Laser-induced Fluorescence Analysis Research Articles

Identification of marine microplastics based on laser-induced fluorescence and principal component analysis

Although the laser-induced fluorescence method shows great potential for microplastic particle detection, overlapping fluorescence signals make accurate type and proportion identification difficult. This paper presents the identification of marine microplastics based on laser-induced fluorescence and principal component analysis. This method works by measuring the fluorescence spectra of water-containing microplastic samples irradiated with a 405-nm laser, which are then analyzed using the principal component analysis (PCA) method. The nine types of microplastics were differentiated based on their positions in the PCA score plot. The mixed sample was positioned between the pure microplastic samples. The component ratio determines its position relative to that of the pure microplastic samples. The first two principal components of the mixed microplastics were linearly dependent. Natural seawater had less influence on the detection, and a mass concentration as low as 0.03% was detected.

Effect of the GnRH stimulation test on Canine Prostatic-Specific Esterase (CPSE).

The gonadotropin-releasing hormone (GnRH) stimulation test is used to investigate testicular production of testosterone (T) when performing a breeding soundness examination. In male dogs with fertility problems, the prostate should also be investigated as prostatic conditions may frequently lower semen quality. Serum concentrations of canine prostatic-specific esterase (CPSE) increase in dogs with benign prostatic hyperplasia (BPH). When performing a breeding soundness examination in a male dog, GnRH administration is frequently done at the beginning of the process and then both T and CPSE are assayed on the same serum sample collected 1 h following the GnRH injection. The aim of this study was to assess whether or not the administration of GnRH may alter CPSE concentrations in dogs with a healthy prostate. Twenty-eight client-owned intact adult male dogs were included in the study. Following a 7-day sexual rest all male dogs underwent a clinical examination and an ultrasonographic examination of the prostatic gland. Prostatic size and parenchyma of every tested dog were evaluated by ultrasonography to assess prostatic conditions. Two different GnRH stimulation protocols were used, A = gonadorelin 50μg/dog SC (n = 15) and B = buserelin 0.12 μg/kg IV (n = 13). T and CPSE concentrations were measured before and 1 h after GnRH administration by a laser-induced fluorescence analysis. Buserelin and gonadorelin were equally effective in causing a significant increase in serum T concentrations in the post GnRH sample. When considering the 28 dogs together, CPSE concentrations did not change following the stimulation test with either GnRH compound; however, in 4/28 cases, the post GnRH value was markedly increased to values compatible with a diagnosis of BPH. There was no difference in the action of buserelin or gonadorelin in causing an increase in serum T concentrations. CPSE secretion was increased in approximately 15% of dogs treated with either buserelin or gonadorelin. Therefore, whenever performing diagnostic testing in intact male dogs, CPSE should not be assayed on a post-GnRH serum sample.

Mechanism insight of shielded methane non-premixed jet flame extinction with water mist: OH-PLIF visualization and quantitative analysis of critical fire extinguishing

Natural gas leaks from pipeline systems or storage sites may highly lead to a fire safety incident as well as a potential major hazard in industries or residential. The leaked jet flame commonly sheltered by an obstacle is more difficult to be extinguished as the result of a reduction in effective extinguishing agent flux and potential re-ignition. Especially in cases where the flame is heavily obscured by obstacles, the interaction of the extinguishing agent and flame can be very different from the unobstructed situation. This study aims to determine the critical characteristics of a water mist to extinguish a shielded non-premixed jet flame with the flame structure visualization of hydroxide planar laser-induced fluorescence (OH-PLIF) and quantitative parametric analysis. The effect of obstacles on water mist and a jet flame is firstly quantitatively evaluated by flame obscuration ratio kf and maximum effective mist ratio k in critical fire-extinguishing cases. Flame dynamical behavior from the base of the flame upwards to extinction is found when the flame Froude number Frf > 0.74 and kf > 0.75. Finally, the preferred water mist nozzles with larger spray angles might have more effective fire extinguishment ability typically under the cases of k < 0.5 and kf > 1.0. This study would be valuable for the optimum design of water mist systems in natural gas leakage incidents under shielded conditions.

Importance of stepwise ionization from the metastable state in electron cyclotron resonance ion thrusters

In electron cyclotron resonance (ECR) thrusters, the plasma mode transition is a critical phenomenon because it determines the maximum thrust performance. In ECR ion thrusters, ionization generally occurs in the magnetic confinement region, where electrons are continuously heated by ECR and confined by magnetic mirrors. However, as the flow rate increases, ionization is also observed outside the magnetic confinement region, and this induces the plasma mode transition. In our previous work, two-photon absorption laser-induced fluorescence (TALIF) analysis revealed that the stepwise ionization from the metastable state plays an important role in the ionization process. However, the distribution of the stepwise ionization has not yet been revealed because of the long lifetime of the metastable state. In this study, this distribution was investigated using one experimental and two numerical approaches. First, TALIF was applied to two types of gas injection with clear differences in thrust performance and ground-state neutral density distribution. In the first simulation, the metastable state particle simulation was used to estimate the excitation rate distribution. In the second study, simulations of the electric field of microwaves were used to estimate the contribution of the stepwise ionization to the plasma density. The experimental and numerical results revealed that the stepwise ionization spreads outside the magnetic confinement region because of the diffusion of metastable particles, and this spread induces the plasma mode transition, explaining the difference between the two types of gas injection.

A spectral library for laser-induced fluorescence analysis as a tool for rare earth element identification

Abstract. With the recurring interest in rare earth elements (REEs), laser-induced fluorescence (LiF) may provide a powerful tool for their rapid and accurate identification at different stages along their value chain. Applications to natural materials such as minerals and rocks could complement the spectroscopy-based toolkit for innovative, non-invasive exploration technologies. However, the diagnostic assignment of detected emission lines to individual REEs remains challenging because of the complex composition of natural rocks in which they can be found. The resulting mixed spectra and the large amount of data generated demand automated approaches of data evaluation, especially in mapping applications such as drill core scanning. LiF reference data provide the solution for robust REE identification, yet they usually remain in the form of tables of published emission lines. We show that a complete reference spectra library could open manifold options for innovative automated analysis. We present a library of high-resolution LiF reference spectra using the Smithsonian rare earth phosphate standards for electron microprobe analysis. We employ three standard laser wavelengths (325, 442, 532 nm) to record representative spectra in the UV-visible to near-infrared spectral range (340–1080 nm). Excitation at all three laser wavelengths yielded characteristic spectra with distinct REE-related emission lines for EuPO4, TbPO4, DyPO4 and YbPO4. In the other samples, the high-energy excitation at 325 nm caused unspecific, broad-band defect emissions. Here, lower-energy laser excitation is shown to be successful for suppressing non-REE-related emission. At 442 nm excitation, REE reference spectra depict the diagnostic emission lines of PrPO4, SmPO4 and ErPO4. For NdPO4 and HoPO4 the most efficient excitation was achieved with 532 nm. Our results emphasise the possibility of selective REE excitation by changing the excitation wavelength according to the suitable conditions for individual REEs. Our reference spectra provide a database for the transparent and reproducible evaluation of REE-bearing rocks. The LiF spectral library is available at zenodo.org and the registered DOI https://doi.org/10.5281/zenodo.4054606 (Fuchs et al., 2020). Primarily addressing the raw material exploration sector, it aids particularly the development of advanced data processing routines for LiF analysis but can also support further research on the REE luminescence in natural rocks or artificial compounds. It gives access to traceable data for the comparison of emission line positions, emission line intensity ratios and splitting into emission line sub-levels or can be used as reference or training data for automated approaches of component assignment.

Exploring formation rationale of skin-core heterogeneity during PVA solutions evaporation by laser-induced fluorescence analysis

The structural heterogeneity is mainly characteristic as skin-core manner during the forming film of polymer solutions volatilization. Due to absence of convenient, efficient and high-sensitivity inspection method, it is still a great challenge to manifest the formation and evolution rules of skin-core heterogeneity. Herein, the real-time monitoring of the drying of poly (vinyl alcohol) (PVA) solutions with different initial concentrations (C0s) was performed by a combination of fluorescence staining and laser-induced fluorescence (LIF) analysis techniques. Thanks to the spatial resolution capability of LIF, the development trend of structural heterogeneity along the thickness direction can be acquired exactly, and the thickness of skin layer determined by the LIF method is in accordance with the result from electron microscopy characterization. Importantly, as increasing solution concentration during evaporation process, there exists a threshold of concentration ～25% for the appearance of skin-core divergence. Meanwhile, although the formation of skin-core structure upon a higher C0 is more readily than a lower one, the increasing of C0 benefits to depress structural heterogeneity. These findings are of significance for completing the scenario of the formation procedure of skin-core structure via solution evaporation, which plays a crucial role on dominating the ultimate performances in polymeric-film materials.

Monitoring the Restoration of a Seventeenth-Century Wooden Artwork Using Laser-Induced Fluorescence and Digital Image Analysis.

The present paper is aimed at demonstrating the capabilities of digital image analysis (DIA) to support conservation of painted artwork. Laser-induced fluorescence (LIF) imaging has been usually used in the diagnosis of wall paintings. In this case, LIF is applied to the case study of a painted wooden canopy, and most successful data processing techniques are presented in the discussion of results. The Jesús del Gran Poder canopy, completed by Francisco Ruiz Gijón in 1692, is an oil panel painting on wood. Eight panels of the canopy have been study by LIF. This technique is capable of remotely acquiring hyperspectral images operating in fluorescence mode following ultraviolet laser excitation. LIF spectra combined with principal component analysis, spectral angle mapper, and DIA provide a chemical mapping of the treated wooden surface of the panels. Besides, LIF spectrum is as a fingerprint of the panels that allows stablishing differences between them. LIF imaging analysis has proven to be a very useful tool for mapping retouching work, tracking previous restorations, and detecting chemicals on the wood in order to monitor restorations.

Time-Resolved Laser-Induced Fluorescence Spectroscopy as a Guidance Tool for Laser Lithotripsy of Gallbladder Stones.

Although laser lithotripsy for fragmentation of gallbladder stones has been applied successfully in many clinical situations, this approach has two major limitations: (1) the potential to damage or perforate the bile duct and (2) the efficiency can be affected by the chemical composition of the gallstones. The present study evaluated the use of time-resolved laser-induced fluorescence spectroscopy to classify stone types and distinguish stone from tissue. Ex vivo time-resolved laser-induced fluorescence analysis (excitation wavelength λex = 400 nm and emission wavelength = 450-700 nm) of 54 gallbladder stones and seven gallbladder tissue samples was conducted. The spectral and temporal parameters were analyzed using linear discrimination analysis (LDA) to differentiate stone from tissue and to classify different stone types using two wavelength regions (λ1 = 510-530 nm and λ2 = 550-570 nm). Examination of 54 gallbladder stones and seven gallbladder tissue samples showed a significant difference in spectral- and temporal-derived parameters. The data were classified using LDA, and the overall accuracy was 94.88%, 84.39%, and 85.79% for both spectral and temporal parameters, only spectral parameters, and only temporal parameters, respectively. Our findings establish the feasibility of using time-resolved laser-induced fluorescence spectroscopy as a tool to identify gallbladder stone types and as a stone-tissue detection system to improve the effectiveness of laser lithotripsy procedures and reduce the risk of damaging biliary tract tissues.

Monitoring of Paddy Rice Varieties Based on the Combination of the Laser-Induced Fluorescence and Multivariate Analysis

Paddy rice is one of three major cereal crops in China, and the number of the paddy rice variety is increasing rapidly. The paddy rice variety is strongly related to crop yield and is also difficult to classify by using the naked eyes. A reliable approach is essential for accurately identifying different paddy rice varieties. Laser-induced fluorescence (LIF) technology has been widely utilized in many fields due to its particular advantages (rapid, non-intrusive, and sensitive). Thus, LIF combined with multivariate analysis that contained principal component analysis (PCA) and support vector machine (SVM) was proposed and was attempted to be utilized to identify different paddy rice varieties in this investigation. These fluorescence spectra displayed a high degree of multi-collinearity, and about 96.58% of the total variance contained in the laser-induced fluorescence spectra which were excited by a 532-nm excited wavelength can be explained by using the first three principle components. A SVM model with the help of threefold cross validation was used for paddy rice variety identification based on new variables calculated utilizing PCA. The numerical and experimental results displayed by using a confusion matrix and the classification accuracy can reach up to 91.36%. Thus, LIF technology combined with multivariate analysis can provide researchers with a faster and more effective tool for identifying different paddy rice varieties.

Investigation of the effects of metal ions in sample buffer on capillary electrophoresis coupled with laser-induced fluorescence analysis of thrombin using a dye-labeled 29-mer DNA aptamer

Metal ions in sample buffer show great effects on affinity CE-LIF analysis of thrombin using a TMR-labeled 29-nt DNA aptamer.

Laser-induced fluorescence analysis of plasmas for epitaxial growth of YBiO3 films with pulsed laser deposition

We record the two-dimensional laser-induced fluorescence (LIF) on multiple plasma constituents in a YBiO3 plasma. This allows us to directly link the influence of oxygen present in the background gas during pulsed laser deposition to the oxidation of plasma species as well as the formation of epitaxial YBiO3 films. With spatiotemporal LIF mapping of the plasma species (Y, YO, Bi, and BiO) in different background gas compositions, we find that little direct chemical interaction takes place between the plasma plume constituents and the background gas. However, a strong influence of the background gas composition can be seen on the YBO film growth, as well as a strong correlation between the oxygen fraction in the background gas and the amount of YO in the plasma plume. We assign this correlation to a direct interaction between the background gas and the target in between ablation pulses. In an O2 background, an oxygen-rich surface layer forms in between ablation pulses, which provides additional oxygen for the plasma plume during target ablation. This differs from our previous observations in STO and LAO plasmas, where species oxidation primarily takes place during propagation of the plasma plume towards the substrate.

Alternative splicing of SMPD1 coding for acid sphingomyelinase in major depression

BackgroundMajor depressive disorder (MDD) is a psychiatric disorder characterized by key symptoms that include depressed mood and a loss of interest and pleasure. A recently developed pathogenic model of MDD involves disturbed neurogenesis in the hippocampus, where the acid sphingomyelinase (ASM)/ceramide system plays an important role and is proposed as a molecular target for antidepressant action. Because alternative splicing of SMPD1 mRNA, coding for ASM, is relevant for the regulation of ASM enzymatic activity, we investigated the frequency of alternatively spliced ASM isoforms in peripheral blood cells of MDD patients versus healthy controls. MethodsBecause the full-length transcript variant 1 of SMPD1 (termed ASM-1) is the only known form within the splicing pattern that encodes an enzymatically fully active ASM, we determined a fraction of splice isoforms deviating from ASM-1 using PCR amplification and capillary electrophoresis with laser-induced fluorescence analysis. ResultsASM alternative splicing events occurred significantly less frequently in MDD patients compared to healthy subjects. After 5 days of antidepressant treatment, the frequency of alternatively spliced ASM isoforms decreased in those patients who were treated with a functional inhibitor of ASM activity (FIASMA) but remained constant in MDD patients treated with other antidepressant drugs. This effect was more pronounced when healthy male volunteers were treated with the FIASMAs fluoxetine or paroxetine, in contrast to a placebo group. LimitationsPatients were treated with different antidepressant drugs, depending on individual parameters and disease courses. ConclusionsThis study shows that the ASM alternative splicing pattern could be a biological target with diagnostic relevance and could serve as a novel biomarker for MDD.

Image Analysis of Hydroxyl-Radical Planar Laser-Induced Fluorescence in Turbulent Supersonic Combustion

Flow visualization and statistical analysis of a supersonic, turbulent reacting flow from nonintrusive hydroxyl radical planar laser-induced fluorescence images are presented. The OH-PLIF images show instantaneous structures of turbulence in two combustor configurations at different fuel-equivalence ratios. Proper orthogonal decomposition and autocorrelations are performed on the OH-PLIF data to extract quantitative information about turbulent fluctuations and length-scale correlations. Changes in correlation length scales, representative of the integral length scales of the flow, and turbulent energy flow patterns are observed as a function of position in the combustor and fuel-equivalence ratio. Correlation length scales were found to increase with streamwise distance for all configurations. Dual-mode operation with supersonic and subsonic combustion is demonstrated in the facility. Correlation length scales and the growth rate of these length scales were found to be smaller in the subsonic combustion mode.

Concentration Field Evolution during the Drying of a Thin Polymer Solution Film near the Contact Line.

An experimental study is performed for polymer concentration field measurements during the drying of an aqueous poly(vinyl alcohol) solution inside a shallow cavity near a vertical side wall. The measurements are based on optical techniques such as 3D confocal microscopy for laser-induced fluorescence analysis. The results reveal a significant concentration heterogeneity across the film near the meniscus during the drying process. The concentration at the solution-air interface remains higher compared to the bulk, and it increases toward the pinned contact line and also over time. A skin layer starts forming as the surface concentration reaches the glass-transition concentration, after which the evaporation rate starts decreasing. Regardless of the cavity depth and the initial polymer concentration, the drying film undergoes a similar concentration evolution during the evaporation process, although minor differences can be recognized. For instance, a low local capillary number at the surface is associated with a wavy surface concentration profile while at higher capillary numbers disturbances are damped and a much more uniform concentration profile is observed.

Selective enzymatic cleavage and labeling for sensitive capillary electrophoresis laser-induced fluorescence analysis of oxidized DNA bases

Oxidatively generated DNA damage is considered to be a significant contributing factor to cancer, aging, and age-related human diseases. It is important to detect oxidatively generated DNA damage to understand and clinically diagnosis diseases caused by oxidative damage. In this study, using selective enzymatic cleavage and quantum dot (QD) labeling, we developed a novel capillary electrophoresis-laser induced fluorescence method for the sensitive detection of oxidized DNA bases. First, oxidized DNA bases are recognized and removed by one DNA base excision repair glycosylase, leaving apurinic and apyrimidinic sites (AP sites) at the oxidized positions. The AP sites are further excised by the AP nicking activity of the chosen glycosylase, generating a nucleotide gap with 5′- and 3′- phosphate groups. After dephosphorylation with one alkaline phosphatase, a biotinylated ddNTP is introduced into the nucleotide space within the DNA strand by DNA polymerase I. The biotin-tagged DNA is further labeled with a QD-streptavidin conjugate via non-covalent interactions. The DNA-bound QD is well-separated from excess DNA-unbound QD by highly efficient capillary electrophoresis and is sensitively detected by online coupled laser-induced fluorescence analysis. Using this method, we can assess the trace levels of oxidized DNA bases induced by the Fenton reaction and UV irradiation. Interestingly, the use of the formamidopyrimidine glycosylase (FPG) protein and endonuclease VIII enables the detection of oxidized purine and pyrimidine bases, respectively. Using the synthesized standard DNA, the approach has low limits of detection of 1.1×10−19mol in mass and 2.9pM in concentration.

Temporally and spectrally resolved UV absorption and laser-induced fluorescence measurements during the pyrolysis of toluene behind reflected shock waves

Toluene is frequently used as fluorescence tracer in high-temperature combustion applications. A quantitative analysis of laser-induced fluorescence (LIF) signals requires the knowledge of photophysical properties and decomposition kinetics. Using spectrally and temporally resolved ultraviolet absorption and LIF measurements, we studied the spectral properties of toluene and its pyrolysis products behind shock waves between 810 and 1,755 K. Transient absorption spectra were acquired between 220 and 300 nm. The temporal behavior of the absorption at 266 nm was compared to simulations based on literature kinetics models of toluene pyrolysis and available high-temperature absorption cross-sections of toluene, benzyl radicals, and C7H6 as a product from benzyl decomposition. Experiment and simulation agree well at the beginning of the pyrolysis process, whereas for longer reaction times deviations occur presumably due to the build-up of high molecular weight species, which contribute to the observed absorption but have unknown spectral properties. Additionally, LIF emission spectra were recorded following 266-nm excitation at selected reaction times. From measurements up to 1,220 K, the relative fluorescence quantum yield of toluene was derived, extending existing data to higher temperatures. Products from toluene pyrolysis were found to be the major contributors to the LIF signal at higher temperatures.

Total internal reflection–based module for fluorescence and absorbance detection

We present a miniaturized polymer-based micro-optical detection unit for ultraviolet and visible laser-induced fluorescence (LIF) and absorbance (ABS) analysis with an interaction length of 3 mm. We use nonsequential optical ray tracing simulations to model the system and to optimize its performance with respect to optical efficiency and system complexity. The design features a compact optical system combining total internal reflection (TIR) mirrors and refractive optics. The detection module is prototyped with deep proton writing in 2-mm-thick polymethylmethacrylate and quantitatively characterized using a three-dimensional coordinate measurement machine. We demonstrate the proof-of-concept of this TIR mirror–based module for coumarin 480 obtaining limits of detection of 50 pM and 500 nM for LIF and ABS, respectively.

Narrowing down the distal border of the copy number variable beta-defensin gene cluster on human 8p23

BackgroundCopy number variation (CNV) in the range from 2 to 12 per diploid genome is an outstanding feature of the beta-defensin gene (DEFB) cluster on human chromosome 8p23.1 numerously demonstrated by different methods. So far, CNV was proven for a 115 kb region between DEFB4 and 21 kb proximal of DEFB107 but the borders for the entire CNV repeat unit are still unknown. Our study aimed to narrow down the distal border of the DEFB cluster.ResultsWe established tests for length polymorphisms based on amplification and capillary electrophoresis with laser-induced fluorescence (CE-LIF) analysis of seven insertion/deletion (indel) containing regions spread over the entire cluster. The tests were carried out with 25 genomic DNAs with different previously determined cluster copy numbers. CNV was demonstrated for six indels between ~1 kb distal of DEFB108P and 10 kb proximal of DEFB107. In contrast, the most distal indel is not affected by CNV.ConclusionOur analysis fixes the minimal length of proven CNV to 157 kb including DEFB108P but excluding DEFB109P. The distal border between CNV and non-CNV part of the DEF cluster is located in the 59 kb interval chr8:7,171,082-7,230,128.

Interplay of Binding Stoichiometry and Recognition Specificity for the Interaction of MBD2b Protein and Methylated DNA Revealed by Affinity Capillary Electrophoresis Coupled with Laser-Induced Fluorescence Analysis

The methyl-CpG binding domain (MBD) family proteins can specifically bind methylated DNA sequences and thereby mediate gene transcription. In this study, we used neutral capillary electrophoresis coupled with laser-induced fluorescence to investigate the interactions of DNA and MBD2b, a model MBD family protein with the highest affinity. For this purpose, we synthesized 13 double-stranded oligonucleotides of varying length (20 bp to 80 bp) and of varying methylation density. The sequences of these oligonucleotides were adapted from a frequently methylated promoter region of human p16(INK4a) gene. We demonstrate that multiple MBD2b proteins can bind to one DNA molecule with a DNA length-dependent binding stoichiometry. Each MBD2b protein can occupy 20 nucleotides in a bound DNA molecule regardless of the methylation status of DNA. By binding multiple MBD2b proteins (up to four protein molecules) to one dsDNA molecule (80 bp), methylated and unmethylated DNA were bound at similar percentages. Although the total amount of the DNA-MBD2b complexes increases with increasing DNA length for both unmethylated and methylated DNA, the DNA-MBD2b complexes of 1:1 display more than 10-fold higher affinity for methylated DNA (e.g., 40 bp DNA) accompanying a 20-fold lower dissociation rate constant. Hence, our study clarifies for the first time that the specificity of MBD2b to methylated DNA decreases as more MBD2b monomers binding to the same region of DNA. Additionally, this study opens a new venue to improve MBD protein-based assays for detecting DNA methylation.

Analysis of Ultraviolet Laser-Induced Fluorescence as Influenced by the Nitrogen Nutritional Condition in Buckwheat Leaves

Analysis of Ultraviolet Laser-Induced Fluorescence as Influenced by the Nitrogen Nutritional Condition in Buckwheat Leaves