Letter to the editors

Toxicity of light-exposed Hepes media

Urine is a nutrient rich stream; it accounts for 70% of the nitrogen load and 40% of the phosphorus load present in domestic wastewater while in volume it only represents 1%. Given the high concentrations of nitrogen (5–7 g N∙L⁻¹) and phosphorus (0.2–0.3 g P∙L⁻¹) in urine, it is more efficient to recover these nutrients from this concentrated stream than from domestic wastewater where they are more diluted. These nutrients can be recovered in form of biomass that could be a source of biobased compounds or could also be used as soil amendment or fertilizer. In this study, the model cyanobacterium Synechocystis sp. PCC6803 was cultivated on synthetic and real, source-separated human urine with different pretreatments to determine if real urine inhibits cyanobacterial growth. Additionally, the nutrient content of urine, including trace elements, was assessed to determine if these are sufficient to support growth to the biomass concentration needed for complete nitrogen and phosphorus recovery. Cultivation of Synechocystis sp. PCC6803 on source separated urine recovered up to 87% of the nitrogen and 99% of the phosphorus in form of biomass, reaching N:P ratios up to 43:1. The biomass reached similar specific growth rates on synthetic urine and source-separated urine demonstrating that there are no negative effects of real urine on growth of Synechocystis sp. PCC6803. Supplementing urine with sulfate, magnesium, iron and trace elements is necessary for balanced growth of Synechocystis sp. PCC6803 and high nutrient recovery.

The determination of reaction rates for the photocatalytic oxidation (PCO) of arsenite (As(III)) using TiO₂ under UV radiation is challenging due to the numerous experimental processes. This includes chemical processes running simultaneously with PCO (e.g. adsorption of arsenic species, direct UV photolysis of As(III)) and the analytical approach used (e.g. whether As(III) or As(V) are measured and used in the calculation of the PCO rate). The various experimental approaches used to date have led to oxidation rates and rate constants which vary by orders of magnitude and contradicting information on rate laws. Here we present the results of a critical examination of possible controls affecting the experimental determination of PCO rates. First, we demonstrate that the choice of analytical technique is not critical, provided that the rate constants are calculated based on the depletion of As(III) after correction of the directly adsorbed As(III). Second, we show the correction of the directly adsorbed As(III) at each time interval is best done by running two parallel experiments (one under UV and the other in dark) instead of running sequential experiment (i.e. running the experiment in the dark then turning on the UV lamp). These findings are supported by XPS analysis of the oxidation state of TiO₂-sorbed As. Third, we demonstrate that photolysis by the light source itself, as well as the chemical composition of the solution (i.e. the effect of HEPES and the ionic strength), can significantly increase As(III) oxidation rates and need to be corrected. Finally, to determine the quantum yield of As(III) oxidation, we measured the photon absorption by the TiO₂ photocatalyst. Our results showed that the quantum yield (Ø) for this oxidation reaction was low, and in the region of 0.1 to 0.2 %.

One diagnosis of cystic fibrosis involves measuring the nasal transepithelial potential difference (NPD) as a complementary technique in the forms of the disease, where the sweat test is non-discriminating. The NPD is measured using solutions with and without chlorides, containing a variety of substances whose activities on nasal mucus membranes are studied or assessed. Among the solutions described in the literature and used in specialized centers, none seems to be best adapted for industrial production for reasons of stability (formulas of the international consensus of Rowe et al. and formulas of Knowles et al.) and/or potential toxicity (formulas of Middleton et al.).

Defining new formulas, according to those of the international consensus, with greater physicochemical and microbiological stability.

The reformulation tests were conducted on the formulas of Rowe et al., using CHESS® (CHemical Equilibrium of Species and Surfaces) software for modeling aqueous systems that substantially reduced the number of experiments. CHESS® software was first validated using models of ideal and non-ideal solutions. Thereafter, experimentation was carried out for the sake of comparison with theoretical data.

CHESS® software using models of ideal and non-ideal solutions were validated. The experimentation confirmed the theoretical data, and new formulas were assessed based on their physicochemical (pH, content, Osmolality) and microbiological stability.

The new formulas defined here guarantee excellent physicochemical and microbiological stability of diagnostic solutions, indispensable criteria for harmonizing and comparing results from different specialized centers using NPD measurements. These new formulas apply to the harmonization approach of techniques for measuring the nasal transepithelial potential difference.

La mesure de la différence de potentiel transépithélial nasal (DPN) est une méthode de diagnostic de la mucoviscidose dans les formes frustes, où le test de la sueur est non-discriminant. La DPN est mesurée à l’aide de solutions avec et sans chlorures, contenant une variété de substances dont les activités sur les muqueuses nasales sont étudiées. Des solutions décrites dans la littérature et utilisées dans les centres spécialisés, aucune ne semble adaptée à une production industrielle pour des raisons de stabilité et/ou de toxicité potentielle.

Définition de nouvelles formules, proches de celles du consensus international, avec une plus grande stabilité physico-chimique et microbiologique.

Les tests de reformulation ont été menés sur les formules de Rowe et al., utilisant le logiciel CHESS® (CHemical Equilibrium of Species and Surfaces) pour modéliser des systèmes aqueux. CHESS® a d’abord été validé à l’aide de modèles de solutions idéales et non idéales. Par la suite, une expérimentation a été menée à des fins de comparaison avec des données théoriques.

Les simulations des modèles de solutions idéales et non idéales ont été validées avec CHESS®. L’expérimentation a confirmé les données théoriques et de nouvelles formules ont été évaluées sur la base de leur stabilité physico-chimique (pH, teneur, osmolalité) et microbiologique.

Les nouvelles formules définies dans ce travail garantissent une excellente stabilité physico-chimique et microbiologique des solutions de diagnostic, critères indispensables pour harmoniser et comparer les résultats de différents centres spécialisés utilisant des mesures de DPN. Ces nouvelles formules s’inscrivent dans la démarche d’harmonisation des techniques de mesure de DPN.

Hydrogen peroxide (H₂O₂) is a reactive oxygen species (ROS) that mediates essential signaling in vivo but may cause irreversible tissue damage under dysregulated or acute exposure conditions. Beverages containing redox-active compounds might produce H₂O₂ during shelf storage and potentially be consumed. Concentrations of H₂O₂ in selected ‘functional’ (including energy, E, n = 28), ‘non-functional’ flavored, (S, n = 6) and mineral water (W, n = 6) drinks were measured under ambient (i.e., produced in situ) and ‘potentiated’ conditions (i.e., H₂O₂ production enhanced by addition of a reducing agent, to simulate availability of reducible substrates in vivo). Under air-saturated conditions, mean H₂O₂ contents were: 15.60 ± 15.84; 1.39 ± 2.06 and 0.30 ± 0.21 µM in E, S and W drinks, respectively. Under air-saturated, potentiated conditions, mean rates of H₂O₂ production were 21.7 ± 33.3, 0.98 ± 2.84, and −0.38 ± 1.18 µM/h for E, S and W drinks, respectively. Using multivariate statistics, the ingredient significantly associated with H₂O₂ production in combination with other ingredients was found to be ascorbic acid.

We report a very simple, green, and eco-friendly route to synthesize three-dimensional branched gold nanoflowers (AuNFs). The process involved reduction of gold salt in presence of two naturally occurring small biomolecules viz. l-tyrosine and sodium citrate which act as mild reducing and shape-directing agent. A detailed picture of the formation mechanism of AuNFs has been proposed after thorough experimental analysis (electron microscopy, X-ray photoelectron spectroscopy [XPS], circular dichroism [CD], UV-vis spectroscopy, dynamic light scattering [DLS] and nanoparticle tracking analysis [NTA]) as well as by theoretical simulations (cellular automata and diffusion-limited aggregation [DLA] simulations). Experimental analysis and numerical simulation pointed out that l-tyrosine molecules self-assemble in a complex way which controls the flower-like shape and structure, whereas trisodium citrate plays a crucial role in controlling the particle diameter. A second shape (quasi-spherical) could also be obtained with same formulation by just changing the sequence of addition of reactants. As such the effect of the shape on surface enhanced Raman spectroscopy [SERS] enhancement has also been evaluated. Finally, in vitro studies were performed on a model cell line of mouse brain endothelium (bEnd.3) to assess biocompatibility.

Typically, live cell analyses are performed outside an incubator in an ambient air, where the lack of sufficient CO₂ supply results in a fast change of pH and the high evaporation causes concentration drifts in the culture medium. That limits the experiment time for tens of minutes. In many applications, e.g. in neurotoxicity studies, a prolonged measurement of extracellular activity is, however, essential.

We demonstrate a simple cell culture chamber that enables stable culture conditions during prolonged extracellular recordings on a microelectrode array (MEA) outside an incubator. The proposed chamber consists of a gas permeable silicone structure that enables gas transfer into the chamber.

We show that the culture chamber supports the growth of the human embryonic stem cell (hESC)-derived neurons both inside and outside an incubator. The structure provides very low evaporation, stable pH and osmolarity, and maintains strong signaling of hESC-derived neuronal networks over three-day MEA experiments.

Existing systems are typically complex including continuous perfusion of medium or relatively large amount of gas to supply. The proposed chamber requires only a supply of very low flow rate (1.5 ml/min) of non-humidified 5% CO₂ gas. Utilizing dry gas supply makes the proposed chamber simple to use.

Using the proposed culture structure on top of MEA, we can maintain hESC-derived neural networks over three days outside an incubator. Technically, the structure requires very low flow rate of dry gas supporting, however, low evaporation and maintaining the pH of the culture.