Novel GaN-Based Substrates with Gold Nanostructures for Ultra-Sensitive SERS Analysis: Micro-Nano Pit Morphology for Enhanced Molecular Detection

Purpose: Surface-enhanced Raman scattering (SERS) is a technique for trace analysis detection based on the interaction of light with matter and between materials. In the past development of SERS, precious metals were primarily chosen as substrates due to their high electromagnetic effect, which leads to significantly enhanced SERS signals. However, the effect of using only precious metals is limited. Therefore, this study utilizes the characteristic micro-nano V-shaped pits that appear on the surface of c-plane GaN after wet etching. By depositing a gold film of various thicknesses, we aim to increase the contact area with the target molecule Rhodamine 6G (R6G), thereby further enhancing the sensitivity of SERS detection. Methods: After fabricating pitted c-plane GaN using chemical etching techniques, we analyzed the sample surface with a scanning electron microscope and assessed the impact of different gold film thicknesses on the SERS intensity of R6G using Raman spectroscopy. The comprehensive biomedical detection effectiveness was also evaluated using contact angle measurement, and fluorescence microscopy. Results: For the target molecule R6G, after depositing a 25 nm gold film, the enhancement factor of the substrate for detection reached 2.21×10⁸, and the limit of detection was achieved at a concentration of 10^{− 10} M. Conclusion: This study confirms the feasibility of using wet etching techniques on hexagonal materials like GaN for SERS applications. The GaN substrate with V-shaped pits provides an increased surface area, effectively enhancing SERS signal strength. This offers different choices and perspectives for SERS substrate selection in the detection of various target molecules.