The designing strategies of graphene-based peroxidase mimetic materials

Synergizing Pyroelectric Catalysis and Enzyme Catalysis: Establishing a Reciprocal and Synergistic Model to Enhance Anti-Tumor Activity

Nanozyme activity is greatly weakened by the microenvironment and multidrug resistance of tumor cells. Hence, a bi-catalytic nanoplatform, which promotes the anti-tumor activity through "charging empowerment" and "mutual complementation" processes involved in enzymatic and pyroelectric catalysis, by loading ultra-small nanoparticles (USNPs) of pyroelectric ZnSnO3 onto MXene nanozyme (V2CTx nanosheets), is developed. Here, the V2CTx nanosheets exhibit enhanced peroxidase activity by reacting V3+ with H2O2 to generate toxic ·OH, accelerated by the near-infrared (NIR) light mediated heat effect. The resulting V4+ is then converted to V3+ by oxidizing endogenous glutathione (GSH), realizing an enzyme-catalyzed cycle. However, the cycle will lose its persistence once GSH is insufficient; nevertheless, the pyroelectric charges generated by ZnSnO3 USNPs continuously support the V4+/V3+ conversion and ensure nanoenzyme durability. Moreover, the hyperthermia arising from the V2CTx nanosheets by NIR irradiation results in an ideal local temperature gradient for the ZnSnO3 USNPs, giving rise to an excellent pyroelectric catalytic effect by promoting band bending. Furthermore, polarized charges increase the tumor cell membrane permeability and facilitate nanodrug accumulation, thereby resolving the multidrug resistance issue. Thus, the combination of pyroelectric and enzyme catalysis together with the photothermal effect solves the dilemma of nanozymes and improves the antitumor efficiency.

Multimodal Imaging and Phototherapy of Cancer and Bacterial Infection by Graphene and Related Nanocomposites

The advancements in nanotechnology and nanomedicine are projected to solve many glitches in medicine, especially in the fields of cancer and infectious diseases, which are ranked in the top five most dangerous deadly diseases worldwide by the WHO. There is great concern to eradicate these problems with accurate diagnosis and therapies. Among many developed therapeutic models, near infra-red mediated phototherapy is a non-invasive technique used to invade many persistent tumors and bacterial infections with less inflammation compared with traditional therapeutic models such as radiation therapy, chemotherapy, and surgeries. Herein, we firstly summarize the up-to-date research on graphene phototheranostics for a better understanding of this field of research. We discuss the preparation and functionalization of graphene nanomaterials with various biocompatible components, such as metals, metal oxides, polymers, photosensitizers, and drugs, through covalent and noncovalent approaches. The multifunctional nanographene is used to diagnose the disease with confocal laser scanning microscopy, magnetic resonance imaging computed tomography, positron emission tomography, photoacoustic imaging, Raman, and ToF-SMIS to visualize inside the biological system for imaging-guided therapy are discussed. Further, treatment of disease by photothermal and photodynamic therapies against different cancers and bacterial infections are carefully conferred herein along with challenges and future perspectives.

Nanomaterials alleviating redox stress in neurological diseases: mechanisms and applications

Overproduced reactive oxygen and reactive nitrogen species (RONS) in the brain are involved in the pathogenesis of several neurological diseases, such as Alzheimer's disease, Parkinson's disease, traumatic brain injury, and stroke, as they attack neurons and glial cells, triggering cellular redox stress. Neutralizing RONS, and, thus, alleviating redox stress, can slow down or stop the progression of neurological diseases. Currently, an increasing number of studies are applying nanomaterials (NMs) with anti-redox activity and exploring the potential mechanisms involved in redox stress-related neurological diseases. In this review, we summarize the anti-redox mechanisms of NMs, including mimicking natural oxidoreductase activity and inhibiting RONS generation at the source. In addition, we propose several strategies to enhance the anti-redox ability of NMs and highlight the challenges that need to be resolved in their application. In-depth knowledge of the mechanisms and potential application of NMs in alleviating redox stress will help in the exploration of the therapeutic potential of anti-redox stress NMs in neurological diseases.

Colorimetric and Fluorescent Dual-Modality Sensing Platform Based on Fluorescent Nanozyme

Compared with natural enzymes, nanozymes based on carbonaceous nanomaterials are advantages due to high stability, good biocompatibility, and the possibility of multifunctionalities through materials engineering at an atomic level. Herein, we present a sensing platform using a nitrogen-doped graphene quantum dot (NGQD) as a highly efficient fluorescent peroxidase mimic, which enables a colorimetric/fluorescent dual-modality platform for detection of hydrogen peroxide (H₂O₂) and biomolecules (ascorbic acid-AA, acid phosphatase-ACP) with high sensitivity. NGQD is synthesized using a simple hydrothermal process, which has advantages of high production yield and potential for large-scale preparation. NGQD with uniform size (3.0 ± 0.6 nm) and a single-layer graphene structure exhibits bright and stable fluorescence. N-doping and ultrasmall size endow NGQD with high peroxidase-mimicking activity with an obviously reduced Michaelis–Menten constant (K_m) in comparison with natural horseradish peroxidase. Taking advantages of both high nanozyme activity and unique fluorescence property of NGQD, a colorimetric and fluorescent dual-modality platform capable of detecting H₂O₂ and biomolecules (AA, ACP) with high sensitivity is developed as the proof-of-concept demonstration. Furthermore, the mechanisms underlying the nanozyme activity and biosensing are investigated.

A green and facile approach to a graphene-based peroxidase-like nanozyme and its application in sensitive colorimetric detection of L-cysteine

A facile and green approach to the preparation of peroxidase-like nanozymes by reducing and functionalizing graphene oxide (rGO) with Ganoderma polysaccharide (GP) has been achieved in this work. Our results showed that the as-fabricated nanozyme, namely rGO-GP, possessed the excellent property of simulating peroxidase with higher catalytic activity compared with GO or rGO obtained by using chitosan, which may be due to the better dispersion of rGO-GP in the solution. Steady-state kinetics studies further showed that the catalytic process conformed to Michaelis-Menten equation and ping-pong mechanism. Benefiting from the excellent peroxidase property of rGO-GP, we have also successfully established a highly sensitive and selective colorimetric detection approach to trace detection of L-cysteine (L-Cys). The limit of detection (LOD) of L-cysteine is 0.1 μM and the linear detection range is 2-30 μM. Furthermore, the nanozyme was successfully applied for detecting L-cysteine in serum. This work therefore demonstrates the advantages of rGO-GP as an effective nanozyme in both its green synthesis and detecting application.

Applications of DNA-nanozyme-based sensors

Since the discovery of the enzyme-like activities of nanomaterials, the study of nanozymes has become one of the most popular research frontiers of diverse areas including biosensors. DNA also plays a very important role in the construction of biosensors. Thus, the idea of combined applications of nanozymes with DNA (DNA-nanozyme) is very attractive for the development of nanozyme-based biosensors, which has attracted considerable interest of researchers. To date, many sensors based on DNA-functionalized or templated nanozymes have been reported for the detection of various targets and highly accelerated the development of nanozyme-based sensors. In this review, we summarize the main applications and advances of DNA-nanozyme-based sensors. Additionally, perspectives and challenges are also discussed at the end of the review.

Counter Anion-Directed Growth of Iron Oxide Nanorods in a Polyol Medium with Efficient Peroxidase-Mimicking Activity for Degradation of Dyes in Contaminated Water

Development of nanozymes, which are nanomaterials with intrinsic enzymatic properties, has emerged as an appealing alternative to the natural enzymes with tremendous application potential from the chemical industry to biomedicine. The self-assembled growth of micrometer-sized oxide materials with controlled nonspherical shapes can be an important tool for enhancing activity as artificial enzymes, as the formation of these superstructures often results in high surface area with favorable impact on catalytic activity. Herein, the growth of rod-shaped Fe3O4 microstructures via a one-pot microwave-based method and using a water-poly(ethylene glycol) mixture as a solvent is reported, without the involvement of external shape-directing agents. The precursor metal salt played a key role in the size, shape, and phase selective evolution of iron oxide micro/nanomaterials. Whereas self-assembled microrod superstructures were obtained using Fe(NO3)3 as the metal salt precursor, use of FeCl3 or Fe-acetate as precursors afforded hollow Fe2O3 microparticles and Fe3O4 nanoparticles, respectively. A graphitic layer was deposited on the Fe3O4 surface, imparting a negative surface charge as a result of a high-temperature treatment of poly(ethylene glycol). The rod-shaped Fe3O4 microcrystals show efficient peroxidase-mimicking activity toward 3,3,5,5'-tetramethylbenzidine and pyrogallol as peroxidase substrates with a Michaelis-Menten rate constant (K m) value of 0.05 and 0.52 mM, respectively. The proficient enzyme mimicking behavior of these magnetic superstructures was further explored for the degradation of organic dyes that includes rhodamine B, methylene blue, and methyl orange with a rate constant (k) of 0.038, 0.011, and 0.007 min-1 respectively, using H2O2. This fast and simple method could help to develop a new pathway for differently shaped oxide nanoparticles in a sustainable and economical manner that can be harnessed as nanozymes for industrial as well as biological applications.

Simulated enzyme inhibition-based strategy for ultrasensitive colorimetric biothiol detection based on nanoperoxidases

A simulated enzyme inhibition-based strategy based on a nanoperoxidase mimic was adopted for ultrasensitive colorimetric glutathione detection.

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.

Controlled-temperature photothermal and oxidative bacteria killing and acceleration of wound healing by polydopamine-assisted Au-hydroxyapatite nanorods

Since skin wounds are subject to bacterial infection and tissue regeneration may be impeded, there is demand for biomaterials that possess rapid bactericidal and tissue repair capability. Herein we report in situ promotion of wound healing by a photothermal therapy (PTT) assisted nanocatalytic antibacterial system utilizing a polydopamine (PDA) coating on hydroxyapatite (HAp) incorporated with gold nanoparticles (Au-HAp). The PDA@Au-HAp NPs produce hydroxyl radicals (OH) via catalysis of a small concentration of H₂O₂ to render bacteria more vulnerable to the temperature change. The antibacterial efficacy against Escherichia coli and Staphylococcus aureus is 96.8% and 95.2%, respectively, at a controlled photo-induced temperature of 45 °C that causes no damage to normal tissues. By combining catalysis with near-infrared (NIR) photothermal therapy, the PDA@Au-HAp NPs provide safe, rapid, and effective antibacterial activity compared to OH or PTT alone. In addition, this system stimulates the tissue repairing-related gene expression to facilitate the formation of granulation tissues and collagen synthesis and thus accelerate wound healing. After the 10-day treatment of skin wounds in vivo, PDA@Au-HAp group exhibits quicker recovery than the control group and both sterilization and healing are completed after the 10-day treatment.

STATEMENT OF SIGNIFICANCE

This study presents in situ promotion of wound healing by a low-temperature photothermal therapy (PTT) assisted nanocatalytic antibacterial system utilizing a polydopamine (PDA) coating on hydroxyapatite (HAp) incorporated with gold nanoparticles (Au-HAp). The PDA@Au-HAp NPs produce hydroxyl radicals (OH) via catalysis of a small concentration of H₂O₂ to render bacteria more vulnerable to temperature change. After irradiation by 808 nm laser, the antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) is 96.8% and 95.2%, respectively, at a low photo-induced temperature of 45 °C which causes no damage to normal tissues. In addition, this system stimulates the tissue repairing-related gene expression to facilitate the formation of granulation tissues and collagen synthesis and accelerate wound healing.