Multidimensional Fluorescence Spectroscopy Research Articles

Multidimensional fluorescence spectroscopy of wine using synchronous excitation/emission matrices and time-resolved fluorescence interferometric detection

Wines are complex mixtures of chemical compounds with broad and overlapping absorption and emission spectral features in the UV and visible spectral regions, making them challenging to study with conventional optical spectroscopic techniques. Multidimensional fluorescence spectroscopies correlate fluorescence spectra with other degrees of freedom, and have proven useful for studying complex molecular systems, offering a pathway for the analysis of wines utilising their inherent fluorescence. Here we employ steady-state excitation-emission matrix (EEM) and time-resolved fluorescence spectral measurements to investigate representative commercial white and red wine samples and a fluorescent ‘model’ wine base. Combining these multidimensional measurement methods provides information on the emission characteristics of the components that wines contain. This investigation illustrates the potential for multidimensional fluorescence techniques as diagnostic tools for the wine industry.

Fast and accurate identification of pathogenic bacteria using excitation-emission spectroscopy and machine learning.

Fast and reliable identification of pathogenic bacteria is of upmost importance to human health and safety. Methods that are currently used in clinical practice are often time consuming, require expensive equipment, trained personnel, and therefore have limited applications in low resource environments. Molecular identification methods address some of these shortcomings. At the same time, they often use antibodies, their fragments, or other biomolecules as recognition units, which makes such tests specific to a particular target. In contrast, array-based methods use a combination of reporters that are not specific to a single pathogen. These methods provide a more data-rich and universal response that can be used for identification of a variety of bacteria of interest. In this report, we demonstrate the application of the excitation-emission spectroscopy of an environmentally sensitive fluorescent dye for identification of pathogenic bacterial species. 2-(4'-Dimethylamino)-3-hydroxyflavone (DMAF) interacts with the bacterial cell envelope resulting in a distinct spectral response that is unique to each bacterial species. The dynamics of dye-bacteria interaction were thoroughly investigated, and the limits of detection and identification were determined. Neural network classification algorithm was used for pattern recognition analysis and classification of spectral data. The sensor successfully discriminated between eight representative pathogenic bacteria, achieving a classification accuracy of 85.8% at the species level and 98.3% at the Gram status level. The proposed method based on excitation-emission spectroscopy of an environmentally sensitive fluorescent dye is a powerful and versatile diagnostic tool with high accuracy in identification of bacterial pathogens.

Non-invasive analysis of natural textile dyes using fluorescence excitation-emission matrices

Multidimensional fluorescence spectroscopy was assessed as a non-invasive and non-destructive method for the analysis of components in natural textile dyes. Results demonstrate that components in the natural dyes fluoresce and wool's intrinsic fluorescence is, in many cases, not a considerable analytical interferent. In the case of some self-dyed reference yarns, like those dyed with northern and lady's bedstraws, wood horsetail, safflower, salted shield lichen, dyer's madder and cochineal, the fluorescence excitation-emission matrices (EEMs) are sufficiently characteristic for using them as a primary means of identification (or assignment to a family of dyes). With most of the studied yellow and green dyes (heather, silver birch, some bloodred webcap treatments, alkanet), however, the spectra can be used as additional information for identification.This study reports multidimensional fluorescence data for a collection of wools dyed with natural dyes (31 dyed wool yarn samples that were self-dyed with 18 different natural dyes) that were used as references in a case study of two historical textiles for which liquid chromatography-mass spectrometry was used as a confirmatory technique. Given its utility as a rapid and non-destructive/non-invasive method with information-rich multidimensional EEM output, the front-face fluorescence spectroscopy of surfaces using a fiber optic probe is a promising technique for the analysis of dyes on cultural heritage textiles.

Quantitative analysis of weakly bound insulin oligomers in solution using polarized multidimensional fluorescence spectroscopy

Being able to measure the size and distribution of oligomers in solution is a critical issue in the manufacture and stability of insulin and other protein formulations. Measuring oligomers reliably can however be complicated, due to their fragile self-assembled structures, which are held together by weak forces. This can cause issues in chromatographic based methods, where dissociation or re-equilibration of oligomer populations can occur e.g. upon dilution in a different eluting buffer, but also for light scattering based methods like dynamic light scattering (DLS) where the size difference involved (often less than a factor 3) does not allow mixtures of oligomers to be resolved. Intrinsic fluorescence offers an attractive alternative as it is non-invasive, sensitive but also because it contains scattered light when implemented via excitation emission matrix (EEM) measurements, that is sensitive to changes in particle size.Here, using insulin at formulation level concentrations, we show for the first time how EEM can both discriminate and quantify the proportion of oligomeric states in solution. This was achieved by using the Rayleigh scatter (RS) band and the fluorescence signal contained in EEM. After validating size changes with DLS, we show in particular how the volume under the RS band correlated linearly with protein/oligomer molecular weight, in agreement with the Debye-Zimm relationship. This was true for the RS data from both EEM and polarized EEM (pEEM) measurements, the latter providing a stronger scatter signal, more sensitive to particle size changes.The fluorescence signal was then used with multivariate curve resolution (MCR) to quantify more precisely the soluble oligomer composition of insulin solutions. In conditions that promoted the formation of mainly one type of oligomer (monomer, dimer, or hexamer), pEEM-MCR helped identify the presence of small amounts of other oligomeric forms, while in conditions that were previously said to favour the insulin tetramer, we show that in the presence of zinc, these insulin samples were instead a heterogenous mixture composed of mostly dimers and hexamers. These MCR results correlated in all cases with the observed discrimination by principal component analysis (PCA), and deviations observed in the RS data. In conclusion, using pEEM scatter and emission components with chemometric data analysis provides a unique analytical method for characterising and monitoring changes in the soluble oligomeric state of proteins.

Multi-level data fusion strategies for modeling three-way electrophoresis capillary and fluorescence arrays enhancing geographical and grape variety classification of wines

Capillary electrophoresis with diode array detection (CE-DAD) and multidimensional fluorescence spectroscopy (EEM) second-order data were fused and chemometrically processed for geographical and grape variety classification of wines. Multi-levels data fusion strategies on three-way data were evaluated and compared revealing their advantages/disadvantages in the classification context. Straightforward approaches based on a series of data preprocessing and feature extraction steps were developed for each studied level. Partial least square discriminant analysis (PLS-DA) and its multi-way extension (NPLS-DA) were applied to CE-DAD, EEM and fused data matrices structured as two-way and three-way arrays, respectively. Classification results achieved on each model were evaluated through global indices such as average sensitivity non-error rate and average precision. Different degrees of improvement were observed comparing the fused matrix results with those obtained using a single one, clear benefits have been demonstrated when level of data fusion increases, achieving with the high-level strategy the best classification results.

Multi-dimensional fluorescence spectroscopy coupled with chemometrics in rapid antibiotic detection and discrimination

Antibiotic residues in animal-derived foods pose risk to human health including chemical poisoning and antimicrobial resistance, and therefore, constant monitoring throughout the food supply chain is important. In the present study multi-dimensional fluorescence spectroscopy (3D and 2D) coupled with chemometric tools were tested for potential application to detect, discriminate and quantify penicillin G (PG), sulfadiazine (SF) and tetracycline (TC) in milk by direct measurement. Qualitative and quantitative calibration models were developed for prediction of antibiotic residues. Results demonstrated optimal discrimination of milk samples on the basis of antibiotic type and concentration with close to 100% of accuracy. Negative correlation between antibiotic concentration and fluorescence peak height was displayed (r ≥ 0.963 and p ≤ 0.002). A great potential for quantitative antibiotic determination was established with R2 > 0.9 and low standard errors of estimation indicating acceptable precision for the developed technique. Fluorescence spectroscopy demonstrated high specificity and sensitivity with detection limit below the maximum residue limit of PG, SF and TC in milk. Therefore, fluorescence spectroscopy can be used as an alternative method for rapid screening of antibiotic residues in milk at collection centers and processing plants to ensure product quality and safety.

Multispectral Depth-Resolved Fluorescence Lifetime Spectroscopy Using SPAD Array Detectors and Fiber Probes.

Single Photon Avalanche Diode (SPAD) arrays are increasingly exploited and have demonstrated potential in biochemical and biomedical research, both for imaging and single-point spectroscopy applications. In this study, we explore the application of SPADs together with fiber-optic-based delivery and collection geometry to realize fast and simultaneous single-point time-, spectral-, and depth-resolved fluorescence measurements at 375 nm excitation light. Spectral information is encoded across the columns of the array through grating-based dispersion, while depth information is encoded across the rows thanks to a linear arrangement of probe collecting fibers. The initial characterization and validation were realized against layered fluorescent agarose-based phantoms. To verify the practicality and feasibility of this approach in biological specimens, we measured the fluorescence signature of formalin-fixed rabbit aorta samples derived from an animal model of atherosclerosis. The initial results demonstrate that this detection configuration can report fluorescence spectral and lifetime contrast originating at different depths within the specimens. We believe that our optical scheme, based on SPAD array detectors and fiber-optic probes, constitute a powerful and versatile approach for the deployment of multidimensional fluorescence spectroscopy in clinical applications where information from deeper tissue layers is important for diagnosis.

Data fusion approaches in spectroscopic characterization and classification of PDO wine vinegars

Spain is one of the major producers of high-quality wine vinegars having three protected designations of origin (a.k.a. PDOs): “Vinagre de Jerez”, “Vinagre de Condado de Huelva” and “Vinagre de Montilla-Moriles”. Their high prices due to their high quality and their high production costs explain the need for developing an adequate quality control technique and the interest in extensive characterization in order to capture the identity of each denomination. In this framework, methodologies based on non-targeted techniques, such as spectroscopies, are becoming popular in food authentication. Thus, for improving vinegar quality assessment, fusion of data blocks obtained from the same samples but different analytical techniques could be a good strategy, since the quantity and quality of sample knowledge could be enhanced providing new insights into the differentiation of vinegars. Therefore, the aim of this manuscript is the development of a multi-platform methodology and a model able to classify the Spanish wine vinegar PDOs. Sixty-five PDO wine vinegars were analyzed by four spectroscopic techniques: Fourier-transform mid-infrared spectroscopy (MIR), near infrared spectroscopy (NIR), multidimensional fluorescence spectroscopy (EEM) and proton nuclear magnetic resonance (1H-NMR). Two different data fusion strategies were evaluated: Mid-level data fusion with different preprocessing, and Common Component and Specific Weights analysis multiblock method. Exploratory and classification analysis on the data from individual techniques were also performed and compared with data fusion models. The data fusion models improved the classification, providing a more efficient differentiation, than the models based on single methods, and supporting the approach to combine these methods to achieve synergies for an optimized PDO differentiation.

Calibration, standardization, and quantitative analysis of multidimensional fluorescence (MDF) measurements on complex mixtures (IUPAC Technical Report)

Abstract This IUPAC Technical Report describes and compares the currently applied methods for the calibration and standardization of multi-dimensional fluorescence (MDF) spectroscopy data as well as recommendations on the correct use of chemometric methods for MDF data analysis. The paper starts with a brief description of the measurement principles for the most important MDF techniques and a short introduction to the most important applications. Recommendations are provided for instrument calibration, sample preparation and handling, and data collection, as well as the proper use of chemometric data analysis methods.

Characterization and authentication of Spanish PDO wine vinegars using multidimensional fluorescence and chemometrics.

This work assesses the potential of multidimensional fluorescence spectroscopy combined with chemometrics for characterization and authentication of Spanish Protected Designation of Origin (PDO) wine vinegars. Seventy-nine vinegars of different categories (aged and sweet) belonging to the Spanish PDOs "Vinagre de Jerez", "Vinagre de Montilla-Moriles" and "Vinagre de Condado de Huelva", were analyzed by excitation-emission fluorescence spectroscopy. A visual assessment of fluorescence landscapes pointed out different trends with vinegar categories. PARAllel FACtor analysis (PARAFAC) extracted the potential fluorophores and their values in the PDO vinegars. This information, coupled with different classification methods (Partial Least Square Discrimination Analysis "PLS-DA" and Support Vectors Machines "SVM"), was able to discriminate the wine vinegar category within each PDO, for which SVM models obtained better results (>92% of classification). In each category, SVM also allows the differentiation between PDOs. The proposed methodology could be used as an analysis method for the authentication of Spanish PDO wine vinegars.

Poly(ferulic acid-co-tyrosine): Effect of the Regiochemistry on the Photophysical and Physical Properties en Route to Biomedical Applications.

The photophysical and mechanical properties of novel poly(carbonate-amide)s derived from two biorenewable resources, ferulic acid (FA) and l-tyrosine ethyl ester, were evaluated in detail. From these two bio-based precursors, a series of four monomers were generated (having amide and/or carbonate coupling units with remaining functionalities to allow for carbonate formation) and transformed to a series of four poly(carbonate-amide)s. The simplest monomer, which was biphenolic and was obtained in a single amidation synthetic step, displayed bright, visible fluorescence that was twice brighter than FA. Multidimensional fluorescence spectroscopy of the polymers in solution highlighted the strong influence that regioselectivity and the degree of polymerization have on their photophysical properties. The regiochemistry of the system had little effect on the wettability, surface free energy, and Young’s modulus (ca. 2.5 GPa) in the solid state. Confocal imaging of solvent-cast films of each polymer revealed microscopically flat surfaces with fluorescent emission deep into the visible region. Fortuitously, one of the two regiorandom polymers (obtainable from the biphenolic monomer in only an overall two synthetic steps from FA and l-tyrosine ethyl ester) displayed the most promising fluorescent properties both in the solid state and in solution, allowing for the possibility of translating this system as a self-reporting or imaging agent in future applications. To further evaluate the potential of this polymer as a biodegradable material, hydrolytic degradation studies at different pH values and temperatures were investigated. Additionally, the antioxidant properties of the degradation products of this polymer were compared with its biphenolic monomer and FA.

A fluorescence anisotropy method for measuring protein concentration in complex cell culture media

The rapid, quantitative analysis of the complex cell culture media used in biopharmaceutical manufacturing is of critical importance. Requirements for cell culture media composition profiling, or changes in specific analyte concentrations (e.g. amino acids in the media or product protein in the bioprocess broth) often necessitate the use of complicated analytical methods and extensive sample handling. Rapid spectroscopic methods like multi-dimensional fluorescence (MDF) spectroscopy have been successfully applied for the routine determination of compositional changes in cell culture media and bioprocess broths. Quantifying macromolecules in cell culture media is a specific challenge as there is a need to implement measurements rapidly on the prepared media. However, the use of standard fluorescence spectroscopy is complicated by the emission overlap from many media components. Here, we demonstrate how combining anisotropy measurements with standard total synchronous fluorescence spectroscopy (TSFS) provides a rapid, accurate quantitation method for cell culture media. Anisotropy provides emission resolution between large and small fluorophores while TSFS provides a robust measurement space. Model cell culture media was prepared using yeastolate (2.5mgmL–1) spiked with bovine serum albumin (0 to 5mgmL–1). Using this method, protein emission is clearly discriminated from background yeastolate emission, allowing for accurate bovine serum albumin (BSA) quantification over a 0.1 to 4.0mgmL–1range with a limit of detection (LOD) of 13.8μgmL–1.

Multidimensional fluorescence studies of the phenolic content of dissolved organic carbon in humic substances

Indicators suggest that the amount of dissolved organic carbon (DOC) in natural waters may be increasing. Climate change has been proposed as a potential contributor to the trend, and under such a mechanism, the phenolic content of DOC may also be increasing. This study explores the assessment of the phenolic character of DOC using multidimensional fluorescence spectroscopy as a more convenient alternative to traditional wet chemistry methods. Parallel factor analysis (PARAFAC) is applied to fluorescence excitation emission matrices (EEMs) of humic samples to analyze inherent phenolic content. The PARAFAC results are correlated with phenol concentrations derived from the Folin-Ciocalteau reagent-based method. The reagent-based method reveals that the phenolic content of five International Humic Substance Society (IHSS) samples varies from approximately 5.2 to 22 ppm Tannic Acid Equivalents (TAE). A four-component PARAFAC fit is applied to the EEMs of the IHSS sample dataset and it is determined by PARAFAC score correlations with phenol concentrations from the reagent-based method that components C2, C3, and C4 have the highest probability of containing phenolic groups. The results show the potential for PARAFAC analysis of multidimensional fluorescence data for monitoring the phenolic content of DOC.

Characterization of dissolved organic matter in a coral reef ecosystem subjected to anthropogenic pressures (La Réunion Island, Indian Ocean) using multi-dimensional fluorescence spectroscopy

La Saline fringing reef is the most important coral reef complex of La Réunion Island (southwestern Indian Ocean; 21°07′S, 55°32′E). This ecosystem is subjected to anthropogenic pressures through river inputs and submarine groundwater discharge (SGD). The goal of this study was to characterize the pool of fluorescent dissolved organic matter (FDOM) in different water bodies of La Saline fringing reef ecosystem using excitation–emission matrix (EEM) spectrofluorometry. From EEMs, we identified the different fluorophores by the peak picking technique and determined two fluorescence indices issued from the literature: the humification index (HIX) and the biological index (BIX). The main known fluorophores were present within the sample set: humic-like A, humic-like C, marine humic-like M, tryptophan-like T1 and T2, and tyrosine-like B1 and B2. In some samples, unknown fluorophores (“U”) were also detected. The surface oceanic waters located beyond the reef front displayed a typical oligotrophic marine signature, with a dominance of autochthonous/biological material (presence of peaks: T1 > B1 > A > T2 > M > C; HIX: 0.9 ± 0.4; BIX: 2.3 ± 1.1). In the reef waters, the autochthonous/biological fingerprint also dominated even though the content in humic substances was higher (same relative distribution of peaks; HIX: 1.6 ± 0.6; BIX: 1.0 ± 0.1). Sedimentary and volcanic SGD showed very different patterns with a strong terrestrial source for the former (A > T1 > C > B1 and A > C > B1; HIX: 9.8 ± 2.0; BIX: 0.8 ± 0.0) and a weak terrestrial source for the latter (A > B1 > U3 > B2 > C and A > U4 > C; HIX: 2.4 ± 0.3; BIX: 0.9 ± 0.0). In the Hermitage River, both humic substances and protein-like material were abundant (T1 > A > U5 > B1 > C > B2; HIX: 2.3; BIX: 1.4). We provide evidences for the presence of anthropogenic DOM in some of these water bodies. Some oceanic samples (presence of peaks U1 and U2) were likely contaminated by oil-derived PAHs from ships navigating around the reef front, whereas the Hermitage River was highly impacted by sewage effluents, numerous in this coastal area of La Réunion Island. We conclude that multi-dimensional fluorescence spectroscopy (EEM) coupled to the determination of HIX and BIX is a good tool for assessing the origin and distribution of DOM in the coral reef ecosystems submitted to anthropogenic impacts.

Influence of Tillage, Cropping, and Nitrogen Source on the Chemical Characteristics of Humic Acid, Fulvic Acid, and Water-Soluble Soil Organic Matter Fractions of a Long-Term Cropping System Study

The characterization of organic matter in agroecosystems is important because of its involvement in many important soil ecosystem processes. Humic acid, fulvic acid, and water-extractable organic matter from a 9-year agroecosystem study investigating the effects of tillage, cropping system, and N source was characterized using multidimensional fluorescence spectroscopy with parallel factor analysis (PARAFAC). The fluorescence spectra suite containing all three types of organic matter fractions was modeled by five PARAFAC components. The distribution of component concentrations was unique to each type of organic matter fraction, indicating that these operational extracted fractions reflect differing chemical pools of soil organic matter. The three treatment factors (tillage, cropping, and N source) investigated in this study did not affect the component distribution of the humic and fulvic acid fractions that are regarded as the refractory pools of soil organic matter. In contrast, the component distribution of the more labile water-extractable organic matter fraction was significantly affected by the N source treatment. The results of this study support the use of multidimensional fluorescence spectroscopy with PARAFAC as a method to investigate how management practices of agroecosystems affect the dynamics and chemical nature of soil organic matter pools.

Influence of foliar phosphorus and nitrogen contents on chemical properties of water extractable organic matter derived from fresh and decomposed sugar maple leaves

The effects of watershed-scale experimental acidification on the macronutrient content and decomposition of sugar maple ( Acer saccharum Marsh) leaves were investigated. Bear Brook Watershed in Maine (BBWM) is a paired forest watershed study where the West Bear (WB) watershed has been treated bi-monthly with 1800 eq ha −1 yr −1 of (NH 4) 2SO 4 since 1989, and the adjacent East Bear (EB) watershed has acted as a reference. Leaf samples collected from the treated WB watershed had significantly higher concentrations of N and P than leaves from the reference EB watershed. Leaves from both watersheds were decomposed for a 10-day laboratory incubation. Extractable total soluble carbon (C TS) content of the leaves decreased following decomposition to a greater extent in WB leaves than in EB leaves. Spectroscopic and chromatographic chemical analyses indicated similar chemical properties for the fresh WB and EB WEOM. However, after decomposition, the WB WEOM was more humified as compared to EB WEOM indicating that the watershed treatment resulted in leaves which were more biodegradable than those in the reference watershed. Multi-dimensional fluorescence spectroscopy with parallel factor analysis (PARAFAC) modeled five components: tyrosine-like, three humic substance-like, and terrestrial/anthropogenic associated-like fluorophores. Following decomposition, the relative concentrations of two of the humic-associated components increased to a significantly greater extent for WB than for EB WEOM. These observations were consistent with greater decomposition-related changes to the WEOM from WB samples relative to EB samples. Pearson correlation analysis showed that foliar N and P concentrations were positively correlated with indices of humification. Adsorption of WEOM to goethite and gibbsite was significantly greater for decomposed WB WEOM than EB WEOM. These results demonstrate that greater leaf N and P contents can increase short-term decomposition, accelerate production of more humic-like WEOM, and thereby potentially influence the distribution of organic matter within the soil carbon pool.

Effects of soil acidification and forest type on water soluble soil organic matter properties

Dissolved organic matter (DOM) plays an important role in ecosystem processes such as nutrient release and utilization, mobilization and transport of metals, and carbon sequestration. We investigated the chemical properties of soils from the Bear Brook Watershed in Maine (BBWM) which is the site of a long-term paired-watershed experimental acidification study that includes both deciduous and coniferous stands. Multi-dimensional fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) of the spectra, nuclear magnetic resonance spectroscopy, and size-exclusion chromatography, were used to characterize the DOM extracted from soils sampled from BBWM at four soil depth increments in 2003. Principal component analysis of the base cation, metal, and total C content of the mineral horizons indicated a strong negative relationship between pH and soil Al, Fe, P, and C. The close clustering of Al, Fe, P, and C loadings for the mineral soils suggests that organic matter is important for Al and Fe mobilization and that P solubility is influenced by the metal mobilization process. PARAFAC modeled the fluorescence spectra with three fluorescing components that were in the landscape regions typical of humic substances: (339 nm excitation/470 nm emission), (324 nm/418 nm), and (< 240/465 nm) and the relative distributions of the three components were similar amongst the four treatments and four soil depth increments. The size exclusion chromatograms also revealed a high degree of similarity between all the extracted DOM. Our data suggests that litter quality as influenced by forest composition and ecosystem acidification exert a minor influence on the chemical composition of the water-soluble soil DOM fraction.

Picosecond Multidimensional Fluorescence Spectroscopy: A Tool to Measure Real-time Protein Dynamics During Function†

Advanced multidimensional time-correlated single photon counting (mdTCSPC) and picosecond time-resolved fluorescence in combination with site-directed fluorescence labeling are valuable tools to study the properties of membrane protein surface segments on the pico- to nanoseconds time scale. Time-resolved fluorescence anisotropy changes of protein bound fluorescent probes reveal changes in protein dynamics and steric restriction. In addition, the change in fluorescence lifetime and intensity of the covalently bound fluorescent dye is indicative of environmental changes at the protein surface. In this study, we have measured the changes in fluorescence lifetime traces of the fluorescent dye fluorescein covalently bound to the first cytoplasmic loop of bacteriorhodopsin (bR) after light activation of protein function. The fluorescence is excited by a picosecond laser pulse. The retinylidene chromophore of bR is light-activated by a 10 ns laser pulse, which in turn triggers recording of a sequence of fluorescence lifetime traces in the mdTCSPC-module. The fluorescence decay changes upon protein function occur predominantly in the 100 ps time range. The kinetics of these changes shows two transitions between three intermediate states in the second part of the bR photocycle. Correlation with photocycle kinetics allows for the determination of reaction intermediates at the proteins surface which are coupled to changes in the retinal binding pocket.

Characterization of Fresh and Decomposed Dissolved Organic Matter Using Excitation−Emission Matrix Fluorescence Spectroscopy and Multiway Analysis

Fresh and decomposed dissolved organic matter (DOM) derived from 13 plant biomass and animal manure sources was characterized using multidimensional fluorescence spectroscopy with parallel factor analysis (PARAFAC), high-performance size-exclusion chromatography, and UV-vis spectroscopy. The PARAFAC analysis modeled seven fluorescence components: tryptophan-like, tyrosine-like, and five humic substance-like components. For most of the plant-derived DOM solutions, decomposition significantly affected the concentration of three humic substance-like-associated components, increasing two and decreasing one. The effect of decomposition upon DOM derived from animal manures was dependent on the manure source. For a majority of the DOM extracts, the ratio of fluorescence intensity to absorptivity at 254 nm increased following decomposition, indicating that fluorescing DOM compounds were generally more resistant to biodegradation than nonfluorescing UV-absorbing compounds. Molar absorptivity, humification index (HIX), and apparent molecular weight (MWAP) increased by 38.0, 38.8, and 370%, respectively, following decomposition. Spearman correlation analysis showed a strong positive relationship between the humic substance-like components and the DOM MWAP, absorptivity, and HIX. The results of this study support the use of multidimensional fluorescence spectroscopy with PARAFAC as a method to monitor the decomposition of carbon-rich soil amendments such as crop residues, green manures, and animal manures.

Dissolved Organic Matter Characterization Using Multiway Spectral Decomposition of Fluorescence Landscapes

Dissolved organic matter (DOM) plays an important role in many soil ecosystem functions. Multidimensional fluorescence spectroscopy of DOM with parallel factor analysis (PARAFAC) of the resulting spectral landscape has been successful in characterizing DOM from a variety of aquatic sources. This study was conducted to assess the multiway PARAFAC approach for quantitatively characterizing the fluorescent landscapes of DOM from aqueous extracts of soils and soil amendments. The DOM was extracted from plant biomass representative of crop, wetlands, and tree species; animal manures; and soils from controlled studies of cropping systems with known histories of organic amendments. The fluorescence landscape spectra were collected in the excitation range from 240 to 400 nm and emission range from 300 to 500 nm in 3‐nm increments. The excitation and emission spectra modeled from the PARAFAC analysis showed that the plant biomass, animal manure, and soil DOM contained five fluorescing components: tryptophan‐like (peak location at excitation 270 nm, emission 354 nm), tyrosine‐like (273/309 nm), and three humic‐substance‐like components (&gt;240/465 nm, 306/405 nm, and 315/447 nm). Principal component analysis of the concentration loading showed that the soil‐derived DOM was very similar despite the different types and quantities of organic amendments incorporated in the different cropping systems. This study shows that PARAFAC analysis of multidimensional fluorescence spectra can model the chemical profile of terrestrial DOM in a chemically meaningful way. This represents a significant advance over current approaches to interpreting the complex DOM fluorescence spectra.