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The use of spoilage indicator films has become widespread in food safety due to their ability to detect the freshness of food in real-time through color change. Here, a novel spoilage indicator film was prepared by combining polyvinyl alcohol (PVA)/cassava starch (CS) with neutral red (NR) as a pH-sensitive indicator. The microstructural properties of NR/PVA/CS film indicated that the addition of NR could greatly increase the compatibility of the membrane. The successful mixing of PVA, CS and NR was confirmed by Fourier transform infrared (FTIR). The film was attached to the upper layer of the inner package relying on the stickiness to avoid contacting with meat. Subsequently, the NR/PVA/CS film was successfully applied as a sticker indicator to monitor the spoilage of meat over time. Changes in color of the film from dark red to orange were observed by the naked eye, and quantified using the CIE color difference (ΔE). Finally, polynomial model between ΔE and TVB-N content in pork, mutton, and chicken during storage were successfully constructed with the coefficient of determination (R2) of 0.8286, 0.9426 and 0.9585, respectively. The results demonstrate the potential of the developed system to monitor the freshness of meat in food packaging. [ABSTRACT FROM AUTHOR]

In this study, activated carbon (AC) obtained with apple peel was used for removal of Neutral Red (NR) from aqueous solutions. The characterization of AC was evaluated with the Brunauer-Emmett-Teller (BET), Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analyses. Isotherm, kinetic, and thermodynamic parameters were determined for NR removal with AC. Eighteen isotherm models and eight kinetic models were analyzed for three temperatures and six initial dye concentrations. The experimental data best agree with the Langmuir model among the isotherm models, and the maximum adsorption capacity (qm) was calculated 142.857 mg/g at 318 K. It was determined that the pseudo-second-order (PSO) model was the best choice among the kinetic models with the highest correlation coefficients. The removal percentage of NR dye with AC obtained 82.13%, 84.79%, and 87.20% for 120 mg/L initial dye concentration at 298 K, 308 K, and 318 K, respectively. The negative free energy, enthalpy, and entropy values of adsorption obtained − 6386 J/mol, 46280 J/mol, and 165.48 J/mol.K for 20 mg/L NR concentration at 318 K, respectively. The results of this separation process shown spontaneous essence, and workability coinciding with the negative free energy and activation energy was found 13.651 kJ/mol. The assessment of the isotherm, kinetic, and thermodynamic results were evaluated with error functions. The highest correlation coefficient (R2) values and the lowest sum of squares (SS), sum of the square of error (SE), and mean square of error (MSE) values were determined with Langmuir isotherm and PSO kinetic models. This research showed that AC prepared from biomass can be used effectively for wastewater treatment using adsorption technique. [ABSTRACT FROM AUTHOR]

Carbon nanodots modified with Neutral Red covalently inserted in the nanostructure (NR-CDs) have been prepared by a simple synthesis method based on microwave irradiation under controlled temperature and pressure. The synthetized NR-CDs have been characterized by different techniques, demonstrating the covalent bonding of Neutral Red molecules to the carbon dots nanostructure. Fluorescence activity of the prepare NR-CDs has been explored showing different interaction pathways with singled and doubled stranded DNA. These studies have been successfully applied to develop a new fluorescence DNA hybridization assay to the detection of a specific DNA sequence of Escherichia coli bacteria. [ABSTRACT FROM AUTHOR]

We evaluated the environmental quality in mangrove areas of the Western Atlantic with different levels and history of contamination, considering biomarkers for the crab Ucides cordatus. For this purpose, specimens were collected in two climatic seasons (rainy and dry seasons) and assays of genotoxicity (MN, micronucleus), cytotoxicity (NRRT, neutral red retention time) and biochemical (MT, metallothionein; and LPO, lipoperoxidation) were conducted. In the most impacted mangroves, there was an increase in the mean of micronucleus (frequency of MN/1000), which was associated with a shorter retention time (minutes of NRRT). In contrast, the most pristine areas showed MN < 3 and NRRT < 100 min, with no seasonal effect, indicating a lower effect of degenerative processes by xenobiotics. The rainy season was more harmful, especially regarding cytogenotoxicity. The use of bioindicator species for environmental monitoring should be guided by an analysis of biomarkers considering the season, because during the period of highest rainfall, biomarkers values can change. [ABSTRACT FROM AUTHOR]

The main goal of this work was the theoretical interpretation of the absorption spectra of neutral red in an aqueous solution (both neutral NR0 and protonated NR+ forms). To achieve this problem, TD-DFT/DFT calculations with different hybrid functionals, the IEFPCM solvent model, and the 6–31 + + G(d,p) basis set were used. MN12SX functional provided the best agreement with the experiment for both dye forms. While the absorption band of the cationic form of the dye in the visible region of the spectrum is due to one transition S0 → S1 (HOMO–LUMO), for its neutral form, there are two transitions S0 → S1 (HOMO → LUMO) and S0 → S2 (HOMO-1 → LUMO), with the latter having a higher intensity. The protonation of the dye chromophore introduces significant changes in HOMO shape. At the same time, LUMOs are almost the same for the protonated and neutral forms of the NR. During the transition from NR0 to the S1 state, its dipole moment increases more significantly than during the transition to the S2 state. Calculations confirmed the assumption of Singh et al. about the existence of two closely spaced excited states of NR0, the first of which has a larger dipole moment. However, the hypothesis of these authors about the corresponding intramolecular charge transfer, as well as the huge value of the dipole moment of this excited state (~ 20 D) declared by them, was not confirmed by present calculations. It was shown that the photoinduced charge redistribution in both the neutral and cationic forms of the dye is local, and the corresponding dipole moment is ~ 10 D. This agrees with other early theoretical work by Aaron et al. The influence on the NR+ absorption spectrum of hydrating water molecules was also analyzed. It was found that the interplay of electrostatic and site-specific contributions leads to the fact that NR solvatochromism does not have a pronounced dependence on the polarity of the solvent. [ABSTRACT FROM AUTHOR]

Although a portion of all copepods in the natural environment are physiologically inactive or dead, there is little data on this aspect in Indian seas. Using the classical neutral red live staining technique, the dead percentage of copepods in the western Bay of Bengal (BoB) is determined for the first time in this study, which takes into account hydrography and zooplankton samples collected on April 2015 (Spring Intermonsoon [SIM]) from 6 inshore and 8 offshore locations in the western BoB. The offshore parts of the research area were infested with a persistent and extensive warm-core eddy/gyre during the sampling time, as demonstrated by satellite data of sea surface temperature, mean sea level anomaly, and surface currents. As a result, the mixed layer depth in the offshore zone was higher, whereas nutrients, chlorophyll a, and turbidity were significantly lower than inshore. Copepods dominated the zooplankton community (> 80%), with abundances ranging from 112 to 2580 No m−3 in the study area. Calanoids (particularly Paracalanidae) dominated nearshore waters (35–65%), whereas cyclopoids (notably Corycaeidae and Oncaeidae) dominated offshore (49–71%). There were 48 species of copepods identified in total, and all of them had dead individuals (carcasses). Offshore waters had a larger percentage of copepod carcasses (27–39%) than inshore seas (18–28%). The larger percentage of carcasses is possibly related to a higher top-down feeding pressure on cyclopoids in offshore waters due to extreme oligotrophy and the dominance of the microbial food web. [ABSTRACT FROM AUTHOR]

The ZnO/CeO2 nanocomposites (Zn1−xCexO2) were fabricated for different concentrations with x = 0(ZC-1), 0.05(ZC-2), 0.1(ZC-3) and 0.3(ZC-4) via the hydrothermal method. We observed a decrease in particle size by an increase in the concentration of CeO2 to ZnO. To ensure this Transmission Electron Microscopy (TEM) analysis has been done and the obtained particles size around 42 nm, 26 nm, 22 nm, and 12 nm for ZC-1, ZC-2, ZC-3, and ZC-4 respectively. The purity and chemical composition were investigated by Energy Dispersive X-ray Analysis (EDX) & X-ray Photoelectron Spectroscopy (XPS) analysis. For the first time, the synthesized ZnO/CeO2 nanocomposites were used as photocatalysts for photocatalytic degradation of the dye neutral red. Initially, the degradation efficiency (ɳ) of ZnO nano catalyst was 45.35%, as we increase the CeO2 concentration the efficiency of the dye degradation increased appreciably to 56.86%. This is because of more occupancy of surface defects by smaller size particles. Furthermore, the synthesized nanocomposites were studied for their antibacterial activity. Due to the doping of CeO2, we observed eventually an increase in the zone of inhibition from 12 mm to 19 mm for gram-negative bacteria. We obtained good results for gram-negative bacteria for the higher concentration of the CeO2 than gram-positive. So, the synthesized Nanocomposites are effective for photocatalytic as well as antibacterial applications. Highlights: ZnO/CeO2 nanocomposites were synthesized by a simple hydrothermal method for different concentrations. Optical and physicochemical properties were investigated thoroughly. For the first time, photo-induced degradation is explained by the effect of particles size over neutral red. The effect of surface morphology and size of NPs examined for antibacterial activities. [ABSTRACT FROM AUTHOR]

We proposed a voltammetric DNA sensor based on glassy carbon modified with carbon black, pillar[5]arene, and electropolymerized Neutral Red. To increase signal sensitivity, Methylene Blue in monomeric and polymeric forms was introduced into the surface layer of the DNA sensor as a specific DNA intercalator and electron transfer mediator. The electrochemical characteristics of the coating are determined, depending on the composition and the preparation method; a consistent change in the peak currents of dyes is observed during the incubation of a DNA sensor in a solution of doxorubicin as a model anticancer drug. Under optimal conditions, the DNA sensor enables the determination of 10 nM to 0.1 mM of doxorubicin. Doxorubicin can also be determined in synthetic blood plasma. [ABSTRACT FROM AUTHOR]

Blue light is known to be antimicrobial, but its effect on normal cutaneous and subcutaneous cells remains unclear. Therefore, we studied the effect of 470-nm light on the viability of adult and neonatal human dermal fibroblasts, Jurkat T-cells, and THP-1 monocytes in vitro. Each culture was irradiated with 0, 3, 55, or 110 J/cm2 of 470-nm light and subjected to trypan blue assay to ascertain viability. Further, MTT, neutral red, and fluorescence assays of fibroblasts were performed, and cell morphology visualized using bright field and fluorescence microscopy. At each dose and in each of the four cell lines, there was no significant difference in cell concentration between irradiated and non-irradiated cultures, even though irradiation with 55 J/cm2 or 110 J/cm2 slightly decreased cell count. Light microscopy showed progressive morphological changes in the fibroblasts as energy fluence increased from 55 to 110 J/cm2. Irradiation at 3 J/cm2 produced a slight but non-significant increase in the viability of Jurkat T-cells and THP-1 monocytes. In contrast, at 110 J/cm2 radiant exposure, irradiation slightly decreased the viability of all four cells. While 3 J/cm2 appears stimulatory, our finding that 110 J/cm2 produces a slight decrease in viability and engenders morphological changes in fibroblasts, suggesting that such high doses should be avoided in blue light treatments. [ABSTRACT FROM AUTHOR]

Cobalt-grafted-mesoporous silica nanoparticles with the Si/Co molar ratio of 70 were synthesized by using sol–gel method (denoted as Co-MSN). Characterization of the Co-MSN was carried out by X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and N2 adsorption/desorption analysis. Photocatalytic activity of the Co-MSN sample was studied for removal of neutral red as one of the most widely used dye pollutants, in presence of H2O2 and UV irradiation. In this regard, effect of various influencing parameters such as pH, Co content, dye concentration, amount of oxidant, and presence/absence of UV irradiation were investigated. It was found that incorporation of the Co2+ ions into the mesoporous silica nanostructure significantly improves the photocatalytic degradation of neutral red. Under the optimized conditions including 0.3 mmol of H2O2 (as an oxidant), catalyst dosage of 0.075 mg, initial dye concentration of 0.08 mM, and UV irradiation (32 W, 254 nm), up to 81% of neutral red was degraded at room temperature for 220 min. [ABSTRACT FROM AUTHOR]

Estimation of realized fecundity (Freal, number of viable oocytes produced) is an essential, yet seldom-achieved element in the understanding of marine animal production and population dynamics. We used the Neutral Red (NR) vital stain to determine oocyte viability in spawns and gonad strippings of four species of commercially-important bivalves: Cerastoderma edule (L), Crassostrea gigas Thunberg, Mytilus edulis L, and Tapes philippinarum (Adams and Reeve). The utility of Trypan Blue as a complementary mortal stain was also assessed, and found to be unnecessary. Normal, live oocytes stained with NR, and were either spherical (mature oocytes) or pedunculated (immature oocytes); atresic/abnormal oocytes also stained with NR, allowing their ready recognition due to their abnormal shapes and cytoplasmic retraction. Dead oocytes did not stain with NR. Across the species studied, a considerable and highly variable proportion of spawned or stripped oocytes was either dead or non-viable; quantitative counts were performed for Cerastoderma edule, the only species for which > 5 spawns occurred. The high level and variability (34–85%) of dead or non-viable oocytes is consistent with a reproductive Red Queen dilemma, in which greater oocyte numbers do not translate to commensurately greater real fecundities, and also with a Sweepstakes Reproductive Success strategy, in which a large range of Freal confronts the considerable variability of intertidal environmental conditions. Neutral Red vital staining is a promising tool for the elucidation and optimization of crucial yet previously intractable aspects of bivalve hatchery production, genetic improvement, restocking, stock management, and conservation. [ABSTRACT FROM AUTHOR]

An impedimetric DNA sensor is developed for the highly sensitive determination of doxorubicin; the signal is charge transfer resistance recorded by electrochemical impedance spectroscopy using a glassy carbon electrode modified by electropolymerized Neutral Red or polyaniline and polyelectrolyte complexes including DNA. The nature of the polymer layer and the composition of the polyelectrolyte complex affect the sensitivity of the determination of doxorubicin. The role of a macrocycle capable of shielding the DNA negative charge and interacting with cationic centers of the substrate is shown. With an optimal composition of polyelectrolytes, the DNA sensor ensures the determination of down to 0.1 nM of doxorubicin. [ABSTRACT FROM AUTHOR]

New strategies are proposed for modification of the anode of a Microbial Fuel Cell (MFC). Immobilization of yeast cells as electrogenic microorganism in MFC was reported using alginate. Yeast cells entrapment within alginate matrices was done through films deposited at the surface of a carbon felt electrode and the resulting anodes were characterized by chronoamperometry. Yeast entrapped within alginate films on carbon felt oxidized glucose and generates a current by direct and mediated electrons transfer from yeast cells to the carbon electrode. The result substantiated that immobilization of yeast for MFC could be a promising method to product green electricity. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy and alternating-current (AC) conductivity (σAC) studies of bulk 3-amino-7-(dimethylamino)-2-methyl-hydrochloride (neutral red, NR) have been carried out over the temperature (T) range from 303 K to 383 K and frequency (f) range from 0.5 kHz to 5 MHz. Dielectric data were analyzed using the complex impedance (Z*) and complex electric modulus (M*) for bulk NR at various temperatures. The impedance loss peaks were found to shift towards high frequencies, indicating an increase in the relaxation time (τ0) and loss in the material, with increasing temperature. For each temperature, a single depressed semicircle was observed at high frequencies, originating from the bulk transport, and a spike in the low-frequency region, resulting from the electrode effect. Fitting of these curves yielded an equivalent circuit containing a parallel combination of a resistance R and constant-phase element (CPE) Q. The carrier transport in bulk NR is governed by the correlated barrier hopping (CBH) mechanism, some parameters of which, such as the maximum barrier height (WM), charge density (N), and hopping distance (r), were determined as functions of both temperature and frequency. The frequency dependence of σAC at different temperatures indicated that the conduction in bulk NR is a thermally activated process. The σAC value at different frequencies increased linearly with temperature. [ABSTRACT FROM AUTHOR]

Purpose: Neutral red (NR) may assist identification of preantral follicles in pieces of cortical tissue prior to cryopreservation in cancer patients requesting fertility preservation. This study is the first to analyze this effect by follicle growth rate after long-term culture in primates. Methods: Ovarian cortex was obtained from adult rhesus macaques, was cut into fragments, and was incubated with NR. Secondary follicles were readily visualized following NR staining and then were encapsulated into alginate beads and cultured individually for 4 weeks in αMEM media supplemented with 10 ng/ml FSH at 5% O2. Results: The survival rates of secondary follicles during culture were similar between those derived from control tissue (71 ± 13%) and those treated with NR (68 ± 9%). The proportion of surviving follicles that formed an antrum were also similar in both groups (70 ± 17% control; 48 ± 24% NR-treated). Follicle diameters were not different between control follicles (184 ± 5μm) and those stained with NR (181 ± 7 μm) on the day of isolation. The percentages of surviving follicles within three cohorts based on their diameters at week 4 of culture were similar between the control group and NR-stained tissue group, fast-grow follicles (24 ± 6% vs. 13 ± 10%), slow-grow follicles (66 ± 5% vs. 60 ± 9%), or no-grow (10 ± 9% vs. 27 ± 6%), respectively. There were no differences in follicle diameters between groups during the culture period. Pre-exposure of secondary follicles to NR diminished their capacity to produce both estradiol and androstenedione by week 4 of culture, when follicles are exhibiting an antrum. Inhibitory effects of NR on steroid production by slow-grow follicles was less pronounced. Conclusions: NR does not affect secondary follicle survival, growth, and antrum formation during long-term culture, but steroid hormone production by fast-grow follicles is compromised. NR can be used as a non-invasive tool for in situ identification of viable secondary follicles in ovarian cortex before tissue cryopreservation without affecting follicle survival and growth in vitro. Whether maturation or developmental competence of oocytes derived from antral follicles in 3D culture that were previously isolated from NR-stained tissue is normal or compromised remains to be determined. Likewise, the functional consequences of pre-exposure to NR prior to ovarian cortical tissue cryopreservation and transplantation are unknown. [ABSTRACT FROM AUTHOR]

In this article, we focused on the calculation of the linear and nonlinear optical properties of neutral red dye samples and silver nanosol incorporated dye samples. Single beam Z-scan technique using an Nd:YAG laser operating at a wavelength of 532 nm is used for the characterization. The dye alone samples showed an interplay between saturable absorption and reverse saturable absorption characteristics on open aperture mode and negative nonlinearity on closed aperture mode. Incorporation of nanosol into the dye samples resulted in an enhancement in the nonlinear optical properties and the saturable absorption to reverse saturable absorption interplay characteristic was suppressed. [ABSTRACT FROM AUTHOR]

Fluorescence spectroscopy, UV-visible absorption spectroscopy, circular dichroism (CD) spectroscopy, viscometry, cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were applied to investigate the competitive interaction of DNA with two aromatic α-aminobisphosphonates and neutral red dye (NR, intercalator) and Hoechst (Ho, groove binder) as spectroscopic probes, in a Tris-hydrogen chloride buffer solution (pH 7.4). The principal component analysis (PCA) was applied to determine the number of chemical components presented in complexation equilibrium of DNA with the aromatic α-aminobisphosphonates (B and B). The spectroscopic and voltammetric studies showed that the groove binding mode of interaction is predominant in the solution containing DNA and α-aminobisphosphonates. Furthermore, the results indicated that α-aminobisphosphonate with the lengthy N-alkyl chains had a stronger interaction. The PCA and theoretical quantum mechanical and molecular mechanic methods were also utilized to determine the structure of DNA with the two α-aminobisphosphonates (B and B). [ABSTRACT FROM AUTHOR]

Viability of keratinocytes of HaCaT immortalized line incubated with sodium dodecyl sulfate for 3 min, 1 and 48 h, was studied by light microscopy, MTT test, and neutral red absorption test. The IC values were determined for each of the studied lengths of exposure. HaCaT cells exhibited a dose-dependent decrease of viability under the effect of sodium dodecyl sulfate, proportional to the length of exposure. The values measured by different methods (MTT test and neutral red absorption test) varied, the differences were determined by the duration of exposure to sodium dodecyl sulfate. The dispersion of values for 1 and 48 h exposure, obtained by MTT method, was greater than of the values obtained by neutral red absorption test. [ABSTRACT FROM AUTHOR]

An electrochemical aptasensor is developed for the highly sensitive determination of cytochrome C, using a change in the redox current of Neutral Red covalently bound to terminal carboxyl groups of decasubstituted pillar[5]arene as a signal. The inclusion of the analyte into the complex with an aptamer reduces peaks of redox current of the dye through the dissociation of electron transfer chain in the surface layer. The aptasensor enables the determination of 1 nM to 1.0 mM of cytochrome C in the presence of 1000-fold excesses of albumin, polyethylene glycol, and lysozyme as models of interfering components in biological fluids. [ABSTRACT FROM AUTHOR]

As alternative microorganisms for butanol production with high butanol tolerant and productivity are in high demand, one excellent butanol-tolerant bacterium, S10, was isolated and identified as Clostridium acetobutylicum S10. In order to enhance the performance of butanol production, organic acids and neutral red were added during butanol fermentation. Synergistic effects were exhibited in the combinations of organic acids and neutral red to promote butanol production. Consequently, the optimal concentrations of combined acetate, butyrate, and neutral red were determined at sodium acetate 1.61 g/L, sodium butyrate 1.88 g/L, and neutral red 0.79 g/L, respectively, with the butanol yield of 6.09 g/L which was 20.89 % higher than that in control. These results indicated that combination of adding organic acid and neutral red is a potential effective measure to improve butanol production. [ABSTRACT FROM AUTHOR]

In the current study, a new cloud point extraction (CPE) procedure was developed for the separation and preconcentration of inorganic soluble As species, As(III), As(V), and total As in water and beverage samples. Selective ion-pairing complex of As(III) with Neutral red (NRH) being a cationic phenazine-based dye in presence of citric acid at pH 2.0 was extracted into the surfactant-rich phase of octylphenoxypolyethoxyethanol (Triton X-114) from samples. After phase separation, the preconcentrated As(III) was determined by means of spectrophotometer at 542 nm. After optimization of the CPE conditions, a preconcentration factor of 50 and the detection and quantification limits of 1.44 and 4.8 μg L with a correlation coefficient of 0.9953 were obtained from the calibration curve constructed in the range of 5-1500 μg L for As(III). The precision of the method (as RSD) was in the range of 2.2-4.5 % (25, 100, and 750 μg L, N = 5). The As(V) contents of samples were calculated from the difference between As(III) and total As contents after the reduction of As(V) to As(III) with mixture of KI and ascorbic acid at HCl media. The method is very versatile and inexpensive because it exclusively used conventional UV-Vis spectrophotometry. The method was succesfully applied to the simultenous determination of inorganic arsenic species in different water and beverage samples. Its accuracy and precision were controlled by analysis of two certified reference materials (CRMs). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The heterogeneous photo-Fenton like process is a green chemical pathway. It has an edge over conventional Fenton and photo-Fenton processes as it does not require the removal of ferrous/ferric ions in the form of sludge. We prepeared copper pyrovanadate or Volborthite (CuV(OH)O∙2HO) composite photocatalyst by wet chemical method. The photocatalyst was characterized by SEM, XRD, IR, TGA/DSC, EDX and BET. Experiments demonstrated that catalyst could effectively catalyze degradation of neutral red and azure-B in presence of HO in visible light. Moreover, the photo-Fenton-like catalytic activity of CuV(OH)O∙2HO was much higher than CuO and VO, when used alone as photocatalyst. The effect of variation of different parameters, i.e., pH, amount of photocatalyst, concentration of dye, amount of HO and light intensity was also investigated. The degradation was well fitted under pseudo-first-order reaction with a rate constant of 2.081×10 sec and 3.876×10 sec for neutral red and azure-B, respectively. Quality parameters of dye solutions before and after photo-Fenton degradation were also determined. A tentative mechanism involving OH radical as an oxidant has been proposed. The high catalytic activity may be due to the CuV(OH)O∙2HO shell, which not only increased the surface hydroxyl groups, but also enhanced the interfacial electron transfer. The catalyst has been found to possess good recyclability. [ABSTRACT FROM AUTHOR]

A cDNA encoding for a laccase was isolated from the white-rot fungus Lenzites gibbosa by RT-PCR and expressed in the Pichia pastoris. The laccase native signal peptide efficiently directed the secretion of the recombinant laccase in an active form. Factors influencing laccase expression, such as pH, cultivation temperature, copper concentration and methanol concentration, were optimized. The recombinant enzyme was purified to electrophoretic homogeneity, and was estimated to have a MW of ~61.5 kDa. The purified enzyme behaved similarly to the native laccase produced by L. gibbosa and efficiently decolorized Alizarin Red, Neutral Red, Congo Red and Crystal Violet, without the addition of redox mediators. The decolorization capacity of this recombinant enzyme suggests that it could be a useful biocatalyst for the treatment of dye-containing effluents. This study is the first report on the synthetic dye decolorization by a recombinant L. gibbosa laccase. [ABSTRACT FROM AUTHOR]

The presence of pharmaceuticals in the environment is now a major concern given their potential adverse effects on organisms, particularly human beings. Because the feeding style and habitat of the crab Carcinus maenas make this species vulnerable to organic contaminants, it has been used previously in ecotoxicological studies. Lysosomal membrane stability (LMS) in crabs is a general indicator of cellular well-being and can be visualized by the neutral red retention (NRR) assay. LMS in crab hemolymph has been evaluated as a cellular biomarker of adverse effects produced by exposure to pharmaceutical compounds. Crabs were exposed in the laboratory to four different pharmaceuticals for 28 days in a semistatic 24-h renewal assay. Filtered seawater was spiked every 2 days with various concentrations (from 0.1 to 50 μg·L) of caffeine, ibuprofen, carbamazepine, and novobiocin. Results showed that NRR time, measured at day 28, was significantly reduced ( p < 0.05) after exposure to environmental concentrations of each pharmaceutical (caffeine = 15 μg·L; carbamazepine = 1 μg·L; ibuprofen = 5 μg·L; and novobiocin = 0.1 μg·L) when compared with control organisms. The predicted 'no environmental effect' concentration/measured environmental concentration results showed that the selected pharmaceuticals are toxic at environmental concentrations and need further assessment. LMS monitoring in crabs is a sensitive tool for evaluating exposure to concentrations of selected drugs under laboratory conditions and provides a robust tier 1 testing approach (screening biomarker) for rapid assessment of marine pollution and environmental impact assessments for analyzing pharmaceutical contamination in aquatic environments. [ABSTRACT FROM AUTHOR]

In this study, we developed a fiber-optic pH sensor based on a sol-gel film immobilized with neutral red (NR). A solgel film was prepared by mixing tetramethylorthosilicate (TMOS), trimethoxymethylsilane (MTMS), ethanol (EtOH), distilled water (HO), and NR powder. Accordingly, the thin pH sol-gel film was fabricated through a sol-gel process with a dip-coating method. The thickness and diameter of the fabricated pH sol-gel film are 0.11 and 0.6 mm, respectively. We measured the optical absorbance and the light intensity with the spectra of reflected light, which change with the color variation of the pH sol-gel film in the fiber-optic sensing probe. From the experimental results, we demonstrated that the proposed fiber-optic pH sensor has good reversibility, reproducibility, and a fast response time, in which the optical properties of the NR-based pH sol-gel film change with the pH value. [ABSTRACT FROM AUTHOR]

Poly(γ-glutamic acid) (γ-PGA) is a promising biomaterial with a wide range of unique applications. To extensively screen γ-PGA-producing bacteria with high yield and different molecular weight, we developed an integrated high-throughput strategy. Firstly, γ-PGA-producing bacteria were selected in a primary screen plate containing a basic dye (neutral red) based on the concentric zone formed through the electrostatic interaction between the dye and the secreted acidic polymer γ-PGA. Then, the isolates were cultured in 50 ml tubes instead of 250 ml flasks. A good correlation of fermentation results in 50 ml tubes and 250 ml flasks was observed. Thirdly, the γ-PGA yield and weight-average molecular weight ( M) were simultaneously determined by spectrophotomic assay (UV assay) and neutral red plate assay. The results showed that the diameter of the concentric zone varied among isolates and was negatively correlated with the weight-average molecular weight of γ-PGA. The accuracy of the methods was comparable to that of high-performance liquid chromatography and gel permeation chromatography assay. Lastly, γ-PGA obtained from the target isolates was rapidly identified using thin layer chromatography assay. With this strategy, 13 bacteria with high yield and various molecular weights of γ-PGA from 500 obvious single colonies on the primary screen plate were obtained. [ABSTRACT FROM AUTHOR]

Many of organophosphorous insecticides are chiral compounds. In this study, the enantioselective effects of organophosphate insecticide methamidophos on the coelomocytes lysosomal membrane stability of earthworm Eisenia fetida were studied: (1) The enantiomers of methamidophos were absolutely separated by high-performance liquid chromatography with a commercial chiral column; (2) The neutral red retention assay was used to judge the lysosomal membrane stability. The results showed that with the concentration increasing, lysosomal membranes have been significantly destroyed by individual stereoisomers and racemate of methamidophos. The neutral red retention times were significantly descended from 76.88 to 29.78 min. Both (+)- and (−)-methamidophos showed more prone to destroy the integrity of the lysosomal membrane than the racemate. However, the different effect between stereoisomers is slight. [ABSTRACT FROM AUTHOR]

An amperometric hydrogen peroxide biosensor using a nanobiocomposite based on neutral red modified carbon nanotubes and co-immobilized glucose oxidase and horseradish peroxidase is reported. Modification of the nanobiocomposite electrode with neutral red resulted in a sensitive, low-cost and reliable H2O2 sensor. The use of carbon nanotubes, as the conductive part of the composite, facilitated fast electron transfer rates. The biosensor was characterized for the influence of pH, potential and temperature. A remarkable feature of the biosensor is the detection of H2O2 at low applied potentials where the noise level and interferences are minimal. The sensor has a fast steady-state measuring time of 10 s with a quick response (2 s). The biosensor showed a linear range from 15 nM to 45 mM of H2O2 and a detection limit of 5 nM. Nafion, which is used as a binder, makes the determination free from other electroactive substances. The repeatability, reproducibility, stability and analytical performance of the sensor are very good. [ABSTRACT FROM AUTHOR]

A fast and cost effective immobilization of electron carriers, methylene blue (MB) and neutral red (NR) by pH shift was proposed to improve bioanodic performance. The adsorption of mediators onto the carbon cloth anode was verified using cyclic voltammogram (CV) and the effect of the immobilized mediators on acclimation, power density, and acetate removal of MFCs was investigated. A peak power density of P(MB) = 11.3 W/m was achieved over days 110 ∼ 120, as compared to P(Control) = 5.4 W/m and P(NR) = 3.1 W/m for the treated anode after 15 sequential fed-batch operations. The VFA removal rates however were similar for all MFC systems, ranging from 82 to 87%. It could be suggested that the increase in power density for the MB treated electrode resulted from an enhanced electron transport from exo-electrogenic bacteria. MB may also have a selective effect on the bacterial community during the start-up stage, increasing the voltage production and acetate removal from day 1 to 16. However, MFC with NR treated anode produced an initial voltage under 100 mV, with lower coulombic efficiency (CE). NR exhibited less favourable mediator molecule binding to the electrode surface, when subject to pH driven physico-chemical immobilization. [ABSTRACT FROM AUTHOR]

Different models have been proposed to explain the operation of oxygen diffusion barrier in root nodules of leguminous plants. This barrier participates in protection of oxygen-sensitive nitrogenase, the key enzyme in nitrogen fixation, from inactivation. Details concerning structural and biochemical properties of the barrier are still lacking. Here, the properties of pea root nodule cortical cells were examined under normal conditions and after shoot removal. Microscopic observations, including neutral red staining and epifluorescence investigations, showed that the inner and outer nodule parenchyma cells exhibit different patterns of the central vacuole development. In opposition to the inner part, the outer parenchyma cells exhibited vacuolar shrinkage and formed cell wall infoldings. Shoot removal induced vacuolar shrinkage and formation of infoldings in the inner parenchyma and uninfected cells of the symbiotic tissue, as well. It is postulated that cells which possess shrinking vacuoles are sensitive to the external osmotic pressure. The cells can give an additional resistance to oxygen diffusion by release of water to the intercellular spaces. Immunolocalization studies proved higher expression of endo-β-1,4-glucanases within expanding cells of the outer cortex of pea nodules comparing with nodule endodermis or nodule parenchyma, so it is suggested that (1) endo-glucanases are involved in growth related modifications of cell walls and (2) enlarged cells decrease nodule conductance to oxygen. [ABSTRACT FROM AUTHOR]

new approach is described for the photoelectrocatalytic oxidation of Reduced ß-Nicotinamide Adenine Dinucleotide (NADH). It is based on a glassy carbon electrode (GCE) modified with a film of poly-Neutral Red (poly-NR) that is obtained by electropolymerization. Electrochemical measurements revealed that the modified electrode displays electrocatalytic and photo-electrocatalytic activity towards oxidation of NADH. If irradiated with a 250-W halogen lamp, the electrode yields a strongly increased electrocatalytic current compared to the current without irradiation. Amperometric and photo-amperometric detection of NADH was performed at +150 mV vs. Ag/AgCl/KCl and the currents obtained are linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 1.0 μM to 1.0 mM for both methods. However, the slope of the current-NADH concentration curve of the photo-electrocatalytic procedure was 2-times better than that obtained without irradiation. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The inclusion complexation behavior of the dye guest molecule neutral red with three kinds of water-soluble p-sulfonated calix[ n]arene sodium ( n=4,6,8) was investigated. p-Sulfonated calix[4,6,8]arene sodium (pSC4, pSC6, pSC8) can react with neutral red to form inclusion complexes, which were confirmed by UV-vis absorption and fluorescence spectroscopy. Fluorescence spectroscopy experiments were performed in pH=4.6 acetic buffer solutions at 25 °C to calculate the stability constants ( K) for the stoichiometric 1:1 inclusion complexes of pSC4, pSC6 and pSC8 with neutral red. The thermodynamic parameters for the inclusion complexes were determined through a van't Hoff analysis. Formation of the inclusion complexes of pSC4, pSC6 and pSC8 with neutral red was driven by favorable enthalpic changes with their accompanying negative entropy changes. The complex stability constants monotonically increased with the number of phenolic units in the calixarene ring, which was attributed mainly to electrostatic interactions and hydrogen bonding, rather than to the cavity size. [ABSTRACT FROM AUTHOR]

The biodegradation of chlorinated organics in vadose zone soils is challenging owing to the presence of oxygen, which inhibits reductive dehalogenation reactions and consequently the growth of dehalorespiring microbes. In addition, the hydraulic conductivity of vadose zone soils is typically high, hence attempts to remediate such zones with biostimulation solutions are often unsuccessful due to the short residence times for these solutions to act upon the native bacterial community. In this study we have identified sodium alginate as a hydrogel polymer that can be used to increase the residence time of a nutrient solution in an unsaturated sandy soil. Additionally we have identified neutral red as a redox active compound that can catalyse the reductive dechlorination of the chlorinated organic hexachloro-1,3-butadiene by activated sludge fed with lactate and acetate. Finally we have shown that a nutrient solution amended with neutral red and sodium alginate can lower the redox potential and reduce hexachloro-1,3-butadiene concentrations in a contaminated vadose zone soil. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for the synthesis of CdTe quantum dots (QDs) capped with β-cyclodextrin in aqueous solution using both TGA and mono-6-thio-β-CD as stabilizers. The interaction between mono-6-thio-β-CD-CdTe QDs and neutral red (NR) was studied with fluorescence, UV-absorption and the resonance Rayleigh scattering spectrum. When its concentration was over 7.5 × 10−6 mol/L, the neutral red began to aggregate on the surface of the mono-6-thio-β-CD-CdTe QDs, which resulted in the mono-6-thio-β-CD-CdTe QDs particle size increasing, the sharply quenched fluorescence, and the marked increase of RRS intensity. [ABSTRACT FROM AUTHOR]

A single-compartmented microbial fuel cell composed of a graphite felt anode modified with Neutral Red (NR-anode) and a porous Fe(II)-carbon cathode (FeC-cathode) were compared for electricity generation from Microbacterium sp. and Pseudomonas sp. under identical conditions. Pseudomonas sp. was more than four times the size of Microbacterium sp. based on SEM images. In cyclic voltammetry, the redox reaction between Microbacterium sp and electrode was three times the rate observed between Pseudomonas sp. and the electrode based on the Y-axis (current) variation of cyclic voltammogram. The electric power generated by Microbacterium sp. was approx 3–4 times higher than that with Pseudomonas sp. during incubation for more than 150 days in the fuel cell. [ABSTRACT FROM AUTHOR]

The kinetics of the oxidation of neutral red by bromate was investigated in the presence of cationic surfactant (Ndodecylpyridinium chloride) and strongly acidic media over the temperature range 22-35 °C. The kinetic studies were carried out as a function of different variables like concentration and temperature. The described reaction rate is greatly catalyzed by the presence of trace amount of Fe(II) ions and followed by pseudo-third-order kinetics with respect to dye concentration. A possible mechanism for the catalyzed reaction is offered which is found to be coincidentally congruent with experimental findings. The derived rate equation is in good agreement with the experimental observations. Thermodynamic parameters were also evaluated. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNP) were synthesized with NaBH4 as reducing agent and oleate as stabilizer. AgNP and L-cysteine (L-cys) were co-deposited on a gold electrode surface to fabricate the AgNP/L-cys modified electrode (AgNP/L-cys/Au). First, we prepared the L-cysteine self-assembled film modified gold electrode through S-Au bond, then it was rinsed into the Ag colloid solution to prepare the Ag nanoparticles/L-cysteine modified electrode through interaction of the silver surface and the carboxylate and amino groups of L-cysteine. After the self-assembled electrode was prepared, the electrochemical behavior of the modified electrode was investigated. The electrochemical response of neutral red (NR) on the modified electrode was investigated. The electrochemical response of cyclic voltammetry and determination by differential pulse voltammetry of neutral red on the modified electrode were reported. We also observed that the modified electrode catalyzes the redox process of neutral red, which provided another way of applying Ag nanoparticles in composite neutral red-AgNP films. [ABSTRACT FROM AUTHOR]

A second generation glucose biosensor was developed by using neutral red (NR) as a mediator and a bismuth film electrode (BiFE) as a transducer along with immobilized glucose oxidase. The linear range was between 0.2 and 2.5 mM, and a correlation coefficient of 0.999 was obtained with this electrode. The standard deviation (at 1 mM glucose for n = 4) and the coefficient of variation were calculated as ±8.07 µM and 3.4%, respectively. The biosensor was used for the determination of glucose in wine samples. [ABSTRACT FROM AUTHOR]

A crude cell extract from a butane-utilizing bacterium, Alcaligenes sp., catalyzed the oxidation of butane to butanol coupled to NADH. A graphite electrode modified with Neutral Red (NR-electrode) catalyzed the reduction of NAD+ to NADH. About 4.9 mM butanol was produced from 50% n-butane/O2 mixture through the combined reactions of the crude enzyme and the NR-electrode in 250 ml reactor for 3 h. [ABSTRACT FROM AUTHOR]

In this study we have investigated the toxicity of soils from the two abandoned pyrite mines Ertelien and Konnerud in the southern part of Norway. Soil samples were collected close to the pithead of the mines, and earthworms were exposed to different concentrations of the contaminated mine soil mixed with commercial plant soil for a period of 14 days. Life-cycle responses such as growth and survival, as well as the biomarker response lysosomal fragility were measured. The body burdens of the four heavy metals Cu, Cd, Zn and Pb were detected in the worms, and the body concentration of the metals generally increased with increasing heavy metal concentration in the soil. The growth and mortality of the earthworms were not influenced when exposed to any of the mine soil concentrations used. The lysosomal fragility of the earthworm coelomocytes measured by the neutral red retention time (NRR-time) was found to be markedly reduced in all the exposed earthworms. This assay seems to be a sensitive and dose dependent endpoint for the toxicity assessment of heavy metal mixtures in pyrite mine soils. [ABSTRACT FROM AUTHOR]

A fast and sensitive protein staining method in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using both an acidic dye, Coomassie Brilliant Blue R-250 (CBBR) and a basic dye, Neutral Red (NR) is described. It is based on a counter ion-dye staining technique that employs oppositely charged two dyes to form an ion-pair complex. The selective binding of the free dye molecules to proteins in an acidic solution enhances the staining effect of CBBR on protein bands, and also reduces gel background. It is a rapid staining procedure, involving fixing and staining steps with short destaining that are completed in about 1 h. As the result, it showed two to fourfold increase in sensitivity comparing with CBBR staining. The stained protein bands can be visualized at the same time of staining. [ABSTRACT FROM AUTHOR]

Atrial myocytes secrete atrial natriuretic peptide (ANP) in response to mechanical stretch and can serve as a challenging model for studying stretch-secretion coupling. We have developed a technique for monitoring ANP secretion from single atrial myocytes, using neutral red and a CCD video camera. Atrial-specific granules (ASGs) containing ANP were stained with neutral red. The cells were illuminated with monochromatic light (550 mm) and the grey value monitored within the region of interest (ROI) surrounding the region in which ASGs were densely located. Assuming that neutral red is evenly distributed in ASGs, the change in optical density (OD) was considered to represent the total amount of secretion. Under control, non-stimulated conditions, the OD decreased spontaneously (19.7±1.4%/10 min, n=14). Direct mechanical stretch (cell length increased by 20%) with two micropipettes or hypotonic swelling (200 mOsm) accelerated the decrease in OD significantly (48.7±7.4%/10 min; n=3, 47.2±2.4%/10 min; n=7, respectively). In conclusion, this method allows monitoring of ANP secretion with a relatively high time resolution while mechanical stress is applied. Furthermore, patch-clamp or intracellular perfusion techniques can be combined with the present technique for studying cellular mechanisms of stretch-secretion coupling. [ABSTRACT FROM AUTHOR]

Histochemical and ultrastructural studies were carried out on a wild-type strain (Guyll) and a melanin-deficient mutant (büβ) of the rice-blast pathogen, Magnaporthe grisea (= Pyricularia oryzae), in order to investigate the destination of lipid storage reserves during appressorium development. Lipid droplets were abundant in conidia and were mobilised upon germination, accumulating in the appressorial hook which developed at the tip of each germ tube. Following the formation of a septum at the base of the nascent appressorium, one or a few closely appressed central vacuoles became established and were observed to enlarge in the course of appressorium maturation. On unyielding artificial surfaces such as glass or plastic, appressoria matured to completion within 36–48 h, by which time the enlarged vacuole filled most of the inside volume of the appressorium. Light and transmission electron microscopical observations revealed that the lipid droplets entered the vacuole by autophagocytosis and were degraded therein. Histochemical approaches confirmed the vacuole as the key lytic element in maturing appressoria. Endocytosis of a vital dye, Neutral Red, progressed via endosomes which migrated into the vacuole and lysed there, releasing their dye content into the vacuolar lumen. Furthermore, activity of the lysosomal marker enzyme, acid phospho-monoesterase, was strongly localised in the vacuole at all stages of appressorium maturation. It is therefore envisaged that vacuoles are involved in the degradation of lipid storage reserves which may act as sources of energy and/or osmotically active metabolites such as glycerol, which generate the very high turgor pressure known to be crucial for penetration of hard surfaces. On softer surfaces such as onion epidermis, appressoria of M. grisea were able to penetrate before degradation of lipid droplets had been completed. [ABSTRACT FROM AUTHOR]

Violacein, a pigment produced by Chromobacterium violaceum, is reported to be a potential drug for the treatment of Chagas' disease. Violacein is also effective against leukemia and lymphoma cells in culture (IC50 10−8 M). Changes in the nuclear acid content, 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide reduction and neutral red uptake in these cells were used to evaluate the cytotoxicity of violacein in V79 Chinese hamster (M-8) fibroblasts. Violacein was highly cytotoxic to V79 fibroblasts (IC50 5–12 μ M). Using the TUNEL method and the Feulgen reaction coupled to image analysis, violacein (5 and 10 μ M) was found to trigger apoptosis but not necrosis in V79 cells. The morphological changes seen in the nuclei of these cells included chromatin condensation and a decrease in deoxyribonucleic acid content. These results demonstrating that violacein induces apoptosis in V79 cells strengthen its potential as a therapeutic agent. [ABSTRACT FROM AUTHOR]

A new kinetic spectrophotometric method for the determination of hydrazine is described. The method is based on the inhibitory effect of hydrazine on the reaction of neutral red with nitrite in acidic media and 28 °C. A product from the reaction of neutral red with nitrite was used to monitor the reaction spectrophotometrically at 352 nm. Hydrazine can be determined in the range 4.7×10−6∼3.1×10−5mol/L with a detection limit of 3.1×10−6mol/L. The method was applied to the determination of hydrazine in water samples. [ABSTRACT FROM AUTHOR]

In a new, simple, and fast flow-cytometric method for the simultaneous measurement of phagocytic activity of human neutrophils and monocytes in whole blood, the fluorescence capability of the well-known vital stain, neutral red was used. The incubation of 0.5 ml heparinized human blood with the phagocytic stimulus of zymosan dose- and time-dependently increased the percentage and the red fluorescence intensity of both neutrophils (4.3 +/- 1.2 times) and monocytes (2.7 +/- 0.7 times) measured cytofluorimetrically. Decreased uptake of neutral red was observed in a patient with phagocytic disorder, based upon impaired engulfment of particles and production of reactive oxygen species. In a patient with chronic granulomatosis, however, no decrease of neutral red uptake was measured. Platelet activating factor and phorbol myristate acetate were also able to increase the uptake of neutral red by both monocytes and neutrophils, but to a lesser extent than zymosan. The advantage of this method is the possibility for the simultaneous measurement of phagocytic activities of monocytes and neutrophils stimulated by either particles or soluble activators. This method is suitable for the selective measurement of activation processes not related to the production of free radicals in the phagocytes. [ABSTRACT FROM AUTHOR]

A simple photometric method for estimating viable cell number in culture is described. When cultured cells are allowed to internalize 0.005-0.01% neutral red for 1 h, the amount of accumulated dye is directly proportional to cell number. The linear relationship holds for adherent and suspended cell lines. Thus, dye content reflects cell number. Since dye content is easily measured by instruments that photometrically scan microtiter trays, proliferative and survival (cytotoxic) responses can be easily quantitated. [ABSTRACT FROM AUTHOR]

Acidic inorganic phosphate (Pi) pool (pH around 6) was detected besides the cytoplasmic pool in intact cells of Chlorella vulgaris 11h by P-in vivo nuclear magnetic resonance (NMR) spectroscopy. It was characterized as acidic compartments (vacuoles) in combination with the cytochemical technique; staining the cells with neutral red and chloroquine which are known as basic reagents specifically accumulated in acidic compartments. Under various conditions, the results obtained with the cytochemical methods were well correlated with those obtained from in vivo NMR spectra; the vacuoles were well developed in the cells at the stationary growth phase where the acidic Pi signal was detected. In contrast, cells at the logarithmic phase in which no acidic Pi signal was detected contained only smaller vesicles that accumulated these basic reagents. No acidic compartment was detected by both cytochemical technique and P-NMR spectroscopy when the cells were treated with NHOH. The vacuolar pH was lowered by the anaerobic treatment of the cells in the presence of glucose, while it was not affected by the external pH during the preincubation ranging from 3 to 10. Possible vacuolar functions in unicellular algae especially with respect to intracellular pH regulation are discussed. [ABSTRACT FROM AUTHOR]

The surface potential, ψ in mV, was determined for the following polyelectrolytes and co-polyelectrolytes in aqueous solution: sodium poly(styrene sulfonate); sodium poly(vinyl sulfonate); poly(vinyl alcohol-co-55% sodium vinyl sulfate); poly(methylmethacrylate-co-40% sodium styrene sulfonate); poly (methylmethacrylate-co-60% sodium styrene sulfonate); poly(styrene-co-56% styrene sulfonate); and poly(styrene-co-80% styrene sulfonate). For comparison, the surface potentials of aqueous sodium dodecyl sulfate and sodium dodecylbenzene sulfonate micelles were also determined. The dyes neutral red and safranine-T were used as indicators. The pKa of the former was calculated from the Henderson-Hasselbach equation, using UV-VIS spectroscopy to determine the concentration of protonated ground state as a function of pH. The surface potential of the aggregates was culculated from the equation: where pKa and pKa refer to the indicator pKa in the presence of charged and nonionic interfaces, respectively, and the other terms have their usual meaning. The protonation kinetics of the triplet state of safranine-T (measured from the decay of its transient absorption at 830 nm) was used to determine hydronium ion concentrations at aggregate interfaces, and the corresponding surface potentials were calculated from: where a and a refer to the hydronium ion activity at the aggregate interface, and in bulk water, respectively. Surface potentials determined by both techniques were in excellent agreement. Values of ψ were found to depend on the structure of the polyelectrolyte, sodium poly(styrene sulfonate) versus sodium poly(vinyl sulfonate) and, for the same type of co-polyelectrolyte, on the percentage of charged monomer. [ABSTRACT FROM AUTHOR]