Size control in the synthesis of 1–6 nm gold nanoparticles using folic acid-chitosan conjugate as a stabilizer

We report a simple and practical method for the preparation of folic acid (FA)-chitosan functionalized gold nanoparticles (AuNPs) with a very small size (1–6 nm). Sodium borohydride was used as a reducing agent. The size of the AuNPs was controlled by adjusting the mass fraction of FA-chitosan conjugate to Au. The AuNPs were characterized using UV–vis spectroscopy and transmission electron microscopy (TEM). The results indicated that the size distribution of AuNPs decreased ranging from 6 nm to 1 nm with increasing the fraction of FA-chitosan conjugate in the reaction systems.