Nanodiamonds synthesis using sustainable concentrated solar thermal energy: applications in bioimaging and phototherapy.

There is a renewed interest in nanodiamonds and their applications in biology and medicine, especially in bioimaging and photothermal therapy. This is due to their small size, chemical inertness and unique photo-properties such as bright and robust fluorescence, resistant to photobleaching and photothermal response under near infrared (NIR) irradiation. However, the biggest challenge limiting the wide-spread use of nanodiamonds is the high-energy consuming, dangerous and sophisticated synthetic methods currently adopted by industry named higher temperature high pressure approach, and detonation method. Despite over a decade of research towards the development of new synthetic approaches, most of the methods developed to date require sophisticated instrumentations and have high energy demand. To circumvent the reliance on high energy demanding sophisticated experimental setups, here we present a simple synthetic approach using solar energy as a sustainable sole energy source. Using low-grade coal as carbon precursor, we used high power magnifying glasses to concentrate and focus sunlight to induce synthesis of nanodiamonds. The synthesized nanodiamonds exhibit similar physicochemical and photo-properties as nanodiamonds synthesized using other synthetic approaches.studies using macrophage Raw 264.7 cells demonstrated rapid uptake and bright fluorescence of the synthesized nanodiamonds with superior biocompatibility (≥95% cell viability). The synthesized nanodiamonds also exhibited dose dependent photothermal response under NIR irradiation.