Biogenic Ceria Nanoparticles (CeO2 NPs) for Effective Photocatalytic and Cytotoxic Activity

Ceria nanoparticles: biomedical applications and toxicity

Ceria nanoparticles (CeO2 NPs) have become popular materials in biomedical and industrial fields due to their potential applications in anti-oxidation, cancer therapy, photocatalytic degradation of pollutants, sensors, etc. Many methods, including gas phase, solid phase, liquid phase, and the newly proposed green synthesis method, have been reported for the synthesis of CeO2 NPs. Due to the wide application of CeO2 NPs, concerns about their adverse impacts on human health have been raised. This review covers recent studies on the biomedical applications of CeO2 NPs, including their use in the treatment of various diseases (e.‍g., Alzheimer's disease, ischemic stroke, retinal damage, chronic inflammation, and cancer). CeO2 NP toxicity is discussed in terms of the different systems of the human body (e.‍g., cytotoxicity, genotoxicity, respiratory toxicity, neurotoxicity, and hepatotoxicity). This comprehensive review covers both fundamental discoveries and exploratory progress in CeO2 NP research that may lead to practical developments in the future.

Preparation of monodisperse cerium oxide particle suspensions from a tetravalent precursor

Cerium oxide particles are a unique material that enables studying the intersection of metal oxides, f-elements, and nanomaterials. Distinct from diverse applications in catalysis, energy, and medicine, cerium possesses additional influence as a non-radioactive actinide surrogate. Herein, we present a synthesis for sub-micron cerium particles using hexamethylenetetramine and ammonium hydroxide as precipitating agents with a CeIV precursor. The combinatorial homogeneous precipitation approach yields monodisperse and moderately-stable CeO2 particle suspensions in ethanol, as determined by powder X-ray diffraction, scanning electron microscopy, dynamic light scattering, and zeta potential measurements. Various additives may be used to moderate and manipulate the surface charge of the particles. Proof-of-concept electrophoretic deposition of the particles produces a uniform layer of CeO2 on graphite. The synthesis and suspension properties are developed as a methodology towards future controlled actinide hydrolysis and film deposition.

Solanum tuberosum tuber-driven starch-mediated green-hydrothermal synthesis of cerium oxide nanoparticles for efficient photocatalysis and antimicrobial activities

In this study, we are reporting for the first time the utilization of Solanum tuberosum tuber-driven, starch-mediated, green-hydrothermally synthesized cerium oxide nanoparticles (G-CeO2 NPs) for the antibacterial activity and photodegradation of cationic (methylene blue, MB) and anionic (methyl orange, MO) dyes separately and in combination, aimed at environmental remediation. The XRD analysis confirms the fluorite structure of G-CeO2 NPs, displaying an average crystallite size of 9.6 nm. Further, XPS confirms the existence of 24% of Ce3+ oxidation states within G-CeO2 NPs. Morphological studies through FE-SEM and TEM reveal that starch-driven OH- ion production leads to a high percentage of active crystal facets, favoring the formation of Ce3+-rich CeO2 NPs. Photocatalytic experiments conducted under UV-A illumination demonstrate the superior degradation performance of G-CeO2 NPs, with MB degradation reaching 93.4% and MO degradation at 77.2% within 90 min. This outstanding catalytic activity is attributed to the mesoporous structure (pore diameter of 5.63 nm) with a narrow band gap, a large surface area (103.38 m2g-1), and reduced charge recombination, as validated by BET, UV-visible, and electrochemical investigations. The identification of photogenerated intermediates is achieved through LCMS, while the mineralization is monitored via total organic carbon analysis. Moreover, the scavenging experiments point towards the involvement of reactive oxygen species in organic oxidation, demonstrating efficiency over five consecutive trials. Additionally, G-CeO2 NPs exhibit potent antibacterial activity against both gram-positive and gram-negative bacteria. This study presents an innovative, and efficient approach to environmental remediation, shedding light on the potential of G-CeO2 NPs in addressing environmental pollution challenges.

A brief study on the role of cerium oxide nanoparticles in growth and alleviation of mercury-induced stress in Vigna radiata and soil bacteria Bacillus coagulans

Cerium oxide nanoparticles have so far been investigated for their role as an antioxidant in pathologies involving inflammation and high oxidative stress. However, its role as a plant and bacterial growth modulator and heavy metal stress reliever has been overlooked to date. Heavy metal contamination poses a major threat to mankind and the life-sustaining ecosystem. This study emphasizes the role of cerium oxide produced by the combustion method in promoting growth in Vigna radiata and Bacillus coagulans in the presence of mercury. The results show that cerium oxide nanoparticles significantly reduce the production of reactive oxygen species, hydrogen peroxide, and product of lipid peroxidation malondialdehyde in plants grown in the presence of 50 ppm mercury, thereby reducing oxidative stress. Nanoceria also increases plant growth with respect to those growing solely in mercury. Nanoceria alone does not significantly affect the growth of Vigna radiata as well as Bacillus coagulans and Escherichia coli, thereby proving its non-hazardous nature. It also significantly increases the growth of Bacillus coagulans at 25 ppm and 50 ppm of mercury. This study throws light upon the biologically non-hazardous nature of this particle by revealing how it promotes the growth of two soil bacteria Bacillus coagulans and E.coli at various dosages. The results of this study pave the way for the use of cerium oxide nanoparticles in plants and various other organisms to combat abiotic stress.

Metal Oxide Nanoparticles: Review of Synthesis, Characterization and Biological Effects

In the last few years, the progress made in the field of nanotechnology has allowed researchers to develop and synthesize nanosized materials with unique physicochemical characteristics, suitable for various biomedical applications. Amongst these nanomaterials, metal oxide nanoparticles (MONPs) have gained increasing interest due to their excellent properties, which to a great extent differ from their bulk counterpart. However, despite such positive advantages, a substantial body of literature reports on their cytotoxic effects, which are directly correlated to the nanoparticles' physicochemical properties, therefore, better control over the synthetic parameters will not only lead to favorable surface characteristics but may also increase biocompatibility and consequently lower cytotoxicity. Taking into consideration the enormous biomedical potential of MONPs, the present review will discuss the most recent developments in this field referring mainly to synthesis methods, physical and chemical characterization and biological effects, including the pro-regenerative and antitumor potentials as well as antibacterial activity. Moreover, the last section of the review will tackle the pressing issue of the toxic effects of MONPs on various tissues/organs and cell lines.

Toxicity of metal-based nanoparticles: Challenges in the nano era

With the rapid progress of nanotechnology, various nanoparticles (NPs) have been applicated in our daily life. In the field of nanotechnology, metal-based NPs are an important component of engineered NPs, including metal and metal oxide NPs, with a variety of biomedical applications. However, the unique physicochemical properties of metal-based NPs confer not only promising biological effects but also pose unexpected toxic threats to human body at the same time. For safer application of metal-based NPs in humans, we should have a comprehensive understanding of NP toxicity. In this review, we summarize our current knowledge about metal-based NPs, including the physicochemical properties affecting their toxicity, mechanisms of their toxicity, their toxicological assessment, the potential strategies to mitigate their toxicity and current status of regulatory movement on their toxicity. Hopefully, in the near future, through the convergence of related disciplines, the development of nanotoxicity research will be significantly promoted, thereby making the application of metal-based NPs in humans much safer.

Enhanced photocatalytic crystal-violet degradation performances of sonochemically-synthesized AC-CeO2 nanocomposites

Semiconductor-based photocatalysis is one of the favorable techniques for the wastewater treatment. Herein, we synthesized the activated carbon-decorated cerium dioxide (AC-CeO₂) nanocomposites via the facile ultrasonication method by using the biomass-derived AC nanoflakes and the sonochemically-synthesized CeO₂ nanoparticles. The AC-CeO₂ nanocomposites exhibited the aggregated morphology with the AC nanoflakes-anchored CeO₂ nanoparticles. Since the hybridization of conductive AC and semiconductive CeO₂ would lead to the increased photocarrier transport and the reduced photocarrier recombination, during the photocatalytic reaction, the AC-CeO₂ nanocomposites showed the enhanced crystal violet dye-degradation efficiency up to 97.9 % within 135 min. The results suggest that the AC-CeO₂ nanocomposites hold promise as a prominent photocatalyst for future green environmental technology.

Cerium oxide decorated 5-fluorouracil loaded chitosan nanoparticles for treatment of hepatocellular carcinoma

Reactive oxygen species (ROS) play a crucial role in the mammalian system in both normal and pathological conditions. Hence, this work prepared and characterized the ROS responsive cerium oxide nanoparticles (CeO₂ NPs) decorated 5-fluorouracil (5FU) loaded chitosan (CS) nanoparticles (CS-5FU NPs) for enhanced anticancer activity in hepatocellular carcinoma (HepG2 cells). CeO₂ NPs decorated CS-5FU NPs were found to be spherical in shape and black dense aggregated particles sized 200 nm. The functional properties and cubic crystalline structure of CeO₂ NPs were studied by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis, respectively. Further, CS-5FU-CeO₂ NPs attenuated the 2,2'-Azobis (2-methylpropionamidine) dihydrochloride (AAPH) induced ROS formation in mouse embryonic fibroblasts (NIH3T3 cells) while enhancing apoptotic cell death in HepG2 cells by controlled delivery of 5FU. Furthermore, CS-5FU-CeO₂ NPs have not exhibited toxicity to red blood cells (RBCs) and chick chorioallantoic membrane (CAM). Hence, this work concluded that CeO₂ NPs decorated CS-5FU NPs synergistically enhanced anticancer activity in HepG2 cells through the regulation of ROS.

Nanoparticle classification, physicochemical properties, characterization, and applications: a comprehensive review for biologists

Interest in nanomaterials and especially nanoparticles has exploded in the past decades primarily due to their novel or enhanced physical and chemical properties compared to bulk material. These extraordinary properties have created a multitude of innovative applications in the fields of medicine and pharma, electronics, agriculture, chemical catalysis, food industry, and many others. More recently, nanoparticles are also being synthesized ‘biologically’ through the use of plant- or microorganism-mediated processes, as an environmentally friendly alternative to the expensive, energy-intensive, and potentially toxic physical and chemical synthesis methods. This transdisciplinary approach to nanoparticle synthesis requires that biologists and biotechnologists understand and learn to use the complex methodology needed to properly characterize these processes. This review targets a bio-oriented audience and summarizes the physico–chemical properties of nanoparticles, and methods used for their characterization. It highlights why nanomaterials are different compared to micro- or bulk materials. We try to provide a comprehensive overview of the different classes of nanoparticles and their novel or enhanced physicochemical properties including mechanical, thermal, magnetic, electronic, optical, and catalytic properties. A comprehensive list of the common methods and techniques used for the characterization and analysis of these properties is presented together with a large list of examples for biogenic nanoparticles that have been previously synthesized and characterized, including their application in the fields of medicine, electronics, agriculture, and food production. We hope that this makes the many different methods more accessible to the readers, and to help with identifying the proper methodology for any given nanoscience problem.

Ceria nanoparticles anchored on graphitic oxide sheets (CeO2-GOS) as an efficient catalyst for degradation of dyes and textile effluents

Herein, we report a Ceria-graphitic oxide sheets (CeO₂-GOS) nanocomposites photo catalyst synthesized by simple and green methods for the degradation of textile effluents and dyes. In the first step, green treated CeO₂ NPs were synthesized through a simple organic reduction method. Further, green synthesized CeO₂ NPs were anchored with GOS to produce CeO₂-GOS nanocomposites by a sol-gel method. The phase morphology and structure of CeO₂-GOS nanocomposites was systematically characterized through X-ray diffraction, Raman spectroscopy, zeta potential, Fourier transform infrared spectroscopy (FT-IR), High-Resolution Transmission Electron Microscope (HR-TEM), and X-ray photoelectron spectroscopy (XPS) analysis. Under visible light irradiation, the CeO₂-GOS nanocomposites photo catalyst exhibited 83%, 78%, and 70% degradation efficiencies for rhodamine B, methylene blue, and textile effluent, respectively. Due to the synergistic impact of GO, it act as an elastic conductive channel permitting improved charge transport, the fabricated CeO₂-GOS nanocomposites showed a significant retort to photo catalysis of rhodamine B, methylene blue, and textile effluent. CeO₂-GOS nanocomposites may yield unique insight into the synthesis of green nanocomposites and their application in environmental remediation due to their better photo catalytic activity.

Methods for Green Synthesis of Metallic Nanoparticles Using Plant Extracts and their Biological Applications - A Review

Nanotechnology, a fast-developing branch of science, is gaining extensive popularity among researchers simply because of the multitude of applications it can offer. In recent years, biological synthesis has been widely used instead of physical and chemical synthesis methods, which often produce toxic products. These synthesis methods are now being commonly adapted to discover new applications of nanoparticles synthesized using plant extracts. In this review, we elucidate the various ways by which nanoparticles can be biologically synthesized. We further discuss the applications of these nanoparticles.

β-Cyclodextrin-Stabilized Biosynthesis Nanozyme for Dual Enzyme Mimicking and Fenton Reaction with a High Potential Anticancer Agent

The myth of inactivity of inorganic materials in a biological system breaks down by the discovery of nanozymes. From this time, the nanozyme has attracted huge attention for its high durability, cost-effective production, and easy storage over the natural enzyme. Moreover, the multienzyme-mimicking activity of nanozymes can regulate the level of reactive oxygen species (ROS) in an intercellular system. ROS can be generated by peroxidase (POD), oxidase (OD), and Fenton-like catalytic reaction by a nanozyme which kills the cancer cells by oxidative stress; therefore, it is important in CDT (chemo dynamic therapy). Our current study designed to investigate the enzyme mimicking behavior and anticancer ability of cerium-based nanomaterials because the cerium-based materials offer a high redox ability while maintaining nontoxicity and high stability. Our group synthesized CeZrO₄ nanoparticles by a green method using β-cyclodextrin as a stabilizer and neem leaf extract as a reducing agent, exhibiting POD- and OD-like dual enzyme activities. The best enzyme catalytic activity is shown in pH = 4, indicating the high ROS generation in an acidic medium (tumor microenvironment) which is also supported by the Fenton-like behavior of CeZrO₄ nanoparticles. Inspired by the high ROS generation in vitro method, we investigated the disruption of human kidney cells by this nanoparticle, successfully verified by the MTT assay. The harmful effect of ROS in a normal cell is also investigated by the in vitro MTT assay. The results suggested that the appreciable anticancer activity with minimal side effects by this synthesized nanomaterial.

Optical Assessment of Tear Glucose by Smart Biosensor Based on Nanoparticle Embedded Contact Lens

Diabetes is a disease condition characterized by a prolonged, high blood glucose level, which may lead to devastating outcomes unless properly managed. Here, we introduce a simple camera-based optical monitoring system (OMS) utilizing the nanoparticle embedded contact lens that produces color changes matching the tear glucose level without any complicated electronic components. Additionally, we propose an image processing algorithm that automatically optimizes the measurement accuracy even in the presence of image blurring, possibly caused by breathing, subtle movements, and eye blinking. As a result, using in vivo mouse models and human tear samples we successfully demonstrated robust correlations across the glucose concentrations measured by three different independent techniques, validating the quantitative efficacy of the proposed OMS. For its methodological simplicity and accessibility, our findings strongly support that the innovation offered by the OMS and processing algorithm would greatly facilitate the glucose monitoring procedure and improve the overall welfare of diabetes patients.

Size-Dependent Cytotoxicity and Reactive Oxygen Species of Cerium Oxide Nanoparticles in Human Retinal Pigment Epithelia Cells

Purpose

The use of cerium oxide nanoparticles (CeO₂ NPs), a lanthanide element oxide and bivalent compound, has been growing continuously in industry and biomedicine. Due to their wide application, the potential human health problems of CeO₂ NPs have attracted attention, but studies on the toxicity of this compound to human eyes are lacking. This study investigated the cytotoxicity and reactive oxygen species (ROS) of CeO₂ NPs in human retinal pigment epithelial cells (ARPE-19 cells).

Methods

Using the transmission electron microscope (TEM), the size distribution and shape of CeO₂ NPs were characterized. To explore the effect of CeO₂ NP size on ophthalmic toxicity in vitro, three sizes (15, 30 and 45 nm) of CeO₂ NPs were investigated using ATP content measurement, LDH release measurement and cell proliferation assay in ARPE-19 cells. ROS values and mitochondrial membrane potential depolarization were evaluated by H₂DCF-DA staining and JC-1 staining. Morphology changes were detected using a phase-contrast microscope.

Results

The cytotoxicity of 15 nm CeO₂ NPs was found to be the highest and hence was further explored. Treatment with 15 nm CeO₂ NPs caused the morphology of ARPE-19 cells to change in a dose- and time-dependent manner. Moreover, the treatment induced excessive ROS generation and mitochondrial membrane potential depolarization. In addition, cytotoxicity was attenuated by the application of a ROS scavenger N-acetyl-L- cysteine (NAC).

Conclusion

CeO₂ NPs induced cytotoxicity in ARPE-19 cells and excessive production of ROS and decreasing mitochondrial membrane potential. The Overproduction of ROS partially contributes to CeO₂ NP-induced cytotoxicity.

Photocatalytic Activity of Fibrous Ti/Ce Oxides Obtained by Hydrothermal Impregnation of Short Flax Fibers

Fibrous Ti/Ce oxide photocatalysts were prepared for the first time by a biomimetic solution process using short flax fibers (flax straw processing waste) as a biotemplate. Titanium polyhydroxy complex solutions with 3% and 5% cerium were used as precursors. Flax fibers were impregnated in an autoclave under hydrothermal conditions. Ti/Ce oxides were obtained from the biotemplate by annealing at 600 °C. The photocatalytic activity of the Ti/Ce oxides was studied by the adsorption and decomposition of the dye rhodamine B under UV irradiation. The photocatalytic decomposition of the dye was 50% and 75% faster for Ti/Ce oxides with 3% and 5% Ce, respectively, than for the analogous undoped fibrous TiO₂. The morphologies, textures, and structures of the photocatalysts were studied by scanning electron microscopy, low temperature N₂ adsorption/desorption, UV-Vis spectroscopy, and X-ray and XPS analytical methods. It was shown that the introduction of Ce into the precursor solution increased the surface irregularity of the Ti/Ce oxide crystallites compared to pure TiO₂. This effect scaled with the Ce concentration. Ce improved the UV light absorption of the material. The Ti/Ce oxides contained Ce⁴⁺/Ce³⁺ pairs that played an important role in redox processes and intensified the photocatalytic activity.

The Advances of Ceria Nanoparticles for Biomedical Applications in Orthopaedics

The ongoing biomedical nanotechnology has intrigued increasingly intense interests in cerium oxide nanoparticles, ceria nanoparticles or nano-ceria (CeO2-NPs). Their remarkable vacancy-oxygen defect (VO) facilitates the redox process and catalytic activity. The verification has illustrated that CeO2-NPs, a nanozyme based on inorganic nanoparticles, can achieve the anti-inflammatory effect, cancer resistance, and angiogenesis. Also, they can well complement other materials in tissue engineering (TE). Pertinent to the properties of CeO2-NPs and the pragmatic biosynthesis methods, this review will emphasize the recent application of CeO2-NPs to orthopedic biomedicine, in particular, the bone tissue engineering (BTE). The presentation, assessment, and outlook of the orthopedic potential and shortcomings of CeO2-NPs in this review expect to provide reference values for the future research and development of therapeutic agents based on CeO2-NPs.

Template Synthesis of Porous Ceria-Based Catalysts for Environmental Application

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.