Cytotoxicity,permeability, and inflammation of metal oxide nanoparticles in human cardiac microvascular endothelial cells

Wide applications and extreme potential of metal oxide nanoparticles (NPs) increase occupational and public exposure and may yield extraordinary hazards for human health. Exposure to NPs has a risk for dysfunction of the vascular endothelial cells. The objective of this study was to assess the cytotoxicity of six metal oxide NPs to human cardiac microvascular endothelial cells (HCMECs) in vitro. Metal oxide NPs used in this study included zinc oxide (ZnO), iron(III) oxide (Fe₂O₃), iron(II,III) oxide (Fe₃O₄), magnesium oxide (MgO), aluminum oxide (Al₂O₃), and copper(II) oxide (CuO). The cell viability, membrane leakage of lactate dehydrogenase, intracellular reactive oxygen species, permeability of plasma membrane, and expression of inflammatory markers vascular cell adhesion molecule-1, intercellular adhesion molecule-1, macrophage cationic peptide-1, and interleukin-8 in HCMECs were assessed under controlled and exposed conditions (12–24 h and 0.001–100 μg/ml of exposure). The results indicated that Fe₂O₃, Fe₃O₄, and Al₂O₃ NPs did not have significant effects on cytotoxicity, permeability, and inflammation response in HCMECs at any of the concentrations tested. ZnO, CuO, and MgO NPs produced the cytotoxicity at the concentration-dependent and time-dependent manner, and elicited the permeability and inflammation response in HCMECs. These results demonstrated that cytotoxicity, permeability, and inflammation in vascular endothelial cells following exposure to metal oxide nanoparticles depended on particle composition, concentration, and exposure time.     

Toxicity Assessment of Silica Coated Iron Oxide Nanoparticles and Biocompatibility Improvement by Surface Engineering

We have studied in vitro toxicity of iron oxide nanoparticles (NPs) coated with a thin silica shell (Fe₃O₄/SiO₂ NPs) on A549 and HeLa cells. We compared bare and surface passivated Fe₃O₄/SiO₂ NPs to evaluate the effects of the coating on the particle stability and toxicity. NPs cytotoxicity was investigated by cell viability, membrane integrity, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) assays, and their genotoxicity by comet assay. Our results show that NPs surface passivation reduces the oxidative stress and alteration of iron homeostasis and, consequently, the overall toxicity, despite bare and passivated NPs show similar cell internalization efficiency. We found that the higher toxicity of bare NPs is due to their stronger in-situ degradation, with larger intracellular release of iron ions, as compared to surface passivated NPs. Our results indicate that surface engineering of Fe₃O₄/SiO₂ NPs plays a key role in improving particles stability in biological environments reducing both cytotoxic and genotoxic effects.     

Assessing the Impact of Iron-based Nanoparticles on pH,Dissolved Organic Carbon,and Nutrient Availability in Soils

With the ongoing commercialization of nanotechnology products, the increasing use of engineered nanoparticles (NPs) could lead potentially to environmental risks. This study investigated the dynamic influences of three iron-based NPs (Fe⁰, Fe₃O₄, and Fe₂O₃) applied into a red soil (RS) and a Wushan soil (WS) with different application rates (2 to 6 g kg^?1) on soil physicochemical properties such as pH, dissolved organic carbon (DOC), available ammonium nitrogen (NH₄ ⁺-N), available phosphorus (AP), and enzymatic activities. The results showed that the addition of Fe⁰ NPs increased DOC and available NH₄ ⁺-N, but significantly decreased AP, while Fe₃O₄ and Fe₂O₃ NPs slightly reduced soil pH in both soils and significantly declined available NH₄ ⁺-N in the WS and AP in the RS. No significant difference was observed between the effects of Fe₃O₄ and Fe₂O₃ NPs on soil properties except AP in the RS. All iron-based NPs decreased the activities of urease and acid phosphatase in both soils. The effects on soil physicochemical properties, especially available NH₄ ⁺-N and AP induced by iron-based NPs, varied greatly with soil types. These results implied that cautions should be paid for the environmental application of iron-based NPs, especially iron oxide NPs in soils.     

Quantifying the Usefulness of Oxide-Encapsulated Silver Nanoparticles in Semiconducting Films

Incorporating plasmonic nanoparticles (NPs) in an organic solar cell (OSC) can improve device performance. In our simulation studies, at NP resonance, absorption in poly(3-hexythiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) can be increased by encapsulating 50 nm Ag NPs with Al₂O₃, HfO₂, MoO₃, and SiO₂. At Ag NP resonance, when the oxide thickness is significant enough, oxides with high relative permittivity induces a higher electric field enhancement at the metal/dielectric interface. This is translated to improved absorption in the polymer layer. By integrating against AM1.5G, overall absorption in P3HT/PCBM is improved when incorporating Ag NPs encapsulated with a thin oxide shell into the polymer film. However, polymeric absorption loss is induced for oxide-encapsulated Ag NPs if MoO₃ and SiO₂ shells are more than 5 nm. For Al₂O₃ and HfO₂, Ag NPs should not be encapsulated with shells thicker than 10 nm. Modeling studies are also extended to absorption in a CH₃NH₃PbI₃ perovskite layer. It is revealed that both Al₂O₃ and HfO₂ have an optimal shell thickness of about 20 nm to ensure maximum absorption in CH₃NH₃PbI₃. The results can be utilized as a useful guideline when designing photovoltaics from an optical point of view.     

Luminol–silver nitrate chemiluminescence enhancement induced by cobalt ferrite nanoparticles

CoFe₂O₄ nanoparticles (NPs) could stimulate the weak chemiluminescence (CL) system of luminol and AgNO₃, resulting in a strong CL emission. The UV–visible spectra, X‐ray photoelectron spectra and TEM images of the investigated system revealed that AgNO₃ was reduced by luminol to Ag in the presence of CoFe₂O₄ NPs and the formed Ag covered the surface of CoFe₂O₄ NPs, resulting in CoFe₂O₄–Ag core–shell nanoparticles. Investigation of the CL reaction kinetics demonstrated that the reaction among luminol, AgNO₃ and CoFe₂O₄ NPs was fast at the beginning and slowed down later. The CL spectra of the luminol ? AgNO₃ ? CoFe₂O₄ NPs system indicated that the luminophor was still an electronically excited 3‐aminophthalate anion. A CL mechanism has been postulated. When the CoFe₂O₄ NPs were injected into the mixture of luminol and AgNO₃, they catalyzed the reduction of AgNO₃ by luminol to produce luminol radicals and Ag, which immediately covered the CoFe₂O₄ NPs to form CoFe₂O₄–Ag core–shell nanoparticles, and the luminol radicals reacted with the dissolved oxygen, leading to a strong CL emission. With the continuous deposition of Ag on the surface of CoFe₂O₄ NPs, the catalytic activity of the core–shell nanoparticles was inhibited and a decrease in CL intensity was observed and also a slow growth of shell on the nanoparticles. Copyright © 2011 John Wiley & Sons, Ltd.     

Biogenic approach to synthesize rod shaped Gd2O3 nanoparticles and its optimization using response surface methodology-Box–Behnken design model

The rare earth metal oxide nanoparticles such as gadolinium oxide nanoparticles (Gd₂O₃ NPs) have been synthesized by green synthesis process using methanolic extract of Moringa oleifera (M oleifera) peel. In this process, the Gd₂O₃ NPs formation was observed at 280–300 nm in UV–Vis spectroscopy. The XRD pattern of the synthesized Gd₂O₃ NPs was exactly matched with JCPDS No 3-065-3181which confirms the crystalline nature of Gd₂O₃ NPs. In addition, Energy-dispersive X-ray spectroscopy (EDX) analysis was stated that Gd and O elements were present as 70.31 and 29.69%, respectively in Gd₂O₃ NPs. The SEM and TEM analysis were said Gd₂O₃ NPs are in rod shape and 26 ± 2 nm in size. Further the synthesized Gd₂O₃ NPs were confirmed by X-ray photoemission spectroscopy (XPS). The synthesized Gd₂O₃ NPs were further examined for anti-fungal activity against Alternaria saloni (A saloni) and Sclerrotium rolfsii (S rolfsii) and it showed moderate activity. Also, Gd₂O₃ NPs evaluated as good antibacterial agent against different Gram +ve and Gram −ve bacteria. Moreover, the toxicity of the Gd₂O₃ NPs on red blood cells (RBCs) of the human blood was determined using hemolytic assay, the obtained results were stated the synthesized Gd₂O₃ NPs are nontoxic to the human erythrocytes. The photocatalytic activity against malachite green (MG) dye was tested and confirmed as 92% of dye was degraded within 2 hr by Gd₂O₃ NPs. The results were stated the green synthesized Gd₂O₃ NPs are good anti-fungal agents, nontoxic and we can use as a photocatalyst. Copyright © 2019 John Wiley & Sons, Ltd.     

The direct permeation of nanoparticles through the plasma membrane transiently modifies its properties

The exposure to metal nanoparticles (NPs) has increased with their widespread use in industry, research and medicine. It is well known that NPs may enter cells and that this mechanism is crucial to exert both the therapeutic and toxicity effects. The main cellular entrance route is endocytosis-based, however, recent experimental studies, have reported that NPs can also enter the cell crossing directly the plasma membrane, it is thus important to investigate this alternative internalization mechanism. Size, surface chemistry, solubility and shape play a role in NP ability of entering the cell, but it is still to be elucidated how these properties act on cell membrane. We have demonstrated that a direct permeation of metal oxide NPs through the lipid bilayer of the cell membrane can occur, giving direct access to the cytoplasm. In this paper, using the powerful tool of Xenopus laevis oocytes and two electrode Voltage Clamp, we have investigated several parameters that can influence the direct crossing. The most significant of them is the NP hydrodynamic size as clearly shown by the comparison of the behaviour between Co₃O₄ and NiO NPs. By collecting biophysical membrane parameters in different conditions, we have shown that NPs that are able to cross the membrane share the ability to maintain a hydrodynamic size lower than 200 nm. The presence of this route of entrance must be considered for a better comprehension of the effect at intracellular level considering possible mechanism in order to a safer design of engineered NPs.     

Toxic effects of nanoparticles on bioluminescence activity,seed germination,and gene mutation

The potential environmental toxicities of several metal oxide nanoparticles (NPs; CuO, TiO₂, NiO, Fe₂O₃, ZnO, and Co₃O₄) were evaluated in the context of bioluminescence activity, seed germination, and bacterial gene mutation. The bioassays exhibited different sensitivities, i.e., each kind of NP exhibited a different level of toxicity in each of the bioassays. However, with a few exceptions, CuO and ZnO NPs had most toxic for germination of Lactuca seed (EC₅₀ 0.46 mg CuO/l) and bioluminescence (EC₅₀ 1.05 mg ZnO/l). Three NPs (Co₃O₄, TiO₂, and Fe₂O₃) among all tested concentrations (max. 1,000 mg/l) showed no inhibitory effects on the tested organisms, except for Co₃O₄ NPs on bioluminescence activity (EC₅₀ 62.04 mg/l). The sensitivity of Lactuca seeds was greater than that of Raphanus seeds (EC₅₀ 0.46 mg CuO/l versus 26.84 mg CuO /l ). The ranking of metal toxicity levels on bioluminescence was in the order of ZnO?>?CuO?>?Co₃O₄?>?NiO?>?Fe₂O₃, TiO₂, while CuO?>?ZnO?>?NiO?>?Co₃O₄, Fe₂O₃, TiO₂ on germination. No revertant mutagenic ratio (greater than 2.0) of Salmonella typhimurium TA 98 was observed under any tested condition. These findings demonstrate that several bioassays, as opposed to any single one, are needed for the accurate assessment of NP toxicity on ecosystems.     

Synthesis of tumor-targeted folate conjugated fluorescent magnetic albumin nanoparticles for enhanced intracellular dual-modal imaging into human brain tumor cells

Superparamagnetic iron oxide nanoparticles (SPIO NPs), utilized as carriers are attractive materials widely applied in biomedical fields, but target-specific SPIO NPs with lower toxicity and excellent biocompatibility are still lacking for intracellular visualization in human brain tumor diagnosis and therapy. Herein, bovine serum albumin (BSA) coated superparamagnetic iron oxide, i.e. γ-Fe₂O₃ nanoparticles (BSA-SPIO NPs), are synthesized. Tumor-specific ligand folic acid (FA) is then conjugated onto BSA-SPIO NPs to fabricate tumor-targeted NPs, FA-BSA-SPIO NPs as a contrast agent for MRI imaging. The FA-BSA-SPIO NPs are also labeled with fluorescein isothiocyanate (FITC) for intracellular visualization after cellular uptake and internalization by glioma U251 cells. The biological effects of the FA-BSA-SPIO NPs are investigated in human brain tumor U251 cells in detail. These results show that the prepared FA-BSA-SPIO NPs display undetectable cytotoxicity, excellent biocompatibility, and potent cellular uptake. Moreover, the study shows that the made FA-BSA-SPIO NPs are effectively internalized for MRI imaging and intracellular visualization after FITC labeling in the targeted U251 cells. Therefore, the present study demonstrates that the fabricated FITC-FA-BSA-SPIO NPs hold promising perspectives by providing a dual-modal imaging as non-toxic and target-specific vehicles in human brain tumor treatment in future.     

Metal–Organic Framework Templated Porous Carbon‐Metal Oxide/Reduced Graphene Oxide as Superior Support of Bimetallic Nanoparticles for Efficient Hydrogen Generation from Formic Acid

Ultrafine PdAg nanoparticles (NPs) are successfully immobilized on zirconia/porous carbon/reduced graphene oxide (ZrO₂/C/rGO) nanocomposite derived from metal organic framework/graphene oxide. Monodispersed PdAg NPs (diameter ≤2.5 nm) can be facilely anchored on the ZrO₂/C/rGO and the aggregation of metal NPs can be avoided utmostly. By virtue of the synergistic effect between metal NPs and support, the resulting PdAg@ZrO₂/C/rGO exhibits excellent activity (turnover frequency, 4500 h^?1 at 333 K) for the dehydrogenation of formic acid. As an effective strategy, it provides an opportunity to immobilize ultrafine metal NPs on metal oxide/porous carbon/reduced graphene oxide, which has tremendous application prospects in various catalytic fields.     

New Insight into the Synthesis of Aromatic Azo Compounds Assisted by Surface Plasmon Resonance

The application of surface plasmon resonance (SPR)-assisted catalysis to synthesize aromatic azo compounds was first reported in 2010. The feasibility of SPR-assisted catalytic decomposition of aromatic azo compounds has also been confirmed, both experimentally and theoretically. Compared with traditional chemical synthesis methods, SPR-assisted catalysis has many advantages, such as high efficiency, low energy consumption, and high selectivity. The synthetic route to aromatic azo compounds and the kinetics thereof can be efficiently monitored by Raman spectroscopy. In this way, it has been confirmed that SPR-assisted catalysis occurs on the surface of noble metal nanoparticles (NPs). Mechanistically, the process involves transfer of electrons excited by the incident laser from noble metal NPs to ³O₂ in air to form ²O₂ ^? for the generation of SPR on the surface of the noble metal nanoparticles. The ²O₂ ^? can then react with the metal to form metal oxides or hydroxides, which in turn can react with the substrate molecule. The substrate molecule can gain a proton from a proton donor or lose a proton to form a radical, which can react further. This mechanism accounts for the conversion of 4-aminothiophenol (PATP) into 4, 4-dimercaptoazobenzene (DMAB). The metal oxide or hydroxide formed reacts with PATP in an acid-base neutralization process. PATP radicals (PATP ^· ) are formed by the loss of a proton, and pairing of two PATP ^· leads to the intermediate product DMHAB. Deprotonation DMHAB then gives the final product DMAB.     

Samarium doped titanium dioxide nanoparticles as theranostic agents in radiation therapy

PurposeTitanium dioxide nanoparticles (TiO₂ NPs) have been investigated for their role as radiosensitisers for radiation therapy. The study aims to increase the efficiency of these NPs by synthesising them with samarium.MethodsSamarium-doped TiO₂ NPs (Ti(Sm)O₂ NPs) were synthesised using a solvothermal method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS) were performed for characterising of the Ti(Sm)O₂ NPs. The intracellular uptake and cytotoxicity were assessed in vitro using A549 and DU145 cancer cell lines. Furthermore, the effect of dose enhancement and generation of reactive oxygen species (ROS) in response to 6 MV X-rays was evaluated. Additionally, the image contrast properties were investigated using computed tomography (CT) images.ResultsThe synthesised Ti(Sm)O₂ NPs were about 13 nm in diameter as determined by TEM. The XRD pattern of Ti(Sm)O₂ NPs was consistent with that of anatase-type TiO₂. EDS confirmed the presence of samarium in the nanoparticles. At 200 μg/ml concentration, no differences in cellular uptake and cytotoxicity were observed between TiO₂ NPs and Ti(Sm)O₂ NPs in both A549 and DU145 cells. However, the combination of Ti(Sm)O₂ NPs and X-rays elicited higher cytotoxic effect and ROS generation in the cells than that with TiO₂ NPs and X-rays. The CT numbers of Ti(Sm)O₂ NPs were systematically higher than that of TiO₂ NPs.ConclusionsThe Ti(Sm)O₂ NPs increased the dose enhancement of MV X-ray beams than that elicited by TiO₂ NPs. Samarium improved the efficiency of TiO₂ NPs as potential radiosensitising agent.     

Application of a fluorescent biosensor based‐on magneto‐γ‐Fe2O3–methyldopa nanoparticles for adsorption of human serum albumin

Understanding and controlling the interaction between the polymer methyldopa (2‐amino‐3‐(3,4‐dihydroxyphenyl)‐2‐methyl‐propanoic acid) (PMDP)–γ‐Fe₂O₃ nanoparticles and biological fluids is important if the potential of nanoparticles (NPs) in biomedicine is to be realized. Physicochemical studies on the interactions between proteins and NPs are influenced by the surface properties of the NPs. To identify the effects of the NP surface, interactions between human serum albumin (HSA) and PMDP–γ‐Fe₂O₃ NPs were investigated. Here, the adsorption of HSA onto small (10–30 nm diameter) PMDP–γ‐Fe₂O₃ NPs was quantitatively analyzed using spectroscopic methods. The fluorescence quenching data were checked for the inner‐filter effect, the main confounding factor in the observed quenching. The binding constants, K_a, were calculated at different temperatures, using a nonlinear fit to the experimental data, and the thermodynamic parameters ?H, ?S and ?G were given. The obtained thermodynamic signature suggests that hydrophobic interactions at least are present. This result indicates that the structure of the protein turns from a structureless denatured state at pH 3 into an ordered biologically active native state on addition of PMDP–γ‐Fe₂O₃ NPs. Copyright © 2015 John Wiley & Sons, Ltd.     

Alpha-Fe2O3 elicits diameter-dependent effects during exposure to an in vitro model of the human placenta

Iron oxide nanoparticles offer unique possibilities due to the change in their physico-chemical parameters when synthesized on the nanoscale (10^?9 m) compared to their bulk forms. While novel uses exist for these materials when synthesized as nanoparticles, their unintended effects on the human body and specifically during pregnancy remain ill defined. In this study, an iron oxide nanoparticle, α-Fe₂O₃, was employed and the potential toxicity due to exposure was assessed in the widely used model human placental cell line BeWo b30. These cells were grown as epithelia, and subsequently assessed for their epithelial integrity, reactive oxygen species production and cellular viability, ultrastructural and morphological disruption, and genotoxicity as a result of exposure to α-Fe₂O₃ nanoparticles. Transepithelial electrical resistance indicated that exposure to the large (50 and 78 nm), but not small (15 nm) diameter particles of α-Fe₂O₃ nanomaterial resulted in leakiness of the epithelium. Exposure to the large diameters of 50 and 78 nm resulted in increases in cell death and reactive oxygen species. Disruption of junctional integrity as monitored by immunolocalization of the tight junction protein ZO-1 was found to occur as a consequence of exposure to large diameter NPs. It was found that there was reduction in the number of microvilli responsible for increased surface area for nutrient absorption after exposing the epithelia to large diameter NPs. Finally, genotoxicity as assessed by DNA microarray and confirmed by QPCR indicated that the large diameter particles (78 nm) induce apoptosis in these cells. These data indicate that large (50 and 78 nm), but not small (15 nm) α-Fe₂O₃ nanoparticles disrupt the barrier function of this epithelium as assessed by in vitro analysis.     

Modified Eu‐doped Y2O3 nanoparticles as turn‐off luminescent probes for the sensitive detection of pyridoxine

Europium‐doped yttrium oxide nanoparticles (Y₂O₃:Eu NPs) modified by captopril were prepared in aqueous solution. In this study, we report the effect of pyridoxine hydrochloride on the photoluminescence intensity of Y₂O₃:Eu NPs in pH 7.2 buffer solution. By increasing the pyridoxine concentration, the luminescence intensity of Y₂O₃:Eu NPs is quenched. The results show that this method demonstrates high sensitivity for pyridoxine determination. A linear relationship is observed between 0.0 and 62.0 μM with a correlation coefficient of 0.995 and a detection limit of 0.023 μM. Copyright © 2014 John Wiley & Sons, Ltd.     

Biosynthesis of Al2O3 and europium-doped Al2O3 nanoparticle using Cymbopogon citratus (lemongrass) extract and its antibacterial property

Cymbopogon citratus-mediated pure aluminium oxide (Al₂O₃) and europium (Eu)-doped Al₂O₃ with different amounts of metal ion were prepared using a green synthesis method. Synthesised nanoparticles were characterised by ultraviolet (UV)-visible spectroscopy, photoluminescence (PL), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Synthesis of nanoparticles is confirmed by using UV-visible spectroscopy showing maximum absorption at 411 and 345 nm for Al₂O₃ and Eu-doped Al₂O₃, respectively. The antibacterial activity of prepared nanoparticles was evaluated against Pseudomonas aeruginosa, Streptococcus aureus, Escherichia coli and Klebsiella pneumoniae using a well-diffusion technique. The effect of pure Al₂O₃ and Eu-doped nanoparticles shows excellent results against P. aeruginosa, S. aureus, E. coli and K. pneumoniae.     

Aluminium oxide nanoparticles inhibit EPS production,adhesion and biofilm formation by multidrug resistant Acinetobacter baumannii

Abstract

Acinetobacter baumannii is a biofilm forming multidrug resistant (MDR) pathogen responsible for respiratory tract infections. In this study, aluminium oxide nanoparticles (Al₂O₃ NPs) were synthesized and characterized by TEM and EDX and shown to be spherical shaped nanoparticles with a diameter < 10?nm. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) for the Al₂O₃ NPs ranged between 125 and 1,000?µg ml^?1. Exposure to NPs caused cellular membrane disruption, indicated by an increase in cellular leakage of the contents. Biofilm inhibition was 11.64 to 70.2%, whereas attachment of bacteria to polystyrene surfaces was reduced to 48.8 to 51.9% in the presence of NPs. Nanoparticles also reduced extracellular polymeric substance production and the biomass of established biofilms. The data revealed the non-toxic nature of Al₂O₃ NPs up to a concentrations of 120?µg ml^?1 in HeLa cell lines. These results demonstrate an effective and safer use of Al₂O₃ NPs against the MDR A. baumannii by targeting biofilm formation, adhesion and EPS production.     

A review of cardiovascular toxicity of TiO<Subscript>2</Subscript>, ZnO and Ag nanoparticles (NPs)

To ensure the safe use of nanoparticles (NPs) in modern society, it is necessary and urgent to assess the potential toxicity of NPs. Cardiovascular system is required for the systemic distribution of NPs entering circulation. Therefore, the adverse cardiovascular effects of NPs have gained extensive research interests. Metal based NPs, such as TiO₂, ZnO and Ag NPs, are among the most popular NPs found in commercially available products. They may also have potential applications in biomedicine, which could increase their contact with cardiovascular systems. This review aimed at providing an overview about the adverse cardiovascular effects of TiO₂, ZnO and Ag NPs. We discussed about the bio-distribution of NPs following different exposure routes. We also discussed about the cardiovascular toxicity of TiO₂, ZnO and Ag NPs as assessed by in vivo and in vitro models. The possible mechanisms and contribution of physicochemical properties of metal based NPs were also discussed.     

Strategic Synthesis of Ultrasmall NiCo2O4 NPs as Hole Transport Layer for Highly Efficient Perovskite Solar Cells

This study proposes a novel strategy of controllable deamination of Co–NH₃ complexes in a system containing Ni(OH)₂ to synthesize ultrasmall ternary oxide nanoparticles (NPs), NiCo₂O₄. Through this approach, ultrasmall (5 nm on average) and well‐dispersed NiCo₂O₄ NPs without exotic ligands are obtained, which enables the formation of uniform and pin‐hole free films. The tightly covered NiCo₂O₄ films also facilitate the formation of large perovskite grains and thus reduce film defects. The results show that with the NiCo₂O₄ NPs as the hole transport layer (HTL), the perovskite solar cells reach a high power conversion efficiency (PCE) of 18.23% and a promising stability (maintained ≈90% PCE after 500 h light soaking). To the best of the author's knowledge, it is the first time that spinel NiCo₂O₄ NPs have been applied as hole transport layer in perovskite solar cells successfully. This work not only demonstrates the potential applications of ternary oxide NiCo₂O₄ as HTLs in hybrid perovskite solar cells but also provides an insight into the design and synthesis of ultrasmall and ligand‐free NPs HTLs to enable cost‐effective photovoltaic devices.     

Fabrication of two- and three-dimensional model catalyst systems with monodispersed platinum nanoparticles as active metal building blocks

Well-defined Pt monodispersed nanoparticles within the catalytically relevant 1–10 nm size regime were synthesized in solution phase by several synthetic methods which differed in the choice of reducing agent, surface stabilizer, reaction temperature and solvent. Three-dimensional model catalysts were fabricated by incorporating the metal nanoparticles into ordered channels of high surface area mesoporous oxides such as SiO₂, Al₂O₃ and Ta₂O₅ through either sonication or direct synthesis of the oxide support around the particles. Deposition of the same nanocrystals onto silica supports by means of the Langmuir–Schaeffer technique produced two-dimensional model catalysts.