Superhydrophobic nanostructured copper substrate as sensitive SERS platform prepared by femtosecond laser pulses

The superhydrophobic surface is considered as an ideal alternative surface-enhanced Raman scattering (SERS) substrate for ultra-trace detection, due to its unique concentration capability for a highly diluted solution. However, the combination of superhydrophobic properties and plasmonic nanostructures which serve as SERS hot spots still remain a challenge. Here, we develop a simple top-down method to fabricate nanostructured superhydrophobic SERS (S-SERS) substrates by femtosecond laser pulses directly on copper (Cu) without additionally Au/Ag coating. The Cu nanostructures not only allow the surface to exhibit superhydrophobic property to concentrate the analyte, but also contribute to the field enhancement. Furthermore, in order to further enhance the Raman signal, Ag nanoparticles with certain consentrations were injected into the droplet before evaporation, by which a concentrated mixture of analyte and Ag nanoparticles can be formed after evaporation. The synergistic effects of Cu nanostructures and Ag nanoparticles make the S-SERS substrate a highly efficient SERS platform with a low detection limit of 10(-13) M, a good recyclability and a long service time of up to 2.5 months under ambient conditions, exhibiting an obvious improvement compared to those silver coating methods.