Initial Fluorescence Intensity Research Articles

Efficacy of plasmapheresis and semi-selective immunoadsorption for removal of anti-HLA antibodies.

In organ transplantation, apheresis is frequently used for removal of anti-HLA antibodies. However, it is unclear whether plasmapheresis (PP) or semi-selective immunoadsorption (IA) should be employed, and the optimal number of apheresis sessions required to reach post-treatment objectives is also unknown. We enrolled 43 patients from Bordeaux University Hospital who were treated with PP (n=29) or IA (n=14) for antibody-mediated rejection or pre-transplant desensitization. Using Luminex single-antigen flow beads, we assessed the initial mean fluorescence intensity (MFI) of 1416 positive beads with MFIs obtained after 7 to 8 apheresis sessions (extended protocol) and, if a serum was available, after the first four sessions (short protocol). MFI reduction after extended apheresis protocol was stronger with IA [87% (61%-100%)] than with PP [73% (22%-100%)] (P < .001). Indeed, 59% of the beads had a final MFI < 2000 with IA, whereas only 38% with PP (P < .001). The efficacy of removal depended on initial MFI but not on HLA specificity. A short protocol of apheresis showed excellent results without superiority of IA over PP for antibodies with an initial MFI < 3000. For antibodies showing MFI ≥2000 after four sessions, the residual MFI predicted the effectiveness of four additional sessions. Monitoring the MFI of anti-HLA antibodies before and during apheresis protocol can guide physicians in the selection of apheresis technique and the number of sessions to be performed.

Molecular Tetrahedrons as Selective and Efficient Ion Transporters via a Two-Station Swing-Relay Mechanism

The traditional approach to utilizing an ion-relay mechanism for ion transport requires three or more ion-relay stations. Herein, we describe a novel strategy, incorporating a swing action to reali...

The fluorescence of resin-based composites: An analysis after ten years of aging.

The long-term preservation of fluorescence qualities of resin-based composite (RBC) restorations is an absolute condition for the implementation of the fluorescence-aided identification technique (FIT) in dentistry and forensic medicine. Therefore, this study assessed the fluorescence of 244 color shades of 16 commercially available RBC brands with a monochromator-based multimode microplate reader. The specimens were stored in the dark at room temperature and reassessed ten years after the initial investigation. The mean intensity of the fluorescence maxima decreased from (31,030±936) RFU to (22,027±632) RFU. Linear regression resulted in r2=0.972 and a slope=0.701±0.005. The fluorescence intensity of the tested RBCs dropped to about 70% of the initial intensity independent of the brand, color shade and initial fluorescence intensity. On the basis of this in vitro 10-year data set, we assume that in vivo RBC fluorescence is also suitable for the detection and differentiation of clinically aged RBC restorations by FIT.

Discerning Detection of Mutagenic Biopollutant TNP from Water and Soil Samples with Transition Metal-Containing Luminescence Metal-Organic Frameworks.

Two luminescent MOFs, Mn@MOF and Cd@MOF, have been reported herein, which are capable of selectively detecting 2,4,6-trinitrophenol (TNP), one of the potent organic water pollutants in the class of mutagenic explosive nitroaromatic compounds (epNACs). It is perceived that the d10-based Cd(II)-constituting MOF shows a better response in the realm of TNP-like nitroaromatic sensing in comparison to the d5-based Mn@MOF which may possess lower electron density over the conjugated building blocks. The sensing competences of these chemosensors have been explored by means of various spectroscopic experimentations, and it is observed that for both d5 and d10-containing MOFs, the initial fluorescence intensity is significantly quenched in response to an aqueous solution of TNP. However, Cd@MOF is more selective and sensitive toward TNP over several other epNACs than Mn@MOF. The high chemical stability of the MOF samples, as well as its amusing sensing efficiency of Cd@MOF, further instigated to investigate the sensing ability in various environmental specimens like soil and water culled from several zones of West Bengal, India.

A facile biosensor for Aβ40O based on fluorescence quenching of prussian blue nanoparticles

Amyloid β peptide oligomeFrs (AβOs) have been proved to be crucial biomarkers of Alzheimer's disease (AD). To explore an applicable method for the determination of AβOs is significant for the early AD diagnosis. Prussian blue nanoparticles (PBNPs), as one excellent nanomaterials, have the advantages of good stability, favorable biocompatibility, low cost, easy preparation and controllable shape. PBNPs was found to be of the fluorescence quenching ability to fluorophores, and the adsorption of DNA onto PBNPs surface occurred via the binding of phosphate skeleton in DNA to Fe2+/Fe3+ in PBNPs. On basis of this, carboxyl fluorescein (FAM) modified Aβ40O-targeting aptamer (FAM-AptAβ) was adsorbed onto PBNPs. And FAM-AptAβ@PBNPs-based fluorescent aptasensor for the determination of Aβ40O was developed. Upon incubating FAM-AptAβ@PBNPs with Aβ40O, the fluorescence intensity of the FAM-AptAβ@PBNPs obviously increased comparing to the initial fluorescence intensity of the FAM-AptAβ@PBNPs. The changes in the fluorescence intensity of the FAM-AptAβ@PBNPs were linear with the Aβ40O concentrations ranging from 1.00 nM to 100 nM. Moreover, AD patients and healthy persons can be distinguished using this method to determine Aβ40O concentrations in human cerebrospinal fluid samples from AD patients and healthy persons. It demonstrates that this PBNPs-based aptasensor is not only simple and cost-effective, but also sensitive, selective and more applicable. This fluorescent sensing strategy is promising for the development of aptasensor in clinical fields.

N-doped carbon dots with tunable emission for multifaceted application: solvatochromism, moisture sensing, pH sensing, and solid state multicolor lighting

Novel N-doped green-emitting carbon dots (N-GCDs) that were responsive to various external stimuli and had high quantum yields (QYs) for multifaceted applications were synthesized from β-resorcylic acid and ethylenediamine using a hydrothermal process followed by a reflux method. The QYs of the N-GCDs were in the range of 17.36%–48.4% and were associated with different photoluminescent color emission in different solvents. Interestingly, the as-synthesized N-GCDs exhibited strict solvent polarity-dependent switchability (solvatochromism) and multicolor excitation-wavelength-independent emission in different solvents. Sensing of an analyte based on the switching of the photoluminescence (PL) emission maxima (λmax) is always preferred over that based on fluorescence quenching to avoid complexity and confusion regarding the initial fluorescence intensity (I0) and thus make the sensing process simple, rapid, ordered, and reliable. The N-GCDs exhibited blue emission in low-polarity organic solvents, but with the increase of the trace water content in the system, the PL emission peak gradually shifted to a higher wavelength (bathochromic shift) at a single-wavelength excitation. Thus, the N-GCDs are sensitive visual probes for the fluorescence detection of the trace water content in organic solvents without sophisticated processes. They also indicate the pH-response behavior. When the pH decreased from 7.6 to 2.4, the fluorescence emission intensity decreased, with a particularly good linear relationship (R2 = 0.990) in the range of 3.8–6.2. Moreover, the polarity-dependent-emission property was observed in the solid state polymer matrices. Multicolor-emissive N-GCD/polymer films were prepared by integrating N-GCDs with the polymer matrices of different polarity, demonstrating the application of carbon dots for solid-state lighting.

CsPbBr3‐Quantum‐Dots/Polystyrene@Silica Hybrid Microsphere Structures with Significantly Improved Stability for White LEDs

AbstractCesium‐lead‐halide perovskite quantum dots (PQDs), which have superior optical and electronic properties, are regarded as excellent materials for various optoelectronic devices. However, their unstable nature greatly hinders their practical application. Herein, a simple hydrolysis encapsulation method is developed to embed PQDs into mesoporous polystyrene microspheres (MPMs) followed by a silica shell covering process, which generates luminescent PQDs/MPMs@SiO2 hybrid microspheres with significantly enhanced stability. The obtained CsPbBr3‐PQDs/MPMs@SiO2 hybrid microspheres show a high photoluminescence quantum yield of 84%. More importantly, the MPMs@silica protective shells effectively cut off direct contact between outer erosive species and the inner embedded PQDs and modify the hybrid microspheres with ultralong alkyl chains for improved resistance to solvents and heat. Hence, these CsPbBr3‐PQDs/MPMs@SiO2 hybrid microspheres exhibit good chemical/physical stabilities, even when exposed to harsh environments, such as deionized water, isopropanol, acid/alkali solution, anion‐exchange reactions, and heating. Particularly, the water stability, which produced the remaining ≈48% proportion of the initial fluorescence intensity after a quite long aqueous storage period of 30 d, is the best reported among the stability‐related studies of PQDs. Meanwhile, white light‐emitting diodes (LEDs) are achieved by mixing green CsPbBr3‐PQDs/MPMs@SiO2 microspheres with red commercial phosphors on a blue chip. High power efficiency of 81 lm W−1 and good electroluminescence stability are obtained.

Graphene Nanobuds: A New Second-Generation Phosgene Sensor with Ultralow Detection Limit in Aqueous Solution.

Selective and sensitive detection of highly toxic chemicals by a suitable, fast, inexpensive, and trustworthy method is vital due to its serious health threats to humankind and breach of public security caused by unexpected terrorist attacks and industrial accidents. Phosgene or carbonyl dichloride is widely employed in many chemical industries and pharmaceuticals, and in pesticide production, which is extremely toxic by severe (short-term) inhalation exposure. Because of the non-existence of a phosgene sensor in aqueous solution and the immense emphasis gained by nanomaterials, especially carbonaceous materials, augmented attention has been given to the development of a fluorophore-functionalized carbon-based method to detect this noxious substance. In this study, surfactant free 1,8-diaminonaphthalene (DAN)-functionalized graphene quantum dots (DAN-GQDs) were prepared to detect phosgene in aqueous solution. The FESEM (field emission scanning electron microscopy) and HRTEM (high-resolution transmission electron microscopy) analyses confirm the as-prepared DAN-GQD morphology as nanobuds (NBs) with an average diameter of ca. 35-40 nm. The crystalline nature, elemental composition, and chemical state of DAN-GQDs were analyzed by standard physiochemical techniques. The edge-termination at the carboxyl functional group of GQDs with DAN was examined by XPS, Raman, FT-IR, and 1H NMR spectroscopy analyses. The aqueous solution of DAN-GQDs (4.89 × 10-9 M) exhibits a strong emission peak at 423 nm upon excitation at 328 nm. The addition of the phosgene molecule (0 → 88 μL) quenches the initial fluorescence intensity of DAN-GQDs (ΦF 53.6 → 34.6%) through the formation of a stable six-membered cyclized product. The DAN-GQDs displayed excellent selectivity and sensitivity for phosgene ( Ka = 3.84 × 102 M-1 and LoD (limit of detection) = 2.26 ppb) over other competing toxic pollutants in water. The time-resolved fluorescence analysis confirms that the quenching of DAN-GQDs follows nonradiative relaxation of excited electrons. Furthermore, bioimaging experiments of phosgene in living human breast cancer (HeLa) cells and cell viability test successfully demonstrated the practicability of DAN-GQDs.

Dissolved organic matter (DOM) in the open Mediterranean Sea. II: Basin–wide distribution and drivers of fluorescent DOM

Fluorescent dissolved organic matter (FDOM) in the Mediterranean Sea was analysed by excitation–emission matrix (EEM) spectroscopy and parallel factor (PARAFAC) analysis during the cruise HOTMIX 2014. A 4–component model, including 3 humic–like and 1 protein–like compounds, was obtained. To decipher the environmental factors that dictate the distributions of these components, we run generalized additive models (GAMs) in the epipelagic layer and an optimum multiparametric (OMP) water masses analysis in the meso– and bathypelagic layers. In the epipelagic layer, apparent oxygen utilization (AOU) and temperature presented the most significant effects on the variability of the marine humic-like peak M fluorescence, suggesting that its distribution was controlled by the net community respiration of organic matter and photobleaching. On the contrary, the variability of the soil humic-like peak E and the protein–like peak T fluorescence was explained mainly by the prokaryotic heterotrophic abundance, which decreased eastwards. In the meso– and bathypelagic layers, water mass mixing and basin–scale mineralization processes explained >72% and 63% of the humic–like and protein–like fluorescence variability, respectively. When analysing the two basins separately, the OMP model offered a better explanation of the distribution of fluorescence in the eastern Mediterranean Sea, as expected from the reduced biological activity in this ultra–oligotrophic basin. Furthermore, while western Mediterranean deep waters display the usual trend in the global ocean (increase of humic–like fluorescence and decrease of protein–like fluorescence with higher AOU values), the eastern Mediterranean deep waters presented an opposite trend. Different initial fluorescence intensities of the water masses that mix in the eastern basin, with Adriatic and Aegean origins, seem to be behind this contrasting pattern. The analysis of the transect–scale mineralization processes corroborate this hypothesis, suggesting a production of humic–like and a consumption of protein–like fluorescence in parallel with water mass ageing. Remarkably, the transect–scale variability of the chromophoric dissolved organic matter (CDOM) absorbing at the excitation wavelength of the humic–like peak M indicates an unexpected loss with increasing AOU, which suggests that the consumption of the non–fluorescent fraction of CDOM absorbing at that wavelength exceeded the production of the fluorescent fraction observed here.

Fluorescence photobleaching of microplastics: A cautionary tale

Fluorescence microscopy is an important step in visual identification of microplastics and is used to highlight white and transparent plastics that are otherwise easily missed or misidentified. Investigators using fluorescence must proceed with caution, however, as fluorescence photobleaching can significantly reduce the fluorescence output of samples within experimentally relevant time frames. We report on the photobleaching rate and subsequent lack of fluorescence recovery of five common plastics. Our results reveal statistically different photobleaching rates across plastic types. In the best-case scenario of low illumination intensity and a robust plastic, initial fluorescence intensity decayed by 10% in just 11(3) s and by 33% in 230(40) s. In all cases, fluorescence failed to recover more than 13(8)% in 3 h. These results indicate that significant bleaching can occur while searching a sample for plastics to identify and that the lack of recovery can compromise samples for further study.

A novel hypobromous acid scavenging activity assay using p-cresol as a spectrofluorometric probe

In this study, a novel spectrofluorometric assay based on $p$-cresol (4-methyl phenol) probe is developed for the measurement of HOBr scavenging activity. It is the first study involving the use of a $p$-cresol probe for the determination of the HOBr scavenging activity of biothiols. While the $p$-cresol probe ($\lambda_{ex}$ = 260 nm, $\lambda_{em}$ = 305 nm) has fluorescence characteristics, its brominated derivatives emerging at the end of the oxidation reaction with HOBr do not show fluorescence. The initial fluorescence intensity of the $p$-cresol probe is decreased in the presence of the brominating agent, HOBr, and this decrease is lower in the presence of HOBr scavenging antioxidants. The scavenging activities of biothiols tested with respect to the developed method decrease in the following order: penicillamine $>$ N-acetyl cysteine $>$ L-glutathione (reduced) $>$ cysteamine $>$ homocysteine $>$ glutathione ethyl ester $>$ cysteine $>$ 1,4-dithiothreitol $>$ lipoic acid $>$ methionine. Penicillamine (IC$_{50}$ = 10.12 $\mu $M) was the most effective HOBr-scavenger among the tested biothiols. The results obtained with the developed method for biothiols and some pharmaceutical samples were statistically compared (using ANOVA) to those found by the reference methods (KI/taurine and UPLC). The advantage of the proposed method over the KI/taurine assay was demonstrated

Reversible photobleaching of photoconvertible SAASoti-FP

SAASoti is a green fluorescent protein suitable for use in super-resolution microscopy as it can be photoconverted to red fluorescence under 405 nm illumination. The green fluorescence of V127T SAASoti variant is reversibly photobleached under exposure to 470 nm light without photoconversion to the red form. The phenomenon can be explained by chromophore protonation that was confirmed by an increase in absorption at 400 nm (chromophore protonated form) and a decrease at 509 nm (anionic form). This light-induced photoswitching can be repeated with the same sample several times without loss of the initial fluorescence intensity. Subsequent sample exposures result in the same fluorescence recovery process. By changing the content of the H-form one can control photoswitching as only the protonated SAASoti may be converted to the red form. This property is extremely important for sub-diffraction microscopy.

A Cyclam‐Based Fluorescent Ligand as a Molecular Beacon for Cu2+ and H2S Detection

A pentadentate cage‐like cyclam‐based fluorescent ligand has been designed, synthesized, and characterized by 1D and 2D NMR spectroscopic analysis. To further characterize the title ligand, ESI‐MS, UV/Vis spectroscopy, and fluorescence experiments have been also performed. Its suitability as a chemosensor for the detection of Cu2+ ions has been successfully explored with a variety of spectroscopic techniques (i.e., ESI‐MS, UV/Vis, and fluorescence). A Job's plot experiment, together with ESI‐MS experiments, indicate a 1:1 stoichiometry for the binding of Cu2+ to the cyclam‐based ligand. Fluorescence experiments corroborate this hypothesis. The resulting system is selective in the recognition of copper and is stable for a week, as assessed by fluorescence spectroscopy. The CuII complex has been isolated and tested as a fluorescent probe for the detection of H2S. NMR spectroscopy and ESI‐MS investigations have provided evidence that H2S recognition occurs through a copper‐displacement mechanism, as reported in the literature for different copper complexes. The system functions with a selective response to HS–, harnessing a concentration‐dependent “turn‐on” of the initial fluorescence intensity.

A new colorimetric and fluorescent probe with a large stokes shift for rapid and specific detection of biothiols and its application in living cells.

In this work, a new reversible colorimetric and fluorescent probe for sequential recognition of copper ions and biothiols is synthesized easily. Based on the chelation-enhanced fluorescence quenching (CHEQ) effect, this probe shows high sensitivity and selectivity towards Cu2+, which can be detected by the naked eye. And this experimental phenomenon can also be realised upon addition of biothiols, restoring their initial fluorescence intensity. This probe also features a very high response speed (less than 5 seconds) and a large stokes shift (178 nm) toward Cu2+ and biothiols. Moreover, the detection limit for Cu2+ and biothiols is as low as 7.34 nM and 10.3 nM, respectively. Additionally, this ON-OFF-ON-type fluorescence recognition cycle can be repeated more than 5 times by addition of Cu2+ and biothiols in turn. Particularly, this 1-Cu2+ ensemble is further successfully applied for GSH detection in living cells.

Comparison of therapeutic efficacy of lipo-doxorubicin and doxorubicin in treating bladder cancer

ObjectivesDoxorubicin is commonly used in the treatment of superficial bladder cancer, but more side effects and shorter intracellular retention time hamper its clinical application. Since lipo-doxorubicin (Lipodox) has the advantages of longer half-life and lower clearance rate than doxorubicin, it should improve the efficacy of tumor therapy and reduce the normal tissue toxicity of doxorubicin. Materials and MethodsIn this study, we compared the cytotoxicity of Lipodox and doxorubicin in different treatment durations on bladder cancer cells by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Drug distribution was tracked under fluorescence microscopy. The metabolic rate after treatment was measured by serial flow cytometry. Finally, an in vivo orthotopic MBT-2 bladder tumor model was established for comparing the differences of therapeutic efficacy, including tumor weight and survival rate. ResultsThe 50% inhibitory concentration (IC50) of doxorubicin and Lipodox for MBT-2 cells was 0.62 μg/mL and 130 μg/mL, respectively, after 48 hours treatment. Lipo-dox presented higher cytotoxicity than doxorubicin at 6 hours (93% vs 73%) and 12 hours (93% vs 80%) treatment. After drug treatment, Lipodox fluorescence distribution was observed mostly in the cell membrane, lysosomes, and nuclei of tumor cells, while doxorubicin was concentrated in the nuclei. Initial fluorescence intensity of doxorubicin was 27.3 times that of Lipodox (p < 0.001) at time of treatment. The fluorescence intensity of doxorubicin decreased to 12% after 24 hours culture but that of Lipodox remained at 81%. In an orthotopic model, the average tumor weight and survival were: control group: 1.0 ± 0.3 g, 25%; doxorubicin treatment group: 0.7 ± 0.05 g, 43%; and Lipodox treatment group: 0.2 ± 0.1 g, 57%. ConclusionOur study demonstrated that Lipodox can enhance doxorubicin cytotoxicity in bladder cancer cells and inhibit tumor growth in orthotopic bladder cancer with improved survival rate. Therefore, we suggest Lipodox may act as an alternative to doxorubicin in the treatment of local bladder cancer.

Highly luminescent tetra(biphenyl-4-yl)ethene-grafted molecularly imprinted mesoporous silica nanoparticles for fluorescent sensing of diethylstilbestrol

A molecularly imprinted mesoporous silica-based fluorescent sensor was prepared using a tetraphenylethene derivative (TBPE) as a signal transducer. Diethylstilbestrol (DES) was chosen as a target molecule and was connected to two triethoxysilane groups via thermally reversible urethane bonds. DES imprinted cavities with two-point binding sites were formed between the pores of the mesoporous silica by the sol-gel reaction and subsequent removal of DES. TBPE was selectively introduced to the pore surface. TBPE-grafted, DES imprinted mesoporous silica nanoparticle (TBPE-DIMSNP) showed a specific binding ability for the target template. The degree of fluorescence quenching of TBPE-DIMSNP was proportional to the concentration of DES. The sensitivity and selectivity of TBPE-DIMSNP were estimated by the Stern-Volmer equation. TBPE-DIMSNP displayed a much larger Stern-Volmer quenching constant for DES than for DES analogs with a high molecular imprinting factor. TBPE-DIMSNP also exhibited a great recovery of its initial fluorescence intensity even after several extraction and rebinding cycles.

Quantitative Tissue Spectroscopy of Near Infrared Fluorescent Nanosensor Implants.

Implantable, near infrared (nIR) fluorescent nanosensors are advantageous for in vivo monitoring of biological analytes since they can be rendered selective for a particular target molecule while utilizing their unique optical properties and the nIR tissue transparency window for information transfer without an internal power source or telemetry. However, basic questions remain regarding the optimal encapsulation platform, geometrical properties, and concentration ranges required for high signal to noise ratio and effective detection through biological tissue. In this work, we systematically explore these variables quantitatively to optimize the performance of such optical nanosensors for biomedical applications. We investigate both alginate and polyethylene glycol (PEG) as model hydrogel systems, encapsulating d(GT)15 ssDNA-wrapped single-walled carbon nanotubes (SWNT) as model fluorescent nanoparticle sensors, responsive to riboflavin. Hydrogel sensors implanted 0.5 mm into thick tissue samples exhibit 50% reduction of initial fluorescence intensity, allowing an optical detection limit of 5.4 mm and 5.1 mm depth in tissue for alginate and PEG gels, respectively, at a SWNT concentration of 10 mg L(-1), and 785 nm laser excitation of 80 mW and 30 s exposure. These findings are supported with in vivo nIR fluorescent imaging of SWNT hydrogels implanted subcutaneously in mice. For the case of SWNT, we find that the alginate system is preferable in terms of emission intensity, sensor response, rheological properties, and shelf life.

A Phosphole Oxide Based Fluorescent Dye with Exceptional Resistance to Photobleaching: A Practical Tool for Continuous Imaging in STED Microscopy.

The development of stimulated emission depletion (STED) microscopy represented a major breakthrough in cellular and molecular biology. However, the intense laser beams required for both excitation and STED usually provoke rapid photobleaching of fluorescent molecular probes, which significantly limits the performance and practical utility of STED microscopy. We herein developed a photoresistant fluorescent dye C-Naphox as a practical tool for STED imaging. With excitation using either a λ=405 or 488 nm laser in protic solvents, C-Naphox exhibited an intense red/orange fluorescence (quantum yield ΦF >0.7) with a large Stokes shift (circa 5900 cm(-1) ). Even after irradiation with a Xe lamp (300 W, λex =460 nm, full width at half maximum (FWHM)=11 nm) for 12 hours, 99.5 % of C-Naphox remained intact. The high photoresistance of C-Naphox allowed repeated STED imaging of HeLa cells. Even after recording 50 STED images, 83 % of the initial fluorescence intensity persisted.

Postsynthetic exterior decoration of an organic cage by copper(I)-catalysed A3-coupling and detection of nitroaromatics.

A new synthetic protocol based on one-pot, copper(I)-catalysed multicomponent reaction of formaldehyde, secondary amine and terminal alkyne has been employed to postsynthetically modify a self-assembled nanoscopic organic cage. By employing this synthetic strategy, three new cages appended with phenyl-, xylyl- and naphthyl-acetylene moieties have been synthesised. The resulting modified cages were characterised by using a range of spectroscopic techniques. The synthesised cages were fluorescent and thus one of them was tested to explore the potential use of such compounds as chemosensors for the detection of nitroaromatics. Experimental findings suggest a high selective quenching of initial fluorescence intensity in the presence of nitroaromatic compounds. Furthermore, it has been observed that among the various nitroaromatics tested, nitrophenolic compounds have better quenching ability.

Exploring the relationship between the optical properties of water and the quality and quantity of dissolved organic carbon in aquatic ecosystems: strong correlations do not always mean strong predictive power.

Optical absorbance and fluorescence spectroscopies have the potential to play an important role in monitoring aquatic ecosystems. This paper explores the relationship between the optical absorption and fluorescence characteristics of water samples taken from 18 sites (spanning a range of aquatic environments including lowland rivers, small and large dams, and floodplain wetlands) with their dissolved organic carbon (DOC) concentration and 28 days bioavailability Both optical absorbance in the ultraviolet region and fluorescence above excitation wavelengths of about 240 nm and emission wavelengths above about 350 were correlated with DOC concentration (r(2) > 0.8). The initial (pre-incubation) optical absorbance in the UV region (r(2) ≈ 0.7-0.8) and fluorescence attributed to both 'humic like' (r(2) = 0.84) and 'tryptophan-like' (r(2) = 0.87) fluorophores correlated with DOC bioavailability. These correlations were used to develop empirical linear models relating the initial optical properties of water with DOC quantity and quality. The robustness of these models was then tested against a second suite of water samples from 12 different sites, collected independently of those used in the model development. Although based on strong correlations, the empirical models were not particularly good at predicting the bioavailability of DOC in the model validation samples. We suggest that one of the reasons for the low predictive power of the models is that the strong correlations observed between DOC bioavailability and optical absorbance in the UV region or fluorescence and are co-incidental rather than causal. Changes in UV-absorbance or fluorescence during the incubation experiments are not consistent with changes in DOC concentration. One of the best predictors of DOC bioavailability is the initial concentration of DOC. We argue the strong correlation between DOC bioavailability and initial fluorescence intensity or UV absorption simply reflects the strong correlation between initial DOC concentration and initial fluorescence intensity or UV absorption. We argue that unless there is an underlying causal relationship between two components (the component of interest and a surrogate measure for that component) care should be taken in extrapolating correlative models beyond the data set used to create them.