Li-Na Zhang, Yu-Hui Ma, Ze-Jia Zhang, Kai-Xuan Hou, Miao-Miao Lin, Guo-Wei Zhang*, Cun-Guang Lou

Erahertz spectral analysis of Xiling Zhimu with different geological conditions and plant age

Li-Na Zhang1, Yu-Hui Ma1, Ze-Jia Zhang1, Kai-Xuan Hou2, Miao-Miao Lin1, Guo-Wei Zhang1*, Cun-Guang Lou2*

1College of Chinese Medicine, Hebei University, Baoding, Hebei, China.2School of Electronics and Information Engineering, Hebei University, Baoding, Hebei, China.

: In order to identify the quality of different geological conditions and plant ages of XilingZhimu.: This article uses the terahertz spectroscopy to detect and analyze different geological conditions and ages of Zhimu () from the same origin.: The terahertz time-domain spectroscopy of different geological conditions and ages has a decrease relative to the reference amplitude and has a delay. The refractive index has obvious differences, and the refractive index can be used as a way to identify the tablets. The absorption coefficients of different ages Zhimu samples has significant differences in the range of 1.0-2.0 THz. The absorption coefficients of different geological conditions Zhimu samples has significant differences in the range of 1.1-2.0 THz.: The differences caused by different production methods should be considered in the identification of genuine regional drug. When the Zhimu is grown due to different geological conditions and plant ages, its efficacy will also change. we can detect this change by terahertz spectroscopy.

terahertz spectrum, XilingZhimu, index of refraction, absorption coefficients

The terahertzian time-domain spectrum of Zhimu () at different plant ages and different geological environments decreased relative to the reference amplitude and showed a delay. The refractive index has obvious difference, which can be used as a way to identify the film. The absorption coefficients of Zhimu at different plant ages were significantly different in the range of 1.0-2.0THz, and the absorption coefficients of Zhimu in different geological environments were different in the range of 1.1-2.0THz. Therefore, the differences caused by different preparation methods should be considered in the identification of authentic medicinal materials. When Zhimu grows at different plant ages and in different geological environments, its pharmacodynamics will change, and we can detect this change by terahertz spectroscopy, which can provide a basis for the identification of Xiling Zhimu.

Background

Zhimu () is the dry rhizome of, which has bitter and cold taste, and has the effect of nourishing yin and moistening dryness, clearing heat and purging fire[1]. Yixian County, Hebei Province, is the genuine producing area of Zhimu. The quality and curative effect of Zhimu is excellent, which called "XilingZhimu"[2]. The content of active ingredients in wild Zhimu and Xiling Zhimu in Yixian County is approximately the same, with similar quality characteristics [3]. Most of the active ingredients in traditional Chinese medicine usually increase with the increase of plant age, but generally it will stop increasing or even turn down after a certain period, or because of the difference of growth geology, the composition is also different. Therefore, the determination of the Zhimu’s quality with different plant ages and different geological conditions is an important development direction to improve the clinical efficacy.

In order to understand the inherent differences of traditional Chinese medicine grown in different plant ages and geological conditions, this article study on the terahertz time-domain spectroscopy, refractive index and absorption spectrum of Anemarrhena Xiling from different plant ages and geologies in Yixian County, Hebei Province, which provided a basis for the identification of Xiling Zhimu from terahertz.

Experimental Part

Experimental samples and preparation

The experimental samples were selected from Xiling Zhimu of Yixian County, Hebei Province,and collected from Taiping Village and Longquanzhuang Village in Xiling Town and Gem Village in Po Cang Town. Its growth geology is divided into gneiss and limestone. The age of the plants is 3 years, 5 years and 6 years (Figure 1). The samples were identified as certified products by Professor Liang Xianmao, a senior experimenter of College of traditional Chinese Medicine, Hebei University. Samples were dried by dryer, crushed by crusher and splited charging. In the process of crushing,attention should be paid to cleaning up the powder remaining in the crusher before crushing the next sample, so as to prevent the ingredients from mixing, otherwise, the accuracy of the final results of the experiment will be seriously affected. The crushed sample powders were sifted through No.100 narrow sieve. Then the powders with the same particle diameter were obtained. Finally, the powders were pressed into 13 mm slice by infrared manual tablet press (JOSVOK (Tianjin) Technology Co.,Ltd,YP-15) with pressure of 3 t. Sample name and thickness as shown in Table 1.

Table 1. Plant type and thickness ofZhimu

Experimental device

In this experiment, terahertz time domain spectrometer (Daheng Science&Technology Co.,Ltd,DH-OTB-1000mm*600mm*500mm) and femtosecond laser (Spectra-Physics,Mai Tai) were used. The laser is a pumping and detecting light source.The wavelength of the central light source is 1560 nm. The output pulse width is about 92.3 fs. The pulse repetition rate is 100 MHz, and the Gauss TEM00 beam is less than 1.2 mm. The emitter is InAs crystal and the detector is ZnTe crystal. The spectrum width of the light source ranges from 0.1 to 3.0 THz.

Experimental method and data processing

Terahertz radiation can penetrate various materials [4, 5], so it can be used for the testing of traditional Chinese medicine. All data in this experiment were collected by terahertz spectroscopy system. Each acquisition adopted several parallel measurement methods, and then the related data were processed. In the course of the experiment, the ambient temperature of the instrument was set at 25+1℃ and the relative humidity was controlled at or below 7% [6].Under this condition,the terahertz time-domain wave of air was measured accurately, and the measured results were taken as the reference basis for the experiment. The terahertz time-domain spectroscopy of Zhimu in different plant ages and geological conditions were then measured. The experiments in each group were repeated twice and the average was calculated. In the process of testing, the terahertz instrument was filled with nitrogen, which reduced the influence of moisture in the air on terahertz generation. The reference signal and the sample signal can be obtained during the experiment, the signal distribution of the two were calculated by Fourier transform to obtain the corresponding frequency domain spectrum [7], the spectra Er(ω) and Es(ω). The amplitude ratio is p(ω)=AS/Ar,the phase difference isφ(ω)=φs-φr, and the calculation formula for refractive index is:

The calculation formula of absorption coefficient is:

The approximate calculation formula for the absorption coefficient is:

In the calculation of the above formulas, c is the velocity of light in vacuum, ωis the angular frequency, n(ω)represents the real number of the refractive index, which is closely related to the dispersion characteristics of the sample, and k(ω) represents the extinction coefficient, where n(ω)=2ωk(ω)/c. This coefficient is also closely related to the absorption characteristics of the sample. A(ω)represents the ratio of the amplitude between the sample and the reference signal. φ(ω)represents the phase difference of terahertz pop signal. d represents the thickness of the measured sample. The value can be obtained during the experiment.The unit of phase is amplitude. Because of the noise effect at low frequency, the phase will jump by 2π [8].In order to make the phase at zero frequency closer to zero, the phase value between the linear range of 0.5-1.2 THz can be recived by linear fitting method to obtain the phase valueφat zero frequency. For example, the phase value at zero frequency can be obtained by integral N ofφ/2π, and then the phase of all frequencies can be subtracted by 2πN [9].

Results

Terahertz time-domain spectroscopyand analysis

According to the experimental data, terahertz time-domain spectroscopy of different plant age samples and reference, different geological samples and reference (Figure 2 and 3) were made respectively. Figure 2 and Figure 3 show the time-domain spectra of different plant age samples and reference, different geological samples and reference at 0-15 PS. From the time-domain spectra, it can be seen that the THz spectral amplitude of the samples decreases to a certain extent compared with the reference wave due to the scattering, reflection and absorption of the samples. At the same time, the THz spectrum of the sample has a certain delay compared with the reference wave because of the difference of the thickness and refractive index of the samples.

Refractive index curve and analysis

The refractive index of three species Zhimu with different plant ages and Xiling Zhimu with different geological conditions were calculated according to the refractive index formula mentioned above. Corresponding refractive index curves were made separately (Figure 4 and 5). By comparing and analyzing the refractive index curves of three species of Zhimu with different plant ages (Figure 4), it is easy to see that the refractive indexes have significant differences in the range of 0-2.0 THz, and generally present a downward trend with the increase of frequency.Among them, the average refractive index of 3 years’Zhimu is about 1.04, that of 5 years’Zhimu is about 0.43, and that of 6 years’Zhimu is about 0.75.

By comparing and analyzing the refractive index curves of Xiling Zhimu from different geologies (Figure 5), it can be concluded that the refractive indexes of Xiling Zhimu from 0 to 1.2 THz have significant difference between the two geologies; in the range of 0-0.3 THz, the refractive indexes increase with the rised frequency; and in the range of 0.3-1.2 THz, the refractive indexes maintain at about 1.1-1.3. Among them, the average refractive index of limestone is 1.28, and that of gneiss is 1.18. The refractive indexes of limestone in two geologies are higher than that of gneiss.

Because the internal structure and component content ofZhimu samples of different plant ages and geological conditions have discrepances, the differences of refractive indexes should be related to the internal structure and component content of the samples.

Figure.2 The terahertz time-domain spectroscopy of different plant ages samples

Figure.3 The terahertz time-domain spectroscopy of different geological samples

Figure.4 The index of refraction of different plant ages samples

Figure.5 The index of refraction of different geological samples

Curve and analysis of absorption coefficients

The experimental datas were calculated according to the absorption coefficient formula as described above, and the absorption coefficients of three kinds of Xiling Zhimu with different geological conditions and plant age were obtained. Then we made corresponding absorption coefficient curves respectively (Figure 6 and 7).

Absorption coefficient curve and analysis

From the absorption spectrums of different ages Zhimu (Figure 6), we can find that when the frequency is between 1.0 and 2.0 THz, the absorption curves of three kinds of Zhimu samples fluctuates greatly and crisscrosses with each other. In the low frequency region, there are some differences between three kinds of samples relative to the absorption spectra., but the difference is small. Given that this curve may be influenced by the Fabry–Pérot effect, there is little significance for reference [10]. However, when the frequency is between 0.1 and 1.0 THz, the absorption coefficients of three kinds of samples also increase linearly with the wave frequency of terahertz incident increased. The trend further shows that the basic substances of Zhimu with different plant age are very similar to some extent. It's related to the fact that all of them are ZhimuIn the high frequency region, the sensitivity of three kinds of samples to terahertz wave is increased, which is convenient to distinguish the three kinds of Zhimu samples. The absorption coefficients of three kinds of samples are 3 years > 5 years > 6 years, and there is no obvious characteristic absorption peak in the range of 0.1 to 0.9 THz. However, the absorption coefficients are obviously different, which can be used as intuitive identification.

From the absorption spectrums of different geological Zhimu (Figure 7), we can find that when the frequency is between 1.0 and 2.0 THz, the absorption curves of different geological Zhimu samples fluctuates greatly and crisscrosses with each other. The sensitivity to terahertz wave tends to increase, which is beneficial to distinguish the Zhimu samples in different geological environments. When the frequency is between 0.1 and 1.1 THz, the absorption coefficients of two different geological samples increase linearly with the wave frequency of terahertz incident increased. The trend shows that the basic substances of Zhimu with different geological conditions are similar. It's related to the fact that both of them are ZhimuThe absorption coefficient of the two geological samples is gneiss > limestone, while in the range of 0.1 to 1.1 THz, there is a linear growth trend and no obvious characteristic absorption peak. However, the absorption coefficients of them are obviously different, which can be used as intuitive identification.

Figure.6 The absorption coefficient of different plant ages samples

Figure.7 The absorption coefficient of different geological samples

Conclusion

Terahertz wave (Terahertz, 1 THz=1012Hz) is an electromagnetic wave with the frequency of 0.1 to 10 THz (wavelength is at 3mm to 30μm) between millimeter wave and infrared light. It is a special transitional region from electronics to photology in electromagnetic spectrum. It is also a transitional region from macroscopic classical theory to micro quantum theory [11], which has been listed as a strategic development direction by Europe, the United States and Japan [12]. Terahertz wave has superior characteristics, which makes it has important academic research and practical application value in physics, biomedicine, material science and so on. Domestic studies have shown that Terahertz time-domain spectroscopy (THz-TDS) technology is an effective method to identify the authenticity, evaluate the quality and analyze the composition of traditional Chinese medicine [13], which has a broad application prospect in the field of quality control or identification of traditional Chinese medicine.

Through the THz-TDS experiment of Zhimu at constant room temperature and dry condition, it was found that the terahertz time-domain spectrum of different geological conditions and plant ages has a decrease relative to the reference amplitude and has a delay. The refractive index of three kinds of Zhimu samples with different plant ages is obviously different. All show a decreasing trend with the increase of frequency. The average refractive index of samples is 1.04, 0.43 and 0.75 for 3 years, 5 years and 6 years in the range of 0 to 10 THz, respectively. The refractive index of Zhimu samples with different geological conditions is also obviously different. The difference of refractive index may be due to the different internal structure and composition of the sample, so the refractive index can be used as a guiding significance for the harvest and commodity identification of Xiling Zhimu. The genuine quality of medicinal materials strengthens the influence of producing area, which means that the quality and the curative effect is good [14]. The absorption coefficients of three kinds of Zhimu samples with different plant ages were significantly different in the range of 1.0-2.0 THz, and the absorption coefficients of two kinds of Zhimu samples with different geological conditions were significantly different in the range of 1.1-2.0 THz. This indicates that even Zhimu from the same place of origin has different absorption coefficients due to different processing methods, so we should consider the difference in the identification of genuine medicinal materials. When the plant age and geological conditions of Zhimu is different, the internal material structure and the interaction between molecules will change, which may be one of the reasons why the clinical efficacy of Zhimu is different in different plant ages and geological conditions. We can detect this change by terahertz spectroscopy.

Due to the sensitivity, safety and strong penetration of terahertz wave, the preliminary application of terahertz wave in the fields of blood detection, canceration tissue and drug detection has achieved good effects [15-19]. The application of terahertz spectroscopy to the quality analysis or identification of traditional Chinese medicine will play an important role in the research and production, such as commodity quality, specification and famous region drug, which will be of positive significance to the modernization of traditional Chinese medicine. With the continuous combination of terahertz technology and traditional Chinese medicine research, it will provide researchers with more diverse Chinese medicine identification and analysis methods.

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：對不同地質(zhì)條件和株齡西陵知母的質(zhì)量進(jìn)行鑒別研究。：本文采用了太赫茲光譜技術(shù)對同一產(chǎn)地不同地質(zhì)和株齡的西陵知母進(jìn)行了檢測與分析。：不同株齡、不同地質(zhì)環(huán)境生長知母的太赫茲時(shí)域譜相對于參考幅度均有所下降，并具有延遲；折射率具有明顯的差異性，折射率可以作為鑒別制片的一種方式；不同株齡知母樣品的吸收系數(shù)在1.0-2.0THz范圍內(nèi)存在顯著的差異性，不同地質(zhì)環(huán)境生長知母的吸收系數(shù)在1.1-2.0THz范圍內(nèi)存在差異性，故而在道地性藥材鑒別時(shí)應(yīng)考慮由于不同制片方式引起的差異。：當(dāng)知母因生長的株齡不同、所生地質(zhì)環(huán)境不同時(shí)，其藥效也會(huì)有所改變，我們可以通過太赫茲光譜技術(shù)檢測這種變化。

太赫茲光譜；西陵知母；折射率；吸收系數(shù)

:Zhang LN, Ma YH, Zhang ZJ, et al.Terahertz spectral analysis of Xiling Zhimu with different geological conditions and plant age.TMR Modern Herbal Medicine, 2019, 2 (3): 158-166.

10.12032/TMRmhm2017A53

Submitted: 31 May 2019,

19 July 2019,

Guo-Wei Zhang, College of Chinese Medicine, Hebei University, Baoding, Hebei, China. E-mail:xxzgw@126.com.Cun-Guang Lou, School of Electronics and Information Engineering, Hebei University, Baoding, Hebei, China. E-mail: loucunguang@163.com.

22 July 2019.

This work was Financial supported by Baoding philosophy social planning project (2018121).

Competing interests: The authors declare that there is no conflict of interests regarding the publication of this paper.

Executive Editor: Jing Sun