Fabrication of Superhydrophobic–Hydrophilic Patterned Cu@Ag Composite SERS Substrate via Femtosecond Laser

Abstract

Ultralow concentration molecular detection is critical in various fields, e.g., food safety, environmental monitoring, and disease diagnosis. Highly sensitive surface-enhanced Raman scattering (SERS) based on ultra-wettable surfaces has attracted attention due to its unique ability to detect trace molecules. However, the complexity and cost associated with the preparation of traditional SERS substrates restrict their practical application. Thus, an efficient SERS substrate preparation with high sensitivity, a simplified process, and controllable cost is required. In this study, a superhydrophobic–hydrophilic patterned Cu@Ag composite SERS substrate was fabricated using femtosecond laser processing technology combined with silver plating and surface modification treatment. By inducing periodic stripe structures through femtosecond laser processing, the developed substrate achieves uniform distribution hotspots. Using the surface wettability difference, the object to be measured can be confined in the hydrophilic region and the edge of the hydrophilic region, where the analyte is enriched by the coffee ring effect, can be quickly located by surface morphology difference of micro-nanostructures; thus, greatly improving detection efficiency. The fabricated SERS substrate can detect Rhodamine 6G (R6G) at an extraordinarily low concentration of 10−15 mol/L, corresponding to an enhancement factor of 1.53 × 108. This substrate has an ultralow detection limit, incurs low processing costs and is simple to prepare; thus, the substrate has significant application potential in the trace analysis field.