Impacts of hematite nanoparticle exposure on biomechanical, adhesive, and surface electrical properties of Escherichia coli cells

How micro-/nano-plastics influence the horizontal transfer of antibiotic resistance genes - A review

Plastic debris such as microplastics (MPs) and nanoplastics (NPTs), along with antibiotic resistance genes (ARGs), are pervasive in the environment and are recognized as significant global health and ecological concerns. Micro-/nano-plastics (MNPs) have been demonstrated to favor the spread of ARGs by enhancing the frequency of horizontal gene transfer (HGT) through various pathways. This paper comprehensively and systematically reviews the current study with focus on the influence of plastics on the HGT of ARGs. The critical role of MNPs in the HGT of ARGs has been well illustrated in sewage sludge, livestock farms, constructed wetlands and landfill leachate. A summary of the performed HGT assay and the underlying mechanism of plastic-mediated transfer of ARGs is presented in the paper. MNPs could facilitate or inhibit HGT of ARGs, and their effects depend on the type, size, and concentration. This review provides a comprehensive insight into the effects of MNPs on the HGT of ARGs, and offers suggestions for further study. Further research should attempt to develop a standard HGT assay and focus on investigating the impact of different plastics, including the oligomers they released, under real environmental conditions on the HGT of ARGs.

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems

Widespread antibiotic resistance genes (ARGs) have emerged as a focus of attention for public health. Transformation is essential for ARGs dissemination in soils and associated environments; however, the mechanisms of how soil components contribute to the transformation of ARGs remain elusive. Here we demonstrate that three representative mineral-humic acid (HA) composites exert contrasting influence on the transformation of plasmid-borne ARGs in Bacillus subtilis. Mineral surface-bound HA facilitated transformation in kaolinite and montmorillonite systems, while an inhibitory effect of HA was observed for goethite. The elevated transformation by HA-coated kaolinite was mainly attributed to the enhanced activity of competence-stimulating factor (CSF), while increased transformation by montmorillonite-HA composites was assigned to the weakened adsorption affinity of DNA and enhanced gene expression induced by flagella-driven cell motility. In goethite system, HA played an overriding role in suppressing transformation via alleviation of cell membrane damage. The results obtained offer insights into the divergent mechanisms of humic substances in modulating bacterial transformation by soil minerals. Our findings would help for a better understanding on the fate of ARGs in soil systems and provide potentials for the utilization of soil components, particularly organic matter, to mitigate the spread of ARGs in a range of settings.

Escherichia coli and phosphate interplay mediates transport of nanoscale zero-valent iron synthesized by green tea in water-saturated porous media

Green synthesized nano-zero-valent iron (GT-nZVI) has been considered an excellent material for in-situ soil remediation due to its high stability and environmental benignity. However, sufficient transportability of GT-nZVI downstream towards the contaminated sites, likely affected by the physicochemical properties of soil-groundwater, is required for improved in-situ remediation. Thus, the effect of soil components (i.e., bacteria and phosphate) on GT-nZVI transportability is significant. Hence, we studied the transport of GT-nZVI (Fe0 core wrapped by green tea polyphenols) with the existence of E. coli and phosphate in water-saturated porous sand media in NaCl and CaCl2 solutions at pHs 6.0 and 8.0. Also studied were the stability, surface characteristics, and two-site kinetics attachment modeling (TKAM) with Escherichia coli or/and phosphate. The results showed that phosphate could further enhance GT-nZVI co-transport with E. coli by increasing the negative charge on GT-nZVI at pH 6.0. However, E. coli reduced GT-nZVI mobility at pH 8.0 because the cell-cell interactions could mask the negative charges of pre-deposited GT-nZVI on E. coli, forming the large clusters between GT-nZVI and E. coli. Then, phosphate occurrence diminished E. coli inhibition by detaching GT-nZVI from nZVI-E. coli-phosphate polymers due to the stronger phosphate adsorption on E. coli than GT-nZVI at pH 8.0. Overall, TKAM describes the transport and retention of GT-nZVI adequately under various conditions, indicating the deposition order with k2str value as follows: GT-nZVI alone > with (w.) E. coli > w. phosphate > w. combined E. coli & phosphate at pH 6.0. By contrast, w. phosphate > w. E. coli > w. combined E. coli & phosphate > GT-nZVI alone ensued at pH 8.0. This investigation highlights the transport behavior of GT-nZVI associated with surface property changes in complex environments for effective in-situ remediation.

Mechanism insights into bacterial sporulation at natural sphalerite interface with and without light irradiation: The suppressing role in bacterial sporulation by photocatalysis

Unveiling the mechanisms of bacterial sporulation at natural mineral interfaces is crucial to fully understand the interactions of mineral with microorganism in aquatic environment. In this study, the bacterial sporulation mechanisms of Bacillus subtilis (B. subtilis) at natural sphalerite (NS) interface with and without light irradiation were systematically investigated for the first time. Under dark condition, NS was found to inactivate vegetative cells of B. subtilis and promote their sporulation simultaneously. The released Zn2+ from NS was mainly responsible for the bacterial inactivation and sporulation. With light irradiation, the photocatalytic effect from NS could increase the bacterial inactivation efficiency, while the bacterial sporulation efficiency was decreased from 8.1 % to 4.5 %. The photo-generated H2O2 and O2- played the major roles in enhancing bacterial inactivation and suppressing bacterial sporulation process. The intracellular synthesis of dipicolinic acid (DPA) as biomarker for sporulation was promoted by NS in dark, which was suppressed by the photocatalytic effect of NS with light irradiation. The transformation process from vegetative cells to spores was monitored by both 3D-fluerecence EEM and SEM observations. Compared with the NS alone system, the NS/light combined system induced higher level of intracellular ROSs, up-regulated antioxidant enzyme activity and decreased cell metabolism activity, which eventually led to enhanced inactivation of vegetative cells and suppressed bacterial sporulation. These results not only provide in-depth understanding about bacterial sporulation as a new mode of sub-lethal stress response at NS interface, but also shed lights on putting forward suitable strategies for controlling spore-producing bacteria by suppressing their sporulation during water disinfection.

Atomic Force Microscopy (AFM) on Biopolymers and Hydrogels for Biotechnological Applications-Possibilities and Limits

Atomic force microscopy (AFM) is one of the microscopic techniques with the highest lateral resolution. It can usually be applied in air or even in liquids, enabling the investigation of a broader range of samples than scanning electron microscopy (SEM), which is mostly performed in vacuum. Since it works by following the sample surface based on the force between the scanning tip and the sample, interactions have to be taken into account, making the AFM of irregular samples complicated, but on the other hand it allows measurements of more physical parameters than pure topography. This is especially important for biopolymers and hydrogels used in tissue engineering and other biotechnological applications, where elastic properties, surface charges and other parameters influence mammalian cell adhesion and growth as well as many other effects. This review gives an overview of AFM modes relevant for the investigations of biopolymers and hydrogels and shows several examples of recent applications, focusing on the polysaccharides chitosan, alginate, carrageenan and different hydrogels, but depicting also a broader spectrum of materials on which different AFM measurements are reported in the literature.

Effects of Nickel Nanoparticles on Rhodococcus Cell Surface Morphology and Nanomechanical Properties

Nickel nanoparticles (NPs) are used for soil remediation and wastewater treatment due to their high adsorption capacity against complex organic pollutants. However, despite the growing use of nickel NPs, their toxicological towards environmental bacteria have not been sufficiently studied. Actinobacteria of the genus Rhodococcus are valuable bioremediation agents degrading a range of harmful and recalcitrant chemicals. Both positive and negative effects of metal ions and NPs on the biodegradation of organic pollutants by Rhodococcus were revealed, however, the mechanisms of such interactions, in addition to direct toxic effects, remain unclear. In the present work, the influence of nickel NPs on the viability, surface topology and nanomechanical properties of Rhodococcus cells have been studied. Bacterial adaptations to high (up to 1.0 g/L) concentrations of nickel NPs during prolonged (24 and 48 h) exposure were detected using combined confocal laser scanning and atomic force microscopy. Incubation with nickel NPs resulted in a 1.25–1.5-fold increase in the relative surface area and roughness, changes in cellular charge and adhesion characteristics, as well as a 2–8-fold decrease in the Young’s modulus of Rhodococcus ruber IEGM 231 cells. Presumably, the treatment of rhodococcal cells with sublethal concentrations (0.01–0.1 g/L) of nickel NPs facilitates the colonization of surfaces, which is important in the production of immobilized biocatalysts based on whole bacterial cells adsorbed on solid carriers. Based on the data obtained, cell surface functionalizing with NPs is possible to enhance adhesive and catalytic properties of bacteria suitable for environmental applications.

Impact of engineered nanoparticles on the fate of antibiotic resistance genes in wastewater and receiving environments: A comprehensive review

Nanoparticles (NPs) and antibiotic resistance elements are ubiquitous in wastewater and consequently, in receiving environments. Sub-lethal levels of engineered NPs potentially result in a selective pressure on antibiotic resistance gene (ARG) propagation in wastewater treatment plants. Conversely, emergent NPs are being designed to naturally attenuate ARGs based on special physical and electrochemical properties, which could alleviate dissemination of ARGs to the environment. The complex interactions between NPs and antibiotic resistance elements have heightened interest in elucidating the potential positive and negative implications. This review focuses on the properties of NPs and ARGs and how their interactions could increase or decrease antibiotic resistance at wastewater treatment plants and in receiving environments. Further, the potential for sub-lethal level NPs to facilitate horizontal gene transfer of ARGs and increase mutagenesis rates, which adds a layer of complexity to combatting antibiotic resistance associated with wastewater management, is discussed. Notably, the literature revealed that sub-lethal exposure of engineered NPs may facilitate conjugative transfer of ARGs by increasing cell membrane permeability. The enhanced permeability is a result of direct damage via NP attachment and indirect damage by generating reactive oxygen species (ROS) and causing genetic changes relevant to conjugation. Finally, current knowledge gaps and future research directions (e.g., deciphering the fate of NPs in the environment and examining the long-term cytotoxicity of NPs) are identified for this emerging field.

Magnetic Nanoparticles-A Multifunctional Potential Agent for Diagnosis and Therapy

Magnetic nanoparticles gained considerable attention in last few years due to their remarkable properties. Superparamaganetism, non-toxicity, biocompatibility, chemical inertness, and environmental friendliness are some of the properties that make iron oxide nanoparticles (IONPs) an ideal choice for biomedical applications. Along with being easily tuneable and a tailored surface for conjugation of IONPs, their physio-chemical and biological properties can also be varied by modifying the basic parameters for synthesis that enhances the additional possibilities for designing novel magnetic nanomaterial for theranostic applications. This review highlights the synthesis, surface modification, and different applications of IONPs for diagnosis, imaging, and therapy. Furthermore, it also represents the recent report on the application of IONPs as enzyme mimetic compounds and a contrasting agent, and its significance in the field as an anticancer and antimicrobial agent.

Antibacterial Activity of Positively and Negatively Charged Hematite (α-Fe2O3) Nanoparticles to Escherichia coli, Staphylococcus aureus and Vibrio fischeri

In the current study, the antibacterial activity of positively and negatively charged spherical hematite (α-Fe2O3) nanoparticles (NPs) with primary size of 45 and 70 nm was evaluated against clinically relevant bacteria Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) as well as against naturally bioluminescent bacteria Vibrio fischeri (an ecotoxicological model organism). α-Fe2O3 NPs were synthesized using a simple green hydrothermal method and the surface charge was altered via citrate coating. To minimize the interference of testing environment with NP's physic-chemical properties, E. coli and S. aureus were exposed to NPs in deionized water for 30 min and 24 h, covering concentrations from 1 to 1000 mg/L. The growth inhibition was evaluated following the postexposure colony-forming ability of bacteria on toxicant-free agar plates. The positively charged α-Fe2O3 at concentrations from 100 mg/L upwards showed inhibitory activity towards E. coli already after 30 min of contact. Extending the exposure to 24 h caused total inhibition of growth at 100 mg/L. Bactericidal activity of positively charged hematite NPs against S. aureus was not observed up to 1000 mg/L. Differently from positively charged hematite NPs, negatively charged citrate-coated α-Fe2O3 NPs did not exhibit any antibacterial activity against E. coli and S. aureus even at 1000 mg/L. Confocal laser scanning microscopy and flow cytometer analysis showed that bacteria were more tightly associated with positively charged α-Fe2O3 NPs than with negatively charged citrate-coated α-Fe2O3 NPs. Moreover, the observed associations were more evident in the case of E. coli than S. aureus, being coherent with the toxicity results. Vibrio fischeri bioluminescence inhibition assays (exposure medium 2% NaCl) and colony forming ability on agar plates showed no (eco)toxicity of α-Fe2O3 (EC50 and MBC > 1000 mg/L).

Disturbance in Mineral Nutrition of Fenugreek Grown in Water Polluted with Nanosized Titanium Dioxide

Nanoparticle (NPs) toxicity in the plant has drawn considerable attention. Fenugreek plants were cultivated for 16 days in hydroponic experiments and treated with 50 and 100 mg L^- 1 titanium oxide (TiO₂) NPs of two sizes [23 ± 1.6 nm (D1) and 83 ± 15 nm. (D2)]. The level of Ti in roots was higher than that of leaves and stems of plants treated with 100 mg L^- 1 of TiO₂ NPs (D1, D2). Ti caused a depletion of Ca and Mn compared with root control. The titane (Ti) damage to root cellular membranes could alter the plant's capacity to absorb and transport some nutrients. In our study, increasing the size of TiO₂ NPs produced increases in the contents of Mg, Zn and Mn, and a decline in the contents of Fe and Cu in leaves and stems. In roots, Fe and Cu decreased after TiO₂ NPs (D2) exposure. Changes in the fenugreek plant mineral composition were assessed, and physiological disturbances could be directly correlated with exposure to NPs.

Surface Roughness of Cu-Bearing Stainless Steel Affects Its Contact-Killing Efficiency by Mediating the Interfacial Interaction with Bacteria

Numerous studies have found that the surface topography affects the material antibacterial properties by reducing the attachment of bacteria on the surfaces without influencing the viability of the adhered cells. For Cu-bearing alloys with excellent contact-killing properties, bacterial adhesion on the surface is also accompanied by short-range interactions which regulate the toxic effects of the material surface against bacterial cells. Thus, the surface topography of Cu-bearing alloys, as an important factor dominating the exposure level of bacteria on the surfaces, should affect the subsequent contact-killing efficiency. In this work, our major focus was on the regulation mechanism of the surface features on the material-bacterial interactions. We correlated the surface properties including different surface roughnesses of Cu-bearing stainless steel (SS) with the bacterial damage pattern and attempted to clarify the role of surface roughness in mediating the contact-killing behavior of Cu-bearing SS. The results of both atomic force microscopy and scanning electron microscopy investigations showed that E. coli cells experienced the most rapid physical and mechanical damages after incubating with the diamond-polished Cu-bearing SS surface. The bacterial cells noticeably stiffened and the adhesion force significantly increased, as evidenced by force-distance curve measurements. Because of the enhanced hydrophobicity and higher surface potential of the diamond-polished surface, which strengthened the Lewis acid-base attractive forces and weakened the electrostatic barrier between the bacteria and the surface, a higher exposure surface for bacteria was generated. Furthermore, the contact-induced charge transfer, manifested by Cu ion burst release, and reactive oxygen species overexpression contribute to an efficient contact-killing process.

Separation, characterization and identification of microplastics and nanoplastics in the environment

Microplastics (MPs) have globally been detected in aquatic and marine environments, which has raised scientific interests and public health concerns during the past decade. MPs are those polymeric particles with at least one dimension <5 mm. MPs possess complex physicochemical properties that vary their mobility, bioavailability and toxicity toward organisms and interactions with their surrounding pollutants. Similar to nanomaterials and nanoparticles, accurate and reliable detection and measurement of MPs or nanoplastics and their characteristics are important to warrant a comprehensive understanding of their environmental and ecological impacts. This review elaborates the principles and applications of diverse analytical instruments or techniques for separation, characterization and quantification of MPs in the environment. The strength and weakness of different instrumental methods in separation, morphological, physical classification, chemical characterization and quantification for MPs are critically compared and analyzed. There is a demand for standardized experimental procedures and characterization analysis due to the complex transformation, cross-contamination and heterogeneous properties of MPs in size and chemical compositions. Moreover, this review highlights emerging and promising characterization techniques that may have been overlooked by research communities to study MPs. The future research efforts may need to develop and implement new analytical tools and combinations of hyphenated technologies to complement respective limitations of detection and yield reliable characterization information for MPs. The goal of this critical review is to facilitate the research of plastic particles and pollutants in the environment and understanding of their environmental and human health effects.

Natural sphalerite nanoparticles can accelerate horizontal transfer of plasmid-mediated antibiotic-resistance genes

Minerals and microorganisms are integral parts of natural environments, and they inevitably interact. Antibiotic-resistance genes (ARGs) significantly threaten modern healthcare. However, the effects of natural minerals on ARG propagation in aquatic systems are not fully understood. The present work studied the effects of natural sphalerite (NS) nanoparticles on the horizontal transfer of ARGs from Escherichia coli DH5α (CTX) (donor) to E. coli C600 (Sm) (recipient), and from E. coli DH5α (MCR) (donor) to E. coli C600 (Sm), and their underlying mechanisms. NS particles (0.5-50 mg L^-1) induced an NS-concentration-dependent increase in conjugative transfer frequency. The underlying mechanisms associated with the facilitated ARG transfer included the production of intracellular reactive oxygen species, the SOS response, changes in bacterial cell morphology, and alteration of mRNA levels of bacterial cell membrane protein-related genes and genes associated with conjugative ARG transfer. The information herein offers new mechanistic understanding of risks of bacterial resistance resulting from NS.

Contact Killing of Cu-Bearing Stainless Steel Based on Charge Transfer Caused by the Microdomain Potential Difference

The addition of copper makes the Cu-bearing stainless steel (SS) possess excellent antibacterial properties. However, the antibacterial mechanism of the Cu-bearing SS is still not accurately understood and recognized. On the one hand, the concentration of released antibacterial Cu ions from its surface is insufficient to generate such an effect. On the other hand, due to the limited Cu content, the area of copper toxicity that can be contacted with bacteria is also much less than that of pure Cu. Therefore, the purpose of this study was to explore the way of bacterial inactivation caused by Cu-bearing SS from the view of the charge transfer. The results showed that the continuous and effective contact between bacteria and Cu-bearing SS is the key to induce the bacteria-killing effect so that the cathode electrons generated by the potential difference of the material microdomain can cause the proton depletion in the bacterial cells, thereby disturbing the respiratory chain and energy generation of the bacterial cells. The proton depletion reaction also catalyzed the conversion of Cu(II) into Cu(I). Cu(I) not only destroys the iron-sulfur protein but also undergoes the redox reaction with Cu(II) to produce reactive oxygen species, causing oxidative damage to cells, eventually accelerating the bacterial death.

Using Atomic Force Microscopy To Illuminate the Biophysical Properties of Microbes

Since its invention in 1986, atomic force microscopy (AFM) has grown from a system designed for imaging inorganic surfaces to a tool used to probe the biophysical properties of living cells and tissues. AFM is a scanning probe technique and uses a pyramidal tip attached to a flexible cantilever to scan across a surface, producing a highly detailed image. While many research articles include AFM images, fewer include force-distance curves, from which several biophysical properties can be determined. In a single force-distance curve, the cantilever is lowered and raised from the surface, while the forces between the tip and the surface are monitored. Modern AFM has a wide variety of applications, but this review will focus on exploring the mechanobiology of microbes, which we believe is of particular interest to those studying biomaterials. We briefly discuss experimental design as well as different ways of extracting meaningful values related to cell surface elasticity, cell stiffness, and cell adhesion from force-distance curves. We also highlight both classic and recent experiments using AFM to illuminate microbial biophysical properties.

Size-Dependent Bacterial Toxicity of Hematite Particles

Submicron-sized iron oxide particles can influence the activity of bacteria, but the exact mechanisms of oxide toxicity toward bacteria remain elusive. By using atomic force microscopy (AFM), soft X-ray tomography (Nano-CT), and Fourier transform infrared (FTIR) spectrometry, we show how the size-dependent interfacial interactions between hematite particles and bacteria in the absence of any ligands contribute to the antimicrobial properties against Gram-positive and Gram-negative bacterial strains. We found that surface adhesion between hematite particles and bacterial cells is initially dominated by Lifshitz van der Waals and electrostatic forces. Subsequently, the rapid formation of P-O-Fe bonds occurs, followed by changes in the structures of membrane proteins in 2 h, resulting in the loss of the structural integrity of the membrane within 10 h. Thus, particles can migrate into the cells. After contact with bacterial cells, reactive oxygen species are generated on the surface of hematite particles, leading to cell permeabilization. G^- bacteria appear to be more susceptible to this process than G⁺ bacteria because the latter exhibit weaker adhesion forces toward hematite and benefit from the protective effects of the peptidoglycan layers. Our work revealed that hematite nanoparticles are more toxic to bacteria than microscaled particles due to their strong interfacial physicochemical interactions with the cells.

Bioaccumulation and effects of titanium dioxide nanoparticles and bulk in the clam Ruditapes philippinarum

Biochemical and cellular responses to low concentrations of TiO₂ nanoparticles (nTiO_2, 1 and 10 μg/L) and bulk (bTiO₂, 10 μg/L) were evaluated in gills, digestive gland and haemolymph of the clam Ruditapes philippinarum after1, 3 and 7 days' exposure. At 7 days, titanium content was determined in gills and digestive gland. nTiO₂ significantly increased antioxidant enzyme activities in both tissues, and lipid peroxidation in digestive gland at 10 μg/L only, and affected glutathione S-transferase activity. Slighter variations were observed in bTiO₂-treated clams. A significant Ti bioaccumulation was detected in both gills and digestive gland of 10 μg nTiO₂/L-exposed clams. In haemolymph, nTiO₂ affected total haemocyte count, haemocyte proliferation, haemocyte diameter and volume, and induced DNA damage. Overall, this study demonstrated that TiO₂ alters most of the biomarkers measured in clams, although responses were differently modulated depending on tissues and exposure conditions, and indicated that nTiO₂ can be accumulated by bivalves, suggesting a potential risk for filter-feeding animals.

Homoagglomeration and heteroagglomeration of TiO2, in nanoparticle and bulk form, onto freshwater and marine microalgae

TiO₂ nanoparticles (TiO₂ NPs) are employed in many products (paints, personal care products, especially sunscreens, plastics, paper, water potabilization and food products) and are then released into the environment from these products. These nanoparticles present potential risk to freshwater and marine microalgae. The primary toxicity mechanism is adsorption between NPs and microalgae (heteroagglomeration); however, studies of interactions of this kind are scarce. We investigated the heteroagglomeration process that occurs between two forms of TiO₂ material, nanoparticles and bulk, and three different microalgae species, and under different environmental conditions (freshwater and marine water), in order to assess the influence of pH and ionic strength (IS). The heteroagglomeration process was examined by means of co-settling experiments and the Derjaguin-Landau-Verwey-Overbeek (DLVO) approach. The homoagglomeration process (only NPs to NPs) did not show differences between culture media (freshwater and marine water). However, in the heteroagglomeration process between NPs and cells, IS played an important role. Ions can compress the electro-double layer between NPs and microalgae, allowing a heteroagglomeration process to take place, as shown by settling experiments. TiO₂ NPs presented a settling rate higher than bulk TiO₂. The DLVO theory could only partially explain heteroagglomeration because, in this model, it is not considered that NP-NP and Cell-Cell homoagglomeration co-occur. In this study neither the role of exopolymeric substances in the interaction between NPs and cells nor detoxification are considered. The authors suggest that the interaction between NPs and microalgae could be considered as the first stage in the process by which nanoparticles affect microalgae.

Effect of gold nanoparticles on thermal gradient generation and thermotaxis of E. coli cells in microfluidic device

Bacteria responds to changing chemical and thermal environment by moving towards or away from a particular location. In this report, we looked into thermal gradient generation and response of E. coli DH5α cells to thermal gradient in the presence and in the absence of spherical gold nanoparticles (size: 15 to 22 nm) in a static microfluidic environment using a polydimethylsiloxane (PDMS) made microfluidic device. A PDMS-agarose based microfluidic device for generating thermal gradient has been developed and the thermal gradient generation in the device has been validated with the numerical simulation. Our studies revealed that the presence of gold nanoparticles, AuNPs (0.649 μg/mL) has no effect on the thermal gradient generation. The E. coli DH5α cells have been treated with AuNPs of two different concentrations (0.649 μg/mL and 0.008 μg/mL). The thermotaxis behavior of cells in the presence of AuNPs has been studied and compared to the thermotaxis of E.coli DH5α cells in the absence of AuNPs. In case of thermotaxis, in the absence of the AuNPs, the E. coli DH5α cells showed better thermotaxis towards lower temperature range, whereas in the presence of AuNPs (0.649 μg/mL and 0.008 μg/mL) thermotaxis of the E. coli DH5α cells has been inhibited. The results show that the spherical AuNPs intervenes in the themotaxis of E. coli DH5α cells and inhibits the cell migration. The reason for the failure in thermotaxis response mechanism may be due to decreased F-type ATP synthase activity and collapse of membrane potential by AuNPs, which, in turn, leads to decreased ATP levels. This has been hypothesized since both thermotaxis and chemotaxis follows the same response mechanism for migration in which ATP plays critical role.

Hybrid AFM for Nanoscale Physicochemical Characterization: Recent Development and Emerging Applications

Atomic force microscopy (AFM) has evolved to be one of the most powerful tools for the characterization of material surfaces especially at the nanoscale. Recent development of AFM has incorporated a suite of analytical techniques including surface-enhanced Raman scattering (SERS) technique and infrared (IR) spectroscopy to further reveal chemical composition and map the chemical distribution. This incorporation not only elevates the functionality of AFM but also increases the resolution limitation of conventional IR and Raman spectroscopy. Despite the rapid development of such hybrid AFM techniques, many unique features, principles, applications, potential pitfalls or artifacts are not well known to the community. This review systematically summarizes the recent relevant literature on hybrid AFM principles and applications. It focuses specially on AFM-IR and AFM-Raman techniques. Various applications in different research fields are critically reviewed and discussed, highlighting the potentials of these hybrid AFM techniques. Here, the major drawbacks and limitations of these two hybrid AFM techniques are presented. The intentions of this article are to shed new light on the future research and achieve improvements in stability and reliability of the measurements.

Magnetite nanoparticles influence the ammonium-oxidizing bacteria activity during nitritation process

With nanotechnology dissemination, nanomaterials' (NMs) release into the environment is inevitable and may adversely affect the wastewater treatment processes. Among the NMs, the iron oxide nanoparticles have a considerable commercial potential, mainly because their magnetic properties, high catalytic ability and antimicrobial activity. However, few studies have examined their potential effect on the biological wastewater treatment. In this process, ammonium-oxidizing bacteria (AOB) are sensitive to the presence of inhibitory compounds and are useful as biosensors to assess contaminant toxicity information. Thus, this work aimed to assess the effect of commercial magnetite nanoparticles (Fe₃O₄-NPs) on AOB activity. Kinetic experiments were carried out where AOB were exposed in a short-term period (14 h) to different concentrations (from 0.2 to 1.0 g L^-1) of Fe₃O₄-NPs. A decrease of the 61.33% in the NO₂^--N production rate was observed to the highest concentration of Fe₃O₄-NPs studied, compared with the control sample. The Fe₃O₄-NPs concentration that reduces 50% of NO₂^--N production rate (IC-50) was estimated 0.483 g Fe₃O₄-NP L^-1. Scanning electron microscopy images revealed that NPs remained incorporated in the biomass (sludge). These results suggest that NPs can reach the environment through sludge disposal, mainly in cases of the reuse as soil fertilizer.

E. coli Surface Properties Differ between Stream Water and Sediment Environments

The importance of E. coli as an indicator organism in fresh water has led to numerous studies focusing on cell properties and transport behavior. However, previous studies have been unable to assess if differences in E. coli cell surface properties and genomic variation are associated with different environmental habitats. In this study, we investigated the variation in characteristics of E. coli obtained from stream water and stream bottom sediments. Cell properties were measured for 77 genomically different E. coli strains (44 strains isolated from sediments and 33 strains isolated from water) under common stream conditions in the Upper Midwestern United States: pH 8.0, ionic strength 10 mM and 22°C. Measured cell properties include hydrophobicity, zeta potential, net charge, total acidity, and extracellular polymeric substance (EPS) composition. Our results indicate that stream sediment E. coli had significantly greater hydrophobicity, greater EPS protein content and EPS sugar content, less negative net charge, and higher point of zero charge than stream water E. coli. A significant positive correlation was observed between hydrophobicity and EPS protein for stream sediment E. coli but not for stream water E. coli. Additionally, E. coli surviving in the same habitat tended to have significantly larger (GTG)₅ genome similarity. After accounting for the intrinsic impact from the genome, environmental habitat was determined to be a factor influencing some cell surface properties, such as hydrophobicity. The diversity of cell properties and its resulting impact on particle interactions should be considered for environmental fate and transport modeling of aquatic indicator organisms such as E. coli.

Assessment of agglomeration, co-sedimentation and trophic transfer of titanium dioxide nanoparticles in a laboratory-scale predator-prey model system

Nano titanium dioxide (nTiO₂) is the most abundantly released engineered nanomaterial (ENM) in aquatic environments. Therefore, it is prudent to assess its fate and its effects on lower trophic-level organisms in the aquatic food chain. A predator-and-prey-based laboratory microcosm was established using Paramecium caudatum and Escherichia coli to evaluate the effects of nTiO₂. The surface interaction of nTiO₂ with E. coli significantly increased after the addition of Paramecium into the microcosm. This interaction favoured the hetero-agglomeration and co-sedimentation of nTiO₂. The extent of nTiO₂ agglomeration under experimental conditions was as follows: combined E. coli and Paramecium > Paramecium only > E. coli only > without E. coli or Paramecium. An increase in nTiO₂ internalisation in Paramecium cells was also observed in the presence or absence of E. coli cells. These interactions and nTiO₂ internalisation in Paramecium cells induced statistically significant (p < 0.05) effects on growth and the bacterial ingestion rate at 24 h. These findings provide new insights into the fate of nTiO₂ in the presence of bacterial-ciliate interactions in the aquatic environment.

Facile synthesis of (55)Fe-labeled well-dispersible hematite nanoparticles for bioaccumulation studies in nanotoxicology

Although water-dispersible engineered nanoparticles (ENPs) have a wide range of applications, the ENPs used in many nanotoxicological studies tend to form micron-sized aggregates in the exposure media and thus cannot reflect the toxicity of real nanoparticles. Here we described the synthesis of bare hematite nanoparticles (HNPs-0) and two poly(acrylic acid) (PAA)-coated forms (HNPs-1 and HNPs-2). All three HNPs were well dispersed in deionized water, but HNPs-0 quickly aggregated in the three culture media tested. By contrast, the suspensions of HNPs-1 and HNPs-2 remained stable, with negligible amounts of PAA and Fe(3+) liberated from either one under the investigated conditions. To better quantify the accumulation of the coated HNPs, a relatively innocuous (55)Fe-labeled form of HNPs-2 was synthesized as an example and its accumulation in three phytoplankton species was tested. Consistent with the uptake kinetics model for conventional pollutants, the cellular accumulation of HNPs-2 increased linearly with exposure time for two of the three phytoplankton species. These results demonstrate the utility of (55)Fe-labeled well-dispersible HNPs as a model material for nanoparticle bioaccumulation studies in nanotoxicology.

The impact of sphingosine kinase inhibitor-loaded nanoparticles on bioelectrical and biomechanical properties of cancer cells

Cancer progression and physiological changes within the cells are accompanied by alterations in the biophysical properties. Therefore, the cell biophysical properties can serve as promising markers for cancer detection and physiological activities. To aid in the investigation of the biophysical markers of cells, a microfluidic chip has been developed which consists of a constriction channel and embedded microelectrodes. Single-cell impedance magnitudes at four frequencies and entry and travel times are measured simultaneously during their transit through the constriction channel. This microchip provides a high-throughput, label-free, automated assay to identify biophysical signatures of malignant cells and monitor the therapeutic efficacy of drugs. Here, we monitored the dynamic cellular biophysical properties in response to sphingosine kinase inhibitors (SphKIs), and compared the effectiveness of drug delivery using poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) loaded with SphKIs versus conventional delivery. Cells treated with SphKIs showed significantly higher impedance magnitudes at all four frequencies. The bioelectrical parameters extracted using a model also revealed that the highly aggressive breast cells treated with SphKIs shifted electrically towards that of a less malignant phenotype; SphKI-treated cells exhibited an increase in cell-channel interface resistance and a significant decrease in specific membrane capacitance. Furthermore, SphKI-treated cells became slightly more deformable as measured by a decrease in their channel entry and travel times. We observed no significant difference in the bioelectrical changes produced by SphKI delivered conventionally or with NPs. However, NPs-packaged delivery of SphKI decreased the cell deformability. In summary, this study showed that while the bioelectrical properties of the cells were dominantly affected by SphKIs, the biomechanical properties were mainly changed by the NPs.

Sensitive Detection of Deliquescent Bacterial Capsules through Nanomechanical Analysis

Encapsulated bacteria usually exhibit strong resistance to a wide range of sterilization methods, and are often virulent. Early detection of encapsulation can be crucial in microbial pathology. This work demonstrates a fast and sensitive method for the detection of encapsulated bacterial cells. Nanoindentation force measurements were used to confirm the presence of deliquescent bacterial capsules surrounding bacterial cells. Force/distance approach curves contained characteristic linear-nonlinear-linear domains, indicating cocompression of the capsular layer and cell, indentation of the capsule, and compression of the cell alone. This is a sensitive method for the detection and verification of the encapsulation status of bacterial cells. Given that this method was successful in detecting the nanomechanical properties of two different layers of cell material, i.e. distinguishing between the capsule and the remainder of the cell, further development may potentially lead to the ability to analyze even thinner cellular layers, e.g. lipid bilayers.

Translocation and biotransformation of CuO nanoparticles in rice (Oryza sativa L.) plants

Metal-based nanoparticles (MNPs) may be translocated and biochemically modified in vivo, which may influence the fate of MNPs in the environment. Here, synchrotron-based techniques were used to investigate the behavior of CuO NPs in rice plants exposed to 100 mg/L CuO NPs for 14 days. Micro X-ray fluorescence (μ-XRF) and micro X-ray absorption near edge structure (μ-XANES) analysis revealed that CuO NPs moved into the root epidermis, exodermis, and cortex, and they ultimately reached the endodermis but could not easily pass the Casparian strip; however, the formation of lateral roots provided a potential pathway for MNPs to enter the stele. Moreover, bulk-XANES data showed that CuO NPs were transported from the roots to the leaves, and that Cu (II) combined with cysteine, citrate, and phosphate ligands and was even reduced to Cu (I). CuO NPs and Cu-citrate were observed in the root cells using soft X-ray scanning transmission microscopy (STXM).

Adsorption of MS2 on oxide nanoparticles affects chlorine disinfection and solar inactivation

Adsorption on colloidal particles is one of the environmental processes affecting fate, transport, viability or reproducibility of viruses. This work studied colloidal interactions (adsorption kinetics and isotherms) between different oxide nanoparticles (NPs) (i.e., TiO2, NiO, ZnO, SiO2, and Al2O3) and bacteriophage, MS2. The results shows that that all oxide NPs exhibited strong adsorption capacity for MS2, except SiO2 NPs, which is supported by the extended Derjaguin and Landau, Verwey and Overbeek (EDLVO) theory. Moreover, the implication of such colloidal interactions on water disinfection is manifested by the observations that the presence of TiO2 and ZnO NPs could enhance MS2 inactivation under solar irradiation, whereas NiO and SiO2 decreased MS2 inactivation. By contrast, all of these oxide NPs were found to mitigate chlorine disinfection against MS2 to different extent, and the shielding effect was probably caused by reduced free chlorine and free MS2 in the solution due to sorption onto NPs. Clearly, there is a pressing need to further understand colloidal interactions between engineered NPs and viruses in water to better improve the current water treatment processes and to develop novel nanomaterials for water disinfection.

Heteroagglomeration of oxide nanoparticles with algal cells: effects of particle type, ionic strength and pH

Discharged oxide nanoparticles (NPs) have been shown toxic to unicellular algae, yet the research on heteroagglomeration between NPs and cells as an important precondition of the toxicity is scarce. This study for the first time investigated heteroagglomerations between various NPs and algal cells (Chlorella pyrenoidosa) and analyzed influencing factors including pH and ionic strength (IS) through cosettling experiment, transmission electron microscopic (TEM) observation, and Derjaguin–Landau–Verwey–Overbeek (DLVO) calculation. The examined NPs included anatase and rutile TiO2, microporous and spherical SiO2, and α-form and β-form Al2O3. The results of cosettling experiments coincided well with the TEM observations, whereas the DLVO theory could only partly explain the NP–cell heteroagglomerations. The NP–cell heteroagglomeration for rutile TiO2 and β-form Al2O3 was weak and insensitive to pH or IS. Preferential heteroagglomeration occurred at low pH or high IS for microporous SiO2, while marked heteroagglomeration only occurred under the neutral and low IS condition for anatase TiO2. The heteroagglomeration for spherical SiO2 was insensitive to pH but increased with increasing IS, while the heteroagglomeration for α-form Al2O3 occurred at low pH and irrelevant to IS. The work will shed new light on the bionano interfacial interaction and help to understand biological effects of NPs.

Influences of surface coating, UV irradiation and magnetic field on the algae removal using magnetite nanoparticles

Magnetophoretic separation is a promising and sustainable technology for rapid algal separation or removal from water. This work demonstrated the application of magnetic magnetite nanoparticles (MNPs) coated with a cationic polymer, polyethylenimine (PEI), toward the separation of Scenedesmus dimorphus from the medium broth. The influences of surface coating, UV irradiation, and magnetic field on the magnetophoretic separation were systematically examined. After PEI coating, zeta potential of MNPs shifted from −7.9 ± 2.0 to +39.0 ± 3.1 mV at a pH of 7.0, which improved MNPs-algae interaction and helped reduce the dose demand of MNPs (e.g., from 0.2 to 0.1 g·g(–1) while the harvesting efficiency (HE) of over 80% remained unchanged). The extended Derjaguin–Landau–Verwey–Overbeek theory predicted a strong attractive force between PEI-coated MNPs and algae, which supported the improved algal harvesting. Moreover, the HE was greater under the UV365 irradiation than that under the UV254, and increased with the irradiation intensity. Continuous application of the external magnetic field at high strength remarkably improved the algal harvesting. Finally, the reuse of MNPs for multiple cycles of algal harvesting was studied, which aimed at increasing the sustainability and lowering the cost.

Comparative evaluation and optimization of off-the-shelf cationic polymers for gene delivery purposes

Commercially sourced cationic polymers for gene delivery are thoroughly characterized, compared and optimized.

Surface potential measurement of bacteria using Kelvin probe force microscopy

Surface potential is a commonly overlooked physical characteristic that plays a dominant role in the adhesion of microorganisms to substrate surfaces. Kelvin probe force microscopy (KPFM) is a module of atomic force microscopy (AFM) that measures the contact potential difference between surfaces at the nano-scale. The combination of KPFM with AFM allows for the simultaneous generation of surface potential and topographical maps of biological samples such as bacterial cells. Here, we employ KPFM to examine the effects of surface potential on microbial adhesion to medically relevant surfaces such as stainless steel and gold. Surface potential maps revealed differences in surface potential for microbial membranes on different material substrates. A step-height graph was generated to show the difference in surface potential at a boundary area between the substrate surface and microorganisms. Changes in cellular membrane surface potential have been linked with changes in cellular metabolism and motility. Therefore, KPFM represents a powerful tool that can be utilized to examine the changes of microbial membrane surface potential upon adhesion to various substrate surfaces. In this study, we demonstrate the procedure to characterize the surface potential of individual methicillin-resistant Staphylococcus aureus USA100 cells on stainless steel and gold using KPFM.

Whole-cell based label-free capacitive biosensor for rapid nanosize-dependent toxicity detection

Despite intensive studies on examining the toxicity of nanomaterials (NMs), our current understanding on potential toxicity in relation to size and cellular responses has remained limited. In this work, we have developed a whole-cell based capacitive biosensor (WCB) to determine the biological toxicity of nanoparticles (NPs) using iron oxide (Fe3O4) NPs as models. This WCB chip comprised of an array of capacitor sensors made of gold interdigitated microelectrodes on which living Escherichia coli cells were immobilized. Cells-on-chip was then allowed to interact with different sizes of Fe3O4 NPs (5, 20 and 100 nm) and concentration-depended cellular-responses were measured in terms of change in dielectric properties (capacitance) as a function of applied AC frequency. The WCB response showed smaller-sized Fe3O4 NPs (5 nm) induced maximum change in surface capacitance because of their effective cellular interaction with E. coli cells-on-chip indicating that the cells suffered from severe cellular deformation, which was confirmed by scanning electron microscopic (SEM) examination. Further our results were validated through their cell viability and E. coli responses at the interface of cell-membrane and NPs as a proof-of-concept. WCB response showed a size-dependent shift in maximum response level from 2 µg/ml of 5 nm sized NPs to 4 µg/ml with NP-sizes greater than 20 nm. The developed WCB offered real-time, label-free and noninvasive detection of cellular responses against Fe3O4 NPs' toxicity with speed, simplicity and sensitivity that can be extended to toxicity screening of various other NPs.

Curvature enhances binding and aggregation of huntingtin at lipid membranes

Huntington disease (HD) is a genetic neurodegenerative disease caused by an expanded polyglutamine (polyQ) domain in the first exon of the huntingtin (Htt) protein, facilitating its aggregation. Htt interacts with a variety of membraneous structures within the cell, and the first 17 amino acids (Nt17) of Htt directly flanking the polyQ domain comprise an amphiphathic α-helix (AH) lipid-binding domain. AHs are also known to detect membrane curvature. To determine if Htt exon 1 preferentially binds curved membranes, in situ atomic force microscopy (AFM) studies were performed. Supported lipid bilayers are commonly used as model membranes for AFM studies of protein aggregation. However, these supported bilayers usually lack curvature. By forming a bilayer on top of silica nanobeads (50 ± 10 nm) deposited on a silicon substrate, model supported lipid bilayers with flat and curved regions were developed for AFM studies. The presence of the bilayer over the beads was validated by continual imaging of the formation of the bilayer, height measurements, and spatially resolved mechanical measurements of the resulting bilayer using scanning probe acceleration microscopy. Interpretation of this data was facilitated by numerical simulations of the entire imaging process. The curved supported bilayers associated with the beads were found to be more compliant than flat supported bilayers, consistent with the altered packing density of lipids caused by the induced curvature. This model bilayer system was exposed to a synthetic truncated Htt exon 1 peptide (Nt17Q35P10KK), and this peptide preferentially accumulated on curved membranes, consistent with the ability of AHs to sense membrane curvature.

High-throughput screening platform for engineered nanoparticle-mediated genotoxicity using CometChip technology

The likelihood of intentional and unintentional engineered nanoparticle (ENP) exposure has dramatically increased due to the use of nanoenabled products. Indeed, ENPs have been incorporated in many useful products and have enhanced our way of life. However, there are many unanswered questions about the consequences of nanoparticle exposures, in particular, with regard to their potential to damage the genome and thus potentially promote cancer. In this study, we present a high-throughput screening assay based upon the recently developed CometChip technology, which enables evaluation of single-stranded DNA breaks, abasic sites, and alkali-sensitive sites in cells exposed to ENPs. The strategic microfabricated, 96-well design and automated processing improves efficiency, reduces processing time, and suppresses user bias in comparison to the standard comet assay. We evaluated the versatility of this assay by screening five industrially relevant ENP exposures (SiO2, ZnO, Fe2O3, Ag, and CeO2) on both suspension human lymphoblastoid (TK6) and adherent Chinese hamster ovary (H9T3) cell lines. MTT and CyQuant NF assays were employed to assess cellular viability and proliferation after ENP exposure. Exposure to ENPs at a dose range of 5, 10, and 20 μg/mL induced dose-dependent increases in DNA damage and cytotoxicity. Genotoxicity profiles of ZnO>Ag>Fe2O3>CeO2>SiO2 in TK6 cells at 4 h and Ag>Fe2O3>ZnO>CeO2>SiO2 in H9T3 cells at 24 h were observed. The presented CometChip platform enabled efficient and reliable measurement of ENP-mediated DNA damage, therefore demonstrating the efficacy of this powerful tool in nanogenotoxicity studies.

Influence of aqueous media on the ROS-mediated toxicity of ZnO nanoparticles toward green fluorescent protein-expressing Escherichia coli under UV-365 irradiation

The aqueous media could affect the physicochemical properties (e.g., surface charge, morphology, and aggregation) of ZnO nanoparticles (nZnO), leading to their different environmental impacts. In this study, the toxicity of nZnO toward the green fluorescent protein-expressing Escherichia coli cells under UV-365 light irradiaiton in various media was assessed, including deionized (DI) water, 0.85% NaCl, phosphate-buffered saline (PBS), minimal Davis medium (MD), and Luria-Bertani medium (LB). The toxicity of nZnO was assessed by the conventional plate count method and the fluorescence intensity method, which consistently demonstrated that the nZnO toxicity was dependent on the medium components that varied the potency of reactive oxygen species (ROS) generation. In DI, NaCl, PBS, and MD medium, nZnO generated three types of ROS (O2(•-), •OH, and (1)O2), whereas in LB medium, nZnO generated O2(•-) and (1)O2. The total concentrations of ROS generated by nZnO in DI, NaCl, PBS, MD, and LB were 265.5 ± 15.9, 153.6 ± 8.6, 144.3 ± 6.9, 123.0 ± 6.0, and 115.6 ± 4.5 μM, respectively. Furthermore, a linear correlation was established between the total concentrations of three types of ROS generated by nZnO and their bacterial mortality rate (R(2) = 0.92) in various media. Since the released Zn(2+) from nZnO under UV irradiation only accounted for less than 10% of the total Zn in all media, the ionic forms of zinc did not significantly contribute to the overall toxicity. This work aims at providing further insight into the medium type influences on the ROS production and the toxicity of nZnO toward the E. coli cells.

Characterization of electrical surface properties of mono- and co-cultures of Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus using Kelvin probe force microscopy

Quantitative nanoscale surface potential measurement of individual pathogenic bacterial cells for understanding the adhesion kinetics using Kelvin probe force microscopy.

Nanoparticles inhibit DNA replication by binding to DNA: modeling and experimental validation

Predictive models are beneficial tools for researchers to use in prioritizing nanoparticles (NPs) for toxicological tests, but experimental evaluation can be time-consuming and expensive, and thus, priority should be given to tests that identify the NPs most likely to be harmful. For characterization of NPs, the physical binding of NPs to DNA molecules is important to measure, as interference with DNA function may be one cause of toxicity. Here, we determined the interaction energy between 12 types of NPs and DNA based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) model and then predicted the affinity of the NPs for DNA. Using the single-molecule imaging technique known as atomic force microscopy (AFM), we experimentally determined the binding affinity of those NPs for DNA. Theoretical predictions and experimental observations of the binding affinity agreed well. Furthermore, the effect of NPs on DNA replication in vitro was investigated with the polymerase chain reaction (PCR) technique. The results showed that NPs with a high affinity for DNA strongly inhibited DNA replication, whereas NPs with low affinity had no or minimal effects on DNA replication. The methodology here is expected to benefit the genotoxicological testing of NPs as well as the design of safe NPs.

Nanoscale mechano-electronic behavior of a metalloprotein as a variable of metal content

In this work, we have explored an approach to finding a correlation between the mechanical response of a metalloprotein against a range of applied force (by force curve analysis) and its electrical response under pressure stimulation (by current sensing atomic force spectroscopy) at the nanoscale. Iron-storage protein ferritin has been chosen as an experimental model system because it naturally contains a semiconducting iron core. This core consists of a large number of iron atoms and is therefore expected to exert a clear influence on the overall mechanical response of the protein structure. Four different ferritins (apoferritin, Fe(III)-ferritins containing ~750 and ~1400 iron atoms, and holoferritin containing ~2600 iron atoms) were chosen in order to identify any relation between the mechano-electronic behavior of the ferritins and their metal content. We report the measurement of Young's modulus values of the ferritin proteins as applicable in a nanoscale environment, for the first time, and show that these values are directly linked to the iron content of the individual ferritin type. The greater the iron content, the greater the Young's modulus and in general the slower the rate of deformation against the application of force. When compressed, all the four ferritins exhibited increased electronic conductivity. A correlation between the iron content of the ferritins and the current values observed at certain bias voltages could be made at higher bias values (beyond 0.7 V), but no such discrimination among the four compressed ferritins could be made at the lower voltages. We propose that only at higher voltages can the iron atoms that reside deeper inside the core of the ferritins be accessed. The iron atoms that could be situated at the inner wall of the protein shell appear to make a general contribution to the electronic conductivity of the four ferritin systems.