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Graphene-oxide (GO) membranes with notable ionic-sieving properties have attracted significant attention for many applications. However, the swelling and unstable nanostructure of GO laminates in water results in enlarged interlayer spacing and a low permeation cut-off, limiting their applicability for water purification and desalination. Herein, we propose novel nitrogen-doped graphene (NG) membranes for use in tunable ion sieving that are made via facile fabrication by a time-dependent N-doping technique. Doping reaction time associated variation in atomic content and bonding configurations strongly contributed to the nanostructure of NG laminates by yielding narrower interlayer spacing and a more-polarized surface than GO. These nanostructural features subsequently allowed ion transport through the combined mechanisms of size exclusion and electrostatic interaction. The stacked NG membranes provided size-dependent permeability for hydrated ions and improved ion selectivity by 1-3 orders of magnitude in comparison to that of a GO membrane. For ions small enough to move through the interlayer spacing, the ion permeation is determined by electrostatic properties of NG membranes with the type of N configuration, especially polarized pyridinic N. Due to these properties, the NG membrane functioned as an unconventionally selective graphene-based membrane with better ion sieving for water purification.

This study investigated the physicochemical interactions between a rhamnolipid biosurfactant and a biofilm layer. A concentration of 300 μg mL(-1) of rhamnolipids, which is around the critical micelle concentration value (240 μg mL(-1)), showed great potential for reducing biofilm. The surface free energy between the rhamnolipids and biofilm layer decreased, as did the negative surface charge, due to the removal of negatively charged humic-like, protein-like, and fulvic acid-like substances. The carbohydrate and protein concentrations composed of extracellular polymeric substances decreased by 31.6% and 79.6%, respectively, at a rhamnolipid concentration of 300 μg mL(-1). In particular, rhamnolipids can interact with proteins, leading to a reduction of the N source and amide groups on the membrane. For carbohydrates, the component ratio of glucosamine was decreased, but the levels of glucose and mannose that form the majority of the carbohydrates remained unchanged. To our knowledge, the present study is the first attempt at studying the interactions of the two phases of rhamnolipids and the biofilm layer, and as such is expected to clarify the mechanism by which rhamnolipids lead to a reduction in biofilm.

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Due to the increased occurrence of cyanobacterial blooms and their toxins in drinking water sources, effective management based on a sensitive and rapid analytical method is in high demand for security of safe water sources and environmental human health. Here, a competitive fluorescence immunoassay of microcystin-LR (MCYST-LR) is developed in an attempt to improve the sensitivity, analysis time, and ease-of-manipulation of analysis. To serve this aim, a bead-based suspension assay was introduced based on two major sensing elements: an antibody-conjugated quantum dot (QD) detection probe and an antigen-immobilized magnetic bead (MB) competitor. The assay was composed of three steps: the competitive immunological reaction of QD detection probes against analytes and MB competitors, magnetic separation and washing, and the optical signal generation of QDs. The fluorescence intensity was found to be inversely proportional to the MCYST-LR concentration. Under optimized conditions, the proposed assay performed well for the identification and quantitative analysis of MCYST-LR (within 30 min in the range of 0.42-25 μg/L, with a limit of detection of 0.03 μg/L). It is thus expected that this enhanced assay can contribute both to the sensitive and rapid diagnosis of cyanotoxin risk in drinking water and effective management procedures.

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The presence of cyanobacterial hepatotoxins such as microcystin-LR poses health threats to humans due to their potential for causing severe physiological effects when contaminated drinking water is ingested. Here, the electrochemical detection of microcystin-LR is explored using a quantum dot/antibody (QD/Ab) probe for nanoparticle-based amplification and direct electrochemical transduction. The immunological recognition of microcystin-LR using the QD/Ab probe was amplified and converted to an electrochemical signal by measuring the cadmium ions released from QD based on square wave stripping voltammetry under optimized electrochemical factors. Whereas a qualitative analysis for microcystin-LR was achieved using the specific peak potential of the anodic voltammogram at -0.6 +/- 0.05 V, concentration of the toxin was quantified based on the charge density of the anodic peak; a dynamic range of 0.227 to 50 microg/L and limit of detection of 0.099 microg/L were obtained with high sensitivity. The extracted microcystin-LR from Microcystis aeruginosa was estimated as 1,944 microg/g of dried weight of the microorganism.