  In the present contribution, specifically designed single-stranded DNA
(ssDNA) sequences composed of adenine and cytosine were used as nanometric
rulers to target the maximum achievable spatial resolution of tip-enhanced
Raman spectroscopy (TERS) under ambient conditions. By stepping along a strand
with a TERS tip, the obtained spectra allowed for a clear spectral
discrimination including conformational information of the nucleobases, and
even sharp adenine-cytosine transitions were detected repeatedly with a spatial
resolution below 1 nm.
