Optimized Biocompatible Gold Nanotriangles with NIR Absorption for Photothermal Applications

Gold nanotriangles (Au NTs) present singular plasmonic properties that are particularly attractive for photothermal applications. However, most syntheses rely on the use of surfactants which present cytotoxic effects, thus limiting the biomedical possibilities. Moreover, these methods have the disadvantage of producing Au NTs that either present absorption at wavelengths <750 nm or have side lengths >200 nm. In this work, we present the post-synthesis optimization and characterization of biocompatible Au NTs produced in a one-step reduction of Au(III) with thiosulfate ions. We demonstrate that the position of the absorption peaks can be fixed at a desired wavelength by the addition of different SH-containing molecules. In all cases, the stabilized Au NTs can be efficiently separated from spherical gold nanoparticles, a byproduct of most Au NT syntheses, by a method based on depletion forces using sodium dodecyl sulphate (SDS), a low-cost, non-toxic surfactant. In addition, we analyze possible cytotoxic effects of surface sulfide species and residual presence of SDS. First, incubation of the Au NTs with H2S-binding hemoglobin I from Lucina pectinata produced no deleterious effect on the protein. Second, we evaluated cytocompatibility by in vitro cellular tests after incubation with the purified Au NTs. Finally, laser irradiation at 808 nm of the Au NT dispersions yields photothermal conversion efficiencies of around 50%, which remained constant after several heating cycles.