Sulfur vacancies affect the environmental fate, corona formation, and microalgae toxicity of molybdenum disulfide nanoflakes

Interactions of monolayer molybdenum disulfide sheets with metalloid antimony in aquatic environment: Adsorption, transformation, and joint toxicity

The tremendous application potentiality of transitional metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) nanosheets, will unavoidably lead to increasing release into the environment, which could influence the fate and toxicity of co-existed contaminants. The present study discovered that 59.8 % of trivalent antimony [Sb(III)] was transformed by MoS2 to pentavalent Sb [Sb(V)] in aqueous solutions under light illumination, which was due to hole oxidation on the nanosheet surfaces. A synergistic toxicity between MoS2 and Sb(III, V) to algae (Chlorella vulgaris) was observed, as demonstrated by the lower median-effect concentrations of MoS2 + Sb(III)/Sb(V) (13.1 and 20.9 mg/L, respectively) than Sb(III)/Sb(V) (38.8 and 92.5 mg/L, respectively) alone. Particularly, MoS2 at noncytotoxic doses notably increased the bioaccumulation of Sb(III, V) in algae, causing aggravated oxidative damage, photosynthetic inhibition, and structural alterations. Metabolomics indicated that oxidative stress and membrane permeabilization were primarily associated with down-regulated amino acids involved in glutathione biosynthesis and unsaturated fatty acids. MoS2 co-exposure remarkably decreased the levels of thiol antidotes (glutathione and phytochelatins) and aggravated the inhibition on energy metabolism and ATP synthesis, compromising the Sb(III, V) detoxification and efflux. Additionally, extracellular P was captured by the nanosheets, also contributing to the uptake of Sb(V). Our findings emphasized the nonignorability of TMDs even at environmental levels in affecting the ecological hazard of metalloids, providing insight into comprehensive safety assessment of TMDs.

Environmental and Health Impacts of Graphene and Other Two-Dimensional Materials: A Graphene Flagship Perspective

Two-dimensional (2D) materials have attracted tremendous interest ever since the isolation of atomically thin sheets of graphene in 2004 due to the specific and versatile properties of these materials. However, the increasing production and use of 2D materials necessitate a thorough evaluation of the potential impact on human health and the environment. Furthermore, harmonized test protocols are needed with which to assess the safety of 2D materials. The Graphene Flagship project (2013-2023), funded by the European Commission, addressed the identification of the possible hazard of graphene-based materials as well as emerging 2D materials including transition metal dichalcogenides, hexagonal boron nitride, and others. Additionally, so-called green chemistry approaches were explored to achieve the goal of a safe and sustainable production and use of this fascinating family of nanomaterials. The present review provides a compact survey of the findings and the lessons learned in the Graphene Flagship.

Earthworm Coelomocyte Internalization of MoS2 Nanosheets: Multiplexed Imaging, Molecular Profiling, and Computational Modeling

Fully understanding the cellular uptake and intracellular localization of MoS2 nanosheets (NSMoS2) is a prerequisite for their safe applications. Here, we characterized the uptake profile of NSMoS2 by functional coelomocytes of the earthworm Eisenia fetida. Considering that vacancy engineering is widely applied to enhance the NSMoS2 performance, we assessed the potential role of such atomic vacancies in regulating cellular uptake processes. Coelomocyte internalization and lysosomal accumulation of NSMoS2 were tracked by fluorescent labeling imaging. Cellular uptake inhibitors, proteomics, and transcriptomics helped to mechanistically distinguish vacancy-mediated endocytosis pathways. Specifically, Mo ions activated transmembrane transporter and ion-binding pathways, entering the coelomocyte through assisted diffusion. Unlike molybdate, pristine NSMoS2 (P-NSMoS2) induced protein polymerization and upregulated gene expression related to actin filament binding, which phenotypically initiated actin-mediated endocytosis. Conversely, vacancy-rich NSMoS2 (V-NSMoS2) were internalized by coelomocytes through a vesicle-mediated and energy-dependent pathway. Mechanistically, atomic vacancies inhibited mitochondrial transport gene expression and likely induced membrane stress, significantly enhancing endocytosis (20.3%, p < 0.001). Molecular dynamics modeling revealed structural and conformational damage of cytoskeletal protein caused by P-NSMoS2, as well as the rapid response of transport protein to V-NSMoS2. These findings demonstrate that earthworm functional coelomocytes can accumulate NSMoS2 and directly mediate cytotoxicity and that atomic vacancies can alter the endocytic pathway and enhance cellular uptake by reprogramming protein response and gene expression patterns. This study provides an important mechanistic understanding of the ecological risks of NSMoS2.

Promotion effects and mechanisms of molybdenum disulfide on the propagation of antibiotic resistance genes in soil

The rapid development of nanotechnology has aroused considerable attentions toward understanding the effects of engineered nanomaterials (ENMs) on the propagation of antibiotic resistance. Molybdenum disulfide (MoS₂) is an extensively used ENM and poses potential risks associated with environmental exposure; nevertheless, the role of MoS₂ toward antibiotic resistance genes (ARGs) transfer remains largely unknown. Herein, it was discovered that MoS₂ nanosheets accelerated the horizontal transfer of RP4 plasmid across Escherichia coli in a dose-dependent manner (0.5-10 mg/L), with the maximum transfer frequency 2.07-fold higher than that of the control. Integration of physiological, transcriptomics, and metabolomics analyses demonstrated that SOS response in bacteria was activated by MoS₂ due to the elevation of oxidative damage, accompanied by cell membrane permeabilization. MoS₂ promoted bacterial adhesion and intercellular contact via stimulating the secretion of extracellular polysaccharides. The ATP levels were maximally increased by 305.7 % upon exposure to MoS₂, and the expression of plasmid transfer genes was up-regulated, contributing to the accelerated plasmid conjugation and increased ARG abundance in soil. Our findings highlight the roles of emerging ENMs (e.g., MoS₂) in ARGs dissemination, which is significant for the safe applications and risk management of ENMs under the development scenarios of nanotechnology.

Systematic stress persistence and recovery patterns of rice (Oryza sativa L.) roots in response to molybdenum disulfide nanosheets

The increasing application of engineered nanomaterials (ENMs) unavoidably leads to environmental release and biological exposure. Understanding the potential hazards of ENMs on crops is essential for appropriate utilization and management. Herein, rice seedlings were hydroponically exposed to molybdenum sulfide (MoS₂, a typical ENM) nanosheets at 5-20 mg/L for 7 days and then depurated for another 7 days in a fresh culture medium. Exposure to MoS₂ triggered irreversible reductions in root length (by 26.3%-69.9%) and tip number (by 22.2%-66.0%). Integration of biochemical assays, transcriptomic and metabolomics found that oxidative stress induced by MoS₂ in roots was persistent, whereas the activation of aquaporins, ionic transportation, and energy synthesis was normalized due to the recovery of nutrient uptake. The down-regulated levels of genes and metabolites associated with peroxidases, hemicellulose synthesis, expansins, and auxins caused persistent structural damages (sclerosis and rupture) of root cell walls. Approximately 64.5%-84.8% of internalized MoS₂ nanosheets were degraded, and the successive up-regulation of genes encoding cytochrome P450s and glutathione S-transferases reflected the biotransformation and detoxification of MoS₂ in the depuration period. These findings provide novel insights into the persistence and recovery of MoS₂ phytotoxicity, which will help advance the risk assessment of MoS₂ application on environment.

Chronic level of exposures to low-dosed MoS2 nanomaterials exhibits more toxic effects in HaCaT keratinocytes

Molybdenum disulfide nanomaterials (MoS₂ NMs) have shown significant role as photocatalysts, lubricating agents and sterilant due to their remarkable physicochemical properties. Because of the increasing demand for MoS₂ NMs in numerous industrial domains, greater occupational exposure and subsequent NMs release into environment would be unavoidable. However, much efforts have been made to uncover the biological effects of NMs at unrealistic high concentration or acute duration, placing constraints on setting the realistic occupational exposure thresholds with confidence. In order to fill the current knowledge gap, this study aimed to evaluate the nanotoxicity of MoS₂ NMs with or without surface defects under the more realistic exposure mode. Noteworthily, the artificial sweat transformed-occupational exposure-cytotoxicity investigation of MoS₂ NMs was established as the main studied line. And the high cellular internalization and augmented oxidative stress triggered by surface defect could be recognized as the main factors for triggering serious cellular damage. Moreover, the HaCaTs exhibited loss of cell membrane integrity, dysfunction of mitochondria, disorder of endoplasmic reticulum and damages of nuclei after chronic exposure, compared with acute exposure. The study provided closely realistic exposure scenarios for NMs which exhibited significant difference from acute toxic investigation, enriching understanding towards real environmental safety of NMs.

Impact of sulfhydryl ligands on the transformation of silver ions by molybdenum disulfide and their combined toxicity to freshwater algae

The transformation of silver ions (Ag⁺) mediated by engineered nanomaterials (ENMs) influences the biosafety of Ag-containing products in natural environments. Actually, modification of biomolecules to ENMs in aquatic ecosystems alters their interactions with Ag⁺. This study discovered that surface functionalization of glutathione (GSH, a sulfhydryl compound ubiquitous in natural waters) on molybdenum disulfide (MoS₂) nanoflakes suppressed the redox reaction between 1 T components and Ag⁺, inhibiting the MoS₂-mediated reduction of Ag⁺ to Ag nanoparticles (AgNPs) in aqueous phase in the dark. However, AgNPs formation (from 2.32 ± 0.35-3.25 ± 0.29 mg/L per day, pH 7.0) and oxidation of MoS₂ were remarkably accelerated after GSH binding under light conditions. The dominant electron donator of MoS₂ to Ag⁺ was transformed from the electron-hole pairs to surface ligands driven by the introduction of chromophoric groups was authenticated as the cause for the elevated Ag⁺ reduction. These processes also occurred between Ag⁺ and MoS₂ at low levels (50 μg/L). Additionally, the joint algal toxicity of GSH-modified MoS₂ with Ag⁺ was weaker than that of pristine MoS₂ due to increased retention of free Ag⁺ and AgNPs formation. Our findings improve the understanding of the interaction between ENMs and Ag⁺ in aquatic ecosystems.

Mitigation Effects and Associated Mechanisms of Environmentally Relevant Thiols on the Phytotoxicity of Molybdenum Disulfide Nanosheets

Thorough investigations of the environmental fate and risks are necessary for the safe application of engineered nanomaterials. Nevertheless, the current understanding of potential transformations of MoS₂ (an intensively studied two-dimensional nanosheet) upon interactions with ubiquitous environmentally relevant thiols (ERTs) in water is limited. This study revealed that two ERTs, l-cysteine and mercaptoacetic acid, could modify MoS₂ by covalently grafting thiol groups on S atoms of 1T phases, improving the colloidal persistence and chemical stability of MoS₂. Compared with the pristine form, MoS₂-thiols with higher dispersity exhibited significantly mitigated envelopment and ultrastructural damage to microalgae. MoS₂-triggered growth inhibition, upregulation of reactive oxygen species, photosynthetic injury, and metabolic perturbation in algae were remarkably attenuated by ERTs. The diminished capability for MoS₂ to generate reactive intermediates and glutathione oxidation driven by ERTs caused the weakness of oxidative stress and negative effects. Additionally, molecular dynamics simulations demonstrated that ERTs altered the extent of the influence of MoS₂ on the secondary structures and functions of adsorbed intracellular proteins, which also contributed to the lower phytotoxicity of MoS₂. Our findings provide evidence for the crucial role of specific organic ligands in the risk of MoS₂ in aquatic environments.

Nano-bio interactions of 2D molybdenum disulfide

Two-dimensional (2D) molybdenum disulfide (MoS₂) is an ultrathin nanomaterial with a high degree of anisotropy, surface-to-volume ratio, chemical functionality and mechanical strength. These properties together enable MoS₂ to emerge as a potent nanomaterial for diverse biomedical applications including drug delivery, regenerative medicine, biosensing and bioelectronics. Thus, understanding the interactions of MoS₂ with its biological interface becomes indispensable. These interactions, referred to as "nano-bio" interactions, play a key role in determining the biocompatibility and the pathways through which the nanomaterial influences molecular, cellular and biological function. Herein, we provide a critical overview of the nano-bio interactions of MoS₂ and emphasize on how these interactions dictate its biomedical applications including intracellular trafficking, biodistribution and biodegradation. Also, a critical evaluation of the interactions of MoS₂ with proteins and specific cell types such as immune cells and progenitor/stem cells is illustrated which governs the short-term and long-term compatibility of MoS₂-based biomedical devices.