Seedless Synthesis of Gold Nanorods with 5–10 nm in Diameters: a Comprehensive Study

Small gold nanorods (AuNRs), namely AuNRs with less than 10 nm in diameter, possess a high absorption-to-scattering ratio, a large surface area-to-volume ratio, as well as high cellular uptake behaviors. In this study, we systematically investigate seedless synthesis of AuNRs with diameters ranging from 5 nm to 10 nm. It has been found that several experimental conditions, including the chain length of the used cationic surfactants, and the concentrations of ascorbic acid, NaBH₄, and AgNO₃ can profoundly affect the obtained products. Under optimal conditions, the production yields of the obtained several AuNRs with different diameters can exceed 90% and even reach almost 100%. The conversion of gold precursors to AuNRs was estimated to be 70%–77% as measured by absorption spectroscopy and inductively coupled plasma mass spectrometry.