Differential Absorption Spectra Research Articles

Application of bi-directional long short-term memory in separating NO and SO2 ultraviolet differential absorption spectrum signals

To safeguard the environment, it is crucial to monitor the emissions of nitrogen oxide (NO) and sulfur dioxide (SO2), harmful pollutants generated during fossil fuel combustion in industries. However, accurately measuring ultra-low concentrations of SO2 and NO remains a challenge. In this study, we developed an optical measurement system based on ultraviolet differential optical absorption spectroscopy (UV-DOAS) to address this issue. The 200–230 nm cross-sensitivity band was chosen for SO2 and NO. Experimental data with a mixed gas concentration range of 1–25 ppm for SO2 and NO was utilized. We proposed a fast algorithm based on Bi-directional Long Short-Term Memory (Bi-LSTM) to extract the differential optical density, overcoming the mutual interference between SO2 and NO. A nonlinear calibration model was employed to invert the separated differential absorption spectra and determine the gas concentrations. The results demonstrated a detection limit (DL) of 0.27 ppm and a full-scale error of 3.15 % for SO2, while for NO, the DL was 0.32 ppm and the full-scale error was 2.81 %. The uncertainties in SO2 and NO detection were calculated as 1.73 % and 1.96 %, respectively.

Multiparameter gas sensor based on UV-SFR combined with wavelet transform-neural network at ppb level

Abnormal concentrations of nitric oxide (NO), ammonia (NH3), carbon disulfide (CS2) and sulphur dioxide (SO2) in exhaled breath are closely associated with diseases in specific organs of the body. Meanwhile, the above gases are also common pollutants in the atmosphere, and effective online detection of them plays a key role in disease prevention and environmental pollution prevention. This study reports a multiparameter gas sensor system based on the combination of ultraviolet segmented fitting reduction (UV-SFR) and wavelet transform-neural network (WT-NN) model for simultaneous online detection of the concentrations of NO, NH3, CS2 and SO2. Firstly, to avoid the occurrence of spectral baseline drift and absorption peak intensity reduction, a UV-SFR method is proposed for the discrete single peak type absorption spectra contained in the UV spectra. Our method can remove the slow change absorption induced by other factors, and ultimately obtain the differential absorption spectra of the gas mixtures. Then, the WT is used to denoise the differential absorption spectra of the gas mixtures. Next, for the presence of severe spectral line overlap in gas mixtures, the NN model is built based on the denoised spectral data. Finally, transfer learning is introduced into NN to improve the detection accuracy. The experimental results show that the sensor system can reliably achieve simultaneous online detection of NO, NH3, CS2, and SO2 at ppb level, and the average absolute errors of their measurements are 0.96 ppb, 1.27 ppb, 0.76 ppb and 0.97 ppb, with measurement accuracies of 3.5 %, 0.8 %, 0.5 % and 0.9 %, respectively.

A ppb-level online detection system for gas concentrations in CS2/SO2 mixtures based on UV-DOAS combined with VMD-CNN-TL model

Carbon disulfide (CS2) and sulfur dioxide (SO2) are the main decomposition products of sulfur hexafluoride (SF6). Detecting the concentrations of these products plays a key role in early fault warning in SF6 electrical equipment. In this study, we report an online ppb-level detection system for a mixture of CS2 and SO2 based on ultraviolet differential optical absorption spectroscopy (UV-DOAS) combined with VMD-CNN-TL model. First, important features are extracted and recombined from the differential absorption spectra by variational modal decomposition (VMD) to obtain the combined differential absorption spectra (CDAS) data and mixed-gas differential absorption spectra (MDAS) data. A multilayer 1D convolutional neural network (CNN) model is then pre-trained on CDAS. Next, the parameters of the model are fine-tuned using transfer learning (TL) based on MDAS. TL solves the small sample size problem in detecting mixed-gas concentrations using neural network models. Lab-based results indicate that the system enables stable detection of CS2 (3.81–179.24 ppb) and SO2 (19.21–942.73 ppb) with mean absolute errors of 0.51 ppb and 1.12 ppb, respectively, which are the best results reported so far. Furthermore, the feasibility of the sensor system is verified for detection of gas mixtures at ppb-level by field testing.

Exploring the physio-elastic properties and optical band gap energies of boro-telluro-dolomite glasses infused with Nd2O3 dopants

In search for the innovative optical glass host, structural stability and optical band gap engineering of glasses infused with rare earth ions dopant is prerequisite. Inspired by this standpoint, a new series of boro-telluro-dolomite glass system activated with Nd2O3 (BTDN) has been developed via classic melt-quenching process. The amorphous status of the as made glasses was validated by XRD spectra whereas its physical features were exposed by inspecting the samples density and related parameters. Further, elastic moduli and its derivatives of these glasses were assessed from the measured ultrasonic wave velocities recorded at 5 MHz frequency. By using UV–Vis absorption spectrum data, the band gap energies and refractive index of our produced BTDN glasses are evaluated through Tauc's, absorption spectrum fitting (ASF) and differential absorption spectrum fitting (DASF) wherein similar results have been obtained by these tripartite models. Our verdicts herein affirmed that Nd3+dopant acts as a glass modifier, which meaningfully augment the physio-elastic performance of the BTDN glasses.

Complexation of copper algaecide and algal organic matter in algae-laden water: Insights into complex metal–organic interactions

Copper-based algicides have been widely used to suppress algae blooms; however, the release of algal organic matter (AOM) on account of cell lysis may cause significant changes in the mitigation, transformation, and bioavailability of Cu(II). In the present work, the binding characteristics of Cu(II) with AOM were explored via combinative characterization methods, such as high-performance size exclusion chromatography, differential absorption spectra analysis, and joint applications of two-dimensional correlation spectroscopy (2D-COS), as well as heterospectral 2D-COS and moving window 2D-COS analyses of UV, synchronous fluorescence, and FTIR spectra. Carboxyl groups displayed a preferential interaction to Cu(II) binding, followed by polysaccharides. The spectral changes of C]O stretching occur after the change of chromophores in complexation with Cu(II). The AOM chromophores exhibit obvious conformations at Cu(II) concentrations higher than 120 μM, while AOM fluorophores and functional groups exhibit the greatest changes at Cu(II) concentrations lower than 20 μM. All these observations have verified the presence of binding heterogeneity and indicate that AOM could interact with Cu(II) through diverse functional moieties. Therefore, our study contributes to the better understanding of the fate of Cu(II)–AOM complexes in aquatic systems.

QUANTITATIVE DETERMINATION OF THE SUM OF FLAVONOIDS OF THE ABOVEGROUND PART OF SCUTELLARIA COMOSA

As a result of pharmacological studies, it was revealed that the sum of flavonoids from the aboveground part of the plant Scutellaria comosa (Lamiaceae family) has adaptogenic and antihypoxic effects. For the introduction into medical practice of a drug based on the sum of flavonoids, studies have been conducted on the standardization of raw materials – the aboveground part of the crested helmet. The analysis of plant raw materials by TLC and HPLC methods showed that the dominant flavonoid of the aboveground part of the crested skullcap is isoscutellarein 7-O-β-D-glucopyranoside.
 A differential spectrophotometric technique has been developed for the quantitative determination of the sum of flavonoids of the aboveground part of the crested helmet in terms of isoscutellarein 7-O-β-D-glucopyranoside. The optimal parameters for the extraction of vegetable raw materials are: extraction with 70% ethyl alcohol in a boiling water bath for 60 minutes in the ratio "raw material – extractant" – 1 : 100, the degree of grinding of raw materials – 2 mm. It was found that with the differential version of spectrophotometric analysis, the flavonoids – AlCl3 system reaches equilibrium after 40 minutes. The maximum of the differential absorption spectrum of the alcohol extraction of Scutellaria comosa is observed at 346 nm and can be used to analyze this group of compounds.
 The content of the sum of flavonoids in the aboveground part of the crested helmet varies from 9.72% to 10.27%. In order to establish the optimal harvesting time of plant raw materials, the content of the sum of flavonoids was determined by the vegetation periods of the plant in terms of isoscutellarein 7-O-β-D-glucopyranoside and it was determined that the maximum accumulation of the sum of flavonoids is observed during the flowering period (10.13% of the weight of air-dry raw materials).

Near-infrared quantum cutting luminescence in Pr3+/Yb3+ doped lead bismuth borate glass

In this paper, thermally stable lead-bismuth-borate glasses were doped with 0.5 mol% of Pr3+ ions at several concentration levels of Yb3+ ions. Structural characterizations were performed via Raman, differential scanning calorimetry, optical absorption and fluorescence spectra. The Judd–Ofelt intensity parameter, {Omega }_2, of Pr3+ doped glass was comparatively higher than those from reported ones, which reflects the increase of co-valency and asymmetry of chemical bonds in the local environment of Pr3+. Near-infrared emission in 900–2200 nm wavelength range was recorded through 443 nm blue laser pumping. Visible to near-IR quantum cutting and concentration quenching mechanisms were discussed to understand the luminescent behaviour. Intense IR emission (sim 1.0,upmu {text {m}}) features generated by absorbing one visible photon leads to quantum efficiencies close to 128% in Pr3+/Yb3+ co-doped samples which may improve the solar spectrum absorption and accordingly, increase the efficiency of c-Si solar cells. Emission cross-section, lifetime, figure of merit and gain bandwidth corresponding to Pr3+: ^3F_2 rightarrow ^3H_4 (sim 2.0,upmum) were comparatively reported suggesting that the glass with molar composition 0.5Pr3+/0.1Yb3+ might be a potential candidate for sim 2.0,upmum laser operation with low pump threshold.

Investigation of intense mid-infrared emission in Ho3+/Yb3+/Er3+ triple-doped tellurite glass

Rare earth ion doping is considered to be a feasible way to improve the optical properties of glass in recent years. We investigate the luminescence characteristics of Ho3 + -Er3 + -Yb3 + triple-doped tellurite glass (TeO2-ZnO-WO3-La2O3) at 2.0 μm. A series of characterization analyses on the prepared samples, such as x-ray diffractometer (XRD) pattern, Raman spectrum, differential scanning calorimetry (DSC) curve analyses, absorption spectrum, emission spectrum, and fluorescence decay curve, were performed. XRD pattern and DSC curve analyses indicate that the glass sample exhibits a typical amorphous structure with excellent thermodynamic stability. Through the absorption spectrum, the position and intensity of the absorption peak of the glass sample can be detected. Under an excitation of 980 nm laser, the 2.0-μm emission peak intensity of the glass sample increases by about 1500%, which is attributed to the energy level transition among Ho3 + , Er3 + , and Yb3 + . By analyzing the energy level transition of Ho3 + , Yb3 + , and Er3 + ions, the energy transfer mechanism and fluorescence lifetime can be obtained, and then the fluorescence enhancement phenomenon of Ho3 + -Er3 + -Yb3 + triple-doped tellurite glass at 2.0 μm can be explained. It is demonstrated that the as-prepared Ho3 + -Er3 + -Yb3 + triple-doped tellurite glass has potential for the application of fiber lasers and fiber amplifiers.

Substituted boron subphthalocyanines – Prospective compounds for theranostics: Synthesis, photochemical properties and in vitro cytotoxicity

Boron subphthalocyanines bearing a wide range of functional groups were tested as prospective photosensitizers and fluorophores. Synthetic protocols to novel 4-ethoxycarbonylphenoxy-substituted subphthalocyanine and phenoxy-substituted subphthalocyanine boron phenolate were presented. Differential triplet-triplet absorption spectra of subphthalocyanines were registered and triplet state lifetimes (τT = 0.6 ÷ 3.1 ms) were obtained. The results of flash photolysis measurements predicted the good ability of target subphthalocyanines to produce singlet oxygen and it was supported by the measurements of 1O2 quantum yields (ΦΔ = 0.47 ÷ 0.85). At the same time, satisfactory yields of fluorescence (Φf = 0.13 ÷ 0.50) were observed for most of the subphthalocyanines. The fluorescence decay kinetics were studied to determine the fluorescence lifetimes (τf = 0.30 ÷ 3.05 ns) and confirm the regularities obtained for fluorescence yields. Pronounced fluorescent properties allowed investigating the distribution of subphthalocyanines in the endoplasmic reticulum. In addition, the binding constants with human serum albumin were determined. tert-Butyl- and iodo-substituted subphthalocyanines demonstrated remarkable photocytotoxicity in human epidermoid carcinoma cells at micromolar concentrations. At the same time, target boron subphthalocyanines exhibited low dark cytotoxicity. All mentioned above make boron subphthalocyanines promising candidates as highly effective photosensitizers for photodynamic therapy and fluorescent labels for diagnostic.

Inhibition mechanisms of Fe2+/Fe3+ and Mn2+ on fungal laccase-enabled bisphenol a polyreaction

Bisphenol A (BPA) is regarded as an endocrine disruptor associated with negative health effects in animals and humans. Laccase from white-rot fungus can enable BPA oxidation and auto-polymerization to circumvent its biotoxicity, but the work concerning the effect mechanisms of divalent and trivalent metal ions (MIs) on BPA polyreaction have rarely been reported. Herein, Trametes versicolor laccase-started BPA conversion within 1 h followed pseudo-first order kinetics, and the rate constant (kprcs) and half-life were respectively 0.61 h−1 and 1.14 h. The presence of Ca2+, Mg2+, Cu2+, Pb2+, Cd2+, Zn2+ and Al3+ exhibited insignificant impact on BPA removal, whereas Fe2+, Fe3+ and Mn2+ had a strong inhibiting effect. Compared with MI-free, the kprcs values of BPA respectively lowered 34.4%, 44.3% and 98.4% in the presence of Fe2+, Fe3+ and Mn2+. Enzymatic activity and differential absorption spectrum disclosed that the inhibitory actions were accomplished by two different mechanisms. One is Fe2+ was preferentially oxidized into Fe3+ that restrained laccase activity at the initial stage of reaction, and subsequently, the formed Fe3+ complex bound with laccase T1-Cu site and thus impeded the single-electron transfer system. The other is Mn2+ was instantly oxidized by laccase to generate Mn3+-citrate complex, which completely consumed the dissolved O2 in solution and consequently terminated BPA removal. Considering environmental bioremediation, T. versicolor laccase-enabled auto-polymerization is a simple and convenient candidate to eliminate BPA in enzymatic wastewater treatment, however the effects of Fe2+/Fe3+ and Mn2+ on BPA decontamination should be cautiously assessed.

Ppm-level oxygen detection system based on deep-ultraviolet-absorption spectroscopy.

Oxygen is a gas essential to human life and industrial processes. Here, we developed a highly sensitive oxygen gas sensor based on deep ultraviolet absorption spectroscopy between 180 and 200 nm. The implemented method relies on differential absorption spectra extracted from the obtained high-resolution absorption spectra. The detection capability was greatly improved (six-fold) by eliminating air from the open optical path, achieved by purging the entire system with pure nitrogen. A linear relationship was obtained between the optical parameter and the oxygen concentration with a slope of 0.107 and determination coefficient of 0.999. A detection limit of 24 ppm per meter was determined with a response time of 25 s. Good repeatability (standarddeviation=16ppm) and stability were confirmed. We demonstrated that this system can detect ppm oxygen levels with high sensitivity and low uncertainty.

Wave Optics of Differential Absorption Spectroscopy in Thick-Junction Organic Solar Cells: Optical Artifacts and Correction Strategies

Differential absorption spectroscopy techniques serve as powerful techniques to study the excited species in organic solar cells. However, it has always been challenging to employ these techniques for characterizing thick-junction organic solar cells, especially when a reflective top contact is involved. In this work, we present a detailed and systematic study on how a combination of the presence of the interference effect and a nonuniform charge-distribution profile, severely manipulates experimental spectra and the decay dynamics. Furthermore, we provide a practical methodology to correct these optical artifacts in differential absorption spectroscopies. The results and the proposed correction method generally apply to all kinds of differential absorption spectroscopy techniques and various thin-film systems, such as organics, perovskites, kesterites, and two-dimensional materials. Notably, it is found that the shape of differential absorption spectra can be strongly distorted, starting from 150-nm active-layer thickness; this matches the thickness range of thick-junction organic solar cells and most perovskite solar cells and needs to be carefully considered in experiments. In addition, the decay dynamics of differential absorption spectra is found to be disturbed by optical artifacts under certain conditions. With the help of the proposed correction formalism, differential spectra and the decay dynamics can be characterized on the full device of thin-film solar cells in transmission mode and yield accurate and reliable results to provide design rules for further progress.

Structural, thermal, optical and luminescence properties of Dy3+ ions doped Zinc Potassium Alumino Borate glasses for optoelectronics applications

Zinc Potassium Alumino Borate (ZnKAlB) glasses doped with dysprosium (Dy3+) ions of different concentrations were synthesized through the process of melt quenching which is commonly used in solid-state lighting (SSL) and laser systems, to comprehend their viability. This article evaluates and analyzes the physical, structural, thermal and optical properties of Dy3+ ions doped glasses by X-ray diffraction (XRD), Infrared Fourier Transform (FT-IR), differential scanning calorimetry (DSC), UV absorption and photoluminescence (PL) spectra to explain their utilization in optoelectronic devices such as lasers and white light-emitting diodes (w-LEDs). The physical parameters viz. density, refractive index, inter-ionic distance, molar volume, polaron radius, field strength, optical electronegativity, dielectric constant, reflection loss and metallization were computed by following the expressions reported in the literature. Glasses are non-crystalline materials and the non-crystallinity of an un-doped Zinc Potassium Alumino Borate glass was proven by the absence of high-pitched peaks in the XRD spectra. FT-IR spectroscopy was used to identify the presence of different functional groups and their bond nature in Dy3+ ions doped ZnKAlB glasses. The transition temperature (Tg), melting temperature (Tm) and thermal stability was calculated by monitoring DSC thermograms of all glasses. Further, the bonding parameters (δ) and nephelauxetic ratio (β) were estimated to explore the bonding nature of Dy3+ ions in its neighborhoods by using UV-absorption data. The optical direct-indirect band gap energy (Eopt) and Urbach's energy (∆E) were enumerated from the absorption spectrum to elaborate electrical properties of as-prepared glasses. Judd-Ofelt theory was employed to find oscillator strengths from absorption spectra and for further calculation of radiative parameters such as the radiative lifetimes (τR), radiative transition probability (AR), total radiative transition probability (AT) and branching ratio (βR) to understand the quantum efficiency (η). Furthermore, the colorimetric parameters such as correlated color temperature (CCT), CIE coordinates and yellow to blue (Y/B) ratio were estimated from the PL emission data. The multipole-multipole interaction was confirmed by Dexter approximation to explain concentration quenching. This work primarily explains the essential features of borate glasses with Dy3+ ions doping to explain their potential use in tricolor w-LEDs and lasers.

Optical and spectroscopic behavior of Eu3+ doped heavy metal phosphate glasses

Europium (Eu3+)-doped heavy metal phosphate glass systems have been synthesized by melt-quench technique. Optical as well as spectroscopic characteristics are analyzed in detail. X-ray diffraction (XRD) pattern of synthesized samples confirms their glassy nature. Optical band-gap (Eg) for the synthesized samples has been calculated using different methods. Refractive index and other parameters such as dielectric constant, molar refraction, reflection losses, and polarizability have also been determined for prepared glass samples. Photoluminescence properties are examined from the excitation as well as emission spectra and results revealed prominent emissions in red region. The optical band gap for the prepared samples has been evaluated using three different methods viz. Tauc's method, absorption spectrum fitting (ASF) method and differential absorption spectrum fitting (DASF) method. Similar results have been obtained by all the three methods. Judd-Ofelt (J-O) theory has been employed to emission bands of Eu3+ ions for determination of phenomenological intensity parameters i.e. Ω2,Ω4 and Ω6, radiative rate, branching ratio and radiative lifetime. J-O analysis revealed that the large value of Ω2 parameter indicated high covalency between metal-ligand bonds along with the distortion among symmetric sites of Eu3+. Branching ratio (βR) is greater than 0.5 for 5D0→7F2 (transition) indicating their prospective for usefulness in laser-based applications. High branching ratio values and color purity suggests the potential use of glass samples for red laser applications.

Application of multi-wavelength dual-position absorption spectrum to improve the accuracy of leukocyte spectral quantitative analysis based on “M + N” theory

Leukocytes are the most important immune cells in human body, which are very important to maintain the immune function of human body. They can phagocytose foreign bodies and produce antibodies to resist the invasion of pathogens. Nowadays, the abuse of antibiotics is widespread, and the detection and analysis of leukocytes is very important for clinical diagnosis. It is of great medical significance to use chemical quantitative analysis method based on spectrum to realize the rapid and trace detection of leukocytes in clinic. It is the development direction of clinical detection in the future and provides a new way to improve the abuse of antibiotics. However, due to the influence of nonlinearity introduced by the measurement, the relationship between absorbance and concentration deviates from Lambert-Beer law, which leads to low measurement accuracy and restricts its development in clinical application. In order to improve the accuracy of spectral analysis, this paper with the guidance of “M + N” theory measured the transmission spectra of 392 whole blood samples under two different optical path lengths, and subtracts them to obtain the multi-band differential absorption spectra for modeling and prediction of leukocyte concentration. The following experiments were designed: using the transmission spectra measured at one position and the absorption spectra obtained by subtracting the transmission spectra measured at position 1 and position 2 as the input of modeling. Partial least squares (PLS) method was proposed in this paper for modeling and predicting the concentration of leukocyte. The experimental results show that the modeling results of dual-position absorption spectrum have been significantly improved and promoted compared with the modeling results of transmission spectrum in one position, and the calibration set correlation coefficient (RC) values has increased by 57.92% to 0.864904, where the prediction set correlation coefficient (RP) increased by 106.81% to 0.8502. The root mean square error of the calibration set (RMSEC) decreased by 40.01% from 3.1149 to 1.8686. The results suggest that modelling and analysing leukocytes with a multi-band dual-position absorption spectrum may reduce the influence of nonlinearity to a certain amount, significantly increase the model's prediction precision and accuracy, and obtain satisfactory results. This paper provides the possibility for rapid clinical micro-detection of leukocytes, as well as the ideas and directions for improving the accuracy of spectral quantitative analysis of components in complex solutions.

COMPARATIVE STUDY OF SPECTRAL CHARACTERISTICS OF COMPLEXES OF HOECHST 33258 AND METHYLENE BLUE WITH BOVINE SERUM ALBUMIN

The comparative study on interaction of bisbenzimidazole compound Hoechst 33258 and thiazine dye methylene blue (MB) with bovine serum albumin (BSA) was carried out by spectroscopic methods. Denaturation curves as well as absorption spectra and differential absorption spectra of protein-ligand complexes
 were obtained. Denaturation temperature of albumin complexes of BSA with Hoechst 33258 was shown to decrease with the growth of concentration ratio of ligand/protein, while for MB, vice versa, denaturation temperature increases. Changes in absorption spectra and differential absorption spectra of the complexes
 of ligands with albumin were revealed, which result from the binding of these DNA-specific ligands to protein. It is supposed that at the interaction of Hoechst 33258 with BSA some loosening of protein compact structure occurs due to the partial loss of helicity of α-structures, while for MB an increase of the protein compact structure takes place.

Absorption properties and Quantum Confinement of colloidal CdSe quantum dots

We investigate the structural and optical properties of CdSe QDs synthesized by the hot-injection technique. High-resolution transmission electron microscopy (HRTEM) analysis reveal the size-dependent of the CdSe QDs. The first through fourth excited states determined from absorption measurements are compared with calculated quantum size levels in s- and p-symmetry. In particular, featureless absorption peaks of the second and third excited states from the first exciton appear in the differential absorption (DA) spectra. These measurements with quantitative analysis enable the estimate error to be derived from anisotropic properties caused by the crystal field.

STUDY OF ABSORPTION SPECTRA OF THE COMPLEXES OF BOVINE SERUM ALBUMIN WITH HOECHST 33258 AND METHYLENE BLUE

The study on the interaction of DNA-specific low-molecular compounds – groove binding material Hoechst 33258 and intercalating ligand methylene blue (MB) with serum albumin has been carried out. The absorption and differential absorption spectra of complexes of the mentioned ligands with protein were obtained. Changes of the absorption and differential absorption spectra indicate the binding of two ligands with albumin. The obtained results indicate that at the interaction with both ligands, the conformational state of the protein alters, though these changes are not similar, since in the case of MB a compactization of the protein folding occurs, while in the case of Hoechst 33258, most apparently, an unfolding of the compact structure takes place as a result of partial loss of helicity of $\alpha$-structures.

Differences in the spectroscopic characteristics of wetland dissolved organic matter binding with Fe3+, Cu2+, Cd2+, Cr3+ and Zn2+

Understanding of the binding characteristics of wetland dissolved organic matter (DOM) and different metals is important for the quantitative assessment of the environmental behavior of metals in wetlands. In this study, different types of spectroscopy including ultraviolet-visible absorption, Fourier transform infrared, and fluorescence spectroscopy was used to investigate the binding characteristics of Fe3+, Cu2+, Cr3+, Cd2+, and Zn2+ with DOM from wetland water. Differential absorption spectra identified binding sites for these five metals in this wetland DOM at 210 nm, 280 nm, 335 nm, and > 400 nm regions. The low binding capacity of DOM in this wetland with Cd and Zn indicated that the toxicity and environmental effects of these metals in this wetland warrant further study. The calculated △EEM combined with fluorescence regional integration (FRI) analysis clearly revealed that Fe and Cu preferred to bind with humic-like DOM while Cd and Zn preferred to bind with protein-like DOM in this wetland. △EEM successfully demonstrated the characteristics of DOM complexing with different metals and could be a compelling tool in evaluating metal-DOM interactions. In addition, 2D-FTIR-COS identified the binding sites and the dynamic processes of binding at the functional group level. Metals preferentially bind with the CO, CO functional group, and then binds to the OH functional group. This study revealed that different DOM components will facilitate the migration of different metals in the environment and provided new slights into an improved understanding of migration and transformation of metals in aquatic environments.

Pulse Radiolysis Investigation of Radicals Derived from Water-Soluble Cyanine Dyes: Implications for Super-resolution Microscopy.

Light-induced blinking, an inherent feature of many forms of super-resolution microscopy, has been linked to transient reduction of the fluorescent cyanine dye used as an imaging agent. There is, however, only scant literature information related to one-electron reduced cyanine dyes, especially in an aqueous environment. Here, we examine a small series of cyanine dyes, possessing disparate π-conjugation lengths, under selective reducing or oxidizing conditions. The experiment allows recording of both differential absorption spectra and decay kinetics of the resultant one-electron reduced or oxidized transient species in water. Relative to the ground state, absorption transitions for the various radicals are weak and somewhat broadened but do allow correlation with the π-conjugation length. In all cases, absorption maxima lie to the blue of the main ground-state transition. Under anaerobic conditions, the transient species decay on the microsecond to millisecond time scale, with the mean lifetime depending on molecular structure, radiation dose, and dye concentration. The experimental absorption spectra recorded for the one-electron reduced radicals and the presumed dimer cation radical compare well to spectra obtained from time-dependent density functional theory calculations. The results allow conclusions to be drawn regarding the plausibility of the reduced species being responsible for light-induced blinking in direct stochastic optical reconstruction microscopy.