Mesoscopically Bi-continuous Ag–Au Hybrid Nanosponges with Tunable Plasmon Resonances as Bottom-Up Substrates for Surface-Enhanced Raman Spectroscopy

Ag-Au hybrid nanosponges (NSs) with controlled porosity and composition ratio were fabricated through a cyclic electroless deposition of Ag into the porous Au NSs. In the Ag-Au hybrid NSs, both Au and Ag components with mesoscaled ligament size are discontinuously percolated over the entire structure. The plasmonic properties of the Ag-Au hybrid NSs differ clearly from those of the Au NSs and the solid Au-Ag alloy nanoparticles, and two distinct plasmon peaks were observed and can be attributed to Au and Ag components, respectively. The plasmonic properties can be well tuned by controlling the cycles of Ag deposition. Both plasmon peaks attributed to Au and Ag components blue shift with increasing amount of Ag. The volume porosity decreases as upon increasing amount of deposited Ag. The results of the theoretical calculations reveal that the deceasing porosity could play an important role in the blue shift. Moreover, the Ag-Au hybrid NSs exhibit higher sensitivity in surface-enhanced Raman spectroscopy (SERS) detection of butter yellow (BY) due to the presence of Ag and of the porous structure. Also, the as-prepared structures present a build-in preference for hydrophobic analytes.