Beyond the Tip Effect: Geometrically Symmetric Gold Nanostars Achieve Uniform Hotspots for Ultrasensitive and Reproducible SERS Monitoring of Hydrogen Sulfide.

Surface-enhanced Raman scattering (SERS) is a powerful technique for ultrasensitive molecular analysis, benefiting from exceptional sensitivity and matrix tolerance. This study moves beyond the conventional tip enhancement strategy by designing geometrically symmetric gold nanostars (S-GNSs) with finely tunable sizes and tip curvatures. A systematic investigation reveals that symmetric geometry not only promotes uniform electromagnetic field distribution but also significantly improves signal reproducibility compared to traditional asymmetric nanostars. Among the synthesized substrates, S-GNSs287 exhibits the highest enhancement factor and remarkable signal uniformity, attributable to its sharper tips and optimal plasmonic coupling. Capitalizing on these advantages, a functional SERS probe is developed by modifying S-GNSs287 with 4-nitrothiophenol (S-GNSs287@4-NTP) for highly sensitive and reliable detection of hydrogen sulfide (H2S). The SERS probe achieves a low detection limit of 0.21 µm and a wide linear range of 5-500 µm, alongside excellent selectivity and stability. Furthermore, it is successfully applied to detect H2S in commercial wine and beer samples, achieving high recoveries (97.88%-100.86%) and low relative standard deviations (0.51%-2.12%), underscoring its practical utility in complex food matrices. By emphasizing the pivotal role of geometric symmetry in plasmonic enhancement, this work provides new insights into the rational design of SERS substrates and offers a robust platform for monitoring gasotransmitters in real-world samples.