The production and application of nanomaterials have grown tremendously during last few decades. The widespread exposure of nanoparticles to the public is provoking great concerns regarding their toxicity to the human body. However, in comparison with the extensive studies carried out to examine nanoparticle toxicity to the human body/organs, one especially vulnerable organ, the eye, is always neglected. Although it is a small part of the body, 90% of outside information is obtained via the ocular system. In addition, eyes usually directly interact with the surrounding environment, which may get severer damage from toxic nanoparticles compared to inner organs. Therefore, the study of assessing the potential nanoparticle toxicity to the eyes is of great importance. Here, the recent advance of some representative manufactured nanomaterials on ocular toxicity is summarized. First, a brief introduction of ocular anatomy and disorders related to particulate matter exposure is presented. Following, the factors that may influence toxicity of nanoparticles to the eye are emphasized. Next, the studies of representative manufactured nanoparticles on eye toxicity are summarized and classified. Finally, the limitations that are associated with current nanoparticle-eye toxicity research are proposed.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201802289

Safety Assessment of Nanomaterials to Eyes: An Important but Neglected Issue.

In this study, the ability of a multiwalled carbon nanotube functionalized with fluorescein isothiocyanate (MWCNT–FITC) was assessed as a prospective central nervous system-targeting drug delivery system to permeate the blood–brain barrier. The results indicated that the MWCNT–FITC conjugate is able to penetrate microvascular cerebral endothelial monolayers; its concentrations in the Transwell® system were fully equilibrated after 48 hours. Cell viability test, together with phase-contrast and fluorescence microscopies, did not detect any signs of MWCNT–FITC toxicity on the cerebral endothelial cells. These microscopic techniques also revealed presumably the intracellular localization of fluorescent MWCNT–FITCs apart from their massive nonfluorescent accumulation on the cellular surface due to nanotube lipophilic properties. In addition, the 1,000 ps molecular dynamics simulation in vacuo discovered the phenomenon of carbon nanotube aggregation driven by van der Waals forces via MWCNT–FITC rapid dissociation as an intermediate phase.

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Blood–brain barrier transport studies, aggregation, and molecular dynamics simulation of multiwalled carbon nanotube functionalized with fluorescein isothiocyanate

Nanocrystalline TiO 2 and MWCNTs are important functional materials that have received considerable research interest in the last few decade. In this work, the composites of TiO 2 nanoparticles with varying amount of functionalized MWCNTs were prepared by using a solution-based method. The physico-chemical properties of these composites were studied in connection with their antibacterial activity. TiO 2 particles have non-spherical shape with size in the range of 8–15 nm; which were confirmed through TEM analysis and these particles were well hosted on the surface of MWCNTs. The tuning of optical band gap of nanocomposites was studied by using DR UV-visible spectroscopy. The photocatalytic inactivation of Escherichia coli and Staphylococcus aureus using TiO 2 -MWCNTs nanocomposites in the presence of visible light (λ > 420 nm) has been carried out. These nanocomposites show efficient antibacterial activity under visible light illumination, whereas bare TiO 2 nanoparticles did not show any inhibitory effect on bacteria under visible light exposure. These results suggest that UV light or TiO 2 alone is not effective for photocatalytic disinfection applications. Also, cytotoxicity study reveals that the nanocomposites show better cell viability than bare TiO 2 nanoparticles. Overall, the experimental results suggest that TiO 2 -MWCNTs nanocomposites have been developed as efficient antibacterial agents against a wide range of microorganisms to prevent and control the persistence and spreading of bacterial infections.

Visible light photo-induced antibacterial activity of TiO2-MWCNTs nanocomposites with varying the contents of MWCNTs

Experimental studies indicate that multiwalled carbon nanotubes (MWCNTs) have the potential to induce cytotoxicity. However, the reports are often inconsistent and even contradictory. Additionally, adverse effects of MWCNTs at low concentration are not well understood. In this study, we systemically compared adverse effects of six MWCNTs including pristine MWCNTs, hydroxyl-MWCNTs and carboxyl-MWCNTs of two different lengths (0.5–2 μm and 10–30 μm) on human hepatoma cell line HepG2. Results showed that MWCNTs induced cytotoxicity by increasing reactive oxygen species (ROS) generation and damaging cell function. Pristine short MWCNTs induced higher cytotoxicity than pristine long MWCNTs. Functionalization increased cytotoxicity of long MWCNTs, but reduced cytotoxicity of short MWCNTs. Further, our results indicated that the six MWCNTs, at nontoxic concentration, might not be environmentally safe as they inhibited ABC transporters’ efflux capabilities. This inhibition was observed even at very low concentrat...

Comparison of Cytotoxicity and Inhibition of Membrane ABC Transporters Induced by MWCNTs with Different Length and Functional Groups

Evaluation of carbon nanotubes network toxicity in zebrafish (Danio rerio) model.

Cytotoxicity and genotoxicity of plasma-modified multi-walled carbon nanotubes (MWCNTs), including hydroxyl-MWCNTs (MWCNT-OH), carboxyl-MWCNTs (MWCNT-COOH) and pristine MWCNTs, with human ocular cells (e.g. retinal pigment epithelium (RPE) cells) have been studied in this work. The addition of MWCNT-based materials caused few change in cell morphology while the presence of MWCNTs was observed inside the cells using transmission electron microscopy (TEM), suggesting possibility of MWCNTs passing through the cell membranes without damaging cells. Cell viability measurements suggested that MWCNT-COOH exhibited better biocompatibility than other MWCNT materials studied in this work. Lactate Dehydrogenase (LDH) release level was found to be less than 30% with all types of MWCNT-based materials. Reactive Oxygen Species (ROS) generation was visible but not severe with addition of nanotubes. A smaller oxidative stress level was obtained from MWCNT-COOH. Cell apoptosis was found to be less than 1.5% with addition of MWCNT-based materials. Particularly MWCNTs were found to be swallowed by cells and released by cells after 72 h without damaging cells, which may be considered as a potential vector for ocular genetic diseases. Plasma modification of MWCNTs particularly with -COOH was found to be an efficient way to improve ocular biocompatibility of MWCNTs, suggesting a fast and useful way to modify MWCNTs for applications in areas such as biology and biomedicine.

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Cytotoxicity and genotoxicity of multi-walled carbon nanotubes with human ocular cells

The world is not on track to meet Sustainable Development Goal 6.1 to provide universal access to safely managed drinking water by 2030. Removal of priority microbial contaminants by disinfection is one aspect of ensuring water is safely managed. Passive chlorination (also called in-line chlorination) represents one approach to disinfecting drinking water before or at the point of collection (POC), without requiring daily user input or electricity. In contrast to manual household chlorination methods typically implemented at the point of use (POU), passive chlorinators can reduce the user burden for chlorine dosing and enable treatment at scales ranging from communities to small municipalities. In this review, we synthesized evidence from 27 evaluations of passive chlorinators (in 19 articles, 3 NGO reports, and 5 theses) conducted across 16 countries in communities, schools, health care facilities, and refugee camps. Of the 27 passive chlorinators we identified, the majority (22/27) were solid tablet or granular chlorine dosers, and the remaining devices were liquid chlorine dosers. We identified the following research priorities to address existing barriers to scaled deployment of passive chlorinators: (i) strengthening local chlorine supply chains through decentralized liquid chlorine production, (ii) validating context-specific business models and financial sustainability, (iii) leveraging remote monitoring and sensing tools to monitor real-time chlorine levels and potential system failures, and (iv) designing handpump-compatible passive chlorinators to serve the many communities reliant on handpumps as a primary drinking water source. We also propose a set of reporting indicators for future studies to facilitate standardized evaluations of the technical performance and financial sustainability of passive chlorinators. In addition, we discuss the limitations of chlorine-based disinfection and recognize the importance of addressing chemical contamination in drinking water supplies. Passive chlorinators deployed and managed at-scale have the potential to elevate the quality of existing accessible and available water services to meet “safely managed” requirements.

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Qian Zhang

Papers

Cytotoxicity and genotoxicity of multi-walled carbon nanotubes with human ocular cells

Passive In-Line Chlorination for Drinking Water Disinfection: A Critical Review