Fluoride-assisted detection of glutathione by surface Ce3+/Ce4+ engineered nanoceria

Nanoceria has evolved as a promising nanomaterial due to its unique enzyme-like properties, including excellent oxidase mimetic activity, which significantly increases in the presence of fluoride ions. However, this significant increase in oxidase activity has never been utilised as a signal enhancer for the detection of biological analytes partly because of the lack of understanding of the mechanism involved in this process. In this study, we show that the surface oxidation state of cerium ions plays a very crucial role in different enzymatic activities, especially the oxidase mimetic activity by engineering nanoceria with three different surface Ce⁴⁺/Ce³⁺ compositions. Using DFT calculations combined with Bader charge analysis, it is demonstrated that stoichiometric ceria registers a higher oxidase mimetic activity than oxygen-deficient ceria with a low Ce⁴⁺/Ce³⁺ ratio due to a higher charge transfer from a substrate, 3,3',5,5' tetramethylbenzidine (TMB), to the ceria surface. We also show that the fluoride ions can significantly increase the charge transfer from the TMB surface to ceria irrespective of the surface Ce⁴⁺/Ce³⁺ ratio. Using this knowledge, we first compare the fluoride sensing properties of nanoceria with high Ce⁴⁺ and mixed Ce⁴⁺/Ce³⁺ oxidation states and further demonstrate that the linear detection range of fluoride ions can be extended to 1-10 ppm for nanoceria with mixed oxidation states. Then, we also demonstrate an assay for fluoride assisted detection of glutathione, an antioxidant with elevated levels during cancer, using nanoceria with a high surface Ce⁴⁺/Ce³⁺ ratio. The addition of fluoride ions in this assay allows the detection of glutathione in the linear range of 2.5-50 ppm with a limit of detection (LOD) of 3.8 ppm. These studies not only underpin the role of the surface Ce⁴⁺/Ce³⁺ ratio in tuning the fluoride assisted boost in the oxidase mimetic activity of nanoceria but also its strategic application in designing better colourimetric assays.

Nanomaterials-based sensors for the detection of COVID-19: A review

With the threat of increasing SARS-CoV-2 cases looming in front of us and no effective and safest vaccine available to curb this pandemic disease due to its sprouting variants, many countries have undergone a lockdown 2.0 or planning a lockdown 3.0. This has upstretched an unprecedented demand to develop rapid, sensitive, and highly selective diagnostic devices that can quickly detect coronavirus (COVID-19). Traditional techniques like polymerase chain reaction have proven to be time-inefficient, expensive, labor intensive, and impracticable in remote settings. This shifts the attention to alternative biosensing devices that can be successfully used to sense the COVID-19 infection and curb the spread of coronavirus cases. Among these, nanomaterial-based biosensors hold immense potential for rapid coronavirus detection because of their noninvasive and susceptible, as well as selective properties that have the potential to give real-time results at an economical cost. These diagnostic devices can be used for mass COVID-19 detection to understand the rapid progression of the infection and give better-suited therapies. This review provides an overview of existing and potential nanomaterial-based biosensors that can be used for rapid SARS-CoV-2 diagnostics. Novel biosensors employing different detection mechanisms are also highlighted in different sections of this review. Practical tools and techniques required to develop such biosensors to make them reliable and portable have also been discussed in the article. Finally, the review is concluded by presenting the current challenges and future perspectives of nanomaterial-based biosensors in SARS-CoV-2 diagnostics.

Tuning the enzyme-like activities of cerium oxide nanoparticles using triethyl phosphite ligand

Cerium oxide nanoparticles (CeNPs) depict excellent in vitro and in vivo antioxidant properties, determined by the redox switching of surface cerium ions between its two oxidation states (Ce3+ and Ce4+)....

Redox Active Cerium Oxide Nanoparticles: Current Status and Burning Issues

Research on cerium oxide nanoparticles (nanoceria) has captivated the scientific community due to their unique physical and chemical properties, such as redox activity and oxygen buffering capacity, which made them available for many technical applications, including biomedical applications. The redox mimetic antioxidant properties of nanoceria have been effective in the treatment of many diseases caused by reactive oxygen species (ROS) and reactive nitrogen species. The mechanism of ROS scavenging activity of nanoceria is still elusive, and its redox activity is controversial due to mixed reports in the literature showing pro-oxidant and antioxidant activity. In light of its current research interest, it is critical to understand the behavior of nanoceria in the biological environment and provide answers to some of the critical and open issues. This review critically analyzes the status of research on the application of nanoceria to treat diseases caused by ROS. It reviews the proposed mechanism of action and shows the effect of surface coatings on its redox activity. It also discusses some of the crucial issues in deciphering the mechanism and redox activity of nanoceria and suggests areas of future research.

Polymer-Coated Cerium Oxide Nanoparticles as Oxidoreductase-like Catalysts

Cerium oxide nanoparticles have been shown to mimic oxidoreductase enzymes by catalyzing the decomposition of organic substrates and reactive oxygen species. This mimicry can be found in superoxide radicals and hydrogen peroxides, which are harmful molecules produced in oxidative stress-associated diseases. Despite the fact that nanoparticle functionalization is mandatory in the context of nanomedicine, the influence of polymer coatings on their enzyme-like catalytic activity is poorly understood. In this work, six polymer-coated cerium oxide nanoparticles are prepared by the association of 7.8 nm cerium oxide cores with two poly(sodium acrylate) and four poly(ethylene glycol) (PEG)-grafted copolymers with different terminal or anchoring end groups, such as phosphonic acids. The superoxide dismutase-, catalase-, peroxidase-, and oxidase-like catalytic activities of the coated nanoparticles were systematically studied. It is shown that the polymer coatings do not affect the superoxide dismutase-like, impair the catalase-like and oxidase-like, and surprisingly improves peroxidase-like catalytic activities of cerium oxide nanoparticles. It is also demonstrated that the particles coated with the PEG-grafted copolymers perform better than the poly(acrylic acid)-coated ones as oxidoreductase-like enzymes, a result that confirms the benefit of having phosphonic acids as anchoring groups at the particle surface.

Nanostructured Carbon Nitrides for CO2 Capture and Conversion

Carbon nitride (CN), a 2D material composed of only carbon (C) and nitrogen (N), which are linked by strong covalent bonds, has been used as a metal-devoid and visible-light-active photocatalyst owing to its magnificent optoelectronic and physicochemical properties including suitable bandgap, adjustable energy-band positions, tailor-made surface functionalities, low cost, metal-free nature, and high thermal, chemical, and mechanical stabilities. CN-based materials possess a lot of advantages over conventional metal-based inorganic photocatalysts including ease of synthesis and processing, versatile functionalization or doping, flexibility for surface engineering, low cost, sustainability, and recyclability without any leaching of toxic metals from photocorrosion. Carbon nitrides and their hybrid materials have emerged as attractive candidates for CO₂ capture and its reduction into clean and green low-carbon fuels and valuable chemical feedstock by using sustainable and intermittent renewable energy sources of sunlight and electricity through the heterogeneous photo(electro)catalysis. Here, the latest research results in this field are summarized, including implementation of novel functionalized nanostructured CNs and their hybrid heterostructures in meeting the stringent requirements to raise the efficiency of the CO₂ reduction process by using state-of-the-art photocatalysis, electrocatalysis, photoelectrocatalysis, and feedstock reactions. The research in this field is primarily focused on advancement in the synthesis of nanostructured and functionalized CN-based hybrid heterostructured materials. More importantly, the recent past has seen a surge in studies focusing significantly on exploring the mechanism of their application perspectives, which include the behavior of the materials for the absorption of light, charge separation, and pathways for the transport of CO₂ during the reduction process.

Combination of humic acid and clay reduce the ecotoxic effect of TiO2 NPs: A combined physico-chemical and genetic study using zebrafish embryo

The series of breakthroughs that have occurred within the realm of nanotechnology have been the source of several new products and technological interventions. One of the most salient examples in this regard is the widespread employment of titanium dioxide (TiO₂) nanoparticles across a range of consumer goods. Given that waste is generated at every stage of the consumer-product cycle (from production to disposal), many items with TiO₂ nanoparticles are likely to end up being discarded into water bodies. In order to understand the interaction of TiO₂ NPs with aquatic ecosystem, the ecological fate and toxicity of TiO₂ NPs was studied by exposing zebrafish embryos to a combination of abiotic factors (humic acid and clay) to assess its effect on the development of zebrafish embryos. The physiological changes were correlated with genetic marker analysis to holistically understand the effect on embryos development. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to analyze the interaction energy between TiO₂ NPs and natural organic matter (NOM) for understanding the aggregation behavior of engineered nanoparticles (ENPs) in media. The study revealed that combination of HA and clay stabilized TiO₂ NPs, compared to bare TiO₂ and HA or clay alone. TiO₂ NPs and TiO₂ NPs + Clay significantly altered the expression of genes involved in development of dorsoventral axis and neural network of zebrafish embryos. However, the presence of HA and HA + clay showed protective effect on zebrafish embryo development. The complete system analysis demonstrated the possible ameliorating effects of abiotic factors on the ecotoxicity of ENPs.

Montmorillonite clay and humic acid modulate the behavior of copper oxide nanoparticles in aqueous environment and induces developmental defects in zebrafish embryo

Copper oxide nanoparticles (CuO NPs) is one of the most commonly used metal oxide nanoparticles for commercial and industrial products. An increase in the manufacturing and use of the CuO NPs based products has increased the likelihood of their release into the aquatic environment. This has attracted major attention among researchers to explore their impact in human as well as environmental systems. CuO NPs, once released into the environment interact with the biotic and abiotic constituents of the ecosystem. Hence the objective of the study was to provide a holistic understanding of the effect of abiotic factors on the stability and aggregation of CuO NPs and its correlation with their effect on the development of zebrafish embryo. It has been observed that the bioavailability of CuO NPs decrease in presence of humic acid (HA) and heteroagglomeration of CuO NPs occurs with clay minerals. CuO NPs, CuO NPs + HA and CuO NPs + Clay significantly altered the expression of genes involved in development of dorsoventral axis and neural network of zebrafish embryos. However, the presence of HA with clay showed protective effect on zebrafish embryo development. These findings provide new insights into the interaction of NPs with abiotic factors and combined effects of such complexes on developing zebrafish embryos genetic markers.

An unexpected phase transformation of ceria nanoparticles in aqueous media

Cerium oxide Nanoparticles (CNPs) are of significant interest to the scientific community due to their wide spread applications in a variety of fields. It is proposed that size dependent variations in the extent of Ce3+ and Ce4+ oxidation states of cerium in CNPs determines the performance of CNPs in application environments. To obtain greater molecular and structural understanding of chemical state transformations previously reported for ceria ≈ 3 nm nanoparticles (CNPs) in response to changing ambient conditions, microXRD and Raman measurements were carried out for various solution conditions. The particles were observed to undergo a reversible transformation from a defective ceria structure to a non-ceria amorphous oxy-hydroxide/peroxide phase in response to the addition of 30% hydrogen peroxide. For CNPs made up of ~8 nm crystallites, a partial transformation was observed and no transformation was observed for CNPs made up of ~ 40 nm crystallites. This observation of differences in size dependent transition behavior may help explain the benefits of using smaller CNPs in applications requiring regenerative behavior.

Ligand-mediated reversal of the oxidation state dependent ROS scavenging and enzyme mimicking activity of ceria nanoparticles

Enzymatic activity of cerium oxide nanoparticles modified by phosphine ligands.

ATP-mediated intrinsic peroxidase-like activity of Fe3O4-based nanozyme: One step detection of blood glucose at physiological pH

Fe₃O₄ nanoparticles (Fe₃O₄ NPs), demonstrating peroxidase-like activity has garnered attention in the detection of several biomolecules, therefore, emerged as an excellent nano-biosensing agent. The intrinsic peroxidase-like activity of Fe₃O₄ NPs at acidic pH is the fundamental action driving the oxidation of substrates like TMB, resulting in a colorimetric product formation used in the detection of biomolecules. Hence, the detection sensitivity essentially depends on the ability of oxidation by Fe₃O₄ NPs in presence of H₂O₂. However, the limited sensitivity and pH condition constraint have been identified as the major drawbacks in the detection of biomolecules at physiological pH. Herein, we report overwhelming of the fundamental limitation of acidic pH and tuning the peroxidase-like activity of Fe₃O₄ NPs at physiological pH by using ATP. In presence of ATP, Fe₃O₄ NPs exhibited enhanced peroxidase-like activity over a wide range of pH and temperatures. Mechanistically, it was found that the ability of ATP to participate in single electron transfer reaction, through complexation with Fe₃O₄ NPs, results in the generation of hydroxyl radicals which are responsible for enhanced peroxidase activity at physiological pH. We utilized this ATP-mediated enhanced peroxidase-like activity of Fe₃O₄ NPs for single step detection of glucose with a colorimetric detection limit of 50μM. Further, we extended this single step detection method to monitor glucose level in human blood serum and detected in a time span of <5min at pH 7.4.

Redox-Sensitive Cerium Oxide Nanoparticles Protect Human Keratinocytes from Oxidative Stress Induced by Glutathione Depletion

Cerium oxide nanoparticles (CeNPs) have gathered much attention in the biomedical field due to its unique antioxidant property. It can protect cells and tissues from oxidative stress induced damage due to its autoregenerative redox cycle. Our study explores the antioxidant and antigenotoxic behavior of PEGylated CeNPs toward oxidative insult produced by buthionine sulfoximine (BSO) in human keratinocytes (HaCaT cells). BSO inhibits the γ-glutamylcysteinesynthetase (γ-GCS) enzyme and thus acts as a glutathione (GSH) depleting agent to modulate the cellular redox potential. GSH is a natural ROS scavenger present in the mammalian cells, and its depletion causes generation of reactive oxygen species (ROS). In this study, we challenged HaCaT cells (keratinocytes) with BSO to alter the redox potential within the cell and monitored toxicity, ROS generation, and nuclear fragmentation. We also followed changes in expressions of related proteins and genes. We found that PEGylated CeNPs can protect HaCaT cells from BSO-induced oxidative damage. BSO-exposed cells, preincubated with PEGylated CeNPs, showed better cell survival and significant decrease in the intracellular levels of ROS. We also observed decrease in lactate dehydrogenase (LDH) release and nuclear fragmentation in CeNP-treated cells that were challenged with BSO as compared to treatment with BSO alone. Exposure of HaCaT cells with BSO leads to altered expression of antioxidant genes and proteins, i.e., thioredoxin reductase (TrxR) and peroxiredoxin 6 (Prx6) whereas, in our study, pretreatment of PEGylated CeNPs reduces the need for induction of genes that produce enzymes involved in the defense against oxidative stress. Since, growing evidence argued the involvement of ROS in mediating death of mammalian cells in several ailments, our finding reinforces the use of PEGylated CeNPs as a potent pharmacological agent under the lower cellular GSH/GSSG ratios for the treatment of diseases mediated by free radicals.

Investigation of trimethylacetic acid adsorption on stoichiometric and oxygen-deficient CeO2(111) surfaces

Adsorption of trimethylacetic acid on the surface of stoichiometric and oxygen deficient cerium oxide studied using in situ XPS show that the dissociative adsorption is preferred on oxygen deficient cerium oxide (111) surface.

Aqueous medium induced optical transitions in cerium oxide nanoparticles

Experimental and theoretical investigations were performed to investigate the effect of water on optical properties of nanoceria as a function of Ce³⁺ concentration.

Influence of Aging and Environment on Nanoparticle Chemistry - Implication to Confinement Effects in Nanoceria

The oxidation state switching of cerium in cerium oxide nanoparticles is studied in detail. The influence of synthesis medium, aging time and local environment on the oxidation state switching, between +3 and + 4, is analyzed by tracking the absorption edge using UV-Visible spectroscopy. It is observed that by tuning the local environment, the chemistry of the nanoparticles could be altered. These time dependent, environmentally induced changes likely contribute to inconsistencies in the literature regarding quantum-confinement effects for ceria nanoparticles. The results in this article indicate that there is a need to carry out comprehensive analysis of nanoparticles while considering the influence of synthesis and processing conditions, aging time and local environment.

Linker-induced anomalous emission of organic-molecule conjugated metal-oxide nanoparticles

Semiconductor nanoparticles conjugated with organic- and dye-molecules to yield high efficiency visible photoluminescence (PL) hold great potential for many future technological applications. We show that folic acid (FA)-conjugated to nanosize TiO(2) and CeO(2) particles demonstrates a dramatic increase of photoemission intensity at wavelengths between 500 and 700 nm when derivatized using aminopropyl trimethoxysilane (APTMS) as spacer-linker molecules between the metal oxide and FA. Using density-functional theory (DFT) and time-dependent DFT calculations we demonstrate that the strong increase of the PL can be explained by electronic transitions between the titania surface oxygen vacancy (OV) states and the low-energy excited states of the FA/APTMS molecule anchored onto the surface oxygen bridge sites in close proximity to the OVs. We suggest this scenario to be a universal feature for a wide class of metal oxide nanoparticles, including nanoceria, possessing a similar band gap (∼3 eV) and with a large surface-vacancy-related density of electronic states. We demonstrate that the molecule-nanoparticle linker can play a crucial role in tuning the electronic and optical properties of nanosystems by bringing optically active parts of the molecule and of the surface close to each other.

A phosphate-dependent shift in redox state of cerium oxide nanoparticles and its effects on catalytic properties

Cerium oxide nanoparticles (CeNPs) have shown promise as catalytic antioxidants in cell culture and animal models as both superoxide dismutase and catalase mimetics. The reactivity of the cerium (Ce) atoms at the surface of its oxide particle is critical to such therapeutic properties, yet little is known about the potential for a protein or small molecule corona to form on these materials in vivo. Moreover Ce atoms in these active sites have the potential to interact with small molecule anions, peptides, or sugars when administered in culture or animal models. Several nanomaterials have been shown to alter or aggregate under these conditions, rendering them less useful for biomedical applications. In this work we have studied the change in catalytic properties of CeNPs when exposed to various biologically relevant conditions in vitro. We have found that CeNPs are resistant to broad changes in pH and also not altered by incubation in cell culture medium. However to our surprise phosphate anions significantly altered the characteristics of these nanomaterials and shifted the catalytic behavior due to the binding of phosphate anions to cerium. Given the abundance of phosphate in biological systems in an inorganic form, it is likely that the action of CeNPs as a catalyst may be strongly influenced by the local concentration of phosphate in the cells and/or tissues in which it has been introduced.

Nanoceria inhibit the development and promote the regression of pathologic retinal neovascularization in the Vldlr knockout mouse

Many neurodegenerative diseases are known to occur and progress because of oxidative stress, the presence of reactive oxygen species (ROS) in excess of the cellular defensive capabilities. Age related macular degeneration (AMD), diabetic retinopathy (DR) and inherited retinal degeneration share oxidative stress as a common node upstream of the blinding effects of these diseases. Knockout of the Vldlr gene results in a mouse that develops intraretinal and subretinal neovascular lesions within the first month of age and is an excellent model for a form of AMD called retinal angiomatous proliferation (RAP). Cerium oxide nanoparticles (nanoceria) catalytically scavenge ROS by mimicking the activities of superoxide dismutase and catalase. A single intravitreal injection of nanoceria into the Vldlr-/- eye was shown to inhibit: the rise in ROS in the Vldlr-/- retina, increases in vascular endothelial growth factor (VEGF) in the photoreceptor layer, and the formation of intraretinal and subretinal neovascular lesions. Of more therapeutic interest, injection of nanoceria into older mice (postnatal day 28) resulted in the regression of existing vascular lesions indicating that the pathologic neovessels require the continual production of excessive ROS. Our data demonstrate the unique ability of nanoceria to prevent downstream effects of oxidative stress in vivo and support their therapeutic potential for treatment of neurodegenerative diseases such as AMD and DR.

PEGylated inorganic nanoparticles

Application of inorganic nanoparticles in diagnosis and therapy has become a critical component in the targeted treatment of diseases. The surface modification of inorganic oxides is important for providing diversity in size, shape, solubility, long-term stability, and attachment of selective functional groups. This Minireview describes the role of polyethylene glycol (PEG) in the surface modification of oxides and focuses on their biomedical applications. Such a PEGylation of surfaces provides "stealth" characteristics to nanomaterials otherwise identified as foreign materials by human body. The role of PEG as structure-directing agent in synthesis of oxides is also presented.

Combined cytotoxic and anti-invasive properties of redox-active nanoparticles in tumor-stroma interactions

Tumor-stroma interaction plays an important role in tumor progression. Myofibroblasts, pivotal for tumor progression, populate the microecosystem of reactive stroma. The formation of myofibroblasts is mediated by tumor derived transforming growth factor β1 (TGFβ1) which initiates a reactive oxygen species cell type dependent expression of alpha-smooth muscle actin, a biomarker for myofibroblastic cells. Myofibroblasts express and secrete proinvasive factors significantly increasing the invasive capacity of tumor cells via paracrine mechanisms. Although antioxidants prevent myofibroblast formation, the same antioxidants increase the aggressive behavior of the tumor cells. In this study, the question was addressed of whether redox-active polymer-coated cerium oxide nanoparticles (CNP, nanoceria) affect myofibroblast formation, cell toxicity, and tumor invasion. Herein, nanoceria downregulate both the expression of alpha-smooth muscle actin positive myofibroblastic cells and the invasion of tumor cells. Furthermore, concentrations of nanoceria being non-toxic for normal (stromal) cells show a cytotoxic effect on squamous tumor cells. The treatment with redox-active CNP may form the basis for protection of stromal cells from the dominating influence of tumor cells in tumor-stroma interaction, thus being a promising strategy for chemoprevention of tumor invasion.

Testing in EHS: What is the Current Status of Experimentation?

This paper explores some of the fundamental and practical issues related to the behavior of nanoparticles in the environment and their potential impacts on human health. In our research we have explored the reactive behaviors of nanoparticles with contaminants in the environment, how nanoparticle change in response to their environment and time, and how nanoparticles interact with biological systems of various types. It has become apparent that researchers often underestimate the difficulties of preparing and delivering well characterized nanoparticles for specific types of testing or applications. Difficulties arise in areas that range from not understanding what imparts the "nano" character of a particle to not knowing the impacts of minor species on the properties of high surface area materials. Some of our adventures and misadventures serve as examples of some of these issues as they relate to providing well defined particles for biological studies.

Tuning hydrated nanoceria surfaces: experimental/theoretical investigations of ion exchange and implications in organic and inorganic interactions

Long-term stability and surface properties of colloidal nanoparticles have significance in many applications. Here, surface charge modified hydrated cerium oxide nanoparticles (CNPs, also known as nanoceria) are synthesized, and their dynamic ion exchange interactions with the surrounding medium are investigated in detail. Time-dependent zeta (zeta) potential (ZP) variations of CNPs are demonstrated as a useful characteristic for optimizing their surface properties. The surface charge reversal of CNPs observed with respect to time, concentration, temperature, and doping is correlated to the surface modification of CNPs in aqueous solution and the ion exchange reaction between the surface protons (H(+)) and the neighboring hydroxyls ions (OH(-)). Using density functional theory (DFT) calculations, we have demonstrated that the adsorption of H(+) ions on the CNP surface is kinetically more favorable while the adsorption of OH(-) ions on CNPs is thermodynamically more favorable. The importance of selecting CNPs with appropriate surface charges and the implications of dynamic surface charge variations are exemplified with applications in microelectronics and biomedical.

Nanoceria exhibit redox state-dependent catalase mimetic activity

In this study we have found that cerium oxide nanoparticles exhibit catalase mimetic activity. Surprisingly, the catalase mimetic activity correlates with a reduced level of cerium in the +3 state, in contrast to the relationship between surface charge and superoxide scavenging properties.

Abstract C42: Suppression of tumor invasion by inorganic nanoparticles

Tumor progression is characterized by local accumulation of extracellular matrix components and connective tissue cells surrounding the tumor cluster, a phenomenon called tumor-stroma interaction. Disturbance in the stroma, composed of endothelial, fibroblastic and myofibroblastic cells as well as inflammatory cells, is suggested to be essential during the invasion process. A range of cytokines and growth factors are expressed by tumor and stromal cells in melanoma and carcinoma that enhance the invasive and metastatic capacity of tumor cells. It was shown previously that the reactive oxygen species (ROS) dependent transdifferentiation of fibroblasts to α-smooth muscle actin expressing myofibroblasts (mesenchymal-mesenchymal transition, MMT) by tumor cell-derived transforming growth factor β-1 (TGFβ1) is a prerequisite for an increase in the aggressive behavior of the tumor cells. In the following work the question was addressed of whether typical antioxidants or inorganic nanoparticles attenuate or completely abrogate tumor-stroma interaction. Cell biological, biochemical, and molecular biological approaches showed that antioxidants such as the thiol N-acetyl L-cysteine and the micronutrient selenite significantly lowered the generation of myofibroblasts and the secretion of proinvasive soluble factors resulting in thinning the capacity of tumor invasion. However, the exclusive treatment of the tumor cells resulted in an opposite effect, namely enhanced tumor cell migration. Therefore, the ability of cerium oxide nanoparticles (CNPs) to control the invasion of tumor cells and specifically the expression of α-smooth muscle actin in stromal cells was evaluated. CNPs can scavenge ROS analogous to naturally occurring enzymes. However, CNPs have an added advantage of being regenerative through changes occurring at molecular level and surrounding electrochemical media, and, therefore, under certain intracellular or extracellular conditions function as pro-oxidant. It is hypothesized that structural oxygen vacancies in nanoceria can act as trapping sites for ROS thereby regulating their over expression in one single dose. As the mode of action of CNPs depends on different physical qualities, it is very important to engineer CNPs carefully thereby providing them with medium dependent properties. Different types of nanoceria were studied for their antioxidant and proxoxidant properties. It was found that the nanoceria treatment showed decreased cell viability of squamous carcinoma cell line (SCL-1) by more than 60% while protecting the human dermal fibroblasts viability at 100%. Such an acute effect of ROS scavenging nanoparticles on lowering the number of myofibroblasts can reaffirm the stromal therapy by protecting the stromal cells against dominating influence of the tumor cells in tumor-stroma interaction. Thus treatment with inorganic nanoceria as antioxidant may form the basis for the prevention of MMT as benign strategy for chemoprevention of tumor invasion.

Citation Information: Cancer Res 2009;69(23 Suppl):C42.

Anti-inflammatory properties of cerium oxide nanoparticles

The valence and oxygen defect properties of cerium oxide nanoparticles (nanoceria) suggest that they may act as auto-regenerative free radical scavengers. Overproduction of the free radical nitric oxide (NO) by the enzyme inducible nitric oxide synthase (iNOS) has been implicated as a critical mediator of inflammation. NO is correlated with disease activity and contributes to tissue destruction. The ability of nanoceria to scavenge free radicals, or reactive oxygen species (ROS), and inhibit inflammatory mediator production in J774A.1 murine macrophages is investigated. Cells internalize nanoceria, the treatment is nontoxic, and oxidative stress and pro-inflammatory iNOS protein expression are abated with stimulation. In vivo studies show nanoceria deposition in mouse tissues with no pathogenicity. Taken together, it is suggested that cerium oxide nanoparticles are well tolerated in mice and are incorporated into cellular tissues. Furthermore, nanoceria may have the potential to reduce ROS production in states of inflammation and therefore serve as a novel therapy for chronic inflammation.

PEGylated nanoceria as radical scavenger with tunable redox chemistry

We report the direct synthesis of cerium oxide nanoparticles (CNPs) in polyethylene glycol (PEG) based solutions with efficient radical scavenging properties. Synthesis of CNPs in PEG demonstrated a concentration dependent (of PEG) redox activity characterized by UV-visible spectroscopy. PEGylated CNPs acted as efficient radical scavengers, and superoxide dismutase (SOD) activity of CNPs synthesized in various concentration of PEG did not reduce compared to bare nanoceria. In addition to superoxide, PEGylated nanoceria demonstrated quenching of peroxide radicals as well. It was observed that the reaction with hydrogen peroxide leads to the formation of a charge transfer complex governed by the concentration of PEG. The stability of the charge transfer complex provides the tunable oxidation state of CNPs. The stability of this complex influences the regenerative capacity of the active 3+ oxidation state of CNPs. The cell viability as well as SOD activity of PEGylated CNPs is compared to those of bare CNPs, and the differences are outlined.

Exposure to titanium dioxide nanomaterials provokes inflammation of an in vitro human immune construct

Nanoparticle technology is undergoing significant expansion largely because of the potential of nanoparticles as biomaterials, drug delivery vehicles, cancer therapeutics, and immunopotentiators. Incorporation of nanoparticle technologies for in vivo applications increases the urgency to characterize nanomaterial immunogenicity. This study explores titanium dioxide, one of the most widely manufactured nanomaterials, synthesized into its three most common nanoarchitectures: anatase (7-10 nm), rutile (15-20 nm), and nanotube (10-15 nm diameters, 70-150 nm length). The fully human autologous MIMIC immunological construct has been utilized as a predictive, nonanimal alternative to diagnose nanoparticle immunogenicity. Cumulatively, treatment with titanium dioxide nanoparticles in the MIMIC system led to elevated levels of proinflammatory cytokines and increased maturation and expression of costimulatory molecules on dendritic cells. Additionally, these treatments effectively primed activation and proliferation of naive CD4(+) T cells in comparison to dendritic cells treated with micrometer-sized (>1 microm) titanium dioxide, characteristic of an in vivo inflammatory response.

The role of cerium redox state in the SOD mimetic activity of nanoceria

Cerium oxide nanoparticles (nanoceria) have recently been shown to protect cells against oxidative stress in both cell culture and animal models. Nanoceria has been shown to exhibit superoxide dismutase (SOD) activity using a ferricytochrome C assay, and this mimetic activity that has been postulated to be responsible for cellular protection by nanoceria. The nature of nanoceria's antioxidant properties, specifically what physical characteristics make nanoceria effective at scavenging superoxide anion, is poorly understood. In this study electron paramagnetic resonance (EPR) analysis confirms the reactivity of nanoceria as an SOD mimetic. X-ray photoelectron spectroscopy (XPS) and UV-visible analyses of nanoceria treated with hydrogen peroxide demonstrate that a decrease in the Ce 3(+)/4(+) ratio correlates directly with a loss of SOD mimetic activity. These results strongly suggest that the surface oxidation state of nanoceria plays an integral role in the SOD mimetic activity of nanoceria and that ability of nanoceria to scavenge superoxide is directly related to cerium(III) concentrations at the surface of the particle.

Self-assembly of cerium oxide nanostructures in ice molds

The formation of nanorods, driven by the physicochemical phenomena during the freezing and after the aging of frozen ceria nanoparticle suspensions, is reported. During freezing of a dilute aqueous solution of CeO2 nanocrystals, some nuclei remain in solution while others are trapped inside micro- and nanometer voids formed within the growing ice front. Over time (2-3 weeks) the particles trapped within the nanometer-wide voids in the ice combine by an oriented attachment process to form ceria nanorods. The experimental observations are consistent with molecular dynamics simulations of particle aggregation in constrained environments. These observations suggest a possible strategy for the templated formation of nanostructures through self-assembly by exploiting natural phenomena, such as voids formed during freezing of water. This research suggests a very simple, green chemical route to guide the formation of one- and three-dimensional self-assembled nanostructures.

Mapping nanostructure: a systematic enumeration of nanomaterials by assembling nanobuilding blocks at crystallographic positions

Nanomaterials synthesized from nanobuilding blocks promise size-dependent properties, associated with individual nanoparticles, together with collective properties of ordered arrays. However, one cannot position nanoparticles at specific locations; rather innovative ways of coaxing these particles to self-assemble must be devised. Conversely, model nanoparticles can be placed in any desired position, which enables a systematic enumeration of nanostructure from model nanobuilding blocks. This is desirable because a list of chemically feasible hypothetical structures will help guide the design of strategies leading to their synthesis. Moreover, the models can help characterize nanostructure, calculate (predict) properties, or simulate processes. Here, we start to formulate and use a simulation strategy to generate atomistic models of nanomaterials, which can, potentially, be synthesized from nanobuilding block precursors. Clearly, this represents a formidable task because the number of ways nanoparticles can be arranged into a superlattice is infinite. Nevertheless, numerical tools are available to help build nanoparticle arrays in a systematic way. Here, we exploit the "rules of crystallography" and position nanoparticles, rather than atoms, at crystallographic sites. Specifically, we explore nanoparticle arrays with cubic, tetragonal, and hexagonal symmetries together with primitive, face centered cubic and body centered cubic nanoparticle "packing". We also explore binary nanoparticle superlattices. The resulting nanomaterials, spanning CeO(2), Ti-doped CeO(2), ZnO, ZnS, MgO, CaO, SrO, and BaO, comprise framework architectures, with cavities interconnected by channels traversing (zero), one, two and three dimensions. The final, fully atomistic models comprise three hierarchical levels of structural complexity: crystal structure, microstructure (i.e., grain boundaries, dislocations), and superlattice structure.

The role of cerium redox state in the SOD mimetic activity of nanoceria

Cerium oxide nanoparticles (nanoceria) have recently been shown to protect cells against oxidative stress in both cell culture and animal models. Nanoceria has been shown to exhibit superoxide dismutase (SOD) activity using a ferricytochrome C assay, and this mimetic activity that has been postulated to be responsible for cellular protection by nanoceria. The nature of nanoceria's antioxidant properties, specifically what physical characteristics make nanoceria effective at scavenging superoxide anion, is poorly understood. In this study electron paramagnetic resonance (EPR) analysis confirms the reactivity of nanoceria as an SOD mimetic. X-ray photoelectron spectroscopy (XPS) and UV-visible analyses of nanoceria treated with hydrogen peroxide demonstrate that a decrease in the Ce 3(+)/4(+) ratio correlates directly with a loss of SOD mimetic activity. These results strongly suggest that the surface oxidation state of nanoceria plays an integral role in the SOD mimetic activity of nanoceria and that ability of nanoceria to scavenge superoxide is directly related to cerium(III) concentrations at the surface of the particle.

Nanoceria as Antioxidant: Synthesis and Biomedical Applications

The therapeutic application of nanomaterials has been a focus of numerous studies in the past decade. Due to its unique redox properties, cerium oxide (ceria) is finding widespread use in the treatment of medical disorders caused by the reactive oxygen intermediates (ROI). The radical-scavenging role of ceria nanoparticles (nanoceria) have been established, as well as the autocatalytic ability of nanoceria to regenerate under various environmental conditions. The synthesis of nanoceria in biocompatible media has also been reported along with cell viability in order to determine the potential use of nanoceria in biomedical applications.

Hierarchical assembly of inorganic nanostructure building blocks to octahedral superstructures-a true template-free self-assembly

A room temperature, template-free, wet chemical synthesis of ceria nanoparticles and their long term ageing characteristics are reported. High resolution transmission electron microscopy and UV-visible spectroscopy techniques are used to observe the variation in size, structure and oxidation state, respectively as a function of time. The morphology variation and the hierarchical assembly (octahedral superstructure) of nanostructures are imputed to the inherent structural aspects of cerium oxide. It is hypothesized that the 3-5 nm individual building blocks will undergo an intra-agglomerate re-orientation to attain the low energy configuration. This communication also emphasizes the need for long term ageing studies of nanomaterials in various solvents for multiple functionalities.

Spiral growth of one dimensional titania nanostructures using anodic oxidation

One dimensional spiral titania nanostructures were obtained by anodization of pure titanium from fluoride containing solutions of phosphoric acid. The formation of nanotubes was found to be dependant on current density. Field Emission Scanning Electron Microscopy (FESEM) shows the diameter of tubes around 70-100 nm which is consistent with the High Resolution Transmission Electron Micrographs (HRTEM) and Atomic Force Microscopy (AFM) images. HRTEM showed the one dimensional growth as spiral in nature which was also supported by AFM images. This anisotropic growth is compared with the possible growth mechanisms.