Observation of terahertz absorption signatures in microliter DNA solutions

Strong, repeatable Terahertz (THz) signatures are measured in small samples of DNA solution using a THz photomixing spectrometer with custom conical-horn coupling. The DNA specimen is linear, single-stranded (ss), 13-mer polynucleotide, and is diluted in buffer solution to have a concentration of 0.15 μmol/ml. The strongest signature is centered ∼717 GHz, and has a strength of 2.5 × 1016 cm−1/mol, linewidth 48 GHz, and damping time of 6.6 ps. The origin of the signature is attributed to the hydrogen bond of locally cross-linked ssDNAs.