Tunable microstructured surface-enhanced Raman scattering substrates via electrohydrodynamic lithography

Readily fine-tuned structures are an important requirement for the optimization of surface-enhanced Raman scattering (SERS) to obtain the highest enhancements. Here, a lateral modulation of an electric field applied to a dielectric interface enables the rapid replication of nearly any topographic morphology with micrometer resolution by electrohydrodynamic lithography (EHL). Gold-covered periodic EHL-generated arrays yielded the reproducible enhancement of adsorbed SERS-active molecules. Periodic arrays of micropillars with square and circular cross sections give rise to the effective coupling of surface plasmon modes, which generate enhanced SERS signals. The overall enhancement factors depend on the geometry of the gold-coated structures, and intriguingly, a strong correlation is found with the gap-to-width ratio of the square pillar morphology. A numerical simulation of the EHL-based SERS substrates is consistent with this dependence. The EHL surface architectures can be easily tailored at micrometer-to-submicrometer dimensions, allowing the fabrication of reliably engineered and cost-effective highly sensitive SERS substrates.