Ultra-Effective Methylene Blue Detection by Nanoporous Gold for Surface-Enhanced Raman Spectroscopy

This study presents the fabrication and optimization of nanoporous gold (Au) substrates for Surface-Enhanced Raman Spectroscopy (SERS). These substrates were obtained by the high-pressure thermal evaporation method, which utilizes a relatively high pressure of a few Torr to form highly porous structures. These nanoporous structures were induced by homogeneous nucleation and growth of the evaporated metal atoms that occurred through repeated collisions during the deposition process. By controlling deposition pressure and film thickness, optimal conditions to achieve enhanced SERS activity were established. The Au nanoporous structures consisted of randomly connected Au nanoparticles and demonstrated numerous nanogaps between these nanoparticles. These nanogaps act as hot spots of localized surface plasmon resonance, enabling significant amplification of Raman signals. The optimized nanoporous Au substrate, deposited at 2.0 Torr with a thickness of 1.65 μm, achieved a limit of detection (LOD) of 10^− 8 M for Rhodamine 6G (R6G). Furthermore, the substrate’s applicability was extended to the detection of methylene blue (MB), an organic dye with known environmental impacts. MB could be detected up to 10^− 6 M by using these nanoporous Au substrates for SERS. This work successfully demonstrated the potential of nanoporous Au for SERS as an effective analytical platform for trace-level detection of MB, paving the way for advancements in environmental monitoring and biological sensing applications.

Graphical Abstract