Characterization and applications of fluorescent nanodiamonds surface-coated with photo-crosslinked lipids

Fluorescent nanodiamonds (FNDs) are emerging as a novel fluorescent probe due to their stable fluorescence showing no photobleaching, negligible toxicity, chemical inertness, and optically detected magnetic resonance property. Recently, several unique applications such as multimodal imaging, single particle tracking, long-term cell tracking have been reported. However, the use of FNDs for those applications is still limited because well-optimized surface coating methods have not been established so far. In this presentation, we report a novel surface coating method based on lipid coating and subsequent photo-initiated radical polymerization. FNDs are first coated with lipids containing diacetylene in the alkyl chain, and subsequently crosslinked by UV irradiation to enhance the stability of the FND-lipid hybrids (FND-PCL: Photo-crosslinked lipid-coated FND). The method does not require complex organic chemistry techniques, and the produced coating layer is thin (ca. 2-3 nm) but highly stable thanks to the covalent bonding. The FND-PCL, as well as the biotin-functionalized FND-PCL, can be prepared in a couple of hours without much difficulty. The FND-PCL has many favorable properties for bioapplications such as strong aggregation resistance and reduced nonspecific adsorption by biomolecules. We further demonstrated two improvements on FND-PCL: enhancement of the production yield and facile surface modification. The coating method enhances the unique fluorescence properties of FNDs and opens interesting pathways of novel bioimaging.