Superhydrophobic/-philic SERS Platform Based on Femtosecond\nLaser-Induced Periodic Surface Structures and Ag Nanoparticles

The\ntrace detection of molecules from highly diluted solutions\nis critical for biomedical diagnostics, environmental monitoring,\nfood safety, and pharmaceutical quality control. We introduce a highly\nsensitive superhydrophobic/-philic surface-enhanced Raman scattering\n(SERS) platform with specific patterns for trace detection. A superhydrophobic\nstructure was fabricated on stainless steel using femtosecond laser-induced\nperiodic surface structures with chemical modification and annealing.\nThe periodic wavy strips, measuring 654 nm in width, are uniformly\ndistributed across a large area. Superhydrophilic patterns of various\nsizes and shapes were then created on the superhydrophobic surface\nthrough nanosecond laser processing. Studying the droplet evaporation\nprocess and deposition characteristics shows that target molecules\nconcentrate at the vertex positions of the superhydrophilic pattern,\nsignificantly enhancing SERS performance. The triangular pattern with\nan 800 μm circumcircle diameter exhibited the highest enhancement\namong the patterns. We demonstrated trace detection of crystal violet\nmixed with Ag nanoparticles averaging 54 nm in diameter, achieving\na Limit of Detection (LOD) of 1.22 × 10<sup>–15</sup> M\nand an enhancement factor of 3.69 × 10<sup>10</sup>. Furthermore,\nwe integrated our platform with COF@Ag. The COFs display a nearly\nspherical morphology with an average diameter of 925 nm, and their\nsurfaces are densely and uniformly covered with Ag nanoparticles.\nThis significantly enhances the platform’s efficiency in trace\ndetection, enabling the successful detection of the antibiotic amoxicillin\nwith an LOD of 1.01 × 10<sup>–11</sup> M. This demonstrates\nthe practical application of the superhydrophobic/-philic SERS platform\nin biosensing and quantitative analysis, positioning it as a powerful\ntool for trace detection across various fields.