Plasma‐Etched Nanograss Surface without Lithographic Patterning to Immobilize Water Droplet for Highly Sensitive Raman Sensing

Abstract The development of reliable, cost‐effective molecular detection at the attomolar level on analyte‐immobilizing surfaces fabricated without lithographic patterning remains a major challenge in chemical sensing technology. This issue is addressed using custom‐designed adhesive superhydrophobic silicon nanograss surfaces produced via plasma etching. When applied to ultrasensitive surface‐enhanced Raman scattering, the nanograss surface enables effective immobilization of water droplets containing Ag nanoparticles and R6G target molecules. Upon water evaporation, the R6G analytes are confined at the edge of the self‐organized coffee‐ring‐like stains with the plasmonic hot spots of the Ag nanoparticles, thus providing a reliable Raman scattering platform for detecting trace analytes. Even at an ultralow concentration of 10⁻¹⁶ m, the corresponding relative standard deviation is 17.57%. A novel plasma‐enabled approach for precise interface nanostructuring, potentially leading to unprecedented capabilities in molecular‐level sensing technologies, is presented.