A Nanodiamond-Based Theranostic Agent for Light-Controlled Intracellular Heating and Nanoscale Temperature Sensing

Temperature is an essential factor in all biological processes and most of the biological activities are related to temperature. However, information about the temperature in living cells are limited. In photothermal therapy, an emerging cancer treatment due to its high spatial control and non-invasive nature, the local effect of intracellular temperature change is not well understood. Fluorescent nanodiamonds (ND) are a unique carbon material possessing optical defects inside the carbon lattice that enable sensing of temperature on a nanoscale completely independent of external conditions. Herein, we coat ND with polymers to form a nanogel shell around NDs that can absorb indocyanine green, a common photothermal agent, to obtain nanodiamond-nanogel-indocyanine green. Upon irradiation, we not only show successful killing of cancer cells with a high control in space but we are also able to sense the increase in temperature using single NDs as nanothermometers in cells.