Synthesis of alginate-cysteine modified gold nanorods for photothermal therapy of oral cancer

Gold nanorods/alginate/cysteine (denoted as GNR@Alg-Cys) nanocomposites with good biocompatibility and cell-targeting ability are synthesized for photothermal therapy (PTT). Owing to the carboxylic acid groups on the alginate, we successfully functionalize alginate polymer with the primary amine groups of the cysteine and with targeting molecules (c(RGDfk)) through the formation of peptide bonds. Then, the thiol groups of the cysteine-functionalized alginate polymer can replace the surface protecting molecules (i.e. Cetyltrimethyl Ammonium Bromide; CTAB) on gold nanorods that were previously synthesized, thus connect the Au NRs with alginate polymer through Au-S bonds. In addition, we utilize c(RGDfK) oligopeptide to target the squamous cell carcinoma (i.e. SAS). The successful synthesis of GNR@Alg-Cys nanocomposites is confirmed with TEM, zeta potential, UV-Vis and FTIR analysis. The enhanced endocytosis of RGD-functionalized GNR@Alg-Cys is 1.95 times more than that of GNR@Alg-Cys, according to ICP-MS measurement. For PTT application, the synthesized samples are illuminated by NIR after SAS cell uptake, and the relative cell viabilities of GNR@Alg-Cys and GNR@Alg-Cys-RGD are 0.5 and 0.1, respectively. This result indicates that our GNR@Alg-Cys-RGD sample show great potential in PDT in the future nanomedicine.