Change In Absorption Intensity Research Articles

Terahertz time-domain spectroscopy as a novel tool for crystallographic analysis in cellulose: tracking lattice changes following physical treatments

The authors’ series of studies aimed to explore the potential of terahertz time-domain spectroscopy (THz-TDS) in cellulose crystallographic studies, since THz radiation can detect most intermolecular vibrations and respond to lattice phonons. In this study, we tracked changes in four types of cellulose after ball milling. As the planetary ball milling time increases, it is observed through electron microscopy that the four types of cellulose particles are gradually destroyed into finer particles, while gel permeation chromatography can prove that the molecular weight gradually decreases after ball milling and the dispersity gradually approaches one, which indicates that the dispersion of the material was reduced. The most fascinating observation was made by THz-TDS, that is we have confirmed that after ball milling, the absorption characteristics of cellulose I and II in cellulose I treated with 10% NaOH (crystalline partial transition from cellulose I to II) exhibited an opposite trend. Specifically, the absorption of cellulose II at 2.40THz and 2.77THz increased, while the absorption of cellulose I at 2.11THz and 3.04THz decreased after ball milling, which suggests an increased conversion rate of cellulose I to cellulose II post-milling. Cellulose with different crystalline allomorphs shows different characteristic absorption in the THz region, and the peak position will not change even after the ball milling, only the absorption intensity changes. Although it can be observed through the most traditional X-ray diffraction method that the crystallinity index of all cellulose samples gradually decreases after ball milling. However, different from the THz results, the change after ball milling of cellulose I treated with 10% NaOH is only reflected in very subtle pattern changes, that is, the peak close to the 200 crystalline plane position is slightly shifted after ball milling.

Dynamic Orientation Control of Gold Nanorods in Polymer Brushes by Their Thickness Changes for Plasmon Switching

AbstractGold nanorods (AuNRs) have unique optical properties such as transverse and longitudinal localized surface plasmon resonance (T‐ and L‐LSPR). As the L‐LSPR absorption depends on the angle of the AuNRs to incident light and polarization, orientational control of AuNRs is a crucial issue. In spite of various techniques to control AuNR orientation, dynamic orientation tuning on a solid substrate remains challenging. Herein, dynamic changes are demonstrated in AuNR orientation in the anionic polymer (DNA) brushes via control of their thickness by salt concentration. AuNRs vertically align toward the substrates when their thickness exceeds the AuNR length. Once their thickness becomes shorter than the AuNR length, the attached AuNRs begin to tilt. The tilt reaches a maximum level close to horizontal when the thickness decreases to half that of the AuNR length. The dynamic control between the vertical (uniform) and tilted (random) orientation of the AuNRs showed not only absorption intensity changes in L‐LSPR but also the switching of side‐by‐side plasmon coupling. The polymer brush‐based system affords a novel platform for the stimuli‐responsive control of AuNR orientation on the substrates via changes in the thickness of polymer brushes for actively tunable plasmonic substrates.

Selective Sensing of Epinephrine by Phenylboronic Acid Tethered Carbon Dot.

The present work depicts development of phenylboronic acid (PBA) derived and appended carbon dots (CD1-PBAs) to detect epinephrine with high sensitivity and selectivity against structurally analogous biomolecules like norepinephrine, L-Dopa and glucose. Carbon dots were synthesized by hydrothermal method. Microscopic and spectroscopic studies ensured the suitability of CD1-PBAs for diol sensing. Catecholic-OH groups of epinephrine primarily form covalent adduct with CD1-PBAs via boronate-diol linkage that caused change in absorption intensity of CD1-PBAs. The limit of detection (LOD) for epinephrine was found to be 2.0 nM. For other analogous biomolecules, formation of boronate-diol linkage might have got retarded by the dominant participation of secondary interactions like hydrogen bonding owing to the presence of varying functional moieties. Subsequently, responsiveness in the change in absorbance intensity of CD1-PBAs was weaker compared to that for epinephrine. Hence, a selective and efficient carbon dot (CD1-PBAs) based epinephrine sensor was developed simply by utilizing boronate-diol linkage.

Evaluation of relative content and crystallization behavior of homogeneous crystals in poly (lactic acid) by terahertz spectroscopy

Poly (lactic acid) (PLA) is a typical polymer with homogeneous polymorphism. Its different crystal forms have their own crystallization paths, which endow it with special properties. Therefore, it is crucial to study the structure and crystallization behavior of PLA to better understand its properties. Here, we investigate PLA films obtained under different crystallization conditions by terahertz (THz) spectroscopy. The α′, α and their mixed crystal forms of PLA exhibit completely different spectral feature. Based on the frequency of THz characteristic peaks, we further determine the relative contents of α′ form and α form in PLA with mixed crystals, the validity of which is verified by comparing X-ray diffraction (XRD). Furthermore, the change of absorption intensity of different PLA films is significantly different with crystallization time, mainly manifested as the change rate of glassy PLA crystallized at 80 °C is faster than that of molten PLA. We believe that this is because the crystallization of the α form of PLA at 80 °C is at a disadvantage, which reduces the speed of conformational adjustment. The results show that THz spectroscopy can not only characterize the crystal changes of polymers, but can also be an effective method to study the kinetics of polymer crystallization.

Colorimetric multi-channel sensing of metal ions and advanced molecular information protection based on fish scale-derived carbon nanoparticles

Some nanosystems based on carbon nanomaterials have been used for fluorescent chemical/biosensing, elementary information processing, and textual coding. However, little attention has been paid to utilizing biowaste-derived carbon nanomaterials for colorimetric multi-channel sensing and advanced molecular information protection (including text and pattern information). Herein, fish scale-derived carbon nanoparticles (FSCN) were prepared and used for colorimetric detection of metal ions, encoding, encrypting and hiding text- and pattern-based information. The morphology and composition of FSCN were analyzed by TEM, XRD, FTIR, and XPS, and it was found that the FSCN-based multi-channel colorimetric sensing system can detect Cr6+ (detection limit of 56.59 nM and 13.32 nM) and Fe3+ (detection limit of 81.55 nM) through the changes of absorption intensity at different wavelengths (272, 370, and 310 nm). Moreover, the selective responses of FSCN to 20 kinds of metal ions can be abstracted into a series of binary strings, which can encode, hide, and encrypt traditional text-based and even two-dimensional pattern-based information. The preparation of carbon nanomaterials derived from waste fish scales can stimulate other researcheres’ enthusiasm for the development and utilization of wastes and promoting resource recycling. Inspired by this work, more researches will continue to explore the world of molecular information technology.

Open chain conjugated azomethine derived optical biosensor for selective and ultrasensitive colorimetric detection of biomarker glutathione in human blood serum

A new approach for visual and colorimetric detection of glutathione (GSH) in an aqueous solution has been developed that is extremely simple and rapid. The designed biosensor SL1 used is simple to make and utilize, with the additional benefits of being cost-effective. By changes in absorption intensity as well as colorimetrically, it shows superb selectivity and ultrasensitivity towards GSH over other amino acids and biomolecules. Based on the information provided above, we developed an approach to determine GSH qualitatively and quantitatively using UV spectrophotometer, paper based test strips, and visually, respectively. A satisfactory linear relationship may be achieved from 0.26 to 52 μM with a detection limit (LOD) of 63 nM and detection quantitation (LOQ) 210 nM. Moreover, the high recovery rates for human blood serum samples demonstrated that the proposed colorimetric technique is practicable, straightforward, and ultrasensitive, with a prominent application in regular biosample analysis.

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Micelle-Type Sensor for Saccharide Recognition by Using Boronic Acid Fluorescence Amphiphilic Probe and Surfactants

ABSTRACT Controlling molecular assembly by analytes is attractive for analytical techniques. Herein, we designed and synthesized amphiphilic boronic acid fluorescent probes (B-Nap-C8) possessing naphthaleneboronic acid as a saccharide recognition site and alkyl chain as a hydrophobic moiety. We evaluated their saccharide recognition function in relation to the fluorescent or absorption intensity changes of the assembled B-Nap-C8. Also, we evaluated the saccharide recognition function of B-Nap-C8 by the effect of co-surfactants. B-Nap-C8 forms micelles and recognizes fructose at pH 10. In the presence of surfactants, B-Nap-C8 with the cetyltrimethylammonium bromide (CTAB) micelle can recognize fructose at neutral pH. On the other hand, B-Nap-C8 with the sodium dodecyl sulfate (SDS) micelle recognizes fructose at pH > 10. This is caused by the decrease of the apparent pK a of B-Nap-C8 on the surface of the cationic CTAB micelle. The micelle formation of B-Nap-C8 with CTAB was confirmed by TEM observation, and the critical micelle concentration of B-Nap-C8 with CTAB was determined to be 1.79 mM from the CTAB titration measurements. From the saccharide titration experiments, B-Nap-C8 with CTAB micelles selectively recognizes fructose at neutral pH. The selectivity for saccharides was not observed in the saccharide titration of B-Nap-C8 with SDS. Thus, the co-surfactant systems with B-Nap-C8 were found to control the selectivity for saccharide recognition in water.

Glucose-water interactions at increasing concentrations and temperatures as revealed by Near-Infrared Spectroscopy

Water is an essential molecule and one of the most intensive research subjects, yet it is a peculiar molecule. The non-invasive measurement of blood glucose levels by near-infrared spectroscopy requires detailed information about the glucose-water interactions. The glucose in water induces strong hydrogen bonds and may influence the tetrahedral structure of water molecules. This knowledge is essential in constructing a non-invasive calibration of the blood glucose prediction model. How they are related to the absorption spectra of water and glucose is particularly valuable to comprehend. The evaluations were carried out using near-infrared spectroscopy, tracing changes in absorption intensity and shifts in corresponding peaks with glucose varying at an increasing concentration from a 0-0.9 molar fraction. The near-infrared spectra analysed were around 6900 cm-1 and 4716 cm-1 corresponding to the overtone and the combination band of water and glucose absorptions, respectively. The analysis suggests that glucose prefers to enter a water cluster, rather than bind to free molecules, and induce bond breaking at low glucose concentrations at which the molecular fraction is less than 0.05.

Colorimetric determination of hydrazine and nitrite using catalytic effect of palladium nanoparticles on the reduction reaction of methylene blue

In this research, hydrazine and nitrite determination was performed based on the reaction of methylene blue with hydrazine in the presence of palladium nanoparticles (PdNPs) as catalyst. The system was monitored spectrophotometrically by measuring the decrease in the absorbance of the methylene blue at 662 nm. Subsequently the inhibitory effect of nitrite on this catalytic reaction was also used for nitrite determination. In fact the depigmentation of methylene blue was postponed by nitrite added to the reaction mixture containing methylene blue, hydrazine and PdNPs. This inhibitory effect enables us to measure nitrite. Several factors influencing the analytical performance of the kinetic method such as concentration of reactants and electrolyte, pH of the sample solution and temperature were studied to achieve the optimum conditions and highest sensitivity. The change in absorption intensity of methylene blue was linearly proportional to the concentration in the range of 6–600 μmol L−1 and 0.3–14.2 μmol L−1 with a limit of detection of 3.85 μmol L−1and 0.21 μmol L−1 for hydrazine and nitrite, respectively. The method was successfully applied to the determination of hydrazine in water samples and nitrite in water, meat and saliva samples.

A colorimetric assay of DNA methyltransferase activity based on peroxidase mimicking of DNA template Ag/Pt bimetallic nanoclusters.

DNA methylation catalyzed by DNA methyl transferase (MTase) is a significant epigenetic process for modulating gene expression. Abnormal levels of DNA MTase enzyme have been regarded as a cancer biomarker or a sign of bacterial diseases. We developed a novel colorimetric method to assay M.SssI MTase activity employing peroxidase-like activity of DNA template Ag/Pt NCs without using restriction enzymes. Based on inhibiting the peroxidase reaction that occurred in the TMB-H2O2 system, in the presence of MTase, a highly sensitive and selective colorimetric biosensor was fabricated with a detection limit (LOD) of 0.05 U/mL and a linear range from 0.5 to 10 U/mL. The changes in absorption intensity were monitored to quantify the M.SssI activity. This strategy had a high selectivity over other proteins. Furthermore, it is also demonstrated that this method can be used for the evaluation and screening of inhibitors for DNA MTase.

Determination of mercury (II) ions based on silver-nanoparticles-assisted growth of gold nanostructures: UV–Vis and surface enhanced Raman scattering approaches

Innovative dual detection methods for mercury(II) ions (Hg(II)) have been developed based on the formation of gold nanostructures (AuNSs) following the addition of mercury-containing solution to a mixture containing an optimized amount of Au(III), H2O2, HCl, and silver nanoparticles (AgNPs). In the absence of Hg(II), the addition of Au(III), H2O2, and HCl to the AgNP solution changes the solution's color from yellow to red, and the absorption peak shifts from 400 to 526nm, indicating the dissolution of AgNPs and the formation of gold nanoparticles (AuNPs). Because of the spontaneous redox reaction of Hg(II) toward AgNPs, the change in the amount of remaining AgNP seed facilitates the generation of irregular AuNSs, resulting in changes in absorption intensity and shifting the peak within the range from 526 to 562nm depending on the concentration of Hg(II). Under optimal conditions, the limit of detection (LOD) for Hg(II) at a signal-to-noise ratio (S/N) of 3 was 0.3μM. We further observed that AgNP-assisted catalytic formation of Au nanomaterials deposited on a surface enhanced Raman scattering active substrate significantly reduced the Raman signal of 4-mercaptobenzoic acid, dependent on the Hg(II) concentration. A linear relationship was observed in the range 0.1nM–100μM with a LOD of 0.05nM (S/N 3.0). As a simple, accurate and precise method, this SERS-based assay has demonstrated its success in determining levels of Hg(II) in real water samples.

Sequential Detection of CN- and HSO4- Anions in an Aqueous Environment Utilizing a New Colorimetric Azoimine Receptor: Mimicking Logic Gate Behaviour and a Security Keypad Lock

A new isonicotiamide-based azoimine receptor has been successfully devised and synthesised for dual-recognition of CN− and HSO4− anions in aqueous media (3 : 2 DMSO–water solution). The devised azomethine probe detected lethal cyanide ions under UV-vis spectroscopy through the rapid appearance of an orange colour. More importantly, the colour and spectroscopic changes of the devised chemosensor could be revived upon the addition of HSO4− to the sensor containing cyanide ions. Furthermore, other surveyed anions failed to induce a similar response. Interestingly, based on changes in absorption intensity at a particular wavelength in the presence of two aforementioned anions, as two chemical inputs, an INHIBIT logic gate has been elaborated. Moreover, the reversibility of the sensory system provided an opportunity to present a sequential logic circuit at a molecular level. In accession, the target chemosensor could operate as a molecular keypad lock with sequential chemical inputs of CN− and HSO4− anions.

Seed-mediated grown silver nanoparticles as a colorimetric sensor for detection of ascorbic acid

A simple and sensitive approach was demonstrated for detection of ascorbic acid (AA) based on seed-mediated growth of silver nanoparticles (Ag NPs). According to the seeding strategy, silver ions existing in the growth solution were reduced to silver atoms on the surface of silver seeds via redox reaction between silver ions and AA. This process -led to appear an absorption band in near 420nm owing to the localized surface plasmon resonance peak of the generated Ag NPs. This change in absorption spectra of Ag NPs caused a change in color of the mixture from colorless to yellow. It was found that the changes in absorption intensity at 420nm have a good relationship with the concentration of AA. Also, detection of AA was achieved through the established colorimetric sensor in the range of 0.25–25μM with detection limit of 0.054μM. Moreover, the selectivity of the method was evaluated with considering potential interferences. The method showed high selectivity toward AA rather than potential interferences and coexisted molecules with AA. It was successfully applied for detection and determination of AA in pharmaceutical tablets and commercial lemonade.

Effect of low temperature plasma on the functional properties of basmati rice flour.

The present study deals with the application of low temperature plasma on basmati rice flour and its effect on functional properties such as gel hydrations properties, flour hydration properties, gelatinization temperatures and antioxidant properties. The water holding capacity and water binding capacity were observed to be increased with increase in plasma power and time of treatment as the air plasma is known to make the surface more hydrophilic. XRD analysis revealed there is no significance difference in the crystalline structure after the plasma treatment. DSC shows a decrease in peak temperatures (Tp) after the treatment. Hot paste viscosities were observed to be decease from 692 to 591 BU was corresponded to decrease in peak temperature. The total polyphenolic content and reducing power was observed to be increased. The effects of plasma treatment on functional groups of polyphenols were observed by changes in absorption intensities using FTIR. This study demonstrates that the low temperature plasma treatmentis capable of improving the functional properties of basmati rice.

Effect of Chitosan Powder Prepared from Snail Shells to Remove Lead (II) Ion and Nickel (II) Ion from Aqueous Solution and Its Adsorption Isotherm Model

The toxic effects of heavy metals have remained a major source of concern globally because of their non-biodegradable nature which makes heavy metal pollution a serious environmental problem. The extents of removal for two heavy metals were investigated on adsorbent dose, temperature, pH, contact time and initial metals ion concentration. Maximum adsorption was obtained at pH 5 for Pb²⁺ ion and pH 7 for Ni²⁺ ion with 82.1% and 68.28%, at maximum adsorption temperature 335K and 355K for both metal ions with 87% and 80% metal removal respectively. The study shows that initial metal ion concentration and adsorbent dose on metals adsorption increases for both metal ions having a maximum adsorption dose at 99.93% and 70.58% removal at 180mins contact time for both metal ions with 99.83% and 70.37%. FTIR spectrum of raw chitosan showed the following peaks; 3263cm^-1, 3109.25cm^-1, 1627cm^-1 and 2854cm^-1 denoting –NH₂/-NH asymmetric stretching,-OH stretching,-C=O stretching and –CH group showing that binding process for both metal ions onto chitosan bands at 3109.25cm^-1 and 2854cm^-1 in the spectrum. The spectra indicated –NH group was involved in the binding process due to substantial changes in absorption intensity of –NH stretching after adsorption and peak 1627cm^-1 assigned to C=O occurred before the binding process. The two peaks in the 2800-2900 cm^-1 region was observed in Pb²⁺ ion which disappear in the Ni²⁺ ion laden spectrum, the spectrum for Ni²⁺ ion has only one peak observed in this region while the Pb²⁺ ion has two and in the finger print region, 600-1000 cm^-1, the spectra of Ni²⁺ ion and Pb²⁺ exhibited two and one peaks respectively. This supported the higher sorption capacity of Pb²⁺ ion over Ni²⁺ ion. The data were evaluated using Langmuir, Frieundlich and Temkin isotherms, the data complied with Frieundlich isotherm with high R² values 0.984 and 0.971 for both metal ions while Temkin isotherm shows high R² values 0.991 and 0.981 for both Pb²⁺ and Ni²⁺ ions respectively.

Absorption intensity changes and frequency shifts of fundamental and first overtone bands for OH stretching vibration of methanol upon methanol-pyridine complex formation in CCl4: analysis by NIR/IR spectroscopy and DFT calculations.

Infrared (IR) and near infrared (NIR) spectra were measured for methanol and the methanol-pyridine complex in carbon tetrachloride. Upon the formation of the methanol-pyridine complex, the frequencies of both the fundamental and first overtone bands of the OH stretching vibration shifted to lower frequencies, and the absorption intensity of the fundamental increased significantly, while that of the first overtone decreased markedly. By using quantum chemical calculations, we estimated the absorption intensities and frequencies of the fundamental and first overtone bands for the OH stretching vibration based on the one-dimensional Schrödinger equation. The calculated results well reproduced the experimental results. The molecular vibration potentials and dipole moment functions of the OH stretching vibration modes were compared between methanol and the methanol-pyridine complex in terms of absorption intensity changes and frequency shifts. The large change in the dipole moment function was found to be the main cause for the variations in absorption intensity for the fundamental and first overtone bands.

Theoretical study of excited states of DNA base dimers and tetramers using optimally tuned range-separated density functional theory.

Excited states of various DNA base dimers and tetramers including Watson-Crick H-bonding and stacking interactions have been investigated by time-dependent density functional theory using nonempirically tuned range-separated exchange (RSE) functionals. Significant improvements are found in the prediction of excitation energies and oscillator strengths, with results comparable to those of high-level coupled-cluster (CC) models (RI-CC2 and EOM-CCSD(T)). The optimally-tuned RSE functional significantly outperforms its non-tuned (default) version and widely-used B3LYP functional. Compared to those high-level CC benchmarks, the large mean absolute deviations of conventional functionals can be attributed to their inappropriate amount of exact exchange and large delocalization errors which can be greatly eliminated by tuning approach. Furthermore, the impacts of H-bonding and π-stacking interactions in various DNA dimers and tetramers are analyzed through peak shift of simulated absorption spectra as well as corresponding change of absorption intensity. The result indicates the stacking interaction in DNA tetramers mainly contributes to the hypochromicity effect. The present work provides an efficient theoretical tool for accurate prediction of optical properties and excited states of nucleobase and other biological systems. © 2015 Wiley Periodicals, Inc.

Large-Area, Low-Cost Infrared Metamaterial Fabrication Via Pulsed Laser Deposition with Metallic Mesh as a Shadow Mask

Metamaterials are artificial periodic structures with negative permittivity and permeability. Several interesting properties can be obtained in metamaterials, such as negative index behavior, which can be used for building perfect lenses, cloaking, antennas, etc. As the metamaterial’s properties are determined by its structure, the key challenge is to reduce the fabrication cost of the periodic structure on the micrometer or nanometer scale for realistic applications. In this paper, we experimentally demonstrate a new one-step method for the fabrication of a large-area infrared metamaterial at extremely low cost. A metallic mesh is used as a shadow mask during the pulsed laser deposition (PLD) process to fabricate a FeNi/SiC/FeNi multilayer sandwich structure on Si substrate (cm2 level). The sample shows a strong absorption peak in the infrared frequency range, and the absorption intensity changes with the sample’s geometry.

Soil organic matter characterization of temperate peatland soil with FTIR‐spectroscopy: effects of mire type and drainage intensity

SummaryPeatlands are an important component of the global carbon cycle because they comprise huge amounts of terrestrial carbon (C). Different conditions during peat formation and secondary peat decomposition affect the quantity and composition of soil organic matter (SOM) in peats. There are few comparative studies on the chemical composition of SOM in temperate peatland soil. This study investigates compositional changes of SOM functional groups in peats and corresponding peat‐forming plants by Fourier transform infrared (FTIR) spectroscopy. Three plant samples and 29 peat samples were taken from seven temperate peatland sites with different genesis and land‐use intensity. Site‐specific differences, such as genesis of the peat, were found to be reflected in the FTIR spectra. In general, there was more variation in FTIR spectra in samples from fens than in those from bogs and peat‐forming plants. The samples from fens have a smaller C–H absorption band than those from bogs and plants, which reflects greater biochemical activity in the minerotrophic than ombrotrophic environments. In addition to peat genesis, drainage and secondary peat decomposition also affect SOM composition substantially. The larger amounts of aliphatic compounds in undrained peats could be explained by selective preservation caused by anaerobic conditions. With increasing drainage of the sites, there was a decrease in the C–H absorption that was accompanied by a relative increase in C=O absorption. These changes in absorption intensities reflect the enhanced aerobic decomposition and mineralization that accompanies drainage and land‐use intensity. However, the ‘degree of peat decomposition’, a diagnostic tool used in the field, is not reflected by OM composition determined by FTIR spectroscopy. Our results contribute to further understanding of changes in SOM composition during peat formation and processes of secondary decomposition caused by drainage.