Characterization of the DNA orientation towards the metal surface. (A) Illustration of the SERS-based detection scheme on the basis of the double-stranded DNA tilt angle. (B) SERS response of double-stranded DNA for various concentrations (spectra 1–5 are related to the concentrations 40, 20, 10, 5 and 1.25 μm). Reprinted with permission from Barhoumi et al. . Copyright 2008 American Chemical Society.