A cellulose nanocrystal-carbon dots@cholestrol fluorescent probe for imaging of plasma membrane with extended time scale

Despite the advancement of plasma membrane imaging techniques, there is an unmet need for fluorescent probes which can "light up" the lipid bilayer with an extended time scale. In this work, a novel fluorescent probe is developed for imaging of plasma membrane. The probe comprises a cellulose nanocrystal (CNC) scaffold derived from low-cost wood pulp, carbon dots (CDs) fluorophore that is in -situ synthesized on the surface of CNC, and cholesterol (Chol) ligand with aminated polyethylene glycol (PEG) spacer. In the CNC-CDs@PEG-Chol configuration, the Chol ligand provides excellent binding affinity onto plasma membrane due to its hydrophobic nature, while CDs contribute to the marvelous optical stability, as well as the high quantum yield of the fluorescent probe. For CNC scaffold, their unique morphological property allows the assembling of dense Chol ligands, and more importantly, impedes the diffusions of imaging moieties into the cytoplasm. Therefore, the fluorescent probe is featured with remarkable specificity and satisfying plasma membrane imaging time window, which covers the co-incubation time from 30 to 90 min. In contrast, the mono-dispersed CDs@PEG-Chol probe can be facilely internalized by the cells at a co-incubation time as short as 20 min. CNC is proven to be responsible for the different imaging time scales by providing the confinement effects. The proposed fluorescent probe is believed to be a promising tool for studying the plasma membrane behaviors associated with cellular physiological processes.