Synthesis and Characterization of PEI-Coated Gold Nanoparticles

AuNPs were prepared by chemical reduction.^{10–12 (link)} The solution of 25 mL 0.056% chloroauric acid (Aladdin, Shanghai, China) in a 50 mL conical bottle was added by 0.8 mL 1% branched polyethylenimine (Shyuanye, Shanghai, China) 25 kD (AuNPs-PEI) and stirred at 500 rpm continuously for 24 hours at room temperature (25 °C). When the color of the solution no longer change, the reaction is completed and the solution is filtered using a 0.2 μm microporous filter (Biofil, Guangzhou, China). The AuNPs modified by PEI were stored in the original volume of distilled water and in a refrigerator at 4 °C. We modified the preparation procedure of AuNPs-PEI, used a 30 kDa dialysis bag (MYM, Beijing, China) for dialysis to remove PEI which was not combined with AuNPs to allow minimization of PEI interference.^{13 (link)} The size and zeta potential of the nanomedicines were measured using ZEN3690 zetasizer (Malvern, USA).
The actual amount of chloroauric acid in preparation: 0.056% g mL⁻¹ × 25 mL = 0.014 g; the actual mass of AuNPs: m_AuNPs/m_{chlorogold acid} = 197/394, m_AuNPs = 0.007 g; so we estimated the concentration of nano gold as follows: 0.007 g/25.8 mL = 2.71 × 10⁻⁴ g mL⁻¹ ≈ 1 mM.