## 3 Experimental Results
### si-RNA and 50-bp Samples  
Our first compelling data were obtained with the si-RNA solution described above. The raw experimental results are plotted in Figure 4a in the frequency range 500 to 1200 THz--a band having four strong water vapor lines at 557 and 758 GHz, even stronger lines at 1098 and 1164 GHz, and a relatively weak line around 990 GHz. The top curve is the \"background\" signal P\({}_{\rm B}\) through the nanochannels containing buffer solution only, the middle curve is the \"sample\" signal P\({}_{\rm S}\) with si-RNA in the channels, and the bottom curve is the noise floor P\({}_{\rm N}\) obtained by blocking the THz path with a metal plate. There is clearly strong absorption from the si-RNA sample between \(\sim\)700 and 1050 GHz. Figure 3: Characteristic of the THz absorption signatures evaluated in this work. Figure 4b shows the transmittance over this range calculated from Equation (1). The transmittance is a mixture of broadband absorption and three prominent signatures centered at 916, 962, and 1034 GHz, and labeled (1), (2), and (3). There is also a broad and weaker signature between 830 and 875 GHz, and narrow but weaker ones around 1075 and 1100 GHz. The latter two are questionable, since they are convolved with strong water vapor lines, evident from the background transmission in Figure 4a. This drives both P\({}_{\rm S}\) and P\({}_{\rm B}\) into the noise floor, which invalidates the use of Equation (1). From Figure 4b, we can calculate the signature absorbance A\({}_{\rm S}\), linewidth, and quality factor for each qualified signature. The required values of T\({}_{\rm min}\) and T\({}_{\rm max}\) are shown in Figure 4b as red and green horizontal lines, respectively. This leads to A\({}_{\rm S}\) = 0.82, 0.86, and 0.88 for the \(\
u_{0}\) = 916, 962, and 1034 GHz signatures, respectively. The corresponding signature frequency widths are \(\Delta\
u\) = 10, 10, and 12 GHz, with corresponding quality factors of Q\({}_{\rm S}\) = 92, 96, and 86. All these parameters are listed in Table 1. We note that the \(\Delta\
u\) values are even narrower than the sharpest THz signatures measured in solid-state samples, such as the 23-GHz width of the 530-GHz line in lactose monohydrate [24]. Figure 4: (**a**) Power spectra for background, sample, and noise floor for si-RNA solution in the nanochannel cell. (**b**) Transmittance using the raw data in (**a**) and computation with Equation (1). The prominent three signatures are labelled (1), (2), and (3). The second sample we investigated was the 50-bp DNA ladder. Like the si-RNA, it displayed no sharp signatures below \(\sim\)700 GHz, just broadband attenuation, so we restricted the scan from 700-1100 GHz and the transmittance is plotted in Figure 5a. The most obvious effect compared to si-RNA is the much higher transmittance in this frequency range, the broadband average being \(\sim\)75%. However, three sharp signatures are evident in Figure 5a centered at 870, 938, and 993 GHz, and labelled (1), (2), and (3), respectively, with their spectral parameters listed in Table 1. The 993 GHz signature is the narrowest, displaying a \(\Delta\
u\) of about 12 GHz, and the other two display \(\Delta\
u\approx\) 20 GHz. The signature absorbance of all three is more than 2\(\times\) below those of the si-RNA sample of Figure 4b, and the \(\Delta\
u\) is larger, too, such that Q\({}_{\rm S}\) = 58, 59, and 50 for (1), (2), and (3), respectively. All these parameters for the 50-bp DNA are also listed in Table 1.