Enhancing Near-Infrared Photothermal Efficiency of Biocompatible Flame-Synthesized Carbon Nano-Onions with Metal Dopants and Silica Coating

As an alternative to eliminating cancer cells with minimal impacts on the nearby tissues, biocompatible nanoparticles based on silica-coated carbon nano-onions, with outstanding photothermal efficiency, are presented. Metal-doped carbon nanoonion@SiO2 materials are produced using flame synthesis. Metal complexes are injected in the flame to tune the carbon organization levels, which results in materials with excellent photostability and total photothermal conversion efficiency, regarding the incident light input, as higher as 48% for 785 nm laser. It was found that the metal dopant, even at a very low content, plays an interesting role in photothermal efficiency. We tested the effect of thin silica layers on the carbon nanosphere, first as a way to improve biocompatibility and provide a more reactive surface toward the modifications process to add vectorizing agents. Despite the primary goal of the silica shell, a notable increase in photothermal efficiency was observed. In vivo studies of the biological response to the materials as probed by the zebrafish model found that the as-prepared carbon nanospheres and the SiO2-coated particles are highly biocompatible. The SiO2-coatedsamples were found to be more suitable for photothermal application, due to the higher colloidal stability and higher photothermal efficiency.