Characterization of Commercial Metal Oxide Nanomaterials: Crystalline Phase, Particle Size and Specific Surface Area

Assessment of skin sensitization potential of zinc oxide, aluminum oxide, manganese oxide, and copper oxide nanoparticles through the local lymph node assay: 5-bromo-deoxyuridine flow cytometry method

The advent of nanotechnology has significantly spurred the utilization of nanoparticles (NPs) across diverse sectors encompassing industry, agriculture, engineering, cosmetics, and medicine. Metallic oxides including zinc oxide (ZnO), copper oxide (CuO), manganese oxide (Mn2O3), and aluminum oxide (Al2O3), in their NP forms, have become prevalent in cosmetics and various dermal products. Despite the expanding consideration of these compounds for dermal applications, their potential for initiating skin sensitization (SS) has not been comprehensively examined. An in vivo assay, local lymph node assay: 5-bromo-2-deoxyuridine-flow cytometry method (LLNA: BrdU-FCM) recognized as an alternative testing method for screening SS potential was used to address these issues. Following the OECD TG 442B guidelines, NPs suspensions smaller than 50 nm size were prepared for ZnO and Al2O3 at concentrations of 10, 25, and 50%, and Mn2O3 and CuO at concentrations of 5, 10, and 25%, and applied to the dorsum of each ear of female BALB/c mice on a daily basis for 3 consecutive days. Regarding the prediction of test substance to skin sensitizer if sensitization index (SI)≥2.7, all 4 NPs were classified as non-sensitizing. The SI values were below 2.06, 1.33, 1.42, and 0.99 for ZnO, Al2O3, Mn2O3, and CuO, respectively, at all test concentrations. Although data presented were negative with respect to adverse SS potential for these 4 NPs, further confirmatory tests addressing other key events associated with SS adverse outcome pathway need to be carried out to arrive at an acceptable conclusion on the skin safety for both cosmetic and dermal applications.

Titanium dioxide nanoparticles - physicochemical characterization and cytotoxic risk

Titanium dioxide (TiO2) nanoparticles (NPs) are incorporated into numerous consumer products yet data as to potential adverse health effects remains inconclusive. In this paper we physically characterize 16 nanoforms of TiO2 from different manufacturers of different size, crystalline structure and surface chemistry. Physical measurements of the particles were performed and compared with those provided by manufacturers revealing several discrepancies. We then examined the biological effects of these particles in cell culture in 3 commonly used cell lines for testing materials. We were unable to validate that anatase particles are more cytotoxic than rutile particles as has been reported, and generally found that the particles produced few effects and no significant production of reactive oxygen species under the conditions used. While some particles do exhibit a dose dependent cytotoxicity that increases over time in some cell lines, the effects were not consistent between cell lines and do not appear to be linked to crystalline structure or any of the specific physical characteristics that were measured including, size, charge and surface composition, nor a correlation with the production of reactive oxygen species.

A Facile Way to Simultaneously Improve Humidity-Immunity and Gas Response in Semiconductor Metal Oxide Sensors

The metal-oxide-based gas sensors show great potential in exhaled breath analysis owing to their simple, fast, and noninvasive characteristics. However, the exhaled breath contains moisture, and the surface-active sites of metal oxides are easily poisoned by water molecules, leading to degradation of the sensor performance, particularly the gas response and selectivity. Therefore, it is essential to develop oxide sensors that can reliably sense target gases over a wide humidity range without sacrificing the gas response. In this study, a facile strategy was proposed to incorporate hydrophobic La into an oxide sensor to simultaneously improve the humidity-stability and sensitivity of NH3 detection for early prediction of kidney failure. WO3 sensors doped with various concentrations of La were successfully synthesized, and their gas-sensing performances under various humid conditions were systematically investigated. Interestingly, a small amount of La doping (1 at. %) effectively prevented water poisoning and improved the gas response simultaneously. This sensor was able to selectively detect NH3 up to 200 ppb with a limit of detection (LOD) of ∼780 ppt over a wide range of humidity. The concurrent enhancement in gas response and humidity-immunity was attributed to the surface hydrophobicity and increased specific surface area caused by the incorporation of La.

Proton conductive 2D MXene-derived potassium titanate nanoribbons fabricated electrochemical platform for trace detection of enrofloxacin

In recent years, due to exceptional properties like broad interlayered spacing and low working potential, MXene-derived titanate nanoribbons have been established as promising electrode materials. Herein, the electrocatalytic activity of MXene-derived potassium titanate nanoribbon was employed to develop a voltammetric sensor for the detection of enrofloxacin. The sensor's significance is to provide a sustainable solution to quantify the presence of enrofloxacin regarding food safety and environmental monitoring. Moreover, to achieve the United Nations' Sustainable Development Goals by preventing antimicrobial resistance to accomplish the One Health approach. Potassium titanate nanoribbons were synthesized using 2D Ti3C2 MXene as an active precursor material, while X-ray diffraction spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction pattern, elemental mapping, and energy-dispersive X-ray spectroscopy were used to characterize the crystallinity, surface and layered morphology of synthesized nanoribbons. The Brunauer-Emmett-Teller (BET) technique was applied to calculate the specific surface area of the synthesized materials. The materials underwent electrochemical characterization using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Later on, the nanoribbons were fabricated on the surface of a glassy carbon electrode, and the electro-oxidative behaviour of enrofloxacin was studied by CV, DPV, square wave voltammetry (SWV) in 0.1 M phosphate buffer (optimized pH 8). The developed sensor depicts a significantly lower limit of quantification of 0.007 μM (≈2.5 μg/L), and an upper limit of quantification of 18 μM (≈6.5 mg/L) along with a limit of detection (LOD) of 0.00279, 0.00803, 0.00881 μM obtained from CV, DPV, and SWV respectively. Furthermore, the developed electrodes show a reliable selectivity to be examined in real complex matrices, i.e. marine water, river water, agricultural soil, organic fertilizer, milk, honey, and poultry egg.

Assessment of Physico-Chemical Behavior and Sorptivity-Diatomaceous Earth as Support for Paraffinic Phase-Change Materials

Diatomite's most common application is its use as a sorbent for petroleum substances. Since paraffin is a petroleum derivative, this paper investigates the sorption capacity of diatomite to absorb it. In this paper, the physical and chemical properties were studied for 4 different fractions of diatomite (0-0.063 mm; 0-2 mm; 0.5-3 mm; and 2-5 mm) in the crude and calcined states, and the sorption capacity of diatomite earth for absorbing paraffinic phase-change substances was determined. The physical and chemical studies of the material included conducting an oxide chemical composition analysis using XRF, examining the composition of the mineral phases using X-ray diffraction, and determining the particle size, porosity, and thermal conductivity of the diatomite. Morphology images were also taken for all 8 diatomite variants using scanning electron microscopy. Each fraction was subjected to static calcination at 850 °C for 24 h. The results showed that the calcination of the diatomite increased the porosity of the material and reduced the thermal conductivity coefficient, and most importantly, the sorption capacity to absorb paraffins. The highest sorption capacity was characterized by calcined diatomite powder, that is, diatomite with the smallest particle size. Absorption of paraffinic substances by diatomite exceeding 200 wt.% is possible. Thus, diatomite is one of the feasible candidates for an economical and lightweight building material for making PCM composites for thermal energy storage in buildings.

Advancements in nanomaterials for nanosensors: a comprehensive review

Nanomaterials (NMs) exhibit unique properties that render them highly suitable for developing sensitive and selective nanosensors across various domains. This review aims to provide a comprehensive overview of nanomaterial-based nanosensors, highlighting their applications and the classification of frequently employed NMs to enhance sensitivity and selectivity. The review introduces various classifications of NMs commonly used in nanosensors, such as carbon-based NMs, metal-based NMs, and others, elucidating their exceptional properties, including high thermal and electrical conductivity, large surface area-to-volume ratio and good biocompatibility. A thorough examination of literature sources was conducted to gather information on NMs-based nanosensors' characteristics, properties, and fabrication methods and their application in diverse sectors such as healthcare, environmental monitoring, industrial processes, and security. Additionally, advanced applications incorporating machine learning techniques were analyzed to enhance the sensor's performance. This review advances the understanding and development of nanosensor technologies by providing insights into fabrication techniques, characterization methods, applications, and future outlook. Key challenges such as robustness, biocompatibility, and scalable manufacturing are also discussed, offering avenues for future research and development in this field.

Towards 3D determination of the surface roughness of core-shell microparticles as a routine quality control procedure by scanning electron microscopy

Recently, we have developed an algorithm to quantitatively evaluate the roughness of spherical microparticles using scanning electron microscopy (SEM) images. The algorithm calculates the root-mean-squared profile roughness (RMS-RQ) of a single particle by analyzing the particle's boundary. The information extracted from a single SEM image yields however only two-dimensional (2D) profile roughness data from the horizontal plane of a particle. The present study offers a practical procedure and the necessary software tools to gain quasi three-dimensional (3D) information from 2D particle contours recorded at different particle inclinations by tilting the sample (stage). This new approach was tested on a set of polystyrene core-iron oxide shell-silica shell particles as few micrometer-sized beads with different (tailored) surface roughness, providing the proof of principle that validates the applicability of the proposed method. SEM images of these particles were analyzed by the latest version of the developed algorithm, which allows to determine the analysis of particles in terms of roughness both within a batch and across the batches as a routine quality control procedure. A separate set of particles has been analyzed by atomic force microscopy (AFM) as a powerful complementary surface analysis technique integrated into SEM, and the roughness results have been compared.

A Systematic Genotoxicity Assessment of a Suite of Metal Oxide Nanoparticles Reveals Their DNA Damaging and Clastogenic Potential

Metal oxide nanoparticles (MONP/s) induce DNA damage, which is influenced by their physicochemical properties. In this study, the high-throughput CometChip and micronucleus (MicroFlow) assays were used to investigate DNA and chromosomal damage in mouse lung epithelial cells induced by nano and bulk sizes of zinc oxide, copper oxide, manganese oxide, nickel oxide, aluminum oxide, cerium oxide, titanium dioxide, and iron oxide. Ionic forms of MONPs were also included. The study evaluated the impact of solubility, surface coating, and particle size on response. Correlation analysis showed that solubility in the cell culture medium was positively associated with response in both assays, with the nano form showing the same or higher response than larger particles. A subtle reduction in DNA damage response was observed post-exposure to some surface-coated MONPs. The observed difference in genotoxicity highlighted the mechanistic differences in the MONP-induced response, possibly influenced by both particle stability and chemical composition. The results highlight that combinations of properties influence response to MONPs and that solubility alone, while playing an important role, is not enough to explain the observed toxicity. The results have implications on the potential application of read-across strategies in support of human health risk assessment of MONPs.

Callistemon viminalis leaf extract phytochemicals modified silver-ruthenium bimetallic zinc oxide nanocomposite biosynthesis: application on nanocoating photocatalytic Escherichia coli disinfection

Antibiotics are of great interest due to antibiotic-resistant problems around the globe due to bacterial resistance to conventional antibiotics. In this study, a novel green biosynthesis of silver-ruthenium bimetallic zinc oxide nanocomposite using Callistemon viminalis leaf extract as a reducing agent using zinc nitrate hexahydrate, silver nitrate, and ruthenium(iii) chloride as capping agents was reported. The results demonstrated that the surface morphology of the prepared bimetallic nanocomposite by scanning electron microscopy was hexagonal in shape for zinc nanoparticle, rectangular in shape for silver nanoparticle, and tetragonal in shape for ruthenium nanoparticle, having an average surface size 25, 35, and 55 nm, respectively. Fourier transform infrared analysis confirmed the presence of compounds containing alkene, halo-, sulfoxide, phenol, nitro-, phenyl-ester, carboxylic acid, amines, and alcohols which act as functional groups attached to the surface of nanocomposites. Results from X-ray diffraction analysis found 81.12% crystallinity and hexagonal structure of zinc nanoparticles, rectangular structure of silver nanoparticles, and tetragonal structure of ruthenium nanoparticles, which are also similar to the results from transmission electron microscopy analysis. The average size distribution by dynamic light scattering of silver-ruthenium bimetallic zinc oxide nanocomposite was 255 nm, which confirms the biosynthesis of non-uniform size. Photo-disinfection activity of a silver-ruthenium bimetallic zinc oxide nanocomposite against Escherichia coli bacteria isolated from hospital wastewater under dark and ultraviolet-A irradiation conditions was observed. The antibacterial activity was calculated at 2.42704239, ensuring the silver-ruthenium bimetallic zinc oxide nanomaterials have photo-disinfection properties. The results from this study revealed that the developed novel antibacterial nanocomposite of silver-ruthenium bimetallic zinc oxide is useful in nanocoating photocatalytic Escherichia coli disinfection and can be applied to disinfect surfaces.

Characterization and Cellular Toxicity Studies of Commercial Manganese Oxide Nanoparticles

Manganese oxide nanoparticles (MnOx NPs) are finding applications in several environmentally important areas such as farming and energy storage. MnOx NPs span a range of metal oxidation states that open up a wide range of applications in catalysis as well. As a result, it is important to understand how such materials can impact human health through incidental exposure. In this study, we examined a range of commercially available Mn2O3 NPs and compared our characterization data to those supplied by manufacturers. Discrepancies were noted and then measured values were used to assess the biological impact of these materials on three mammalian cell lines-A549, HepG2 and J774A.1 cells. Cell toxicity assays showed that all Mn2O3 particles exhibited cytotoxic effects that may be correlated, at least in part, to the production of reactive oxygen species. All eight nanoforms also activated caspase 3 but not caspase 1, although the magnitude of these changes varied greatly between materials.

Toxicity of Metal Oxide Nanoparticles: Looking through the Lens of Toxicogenomics

The impact of solubility on the toxicity of metal oxide nanoparticles (MONPs) requires further exploration to ascertain the impact of the dissolved and particulate species on response. In this study, FE1 mouse lung epithelial cells were exposed for 2-48 h to 4 MONPs of varying solubility: zinc oxide, nickel oxide, aluminum oxide, and titanium dioxide, in addition to microparticle analogues and metal chloride equivalents. Previously published data from FE1 cells exposed for 2-48 h to copper oxide and copper chloride were examined in the context of exposures in the present study. Viability was assessed using Trypan Blue staining and transcriptomic responses via microarray analysis. Results indicate material solubility is not the sole property governing MONP toxicity. Transcriptional signaling through the 'HIF-1α Signaling' pathway describes the response to hypoxia, which also includes genes associated with processes such as oxidative stress and unfolded protein responses and represents a conserved response across all MONPs tested. The number of differentially expressed genes (DEGs) in this pathway correlated with apical toxicity, and a panel of the top ten ranked DEGs was constructed (Hmox1, Hspa1a, Hspa1b, Mmp10, Adm, Serpine1, Slc2a1, Egln1, Rasd1, Hk2), highlighting mechanistic differences among tested MONPs. The HIF-1α pathway is proposed as a biomarker of MONP exposure and toxicity that can help prioritize MONPs for further evaluation and guide specific testing strategies.

An expanding horizon of complex injectable products: development and regulatory considerations

There has been a constant evolution in the pharmaceutical market concerning the new technologies imbibed in delivering drug substances for various indications. This is either market-driven or technology-driven to improve the overall therapeutic efficacy and patients' quality of life. The pharmaceutical industry has experienced rapid growth in the area of complex injectable products because of their effectiveness in the unmet market. These novel parenteral products, viz, the nanoparticles, liposomes, microspheres, suspensions, and emulsions, have proven their worth as "Safe and Effective" products. However, the underlying challenges involved in the development, scalability, and characterization of these injectable products are critical. Moreover, the guidelines available do not provide a clear understanding of these complex products, making it difficult to anticipate the regulatory requirements. Thus, it becomes imperative to comprehend the criticalities and develop an understanding of these products. This review discusses various complexities involved in the parenteral products such as complex drug substances, excipients, dosage forms, drug administration devices like pre-filled syringes and injector pens, and its different characterization tools and techniques. The review also provides a brief discussion on the regulatory aspects and associated hurdles with other parenteral products.

Physical Characterization and Cellular Toxicity Studies of Commercial NiO Nanoparticles

Nickel oxide (NiO) nanoparticles from several manufacturers with different reported sizes and surface coatings were characterized prior to assessing their cellular toxicity. The physical characterization of these particles revealed that sizes often varied from those reported by the supplier, and that particles were heavily agglomerated when dispersed in water, resulting in a smaller surface area and larger hydrodynamic diameter upon dispersion. Cytotoxicity testing of these materials showed differences between samples; however, correlation of these differences with the physical properties of the materials was not conclusive. Generally, particles with higher surface area and smaller hydrodynamic diameter were more cytotoxic. While all samples produced an increase in reactive oxygen species (ROS), there was no correlation between the magnitude of the increase in ROS and the difference in cytotoxicity between different materials.

Non-antimicrobial and Non-anticancer Properties of ZnO Nanoparticles Biosynthesized Using Different Plant Parts of Bixa orellana

As traditional cancer therapy is toxic to both normal and cancer cells, there is a need for newer approaches to specifically target cancer cells. ZnO nanoparticles can be promising due their biocompatible nature. However, ZnO nanoparticles have also shown cytotoxicity against mammalian cells in some cases, because of which there is a need for newer synthesis approaches for biocompatible ZnO nanoparticles to be used as carrier molecules in drug delivery applications. Here, we report the biosynthesis of ZnO nanoparticles using different plant parts (leaf, seed, and seed coat) of Bixa orellana followed by different characterizations. The UV-visible spectra of ZnO showed absorption maxima at 341 and 353 nm, 378 and 373 nm, and 327 and 337 nm, respectively, before and after calcination corresponding to the band gap energy of 3.636 and 3.513 eV, 3.280 and 3.324 eV, and 3.792 and 3.679 eV for L-ZnO, S-ZnO, and Sc-ZnO, respectively. X-ray diffraction analysis confirmed the formation of hexagonal wurtzite structures. Attenuated total reflectance infrared spectra revealed the presence of stretching vibrations of C-C, C=C, C=O, and NH₃ ⁺ groups along with C-H deformation involving biomolecules from extracts responsible for reduction and stabilization of nanoparticles. Field emission scanning electron microscopy and transmission electron microscopy images showed spherical and almond-like morphologies of L-ZnO and Sc-ZnO with spherical morphologies, whereas S-ZnO showed almond-like morphologies. The presence of antibacterial activity was observed in L-ZnO against Staphylococcus aureus and Bacillus subtilis, in S-ZnO nanoparticles only against Escherichia coli, and in Sc-ZnO only against Staphylococcus aureus. Uncalcinated ZnO nanoparticles showed weak antibacterial activities, whereas calcinated ZnO nanoparticles showed a non-antibacterial nature. The antifungal activity against different fungi (Penicillium sp., Aspergillus flavus, Fusarium oxysporum, and Rhizoctonia solani) and cytotoxicity against HCT-116 cancer cells were not observed before and after calcination in all three ZnO nanoparticles. The antimicrobial nature and biocompatibility of ZnO nanoparticles were influenced by different parameters of the nanoparticles along with microorganisms and the human cells. Non-antimicrobial properties of ZnO nanoparticles can be treated as a pre-requisite for its biocompatibility due to its inert nature. Thus, biosynthesized ZnO nanoparticles showed a nontoxic nature, which can be exploited as promising alternatives in biomedical applications.

Quantification and Characterization of Metals in Ultrafine Road Dust Particles

Road dust is an important source of resuspended particulate matter (PM) but information is lacking on the chemical composition of the ultrafine particle fraction (UFP; <0.1 µm). This study investigated metal concentrations in UFP isolated from the “dust box” of sweepings collected by the City of Toronto, Canada, using regenerative-air-street sweepers. Dust box samples from expressway, arterial and local roads were aerosolized in the laboratory and were separated into thirteen particle size fractions ranging from 10 nm to 10 µm (PM10). The UFP fraction accounted for about 2% of the total mass of resuspended PM10 (range 0.23–8.36%). Elemental analysis using ICP-MS and ICP-OES revealed a marked enrichment in Cd, Cr, Zn and V concentration in UFP compared to the dust box material (nano to dust box ratio ≥ 2). UFP from arterial roads contained two times more Cd, Zn and V and nine times more Cr than UFP from local roads. The highest median concentration of Zn was observed for the municipal expressway, attributed to greater volumes of traffic, including light to heavy duty vehicles, and higher speeds. The observed elevated concentrations of transition metals in UFP are a human health concern, given their potential to cause oxidative stress in lung cells.

Highly Efficient Iron Oxide Nanoparticles Immobilized on Cellulose Nanofibril Aerogels for Arsenic Removal from Water

The application and optimal operation of nanoparticle adsorbents in fixed-bed columns or industrial-scale water treatment applications are limited. This limitation is generally due to the tendency of nanoparticles to aggregate, the use of non-sustainable and inefficient polymeric resins as supporting materials in fixed-bed columns, or low adsorption capacity. In this study, magnesium-doped amorphous iron oxide nanoparticles (IONPs) were synthesized and immobilized on the surface of cellulose nanofibrils (CNFs) within a lightweight porous aerogel for arsenic removal from water. The IONPs had a specific surface area of 165 m2 g-1. The IONP-containing CNF aerogels were stable in water and under constant agitation due to the induced crosslinking using an epichlorohydrin crosslinker. The adsorption kinetics showed that both As(III) and As(V) adsorption followed a pseudo second-order kinetic model, and the equilibrium adsorption isotherm was best fitted using the Langmuir model. The maximum adsorption capacities of CNF-IONP aerogel for As(III) and As(V) were 48 and 91 mg As g-IONP-1, respectively. The optimum IONP concentration in the aerogel was 12.5 wt.%, which resulted in a maximum arsenic removal, minimal mass loss, and negligible leaching of iron into water.

Work Function Tuning in Hydrothermally Synthesized Vanadium-Doped MoO3 and Co3O4 Mesostructures for Energy Conversion Devices

The wide interest in developing green energy technologies stimulates the scientific community to seek, for devices, new substitute material platforms with a low environmental impact, ease of production and processing and long-term stability. The synthesis of metal oxide (MO) semiconductors fulfils these requirements and efforts are addressed towards optimizing their functional properties through the improvement of charge mobility or energy level alignment. Two MOs have rising perspectives for application in light harvesting devices, mainly for the role of charge selective layers but also as light absorbers, namely MoO3 (an electron blocking layer) and Co3O4 (a small band gap semiconductor). The need to achieve better charge transport has prompted us to explore strategies for the doping of MoO3 and Co3O4 with vanadium (V) ions that, when combined with oxygen in V2O5, produce a high work function MO. We report on subcritical hydrothermal synthesis of V-doped mesostructures of MoO3 and of Co3O4, in which a tight control of the doping is exerted by tuning the relative amounts of reactants. We accomplished a full analytical characterization of these V-doped MOs that unambiguously demonstrates the incorporation of the vanadium ions in the host material, as well as the effects on the optical properties and work function. We foresee a promising future use of these materials as charge selective materials in energy devices based on multilayer structures.

Impact of copper oxide particle dissolution on lung epithelial cell toxicity: response characterization using global transcriptional analysis

The in vitro and in vivo toxicity of copper oxide nanoparticles (CuO NPs) is attributed to both particle and dissolved copper ion species. However, a clear understanding of (1) the specific cellular responses that are modulated by the two species and (2) the temporal dynamics in toxicity, as the proportional amount of particulate and ionic forms change over time, is lacking. In the current study, in vitro responses to microparticulate CuO (CuO MPs), CuO NPs, and dissolved Cu²⁺ were characterized in order to elucidate particle and ion-induced kinetic effects. Particle dissolution experiments were carried out in a relevant cell culture medium, using CuO NPs and MPs. Mouse lung epithelial cells were exposed for 2-48 h with 1-25 µg/mL CuO MPs, CuO NPs, or 7 and 54 µg/mL CuCl₂. Cellular viability and genome-wide transcriptional responses were assessed. Dose and time-dependent cytotoxicity were observed in CuO NP exposed cells, which was delayed and subtle in CuCl₂ and not observed in CuO MPs treated cells. Analyses of differentially expressed genes and associated pathway perturbations showed that dissolved ions released by CuO NPs in the extracellular medium are insufficient to account for the observed potency and cytotoxicity. Further organization of gene expression results in an Adverse Outcome Pathway (AOP) framework revealed a series of key events potentially involved in CuO NPs toxicity. The AOP is applicable to toxicity induced by metal oxide nanoparticles of varying solubility, and thus, can facilitate the development of in vitro alternative strategies to screen their toxicity.