Synthesis of Au Nanorods by Using Gamma-ray Irradiation

To synthesize Au nanorods without the use of seed crystals, we applied gamma-ray irradiation from 60 Co radioactive source to reduce aqueous solution containing Au ions. The total dose was fixed to 6.0 kGy with various dose rates from 0.4 to 13.6 kGy/h. After the irradiation, two surface plasmon bands in the range around 530 nm and above 700 nm were observed in UV/vis spectra. We observed by a transmission electron microscopy (TEM) that rod-shaped Au nanoparticles with the length of 20--25 nm, and the width of about 7--15 nm were produced as well as a small amount of spherical particles. The size and the aspect ratio of the Au nanorods are well correlated with gamma-ray irradiation dose rate; with increasing the dose rate, their size decreases and the aspect ratio increases.