Surface-enhanced fluorescence of rhodamine 6G based on uniform and stable hierarchical nanoporous gold substrates

Nanoporous gold (NPG) is widely used in surface-enhanced fluorescence (SEF), but the adjustment capabilities of NPG, such as pore size and ligament dimensions, are inherently constrained, resulting in a relatively low density of electromagnetic hotspots. In this work, we report a two-step dealloying process to fabricate hierarchical nanoporous gold (H-NPG) with adjustable secondary mesopores and ligament sizes, which can enhance the density of electromagnetic hotspots and further improve SEF. The fluorescence enhancement of H-NPG with varying ligament sizes was investigated using Rhodamine 6G (R6G) dye molecules. The results show that the H-NPG sample with a ligament size of approximately 105 nm exhibited significantly higher fluorescence enhancement compared to NPG, achieving a further enhancement factor of about 5.3. Additionally, the substrates demonstrated good uniformity, providing valuable insights for developing new SEF substrates and their applications in molecular tagging and detection.