Temperature evaluation of colloidal nanoparticles by the thermal lens technique

The use of highly sensitive thermometric methods is essential for the evaluation of nanoplatforms for photothermal therapy. In this study, the thermal lens technique was introduced to assess the optically induced temperature changes in colloidal samples of gold nanoparticles. Thermal lens measurements also allowed the acquisition of the nanoparticle absorption cross-section value, regardless of knowing the nanostructure scattering properties. The developed thermometric system exhibited 0.2 °C^-1 sensitivity and was capable of measuring temperature variations of metallic colloidal samples with a resolution of 0.01 °C. Measuring colloidal temperature changes allows for the estimation of the localized temperature variation reached by each nanoheater, before thermalization of the excitation volume. Our results establish a practical and effective method to evaluate optically induced temperature changes on metallic colloids.