*2.9. Photothermal Therapy (PTT)*

In vitro and in vivo PTT experiments were performed using a home-built laser setup [12]. For in vitro PTT, nanostars (2.3 <sup>×</sup> 1010 particles in 1 mL) were added to a 12-well plate containing 100,000 cells/well that were pre-incubated overnight. Nanostar concentrations were calculated as previously described in the supplementary methods section of [13]. The cells were then incubated with the nanostars for 24 h or with fresh medium as a control sample and washed twice with PBS. Next, the incubated cells were exposed to laser irradiation (690 nm, 20 W/cm2, 5 min) and incubated for an additional 2 h at 37 ◦C. Afterwards, the cells were washed with PBS. The cell viability was assessed using a live/dead staining (Calcein AM/Hoechst; Life Technologies Europe B.V., Gent, Belgium). After staining, the cells were imaged using a fluorescence microscope with 5× objective (CellR system, Olympus, Aartselaar, Belgium). During the in vivo experiments, the mice were irradiated for five minutes with a laser (λ = 690 nm; 2 W/cm2), inducing PTT one day after nanostar administration. During this laser treatment, the mice were anesthetized with ketamine/domitor [43].
