Quantifying Magnetic Nanoparticles Thermal Signatures at High Precision By Lock-in Thermography

Superparamagnetic iron oxide nanoparticles are the topic of a broad research activity in the biomedical domain because of their unique properties. One of the most investigated one is their ability to generate heat in response to an alternating magnetic field. Traditionally, the amount of heat generated by particles is measured by means of fiber optics. However, the application of this method is not optimal, and suffers from severe limitations. In this work, we present a fundamentally different approach based on lock-in thermography to probe the thermal emissions of stimuli-responsive nanoparticles. Highly monodisperse iron oxide nanoparticles, prepared from thermal decomposition of iron oleate at high temperature have been prepared in three different sizes. After ligand exchange to transfer them in water, these model nanoparticles have been exposed to an alternating magnetic field and the heat generated was measured by means of lock-in tomography. Quantitative and qualitative information at high thermal resolutions could be obtained. The amount of heat generated was modeled mathematically using Rosensweig linear response theory. Compared to conventional techniques, this approach offers a fast, sensitive and non-invasive alternative to investigate multiple and dilute specimens simultaneously, which is essential in optimizing and speeding up screening procedures for various fields of application.