Fluorescent Nanodiamond–Nanogels for Nanoscale Sensing and Photodynamic Applications

Fluorescent nanodiamonds (NDs) are carbon-based nanoparticles with various outstanding magneto-optical properties. After preparation, NDs have a variety of different surface groups that determine their physicochemical properties. For biological applications, surface modifications are crucial to impart a new interphase for controlled interactions with biomolecules or cells. Herein, a straight-forward synthesis concept denoted "adsorption-crosslinking" is applied for the efficient modification of NDs, which sequentially combines fast non-covalent adsorption based on electrostatic interactions and subsequent covalent cross-linking. As a result, a very thin and uniform nanogel coating surrounding the NDs is obtained, which imparts reactive groups as well as high colloidal stability. The impact of the reaction time, monomer concentration, molecular weight, and structure of the cross-linker on the resulting nanogel shell, the availability of reactive chemical surface functions and the quantum sensing properties of the coated NDs has been assessed and optimized. Post-modification of the nanogel-coated NDs was achieved with phototoxic ruthenium complexes yielding ND-based probes suitable for photodynamic applications. The adsorption-crosslinking ND functionalization reported herein provides new avenues towards functional probes and traceable nanocarriers for high resolution bioimaging, nanoscale sensing and photodynamic applications.