Silver nanocrystallites are obtained through immersion of porous silicon samples in AgNO3 solutions and a successive thermal annealing. The efficiency of nanostructures as surface enhanced Raman scattering (SERS) substrates is checked on cyanine-based dyes and horseradish peroxidase, evidencing detectable concentrations as low as 10(-7) to 10(-8) M. The substrate efficiency is strictly related to the Ag particle morphology, which could yield to either local surface plasmons (LSP) coupled to individual particles or to inter-particle short-range interaction. (C) 2008 Elsevier B. V. All rights reserved.