The Quest for Shape Control: A History of Gold Nanorod Synthesis

The development of facile seeded growth syntheses for anisotropic gold nanoparticles (particularly gold nanorods) has spurred an interest in their optical properties and applications. The development of the first seeded growth synthesis for gold nanorods in 2001 was a transformative event, providing the first simple, convenient wet chemistry route to these nanomaterials. Over the past decade, the original seeded growth procedure has been the subject of further modifications that have continuously expanded researchers' access to anisotropic gold nanoparticles. Recent modifications to the synthesis have improved synthetic control over gold nanorod aspect ratio, increased synthesis up to the gram scale, and provided the opportunity to tightly control the absolute dimensions of AuNRs. Despite these advances, the mechanism of gold nanorod growth in this synthesis remains poorly understood. Recent investigations into gold nanorod growth mechanisms have revealed the process to be unexpectedly complex, suggesting that many different reagents interact synergistically to promote shape control, and that growth of the AuNR core may proceed by complex processes, such as stochastic nanorod growth. Nevertheless, the advent of new in situ characterization techniques promises to shortly reveal new insights into gold nanorod core growth, and may inform further significant modifications, improving the efficiency and versatility of seeded growth synthesis. In this review, we recount the history of the seeded growth synthesis for gold nanorods, examine the impact of recent advances in this synthesis, and current investigations into the mechanism of gold nanorod growth.