Publication / Precision-Engineered Plasmonic Nanostar Arrays for High-Performance SERS Sensing

Lumerical simulation setup and results for nanodisk and asymmetric nanostar geometries. A). STL files of (left) nanodisk and (right) asymmetric nanostars to show the geometry of the features imported into Lumerical for simulation. B) Lumerical simulation area setup: (Left) diagram/top-down view of the 75 nm nanostars on a substrate with a 500 nm pitch distance. Grid square is 100 nm × 100 nm; (Right) 3D diagram of Lumerical setup, where the red region represents silicon, the grey region represents silicon oxide, the yellow stars represents gold, and the orange box outlines the FDTD simulation area. The white box indicates the source location. C) Simulation results showing electric field magnitudes for 50 nm nanodisks and 75 nm nanostars at different pitch spacings. D) Simulation results demonstrating local field magnitude at the sharp tips of nanostars of several sizes compared to nanodisks of 50 nm.

Surface-enhanced Raman scattering (SERS) spectroscopy has emerged as a powerful tool for ultrasensitive and rapid analysis, with applications across several fields. The core mechanism of SERS is the interaction between molecules and plasmonic nanostructures, where localized surface plasmon resonances induce strong electromagnetic fields resulting in remarkable enhancements of Raman signals. The effectiveness of SERS substrates depends on their ability to generate strong electromagnetic fields at nanoscale hot spots, but achieving both reliable enhancement and reproducibility remains a challenge. This work presents a novel SERS substrate that combines a top-down fabrication approach with bottom-up wet chemistry to obtain an array of nanostars. Using electron beam lithography (EBL), uniform nanodisk arrays are first created, providing a controlled template. A subsequent chemical transformation reshapes these structures into nanostars, introducing sharp protrusions that significantly intensify localized electromagnetic fields. Finite-difference time-domain (FDTD) shows that nanodisks produce weak, symmetric field enhancements, while nanostars generate intense, highly localized electric fields at their spikes. Experimental SERS measurements using 1-naphthalenethiol (1-NAT), and tryptophan validate this transformation, demonstrating notable signal amplification with nanostar substrates. This work introduces a scalable and reproducible fabrication method for high-performance plasmonic SERS substrates, paving the way for a wide range of applications in distinct fields.

Read the full article here.