Synchronous Scanning Fluorescence Research Articles

Simultaneous detection of breast cancer biomarkers circROBO1 and BRCA1 based on a CRISPR-Cas13a/Cas12a system

Breast cancer is reported to be one of the most lethal cancers in women, and its multi-target detection can help improve the accuracy of diagnosis. In this work, a cluster regularly interspaced short palindromic repeats (CRISPR)-Cas13a/Cas12a-based system was established for the simultaneous fluorescence detection of breast cancer biomarkers circROBO1 and BRCA1. CRISPR-Cas13a and CRISPR-Cas12a were directly activated by their respective targets, resulting in the cleavage of short RNA and DNA reporters, respectively, thus the signals of 6-carboxyfluorescein (FAM) and 6-carboxy-xrhodamine (ROX) were restored. As the fluorescence intensities of FAM and ROX were dependent on the concentrations of circROBO1 and BRCA1, respectively, synchronous fluorescence scanning could achieve one-step detection of circROBO1 and BRCA1 with detection limits of 0.013 pM and 0.26 pM, respectively. The system was highly sensitive and specific, holding high diagnostic potential for the detection of clinical samples. Furthermore, the competing endogenous RNA mechanism between circROBO1 and BRCA1 was also explored, providing a reliable basis for the intrinsic regulatory mechanism of breast cancer.

Authentication of Covid-19 Vaccines Using Synchronous Fluorescence Spectroscopy

The present study demonstrates the potential of synchronous fluorescence spectroscopy and multivariate data analysis for authentication of COVID-19 vaccines from various manufacturers. Synchronous scanning fluorescence spectra were recorded for DNA-based and mRNA-based vaccines obtained through the NHS Central Liverpool Primary Care Network. Fluorescence spectra of DNA and DNA-based vaccines as well as RNA and RNA-based vaccines were identical to one another. The application of principal component analysis (PCA), PCA-Gaussian Mixture Models (PCA-GMM)) and Self-Organising Maps (SOM) methods to the fluorescence spectra of vaccines is discussed. The PCA is applied to extract the characteristic variables of fluorescence spectra by analysing the major attributes. The results indicated that the first three principal components (PCs) can account for 99.5% of the total variance in the data. The PC scores plot showed two distinct clusters corresponding to the DNA-based vaccines and mRNA-based vaccines respectively. PCA-GMM clustering complemented the PCA clusters by further classifying the mRNA-based vaccines and the GMM clusters revealed three mRNA-based vaccines that were not clustered with the other vaccines. SOM complemented both PCA and PCA-GMM and proved effective with multivariate data without the need for dimensions reduction. The findings showed that fluorescence spectroscopy combined with machine learning algorithms (PCA, PCA-GMM and SOM) is a useful technique for vaccination verification and has the benefits of simplicity, speed and reliability.

Green fitted second derivative synchronous spectrofluorometric method for simultaneous determination of remdesivir and apixaban at Nano gram scale in the spiked human plasma

Remdesivir and apixaban have been included in the treatment guidelines of several countries for severe COVID-19 infections. To date, no analytical method has been developed for the determination of remdesivir and apixaban in plasma matrix. The main objective of this work was to develop a highly sensitive, green-adapted spectrofluorometric method for the determination of remdesivir and apixaban at the Nanoscale. Remdesivir and apixaban showed overlapping fluorescence emission spectra at 403 nm and 456 nm when excited at 246 nm and 285 nm, respectively. This overlap was resolved in two steps. The first step was synchronous fluorescence scanning of remdesivir and apixaban, and the second step was manipulation of the second-order derivative for the obtained spectra. These steps allowed complete resolution of the overlapping fluorescence spectra and selective determination of remdesivir and apixaban at 410 and 469 nm, respectively. The variables affecting the synchronous scanning of the aforementioned drugs were optimized in terms of sensitivity parameters and principles of green analytical chemistry. The described method allowed sensitive determination of remdesivir and apixaban over the concentration range of 5–200 ng/mL and 50–3000 ng/mL, respectively. The described method was validated and successfully applied for the simultaneous determination of the mentioned drugs in pure form and in spiked human plasma.

Exploring the interaction of calycosin with cyclin D1 protein as a regulator of cell cycle progression in lung cancer cells

Cyclin D1 has been shown to play a pivotal role in the proliferation of lung cancer cells through regulation of cell cycle progression. Therefore, targeting this protein can be used as a potential strategy in lung cancer treatment. Calycosin has been reported to show potential anticancer effects, however, its possible anticancer mechanisms remain unclear. Therefore, in this study we aimed to explore the interaction of cyclin D1 and calycosin to determine the binding properties and probable structural changes of cyclin D1. We carried out in-depth experimental and computational binding assays of calycosin with cyclin D1 under simulated physiological environment, using intrinsic, extrinsic, synchronous fluorescence, circular dichroism, and differential scanning calorimetry (DSC) analysis. The results showed a spontaneous static mechanism driven from hydrogen bonding and van der Waals forces between hydrophilic residues of cyclin D1 with hydroxyl groups of calycosin. We determined that calycosin led to secondary and tertiary structural changes of cyclin D1 through exposure of hydrophobic residues. Also, it was determined that calycosin resulted in an apparent decrease in the heat capacity changes (ΔCp) and midpoint of unfolding transition (Tm) values of cyclin D1. Cellular studies also indicated that calycosin caused the inhibition of lung cancer cell proliferation through cell cycle arrest at G1 phase, which may be due to denaturation of cyclin D1, although it needs further investigation in the future studies. In general, this study may provide useful preliminary data about the development of calycosin-based anticancer platforms.

Impact of temperature and sunlight exposition on locally brewed beers composition revealed by fluorescence spectroscopy coupled with chemometric methods.

Fluorescence excitation-emission matrix (EEM) and synchronous scanning fluorescence (SF), coupled with parallel factor (PARAFAC) analysis, principal component analysis (PCA) and Linear discriminant analysis (LDA) methods were used to differentiate 49 lager beer samples and monitor the effects of temperature and sunlight exposition on their composition. EEMs were decomposed into independent fluorescent components. The beer samples were characterized by the presence of excitation/emission (exc/em) peaks at 290/350, 315/345, 340/410, 375/455, 360/420, 400/460, and 437/525nm, which were ascribed, according to the known beer fluorescent components, respectively to aromatic amino acids, vitamin B6 (pyridoxal), vitamin B6 (pyridoxic acids), vitamin B3, iso-α-acids, vitamin B1, and vitamin B2. The variation of the relative concentration of iso-α-acids in the different beer brands presented the same trend with that of their relative IBU, thus revealing the potency of our method in the assessment of beer bitterness. The impact of temperature and sunlight was assessed by separately monitoring the modifications of the EEMs after 5h exposition to 40°C temperature and sunlight respectively. Noticeably a variation of the peaks intensity of the iso-α-acids, carbonyl and polyphenols compounds were observed, accompanied by a decrease of the alcohol content, thus indicating beer aging. This method can be useful for the identification and monitoring of beer state during the technological production cycle and storage. PRACTICAL APPLICATION: The present work demonstrates the potency of the fluorescence technique used together with chemometric methods to give valuable information on beer bitterness. Development of rapid quantitative methods for beer bitterness assessment is of great importance for brewing industries.

Formation control of bromate and trihalomethanes during ozonation of bromide-containing water with chemical addition: Hydrogen peroxide or ammonia?

To ensure the safety of drinking water, ozone (O3) has been extensively applied in drinking water treatment plants to further remove natural organic matter (NOM). However, the surface water and groundwater near the coastal areas often contain high concentrations of bromide ion (Br−). Considering the risk of bromate (BrO3−) formation in ozonation of the sand-filtered water, the inhibitory efficiencies of hydrogen peroxide (H2O2) and ammonia (NH3) on BrO3− formation during ozonation process were compared. The addition of H2O2 effectively inhibited BrO3− formation at an initial Br− concentration amended to 350 µg/L. The inhibition efficiencies reached 59.6 and 100% when the mass ratio of H2O2/O3 was 0.25 and > 0.5, respectively. The UV254 and total organic carbon (TOC) also decreased after adding H2O2, while the formation potential of trihalomethanes (THMsFP) increased especially in subsequent chlorination process at a low dose of H2O2. To control the formation of both BrO3− and THMs, a relatively large dose of O3 and a high ratio of H2O2/O3were generally needed. NH3 addition inhibited BrO3− formation when the background ammonia nitrogen (NH3N) concentration was low. There was no significant correlation between BrO3− inhibition efficiency and NH3 dose, and a small amount of NH3N (0.2 mg/L) could obviously inhibit BrO3− formation. The oxidation of NOM seemed unaffected by NH3 addition, and the structure of NOM reflected by synchronous fluorescence (SF) scanning remained almost unchanged before and after adding NH3. Considering the formation of BrO3− and THMs, the optimal dose of NH3 was suggested to be 0.5 mg/L.

Bimetallic organic framework-based aptamer sensors: a new platform for fluorescence detection of chloramphenicol.

A fluorescence method for the quantitative detection of chloramphenicol (CAP) has been developed using phosphate and fluorescent dye 6-carboxy-x-rhodamine (ROX) double-labeled aptamers of CAP and the bimetallic organic framework nanomaterial Cu/UiO-66. Cu/UiO-66 was prepared by coordinate bonding of metal organic framework (MOF) nanomaterial UiO-66 with copper ions. Cu/UiO-66 contains a large number of metal defect sites, which can be combined with phosphate-modified nucleic acid aptamers through strong coordination between phosphate and zirconium to form "fluorescence turn-on" sensors. In the absence of CAP, all single-stranded aptamers were adsorbed on the surface of Cu/UiO-66 through π-π stacking between single-stranded DNA and Cu/UiO-66, which brings the ROX fluorophores and Cu/UiO-66 into close proximity. The ROX fluorescence of aptamers was then quenched by Cu/UiO-66 through photoinduced electron transfer (PET). In the presence of CAP, however, CAP reacted with nucleic acid aptamers to form a special spatial structure, in which the ROX fluorophores were far away from the MOF surface via a change in the spatial structure of the aptamers, and the fluorescence of ROX was able to be recovered. The quantitative detection of CAP can be achieved by measuring the fluorescence signal of ROX using synchronous scanning fluorescence spectrometry. Under optimum conditions, the fluorescence intensities of ROX exhibit a good linear dependence on the concentration of CAP in the range of 0.2-10nmol/L, with a detection limit of 0.09nmol/L. The method has advantages of high sensitivity, good selectivity, and a low limit of detection. Graphical abstract.

Identification of milk types using two different fluorescence spectroscopy techniques

Fluorescence spectroscopy is a technique used to determine fluorescence spectrum that emits by fluorescent compounds. Milk had more than one fluorescent compounds such as tryptophan, vitamin A and etc. Quick identification of milk types is needed in dairy plants for milk quality control and safety. The ability of two different fluorescence spectroscopy techniques (front face fluorescence spectroscopy and synchronous scanning fluorescence spectroscopy) was determined to discriminate 40 milk samples according to milk species (10 samples for each of buffalo's, cow's, goat's and sheep's milk). The statistical methods, principal component analysis PCA and factorial discriminant analysis FDA, were used for more illustrating the obtained results. FDA was applied separately on the first five principal components obtained from PCA which performed on the two different fluorescence techniques. Results obtained from FDA showed that 100% of correct classification was obtained for data sets from the two different fluorescence techniques. The obtained results confirmed that the front face fluorescence spectroscopy and synchronous scanning fluorescence spectroscopy were capable of differentiate milk species.

Ozonation of natural organic matter and aquatic humic substances: the effects of ozone on the structural characteristics and subsequent trihalomethane formation potential

Abstract The effect of ozonation on the structural and chemical characteristics of natural organic matter (NOM) and its isolated humic fractions, humic acid (HA) and fulvic acid, were studied using Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR), ultraviolet/visible (UV/Vis) spectroscopy, and synchronous scanning fluorescence (SSF) spectroscopy. The results were linked to the effect of ozonation on trihalomethane formation potential (THMfp) reduction for water standards with high THM precursors. Results showed that ozonation at a dose of 1 mg ozone/mg dissolved organic carbon (DOC) was capable of reducing DOC, UV absorbance at 254 nm (UV254), and THMfp by up to 42%, 95%, and 89% for the HA water standard, respectively. The study of UV/Vis, FTIR-ATR, and SSF revealed trends showing that ozone can alter the composition of DOC in the water standards, causing a significant reduction in aromaticity. The reduction of UV254 for each ozonated sample also affirms that ozone mainly targets aromatic moieties contained in NOM. FTIR-ATR results showed that the reduction of unsaturated functional groups, including aromatic rings and C = C bonds in the water standards tested, were the main components impacted by ozone application. SSF results also revealed that ozonation decreases the fluorescence intensity of the maximum peak – as well as the whole spectra.

Structural Analysis of Humic Acid in Soil at Different Corn Straw Returning Modes through Fluorescence Spectroscopy and Infrared Spectroscopy.

The purpose of this study is to analyze the effects of different straw returning modes on the structure of humic acid (HA) in soil by fluorescence spectroscopy and infrared (IR) spectroscopy. Four different straw returning modes, including straw returning to topsoil (St), straw returning to subsoil (Ss), straw mixing with topsoil (Smt), and straw mixing with subsoil (Sms), were used in this study; the soil HA was analyzed after 12 months of corn straw returning by a combination of fluorescence spectroscopy and IR spectroscopy. Based on the results, it was established that IR spectroscopy can estimate the complication and oxidation degree of soil HA and also evaluate its aliphaticity and aromaticity. Monodimensional fluorescence spectroscopy could preliminarily determine the changes in the humification of HA through the fluorescence intensities. The intensity ratio of I456/I380 calculated from synchronous-scan fluorescence spectra could be used to evaluate the humification degree of soil HA. The total luminescence spectra of HAs provided more information on the fluorophores in the structure, including the amount and peak position of lignin-like structures and phenol-like or naphthol-like structures. Among the four straw returning modes, Ss is the most beneficial for reducing the oxidation degree and increasing the aromatization and humification degree of subsoil HA. It is believed that fluorescence spectroscopy and IR spectroscopy are relatively simple and sensitive methods for analyzing soil HA.

Analysis of Australian Beers Using Fluorescence Spectroscopy

Classification of a series of Australian beers was performed using synchronous scanning fluorescence spectroscopy and emission-excitation matrices based on the IR fingerprint regions. The results indicate that synchronous scanning fluorescence spectroscopy is a robust and valuable method to discriminate between Australian lager beers based on their brand name. In addition, a subsequent spoiling study revealed that when beers are opened and stored at 4 °C for 4 weeks, the results demonstrated that the beers were not statistically different. The methods and techniques outlined may be of interest to brewing companies and microbrewers to determine the unique beer spectrum.

Potential of Periophthalmus sobrinus and Siganus sutor as bioindicator fish species for PAH pollution in tropical waters

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous class of toxic organic compounds in coastal waters. The aim of this study was to assess the potential of goby fish (Periophthalmus sobrinus) and rabbit fish (Siganus sutor) as bioindicators for PAH pollution in Zanzibar coastal waters. The fish samples were collected from four sites along the coasts of Zanzibar between February to July, 2016. The analysis of PAH metabolites from bile was conducted using Synchronous Fluorescence Scanning (SFS) spectroscopy. The parent PAH compounds (naphthalene; fluorene; phenanthrene; pyrene; fluoranthene; anthracene; benzo (a) pyrene) in the fish muscle tissues were analyzed using Gas Chromatography with Mass Spectrometric detection (GC/MS). The levels of PAH metabolites in bile of goby fish (P. sobrinus) ranged from 100 ng mL−1 to 690 ng mL−1. The PAH contents in goby tissues fish ranged from 0.028 ± 0.008 ng g−1 ww to 0.037 ± 0.005 ng g−1 ww with the average of 0.032 ± 0.005 ng g−1 ww. PAH metabolites were not detected in the bile samples from rabbit fish (S. sutor) in any sampled areas. The results suggest that the goby fish (P. sobrinus) could be promising PAH biondicator in coastal waters of tropical regions including Zanzibar islands. This is the first study applying biliary PAH metabolites in bioindicator fish species to trace PAH pollution conducted in West Indian Ocean region that can serve as a baseline information of biliary PAH metabolites as biomarkers of fish PAH pollution in the regional waters.

Screening of Antioxidant Properties of the Apple Juice Using the Front-Face Synchronous Fluorescence and Chemometrics

Fluorescence spectroscopy is gaining increasing attention in food analysis due to its higher sensitivity and selectivity as compared to other spectroscopic techniques. Synchronous scanning fluorescence technique is particularly useful in studies of multi-fluorophoric food samples, providing a further improvement of selectivity by reduction in the spectral overlapping and suppressing light-scattering interferences. Presently, we study the feasibility of the prediction of the total phenolics, flavonoids, and antioxidant capacity using front-face synchronous fluorescence spectra of apple juices. Commercial apple juices from different product ranges were studied. Principal component analysis (PCA) applied to the unfolded synchronous fluorescence spectra was used to compare the fluorescence of the entire sample set. The regression analysis was performed using partial least squares (PLS1 and PLS2) methods on the unfolded total synchronous and on the single-offset synchronous fluorescence spectra. The best calibration models for all of the studied parameters were obtained using the PLS1 method for the single-offset synchronous spectra. The models for the prediction of the total flavonoid content had the best performance; the optimal model was obtained for the analysis of the synchronous fluorescence spectra at Δλ = 110 nm (R2 = 0.870, residual predictive deviation (RPD) = 2.7). The optimal calibration models for the prediction of the total phenolic content (Δλ = 80 nm, R2 = 0.766, RPD = 2.0) and the total antioxidant capacity (Δλ = 70 nm, R2 = 0.787, RPD = 2.1) had only an approximate predictive ability. These results demonstrate that synchronous fluorescence could be a useful tool in fast semi-quantitative screening for the antioxidant properties of the apple juices.

Simultaneous determination of zeatin and systemin by coupling graphene oxide-protected aptamers with catalytic recycling of DNase I

Plant hormones are a collection of small molecules which play important roles in regulating the growth and development processes of plants. In this work, a sensitive and novel sensing platform for simultaneous multiplex detection of plant hormones is presented with choosing systemin and zeatin as the model targets. In the absence of the targets, the dye-labeled aptamers were adsorbed on the surface of graphene oxide (GO), result in the fluorescences of the dyes intensively quenched by GO which could also protect the aptamers from nuclease cleavage. While in the presence of the targets, the aptamers could be detached from the GO surface by specifically binding with targets. The fluorescences of the dyes were synchronously recovered and could be further amplified by DNase I catalytic recycling of self-produced reactants. So the two plant hormones can be simultaneously quantitatively determined by using synchronous scanning fluorescence spectrometry with no cross reaction between the two probes. The experimental results reveal that fluorescence intensities of two dyes exhibit good linear dependence on their target concentrations in the range of 0.67–6.0μM and 0.33–5.0μM with the detection limit of 60nM and 35nM for zeatin and systemin, respectively.

Investigation of fixed wavelength fluorescence results for biliary metabolites of polycyclic aromatic hydrocarbons formed in Atlantic cod (Gadus morhua).

Fixed wavelength fluorescence (FF) and synchronous fluorescence scanning (SFS) of fish bile are commonly used methods to analyze for exposure to polycyclic aromatic hydrocarbons (PAHs) from petrogenic and pyrogenic sources. A range of conjugated oxidation products from petrogenic PAHs are normally accumulated in the bile. Therefore their detection is important. In the present study, phenanthrene and naphthalene metabolites, formed invivo in Atlantic cod (Gadus morhua), were used to study the response of these compounds in both FF and SFS analyses. The selected synthetic metabolites were (-)-(1R,2R)-1,2-dihydrophenanthrene-1,2-diol and (-)-(1R,2R)-1,2-dihydronaphthalene-1,2-diol. The study findings showed that the recommended excitation and emission wavelengths for FF analysis do not comprise the maximum emission wavelengths for these metabolites, providing an incorrect estimation of the PAH exposure. A method developed in our laboratory for the synthesis of (-)-(1R,2R)-1,2-dihydrophenanthrene-1,2-diol is also described.

Using fluorescence spectroscopy coupled with chemometric analysis to investigate the origin, composition, and dynamics of dissolved organic matter in leachate-polluted groundwater.

Groundwater was collected in 2011 and 2012, and fluorescence spectroscopy coupled with chemometric analysis was employed to investigate the composition, origin, and dynamics of dissolved organic matter (DOM) in the groundwater. The results showed that the groundwater DOM comprised protein-, fulvic-, and humic-like substances, and the protein-like component originated predominantly from microbial production. The groundwater pollution by landfill leachate enhanced microbial activity and thereby increased microbial by-product-like material such as protein-like component in the groundwater. Excitation-emission matrix fluorescence spectra combined with parallel factor analysis showed that the protein-like matter content increased from 2011 to 2012 in the groundwater, whereas the fulvic- and humic-like matter concentration exhibited no significant changes. In addition, synchronous-scan fluorescence spectra coupled with two-dimensional correlation analysis showed that the change of the fulvic- and humic-like matter was faster than that of the protein-like substances, as the groundwater flowed from upstream to downstream in 2011, but slower than that of the protein-like substance in 2012 due to the enhancement of microbial activity. Fluorescence spectroscopy combined with chemometric analysis can investigate groundwater pollution characteristics and monitor DOM dynamics in groundwater.

Metal–organic framework-based molecular beacons for multiplexed DNA detection by synchronous fluorescence analysis

We report a new sensor combined two dimensional metal-organic framework (MOF), N,N-bis(2-hydroxy-ethyl)dithiooxamidato copper(II) (H2dtoaCu), with the hairpin-structured oligonucleotides and demonstrate its feasibility in detecting multiplexed sequence-specific DNA. The key component of this sensor (MOF-MBs) is the hairpin-structured fluorescent oligonucleotide that allows the MOFs to function as both a "nanoscaffold" for the oligonucleotide and a "nanoquencher" of the fluorophore. An oligonucleotide sequence fragment of wild-type HBV (T1) and a reverse-transcription oligonucleotide sequence of RNA fragment of HIV (T2) were used as model systems. While in the presence of the targets, the fluorescence of dyes was recovered by forming a double strand structure. Multiplex DNA detection can be realized by synchronous scanning fluorescence spectrometry, and there was no cross reaction between the two probes. Under the optimum conditions, the fluorescence intensities of two dyes all exhibit good linear dependence on their target DNA concentration in the range of 1-10 nM with the detection limit of 0.87 nM and 0.22 nM for T1 and T2, respectively. As a proof of concept, the MOF-MBs have been successfully used as a potential sensing platform for simultaneous detection of multiplexed DNA.

RIGHT-ANGLE FLUORESCENCE SPECTROSCOPY FOR DIFFERENTIATION OF DISTILLED ALCOHOLIC BEVERAGES

Abstract Total luminescence and synchronous scanning fluorescence spectroscopic techniques were investigated for differentiating brandies from mixed wine spirits. The studies were performed on 16 brandies from 3 different producers and 30 mixed wine spirits from 5 different producers. Differentiation between samples was accomplished by multivariate data analysis methods (principal component analysis, hierarchical cluster analysis, and linear discriminant analysis). Correct classification was obtained using emission spectra (400-650 nm) recorded at excitation wavelength 390 nm, excitation spectra (225-460 nm) obtained at emission wavelength 470 nm and synchronous fluorescence spectra (200-700 nm) collected at wavelength interval 80 nm. These results indicate that right-angle fluorescence spectroscopy offers a promising approach for the authentication of brandies as neither sample preparation nor special qualification of the personnel are required, and data acquisition and analysis are relatively simple when compared to front-face technique.

Effect of humic acid source on humic acid adsorption onto titanium dioxide nanoparticles

In many studies, different humic acid (HA) sources are used interchangeably to evaluate the effect of organic matter on geochemical processes in the environment. This research looks more specifically at the effect of HA source on HA adsorption onto nano-TiO2 and how HA adsorption affects the fate and transport of nano-TiO2. In this study, six humic acids (HAs) were studied which were derived from soils (SLHA), or from sediments (SDHA) all originating from the state of Florida. Humic acid adsorption onto titanium dioxide nanoparticles (nano-TiO2) and the sedimentation of HA-coated and uncoated nano-TiO2 were monitored by Ultraviolet–visible (UV–vis) spectroscopy. Synchronous scan fluorescence (SSF) spectroscopy was used to complement the study of HA adsorption onto nano-TiO2. Phosphate buffer was found to reduce the amount of HA adsorbed onto nano-TiO2 relative to solutions of NaCl of the same pH and ionic strength. Adsorption constant values (Kads) for HAs varied in the order SLHA>FSDHA (freshwater sedimentary HA)>ESDHA (estuarine sedimentary HA). SSF results suggested that the more highly conjugated fractions of HA, which are more prevalent in SLHAs versus SDHAs, were preferentially adsorbed. In order to better understand the relationship between adsorption and aggregation, sedimentation studies were conducted and it was found that the percentage of nano-TiO2 sedimentation was preferentially enhanced in the order of the presence of SLHA>FSDHA>ESDHA. The extent of nano-TiO2 sedimentation was decreased with increasing HA concentration. TEM imaging of nano-TiO2 confirmed that nano-TiO2 was aggregated in the presence of HAs. The findings in this study suggest that HAs from different sources influence the fate and transport of nano-TiO2 in the environment differently.

Photolytic and photocatalytic degradation of surface oil from the Deepwater Horizon spill

The photochemical behavior of Deepwater Horizon oil collected from the surface of the Gulf of Mexico was studied. Thin oil films on water were subjected to simulated sunlight, and the resulting chemical and optical changes were observed. Polycyclic aromatic hydrocarbons (PAHs) showed substantial photodegradation, with larger PAHs being more rapidly decomposed. About 60% of the fluorescence at the excitation and emission maxima was observed with 12h of simulated solar irradiation equivalent to approximately 3d of sunlight. Synchronous scan fluorescence measurements showed 80–90% loss of larger PAHs with 12h of simulated solar irradiation. Absorbance of the oil decreased by only 20% over the same time period. Alkanes showed no significant photochemical losses. After irradiation, the toxicity of water in contact with the oil significantly increased, presumably due to the release of water soluble photoproducts that were toxic. Photocatalyst addition resulted in enhanced degradation rate for PAHs, and toxicity of the aqueous layer was altered in the presence of photocatalysts added to the oil film. Photochemistry is an important pathway for degradation of large PAHs, which are typically resistant to biodegradation.