Wet-chemical synthesis of two-dimensional complex nanorings for near-field focusing

Plasmonic nanorings are promising building blocks for a variety of applications, including optical and biological sensing, and energy because the open inner spaces of the nanorings exhibit a high surface-to-area ratio and possess unique optical properties that are different from solid nanostructures. However, the simple architecture of mono-rim based structures leads to low electromagnetic near-field confinement, which requires a more complex structure to facilitate effective interaction with light. Herein, we report on recent progress of synthetic strategies for fabricating plasmonic nanorings using both top-down and bottom-up approaches. First, we introduce the conventional methods for achieving classical ring architectures. Then, we discuss rationally designed synthesis methods for creating advanced and structurally unique nanostructures to increase near-field enhancement. This process involves multi-step chemical toolkits that enable control over the shape and the introduction of repeated units in a single entity. Then, we explore the potential applications of complex nanoring architectures.