Photothermal property assessment of gold nanoparticle assemblies obtained by hydroxylamine reduction

The ideal photothermal therapy agent should exhibit a high energy conversion capacity, but it should not induce any cytotoxic effects unless it is exposed to electromagnetic radiation. We present data on biocompatibility and photothermal conversion capacity of colloidal gold nanoparticle assemblies (NPAs), obtained by hydroxylamine hydrochloride reduction at room temperature. The cytotoxic profile of NPAs with a mean diameter of 20 and 120 nm, respectively, was assessed using 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, demonstrating tolerable cytotoxic effect on A549 human lung adenocarcinoma cell line at gold concentrations up to 150 μg gold/mL. Insights regarding the oxidative stress were gained using peroxide-sensitive fluorescent probes, which showed no additional oxidative stress due to NPA exposure. Using infrared thermal imaging, the photothermal conversion was evidenced, the effect being more prominent for the 120-nm diameter NPAs irradiated with the 785-nm laser. The photothermal capabilities of NPAs were highlighted also by Raman imaging studies, showing intracellular carbon by-products due to the thermal damage. Intracellular carbon deposits overlapping with the nanoparticle-rich sites were identified. These results highlight that NPAs are a versatile platform with possible applications in nanoparticle-based photothermal therapy.