“…Consequently, fluorescence enhancements up to three orders of magnitude have been realized in solid assays created by the atomic-layer deposition, by which a thickness-tailorable spacer can be formed at the atomic level to achieve an optimal metalreporter distance for both modes (≈4 nm, slightly varying in spacers of different refractive indices [24,25] ). Approaches using colloidal NPs have proved much more challenging due to the fabrication challenges of wet chemistry (i.e., coating thickness, [24] random adsorption site of the reporter, [26] etc.). [25] Typical methods for forming the spacer on colloidal NPs include polymer, [24] DNA, [13] SiO 2 , [27][28][29] CTAB, [30,31] and pluronic, [3] among others, most of which only result in single to double-digit fluorescence enhancement factors (EFs) and severe loss of SERS intensity due to the weakened EM field.…”