Modifying the mechanical properties of gold nanorods by copper doping and triggering their cytotoxicity with ultrasonic wave.

We proposed the use of copper (Cu) doping to modify the mechanical properties of gold nanorods (AuNRs) and demonstrated the triggering of the cytotoxicity of Cu-doped AuNRs with ultrasonic wave. The mechanical properties of Cu-doped AuNRs were analyzed theoretically by using the density-function calculation and it was found that Cu-Au bond is much weaker than Au-Au bond. In experiments, AuNRs without and with Cu doping were synthesized and they were found to be low cytotoxic to both human liver hepatocellular carcinoma (HepG2) cells and normal liver cells (L02). It was found that Cu-doped AuNRs can be broken into small gold nanoparticles (<5 nm) under high-power ultrasonic wave while undoped AuNRs were quite stable, although the amount of Cu doped into AuNRs was quite small (0.2%). The small gold nanoparticles are found to be with high toxicity to HepG2 cells. The cellular viability of the HepG2 cells dropped to nearly zero after being incubated with Cu-doped AuNRs (50 nM), which had been treated with a 300-W ultrasonic wave. Our findings suggest a novel method for modifying the mechanical properties of AuNRs and especially for triggering their cytotoxicity which is quite useful for in vitro therapy of cancer cells.