Length-Controlled Synthesis of Calcium Phosphate Nanorod and Nanowire and Application in Intracellular Protein Delivery

Although calcium phosphate based nanomaterials are widely used in various biomedical application, the synthesis of high quality examples of such nanomaterials with controlled size and shape is challenging. Here, we report a single-phase approach for the length-controlled synthesis of calcium phosphate nanorods and nanowires of 2-5 nm diameter and 10-1000 nm length. The synthetic method involves the injection of tetrabutylammonium phosphate into an oleic acid solution of calcium oleate at 200-330 °C and controlling the nucleation-growth kinetics of calcium phosphate by temperature, molar ratio of calcium to phosphate, reaction time, and solvent. Nanorods are formed at a calcium to phosphate molar ratio of 2:1, and with increasing temperature, more anisotropic nanowires are formed. As the reaction progresses at a certain growth condition, the length of the nanorods and nanowires increases with time and attains a maximum, and then the length distribution becomes broad. Thus, the best-quality nanomaterials are obtained by selecting the reaction temperature and then quenching the reaction at right time. These hydrophobic nanorods and nanowires are highly soluble, can be processed like conventional high-quality hydrophobic nanoparticles, and can be transformed into water-soluble functional nanoparticles via ligand-exchange or polymer-coating approaches. To demonstrate the application potential, we have transformed synthesized hydrophobic nanorods into water-soluble nanorods via polymer coating and used them as carriers for the cellular delivery of protein. These nanorods and nanowires can be viewed as potential cellular delivery carriers.