Tip-enhanced Raman scattering (TERS), a scattering type scanning near-field optical microscope (s-SNOM), is a technique which combines Raman spectroscopy with an optically active silver coated scanning probe microscopy tip. Only the molecules located in a small area close to the tip apex will experience the field enhancement. This provides a unique tool to obtain highly enhanced Raman signals together with a high lateral-resolution. In this paper, preliminary
investigation of the interaction between methylene blue and calf-thymus double-stranded (ds) DNA has been carried out by SERS. Furthermore, TERS spectra of methylene blue have been collected for the first time, and are compared with standard surface enhanced Raman scattering (SERS). The results are discussed in terms of possible biological applications.