abstract

Fluorescent nanodiamonds (FNDs) are promising bio-imaging probes compared with other fluorescent nanomaterials such as quantum dots, dye-doped nanoparticles, and metallic nanoclusters due to their unique optical properties and excellent biocompatibility. Nevertheless, they are prone to aggregation in physiological salt solutions, and modifying their surface to conjugate biologically active agents remains challenging. We describe encapsulation of FNDs into polydopamine (PDA) shells, which is inspired by the adhesive protein of marine mussels. The PDA shells can be further functionalized via Michael addition or Schiff base reactions with molecules presenting thiol or nitrogen derivatives. We demonstrate PDA shells modified by thiol terminated polyethylene glycol (PEG) molecules, which enhance stability in biological solutions and biocompatibility of PDA coated FND ([email protected]). The PEG modified [email protected] nanoparticles were utilized as fluorescent probes for cell imaging with immature bone marrow derived dendritic cells. Furthermore, functionalization with biotin-PEG-SH permitted long-term high-resolution single-molecule fluorescence-based tracking of FNDs tethered via streptavidin to individual biotinylated DNA molecules. This robust polydopamine encapsulation and functionalization strategy presents a facile route to develop FNDs as multifunctional labels, drug delivery vehicles, and targeting agents for biomedical applications.