Aggregation Kinetics of TiO2 Nanoparticles in Human and Artificial Sweat Solutions: Effects of Particle Properties and Sweat Constituents

Play on Electrodes

Maximizing the efficiency of electrode usage is a crucial step in enhancing the integration of wearables. Currently, electrodes are combined in an additive manner to enable multiplexed sweat screening. The additive sensor requires significant space to accommodate single-function electrodes, which limits the integration of the wearable sensors. Here, we report that the versatility of a single electrode is achieved by assigning different roles to the electrode at different times, resulting in a flexible, disposable, epidermal sweat-sensing platform that integrates in situ iontophoresis and three electrochemical sensors on only four electrodes, while previous platforms required at least seven electrodes. For example, the iontophoresis electrode serves as the working electrode (WE) for chloride sensing and as the counter electrode (CE) for pH sensing after its controllable release of pilocarpine, and the sulfonated polyaniline (SPAN) modified glucose oxidase (GOx) serves as the WE for both pH and glucose sensing. All four functions are integrated into an 8 mm2 (1.8 × 4.45 mm) sensing area, requiring a sample volume of approximately 1 μL. These results open possibility for highly integrated wearable sweat sensors and multimodal sensors.

Aggregation behavior of photoaging nanoplastics in artificial sweat solutions

The aging process and aggregation behavior of nanoplastics govern their fate and ecological risk in aquatic environments. Unfortunately, the aggregation behavior of nanoplastics in sweat and the effect of aging on this process remains unknown. This study investigated the aggregation kinetics of polystyrene nanoplastics (PS-NPs) in three types of artificial sweat before and after photoaging. The aggregation rates (k) of PS-NPs before and after photoaging followed the order ofAmerican-Association-of-Textile-Chemists-and-Colorists-pH-4.3 (kaged =0.6381 nm/s, koriginal =0.4337 nm/s) > British-Standard-pH-6.5 (kaged =0.3589 nm/s, koriginal =0.1297 nm/s) >International-Standard-Organization-pH-8.0 (kaged =0 nm/s, koriginal =0 nm/s). Photoaging decreased the C-O content on the surface of PS-NPs from 4.47 % to 1.97 %, thus to promote the aggregation of PS-NPs. Moreover, decrease of the pH value of three types of artificial sweat (from 8.0 to 4.3) all increased the aggregation rate of the PS-NPs. Inorganic constituents (NaCl and Na2HPO4) promoted the aggregation of PS-NPs by increasing the positive charges on the surface of PS-NPs, while organic constituents (L-histidine, lactic acid, and urea) stabilized PS-NPs by adsorbing on the surface of PS-NPs. These findings demonstrated that the solution conditions of sweat and photoaging process together determined the transport and distribution of nanoplastics in sweat, offering new insights for assessing and predicting the skin exposure risk of nanoplastics.

UV-aging process of titanium dioxide nanoparticles aggravates enterohepatic toxicity of bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate to zebrafish

The physicochemical characteristics of titanium dioxide nanoparticles (n-TiO2) may change during the aging process once discharged into aquatic environment. However, how the aging process affects their interactions with co-existing pollutants, as well as the joint toxicity has not been explored. This study investigated how UV-aging impacts n-TiO2 in aquatic environments and their interactions with bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH), focusing on their joint toxicity in adult female zebrafish. UV-aging process significantly increased the specific area and hydrophobicity of n-TiO2, promoting the adsorption of TBPH. In vivo experiments revealed that aged n-TiO2 enhanced the bioaccumulation of TBPH in the liver and intestine, worsening hepatic steatosis and intestinal barrier damage. A combined analysis of hepatic lipidomic profiling and intestinal microbiota 16S rRNA sequencing revealed that co-exposure of aged n-TiO2 and TBPH altered gut microbial composition and abundances, facilitating the circulation of lipopolysaccharides (LPS) through the gut-liver axis. Subsequentially, the elevated LPS level in the liver activated the sphingolipid metabolic pathway, resulting in severer lipid metabolism disorders and hepatotoxicity. This study found that UV-aging increases the hydrophobicity and surface area of n-TiO2, enhancing their interaction with the TBPH, which leads to greater bioaccumulation and hepatoxicity through mechanisms involving changes in gut microbiomes and sphingolipid metabolism.

Ex vivo skin diffusion and decontamination studies of titanium dioxide nanoparticles

This study aims to adapt an experimental model based on Franz diffusion cells and porcine skin explants to characterize the diffusion of TiO2 NPs and to compare the efficacy of different cleansing products, soapy water and a calixarene cleansing nanoemulsion compared with pure water, as a function of the time of treatment. While TiO2 NPs tend to form agglomerates in aqueous solutions, a diffusion through healthy skin was confirmed as particles were detected in the receptor fluid of Franz cells using sp-ICP-MS. In the absence of treatment, SIMS images showed the accumulation of TiO2 agglomerates in the stratum corneum, the epidermis, the dermis, and around hair follicles. Decontamination assays showed that the two products tested were comparably effective in limiting Ti penetration, whatever the treatment time. However, only calixarene nanoemulsion was statistically more efficient than water in retaining TiO2 in the donor compartment (>89%), limiting retention inside the skin (<1%) and preventing NP diffusion through the skin (<0.13%) when treatments were initiated 30 min after skin exposure. When decontamination was delayed from 30 min to 6 h, the amount of Ti diffusing and retained in the skin increased. This study demonstrates that TiO2 NPs may diffuse through healthy skin after exposure. Thus, effective decontamination using cleansing products should be carried out as soon as possible.

Aging effects of titanium dioxide on Cu toxicity to Daphnia magna: Exploring molecular docking and significance of surface properties

Cosmetics and personal care products containing titanium dioxide nanoparticles (TiO2 NPs) may enter aquatic environments, where the surface coatings of TiO2 NPs may change with aging due to environmental factors such as light, and potentially affect their bioaccumulation and toxicity. This study examined how aging impacted the physicochemical properties of three commercially available TiO2 NPs and subsequent influence on the bioaccumulation and toxicity of copper (Cu) in Daphnia magna (D. magna). We demonstrated that aging significantly affected the hydrophobicity of TiO2 NPs, which affected their binding to water molecules and adsorption of Cu. Changes of bioaccumulation of TiO2 NPs and Cu in D. magna ultimately affected the activities of intracellular antioxidant enzymes such as SOD, CAT, GSH-Px, and the transmembrane protein Na+/K+-ATPase. Molecular docking calculations demonstrated that changes of activities of these biological enzymes were due to the interaction between TiO2 NPs, Cu, and amino acid residues near the sites with the lowest binding energy and active center of the enzyme. Such effect was closely related to the hydrophobicity of TiO2 NPs. Our study demonstrated the close relationship between surface properties of TiO2 NPs and their biological effects, providing important evidence for understanding the behavior of nanomaterials in aquatic environments.

Heat Transfer by Sweat Droplet Evaporation

Sweating regulates the body temperature in extreme environments or during exercise. Here, we investigate the evaporative heat transfer of a sweat droplet at the microscale to unveil how the evaporation complexity of a sweat droplet would affect the body's ability to cool under specific environmental conditions. Our findings reveal that, depending on the relative humidity and temperature levels, sweat droplets experience imperfect evaporation dynamics, whereas water droplets evaporate perfectly at equivalent ambient conditions. At low humidity, the sweat droplet fully evaporates and leaves a solid deposit, while at high humidity, the droplet never reaches a solid deposit and maintains a liquid phase residue for both low and high temperatures. This unprecedented evaporation mechanism of a sweat droplet is attributed to the intricate physicochemical properties of sweat as a biofluid. We suppose that the sweat residue deposited on the surface by evaporation is continuously absorbing the surrounding moisture. This route leads to reduced evaporative heat transfer, increased heat index, and potential impairment of the body's thermoregulation capacity. The insights into the evaporative heat transfer dynamics at the microscale would help us to improve the knowledge of the body's natural cooling mechanism with practical applications in healthcare, materials science, and sports science.

The distribution, fate, and environmental impacts of food additive nanomaterials in soil and aquatic ecosystems

Nanomaterials in the food industry are used as food additives, and the main function of these food additives is to improve food qualities including texture, flavor, color, consistency, preservation, and nutrient bioavailability. This review aims to provide an overview of the distribution, fate, and environmental and health impacts of food additive nanomaterials in soil and aquatic ecosystems. Some of the major nanomaterials in food additives include titanium dioxide, silver, gold, silicon dioxide, iron oxide, and zinc oxide. Ingestion of food products containing food additive nanomaterials via dietary intake is considered to be one of the major pathways of human exposure to nanomaterials. Food additive nanomaterials reach the terrestrial and aquatic environments directly through the disposal of food wastes in landfills and the application of food waste-derived soil amendments. A significant amount of ingested food additive nanomaterials (> 90 %) is excreted, and these nanomaterials are not efficiently removed in the wastewater system, thereby reaching the environment indirectly through the disposal of recycled water and sewage sludge in agricultural land. Food additive nanomaterials undergo various transformation and reaction processes, such as adsorption, aggregation-sedimentation, desorption, degradation, dissolution, and bio-mediated reactions in the environment. These processes significantly impact the transport and bioavailability of nanomaterials as well as their behaviour and fate in the environment. These nanomaterials are toxic to soil and aquatic organisms, and reach the food chain through plant uptake and animal transfer. The environmental and health risks of food additive nanomaterials can be overcome by eliminating their emission through recycled water and sewage sludge.

Unveiling the Potential of Bioinoculants and Nanoparticles in Sustainable Agriculture for Enhanced Plant Growth and Food Security

The increasing public concern over the negative impacts of chemical fertilizers and pesticides on food security and sustainability has led to exploring innovative methods that offer both environmental and agricultural benefits. One such innovative approach is using plant-growth-promoting bioinoculants that involve bacteria, fungi, and algae. These living microorganisms are applied to soil, seeds, or plant surfaces and can enhance plant development by increasing nutrient availability and defense against plant pathogens. However, the application of biofertilizers in the field faced many challenges and required conjunction with innovative delivering approaches. Nanotechnology has gained significant attention in recent years due to its numerous applications in various fields, such as medicine, drug development, catalysis, energy, and materials. Nanoparticles with small sizes and large surface areas (1-100 nm) have numerous potential functions. In sustainable agriculture, the development of nanochemicals has shown promise as agents for plant growth, fertilizers, and pesticides. The use of nanomaterials is being considered as a solution to control plant pests, including insects, fungi, and weeds. In the food industry, nanoparticles are used as antimicrobial agents in food packaging, with silver nanomaterials being particularly interesting. However, many nanoparticles (Ag, Fe, Cu, Si, Al, Zn, ZnO, TiO2, CeO2, Al2O3, and carbon nanotubes) have been reported to negatively affect plant growth. This review focuses on the effects of nanoparticles on beneficial plant bacteria and their ability to promote plant growth. Implementing novel sustainable strategies in agriculture, biofertilizers, and nanoparticles could be a promising solution to achieve sustainable food production while reducing the negative environmental impacts.