Monodisperse,\nHighly Spherical, Single Crystalline\nAu Nanospheres for Uniform and Reproducible Hot Spots in Surface-Enhanced\nRaman Scattering at the Single-Particle Level

Hot\nspots can generate intense local electromagnetic (EM) fields,\nthereby boosting diverse innovative applications. However, these applications\nmay face challenges due to their subtle structural changes that can\nsignificantly impact their EM field strength. Herein, we report a\nlarge-scale synthesis of monodisperse, highly spherical, single crystalline\n(SC) Au nanospheres (Au NSs) with tunable sizes ranging from 38 to\n92 nm for constructing uniform and reproducible hot spots with a nanosphere-on-mirror\n(NSoM) configuration. Surface-enhanced Raman scattering tests reveal\nthat single NSoM hot spots generate homogeneous EM fields with intensity\nvariation of <4.0% due to their identical “point-to-mirror”\nconfiguration. Moreover, the SC nature of the Au NSs can further increase\nthe EM field by 9% because of their higher quality factor, resulting\nin less energy dissipation in the plasmon. Therefore, these Au NSs\nmay serve as ideal building blocks for the construction of hot spots\nwith homogeneous EM fields.