Self‐Controlled Automated Strategy for the Synthesis of Gold Nanorods With Fine‐Tuned Longitudinal Absorption

Reproducibility is the main weak point of most of the currently available synthetic strategies for metal nanostructures, and this issue is hampering both production and research on such materials. While several synthetic strategies can be found in literature, most of them are fundamentally based on strict protocols consisting of lists of subsequential predefined operations to be executed in a time-defined manner. Such protocols are designed and optimized on the basis of pilot runs and are intrinsically affected by noncontrollable fluctuations in the experimental conditions. In this work an innovative, intrinsically flexible, automatized, and self-correcting strategy is proposed, which, in combination with real-time monitoring of the optical properties of the reaction mixture, allows to synthesize precisely tuned gold nanorods. This strategy is based on the fast and precisely controlled oxidation of precursor AuNRs. The fast reaction allows the selective and predictable etching of the nanorods by online-controlled subsequential additions of small amounts of oxidants, which are also able to remove undesirably shaped byproducts possibly present in the sample. Due to these features, this process can be automated and allows starting from nonpurified nanorod dispersions with variable aspect-ratio. Furthermore, the reaction can be stopped by oxidizer quenching, providing stable dispersions.