Self-Metered and Uniform Droplet Deposition within Defined Areas for Quantitative Surface-Enhanced Raman Scattering Detection

Achieving quantitative and reproducible surface-enhanced Raman scattering (SERS) detection remains challenging due to the stochastic nature of molecular distribution and the nonuniform enhancement of localized plasmonic "hot spots". Here, we present a wettability-patterned Ag nanoparticles and ZnO nanorod (Ag/ZnO)-nanostructured substrate that enables self-metered droplet partitioning and uniform molecular deposition for quantitative SERS sensing. By exploiting the strong contrast between hydrophilic and hydrophobic regions, a bulk liquid droplet can spontaneously split into an array of equal-volume microdroplets without any external confinement. During evaporation, the hydrophilic Ag/ZnO nanocolumns induce capillary-driven infiltration, which, in combination with wettability confinement, effectively suppresses the coffee ring effect and ensures homogeneous solute deposition within a defined area. Systematic comparisons among hydrophilic, flat-patterned, and nanostructured-patterned substrates reveal distinct drying dynamics, confirming that the synergistic control of capillary infiltration and wettability patterning governs uniform analyte distribution. Consequently, the designed substrate delivers highly linear and reproducible (RSD < 5%) SERS responses across multiple domains and analyte types. This simple yet robust self-metered droplet strategy provides a practical route toward uniform, quantitative, and molecule-independent SERS detection, offering new opportunities for reliable chemical and biosensing applications.