Heat Generation in Single Magnetic Nanoparticles under Near-Infrared Irradiation

Heat generation by pointlike structures is an appealing concept for its implications in nanotechnology and biomedicine. The way to pump energy that excites heat locally and the synthesis of nanostructures that absorb such energy are key issues in this endeavor. High-frequency alternating magnetic or near-infrared optical fields are used to induce heat in iron oxide nanoparticles, a combined solution that is being exploited in hyperthermia treatments. However, the temperature determination around a single iron oxide nanoparticle remains a challenge. We study the heat released from iron oxide nanostructures under near-infrared illumination on a one-by-one basis by optical tweezers. To measure the temperature, we follow the medium viscosity changes around the trapped particle as a function of the illuminating power, thus avoiding the use of thermal probes. Our results help interpret temperature, a statistical parameter, in the nanoscale and the concept of heat production by nanoparticles under thermal agitation.