Total Transmittance Spectra Research Articles

Prediction of soluble solids content using near-infrared spectra and optical properties of intact apple and pulp applying PLSR and CNN

Soluble solids content (SSC) is one of the most important internal quality attributes of fruit and could be predicted using near-infrared (NIR) spectra and optical properties. Partial least squares regression (PLSR) is a conventional regression method in SSC prediction. In recent years, deep learning methods represented by convolutional neural network (CNN) was suggested to be implied in spectral analysis. However, researchers are inevitably facing problems with regard to the selection of spectral pretreatment methods and the evaluation of the performance of the chosen regression. This study employed PLSR and CNN regression to predict SSC of apple based on the collected diffuse reflectance spectra of intact apple, total reflectance and total transmittance spectra of apple pulp, and the calculated optical property spectra, i.e., absorption coefficient and reduced scattering coefficient spectra of apple pulp. Five different spectral pretreatment methods were exerted on these spectra. Results showed that at a given regression (PLSR or CNN), the built models based on the diffuse reflectance spectra of intact apple had the best SSC prediction, and the built models based on pulp’s reduced scattering coefficient spectra had the poorest prediction performance. The best prediction performance was achieved by PLSR models using Savitzky-Golay with multiple scattering correction (Rp = 0.96, RMSEP = 0.54 %) and CNN regressions using Savitzky-Golay with standard normal variational transformation (Rp = 0.95, RMSEP = 0.59 %), respectively. Additionally, when the unknown original spectra were used for modeling, CNN had a better performance compared to PLSR, indicating the outstanding preponderance of CNN in spectral analysis. This study provides an effective reference for the selection of chemometric method based on NIR spectra.

Effect of the TiO2 surface modification with 3-glycidyloxypropyltrimethoxysilane on the aggregation of cresyl violet: Application to a dye-sensitized solar cell

Dye aggregation is a typical phenomenon occurring in dye-sensitized solar cells (DSSCs), which causes a decrease in the electron injection efficiency from the photoexcited dye to titanium dioxide (TiO2). As this results in a decrease in the photovoltaic performance, it cannot be ignored in the study of DSSCs. This paper reports a DSSC involving a TiO2 electrode chemically modified by cresyl violet (CV) covalently attached to 3-glycidyloxypropyltrimethoxysilane (GPTMS). The aim of the study is to understand the influence of silane coupling agents (SCAs) on dye aggregation. Aggregation of CV occurring on the TiO2 surface was prevented by GPTMS treatment on the TiO2 surface. This result was revealed by the decreased absorption intensity of the dimeric band observed in the total transmittance spectra. Density functional theory calculations and fluorescence decay curve measurements indicated that the CV covalently attached to GPTMS acts as a photosensitizing dye in DSSCs. As a result, the photovoltaic performance of DSSCs containing CV was enhanced by preventing its aggregation upon GPTMS treatment onto the TiO2 surface (7-fold increase: 0.0020%–0.014%). We concluded that TiO2 surfaces treated with SCAs can help to prevent dye aggregation, and therefore, enhance the photovoltaic performance of DSSCs.

Scattering of light by ZnO nanorod arrays.

The optical properties of ZnO nanorod (NR) arrays were investigated by optical total transmittance (TT) and diffuse reflectance (DR) spectroscopy in the visible region. The NRs were grown electrochemically in a three-electrode cell over a glass/fluorine-doped tin oxide (FTO) substrate. The mean length, radius, and density of NR samples were characterized by scanning electron microscopy. The results were correlated with the observed optical properties. Since light scattering for these NR arrays is highly dependent on their morphology, therefore, a model for light scattering based in the Mie theory for cylinders was implemented to understand the observed spectra. The mean scattering and extinction cross sections were calculated from the morphology of the samples. They were used to fit the DR spectra. From the fittings, the TT spectra of the samples could be calculated. A good agreement with the experimental results was obtained. This indicates that the implemented model represents well the observed scattering phenomena.

Agarose-based Tissue Mimicking Optical Phantoms for Diffuse Reflectance Spectroscopy.

This protocol describes how to make agarose-based tissue-mimicking phantoms and demonstrates how to determine their optical properties using a conventional optical system with an integrating sphere. Measuring systems for the acquisition of the diffuse reflectance and total transmittance spectra are constructed with a broadband white light source, a light guide, an achromatic lens, an integrating sphere, a sample holder, an optical fiber probe, and a multi-channel spectrometer. An acrylic mold consisting of two rectangular acrylic pieces and a U-shaped acrylic piece is constructed to create an epidermal phantom and a dermal phantom with whole blood. The application of a sodium dithionite (Na2S2O4) solution to the dermal phantom enables the researcher to deoxygenate hemoglobin in red blood cells distributed in the dermal phantom. The inverse Monte Carlo simulation with the diffuse reflectance and total transmittance spectra measured by a spectrometer with an integrating sphere is performed to determine the absorption coefficient spectrum µa(λ) and the reduced scattering coefficient spectrum µs'(λ) of each layer phantom. A two-layered phantom mimicking the diffuse reflectance of human skin tissue is also demonstrated by piling up the epidermal phantom on the dermal phantom.

Structural, morphological, optical and electrical properties of Sb-doped SnO2 thin films obtained by aerosol assisted chemical vapor deposition

In this work, we report the synthesis and characterization of antimony doped tin oxide thin films for their possible application as transparent conducting oxides. Thin films of antimony doped tin oxide were deposited by aerosol assisted chemical vapor deposition. Surface morphology and microstructure were studied by field emission scanning electron microscopy. X-ray diffraction results indicate the presence of two tin oxide phases in some samples (from thickness of 30–120nm) and only the cassiterite phase in samples with thicknesses greater than of 140nm. Optical properties of the samples were analyzed by total transmittance spectra. Resistivity of the films was obtained by the sheet resistance method. Electrical properties and conductivity type of samples were determined by Hall effect method. The results show low resistivity in antimony doped tin oxide materials decreasing up to six orders of magnitude compared to pure tin oxide, and obtaining resistivity in the order of magnitude of 10−4Ω·cm. Thermal treatment was performed on some materials and stability was observed because it did not decrease its resistivity and in addition the thermal treatment improved Hall mobility.

Simulation Method Linking Dense Microalgal Culture Spectral Properties in the 400-750 nm Range to the Physiology of the Cells.

This work describes a method to model the optical properties over the (400-750 nm) spectral range of a dense microalgal culture using the chemical and physical properties of the algal cells. The method was based on a specific program called AlgaSim coupled with the adding-doubling method: at the individual cell scale, AlgaSim simulates the spectral properties of one model, three-layer spherical algal cell from its size and chemical composition. As a second step, the adding-doubling method makes it possible to retrieve the total transmittance of the algal medium from the optical properties of the individual algal cells. The method was tested by comparing the simulated total transmittance spectra for dense marine microalgal cultures of Isochrysis galbana (small flagellates) and Phaeodactylum tricornutum (diatoms) to spectra measured using an experimental spectrophotometric setup. Our study revealed that the total transmittance spectra simulated for the quasi-spherical cells of Isochrysis galbana were in good agreement with the measured spectra over the whole spectral range. For Phaeodactylum tricornutum, large differences between simulated and measured spectra were observed over the blue part of the transmittance spectra, probably due to non-spherical shape of the algal cells. Prediction of the algal cell density, mean size and pigment composition from the total transmittance spectra measured on algal samples was also investigated using the reversal of the method. Mean cell size was successfully predicted for both species. The cell density was also successfully predicted for spherical Isochrysis galbana, with a relative error below 7%, but not for elongated Phaeodactylum tricornutum with a relative error up to 26%. The pigments total quantity and composition, the carotenoids:chlorophyll ratio in particular, were also successfully predicted for Isochrysis galbana with a relative error below 8%. However, the pigment predictions and measurements for Phaeodactylum tricornutum showed large discrepancies, with a relative error up to 88%. These results give strong support for the development of a promising tool providing rapid and accurate estimations of biomass and physiological status of a dense microalgal culture based on only light transmittance properties.

Study on the refractive index matching effect of ultrasound on optical clearing of bio-tissues based on the derivative total reflection method.

In recent years, the tissue optical clearing (OC) technique in the biomedicine field has drawn lots of attention. Various physical and chemical methods have been introduced to improve the efficacy of OC. In this study, the effect of the combination of glycerol and ultrasound treatment on OC of in vitro porcine muscle tissues has been investigated. The refractive index (RI) matching mechanism of OC was directly observed based on the derivative total reflection method. A theoretical model was used to simulate the proportion of tissue fluid in the illuminated area. Moreover, the total transmittance spectra have been obtained by a spectrometer over the range from 450 nm to 700 nm. The administration of glycerol and ultrasound has led to an increase of the RI of background medium and a more RI matching environment was achieved. The experimental results support the validity of the ultrasound treatment for OC. The RI matching mechanism has been firstly quantitatively analyzed based on the derivative total reflection method.

Effect of storage conditions of skin samples on their optical characteristics

The optical characteristics of skin samples are experimentally studied ex vivo and in vitro at different storage conditions. The experiments are performed on a Cary-2415 spectrophotometer in the spectral range 400–700 nm. Based on the measured diffuse reflectance and total transmittance spectra, the spectra of the absorption and reduced scattering coefficients are calculated in terms of the inverse adding-doubling method. It is shown that the method of storage of samples mainly affects the reduced scattering coefficient of biotissue. Thus, upon storage of skin in an isotonic solution and in its absence, the reduced scattering coefficient increases ∼1.5 and ∼2 times, respectively, compared to the value of this parameter for the intact sample. The differences in the absorption spectra of ex vivo samples and samples stored under different conditions are the most noticeable in the absorption range of blood and are significant above 600 nm.

Optical Properties of the Subcutaneous Adipose Tissue in the Spectral Range 400–2500 nm

The optical characteristics of subcutaneous adipose tissue are studied in the wavelength range 400–2500 nm. The experiments are conducted in vitro using a Cary 2415 spectrophotometer. Based on the measured diffuse reflectance and total transmittance spectra, the spectra of the absorption and transport scattering coefficients are calculated in terms of the inverse adding-doubling method.

Photophysical Properties of Supported Dyes. Quantum Yield Calculations in Scattering Media

Aluminum tricarboximonoamidephthalocyanine and Rose Bengal were immobilized by adsorption and covalent linkage to different solid supports: silica, silanized silica, silanized silica modified with polylysine chains and NovaSyn® TG amino resin (low cross-linked polystyrene with polyethyleneglycol chains). Specially designed tools were used to evaluate absolute quantum yields in scattering media. A previously developed model was used to calculate fluorescence quantum yields in the solid state and a method is presented for the evaluation of singlet molecular oxygen quantum yields in suspensions. The method yields reliable results for dilute suspensions of particles with diameters much greater than the irradiation wavelength. Diffuse reflectance and, in the case of suspensions, total transmittance spectra are the basic inputs required. In this way the efficiencies of suspended solid photosensitizers were obtained for all samples and correlated with the dye concentration and the way of linking to the surface.