Worm-like gold nanocrystals fabricated using a self-assembling peptide and inducing cell death upon exposure to near...

Gold nanorods (GNRs) can perform photothermal energy conversion by absorbing near-infrared (NIR) light and converting it to heat, and are therefore promising for applications in photothermal cancer therapy. However, to synthesize these nanorods, the highly cytotoxic compound cetyltrimethylammonium bromide (CTAB) is required. In the present study, to overcome this difficulty, we developed a method for synthesizing CTAB-free nanocrystals in the form of gold nanoworms (GNWs) using a self-assembling peptide exhibiting a positively-charged nuclear localization signal (NLS) sequence. We investigated the photothermal conversion performance of the GNWs and their ability to induce cell death under NIR irradiation. Based on transmission electron microscopy observations, the NLS-GNWs were determined to be approximately 80 nm in length and 9 nm in width. Their photothermal conversion efficiency was estimated to be 0.27 ± 0.06. Interestingly, in the absence of NLS-GNWs, following three cycles of NIR light exposure for 5 min at an intensity of 5 W/cm² separated by 10 min intervals, no significant change in cytotoxicity of HeLa cells was observed compared with the control. However, in the presence of NLS-GNWs, the cell viability after the first, second and third cycles was approximately 25 %, 18 % and 10 %, respectively. The intracellular localization of NLS-GNWs was also investigated using fluorescein labelled-NLS-GNWs, and it was found that many of the GNWs were present at the nuclei of the HeLa cells. The positively-charged NLS-GNWs are thought to have been attracted to the relatively acidic surfaces of the cancer cells.