Fabrication of blue-fluorescent nanodiamonds modified with alkyl isocyanate for cellular bioimaging

This paper describes the fabrication of water-dispersible nanodiamond (ND) clusters with blue fluorescence for cellular bioimaging. Poly(ethylene glycol) carboxyl methyl acid (mPEG-COOH) and alkyl isocyanates with different chain lengths were conjugated onto the surface of the ND clusters for water dispersibility and fluorescence via carbodiimide chemistry. The relative fluorescence intensity was increased with the increases in the chain length of alkyl isocyanate and also their conjugated concentration. The ND clusters (average size of 37.6 nm and zeta potential of 26.6 mV) with mPEG-COOH and octadecyl isocyanate (ODI) emitted relatively higher blue fluorescence intensity under excitation at 350 nm as well as favorable water dispersibility. After cellular uptake of the ND clusters, blue fluorescence inside the cells was confirmed by confocal laser scanning microscopy. The ND clusters conjugated with mPEG-COOH and ODI can potentially be used for cellular bioimaging.