Elemental selenium particles at nano-size (Nano-Se) are more toxic to Medaka (Oryzias latipes) as a consequence of hyper-accumulation of selenium: A comparison with sodium selenite Recent studies have shown that elemental selenium particles at nano-size (Nano-Se) exhibited comparable bioavailability and less toxicity in mice and rats when compared to sodium selenite, selenomethinine and methylselenocysteine. However, little is known about the toxicity profile of Nano-Se in aquatic animals. In the present study, toxicities of Nano-Se and selenite in selenium-sufficient Medaka fish were compared. Selenium bioaccumulation and subsequent clearance in fish livers, gills, muscles and whole bodies were examined after 10 days of exposure to Nano-Se and selenite (100 g Se/L) and again after 7 days of depuration. Both forms of selenium exposure effectively increased selenium concentrations in the investigated tissues. Surprisingly, Nano-Se was found to be more hyper-accumulated in the liver compared to selenite with differences as high as sixfold. Selenium clearance of both Nano-Se and selenite occurred at similar ratios in whole bodies and muscles but was not rapidly cleared from livers and gills. Nano-Se exhibited strong toxicity for Medaka with an approximately fivefold difference in terms of LC 50 compared to selenite. Nano-Se also caused larger effects on oxidative stress, most likely due to more hyper-accumulation of selenium in liver. The present study suggests that toxicity of nanoparticles can largely vary between different species and concludes that the evaluation of nanotoxicology should be carried out on a case-by-case basis.

Two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4MIM]Cl) and 1-octyl-3-methylimidazolium chloride ([C8MIM]Cl), are demonstrated to associate strongly with dissolved organic matter (DOM) with distribution coefficients (KDOC) in the range of 10(4.2) to 10(4.6) for Aldrich humic acid (used as model DOM). With the increase of humic acid concentration to 11 μg/mL DOC (dissolved organic carbon), the free fraction (ratio of freely dissolved to total concentration) of [C4MIM]Cl and [C8MIM]Cl reduced to about 0.85 and 0.79, respectively. This reduction of freely dissolved concentration gave rise to remarkable reduction of bioavailability and toxicity of the two ILs. MTT assay with HepG2 cell lines showed that the EC50 values were 459 μmol/L for [C4MIM]Cl and 12 μmol/L for [C8MIM]Cl, respectively, and the cell viability increased about 50% in the presence of trace amount of humic acid (1 μg/mL DOC). The SOS/umu test indicated mutagenicity for [C4MIM]Cl at levels above 664 μmol/L, and the genotoxicity was diminished with the addition of trace humic acid (0.00000374-0.374 μg/mL DOC). The studied ILs showed acute toxicity toward model fish medaka with a 96 h median lethal concentration (LC50) of 2254 μmol/L for [C4MIM]Cl and 366 μmol/L for [C8MIM]Cl. The addition of humic acid (5.49 μg/mL DOC for [C8MIM]Cl, 1.37 μg/mL DOC for [C4MIM]Cl) to IL solutions reduced the death rate of medaka to a minimum value of ∼25% of that at zero DOC. Our results suggest that DOM may play an important role in determining the environmental fate and toxicity of imidazolium-based ILs, and its effects should be taken into account in assessing the environmental risk of ILs.

Nucleic acid electrophoresis separation heavily depends upon gel or nongel sieving matrix. Here we propose a metal ion mediated-capillary electrophoresis (MCE-CE) by utilizing the nonspecific interactions of Mg 2+ and Ca 2+ and demonstrate the size, conformation, or sequence based separation and characterization of versatile nucleic acid molecules in free solution. Mg 2+ and Ca 2+ can induce DNA separation at the concentrations as low as 100 and 50 µM, respectively. Noteworthy, the two naturally occurring polymorphisms of one base substitution that may change the secondary folding structure or base stacking can be discriminated by MCM-CE, showing its unique capability of resolving length-identical but conformation-different ssDNA. Benefiting from the achieved separation, we further demonstrate that the folding conformation of oligomers and its change caused by single base substitution can be promptly sensed by online coupled fluorescence polarization. We anticipate that this method will be applicable in length polymorphism analysis, singlestrand polymorphism analysis, hybridization analysis, microRNA analysis, and study of protein-nucleic acid interactions and the conformation-function relationship.Beyond the well-known coding of inheritable information by the primary structure of nucleic acids, recent landmark discoveries reveal that versatile nucleic acid molecules function as regulation of gene expression (RNA interference, microRNA, riboswitch, DNA methylation), recognition of specific substrates (aptamer), and/or catalysis (DNAzyme, ribozyme, aptazyme), which may be underlined by their secondary or tertiary structures. 1 Although sieving matrix-dependent capillary electrophoresis can provide high throughput and accurate sequencing for the primary structure and methylation of DNA now, 2-5 there is a lack of an efficient separation means to identify and characterize complex secondary and tertiary structures of nucleic acids in free solution. In traditional electrophoresis (as gel or nongel sieving electrophoresis), nucleic acid molecules are often required to interact with the polymer based sieving matrix, 6,7 which may interfere with their native conformations. Free solution capillary electrophoresis is ideal for conformational separation and analysis because of the preservation of native conformations of nucleic acids. Although nucleic acids are negatively charged, the separation of oligonucleotides in free solution was only observed up to 10 bases because of the well-known small difference in electrophoretic mobility for nucleic acids as the base number increases. [8][9][10][11] The sizeseparation may be achieved through the modification of DNA by a neutral drag-tag polymer 12 or DNA binding proteins. 13,14 With the use of a buffer system containing zinc and sodium dodecyl sulfate (SDS) micelle, it is possible to separate 14 out of 18 oligonucleotides of 8 bases. 8 The specific interactions of metal ions and oligonucleotides (e.g., K + and G-quadruplex and Ni 2+ and guanosine) were also used to separate...