A Superhydrophilic Au-Coated Monolayer Polystyrene Sphere Substrate for Uniform Surface-Enhanced Raman Spectroscopy

Uniform molecular dispersion and strong signal enhancement are critical for reproducible surface-enhanced Raman spectroscopy (SERS). However, conventional SERS substrates often suffer from poor wettability, leading to nonuniform analyte deposition and signal fluctuation. Herein, we present a superhydrophilic SERS substrate composed of gold-coated monolayer polystyrene spheres (Au-MPS), fabricated via doctor-blade-assisted colloidal lithography, followed by gold sputtering. The resulting Au-MPS exhibits both excellent wettability and tunable plasmonic properties. Optical, morphological, and spectroscopic characterizations reveal distinct plasmonic coupling behavior, with a maximum enhancement factor of ∼10⁵-fold and a limit of detection down to the micromolar range using Rhodamine 6G as a probe molecule. The scalable fabrication and consistent performance highlight the potential of this substrate for cost-effective and practical sensing applications. Furthermore, detecting trace levels of the toxic paraquat herbicide is demonstrated, indicating the potential for real-world applications.