## 3 Results and Discussion  
The optical absorption properties of RNA-CTMA complex thin-film are shown in Figure 2a. A broad absorption peak was obtained at 260 nm, which could be assigned to the signature of \(\pi\)-\(\pi^{*}\) transition of the nuclei bases. The same peak has also been observed in the DNA-OTMA complex as previously reported [19]. Above 300 nm, there is no observable absorption in the RNA-CTMA film, which exhibits excellent optical transparency in the visible range, and indicates RNA-CTMA was also the potential candidate in the application of transparent electronic devices. In order to further study the configuration of the RNA-CTMA complex, the CD spectrum of the RNA-CTMA complex was measured, which is an important toll to investigate the characteristics of the secondary structure of biopolymer [24]. As shown in the Figure 2b, two negative Cotton effects at about 251 nm and 232 nm, and a positive Cotton effect at about 286 nm, were observed, which are different from the natural DNA and DNA-CTMA complex, as shown in previous studies [19]. Compared with DNA-CTMA complex, the Cotton effect in the RNA-CTMA complex is weaker, indicating that the RNA-CTMA complex shows weaker structure regularity than that in DNA-CTMA complex. The reason could be attributed to the single helix structure of the RNA complex. The IR spectra of the RNA and RNA-CTMA film were measured and compared, as shown in Figure 3. The different wave numbers of each different film are summarized in Table 1. As shown in the table, compared with the RNA film, the vibration wave number of antisymmetric and symmetric of PO\({}_{2}\) group in RNA-CTMA film showed a red shift, which was attributed to the interaction between RNA and the CTMA surfactant, indicating that the CTMA group was successful aligned to RNA molecules. Figure 3: IR spectra of (**top**) RNA, (**middle**) RNA–CTMA, and (**bottom**) DNA–CTMA films. Figure 2: (**a**) UV spectra of the RNA–CTMA complex. (**b**) CD spectra of the RNA–CTMA complex. Furthermore, thermostability of RNA-CTMA was also measured as one of the important parameters of physical and chemical performance. The upper limit of the temperature where they can retain the key properties defines their processing temperature and device working temperatures. Hence, the thermogravimetry analysis (TGA) in nitrogen atmosphere has been used to investigate the polymers. Figure 4a shows the thermal degradation curves for CTMA alone, and RNA-CTMA surfactant complex, respectively. Both the samples exhibit good thermal stability and, especially, it is very surprising to find that the CTMA cationic surfactant can be stable until 250 \({}^{\circ}\)C. In addition, the RNA-CTMA surfactant complex also shows excellent heat resistance, and is thermally stable up to 240 \({}^{\circ}\)C. As a consequence, the RNA complex can tolerate normal printing and processing, and the devices could work in traditional circuits. Especially, the RNA complex may also be a potential candidate for a temperature sensor that operates under high temperature environments. Figure 4b shows the DSC curve of the RNA and RNA-CTMA complex film at a temperature range from 0 to 120 \({}^{\circ}\)C, with a heating rate of 10 \({}^{\circ}\)C/min. A baseline shift at around 55 \({}^{\circ}\)C and 42 \({}^{\circ}\)C of RNA and RNA-CTMA complex were obtained, respectively, which could be attributed to the phase transition. These results indicate that as the temperature increases and exceeds the phase transition, the volume of the RNA and RNA-CTMA complex would be expected, and the singe helix main chain could be moved, so the dipoles aligning to the main chain also could be oriented along the direction of the applied voltage. Besides the optical, structural, and thermal properties of the complex, the morphology of the complex film was also characterized. For electronic devices, the surface roughness of the biopolymer film plays an important role, especially when it acts as the interface for charge accumulation and transport [25].