Optimized thermal response of Au nanoframes in NIR-II window: a numerical study

Au nanoframes are promising tools for photothermal drug delivery and cancer treatment because their red-shifted localized surface plasmon resonance (LSPR) can be effectively excited in the near-infrared (NIR) region. Photothermal therapy using Au nanoframes is favorable due to its affordability, nontoxicity, and minimal effect on healthy cells. However, the nanoparticles currently used in this field are affected by various problems, such as thermal deformation and the risk of the LSPR deviating from the NIR range. Here, we present the double-torus (DT) nanoframe design, where two tori are oriented perpendicularly to each other, for enhanced optical and thermal responses. We compare the photothermal properties of DT and several standard nanoparticles in the second NIR (NIR-II) window (1000–1400 nm), simulate their optical and thermal behavior and optimize their size to achieve the desired therapeutic temperature range of 40–49 °C within the NIR-II window, demonstrate how their shape and symmetry influence their thermal efficiency, and investigate their thermal responses across different sizes. Our findings indicate that controlling heat generation within the therapeutic range highly depends on nanoparticle shape, symmetry, and metallic volume. Regarding the sensitivity of nanoparticle heat generation to nanoparticle volume, the DT structure is the most effective for heat regulation. Moreover, the curved design of the toroidal nanoframe minimizes the risk of the LSPR shifting beyond the NIR-II range. Having robust optical and thermal properties, the DT structure is an excellent candidate for use as a colloidal nanoparticle in biomedicine.