Toxicity responses of different organs of zebrafish (Danio rerio) to silver nanoparticles with different particle sizes and surface coatings

Cellular accumulation and cytotoxic effects of zinc oxide nanoparticles in microalga Haematococcus pluvialis

Background

Zinc oxide nanoparticles (ZnO NPs) are widely used in household and cosmetic products which imply an increased releasing of these particles into the environment, especially aquatic ecosystems, resulting in the need of assessing the potential toxic effects of ZnO NPS on the aquatic organisms, particularly on microalgae which form the base for food chain of aquatic biota. The present study has investigated the dose- and time-dependent cellular accumulation and the corresponding cytotoxic effects of increasing concentrations of ZnO NPs from 10–200 μg/mL on microalga Haematococcus pluvialis at an interval of 24 h for 96 h.

Methods

The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) was used to qualitatively detect the cellular accumulation of ZnO NPs in algal cells, while inductively coupled plasma optical emission spectrometry (ICP OES) was performed to quantify the cell associated-zinc in algal cells. The percentage of cell death, reduction in algal biomass, and loss in photosynthetic pigments were measured to investigate the cytotoxic effects of ZnO NPs on H. pluvialis. Extracellular and intracellular changes in algal cells resulted from the treatment of ZnO NPs were demonstrated through optical, scanning, and transmission electron microscopic studies.

Results

SEM-EDX spectrum evidenced the accumulation of ZnO NPs in algal biomass and ICP OES results reported a significant (p < 0.05) dose- and time-dependent accumulation of zinc in algal cells from 24 h for all the tested concentrations of ZnO NPs (10–200 μg/mL). Further, the study showed a significant (p < 0.05) dose- and time-dependent growth inhibition of H. pluvialis from 72 h at 10–200 μg/mL of ZnO NPs. The morphological examinations revealed substantial surface and intracellular damages in algal cells due to the treatment of ZnO NPs.

Discussion

The present study reported the significant cellular accumulation of ZnO NPs in algal cells and the corresponding cytotoxic effects of ZnO NPs on H. pluvialis through the considerable reduction in algal cell viability, biomass, and photosynthetic pigments together with surface and intracellular damages.

The effects of graphene oxide on nitrification and N2O emission: Dose and exposure time dependent

With the extensive application of graphene oxide (GO), its leakage and release into wastewater treatment plants become inevitable. However, the toxicity of graphene oxide (GO) on nitrification process and the underlying mechanisms still remain unclear. In this study, the toxic effects of GO at concentration of 10 and 100 mg/L in 4 h and 10 days were evaluated with sealed reactors operated in sequencing batch mode. In the initial 4 h, both GO concentrations showed no negative effect on nitrogen conversion. However, the exposure to 100 mg/L GO significantly weakened the NH+ 4-N and NO- 2-N conversion capabilities and intensified the nitrous oxide (N₂O) generation after 10 days. Extracellular polymeric substance (EPS) analysis suggested that 100 mg/L GO decreased the protein content of the nitrifying activated sludge. Moreover, reactive oxygen species (ROS) level was promoted by 100 mg/L GO owing to the impaired endogenous antioxidant enzymes including superoxide dismutase (SOD) and catalase (CAT), which caused oxidative stress to bacteria. Finally, quantitative PCR results confirmed that nitrite-oxidizing bacteria (NOB) and complete ammonia oxidizing bacteria (CAOB) were more sensitive to GO, which was the primary cause for the significant promotion of N₂O generation in the high GO concentration. This study offered new insights in the toxicity of GO on nitrification and N₂O generation in the terms of dose and exposure time.

Mechanism of toxic effects of Nano-ZnO on cell cycle of zebrafish (Danio rerio)

The release of nano-zinc oxide (nano-ZnO) into the environment may lead to unpredictable risks, thus it is necessary to study its potential harm to organisms. In this study, zebrafish exposed to nano-ZnO were analyzed through cDNA microarrays to provide insight into the toxic effect of nano-ZnO on aquatic organisms at the molecular level. Results found that nano-ZnO inhibited the normal growth and development of zebrafish and other life activities by affecting the process of cell cycle. The nano-ZnO inhibited the expression of the cyclins (Cycs), cyclin-dependent kinases (CDK) and the minichromosome maintenance (MCM), making the activation of Cyc/CDK complexs (CycD/CDK4, 6; CycE/CDK2; CycA/CDK2) and MCM fail and resulting in DNA replication disorder in different periods (G1, M and G2 phase). Therefore, the normal activities of individual organism such as cell division, differentiation and proliferation and the functions of DNA binding and intracellular transfer were disturbed. These findings contribute to our understanding of the toxicity of ZnO NPs to aquatic organisms, and also provide an evaluation basis for assessing the environmental impact of nano materials.

One-step separation of the recombinant protein by using the amine-functionalized magnetic mesoporous silica nanoparticles; an efficient and facile approach

The separation process is the main stage of recombinant production. With the advancement of nanotechnology and the development of magnetic nanoparticles, these structures are increasingly used in different applications. In the present study, we produced the recombinant human growth hormone from Pichia pastoris and for protein separation provided the surfaces similar to chromatographic columns on the surface of magnetic nanoparticles. For this purpose, using a co-precipitation method, the core of Fe₃O₄ was prepared and coated by silica. To increase the protein availability, silica mesoporous formation and its amine functionalization were performed. The specific surface area and the pore size were determined 78.3189 m²/g and 7.44 nm. After the magnetic separation, the sample loading in SDS gel shows a reduction in protein band and the protein absorption at a wavelength of 280 nm. Finally, we evaluate the ability of amine functionalized nanoparticles for protein separation that demonstrate the adsorption capacity significantly increased compare with silica-coated nanoparticles. The amine functionalized nanoparticles provide the maximum adsorption capacity of 235.21 μg/mg and after the elution, protein concentration determined 476 mg/L. This work indicates the functionalized magnetic mesoporous silica nanoparticles can be used as the best candidate for the separation of different biological macromolecules.

Enhanced of antibacterial activity of antibiotic-functionalized silver nanocomposites with good biocompatibility

Antimicrobial resistance to traditional antibiotics leads to a serious concern for medical care owing to ineffective antibiotic therapies. This study focused on the preparation of silver nanocomposites (AgNPs@Tob&PAGA) by modifying AgNPs with tobramycin (Tob) and carbohydrate polymer of poly(2-(acrylamido) glucopyranose) (PAGA). The enhanced antibacterial activities of nanocomposites against common pathogens of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were explored. The introduction of PAGA onto silver nanocomposites improved both citocompatibility and antibacterial activity. Compared with nude Tob, AgNPs@Tob&PAGA showed more fascinating antimicrobial effect against E. coli and S. aureus with about 20-fold increase in the antibacterial activity, simultaneously no detectable resistance was observed. Consequently, the silver nanocomposite as an antimicrobial agent presents promising prospects in the treatment of bacterial infections caused by antimicrobial resistant bacteria.