The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review

Metal-based nanomaterials as antimicrobial agents: A novel driveway to accelerate the aggravation of antibiotic resistance

The consequences of antibiotic tolerance directly affect human health and result in socioeconomic loss. Nanomaterials as antimicrobial agents are considered a promising alternative to antibiotics and have been blended with various medical applications. However, with increasing evidence that metal-based nanomaterials may induce antibiotic tolerance, there is an urgent need to scrutinize how nanomaterial-induced microbial adaption affects the evolution and spread of antibiotic tolerance. Accordingly, within this investigation, we summarized the principal factors influencing the resistance development exposed to metal-based nanomaterials, including physicochemical properties, exposure scenario, as well as bacterial response. Furthermore, the mechanisms of metal-based nanomaterial-induced antibiotic resistance development were comprehensively elucidated from acquired resistance by horizontal transfer of antibiotic resistance genes (ARGs), intrinsic resistance by genetic mutation or upregulated resistance-related gene expression, and adaptive resistance by global evolution. Overall, our review raises concerns about the safety of nanomaterials as antimicrobial agents, which will facilitate assistance in the safe development of antibiotic-free antibacterial strategies.

Analytical methods for assessing antimicrobial activity of nanomaterials in complex media: advances, challenges, and perspectives

Assessing the antimicrobial activity of engineered nanomaterials (ENMs), especially in realistic scenarios, is of great significance for both basic research and applications. Multiple analytical methods are available for analysis via off-line or on-line measurements. Real-world samples are often complex with inorganic and organic components, which complicates the measurements of microbial viability and/or metabolic activity. This article highlights the recent advances achieved in analytical methods including typical applications and specifics regarding their accuracy, cost, efficiency, and user-friendliness. Methodological drawbacks, technique gaps, and future perspectives are also discussed. This review aims to help researchers select suitable methods for gaining insight into antimicrobial activities of targeted ENMs in artificial and natural complex matrices.

Theoretical basis and experimental verification for evaluating the distribution of engineered nanoparticles in water-oil system

The distribution of nanoparticles between aqueous and organic phases is universally considered as the starting point in predicting the fate and bioavailability of engineered nanoparticles in the environment. However, the theoretical basis for determining the distribution of nanoparticles in the immiscible water-oil system remains unclear. Here, for the first time, theoretical calculations were conducted to illustrate the underlying mechanism. It was suggested that the distribution of nanoparticles was largely controlled by the surface charge, particle size and surface hydrophobicity, and the water-oil interface was not the favorable phase for nanoparticles until a size threshold (10 nm) was met and the particle surface became amphiphilic. The theoretical results were verified by the experimental approaches of different nanoparticles distributed in the water-octanol mixture. The neutralization of a charged surface led to enhanced distribution into octanol for hydrophobic nanoparticles (e.g., aqueous C₆₀), yet it had little effect on hydrophilic nanoparticles (e.g., fullerol). More nanoparticles were trapped at the water-oil interface when size grew larger (e.g., Ag-CIT and Au-CIT with citrate) and the surface rendered amphiphilic by polymeric coatings (e.g., Ag-PVP with polyvinylpyrrolidone), though larger hydrophobic nanoparticles like aqu-nC₆₀ tended to stay in the octanol. The surface charge and hydrophobicity may have an important impact on the path-dependent distribution of nanoparticles in water- octanol system. The mechanistic insights based on theoretical calculations and experimental approaches will facilitate the accurate prediction of the distribution of engineered nanoparticles in biological and environmental systems.

Review and Prospects on the Ecotoxicity of Mixtures of Nanoparticles and Hybrid Nanomaterials

The rapid development of nanomaterials (NMs) and the emergence of new multicomponent NMs will inevitably lead to simultaneous exposure of organisms to multiple engineered nanoparticles (ENPs) at varying exposure levels. Understanding the joint impacts of multiple ENPs and predicting the toxicity of mixtures of ENPs are therefore evidently of importance. We reviewed the toxicity of mixtures of ENPs to a variety of different species, covering algae, bacteria, daphnia, fish, fungi, insects, and plants. Most studies used the independent-action (IA)-based model to assess the type of joint effects. Using co-occurrence networks, it was revealed that 53% of the cases with specific joint response showed antagonistic, 25% synergistic, and 22% additive effects. The combination of nCuO and nZnO exhibited the strongest interactions in each type of joint interaction. Compared with other species, plants exposed to multiple ENPs were more likely to experience antagonistic effects. The main factors influencing the joint response type of the mixtures were (1) the chemical composition of individual components in mixtures, (2) the stability of suspensions of mixed ENPs, (3) the type and trophic level of the individual organisms tested, (4) the biological level of organization (population, communities, ecosystems), (5) the exposure concentrations and time, (6) the endpoint of toxicity, and (7) the abiotic field conditions (e.g., pH, ionic strength, natural organic matter). This knowledge is critical in developing efficient strategies for the assessment of the hazards induced by combined exposure to multiple ENPs in complex environments. In addition, this knowledge of the joint effects of multiple ENPs assists in the effective prediction of hybrid NMs.

The key to maximizing the benefits of antimicrobial and self-cleaning coatings is to fully determine their risks

Antimicrobial and self-cleaning nanomaterial coatings have attracted significant research attention in recent years due to the growing global threat of infectious diseases, the emergence of new diseases such as COVID-19, and increases in healthcare-associated infections. Although there are many reportedly successful coating technologies, the evaluation of antimicrobial performance is primarily conducted under simple laboratory conditions without adequate testing under real environmental conditions that reflect practical use and more importantly, reveal unintended outcomes. Furthermore, there is no standardized evaluation methodology to assess the long-term stability or the consequences associated with coating deterioration, such as the ecological impacts of nanomaterials or the proliferation of antibiotic-resistant bacteria/genes. In this review, we propose a precautionary framework that integrates a rigorous assessment of potential risks and limitations of nanomaterial coatings for antimicrobial applications as intrinsic to a comprehensive evaluation of their benefits. In addition, we summarize some emerging coating technologies as promising strategies to minimize unintended risks and enhance performance.

Fate and toxicity of engineered nanomaterials in the environment: A meta-analysis

The global environment annually receives thousands of tons of engineered nanomaterials (ENMs, particles less than 100 nm diameter). These particles have high active surface area, unique chemical properties, and can enter cells. Humanity uses many ENMs for their biological reactivity (e.g. microbicides), but their environmental effects are complex. We cataloged 2102 experimental results on whole organisms for 22 particle classes (mainly on Ag, Zn, Ti, and Cu) to assess biological responses, effective and lethal concentrations, and bioaccumulation of ENMs. Most responses were negative and varied significantly by particle type, functional group of organism, and type of response. Smaller particles tended to be more toxic. Aquatic organisms responded more negatively than did terrestrial organisms. Animals generally were most sensitive and plants least. Silver ENMs generally had the strongest negative effects. Effective and lethal concentrations generally exceeded modeled environmentally relevant concentrations and organisms usually did not accumulate or biomagnify to concentrations above those in their environment. However, most experiments lasted less than a week and were not field studies. Research to date is probably insufficient to understand chronic effects and long-term biomagnification. Numerous unique and untested ENMs continue to enter environments at accelerating rates, and our analysis indicates potential for negative effects. Our data suggest substantial research is still required to understand the ultimate influence of ENMs as they continue to accumulate in the environment. Around 40% of the papers with experimental data for ENMs failed with respect to reporting means, sample sizes, or experimental error, or they did not have proper experimental design (e.g. lack of true controls). We need more high-quality experiments that are more realistic (field or mesocosm), longer duration, contain a wider range of organisms, and account for complex food web structure.