Fluorescence Excitation Emission Spectra Research Articles

A new three-dimensional modeling of fluorescence excitation-emission measurements to explore the interaction of hydroxychloroquine and DNA, and to quantify their binding constant

A new three-dimensional chemometric approach was introduced to explore the interaction of hydroxychloroquine (HCQ)-calf thymus deoxyribonucleic acid (DNA) and quantify binding constant using fluorescence excitation and emission measurements. The fluorescence excitation-emission spectra were recorded after gradual titration of HCQ with DNA. Then, the excitation and emission curves and relative concentrations of the drug and drug-DNA complex were quantitatively estimated using a three-dimensional model called Parallel Factor Analysis (PARAFAC) to a cubic fluorescence data array. The interaction of HCQ and DNA was predicted by applying newly modified Stern-Volmer equations to the relationship between the actual DNA concentration, and the HCQ concentration in the relative concentration profile of the PARAFAC model. In the PARAFAC application, the binding constants of the HCQ-DNA complex at 288, 298, and 310K were found as 6.78×103, 5.07×103, and 3.74×103Lmol-1, respectively. From the temperature studies, the thermodynamic parameters (ΔS0= 3.528Jmol-1 K-1, ΔH0= -20.099kJmol-1 and ΔG0=-21.11, -21.12, and -21.19kJmol-1 at 288, 298, and 310K, respectively) were calculated. The drug-DNA interaction is spontaneous due to negative ΔG0 values. The positive ΔS0 and negative ΔH0 values revealed the major role of the electrostatic force on the binding of HCQ to DNA. Assay results obtained from the proposed three-way modeling were compared to those provided by the traditional spectrofluorimetric method.

Animal Feedlots and Domestic Wastewater Discharges are Likely Sources of N-Nitrosodimethylamine (NDMA) Precursors in Midwestern Watersheds.

N-nitrosodimethylamine (NDMA) precursor concentrations along four major rivers in Minnesota, USA were quantified and correlated with watershed land cover types, anthropogenic activity, and organic matter characteristics. River water samples (36 in total) were chloraminated under uniform formation conditions (UFC) before and after lime-softening treatment, and the resulting NDMA concentrations were quantified (NDMAUFC). Regarding land cover, NDMAUFC in raw river water exhibited weak positive correlations with urban land (ρ = 0.33, p = 0.05) and cropland coverage (ρ = 0.35, p = 0.04). For anthropogenic activity, NDMAUFC in raw river water positively correlated with the number of feedlots (ρ = 0.57), total weight of animals (ρ = 0.68), and total number of domestic wastewater treatment plants (WWTPs; ρ = 0.63) with p < 0.01. NDMAUFC positively correlated with region IV fluorescence intensity from fluorescence excitation-emission spectra (ρ = 0.70, p < 0.01). Lime softening of river water typically increased NDMAUFC and preferentially removed organic matter that fluoresces in region V, suggesting that the organic matter in this region decreases NDMAUFC by competing for available chloramines. Overall, animal feedlots, along with domestic WWTPs, are predominant sources of NDMA precursors in the studied watersheds, while croplands and urban runoff are of lesser importance.

Preparation and Physicochemical Properties of Organic Semiconducting Materials from the Reaction of Imidazo[1,2‐a]pyridines with Tetracyanoethylene

AbstractOrganic donor‐acceptor (DA) complexes have emerged in recent years as materials of choice for organic binary electronics. The reactivity descriptors derived from the conceptual DFT reveal imidazo[1,2‐a]pyridines as potential donors. Thus, four imidazo[1,2‐a]pyridines were reacted with tetracyanoethylene (TCNE) in 1 : 2 molar ratio to afford four new DA complexes. The spectral studies, namely IR, 1H, 13C, DEPT 135, 2D HMQC NMR, and HRMS were used to establish structures of the products. The UV‐vis. spectroscopy reveals intramolecular charge transfer. All the four compounds fluoresce giving excitation emission fluorescence spectra with a red shift ranging from 64 to 151 nm and quantum yields from 0.004 to 16.35. Unexpectedly, nitro group in one of the products does not act as quencher; instead, it enhances the quantum yield to make it highest in this series. The products exhibit electrical conductivity which increases with temperature. The FESEM and HRTEM images reveal distinct and homogenous surface morphology with holes which facilitate flow of electrons as manifested by electrical conductivity. The powder XRD and SAED results establish the polycrystalline nature of the products. The theoretical studies indicate an alternate donor acceptor stacking pattern.

Identification and quantification of ciprofloxacin, enrofloxacin and difloxacin residues in milk using excitation-emission fluorescence and second-order standard addition methods

In the presence of non-modeled components and analyte-matrix interaction in real samples, a combination of second-order multivariate calibration and standard addition is desired to achieve accurate results via second-order advantage. Enrofloxacin (ENR), Difloxacin (DIF), and Ciprofloxacin (CIP) are Fluoroquinolones widely considered antibiotic residues in milk. Excitation-emission fluorescence spectra of these antibiotics at pH = 9.1 provide second-order data for identifying and quantifying them in a mixture using second-order calibration modeling.Rank annihilation factor analysis (RAFA) and multivariate curve resolution-alternating least squares (MCR-ALS) with trilinearity constraints are applied to determine the CIP, ENR, and DIF residues in synthetic mixtures and milk using second-order excitation-emission fluorescence spectroscopy. In both methods, the trilinearity constraint guarantees a unique true solution to the spectral profiles of analytes. The combination of second-order standard addition and higher-order calibration modeling with RAFA and MCR-ALS supports the second-order advantage in milk analysis.

Early rapid detection of ichthyotoxic algae based on fluorescent quaternion features via neural network

We developed a fast fluorescent ichthyotoxic algae identification (FFIAI) model based on a specially designed convolutional neural network to predict if ichthyotoxic algae exist in water bodies by simply inputting the initial 3D fluorescence spectrum data of an algal testing sample. Discrete excitation-emission fluorescence spectra were used to characterize the fingerprint of each ichthyotoxic algae species and applied to the fluorescent quaternion representation model to form the fluorescent quaternion feature. We trained the FFIAI model with the fluorescent quaternion features of the training database. In our experiment, the well-trained FFIAI model can achieve 100 % accuracy in identifying six species of ichthyotoxic algae, including Amphidinium carterae, Karenia mikimotoi, Phaeocystis globose, Chattonella antique, Heterosigma akashiwo, and Prymnesium parvum. The corresponding detection limits are as low as 1800, 120, 3600, 60, 2000, and 2300 cells/mL, which meets the basic detection requirements of harmful algae blooms (HABs). Moreover, this model also performed well in mixed testing samples, with the identification accuracy of ichthyotoxic algae reaching 90 % when the ichthyotoxic algae are dominant in the mixture. The model could also recognize the ichthyotoxic algae correctly even with a relatively low concentration, with an overall identification accuracy of 75 %, demonstrating its potential for precise monitoring of ichthyotoxic algae in field studies.

Nutrient limitation masks the dissolved organic matter composition effects on bacterial metabolism in unproductive freshwaters

AbstractAquatic microbial responses to changes in the amount and composition of dissolved organic carbon (DOC) are of fundamental ecological and biogeochemical importance. Parallel factor (PARAFAC) analysis of excitation–emission fluorescence spectra is a common tool to characterize DOC, yet its ability to predict bacterial production (BP), bacterial respiration (BR), and bacterial growth efficiency (BGE) vary widely, potentially because inorganic nutrient limitation decouples microbial processes from their dependence on DOC composition. We used 28‐d bioassays with water from 19 lakes, streams, and rivers in northern Sweden to test how much the links between bacterial metabolism and fluorescence PARAFAC components depend on experimental additions of inorganic nutrients. We found a significant interaction effect between nutrient addition and fluorescence on carbon‐specific BP, and weak evidence for influence on BGE by the same interaction (p = 0.1), but no corresponding interaction effect on BR. A practical implication of this interaction was that fluorescence components could explain more than twice as much of the variability in carbon‐specific BP (R2 = 0.90) and BGE (R2 = 0.70) after nitrogen and phosphorus addition, compared with control incubations. Our results suggest that an increased supply of labile DOC relative to ambient phosphorus and nitrogen induces gradually larger degrees of nutrient limitation of BP, which in turn decouple BP and BGE from fluorescence signals. Thus, while fluorescence does contain precise information about the degree to which DOC can support microbial processes, this information may be hidden in field studies due to nutrient limitation of bacterial metabolism.

Quantitative and qualitative spectroscopic parameters determination of major cannabinoids

Cannabis based products are widely used for various medicinal conditions. Currently, the most common method to identify and quantify cannabinoids are liquid chromatographic methods coupled to UV-VIS or mass spectrometric detectors. As cannabinoids are fluorescent compounds, fluorescent-based detection methods are gaining increasing interest. Consequently, a comprehensive qualitative and quantitative determination of fluorescence characteristics of major cannabinoids is warranted. In the present study we have determined the fluorescent excitation-emission-spectrum of 13 major cannabinoid standards and calculated their molar extinction coefficient (ε) and quantum yield (Φ) values. Furthermore, we examined the correlation between ε and Φ to available physico-chemical substance descriptors, namely, octanol/water partitioning coefficient, molar weight and boiling point. The cannabinoids displayed a characteristic fluorescence excitation (225–400 nm)-emission (300–525 nm) signal. Neutral and acid cannabinoids could be distinguished based on their characteristic excitation-emission spectrum, namely neutral cannabinoids exhibited maximal intensities at 280 nm excitation and 300 nm emission, while acidic cannabinoids displayed maximal intensity at 300 nm excitation and 400 nm emission. Moreover, cannabinoids with overlapping UV spectrum (such as Δ9-trans-tetrahydrocannabinolic acid, cannabidiolic acid and Cannabigerolic acid) were found to have overlapping fluorescence excitation-emission spectrum, due to the same number of conjugated double bonds and the presence or absence of a carboxylic group. The calculated ε and Φ values were found to negatively correlate with each other. The spectral data provided hereby could assist to develop tools for initial screening of extracted samples for the presence of cannabinoids.

Changes in the Spectral Characteristics of Hydrophilic Fraction in Compost Organic Matter

The hydrophilic fraction (HyI) is one of the important components of humus, and its structure and composition are important factors for evaluating the stability and maturity of compost. This study used spectroscopy to analyze the composition and structure of HyI. The results showed that with the passage of composting time, the UV–Vis curve had a red shift, indicating that the conjugated structure of the substance increased and the aromaticity is enhanced. The three-dimensional fluorescence excitation–emission spectrum (3D-EEM) showed that the fluorescence intensity of humus-like substances in HYI was significantly enhanced, and microbial metabolites such as protein-like substances, carbohydrates and other small molecules were continuously degraded, and the relative content decreased from 21% to 8%, the humus-like substances rose from 54% to 68%, which showed that the organic matter in the compost is continuously condensing and polymerizing, and the maturity and stability of the compost product are deepened.

Insight into the comparison of thermally and Fe(II) activated persulfate on sludge dewaterability and disintegration.

The effects of thermally and Fe(II) activated potassium persulfate (PPS) on sludge dewatering performance were compared systematically. Sludge dewaterability was monitored by measuring capillary suction time (CST) and sludge specific resistance to filtration (SRF), and the degradation effect was characterized by chemical oxygen demand (COD), total organic carbon (TOC), ammonia nitrogen (NH4+-N) and extracellular polymeric substances (EPS). The change of extracellular polymer substance (EPS) including soluble, loosely bound and tightly bound EPS (S-EPS, LB-EPS and TB-EPS) with time and PPS dosage was monitored to discuss the oxidation efficiency of thermally and Fe(II) activated PPS. Sludge supernatant was analyzed by three-dimensional fluorescence excitation-emission spectra (3D-EEM) to confirm the protein transformation. The result showed that sludge dewaterability in terms of CST and SRF were enhanced with increasing PPS dosage and condition time of two activated methods. While Fe(II) activated PPS could reduce sludge CST and SRF to preferred values at low PPS dosage and short condition time. Meanwhile, sludge degradation effect was also more obvious. Mechanically, sludge TB-EPS in proteins and polysaccharides converted to SB-EPS was faster with Fe(II) activated PPS. In addition, thermally activated PPS tended to oxidize the protein in the supernatant first.

Interactions between natural organic matter fractions and nanoscale zero-valent iron

The presence of natural organic matter (NOM) in groundwater could play an important role in the removal of contaminants by nanoscale zero-valent iron (NZVI). NOM has a heterogeneous structure and can be divided into 6 fractions based on polarity and charges: hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic neutral (HPON), hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral (HPIN). The objective of this study was to evaluate the interactions between NOM fractions and NZVI using two approaches: 1) the interaction between NOM fraction isolates and NZVI and 2) bulk NOM fractionation before and after reaction with NZVI. Two sources of NOM—groundwater (GWNOM), Khon Kaen, Thailand and Suwannee River NOM (SRNOM), USA—were examined. The isolated NOM had more interactions with NZVI at pH 5 compared to pH 7 and 9 for both GWNOM and SRNOM. HPOA of GWNOM had the highest adsorption capacity (qe) of 6.95 mg/g (pH 5), and that was also the case for HPIA of SRNOM (18.66 mg/g, pH 5). HPIN of both GWNOM and SRNOM yielded the lowest qe among the six fractions. The adsorption capacities of NOM fractions were well correlated with specific ultraviolet absorbance. Fluorescence excitation–emission spectra revealed that protein-like components preferentially reacted with NZVI. The results of bulk NOM fractionation after reacting with NZVI indicated that NOM not only adsorbed on NZVI but also reacted with NZVI and transformed to become more hydrophilic and neutral. This study's findings suggest that different NOM fractions had varying interactions with NZVI. The acid fractions tended to interact more than the other fractions. This work provides a deeper understanding of the reactivity between NOM and NZVI.

Improvement of sludge dewaterability and disintegration efficiency using electrolytic zero-valent iron activated peroxymonosulfate.

Electrolysis zero-valent iron activated peroxymonosulfate (EZVI-PMS) was applied to enhance sludge dewaterability and disintegration performance. Sludge dewaterability was characterized by capillary suction time (CST), specific resistance to filtration (SRF), and disintegration performance was explored by measuring sludge DNA content, ammonia nitrogen, chemical oxygen demand (COD), extracellular polymeric substances (EPS) and dissolved organic carbon (DOC). EPS, including soluble EPS (SB-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) were analyzed by three dimensional fluorescence excitation-emission spectrum (3D-EEM) to confirm the proteins' transformation tendency. DOC, protein and polysaccharide in EPSs were quantified to investigate the conditioning mechanism. The results showed that sludge CST and SRF were reduced significantly when the current was 0.2 A and PMS dosage was 130 mg/gDS with the reductions of 43.8% and 74.1%, respectively, and DNA was released from sludge cells to the liquid phase. Mechanically, sludge TB-EPS converted to SB-EPS with DOC in TB-EPS decreasing from 367.0 mg/L to 210 mg/L, while DOC in SB-EPS increased from 44 mg/L to 167.4 mg/L. Besides, the changes of protein and polysaccharide contents in SB-EPS and TB-EPS were similar to DOC, and protein in TB-EPS transformed to other protein-like or organic substances obviously.

Monitoring Virgin Olive Oil Shelf-Life by Fluorescence Spectroscopy and Sensory Characteristics: A Multidimensional Study Carried Out under Simulated Market Conditions

The control of virgin olive oil (VOO) freshness requires new tools that reflect the diverse chemical changes that take place during the market period. Fluorescence spectroscopy is one of the techniques that has been suggested for controlling virgin olive oil (VOO) freshness during its shelf-life. However, a complete interpretation of fluorescence spectra requires analyzing multiple parameters (chemical, physical–chemical, and sensory) to evaluate the pace of fluorescence spectral changes under moderate conditions with respect to other changes impacting on VOO quality. In this work, four VOOs were analyzed every month with excitation–emission fluorescence spectra. The same samples were characterized with the concentration of fluorophores (phenols, tocopherols, chlorophyll pigments), physical–chemical parameters (peroxide value, K232, K270, free acidity), and sensory attributes (medians of defects and of the fruity attribute). From the six components extracted with parallel factor analysis (PARAFAC), two components were assigned to chlorophyll pigments and those assigned to tocopherols, phenols, and oxidation products were selected for their ability to discriminate between fresh and aged oils. Thus, the component assigned to oxidation products correlated with K270 in the range 0.80–0.93, while the component assigned to tocopherols–phenols correlated with the fruity attribute in the range 0.52–0.90. The sensory analysis of the samples revealed that the changes of these PARAFAC components occurred at the same time as, or even before, the changes of the sensory characteristics.

Effects of ZnO nanoparticles on flocculation and sedimentation of activated sludge in wastewater treatment process

Despite the behaviors of ZnO nanoparticles (ZnO NPs) in wastewater treatment processes have been widely explored, the impacts of ZnO NPs on the activated sludge's flocculation and sedimentation performances for solid-liquid separation have rarely been involved yet. In this study, ZnO NPs were observed to exert a dose-dependent negative effect on the sludge's flocculation performance but did not significantly impact the sludge’ sedimentation behaviors. Furthermore, it was NPs themselves rather than the dissolved Zn2+ who impaired on the sludge flocculation performance because the Zn2+ alone would not compromise the sludge's flocculation efficiency. In addition, the sludge flocculation performance was revealed to be inversely related to the extracellular polymeric substances (EPS) content in the sludge and the direct contacts between ZnO NPs and the cells in the sludge should be the prerequisite to stimulate the secretion of the sludge EPS. The poor sludge flocculation performance could also be caused by the reduced protein/polysaccharide (PN/PS) ratio and the zeta (ζ) potential in the loosely bound (LB-EPS) after the sludge exposure to ZnO NPs. Fourier transform-infrared spectra (FT-IR) and three dimensional - excitation emission fluorescence spectra (3D-EEM) analysis further revealed that the decrease of the tyrosine PN-like substance level in the LB-EPS was probably the key reason for the decreased PN/PS ratio and ζ potential in the LB-EPS, which eventually induced the decline of the sludge flocculation performance under the ZnO NP stress. These results could potentially expand the knowledge on sludge flocculation and sedimentation in the presence of ZnO NPs.

Variation of dissolved organic matter during excess sludge reduction in microbubble ozonation system.

Sewage sludge is the major by-product of wastewater treatment plants, and about 30% readily biodegradable organic matters might be reused through the mass reduction process, which could be also reduced the disposal fee. In this study, the microbubble ozonation (MB-O3) was employed to improve the oxidation efficiency for sludge solubilization. At 160 mgO3/gSS, the maximum mixed liquor suspended solids (MLSS) reduction ratio was 37.5% and the protein and polysaccharide contents increased to 31.6 and 138.6 mg/L, respectively. It was proposed that aromatic protein and soluble microbial in sludge were oxidized preferentially by MB-O3, and the dissolved organic matter (DOM) fractions (mainly humic-acid-like substances) exhibited low degradability according to the variations of fluorescence excitation-emission spectrum coupled with fluorescence regional integration. MB-O3 could enhance the settleability, but deteriorate sludge dewaterability at low dosage (< 160 mgO3/gSS) due to a reduction in particle size from 61.7 to 47.5 μm. MB-O3 has a good performance on the mass reduction of sludge through the improvement of the radical generated.

Sorption and transformation of arsenic by extracellular polymeric substances extracted from Synechocystis sp. PCC6803

Cyanobacteria widely distribute in the aqueous ecosystem and produce abundant extracellular polymeric substances (EPS), yet little is known about how the quantity and composition of cyanobacterial EPS change upon As exposure, and what are functions of these complex biopolymers in the As sorption and transformation processes. Here we extracted the EPS from Synechocystis sp. PCC6803, characterized their properties, quantified their components upon exposure to arsenite (As(III))/arsenate (As(V)) treatments, and investigated As binding and speciation as affected by the levels of EPS and solution pH. The total binding sites, zeta potential and reducing power of EPS were 17.47 mmol g−1, -19.72 mV and 1.71. The amounts of EPS increased by 22–65.3% and 13.8–39% when the cells were treated with 10–500 μM As(III) and As(V) respectively. The As removal was influenced by the EPS doses and solution pH, with 52.8% at pH 8.5 for As(III) and 49.5% at pH 4.5 for As(V) at 300 mg L−1 EPS. In addition, As speciation was transformed with the addition of EPS. As(V) and As(III) respectively accounted for 4.9–20.3% and 6.5–26.7% of the total dissolved As after the EPS were added (100–300 mg L−1) to the As(III) and As(V) solutions. Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission fluorescence spectra (3D-EEM) revealed that As was bound to functional groups such as C═O, ─NH, and ─OH in the EPS via surface complexation/hydrophobic interactions. Taken together, this study demonstrated that the EPS extracted from Synechocystis were capable to bind and transform As and could be potentially applied to remove or detoxify As in solutions.

Effects of Varied Tyrosine Concentrations on FEEM and SFS of Constant Tryptophan concentration

In recent years, the 3D fluorescence excitation emission spectrum has been widely applied into the analysis of the properties of soluble organic matter in water bodies, but there is very little research on the fluorescence properties of protein residues in water quality detection by Fluorescence Excitation Emission Matrix (FEEM), and synchronous fluorescence excitation emission spectra (SFS). The characteristics of luminescent of amino acids, including tryptophan, tyrosine and phenylalanine, where tryptophan and tyrosine fluorescence are relatively strongest, and the effects of tyrosine on the fluorescence properties of tryptophan are seldom discussed in different mixing ratios for both amino acids. The fluorescent peak positions and intensities of the three amino acids are related to the angle size of conjugate plane, N hybrids and hydroxyls on benzene rings. When the ratio of tyrosine to tryptophan content is less than 150:100, tryptophan will quench the fluorescent peak of the tyrosine. Constant tryptophan content, tyrosine at excitation wavelength of 228 nm, its concentration changes with the corresponding fluorescence intensity has a good linear relationship; however, at 276-278 nm of tyrosine, the varied concentrations and fluorescence intensities are opposite.

Designating the geographical origin of Iranian almond and red jujube oils using fluorescence spectroscopy and l1-penalized chemometric methods

Assessment of the geographical origin of medical plants (MP) has received a lot of attention in traditional medicine for determination of the quality of the products and detection of food/drug adulteration. In the present contribution, the sparse version of N-way partial least square discriminant analysis (sNPLS-DA) has been used for classification of almond and red jujube oil samples using their excitation-emission (EEM) fluorescence spectra, for the first time. Seven types of almond seeds and six species of red jujube samples were collected from mountains and hills in Fars and Khorasan provinces in Iran, respectively. The sNPLS-DA algorithm with l1-norm constraint was utilized for calculation of sparse loading vectors. This method merges variable selection and modeling steps into one phase, and due to sparse loading vectors, models are easily interpretable. The number of latent variables and non-zero elements in the first and second loading spaces for the sNPLS-DA models in this work was optimized using a central composite design (CCD) approach. The optimized models were used for classification of almond and red jujube oil samples according to their geographical origins in Iran. The average accuracies of the sNPLS-DA models were 0.95 and 0.89 for bootstrapping cross validation and 0.97 and 1.00 for external validation for almond and red jujube samples, respectively. The performance of the sNPLS-DA models was compared with PLS-DA, parallel factor analysis (PARAFAC), counter propagation artificial neural networks (CPANN), and supervised Kohonen networks (SKN). The results of the optimized sNPLS-DA models were superior to PARAFAC-DA and comparable to those of CPANN and SKN models. The results in this work reveal that the sNPLS-DA method can be used as a reliable and interpretable tool for quality control and classification of food samples using their EEM fluorescence data.

Effects of land use on the characteristics and composition of fluvial chromophoric dissolved organic matter (CDOM) in the Yiluo River watershed, China

• Effects of land use on CDOM and DOC in the Yiluo River watershed were quantified. • Atypical CDOM absorption curve exhibited a shoulder near 390 nm. • Water samples showed high tryptophan-like and humic-like fluorophores. • Crop-dominated and built-up areas had high CDOM and DOC concentrations. Chromophoric dissolved organic matter (CDOM) is a key indicator of water quality, biogeochemical state and nutrient content in freshwaters. Land use affects the concentration, quality, source, and age of CDOM in rivers. To investigate the characteristics and composition of fluvial CDOM and the effects of land use on carbon components, 37 sites were sampled during May 2017 in the Yiluo River watershed, China. In addition, water parameters, absorption and fluorescence spectral parameters of CDOM were measured in situ and in the lab. Some samples showed atypical CDOM absorption curves with an absorption shoulder at 390 nm. CDOM absorption at 440 nm [a CDOM (440)] was positively correlated with dissolved organic carbon (DOC) and fluorescence intensity (Fn). Fluorescence excitation-emission spectra indicated the presence of strong humic-like and tryptophan-like fluorophores revealing terrestrial, anthropogenic influence. Low recent autochthonous contribution index (BIX) and humification index (HIX) values indicated that autochthonous production was an important contributor to CDOM levels. Cropland-dominated subwatersheds (SWs) exhibited high a CDOM (440), Fn and DOC and forest-dominated SWs showed low CDOM concentration. At the riparian buffer scale, CDOM in the built-up-dominated areas showed the highest CDOM concentration. Moreover, built-up areas greatly influenced the concentrations of DOC and CDOM quantificationally at both the SW and riparian buffer scales; more than 64% of the overall variation in carbon components at the SW scale and 46% of DOC variation at the riparian buffer scale was explained by built-up areas. Overall, the results of our study showed that the properties of fluvial CDOM are dependent on the surrounding land use, further highlighting the importance of land use for CDOM photoreactivity in SWs and riparian buffer zones.

An Assemble Based on Clustering and Monte Carlo for the Wavelengths Selection of Excitation Emission Fluorescence Spectra

Excitation-emission fluorescence spectra is very effective to predict the concentration of organics in samples. However, redundant information and noises in the excitation-emission matrix (EEM) decrease the accuracy of the prediction concentration. Here we proposed a method to select more useful excitation and emission spectra from the EEM to increase the accuracy of prediction concentration and reduce the processing time. First, the excitation wavelengths were selected based on the clustering method to limit the redundant information in the EEM. Then the emission wavelengths were selected based on the Monte-Carlo method. To validate this method, we established the concentration prediction model with the spectra corresponding to the selected wavelengths by partial least square regression and predicted the multi component concentrations in the test samples. Our studies indicate that incorporation of this method increases the accuracy of the prediction concentration of organics and reduces the processing time.

Optimization of cyanobacterial harvesting and extracellular organic matter removal utilizing magnetic nanoparticles and response surface methodology: A comparative study

Improvements in the microalgal harvesting efficiency and separation processes will accelerate cost-effective biomass utilization. Magnetic harvesting is known as a low-cost and environmentally friendly downstream processing technology, but information on optimization of the harvesting procedures is rare. Here, we present optimized harvesting factors for Microcystis aeruginosa 1343 (M1) and 905 (M9) based on polyethylenimine (PEI)-coated iron oxide nanoparticles (IONPs) and response surface methodology. Four important factors including mass ratio (PEI-coated IONPs to dried cell biomass, g/g), stirring speed (rpm), stirring time (s), and adsorption time (min) were evaluated to obtain the optimal operational parameters for different types of cyanobacteria under natural environmental conditions. The maximum harvesting efficiencies for M1 and M9 were 93.3% and 97.5%, respectively; the optimal mass ratio, stirring speed, stirring time, and adsorption time were 0.14–0.18, 85–120 rpm, 70–95 s, and 5.5–7 min, respectively. Our results indicated that the mass ratio was the leading factor in algal harvesting. Changes in the number of cells bound with PEI-coated IONPs were closely related to the mass ratio, and this was confirmed via scanning electron microscopy results. Moreover, the PEI-coated IONPs were able to remove extracellular organic matter (EOM) synchronously via charge neutralization. Variations in fluorescence excitation emission spectra demonstrated an effective EOM removal. Quantitatively, over 34.97% and 45.35% of EOM in M1 and M9 were reduced, respectively, based on total organic carbon analysis. This study provides new insights into algal harvesting operations using magnetic separation technologies and provides practical guidance for performing magnetic separation under environmental conditions.