Evaporation-driven micro-patterning of gold nanorod core@silver shell composites enables trace cesium ion detection through surface-enhanced Raman scattering

In this study, we report a robust and scalable strategy for fabricating gold nanorod core@silver shell (GNR@Ag)-based surface-enhanced Raman scattering (SERS) substrates using an evaporation-assisted micro-patterning technique. The proposed method enables the formation of highly uniform and reproducible arrays by controlling the deposition number, substrate thickness, and silver shell coating thickness. By optimizing these structural parameters, we achieved significant Raman signal enhancement, enabling the trace-level detection of molecular analytes such as Rhodamine 6 G (R6G) and methylene blue (MB) across a wide concentration range. Notably, the platform demonstrated excellent signal linearity and reproducibility, and maintained performance in mixed-analyte environments, supporting its utility for multiplexed chemical sensing. In addition to its physical optimization, the SERS substrate was chemically functionalized with cucurbit[6]uril (CB[6]) to improve chemical selectivity. This functionalization strategy resulted in selective enhancement of cesium ion (Cs⁺) signals, while showing negligible response to other heavy metal ions such as Hg²⁺ and Zn²⁺. The platform enabled reliable detection of Cs⁺ down to the nanomolar level, highlighting its applicability for environmental monitoring of trace contaminants. Importantly, the combination of geometrically controlled nanostructure and ligand-based surface chemistry allowed for synergistic optimization of sensitivity and selectivity. Overall, this work presents a comprehensive framework for designing multifunctional SERS substrates with precise control over both structural and chemical parameters. The proposed micro-patterned GNR@Ag assemblies are promising candidates for portable, high-performance SERS-based sensors targeting trace-level detection and discrimination of specific analytes in complex environments.