Label-free DNA detection applying SERS for read-out. Recorded SERS spectra of (A) adenine containing and (B) adenine non-containing DNA sequence are shown. Within the inset, the hybridization model between probe DNA having 2-aminopurine substituted for adenine and unlabeled target DNA is illustrated. Reprinted with permission from Barhoumi et al. . Copyright 2010 American Chemical Society.