Accurate Droplet Manipulation on the Central Radiant Grating Array: Effective Interfacial Enrichment and Spatial Localization for Ultrasensitive Label-Free SERS Biosensing

Droplet manipulation holds significant promise for advancing biosensing technologies, yet achieving spatiotemporally synchronized coenrichment and localization of analytes and plasmonic nanoparticles remains a critical challenge for ultrasensitive surface-enhanced Raman scattering (SERS) detection. Herein, we develop an integrated SERS platform based on a central radiant grating structure for simultaneous analyte enrichment and plasmonic hotspot localization. The radiant grating, fabricated through a template replication and low surface energy modification method, enables scalable production and high-throughput detection while maintaining ∼100 μm spatial precision. Crucially, the hydrophobic design sustains droplet stability with evaporation-driven directional transport; even as their volume diminishes to 0.4 mm, the contact angle of the droplets containing solutes is still close to 40°, suppressing self-pinning effects to achieve 2.24 × 103-fold analyte enrichment, directly overcoming size-dependent adsorption heterogeneity in nanospecimens such as exosomes. By integration of plasmonic particles within 100-μm sensing zones, the platform attains label-free detection limits of 10-10 M for ssDNA and 103 particles/mL for exosomes, significantly enhancing sensitivity and spectral resolution. Combined with multivariate analysis, this integrated enrichment-localized SERS technology reveals tumor exosome heterogeneity via intrinsic Raman spectral correlations, demonstrating the potential for early cancer diagnostics.