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Abstract We report the exfoliation process optimization, physicochemical characterizations, and comparative aggregation behavior of the inorganic 2D nanomaterial hexagonal Boron Nitride (h-BN) produced from two repetitive sonication-centrifugation processes with varying centrifugation speeds and recycle frequency: Continuous and Segmented protocols. Enhancing exfoliation efficiency and understanding aqueous stability are essential for sustainable design and environmental applications. Results showed that the Segmented protocol outperformed the Continuous protocol by having a six-fold increase in the exfoliated h-BN nanosheet yield by reusing the unexfoliated bulk h-BN and decreasing centrifugation speeds. Centrifugation speeds of 1880 and 950 rpm produced nanosheets of similar sizes due to the slight difference in the centrifugal force generated in both protocols. Moreover, nanosheets from both protocols had enhanced polarity due to the higher amounts of −OH bonds attached to the exposed edges of the nanosheets. However, the hydroxylation percentage of the nanosheets decreased with centrifugation speed. Both protocols produced h-BN nanosheets that were stable in DI water dispersion. The comparatively lower initial aggregation rate at all centrifugation speeds supported the fact that the Segmented protocol nanosheets were more stable than the Continuous ones. The Segmented protocol h-BN nanosheets showed better overall stability at lower speeds than the other centrifugation speeds. Segmented protocol nanosheets from 3750 rpm had the lowest aggregation rate than the other centrifugation speed. These findings assist in finding the balance between exfoliation protocol, environmental application, and implication of h-BN nanosheets. 

Nitrogen fertilizer delivery inefficiencies limit crop productivity and contribute to environmental pollution. Herein, we developed Zn- and Fe-doped hydroxyapatite nanomaterials (ZnHAU, FeHAU) loaded with urea (∼26% N) through hydrogen bonding and metal-ligand interactions. The nanomaterials attach to the leaf epidermal cuticle and localize in the apoplast of leaf epidermal cells, triggering a slow N release at acidic conditions (pH 5.8) that promote wheat (Triticum aestivum) growth and increased N uptake compared to conventional urea fertilizers. ZnHAU and FeHAU exhibited prolonged N release compared to urea in model plant apoplast fluid pH in vitro (up to 2 days) and in leaf membranes in plants (up to 10 days) with a high N retention (32% to 53%) under simulated high rainfall events (50 mm). Foliar N delivery doses of up to 4% as ZnHAU and FeHAU did not induce toxicity in plant cells. The foliar-applied ZnHAU and FeHAU enhanced fresh and dry biomass by ∼214% and ∼161%, and N uptake by ∼108% compared to foliar-applied urea under low soil N conditions in greenhouse experiments. Controlled N release by leaf-attached nanomaterials improves N delivery and use efficiency in crop plants, creating nanofertilizers with reduced environmental impact. 

The removal of small molecular weight charged compounds from aqueous solutions using membrane remains a challenge. In this study, polysulfone (PSf)- and sulfonated polyether ether ketone (SPEEK)-based membranes were fabricated via non-solvent induced phase separation process (NIPS) using N-Methyl-2-Pyrrolidone (NMP) as solvent and water as non-solvent. Membranes were characterized structurally and morphologically, followed by toxicity assessment conducted before and after filtration, both with and without annealing at various pH values to evaluate potential leaching of trapped solvent from the membrane pores. Additionally, membrane performance was characterized using binary mixtures of cationic and anionic dyes. The results demonstrated selective filtration behavior, with cationic dyes being preferentially rejected due to size exclusion and electrostatic interactions. Additionally, a key focus of this work was the investigation of solvent leaching, framed within a Safe(r)-by-Design (SbD) approach aimed at enhancing functional performance while minimizing environmental toxicity. Toxicity assessments using a model organism, a nematode Caenorhabditis elegans, revealed that annealing reduced solvent leaching and thus permeate toxicity, particularly at neutral pH values, by facilitating trapped solvent release prior to membrane use. These findings provide insights for the importance of including an SbD approach during membrane casting to fabricate membranes with desirable properties while minimizing toxicity. 

Multigenerational and transgenerational reproductive toxicity in a model nematode Caenorhabditis elegans has been shown previously after exposure to silver nanoparticles (Ag-NPs) and silver ions (AgNO3). However, there is a limited understanding on the transfer mechanism of the increased reproductive sensitivity to subsequent generations. This study examines changes in DNA methylation at epigenetic mark N6-methyl-2′-deoxyadenosine (6mdA) after multigenerational exposure of C. elegans to pristine and transformed-via-sulfidation Ag-NPs and AgNO3. Levels of 6mdA were measured as 6mdA/dA ratios prior to C. elegans exposure (F0) after two generations of exposure (F2) and two generations of rescue (F4) using high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS). Although both AgNO3 and Ag-NPs induced multigenerational reproductive toxicity, only AgNO3 exposure caused a significant increase in global 6mdA levels after exposures (F2). However, after two generations of rescue (F4), the 6mdA levels in AgNO3 treatment returned to F0 levels, suggesting other epigenetic modifications may be also involved. No significant changes in global DNA methylation levels were observed after exposure to pristine and sulfidized sAg-NPs. This study demonstrates the involvement of an epigenetic mark in AgNO3 reproductive toxicity and suggests that AgNO3 and Ag-NPs may have different toxicity mechanisms. 

Biosensors often combine biological recognition elements with nanomaterials of varying compositions and dimensions to facilitate or enhance the operating mechanism of the device. While incorporating nanomaterials is beneficial to developing high-performance biosensors, at the stages of scale-up and disposal, it may lead to the unmanaged release of toxic nanomaterials. Here we attempt to foster connections between the domains of biosensors development and human and environmental toxicology to encourage a holistic approach to the development and scale-up of biosensors. We begin by exploring the toxicity of nanomaterials commonly used in biosensor design. From our analysis, we introduce five factors with a role in nanotoxicity that should be considered at the biosensor development stages to better manage toxicity. Finally, we contextualize the discussion by presenting the relevant stages and routes of exposure in the biosensor life cycle. Our review found little consensus on how the factors presented govern nanomaterial toxicity, especially in composite and alloyed nanomaterials. To bridge the current gap in understanding and mitigate the risks of uncontrolled nanomaterial release, we advocate for greater collaboration through a precautionary One Health approach to future development and a movement towards a circular approach to biosensor use and disposal. 

We investigated the ability of chitosan/double-stranded RNA polyplex nanoparticles to silence genes in Caenorhabditis elegans in different environmentally analogous media. Using fluorescence microscopy, we were able to rapidly assess gene knockdown and dsRNA uptake under numerous conditions. Scanning transmission electron micrographs of polyplexes confirms heterogeneous distribution of chitosan and RNA in single particles and a wide range of particle morphologies. High pH and the presence of natural organic matter inhibited the ability of polyplex nanoparticles to silence genes, but were unaffected by the presence of inorganic nitrate and phosphate. Environmental media did not affect particle size in any specific pattern, as determined by dynamic light scattering and fluorescence correlation spectroscopy. The efficacy of polyplexes seems to be closely tied to zeta potential, as all treatments that resulted in a net negative zeta potential (high pH and high natural organic matter) failed to achieve gene knockdown. These results support earlier work that emphasized the importance of charge in gene carriers and will aid in the development of effective gene silencing biological control agents.