Monodisperse, Highly Spherical, Single Crystalline Au Nanospheres for Uniform and Reproducible Hot Spots in Surface-Enhanced Raman Scattering at the Single-Particle Level.

Hot spots can generate intense local electromagnetic (EM) fields, thereby boosting diverse innovative applications. However, these applications may face challenges due to their subtle structural changes that can significantly impact their EM field strength. Herein, we report a large-scale synthesis of monodisperse, highly spherical, single crystalline (SC) Au nanospheres (Au NSs) with tunable sizes ranging from 38 to 92 nm for constructing uniform and reproducible hot spots with a nanosphere-on-mirror (NSoM) configuration. Surface-enhanced Raman scattering tests reveal that single NSoM hot spots generate homogeneous EM fields with intensity variation of <4.0% due to their identical "point-to-mirror" configuration. Moreover, the SC nature of the Au NSs can further increase the EM field by 9% because of their higher quality factor, resulting in less energy dissipation in the plasmon. Therefore, these Au NSs may serve as ideal building blocks for the construction of hot spots with homogeneous EM fields.