RESUMEN

A THz-TDS spectrometer (terahertz time-domain spectroscopy) with ASOPS technology (asynchronous optical sampling) was employed in this study, aiming to explore the potential of the technique and to develop analytical applications for the identification of some saccharides. Analytical curves with linear responses were obtained in the saccharide concentration range from 1.7 to 11.7 (w/w). The characteristic peaks used for each sugar for univariate calibrations were fructose (1.704 THz), sucrose (1.827 THz), glucose (1.435 THz), lactose (1.373 THz), saccharin (2.664 THz), and sucralose (2.219 THz). Limits of detection around 1.0% (m/m) were obtained. Gaussian peak fitting was also employed as a tool to aid in the identification of saccharide components in mixtures and it was observed that the region between 0.5 and 2.0 THz is more adequate for such analysis since scattering is less evident. It was observed that in a mixture of sucrose, glucose and lactose (5% or 10% (m/m) each) in the range of 1.31 to 1.51 THz some sub-peaks of pure lactose and glucose can be identified.

Asunto(s)

RESUMEN

For non-destructive detection of water stress in lettuce, terahertz time-domain spectroscopy (THz-TDS) was used to quantitatively analyze water content in lettuce. Four gradient lettuce water contents were used . Spectral data of lettuce were collected by a THz-TDS system, and denoised using the S-G derivative, Savitzky-Golay (S-G) smoothing and normalization filtering. The fitting effect of the pretreatment method was better than that of regression fitting, and the S-G derivative fitting effect was obtained. Then a calibration set and a verification set were divided by the Kennan-Stone algorithm, sample set partitioning based on joint X-Y distance (SPXY) algorithm, and the random sampling (RS) algorithm, and the parameters of RS were optimized by regression fitting. The stability competitive adaptive reweighted sampling, iteratively retained information variables and interval combination optimization were used to select characteristic wavelengths, and then continuous projection was used on basis of the three algorithms above. After the successive projection algorithm was re-screened, partial least squares regression was used into modeling. The regression coefficients R²c and RMSEC reach 0.8962 and 412.5% respectively, and R²p and RMSEP of the verification set are 0.8757 and 528.9% respectively.

Para a detecção não destrutiva de estresse hídrico da alface, espectroscopia no domínio do tempo em terahertz (THz-TDS) foi usada para analisar quantitativamente o conteúdo de água na alface. Quatro gradientes de conteúdo de água de alface foram usados. Os dados espectrais da alface foram coletados por um sistema THz-TDS e denoised usando o derivado S-G, Savitzky-Golay (S-G) suavização e filtragem de normalização. O efeito de ajuste do método de pré-tratamento foi melhor do que o do ajuste de regressão, e o efeito de ajuste da derivada S-G foi obtido. Em seguida, um conjunto de calibração e um conjunto de verificação foram divididos pelo algoritmo Kennan-Stone, particionamento do conjunto de amostra com base no algoritmo de distância X-Y conjunta (SPXY) e o algoritmo de amostragem aleatória (RS), e os parâmetros de RS foram otimizados por ajuste de regressão. A amostragem adaptativa de estabilidade competitiva reponderada, variáveis de informação retidas iterativamente e otimização de combinação de intervalo foram usadas para selecionar comprimentos de onda característicos e, em seguida, a projeção contínua foi usada com base nos três algoritmos acima. Depois que o algoritmo de projeção sucessivo foi reprojetado, a regressão de mínimos quadrados parcial foi usada na modelagem. Os coeficientes de regressão R2 e erro quadrático médio (RMSEP) atingem 0,8962 e 412,50%, respectivamente, e R2 e RMSEP do conjunto de verificação são 0,8757 e 528,93%, respectivamente.

Asunto(s)

RESUMEN

While terahertz imaging has been used before for the determination of water content in vegetative tissue, most studies have either presented measurements of the temporal evolution of water content at a single-point of the plant or have presented two-dimensional images of leaves, demonstrating the potential of the technique, but relatively little of such information has been used to support biologically relevant conclusions. In this article we introduce terahertz time-domain spectroscopic imaging as a technique for the determination of the three-dimensional distribution of water in succulent plant tissues. We present the first three-dimensional water mapping of an agave leaf, which demonstrates an unprecedented capability to study the water retention mechanisms within succulent plants. We found that agave leaves are composed of a low-hydration outer tissue layer, defined by the outermost layer of vascular tissue that surrounds a high-hydration tissue, the carbohydrate rich hydrenchyma. The findings are supported by histological images and the correlation between the water content and carbohydrate presence is consistent with recently published findings of a remarkably large hydration shell associated with agave fructans.

Asunto(s)

RESUMEN

Terahertz-time domain spectroscopy (THz-TDS) has the ability to probe the crystallinity of several materials, due to the interaction of THz radiation with optical phonons in crystal lattices. In this work, THz-TDS has been used to quantify the degree of crystallinity of microcrystalline cellulose (MCC) samples. The THz spectra of cellulose present absorption features which could be directly correlated with the crystallinity index (CI) obtained by means of the well-established powder X-ray diffraction (PXRD) technique. The effect of THz time-domain signal processing was investigated, and both univariate and multivariate, based on partial least-squares (PLS), regressions were carried out with the signal in the frequency domain to correlate the THz spectra with CI. Results show that the multivariate regression models based on spectral data, collected with the sample displaced from the focal plane of the THz optics to improve representativeness and measurement repeatability, present the best performance with external validation achieving an absolute root-mean-square error of prediction (RMSEP) of 4% for CI. This result compares well with the PXRD technique.

Asunto(s)

RESUMEN

The declining water availability for agriculture is becoming problematic for many countries. Therefore the study of plants under water restriction is acquiring extraordinary importance. Botanists currently follow the dehydration of plants comparing the fresh and dry weight of excised organs, or measuring their osmotic or water potentials; these are destructive methods inappropriate for in-vivo determination of plants' hydration dynamics. Water is opaque in the terahertz band, while dehydrated biological tissues are partially transparent. We used terahertz spectroscopy to study the water dynamics of Arabidopsis thaliana by comparing the dehydration kinetics of leaves from plants under well-irrigated and water deficit conditions. We also present measurements of the effect of dark-light cycles and abscisic acid on its water dynamics. The measurements we present provide a new perspective on the water dynamics of plants under different external stimuli and confirm that terahertz can be an excellent non-contact probe of in-vivo tissue hydration.

Asunto(s)