Ultrahigh Raman‐Fluorescence Dual‐Enhancement in Nanogaps of Silver‐Coated Gold Nanopetals

Abstract Raman‐fluorescence dual‐mode enhanced nanoparticles have enormous potential for bioimaging with combined advantages of sensitivity and speed. This is primarily achieved through a trade‐off between fluorescence quenching and electromagnetic (EM) enhancement on the plasmonic metal surface, as demonstrated in previous research. A strategy that can minimize EM‐field attenuation and temporal photobleaching would be highly desirable. In this study, a novel approach using Raman‐fluorescence enhanced dual‐mode nanoparticles with the near‐infrared fluorescence reporter IR780 directly embedded in the ultra‐high EM fields between gold (Au) nanopetals of various morphology and a silver (Ag) coating without a spacer is presented. The results show these nanoparticles to be single‐nanoparticle Raman sensitive and that they can generate a fluorescence enhancement factor as high as 1113 experimentally and 2000 by numerical simulation. The random morphology of the nanopetals supports broadband resonances for both fluorescence excitation and emission, resulting in nanowatt detectability, the dual‐mode photostability of more than 30 min under continuous laser irradiation, and a long shelf life, making them promising for wide applications in bioimaging with ultra‐brightness, low laser power, and long‐duration monitoring. In summary, they represent a novel strategy for high‐performance Raman‐fluorescence enhancement dual‐mode nanotags.