Direct, label-free
sequence analysis of DNA hybridization has been
achieved by surface-enhanced Raman spectroscopy. In this work, aluminum-ion-aggregated
and iodide-modified silver nanoparticles were used as substrates to
obtain Raman spectra of the DNA strands with the same base composition
but different sequences, which form random coils or various hairpin
conformations. Upon DNA hybridization, reproducibly enhanced bands
were easily observed, corresponding well to the formation of Watson–Crick
hydrogen bonds, base ring breathing vibrations, and hairpin loops.
These characteristic bands can be used to unambiguously distinguish
the hairpins from the random DNA conformation. Moreover, by using
the deoxyribose band (959 cm–1) as an internal standard
to normalize the characteristic bands at 1703 cm–1 corresponding to the dG νC=O H bond, the guanine–cytosine
base-pair contents and sequence in DNA hairpins can be accurately
measured. Applying this method, a single base mutation in a functional
double helix was confidently identified.