Synthesis of Chitosan and Sodium Citrate Capped Gold Nanoparticles

The Turkevich method, previously described in [19 (link)], was used to synthetize the CH-AuNPs and SC-AuNPs. For the CH-AuNP synthesis, we prepared an acid solution of chitosan (CH, 2% w/w in acetic acid 0.4 M) by dissolving CH (medium molecular weight, 300,000 g/mol, with 75–85% of deacetylation) in 2 mM hydrochloroauric acid solution (HAuCl₄), then we homogenized the solution on a magnetic plate at room temperature for 15 min at 80–90 rpm until it changed to the color of red wine [18 (link)]. For the SC-AuNP synthesis, sodium citrate and HAuCl₄ were purchased from Sigma-Aldrich, sodium citrate was dissolved in distilled water to obtain a 1% solution, the 1 mM HAuCl₄ solution was mixed with sodium citrate and placed in a water bath for 15 min at 100 °C ± 2 °C, to a ratio of 1:1 (HAuCl₄/sodium citrate) volume/volume, until it changed to the color of red wine. Finally, the synthesis was allowed to settle at room temperature, and was stored for later use. The CH-AuNPs and SC-AuNPs were diluted 1:1 in RPMI 1640 medium (GIBCO^® by Life Technologies). The concentrations were determined based on precursor salt (HACl₄) concentration (μM) involved in AuNPs synthesis.