Size effect of SnO2 nanoparticles on bacteria toxicity and their membrane damage

Key genomes, transcriptomes, proteins, and metabolic factors involved in the detoxification/tolerance of TNT and its intermediates by bacteria in anaerobic/aerobic environments

Novel microbial strains capable of efficient degradation of TNT and typical intermediates (2-ADNT and 4-ADNT) in aerobic/anaerobic environment were screened and isolated from ammunition-contaminated sites. The key genomes, transcriptomes, proteins, and metabolic factors for microbial detoxification/tolerance to pollutants in anaerobic and aerobic environments were analyzed for the first time. The bacterial genome, which is rich in metabolism and environmental information-processing functional genes, provides transcriptional and translational-related proteins for detoxifying/tolerating pollutants. At the transcriptional level, bacteria significantly expressed genes related to inositol phosphate metabolism for regulating membrane transport, maintaining the cytoskeleton, and signal transduction. At the protein level, genes involved in antioxidation, fat metabolism, sugar synthesis/degradation, and pyruvate metabolism were significantly expressed. At the metabolic level, riboflavin metabolism, which regulates membrane integrity, protects against oxidative stress, and maintains the sugar-protein-fat balance, showed significant responses. Bacteria simultaneously regulate amino acid metabolism, carbohydrate metabolism, and N/P/S cycles to maintain homeostatic cellular energy supplies. The key pathway for pollutant degradation in bacteria is nitrotoluene degradation. The molecular mechanism of bacterial tolerance to pollutants involves the regulation of oxidative phosphorylation and basic cycle pathways to maintain gene transcription, protein translation, and metabolic cycles.

The impact of engineered nanomaterials on the environment: Release mechanism, toxicity, transformation, and remediation

The presence and longevity of nanomaterials in the ecosystem, as well as their properties, account for environmental toxicity. When nanomaterials in terrestrial and aquatic systems are exposed to the prevailing environmental conditions, they undergo various transformations such as dissociation, dissolution, and aggregation, which affects the food chain. The toxicity of nanomaterials is influenced by a variety of factors, including environmental factors and its physico-chemical characteristics. Bioaccumulation, biotransformation, and biomagnification are the mechanisms that have been identified for determining the fate of nanomaterials. The route taken by nanomaterials to reach living cells provides us with information about their toxicity profile. This review discusses the recent advances in the transport, transformation, and fate of nanomaterials after they are released into the environment. The review also discusses how nanoparticles affect lower trophic organisms through direct contact, the impact of nanoparticles on higher trophic organisms, and the possible options for remediation.

Comparison of copper and aluminum doped cobalt ferrate nanoparticles for improving biohydrogen production

Two various materials, copper and aluminum doped cobalt ferrite nanoparticles (NPs) were fabricated for investigating their effects of addition amounts on hydrogen (H₂) synthesis and process stability. CoCu_0.2Fe_1.8O₄NPs enhanced H₂ production more than CoAl_0.2Fe_1.8O₄ NPs under same condition. The highest H₂ yield of 212.25 ml/g glucose was found at optimal dosage of 300 mg/L CoCu_0.2Fe_1.8O₄ NPs, revealing the increases of 43.17% and 6.67% compared with the control without NPs and 300 mg/L CoAl_0.2Fe_1.8O₄ NPs groups, respectively. NPs level of more than 400 mg/L inhibited H₂ generation. Further investigations illustrated that CoCu_0.2Fe_1.8O₄ NPs were mainly distributed on extracellular polymer substance while CoAl_0.2Fe_1.8O₄ NPs were mostly enriched on cell membrane, which facilitated electron transfer behavior. Community structure composition demonstrated that CoCu_0.2Fe_1.8O₄ and CoAl_0.2Fe_1.8O₄ separately caused a 9.67% and 9.03% increase in Clostridium sensu stricto 1 compared with the control reactor without NPs exposure.

Targeted specific inhibition of bacterial and Candida species by mesoporous Ag/Sn–SnO2 composite nanoparticles: in silico and in vitro investigation

Invasive bacterial and fungal infections have notably increased the burden on the health care system and especially in immune compromised patients. These invasive bacterial and fungal species mimic and interact with the host extracellular matrix and increase the adhesion and internalization into the host system. Further, increased resistance of traditional antibiotics/antifungal drugs led to the demand for other therapeutics and preventive measures. Presently, metallic nanoparticles have wide applications in health care sectors. The present study has been designed to evaluate the advantage of Ag/Sn–SnO₂ composite nanoparticles over the single oxide/metallic nanoparticles. By using in silico molecular docking approaches, herein we have evaluated the effects of Ag/Sn–SnO₂ nanoparticles on adhesion and invasion responsible molecular targets such as LpfD (E. coli), Als3 (C. albicans) and on virulence/resistance causing PqsR (P. aeruginosa), RstA (Bmfr) (A. baumannii), FoxA (K. pneumonia), Hsp90 and Cyp51 (C. albicans). These Ag/Sn–SnO₂ nanoparticles exhibited higher antimicrobial activities, especially against the C. albicans, which are the highest ever reported results. Further, Ag/Sn–SnO₂ NPs exhibited interaction with the heme proionate residues such as Lys143, His468, Tyr132, Arg381, Phe105, Gly465, Gly464, Ile471 and Ile304 by forming hydrogen bonds with the Arg 381 residue of lanosterol 1 4α-demethylase and increased the inhibition of the Candida strains. Additionally, the Ag/Sn–SnO₂ nanoparticles exhibited extraordinary inhibitory properties by targeting different proteins of bacteria and Candida species followed by several molecular pathways which indicated that it can be used to eliminate the resistance to traditional antibiotics.

Mesoporous Ag/Sn–SnO₂ composite nanoparticles exhibits extraordinary inhibitory properties by targeting different proteins of bacteria and Candida species which can be used to eliminate the resistance of traditional antibiotics.

Differential response of immobile (pneumocytes) and mobile (monocytes) barriers against 2 types of metal oxide nanoparticles

BACKGROUND

Inhaled nanoparticles (NPs) challenges mobile and immobile barriers in the respiratory tract, which can be represented by type II pneumocytes (immobile) and monocytes (mobile) but what is more important for biological effects, the cell linage, or the type of nanoparticle? Here, we addressed these questions and we demonstrated that the type of NPs exerts a higher influence on biological effects, but cell linages also respond differently against similar type of NPs.

DESIGN

Type II pneumocytes and monocytes were exposed to tin dioxide (SnO₂) NPs and titanium dioxide (TiO₂) NPs (1, 10 and 50 μg/cm²) for 24 h and cell viability, ultrastructure, cell granularity, molecular spectra of lipids, proteins and nucleic acids and cytoskeleton architecture were evaluated.

RESULTS

SnO₂ NPs and TiO₂ NPs are metal oxides with similar physicochemical properties. However, in the absence of cytotoxicity, SnO₂ NPs uptake was low in monocytes and higher in type II pneumocytes, while TiO₂ NPs were highly internalized by both types of cells. Monocytes exposed to both types of NPs displayed higher number of alterations in the molecular patterns of proteins and nuclei acids analyzed by Fourier-transform infrared spectroscopy (FTIR) than type II pneumocytes. In addition, cells exposed to TiO₂ NPs showed more displacements in FTIR spectra of biomolecules than cells exposed to SnO₂ NPs. Regarding cell architecture, microtubules were stable in type II pneumocytes exposed to both types of NPs but actin filaments displayed a higher number of alterations in type II pneumocytes and monocytes exposed to SnO₂ NPs and TiO₂ NPs. NPs exposure induced the formation of large vacuoles only in monocytes, which were not seen in type II pneumocytes.

CONCLUSIONS

Most of the cellular effects are influenced by the NPs exposure rather than by the cell type. However, mobile, and immobile barriers in the respiratory tract displayed differential response against SnO₂ NPs and TiO₂ NPs in absence of cytotoxicity, in which monocytes were more susceptible than type II pneumocytes to NPs exposure.

Comparative Acute Toxicity and Oxidative Stress Responses in Three Aquatic Species Exposed to Stannic Oxide Nanoparticles and Stannic Chloride

We experimentally investigated the toxicity of stannic oxide nanoparticles (SnO₂ NPs) to three freshwater species including Scenedesmus obliquus, Daphnia magna, and Danio rerio. To evaluate effect, toxicological impacts were compared to that of stannic chloride (SnCl₄). Based on the actual concentration of Sn, SnO₂ NPs suspensions inhibited growth of S. obliquus in a dose-dependent manner, demonstrating a median effect concentration of 2.28 ± 0.53 mg/L. However, SnO₂ NP suspensions were found to exhibit limited acute toxicity in D. magna and D. rerio. Moreover, the toxicity of the SnO₂ NP suspension was lower than SnCl₄ for all three trophic aquatic organisms. Comparison of component-specific contribution to overall toxicity indicated that, in SnO₂ NP suspensions, particulate Sn more significantly contributed to toxicity than dissolved Sn-ions. Furthermore, we found that the toxic mechanism of the SnO₂ NP suspension involved the induction of oxidative stress by increasing intracellular ROS accumulation.

Extraction of Graphene Nanostructures from Colocasia esculenta and Nelumbo nucifera Leaves and Surface Functionalization with Tin Oxide: Evaluation of Their Antibacterial Properties

Expeditious evolution of antimicrobial resistance in recent years has been identified as a growing concern by various health organizations around the world. Herein, facile and environmentally benign production of highly antibacterial carbonaceous nanomaterials from Colocasia esculenta and Nelumbo nucifera leaves is reported. After carbonization and oxidative treatment, smaller graphene domains are formed in Colocasia esculenta derivatives, whereas larger sheetlike structures are observed in the case of Nelumbo nucifera. Smaller particle size makes quantum confinement effects more prominent, as is evident in fine-tuning of the photoluminescence emission after each stage of treatment. The influence of precursor materials on the antibacterial properties of the nanosystems is also demonstrated. When microbiocidal activity was tested against model bacteria Pseudomonas aeruginosa, the nanocomposite derived from Colocasia esculenta leaves showed higher activity than the antibiotic drug clarithromycin (control) with a measured zone of inhibition of 40±0.5 mm. This is one of the highest values reported in comparison with plant-based carbon-silver nanosystems. Quantitative analysis revealed that the nanocomposite obtained from Colocasia esculenta leaves has antimicrobial efficacy equivalent to those of commercial antibiotic drugs and is able to eradicate bacteria at much lower concentrations than that obtained from Nelumbo nucifera leaves.

Antibiotic-Free Antibacterial Strategies Enabled by Nanomaterials: Progress and Perspectives

Bacterial infection is one of the top ten leading causes of death globally and the worst killer in low-income countries. The overuse of antibiotics leads to ever-increasing antibiotic resistance, posing a severe threat to human health. Recent advances in nanotechnology provide new opportunities to address the challenges in bacterial infection by killing germs without using antibiotics. Antibiotic-free antibacterial strategies enabled by advanced nanomaterials are presented. Nanomaterials are classified on the basis of their mode of action: nanomaterials with intrinsic or light-mediated bactericidal properties and others that serve as vehicles for the delivery of natural antibacterial compounds. Specific attention is given to antibacterial mechanisms and the structure-performance relationship. Practical antibacterial applications employing these antibiotic-free strategies are also introduced. Current challenges in this field and future perspectives are presented to stimulate new technologies and their translation to fight against bacterial infection.

Arsenic removal and activity of a sulfate reducing bacteria-enriched anaerobic sludge using zero valent iron as electron donor

Arsenic (As) removal from water, subject to sulfate-reducing conditions has been shown to result in safe As levels. We evaluated sulfate-reducing activity and arsenic removal by an anaerobic sludge enriched with sulfate-reducing bacteria (SRB), using zero valent iron (ZVI) as electron donor and different concentrations of As^V or As^III (up to 5 mg/L). Sulfate and As removal were monitored in aqueous samples of batch assays. Likewise, precipitates resulting from As removal were characterized in solids. Sulfate-reducing activity on the part of anaerobic sludge was slightly decreased by As^III and it was 50% decreased, particularly at 5 mg/L As^V, for which arsenic removal equaled 98%. At all other As concentrations assayed, 100% As was removed. The co-existence of S, As and Fe in solids from assays with As, was demonstrated by scanning electron microscopy (SEM-EDS) and by micro-X-ray fluorescence, corroborating the possible formation of Fe-As-S type minerals for As precipitation. Pharmacosiderite and scorodite minerals were identified by micro-X-ray absorption near edge structure and confirmed by extended X-ray adsorption fine structure, and these were related to the oxidation of arsenopyrite during analysis. Results indicate the suitability of the anaerobic sludge for bioremediating arsenic-contaminated groundwater under sulfidogenic conditions with ZVI as electron donor.

Aqueous-phase synthesis of nanoparticles of copper/copper oxides and their antifungal effect against Fusarium oxysporum

Different copper based-materials have been used for controlling some fungal and bacterial pathogens. However, the antifungal activity of the copper-based materials depends on different parameters, such as the crystal phase, synthesis route, and size of the particles. Herein a facile route synthesis method of Cu/Cu_xO-NPs was achieved through the aqueous phase. The influence of NaBH₄ concentration on the phase composition was studied. The synthesized Cu/Cu_xO-NPs were characterized by X-Ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering. Five Cu/Cu_xO-NPs with different phase composition and nanoparticle size were obtained. The antifungal activity of the synthesized Cu/Cu_xO-NPs was studied in vitro against Fusarium oxysporum. The results indicate that a high percent of inhibition of radial growth (IGR) was obtained with NPs, which have a higher proportion of Cu₂O phase and relatively smaller size particles. Furthermore, hypha morphology, membrane damage and production of reactive oxygen species (ROS) was evaluated with SEM and confocal microscopy.

Metal(loid) oxide (Al2O3, Mn3O4, SiO2 and SnO2) nanoparticles cause cytotoxicity in yeast via intracellular generation of reactive oxygen species

In this work, the physicochemical characterization of five (Al₂O₃, In₂O₃, Mn₃O₄, SiO₂ and SnO₂) nanoparticles (NPs) was carried out. In addition, the evaluation of the possible toxic impacts of these NPs and the respective modes of action were performed using the yeast Saccharomyces cerevisiae. In general, in aqueous suspension, metal(loid) oxide (MOx) NPs displayed an overall negative charge and agglomerated; these NPs were practically insoluble (dissolution < 8%) and did not generate detectable amounts of reactive oxygen species (ROS) under abiotic conditions. Except In₂O₃ NPs, which did not induce an obvious toxic effect on yeast cells (up to 100 mg/L), the other NPs induced a loss of cell viability in a dose-dependent manner. The comparative analysis of the loss of cell viability induced by the NPs with the ions released by NPs (NPs supernatant) suggested that SiO₂ toxicity was mainly caused by the NPs themselves, Al₂O₃ and SnO₂ toxic effects could be attributed to both the NPs and the respective released ions and Mn₃O₄ harmfulness could be mainly due to the released ions. Al₂O₃, Mn₃O₄, SiO₂ and SnO₂ NPs induced the loss of metabolic activity and the generation of intracellular ROS without permeabilization of plasma membrane. The co-incubation of yeast cells with MOx NPs and a free radical scavenger (ascorbic acid) quenched intracellular ROS and significantly restored cell viability and metabolic activity. These results evidenced that the intracellular generation of ROS constituted the main cause of the cytotoxicity exhibited by yeasts treated with the MOx NPs. This study highlights the importance of a ROS-mediated mechanism in the toxicity induced by MOx NPs.

Comparative evaluation of nano and bulk tin dioxide cytotoxicity on dermal fibroblasts by real-time impedance-based and conventional methods

In this study, the possible cellular effects of tin dioxide (SnO₂) nanoparticles, together with its bulk form, on mouse dermal fibroblasts (DFs) were revealed using in vitro assays. Particle characterizations were carried out with AFM, Braun-Emmet-Teller, and DLS analyses. The cells were treated with nano and bulk SnO₂ at concentrations of 0.1, 1, 10, 50, and 100 μg/mL for 6, 24, and 48 h. At the end of the exposure periods, the morphology, viability, particle uptake, and membrane leakage statuses of the cells were evaluated. Furthermore, real-time monitoring of cell responses was performed by using an impedance-based label-free system. Findings showed that at concentrations of 0.1-10 μg/mL, cells had similar doubling time to that of control cells (20.4 ± 2.6 h), while the doubling time of cells exposed to 100 μg/mL of nano and bulk SnO₂ increased slightly (P ˃ 0.05) to 25.1 ± 3.9 h and 26.2 ± 5.9 h, respectively. The results indicated that DFs exhibited a similar toxicity response to nano and bulk SnO₂; thus, 50 and 100 μg/mL of nano and bulk SnO₂ had mild toxic effects on DFs. In conclusion, this study provides information and insight necessary for the safe use of SnO₂ in medical and consumer products.

M. Biowaste derived graphene quantum dots interlaced with SnO2 nanoparticles – a dynamic disinfection agent against Pseudomonas aeruginosa

A biocidal GQD/SnO₂ nanocomposite derived from discarded sugarcane bagasse is a cost effective, renewable and green replacement for the traditional hazardous microbicides.

Factors impacting the interactions of engineered nanoparticles with bacterial cells and biofilms: Mechanistic insights and state of knowledge

Since their advent a few decades ago, engineered nanoparticles (ENPs) have been extensively used in consumer products and industrial applications and their use is expected to continue at the rate of thousands of tons per year in the next decade. The widespread use of ENPs poses a potential risk of large scale environmental proliferation of ENPs which can impact and endanger environmental health and safety. Recent studies have shown that microbial biofilms can serve as an important biotic component for partitioning and perhaps storage of ENPs released into aqueous systems. Considering that biofilms can be one of the major sinks for ENPs in the environment, and that the field of biofilms itself is only three to four decades old, there is a recent and growing body of literature investigating the ENP-biofilm interactions. While looking at biofilms, it is imperative to consider the interactions of ENPs with the planktonic microbial cells inhabiting the bulk systems in the vicinity of surface-attached biofilms. In this review article, we attempt to establish the state of current knowledge regarding the interactions of ENPs with bacterial cells and biofilms, identifying key governing factors and interaction mechanisms, as well as prominent knowledge gaps. Since the context of ENP-biofilm interactions can be multifarious-ranging from ecological systems to water and wastewater treatment to dental/medically relevant biofilms- and includes devising novel strategies for biofilm control, we believe this review will serve an interdisciplinary audience. Finally, the article also touches upon the future directions that the research in the ENP-microbial cells/biofilm interactions could take. Continued research in this area is important to not only enhance our scientific knowledge and arsenal for biofilm control, but to also support environmental health while reaping the benefits of the 'nanomaterial revolution'.

Cytotoxic consequences of Halloysite nanotube/iron oxide nanocomposite and iron oxide nanoparticles upon interaction with bacterial, non-cancerous and cancerous cells

Cytotoxic effects of iron oxide (Fe₃O₄) nanoparticles and Halloysite nanotube/iron oxide (HNT/Fe₃O₄) nanocomposite are compared based on their interaction with Gram-negative bacteria Escherichia coli and Gram-positive bacteria Bacillus subtilis. Similarly, the action of these two nanomaterials on non-cancerous Vero cell lines and human lung cancerous (A-549) cell lines are compared. The cytotoxicity studies on Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite showed difference in the rate of killing of bacterial cells. This is reflected in differential cell growth, cell membrane integrity loss, lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) production. These factors are measured over a range of concentrations of Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite and at specified time intervals, to test if there is any statistically significant difference between the toxicity of the two nanomaterials. Between the two nanomaterials, HNT/Fe₃O₄ nanocomposite is found to be less toxic to bacterial cells than Fe₃O₄ nanoparticles. HNT, when attached to the Fe₃O₄ nanoparticles, changes their surface characteristics and suppresses their inherent toxicity on bacteria. In the study on the effect on cell lines, Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite are both seen to be biocompatible with Vero cell lines. However, HNT/Fe₃O₄ nanocomposite showed more cytotoxicity than Fe₃O₄ nanoparticles on A-549 cell lines.

Evaluating the cytotoxicity of tin dioxide nanofibers

Tin dioxide nanofibers (SnDNFs) are small fibers that have many applications. Tin dioxide nanofibers can be used in cosmetics, solar cells, toxic gas release sensors, and air pollution control. To date there have been few studies on the cytotoxicity of SnDNFs. The goal of this research is to determine if electrospun SnDNFs are toxic in a lung cancer cell line (A549). Considering the nano-scale size of the fibers, they can easily be inhaled and enter the pulmonary system and cause toxic effects in the lung. Occupational exposure to SnDNFs has been linked to pulmonary disease, making the A549 cell line important in this study. Nanofiber toxicity can vary based upon the characteristics of the fibers. Smaller nanofibers have been shown to have more toxic effects than their larger counterparts. The synthesized SnDNFs were characterized using SEM, Raman spectroscopy, and powder X-ray diffractometer (PXRD). SEM images showed the fibers to be 200-300 nm in diameter. Raman spectroscopy and PXRD indicated that the fibers were in the rutile phase. After quantifying the SnDNFs, the fibers were introduced to A549 cells at concentrations ranging from 0.02-500 µg mL^-1 and incubated at 37°C. These cells were quantified with the MTT assay to measure cell proliferation (IC₅₀ = 0.02 mg mL^-1), while lactate dehydrogenase (LDH) leakage was used to determine cytotoxicity, and apoptosis assays to assess the mechanism of cell death. Increasing concentration of SnDNF generated a consequential decrease in cell proliferation and viability. The percent cytotoxicity of SnDNF was not significantly changed at the various concentrations and time frames. In order to gain additional insight about the mechanism of cytotoxicity of SnDNFs, genes with links to inflammation and apoptosis were evaluated and found to be over-expressed in treated cells. At the concentrations of SnDNF examined, SnDNF was mildly toxic to the A549 cells.

Environmental Transformations and Algal Toxicity of Single-Layer Molybdenum Disulfide Regulated by Humic Acid

The environmental transformations of nanomaterials are correlated with their behaviors and ecological risks. The applications of single-layer molybdenum disulfide (SLMoS₂) have rapidly developed in environmental fields, but the potential transformations and biological effects of SLMoS₂ remain largely unknown. This study revealed that humic acid (HA, over 10 mg/L) induced the scrolling of SLMoS₂ with light irradiation over a 56-day incubation. The colloidal stability of SLMoS₂ increased, and the aggregation ratio decreased from 0.59 ± 0.07 to 0.08 ± 0.01 nm/min after HA hybridization. Besides, compared with pristine SLMoS₂, the chemical dissolution rate of SLMoS₂ was up to 4.6-fold faster with HA exposure. These results demonstrate that HA affects the environmental fate and transformations of SLMoS₂. SLMoS₂-HA possessed a significantly widened direct band gap (2.06 eV) compared with that of SLMoS₂ (1.8 eV). SLMoS₂ acted as an electronic acceptor from HA, resulting in the separation of electron-hole pairs. Consequently, SLMoS₂-HA exhibited stronger peroxidase-like catalytic activity, which was approximately 2-fold higher than that of SLMoS₂. Moreover, the morphology and layered structure of SLMoS₂ changed, and the damage SLMoS₂ inflicted on microalgae was significantly reduced. This work provides insights into the behaviors and related biological risks of SLMoS₂ in aqueous environments.

Probing the interaction of silver nanoparticles with tau protein and neuroblastoma cell line as nervous system models

Interestingly pharmaceutical sciences are using nanoparticles (NPs) to design and develop nanomaterials-based drugs. However, up to recently, it has not been well realized that NPs themselves may impose risks to the biological systems. In this study, the interaction of silver nanoparticles (AgNPs) with tau protein and SH-SY5Y neuroblastoma cell line, as potential nervous system models, was examined with a range of techniques including intrinsic fluorescence spectroscopy, circular dichroism (CD) spectroscopy, 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and acridine orange/ethidium bromide (AO/EB) dual staining method. Fluorescence study showed that AgNPs with a diameter of around 10-20 nm spontaneously form a static complex with tau protein via hydrogen bonds and van der Waals interactions. CD experiment revealed that AgNPs did not change the random coil structure of tau protein. Moreover, AgNPs showed to induce SH-SY5Y neuroblastoma cell mortality through fragmentation of DNA which is a key feature of apoptosis. In conclusion, AgNPs may induce slight changes on the tau protein structure. Also, the concentration of AgNPs is the main factor which influences their cytotoxicity. Since, all adverse effects of NPs are not well detected, so probably additional more specific testing would be needed.

ZnO nanoparticles modulate the ionic transport and voltage regulation of lysenin nanochannels

Background

The insufficient understanding of unintended biological impacts from nanomaterials (NMs) represents a serious impediment to their use for scientific, technological, and medical applications. While previous studies have focused on understanding nanotoxicity effects mostly resulting from cellular internalization, recent work indicates that NMs may interfere with transmembrane transport mechanisms, hence enabling contributions to nanotoxicity by affecting key biological activities dependent on transmembrane transport. In this line of inquiry, we investigated the effects of charged nanoparticles (NPs) on the transport properties of lysenin, a pore-forming toxin that shares fundamental features with ion channels such as regulation and high transport rate.

Results

The macroscopic conductance of lysenin channels greatly diminished in the presence of cationic ZnO NPs. The inhibitory effects were asymmetrical relative to the direction of the electric field and addition site, suggesting electrostatic interactions between ZnO NPs and a binding site. Similar changes in the macroscopic conductance were observed when lysenin channels were reconstituted in neutral lipid membranes, implicating protein-NP interactions as the major contributor to the reduced transport capabilities. In contrast, no inhibitory effects were observed in the presence of anionic SnO₂ NPs. Additionally, we demonstrate that inhibition of ion transport is not due to the dissolution of ZnO NPs and subsequent interactions of zinc ions with lysenin channels.

Conclusion

We conclude that electrostatic interactions between positively charged ZnO NPs and negative charges within the lysenin channels are responsible for the inhibitory effects on the transport of ions. These interactions point to a potential mechanism of cytotoxicity, which may not require NP internalization.

Electronic supplementary material

The online version of this article (10.1186/s12951-017-0327-9) contains supplementary material, which is available to authorized users.

Oxidative damage to Pseudomonas aeruginosa ATCC 27833 and Staphylococcus aureus ATCC 24213 induced by CuO-NPs

The cytotoxicity of nanoparticles (NPs) and their properties are important issues in nanotechnology research. Particularly, NPs affect the metabolism of microorganisms due to NP interactions with some biomolecules. In order to assess the mechanisms underlying NPs toxicity, we studied the damage caused by copper oxide nanoparticles (CuO-NPs) on Staphylococcus aureus ATCC 24213 and Pseudomonas aeruginosa ATCC 27833. Spherical CuO-NPs characterized by their diameter (13 ± 3 nm) were synthesized with a maximum of 254 nm. These NPs reduced cell viability, with a minimum inhibitory concentration (MIC) of 500 and 700 ppm for Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Surfactant was added to reduce the NP agglomeration, but it did not present any effect. The mechanism of CuO-NPs as antimicrobial agent was assessed by analyzing solubilized Cu²⁺, quantifying DNA release in the culture media, and measuring intracellular reactive oxygen species (ROS). CuO-NPs induced severe damage on cells as revealed by confocal optical microscopy and scanning electron microscopy (SEM). Our results indicated that CuO-NPs interacted with bacteria, triggering an intracellular signaling network which produced oxidative stress, leading to ROS generation. Finally, we concluded that CuO-NPs exhibited higher antibacterial activity on Gram-negative bacteria than on Gram-positive ones.

Strategies and knowledge gaps for improving nanomaterial biocompatibility

With rapid development of nanotechnology and nanomaterials, nanosafety has attracted wide attention in all fields related to nanotechnology. As well known, a grand challenge in nanomaterial applications is their biocompatibility. It is urgent to explore effective strategies to control the unintentional effects. Although many novel methods for the synthesis of biocompatible and biodegradable nanomaterials are reported, the control strategy of nanotoxicity remains in its infancy. It is urgent to review the archived strategies for improving nanomaterial biocompatibility to clarify what we have done and where we should be. In this review, the achievements and challenges in nanomaterial structure/surface modifications and size/shape controls were analyzed. Moreover, the chemical and biological strategies to make nanomaterial more biocompatible and biodegradable were compared. Finally, the concerns that have not been studied well were prospected, involving unintended releases, life-cycle, occupational exposure and methodology.