Evaluating plasmonic nanosctructures for high performance photothermal therapy

Abstract

Tissue temperature control has been widely used for therapeutic application in several areas of medicine as oncology, physiotherapy, urology, cardiology and ophthalmology. Photothermal therapy (PTT) is based on the induction of cellular damage by light absorption in a target tissue. For an effective use of light on PTT, controlled and localized heating should be achieved. Localized heating has been accomplished by exploring plasmonic nanostructures. This work has as its main objective the evaluation of nanoheaters for high performance PTT. Experimental and theoretical analysis were employed to assess thermo-optical properties of gold nanostructures and metallic colloids. Crucial optical parameters ruling plasmonic heating were appraised, exploiting a nanoparticle size-dependence approach. Based on the finite-element method, the optimum size of gold nanorods for high performance infrared thermal therapy were found to be 45 nm and 60 nm at wavelengths of 800 nm and 1064 nm respectively for nanosecond pulse. For continuous excitation, particle morphology presents high significance, and heat generation shows the tendency to peak at lengths longer than 100 nm. The performance evaluation of nanoparticles as nanoheaters is a fundamental step to the development of efficient nanoplatforms for photothermal therapy. Here, the use of Thermal Lens technique on the characterization of nanoheaters was introduced. Optical heating of a colloidal solution of 50 nm diameter gold nanospheres were assessed by mode-mismatched Dual-Beam Thermal Lens technique. Temperature variations up to 1.28 °C were evaluated at the region of the excitation beam. The introduction of the Thermal Lens technique for the evaluation of heat generation in colloidal solutions of nanoparticles consists in a innovative approach for nanoheater characterization, with great potential.