Moire Patterns-Based Low-Cost Flexible SERS Substrates for Multi-Analyte Detection of Biological and Chemical Molecules

Abstract Reliable detection across diverse analyte classes remains a significant challenge in surface-enhanced Raman spectroscopy (SERS), particularly when a single platform must address both biological and environmental targets. This work develops a geometrically engineered Moiré-patterned plasmonic substrate that delivers consistent, enhanced SERS performance for multifunctional sensing applications. Unlike conventional disc-templated SERS substrates with single-periodicity grating geometries, sequential thermal nanoimprint lithography (TNIL) using a commercial DVD is employed to fabricate flexible Moiré-patterned substrates with a continuously varying pitch distribution across the substrate surface, providing multiple analyte-trapping sites of varying gap dimensions. The interwoven fringe structure introduces controlled periodicity and inclination, promoting enhanced plasmonic coupling and dense hotspot formation, with the measured structural parameters in close agreement with theoretical predictions. The periodic and inclined Moiré geometry promoted effective electromagnetic confinement within the nanostructured regions, yielding an analytical enhancement factor of 6.69 × 106 using Rhodamine 6G (Rd6G) as a probe molecule, together with a statistically determined limit of detection of 1.36 × 10−11 M and good signal uniformity and reproducibility. Finite-element simulations provide qualitative insight into field localization, highlighting the role of pitch variation in hotspot formation. The substrate retained a consistent SERS performance under bending and repeated crumpling. As a proof-of-concept demonstration of dual-analyte capability, hemoglobin (Hb), an oxygen-transport biomolecule of diagnostic relevance, and tetramethylthiuram disulfide (Thiram), a toxic fungicide residue of environmental concern, were detected at 1 μM and 1 mM, respectively, illustrating the ability of the Moiré geometry to accommodate analytes of differing sizes and chemistry. These results establish the substrate as a proof-of-concept platform for dual-analyte detection, while comprehensive validation in complex real-world matrices remains the focus of future work.