Surface-Enhanced Raman Scattering (SERS) is of substantial interest as a means of amplifying the typically relatively weak Raman signal. One issue with SERS is finding substrates with high enhancement factors that are cost-effective to produce. Recent years have seen an explosion in the number of potential substrates, including those produced by lithography, films over nanospheres, and as nanostructures deposited on porous silicon (pSi). The problem with all of these has traditionally been cost. Even the pSi substrates have traditionally been highly-doped silicon, and the time/concentrations used in the deposition of the active substance on the substrate have been large.
In an interesting recent paper, Kosovic and colleagues use low-doped mico- and mesoporous pSi immersively plated in silver nitrate solution to prepare SERS substrates. After substantial characterization, they show a Raman enhancement factor of at least 106, and possibly 1012. As they were nearing the level of single-molecule detection, the actual enhancement factor was hard to determine, because the target (R6G dye) was so dilute, and the confluence of a target molecule and a SERS particle hotspot was not guaranteed. Further characterization is thus needed, but it seems that this SERS substrate – offering low cost and ease of fabrication – may have great potential for achieving wide use in Raman spectroscopy.
Read more: Marin Kosović, Maja Balarin, Mile Ivanda, Vedran Đerek, Marijan Marciuš, Mira Ristić, and Ozren Gamulin, “Porous Silicon Covered with Silver Nanoparticles as Surface-Enhanced Raman Scattering (SERS) Substrate for Ultra-Low Concentration Detection,” Appl. Spectrosc. 69, 1417-1424 (2015).