Reproducibility of Terahertz Peaks in a Frozen Aqueous Solution of 5-Methylcytidine

Abnormally high level of methylation in the epigenome is a biomarker for various forms of cancer. It has been reported that a methylated nucleoside, 5-methylcytidine, when dissolved in water and then frozen, has a resonance absorption peak around 1.6 THz, which could allow for the determination of the degree of methylation using terahertz spectroscopy. This study attempts to replicate the experiment and reproduce this observation independently. Samples of ice were measured at 173 K to establish a baseline and frozen solutions of 5-methylcytidine were measured. Normal (physiological) 0.15 M saline, which is known to have a peak at 1.6 THz, was also measured. The use of a Gaussian function to fit a baseline to the broad (0.2 to 2.5 THz) absorption spectra consistently produced a peak residual around 1.6 THz for all three types of samples, with saline having the highest peak followed by ice. The peak for 5-methylcytidine was found to be smaller than that for ice, which contradicts previously published findings and illustrates the strong dependence of the result on the method of baseline fitting.