Symposium S.NM04—Nanosafety

There has been much interest in developing multimodal imaging platforms, using colloidal nanocrystals made of luminescent quantum dots and plasmonic nanomaterials. Such approach is highly promising. However, the lack of adequate and effective strategies to deliver these nanocrystals into the cytoplasm of live cells has been a major challenge. We have designed a set of high affinity hydrophilic polymer ligands and tested them for the stabilization of various inorganic nanocrystals (e.g., luminescent quantum dots and Au nano-colloids) in biological media. Furthermore, introducing additional reactive groups facilities easy coupling of the polymer-coated nanocrystals to specific cell targeting peptides or/and NMR-active labels.
Here, we report on the ability of an anti-microbial peptide to promote the uptake of three types of nanomaterials (QDs, AuNPs and AuNRs) into mammalian cells. Using fluorescence microscopy experiments, we found that incubation with these conjugates yielded nanocrystal staining throughout the cell volumes. Additional experiments showed that uptake persisted under endocytosis inhibition conditions, such as incubation at low temperature and in the presence of hypertonic sucrose solution. These findings were complemented with flow cytometry measurements and confocal microcopy imaging. Overall, the imaging data support the hypothesis of physical translocation of these conjugates through the membrane rather than endocytosis.

Titanium dioxide nanoparticles (TiO₂ NPs) are indispensable in consumer products due to their function as pigments and photocatalysts. For example, TiO₂ NPs are included in food products and cosmetics to brighten white colors and in sunscreen to block UV rays from reaching the skin. Previous work has shown that the effects of TiO₂ NP exposure on human cells through food consumption and skin contact are negligible, but the effects of TiO₂ NP inhalation are unknown. Using fluorescence microscopy and transmission electron microscopy, we have found that TiO₂ NPs are internalized by human lung cells (A549). In these cells, TiO₂ NPs accumulate in lysosomes, membrane-bound organelles responsible for the transport and degradation of cell cargo. Enlargement of these organelles can have significant effects on cell health. We have found that TiO₂ NP-containing lysosomes are 1.85 times larger on average than lysosomes in untreated cells when compared through representative distributions of size.

We used single particle tracking fluorescence microscopy to follow the motion of TiO₂ NP-containing lysosomes in living cells. Lysosomes were fluorescently labeled with fluorescent proteins and by the absorption of fluorescently-labeled proteins on the TiO₂ NPs. In both of these cases, and for any single particle tracking experiment, observation time is limited by photobleaching, cell viability, and microscope stability. As such, a stochastic model of lysosome motion is warranted to extrapolate beyond trajectory limitations and establish confidence in data validity.

Our goal was to determine the trajectory length necessary to establish confidence in the validity of the observed velocity and diffusivity of lysosome motion. Using Bayesian methods, we estimated unknown information given a set of single particle trajectories. With this information from lysosome trajectories, we could then assign a likelihood that each lysosome was in a specific state of motion (e.g., active transport or diffusion) during a given time interval. This provides insights on the mobility distribution of lysosomes in the cell as a function of TiO₂ NP transport. Based on the inferred relative frequencies of the various states of motion, we then built a forward simulation to explore what the long-term distributions of enlarged lysosomes might be compared to normal lysosomes. Our stochastic model, in combination with experimental data, verifies the validity of our observed trajectories and predicts lysosome transport modes for both untreated control and TiO₂ NP-containing cells. This confidence in the stochastic modeling of particle tracking is useful not only for TiO₂ NP-containing lysosomes, but also broad questions of cellular transport studied with single particle tracking.

For the last two decades, breakthrough research has been going on in all aspects of materials science, including nanotechnology at an accelerated pace. New nanomaterials of unprecedented functionality and performance are being developed and characterized. However, environmental exposure to nanomaterials is inevitable as nanomaterials become part of our daily life, and as a result, nanotoxicity assessment is getting increasingly important.
Here we show the adaptation and application of various computational and cheminformatics methods in nanomaterials toxicity prediction. Since nanomaterials are complex entities from a chemical point of view and the study of these kind of materials requires an interdisciplinary approach, involving multiple aspects ranging from physics and chemistry to biology, informatics and medicine. We show how the combination of computational chemistry, available experimental data, machine learning and cheminformatics approaches can help in nanomaterials toxicological risk assessment. We discuss here a few case studies where data-driven models developed help to decode the relationships between the toxicity of nanomaterials and their physicochemical characteristics, by application quantum chemical, protein-ligand docking, developed nanodescriptors and cheminformatics approaches, including a quantitative multi-nano-read-across approach that combines interspecies correlation analysis.

Outdoor applications of superhydrophobic coatings require synthetic approaches that allow their simple, fast, scalable, and environmentally benign deployment on large, heterogeneous surfaces and their rapid regeneration in situ. We show that the thermal degradation of silicones by flames fulfills these characteristics by spontaneously structuring silicone surfaces into a hierarchical, textured structure that provides wear-resistant, healable superhydrophobicity. We will elucidate how flame processing is a simple, rapid, and out-of-equilibrium process that is counterintuitively reliable and robust in producing such a complex structure. A comprehensive study of the effect of the processing speed and flame temperature on the chemical and physical properties of the coatings yielded three surprising results. (i) Three thermal degradation mechanisms drive the surface texturing: depolymerization (in the O2-rich conditions of the surface), decomposition (in the O2-poor conditions found a few micrometers from the surface), and pyrolysis at excessive temperatures. (ii) The operational condition is delimited by the onset of the depolymerization at low temperatures and the onset of pyrolysis at high temperatures. (iii) The remarkably wide operational conditions and robustness of this approach result from self-limiting growth and oxidation of the silicone particles that are responsible for the surface texturing and in the extent of their deposition. As a result of this analysis, we show that superhydrophobic surfaces can be produced or regenerated with this approach at a speed of 15 cm s−1 (i.e., the length of an airport runway in ∼4.5 h).

Detection of the nitro-fragrant compound at trace level is critical in combating terrorism, for keeping up national security and for providing environmental and clinical safety. Among various nitroaromatics compounds (NACs), the importance of picric acid (PA) owe to its extensive usage in the manufacture of rocket fuels, fireworks, deadly explosives, leather processing and sensitizers in photographic emulsions.[1] As of now, many fluorescence chemosensors/probes have been effectively applied for the detection of PA with functional specificity based on its characteristic properties, particularly resonance energy transfer and electron-deficient nature of the nitro group (-NO2), yet only a few appeared closer to the practical applications. Late reports on CdSe nanoparticles and expedient to surface modification showed its fate in the detection of NACs. Quantum dots have a clear advantage over molecule-based emitters; however, these multi-model sensors are inconvenient for the removal of the target species, which might cause secondary contamination. Towards this end, the incorporation of a fluorescent and magnetic functionality in a single nanocomposite particle would be a promising alternative.[2]
Here, we present a methodology and promising novel hybrid nano-structure that comprises of magnetic core encapsulated inside a thin silica shell (Fe2O3@SiO2 NPs), electrostatically adsorbed through the free anionic carboxyl group with a positively charged spacer arm of florescent Cysteamine-capped CdSe quantum dot (QD) (particle size ≈ 12.7 nm). This multimodal nanosensor provides an efficient sensitive and selectivity detection of PA over a number of other explosive (NACs) in DMSO, (LOD ≈ 2.2 µM) (Quenching constant K_PA ≈ 4.3×10⁴ M^-1) in solution via photo-induced electron transfer mechanism. The sensing mechanism is probed via UV-Vis spectroscopy, steady-state and time-resolved fluorescence spectroscopy which was found to be a mixture of immediate dynamic and static quenching as the lifetime of nanosensor (0.98 ns) is reduced to 0.63 in presence of PA. In addition to solution-phase sensing, this magneto-fluorescent nanosensor also showed an excellent ability for the removal of detected PA molecules with the use of an external magnet, staging as a possibility for the potential application of low-cost and stand-off sensor. In summary, this elegant architecture results in an ultra-small magneto-fluorescent nanoparticle offering a novel platform for the development of a field-based PA sensor.
References
1. Abbasi, F. et. al. Spectrochim Acta A. 2019, 216, 230-5.
2. Sun, X. et. al. Chem. Soc. Rev. 2015,44,8019-8061.

Microplastics or plastic particles less than 5 mm in size are a common and damaging pollutant in the marine ecosystem. However, the full adverse impacts of these particles on marine microorganisms are just starting to be understood. Polyethylene is one of the most abundant microplastics found within the marine environment, but few studies have been performed on microorganisms exposed to these particles. Additionally, little work has been done to identify the cytotoxic, genetic, enzymatic and morphological effects that nanoplastics and microplastics have on marine microorganisms. This study used molecular techniques such as High-Resolution Automated Electrophoresis and RT-PCR to quantitatively analyze expression changes in characteristic marine organism (Synechococcus sp. PCC 7002) exposed to polyethylene nanoparticles and polyethylene microparticles. Novel visualization techniques such as scanning electron cryomicroscopy (CryoSEM) were also used by this investigation to measure morphological changes in bacterial colonization on these particles. Results of this study showed significant differences between nanoparticle, microparticle and control samples. A viability analysis using neutral red showed decreases in the number of viable cells after 5 days of exposure to polyethylene nanoparticles that were not seen in microparticle or control samples. RT-PCR analyses showed differences in the expression of esterase and hydrolase genes. For samples exposed to polyethylene nanoparticles, increases in expression occurred at 5 days of exposure. In samples exposed to polyethylene microparticles, however, expression increased more substantially at 10 days of exposure. A plate based enzymatic assay showed increased esterase activity at the 5 day time point in the nanoparticle exposed samples. Cryo-scanning electron microscopy results identified changes in exopolymer formation in all samples exposed to polyethylene particles. These results illustrate that exposure to polyethylene microparticles and nanoparticles results in genetic, enzymatic and morphological changes in Synechococcus sp. PCC 7002 and argue for further molecular study of the effects of anthropogenic stressors on marine microorganisms.