Tip-enhanced Raman spectra of picomole quantities of DNA nucleobases at Au(111)

We show that label-free detection of picomole amounts of the four nucleobases, respectively, adsorbed at atomically smooth Au(111) is straightforward with tip-enhanced Raman (TER) spectroscopy. In addition to TER spectra that allow identification of the corresponding DNA base, topographic images of the nanometer-sized sample can be obtained. Only 130 adenine molecules present in the enhanced field region in the tip-sample gap are sufficient to record the adenine fingerprint, that is, the Raman band of the characteristic ring-breathing mode at 734 cm-1