Using Thermally Regenerable Cerium Oxide Nanoparticles in Biocomputing to Perform Label-free, Resettable, and Colorimetric Logic Operations

Synergistic anti-oxidant and anti-inflammatory effects of ceria/resatorvid co-decorated nanoparticles for acute lung injury therapy

BACKGROUND

Acute lung injury (ALI) is a critical inflammatory response syndrome that rapidly develops into acute respiratory distress syndrome (ARDS). Currently, no effective therapeutic modalities are available for patients with ALI/ARDS. According to recent studies, inhibiting both the release of pro-inflammatory cytokines and the formation of reactive oxygen species (ROS) as early as possible may be a promising therapy for ALI.

RESULTS

In this study, a ROS-responsive nano-delivery system based on oxidation-sensitive chitosan (Ox-CS) was fabricated for the simultaneous delivery of Ce NPs and RT. The in vitro experiments have shown that the Ox-CS/Ceria-Resatorvid nanoparticles (Ox-CS/CeRT NPs) were rapidly and efficiently internalised by inflammatory endothelial cells. Biological evaluations validated the significant attenuation of ROS-induced oxidative stress and cell apoptosis by Ox-CS/CeRT NPs, while maintaining mitochondrial function. Additionally, Ox-CS/CeRT NPs effectively inhibited the release of pro-inflammatory factors. After intraperitoneal (i.p.) administration, Ox-CS/CeRT NPs passively targeted the lungs of LPS-induced inflamed mice and released the drug activated by the high ROS levels in inflammatory tissues. Finally, Ox-CS/CeRT NPs significantly alleviated LPS-induced lung injury through inhibiting both oxidative stress and pro-inflammatory cytokine expression.

CONCLUSIONS

The created Ox-CS/CeRT NPs could act as a prospective nano-delivery system for a combination of anti-inflammatory and anti-oxidant therapy of ALI.

Chromophoric cerium oxide nanoparticle-loaded sucking disk-type strip sensor for optical measurement of glucose in tear fluid

BACKGROUND

Noninvasive monitoring of tear glucose levels can be convenient for patients to manage their diabetes mellitus. However, there are issues with monitoring tear glucose levels, such as the invasiveness of some methods, the miniaturization, inaccuracy, or the high cost of wearable devices. To overcome the issues, we newly designed a sucking disk-type (SD) strip biosensor that can quickly suck tear fluid and contains cerium oxide nanoparticle (CNP) that causes a unique color change according to the glucose level of the tear without complicated electronic components.

METHODS

The SD strip biosensor composed of three distinct parts (tip, channel, and reaction chamber) was designed to contain the sensing paper, onto which tear fluid can be collected and delivered. The sensing paper treated with CNP/APTS (aminopropyltriethoxysilane) /GOx (glucose oxidase) was characterized. Then we carried out the reliability of the SD strip biosensor in the diabetic rabbit animals. We quantitatively analyzed the color values of the SD strip biosensor through the colorimetric analysis algorithm.

RESULTS

We contacted the inferior palpebral conjunctiva (IPC) of a diabetic rabbit eye using an SD strip biosensor to collect tears without eye irritation and successfully verified the performance and quantitative efficacy of the sensor. An image processing algorithm that can optimize measurement accuracy is developed for accurate color change measurement of SD strip biosensors. The validation tests show a good correlation between glucose concentrations measured in the tear and blood.

CONCLUSION

Our findings demonstrate that the CNP-embedded SD strip biosensor and the associated image processing can simply monitor tear glucose to manage diabetes mellitus.

Cerium oxide nanoparticles-carrying human umbilical cord mesenchymal stem cells counteract oxidative damage and facilitate tendon regeneration

BACKGROUND

Tendon injuries have a high incidence and limited treatment options. Stem cell transplantation is essential for several medical conditions like tendon injuries. However, high local concentrations of reactive oxygen species (ROS) inhibit the activity of transplanted stem cells and hinder tendon repair. Cerium oxide nanoparticles (CeONPs) have emerged as antioxidant agents with reproducible reducibility.

RESULTS

In this study, we synthesized polyethylene glycol-packed CeONPs (PEG-CeONPs), which were loaded into the human umbilical cord mesenchymal stem cells (hUCMSCs) to counteract oxidative damage. H2O2 treatment was performed to evaluate the ROS scavenging ability of PEG-CeONPs in hUCMSCs. A rat model of patellar tendon defect was established to assess the effect of PEG-CeONPs-carrying hUCMSCs in vivo. The results showed that PEG-CeONPs exhibited excellent antioxidant activity both inside and outside the hUCMSCs. PEG-CeONPs protect hUCMSCs from senescence and apoptosis under excessive oxidative stress. Transplantation of hUCMSCs loaded with PEG-CeONPs reduced ROS levels in the tendon injury area and facilitated tendon healing. Mechanistically, NFκB activator tumor necrosis factor α and MAPK activator dehydrocrenatine, reversed the therapeutic effect of PEG-CeONPs in hUCMSCs, indicating that PEG-CeONPs act by inhibiting the NFκB and MAPK signaling pathways.

CONCLUSIONS

The carriage of the metal antioxidant oxidase PEG-CeONPs maintained the ability of hUCMSCs in the injured area, reduced the ROS levels in the microenvironment, and facilitated tendon regeneration. The data presented herein provide a novel therapeutic strategy for tendon healing and new insights into the use of stem cells for disease treatment.

Stimuli-responsive nanozymes for biomedical applications

With the rapid development of nanotechnology, nanozymes are regarded as excellent substitutes for natural enzymes due to their high activity, convenient preparation, low cost, robust stability and other unique properties of nanomaterials. In biomedical applications, the always-on activity of nanozymes is undesirable as it poses a potential threat to normal tissues. Stimuli-responsive nanozymes were designed to manipulate the activities of nanozymes. This review introduces two types of stimuli-responsive nanozymes. One is smart responsive nanozymes with stimuli-switchable activities, further divided into those with on/off switchable activity and one/another switchable activity. Another is nanozymes exhibiting responsive release from specific carriers. Additionally, the biomedical applications of stimuli-responsive nanozymes in cancer therapy, antibacterial therapy, biosensing and anti-inflammatory therapy are briefly reviewed. Finally, we address the challenges and prospects in this field.

Advances in the application of metal-organic framework nanozymes in colorimetric sensing of heavy metal ions

Nanozymes, which can be defined as nanomaterials with excellent catalytic function, are well known to the scientific community due to their distinct merits, such as low cost and high stability, which render them preferable to natural enzymes. As porous organic-inorganic coordination materials, metal-organic frameworks (MOFs) possess a large number of active sites and thus can effectively mimic the properties of natural enzymes. Recently, MOF-based nanozymes have also exhibited good application potential for the analysis of heavy metal ions. In comparison to the traditional detection methods for heavy metal ions, nanozyme-based colorimetric sensing permits intuitive visual analysis by using relatively simple instruments, facilitating rapid and simple on-site screening. In this minireview, the preparation of MOF-based nanozymes and the different nanozyme activity types are briefly described, such as peroxidase-like and oxidase-like, and the relevant catalytic mechanisms are elaborated. Based on this, different response mechanisms of MOF-based colorimetric methods to heavy metal ions, such as turn-off, turn-on, and turn-off-on, are discussed. In addition, the colorimetric sensing applications of MOF-based nanozymes for the detection of heavy metal ions are summarized. Finally, the current research status of MOF-based nanozymes and the future development direction are discussed.

Carboxylic acids and light interact to affect nanoceria stability and dissolution in acidic aqueous environments

Cerium atoms on the surfaces of nanoceria (i.e., cerium oxide in the form of nanoparticles) can store or release oxygen, cycling between Ce3+ and Ce4+; therefore, they can cause or relieve oxidative stress within living systems. Nanoceria dissolution occurs in acidic environments. Nanoceria stabilization is a known problem even during its synthesis; in fact, a carboxylic acid, namely citric acid, is used in many synthesis protocols. Citric acid adsorbs onto nanoceria surfaces, limiting particle formation and creating stable dispersions with extended shelf life. To better understand factors influencing the fate of nanoceria, its dissolution and stabilization have been previously studied in vitro using acidic aqueous environments. Nanoceria agglomerated in the presence of some carboxylic acids over 30 weeks, and degraded in others, at pH 4.5 (i.e., the pH value in phagolysosomes). Plants release carboxylic acids, and cerium carboxylates are found in underground and aerial plant parts. To further test nanoceria stability, suspensions were exposed to light and dark conditions, simulating plant environments and biological systems. Light induced nanoceria agglomeration in the presence of some carboxylic acids. Nanoceria agglomeration did not occur in the dark in the presence of most carboxylic acids. Light initiates free radicals generated by ceria nanoparticles. Nanoceria completely dissolved in the presence of citric, malic, and isocitric acid when exposed to light, attributed to nanoceria dissolution, release of Ce3+ ions, and formation of cerium coordination complexes on the ceria nanoparticle surface that inhibit agglomeration. Key functional groups of carboxylic acids that prevented nanoceria agglomeration were identified. A long carbon chain backbone containing a carboxylic acid group geminal to a hydroxy group in addition to a second carboxylic acid group may optimally complex with nanoceria. The results provide mechanistic insight into the role of carboxylic acids in nanoceria dissolution and its fate in soils, plants, and biological systems.

Integrated cascade catalysis of microalgal bioenzyme and inorganic nanozyme for anti-inflammation therapy

Combinations of multiple enzymes for cascade catalysis have been widely applied in biomedicine, but the integration of a natural bioenzyme with an inorganic nanozyme is less developed. Inspired by the abundant content of superoxide dismutase (SOD) in Spirulina platensis (SP), we establish an integrated cascade catalysis for anti-inflammation therapy by decorating catalase (CAT)-biomimetic ceria nanoparticles (CeO₂) onto the SP surface via electrostatic interaction to build microalgae-based biohybrids. The biohybrids exhibit combined catalytical competence for preferentially transforming superoxide anion radicals (O₂˙^-) to hydrogen peroxide (H₂O₂), and subsequently catalyzing H₂O₂ disproportionation to water and oxygen. In ulcerative colitis and Crohn's disease, the biohybrids reveal a satisfactory therapeutic effect owing to the synergistic reactive oxygen species (ROS)-scavenging capacity, suggesting a new train of thought for enzyme-based biomedical application.

Modulating Nanozyme-Based Nanomachines via Microenvironmental Feedback for Differential Photothermal Therapy of Orthotopic Gliomas

Gliomas are common and refractory primary tumors closely associated with the fine structures of the brain. Photothermal therapy (PTT) has recently shown promise as an effective treatment for gliomas. However, nonspecific accumulation of photothermal agents may affect adjacent normal brain structures, and the inflammatory response induced during PTT may result in an increased risk of brain tumor recurrence or metastasis. Here, the design and fabrication of an intelligent nanomachine is reported based on Gd₂ O₃ @Ir/TMB-RVG29 (G@IT-R) hybrid nanomaterials. These nanomaterials enable tumor-specific PTT and eliminate inflammation to protect normal brain tissue. The mechanism involves the rabies virus glycopeptide-29 peptide (RVG29) passing through the blood-brain barrier (BBB) and targeting gliomas. In the tumor microenvironment, Ir nanozymes can act as logic control systems to trigger chromogenic reaction amplification of 3,3',5,5'-tetramethylbenzidine (TMB) for tumor-specific PTT, whereas in normal brain tissues, they scavenge reactive oxygen species (ROS) generated by poor therapy and function as protective agents. Autophagy inhibition of Gd₂ O₃ enables excellent photothermal therapeutic effects on orthotopic gliomas and protection against inflammation in normal cells. The results of this study may prove useful in developing highly efficient nanomedicines for glioma treatment.

One-Pot Preparation of Imidazole-Ring-Modified Graphitic Carbon Nitride Nanozymes for Colorimetric Glucose Detection

Nanozymes are highly desired to overcome the shortcomings of natural enzymes, such as low stability, high cost and difficult storage during biosensing applications. Herein, by imitating the structure of natural enzymes, we propose a one-pot annealing process to synthesis imidazole-ring-modified graphitic carbon nitride (g-C₃N₄-Im) with enhanced peroxidase-like activity. g-C₃N₄-Im shows enhanced peroxidase-like activity by 46.5 times compared to unmodified g-C₃N₄. Furthermore, imidazole rings of g-C₃N₄-Im make it possible to anchor Cu(II) active sites on it to produce g-C₃N₄-Im-Cu, which shows a further increase in peroxidase-like activity by three times. It should be noted that the as-prepared g-C₃N₄-Im-Cu could show obvious peroxidase-like activity over a broad range of pH values and at a low temperature (5 °C). The ultrahigh peroxidase-like activity is attributed to the electronic effect of imidazole rings and the active sites of Cu(II) for ·OH production. Based on the enhanced peroxidase-like activity, a H₂O₂ and glucose biosensor was developed with a high sensitivity (limit of detection, 10 nM) and selectivity. Therefore, the biosensor shows potential for applications in diabetic diagnoses in clinical practice.

Catalase-Like Nanozymes: Classification, Catalytic Mechanisms, and Their Applications

The field of nanozymes has developed rapidly over the past decade. Among various oxidoreductases mimics, catalase (CAT)-like nanozyme, acting as an essential part of the regulation of reactive oxygen species (ROS), has attracted extensive research interest in recent years. However, CAT-like nanozymes are not as well discussed as other nanozymes such as peroxidase (POD)-like nanozymes, etc. Compared with natural catalase or artificial CAT enzymes, CAT-like nanozymes have unique properties of low cost, size-dependent properties, high catalytic activity and stability, and easy surface modification, etc., which make them widely used in various fields, especially in tumor therapy and disease treatment. Consequently, there is a great requirement to make a systematic discussion on CAT-like nanozymes. In this review, some key aspects of CAT-like nanozymes are deeply summarized as: 1) Typical CAT-like nanozymes classified by different nanomaterials; 2) The catalytic mechanisms proposed by experimental and theoretical studies; 3) Extensive applications in regard to tumor therapy, cytoprotection and sensing. Therefore, it is prospected that this review will contribute to the further design of CAT-like nanozymes and optimize their applications with much higher efficiency than before.

Bioengineered immunomodulatory organelle targeted nanozymes for photodynamic immunometabolic therapy

Intelligent nanomedicines integrated with stimuli-responsive components enable on-demand customizable treatment options which would improve therapeutic outcome and reduce systemic toxicity. In this work, we explore the synergistic therapeutic potential of photodynamic therapy and immunometabolic modulation to achieve tumour regression and to trigger an adaptive immunity to prevent tumour recurrence. The therapeutic potential of the fabricated Bioengineered Immunomodulatory Organelle targeted Nanozymes (BIONs) was tested on 3D printed mini-brains which could effectively recapitulate the biologically relevant interactions between glioblastoma cells and macrophages. In the presence of glioblastoma organotypic brain slices, activated BIONs upregulated the cell surface expression of CD86, a costimulatory molecule and CD83, maturation marker, on monocyte derived dendritic cells, suggesting its ability to elicit a strong immune response. Furthermore, the antigen pulsed dendritic cells by chemotaxis and transendothelial migration readily relocate into the draining lymph node where they present the antigenic cargo to enable the proliferation of T lymphocytes. The stealth and tunable catalytic activity of BIONs prevent ROS mediated diseases such as acute kidney injury by providing environment dependent protection without compromising on its promising anti-cancer activity.

Stimuli-Responsive Gold Nanocages for Cancer Diagnosis and Treatment

With advances in nanotechnology, various new drug delivery systems (DDSs) have emerged and played a key role in the diagnosis and treatment of cancers. Over the last two decades, gold nanocages (AuNCs) have been attracting considerable attention because of their outstanding properties. This review summarizes current advancements in endogenous, exogenous, and dual/multi-stimuli responsive AuNCs in drug delivery. This review focuses on the properties, clinical translation potential, and limitations of stimuli-responsive AuNCs for cancer diagnosis and treatment.

In Situ Fabrication of Nanoceria with Oxidase-like Activity at Neutral pH: Mechanism and Boosted Bio-Nanozyme Cascades

Catalytic cascades have drawn much attention by avoiding the isolation of intermediates and due to high atom economy. Yet, developing an efficient, one-pot biocatalytic cascade remains challenging. Combined with the selectivity of biological enzymes and tunable activity of nanozymes, we herein demonstrate an effective bio-nanozyme cascade formed by glucose oxidase (GOx) and in situ-generated nanoceria. The prepared H₂O₂-nanoceria complex shows strong oxidative activity for common chromogenic substrates under physiological conditions, which are the optimal reaction conditions for most biological enzymes. Interestingly, GOx not only provides H₂O₂ for the second step reaction but also simultaneously leads to 7.4-fold enhancement of activity. We characterized the process of in situ generation of nanoceria at pH 7.0 and how proteins boost the activity by enhancing product desorption. In addition, the proposed one-pot bio-nanozyme cascade shows high stability and analytical performance for serum glucose with a detection limit of 5 μM.

Engineering the Stability of Nanozyme-Catalyzed Product for Colorimetric Logic Gate Operations

Recently, the design and development of nanozyme-based logic gates have received much attention. In this work, by engineering the stability of the nanozyme-catalyzed product, we demonstrated that the chromogenic system of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) can act as a visual output signal for constructing various Boolean logic operations. Specifically, cerium oxide or ferroferric oxide-based nanozymes can catalyze the oxidation of colorless TMB to a blue color product (oxTMB). The blue-colored solution of oxTMB could become colorless by some reductants, including the reduced transition state of glucose oxidase and xanthine oxidase. As a result, by combining biocatalytic reactions, the color change of oxTMB could be controlled logically. In our logic systems, glucose oxidase, β-galactosidase, and xanthine oxidase acted as inputs, and the state of oxTMB solution was used as an output. The logic operation produced a colored solution as the readout signal, which was easily distinguished with the naked eye. More importantly, the study of such a decolorization process allows the transformation of previously designed AND and OR logic gates into NAND and NOR gates. We propose that this work may push forward the design of novel nanozyme-based biological gates and help us further understand complex physiological pathways in living systems.

Potentiality of Nanoenzymes for Cancer Treatment and Other Diseases: Current Status and Future Challenges

Studies from past years have observed various enzymes that are artificial, which are issued to mimic naturally occurring enzymes based on their function and structure. The nanozymes possess nanomaterials that resemble natural enzymes and are considered an innovative class. This innovative class has achieved a brilliant response from various developments and researchers owing to this unique property. In this regard, numerous nanomaterials are inspected as natural enzyme mimics for multiple types of applications, such as imaging, water treatment, therapeutics, and sensing. Nanozymes have nanomaterial properties occurring with an inheritance that provides a single substitute and multiple platforms. Nanozymes can be controlled remotely via stimuli including heat, light, magnetic field, and ultrasound. Collectively, these all can be used to increase the therapeutic as well as diagnostic efficacies. These nanozymes have major biomedical applications including cancer therapy and diagnosis, medical diagnostics, and bio sensing. We summarized and emphasized the latest progress of nanozymes, including their biomedical mechanisms and applications involving synergistic and remote control nanozymes. Finally, we cover the challenges and limitations of further improving therapeutic applications and provide a future direction for using engineered nanozymes with enhanced biomedical and diagnostic applications.

Micro-Bio-Chemo-Mechanical-Systems: Micromotors, Microfluidics, and Nanozymes for Biomedical Applications

Wireless nano-/micromotors powered by chemical reactions and/or external fields generate motive forces, perform tasks, and significantly extend short-range dynamic responses of passive biomedical microcarriers. However, before micromotors can be translated into clinical use, several major problems, including the biocompatibility of materials, the toxicity of chemical fuels, and deep tissue imaging methods, must be solved. Nanomaterials with enzyme-like characteristics (e.g., catalase, oxidase, peroxidase, superoxide dismutase), that is, nanozymes, can significantly expand the scope of micromotors' chemical fuels. A convergence of nanozymes, micromotors, and microfluidics can lead to a paradigm shift in the fabrication of multifunctional micromotors in reasonable quantities, encapsulation of desired subsystems, and engineering of FDA-approved core-shell structures with tuneable biological, physical, chemical, and mechanical properties. Microfluidic methods are used to prepare stable bubbles/microbubbles and capsules integrating ultrasound, optoacoustic, fluorescent, and magnetic resonance imaging modalities. The aim here is to discuss an interdisciplinary approach of three independent emerging topics: micromotors, nanozymes, and microfluidics to creatively: 1) embrace new ideas, 2) think across boundaries, and 3) solve problems whose solutions are beyond the scope of a single discipline toward the development of micro-bio-chemo-mechanical-systems for diverse bioapplications.

Biocomputing Based on DNA Strand Displacement Reactions

The high sequence specificity and precise base complementary pairing principle of DNA provides a rich orthogonal molecular library for molecular programming, making it one of the most promising materials for developing bio-compatible intelligence. In recent years, DNA has been extensively studied and applied in the field of biological computing. Among them, the toehold-mediated strand displacement reaction (SDR) with properties including enzyme free, flexible design and precise control, have been extensively used to construct biological computing circuits. This review provides a systemic overview of SDR design principles and the applications. Strategies for designing DNA-only, enzymes-assisted, other molecules-involved and external stimuli-controlled SDRs are described. The recently realized computing functions and the application of DNA computing in other fields are introduced. Finally, the advantages and challenges of SDR-based computing are discussed.

Catalytic activity tunable ceria nanoparticles prevent chemotherapy-induced acute kidney injury without interference with chemotherapeutics

Acute kidney injury (AKI) is a prevalent and lethal adverse event that severely affects cancer patients receiving chemotherapy. It is correlated with the collateral damage to renal cells caused by reactive oxygen species (ROS). Currently, ROS management is a practical strategy that can reduce the risk of chemotherapy-related AKI, but at the cost of chemotherapeutic efficacy. Herein, we report catalytic activity tunable ceria nanoparticles (CNPs) that can prevent chemotherapy-induced AKI without interference with chemotherapeutic agents. Specifically, in the renal cortex, CNPs exhibit catalytic activity that decomposes hydrogen peroxide, and subsequently regulate the ROS-involved genes by activating the Nrf2/Keap1 signaling pathway. These restore the redox homeostasis for the protection of kidney tubules. Under an acidic tumor microenvironment, CNPs become inert due to the excessive H+ that disrupts the re-exposure of active catalytic sites, allowing a buildup of chemotherapy-mediated ROS generation to kill cancer cells. As ROS-modulating agents, CNPs incorporated with context-dependent catalytic activity, hold a great potential for clinical prevention and treatment of AKI in cancer patients.

A reusable colorimetric assay based on mixed valence state Ce-MOF@Pt nanoparticles for highly sensitive detection of visfatin

In this work, a colorimetric assay for visfatin detection is described. The mixed valence state Ce-MOF (MVCM) modified by platinum nanoparticles (Pt NPs) is used as a novel catalyst. MVCM exhibits excellent intrinsic peroxidase-like catalytic activity due to the spontaneous recycling of the Ce(III)/Ce(IV) system. Pt NPs serve not only as a carrier of the -NH₂-modified single strand DNA (S1) but also as a synergistic catalyst of MVCM. The capture probe (S2) attached to the streptavidin-modified magnetic beads (Mag-SA) could combine with the aptamer to form the Mag-SA/S2/aptamer complex. When in the presence of the target visfatin, aptamer specifically combines with the visfatin, which induces the release of Mag-SA/S2 from the Mag-SA/S2/aptamer complex. At this time, the MVCM@Pt/S1 complex connects with the released Mag-SA/S2, which quickly catalyzes the 3,3,3',3'-tetramethylbenzidine (TMB), leading to a color change. Under optimal conditions, the absorbance increases linearly when the concentration ranges from 1 ng mL^-1 to 100 ng mL^-1, and the detection limit is as low as 0.11 ng mL^-1. Furthermore, Mag-SA/S2 can be reused at least five times by using the uracil-DNA glycosylase (UDG) and an external magnetic field. The proposed method shows satisfying reproducibility, stability, specificity, and sensitivity, and it was successfully applied to detect visfatin in spiked human serum samples. Thus, it has great potential for clinical research, detection, and catalytic applications.

A Cerium Vanadate Nanozyme with Specific Superoxide Dismutase Activity Regulates Mitochondrial Function and ATP Synthesis in Neuronal Cells

Nanoparticles that functionally mimic the activity of metal-containing enzymes (metallo-nanozymes) are of therapeutic importance for treating various diseases. However, it is still not clear whether such nanozymes can completely substitute the function of natural enzymes in living cells. In this work, we show for the first time that a cerium vanadate (CeVO₄ ) nanozyme can substitute the function of superoxide dismutase 1 and 2 (SOD1 and SOD2) in the neuronal cells even when the natural enzyme is down-regulated by specific gene silencing. The nanozyme prevents the mitochondrial damage in SOD1- and SOD2-depleted cells by regulating the superoxide levels and restores the physiological levels of the anti-apoptotic Bcl-2 family proteins. Furthermore, the nanozyme effectively prevents the mitochondrial depolarization, leading to a significant improvement in the cellular levels of ATP under oxidative stress.

The prototypes of nanozyme-based nanorobots

Artificial nanorobot is a type of robots designed for executing complex tasks at nanoscale. The nanorobot system is typically consisted of four systems, including logic control, driving, sensing and functioning. Considering the subtle structure and complex functionality of nanorobot, the manufacture of nanorobots requires designable, controllable and multi-functional nanomaterials. Here, we propose that nanozyme is a promising candidate for fabricating nanorobots due to its unique properties, including flexible designs, controllable enzyme-like activities, and nano-sized physicochemical characters. Nanozymes may participate in one system or even combine several systems of nanorobots. In this review, we summarize the advances on nanozyme-based systems for fabricating nanorobots, and prospect the future directions of nanozyme for constructing nanorobots. We hope that the unique properties of nanozymes will provide novel ideas for designing and fabricating nanorobotics.

Recent advances in the construction of nanozyme-based logic gates

Nanozymes, nanomaterials with enzyme-like activity, have been considered as promising alternatives of natural enzymes. Molecular logic gates, which can simulate the function of the basic unit of an electronic computer, perform Boolean logic operation in response to chemical, biological, or optical signals. Recently, the combination of nanozymes and logic gates enabled bioinformation processing in a logically controllable way. In the review, recent progress in the construction of nanozyme-based logic gates integrated with their utility in sensing is introduced. Furthermore, the issues and challenges in the construction processes are discussed. It is expected the review will facilitate a comprehensive understanding of nanozyme-based logic systems.

Modular AND Gate-Controlled Delivery Platform for Tumor Microenvironment Specific Activation of Protein Activity

Protein therapeutics have inspired intensive research interest in a variety of realms. It is still urgently required to avoid premature or unexpected activation of therapeutic proteins to achieve great specificity for therapy. Herein, we reported a modular AND gate-controlled delivery platform for tumor microenvironment specific activation of therapeutic protein activity based on biomineralization of molecular glue-adhered protein enzyme. The AND gate integrates the specific microenvironment of tumor tissues (acidic pH and a certain concentration of ATP) as inputs and activates the therapeutic activity of protein only when both inputs are active. More importantly, the activity of therapeutic protein would not be activated either at acidic pH or in the presence of ATP, which could greatly avoid the deleterious effect on normal tissues. Besides, this AND gate can be modular design and suitable for a variety of therapeutic proteins and nucleic acids.

MOF-encapsulated nanozyme enhanced siRNA combo: Control neural stem cell differentiation and ameliorate cognitive impairments in Alzheimer's disease model

Neural stem cells (NSC) transplantation is garnering considerable attention in the treatment of neurodegenerative diseases that are associated with cognitive decline. Current methods are mainly based on neuron-directional differentiation and NSC niche components majorization to promote neurogenesis. Unfortunately, the pathologically high level of oxidative stress will damage the neurons derived from NSC during therapy, compromising the neurogenesis effect. Herein, a facile and effective strategy has been presented for modulation of neuron-directional differentiation and amelioration of oxidative stress by integrating antioxidative nanozymes (ceria) into metal-organic frameworks (MOF) for synergistically enhancing neurogenesis. Specially, small interfering RNA (siSOX9) and retinoic acid (RA) are loaded in the MOF. The H₂O₂-responsive MOF would release cargos in the lesion area to promote neuron-directional differentiation. Moreover, the integrated ceria can perform robust SOD and CAT mimetic activities, which are capable of eliminating ROS and circumventing its oxidative damage to newborn neurons, leading to the longer survival rate and more enhanced outgrowth of the newborn neurons. With the gratifying drug delivery efficiency of MOF and excellent antioxidative capacity of nanozymes, the rational-designed nanoparticles can considerably promote neurogenesis and improve the cognitive function of aged 3 × Tg-AD (triple transgenic AD mouse model) mice. Our work provides a new way to promote nerve regeneration with the help of nanozymes.

Constructing dual-readout logic operations based on the silk fibroin sol-gel transition

Inspired by an H₂O₂-induced chemical gelation of silk fibroin (SF) and biochemical computing, we demonstrated for the first time that the phase transformation of SF can serve as a visual output signal for constructing multiple Boolean logic operations. In our biological logic gates, three common enzymes, β-galactosidase (β-Gal), glucose oxidase (GOx) and catalase (CAT), were used as inputs and the SF state (sol or gel) was defined as an output. The designed logic gates could be observed by the naked eye and UV-Vis absorption change. Since a distinctive advantage of biocomputing is that different enzymatic reactions can take place smoothly when they work together, our logic system could be further scaled up to generate a multi-input logic network without any "crosstalk" and interference between them. We hope that such a constructed system might help us understand complex physiological processes in living systems, and have potential applications in digital bio-diagnosis.

Evaluation of the Cytotoxicity and Oxidative Stress Response of CeO2-RGO Nanocomposites in Human Lung Epithelial A549 Cells

Graphene-based nanocomposites have attracted enormous interest in nanomedicine and environmental remediation, owing to their unique characteristics. The increased production and widespread application of these nanocomposites might raise concern about their adverse health effects. In this study, for the first time, we examine the cytotoxicity and oxidative stress response of a relatively new nanocomposite of cerium oxide-reduced graphene oxide (CeO₂-RGO) in human lung epithelial (A549) cells. CeO₂-RGO nanocomposites and RGO were prepared by a simple hydrothermal method and characterized by relevant analytical techniques. Cytotoxicity data have shown that RGO significantly induces toxicity in A549 cells, evident by cell viability reduction, membrane damage, cell cycle arrest, and mitochondrial membrane potential loss. However, CeO₂-RGO nanocomposites did not cause statistically significant toxicity as compared to a control. We further observed that RGO significantly induces reactive oxygen species generation and reduces glutathione levels. However, CeO₂-RGO nanocomposites did not induce oxidative stress in A549 cells. Interestingly, we observed that CeO₂ nanoparticles (NPs) alone significantly increase glutathione (GSH) levels in A549 cells as compared to a control. The GSH replenishing potential of CeO₂ nanoparticles could be one of the possible reasons for the biocompatible nature of CeO₂-RGO nanocomposites. Our data warrant further and more advanced research to explore the biocompatibility/safety mechanisms of CeO₂-RGO nanocomposites in different cell lines and animal models.

Nanozyme: new horizons for responsive biomedical applications

Nanozymes are nanomaterial-based artificial enzymes. By effectively mimicking catalytic sites of natural enzymes or harboring multivalent elements for reactions, nanozyme systems have successfully served as direct surrogates of traditional enzymes for catalysis. With the rapid development and ever-deepening understanding of nanotechnology, nanozymes offer higher catalytic stability, ease of modification and lower manufacturing cost than protein enzymes. Additionally, nanozymes possess inherent nanomaterial properties, providing not only a simple substitute of enzymes but also a multimodal platform interfacing complex biologic environments. Recent extensive research has focused on designing various nanozyme systems that are responsive to one or multiple substrates by tailored means. Catalytic activities of nanozymes can be regulated by pH, H2O2 and glutathione concentrations and levels of oxygenation in different microenvironments. Moreover, nanozymes can be remotely-controlled via different stimuli, including a magnetic field, light, ultrasound, and heat. Collectively, these factors can be adjusted to maximize the diagnostic and therapeutic efficacies of different diseases in biomedical settings. Therefore, by integrating the catalytic property and inherent nanomaterial nature of nanozyme systems, we anticipate that stimuli-responsive nanozymes will open up new horizons for diagnosis, treatment, and theranostics.

Cu (II)-based metal-organic xerogels as a novel nanozyme for colorimetric detection of dopamine

Cu (II)-based metal-organic gels (Cu-MOGs), which are formed by 4-[2,2':6',2″-terpyridine]-4'-ylbenzoic acid (Hcptpy) and Cu (II) through ionic interactions, π-π stacking, van der Waals and hydrogen bonding, have been simply synthesized and used for the preparation of Cu (II)-based metal-organic xerogels (Cu-MOXs). Owing to the metal active sites in Cu-MOXs, Cu-MOXs were successfully applied to chromogenic experiment. The peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB), which could be catalyzed by Cu-MOXs from TMB to the oxidation state of TMB (oxTMB) and the color of TMB could be changed from colorless to blue with maximum absorbance at 657 nm, was selected as chromogenic agent. Thus, the Cu-MOXs-TMB-H₂O₂ system based on MOXs was established. Due to the inhibitory effect of dopamine (DA) on oxidation process of TMB, the characteristic absorption peak intensity of oxTMB decreased when the DA was added into the mixed solution. Subsequently, the Cu-MOXs-TMB- H₂O₂ system was used for DA detection. The linear range for DA was 0.5 μM-20 μM and the detection limit was 85.76 nM. Our work has helped to develop the promising application of Cu-MOGs material in the field of nanozymes property.

Electrospun silica nanofiber mats functionalized with ceria nanoparticles for water decontamination

This study demonstrates the fabrication of nanoceria-immobilized silica nanofibers for efficient water decontamination with easy reuse and regeneration properties.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Phosphorescent Carbon Dots for Highly Efficient Oxygen Photosensitization and as Photo-oxidative Nanozymes

Materials for photosensitized oxygen activation are extremely important for a suite of photodynamic applications in biomedical, analytical, and energy sectors. Carbon-based photosensitizers are attractive for their low cost and high stability, but most of them such as fullerene and graphene quantum dots suffer from low efficiency, and the rational design of carbon-based photosensitizers remains a challenge. Given the similar chemical origin of phosphorescence and photosensitization, we herein synthesized a series of nitrogen-doped carbon dots (C-dots) and confirmed that their photo-oxidation activity correlated with their phosphorescence quantum yields, providing a direction for the rational designing of such materials. Compared to other carbon nanomaterials and molecular photosensitizers, these C-dots have the highest activity, and they can finish oxidation reactions in a few seconds. The excellent photosensitized oxygen activation makes these water-soluble C-dots a promising oxidase-mimicking nanozyme for photodynamic antimicrobial chemotherapy and other applications.

Metal Oxide Nanoparticle Based Electrochemical Sensor for Total Antioxidant Capacity (TAC) Detection in Wine Samples

A single-use electrochemical screen-printed electrode is reported based on biomimetic properties of nanoceria particles (CeNPs). The developed tool showed an easy approach compared to the classical spectrophotometric methods reported in literature in terms of ease of use, cost, portability, and unnecessary secondary reagents. The sensor allowed the detection of the total antioxidant capacity (TAC) in wine samples. The sensor has been optimized and characterized electrochemically and then tested with antioxidant compounds occurred in wine samples. The electrochemical CeNPs modified sensor has been used for detection of TAC in white and red commercial wines and the data compared to the 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid (ABTS)-based spectrophotometric method. Finally, the obtained results have demonstrated that the proposed sensor was suitable for the simple and quick evaluation of TAC in beverage samples.

Nucleobases, nucleosides, and nucleotides: versatile biomolecules for generating functional nanomaterials

The incorporation of biomolecules into nanomaterials generates functional nanosystems with novel and advanced properties, presenting great potential for applications in various fields. Nucleobases, nucleosides and nucleotides, as building blocks of nucleic acids and biological coenzymes, constitute necessary components of the foundation of life. In recent years, as versatile biomolecules for the construction or regulation of functional nanomaterials, they have stimulated interest in researchers, due to their unique properties such as structural diversity, multiplex binding sites, self-assembly ability, stability, biocompatibility, and chirality. In this review, strategies for the synthesis of nanomaterials and the regulation of their morphologies and functions using nucleobases, nucleosides, and nucleotides as building blocks, templates or modulators are summarized alongside selected applications. The diverse applications range from sensing, bioimaging, and drug delivery to mimicking light-harvesting antenna, the construction of logic gates, and beyond. Furthermore, some perspectives and challenges in this emerging field are proposed. This review is directed toward the broader scientific community interested in biomolecule-based functional nanomaterials.

Peroxidase-Mimicking Nanozyme with Enhanced Activity and High Stability Based on Metal-Support Interactions

Peroxidase-mimicking nanozymes offer unique advantages in terms of high stability and low cost over natural peroxidase for applications in bioanalysis, biomedicine, and the treatment of pollution. However, the design of high-efficiency peroxidase-mimicking nanozymes remains a great challenge. In this study, we adopted a structural-design approach through hybridization of cube-CeO₂ and Pt nanoparticles to create a new peroxidase-mimicking nanozyme with high efficiency and excellent stability. Relative to pure cube-CeO₂ and Pt nanoparticles, the as-hybridized Pt/cube-CeO₂ nanocomposites display much improved activities because of the strong metal-support interaction. Meanwhile, the nanocomposites also maintain high catalytic activity after long-term storage and multiple recycling. Based on their excellent properties, Pt/cube-CeO₂ nanocomposites were used to construct high-performance colorimetric biosensors for the sensitive detection of metabolites, including H₂ O₂ and glucose. Our findings highlight opportunities for the development of high-efficiency peroxidase-mimicking nanozymes with potential applications such as diagnostics, biomedicine, and the treatment of pollution.

Electrogenerated chemiluminescence logic gate operations based on molecule-responsive organic microwires

Complex logic gate operations using organic microwires as signal transducers based on electrogenerated chemiluminescence (ECL) intensity as the optical readout signal have been developed by taking advantage of the unique ECL reaction between organic semiconductor 9,10-bis(phenylethynyl)anthracene (BPEA) microwires and small molecules. The BPEA microwires, prepared on cleaned-ITO substrate using a simple physical vapor transport (PVT) method, were subsequently used for construction of the ECL sensors. The developed sensor exhibits high ECL efficiency and excellent stability in the presence of co-reactant tripropylamine. Based on the remarkable detection performance of BPEA MWs/TPrA system, the sensors manifested high sensitive ECL response in a wide linear range with low detection limit for the detection of dopamine, proline or methylene blue, which behaves on the basis of molecule-responsive ECL properties based on different ECL reaction mechanisms. Inspired by this, these sensing systems can be utilized to design OR, XOR and INHIBIT logic gates, which would be used for the determination of dopamine, proline and ethylene blue via logic outputs. Importantly, the individual logic gates can be easily brought together through three-input operations to function as integrated logic gates.

Cerium oxide nanoparticles: green synthesis and biological applications

CeO2 nanoparticles (NPs) have shown promising approaches as therapeutic agents in biology and medical sciences. The physicochemical properties of CeO2-NPs, such as size, agglomeration status in liquid, and surface charge, play important roles in the ultimate interactions of the NP with target cells. Recently, CeO2-NPs have been synthesized through several bio-directed methods applying natural and organic matrices as stabilizing agents in order to prepare biocompatible CeO2-NPs, thereby solving the challenges regarding safety, and providing the appropriate situation for their effective use in biomedicine. This review discusses the different green strategies for CeO2-NPs synthesis, their advantages and challenges that are to be overcome. In addition, this review focuses on recent progress in the potential application of CeO2-NPs in biological and medical fields. Exploiting biocompatible CeO2-NPs may improve outcomes profoundly with the promise of effective neurodegenerative therapy and multiple applications in nanobiotechnology.

Co3O4@CeO2 hybrid flower-like microspheres: a strong synergistic peroxidase-mimicking artificial enzyme with high sensitivity for glucose detection

In recent years, the development of artificial nanostructured enzymes has received enormous interest in nanobiotechnology due to their advantages over natural enzymes. In the present work, different amounts (5, 10, and 20 wt%) of Co₃O₄ nanoparticle decorated CeO₂ hybrid flower-like microspheres (Co₃O₄@CeO₂) have been investigated for peroxidase-like activity and it was found that 10 wt% of Co₃O₄@CeO₂ exhibited excellent peroxidase-like activity for the catalytic oxidation of the 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the presence of H₂O₂. The formation of more Ce³⁺ ions associated with the oxygen vacancies and a strong synergistic interaction between CeO₂ and Co₃O₄ may be responsible for the enhanced peroxidase-like activity. Based on their peroxidase activity, Co₃O₄@CeO₂ hybrid microspheres were used for the colourimetric detection of glucose. It was found that Co₃O₄@CeO₂ hybrid microspheres showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also improved with a limit as low as 1.9 μM. Thus, we believe that Co₃O₄@CeO₂ hybrid flower-like microspheres with high peroxidase-like activity can be exploited for biosensing applications.

Pattern-based sensing of triple negative breast cancer cells with dual-ligand cofunctionalized gold nanoclusters

Early detection of breast cancer is a critical component in patient prognosis and establishing effective therapy regimens. Here, we developed an easily accessible yet potentially powerful sensor to detect cancer cell targets by utilizing seven dual-ligand cofunctionalized gold nanoclusters (AuNCs) as both effective cell recognition elements and signal transducers. On the basis of this AuNC multichannel sensor, we have successfully distinguished healthy, cancerous and metastatic human breast cells with excellent reproducibility and high sensitivity. Triple negative breast cancer cells (TNBCs), which exhibit low expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2, were identified. The high accuracy of the blind breast cell sample tests further validates the practical application of the sensor array. In addition, the versatility of the sensor array is further justified by identifying amongst distinct cell types, different cell concentrations and cell mixtures. Notably, the drug-resistant cancer cells can also be efficiently discriminated. Furthermore, the dual-ligand cofunctionalized AuNCs can efficiently differentiate different cells from the peripheral blood of tumor-free and tumor-bearing mice. Taken together, this fluorescent AuNCs based array provides a powerful cell analysis tool with potential applications in biomedical diagnostics.