Carbon Dot Nanozymes: How to Be Close to Natural Enzymes

The design, catalytic process, and property study of nanozymes are of importance for both fundamental research and application demand. Here, the peroxidase-mimicking properties of a series of carbon dots (C-dots) was systematically investigated and they were found to be probably closer to their natural counterparts, as compared to the known corresponding nanozymes. Firstly, four kinds of metal-free and surface-modulated C-dots were bottom-up fabricated using glucose, α-cyclodextrin (CD), β-CD, and γ-CD as precursors, respectively, and their formation processes, structures, as well as surface chemistry were investigated. Secondly, in the peroxidase-mimicking catalytic system, no hydroxyl radicals were produced, which indicates a different and special catalytic mode. By employing a joint experimental–theoretical study, a probable catalytic mechanism is proposed. Thirdly, the present C-dots maintained well their catalytic activity even in complicated serum matrices because their catalytic performances are completely irrelevant of any cation-related binding sites. Finally, the catalytic performances of the as-prepared C-dots were modulated by either pre-engineering NP surface structures or subsequently introducing photo-regulated host–guest reactions.     

Peroxidase-Mimetic Copper-Doped Carbon-Dots for Oxidative Stress-Mediated Broad-Spectrum and Efficient Antibacterial Activity

Carbon dots (CDs) have recently emerged as antibacterial agents and have attracted considerable attention owing to their fascinating merits of small size, facile fabrication, and surface functionalization. Most of them are involved in external light activation or hybridization with other functional nanomaterials. Herein, we present peroxidase-like Cu-doped CDs (Cu-CDs) for in vitro antibacterial applications. The unique peroxidase-mimicking property of the Cu-CDs was demonstrated by tetramethylbenzidine chromogenic assay, electron paramagnetic resonance spectra, and hydroxy radical probe. Escherichia coli and Staphylococcus aureus were chosen as representative gram-negative/positive models against which Cu-CDs exhibited superior antimicrobial activity even at a dosage down to 5 μg/mL. A possible mechanism of action was that the Cu-CDs triggered a catalytic redox reaction of endogenous H₂O₂ and glutathione depletion in the bacteria cells, with subsequent oxidative stress and membrane disruption. This work provides a new strategy for the design of microenvironment-responsive antimicrobial nano-agents.     

Self-Indicative Gold Nanozyme for H2O2 and Glucose Sensing

In addition to superior enzyme-mimicking abilities, nanozymes also have intrinsic physicochemical properties. Integrating the enzyme-like activities and tunable physicochemical properties into a single nanoparticle is a promising strategy for versatile nanozyme design and application. Herein, a composite nanozyme in which Au nanoparticles are encapsulated by Au nanoclusters (AuNP@AuNCs) is presented. By integrating the peroxidase-mimicking ability of fluorescent Au NCs with the glucose oxidase-like activity of Au NPs, the composite nanozyme realized cascade assay of glucose without the aid of external indicators. Compared to traditional multistep colorimetric methods, the analytical process was highly simplified by using the self-responsive nanozyme. This synthetic strategy provided valuable insights into exploring talented nanozymes for sensing diverse targets.     

纳米酶

纳米酶(Nanozymes)是由我国科学家首次提出的新概念,它是一类具有生物催化功能的纳米材料,能够基于特定的纳米结构催化天然酶的底物并作为酶的代替品。自2007年首次报道以来,全球已有来自于55个国家的420多个研究机构证实了纳米酶的普遍规律。纳米酶的发现第一次揭示纳米材料蕴含一种独特的纳米效应——类酶催化效应。纳米酶作为一种新材料,既有纳米材料本身的理化性质,又有类似酶的催化功能,兼具天然酶与人工酶的优势于一身。其中,纳米结构不仅赋予纳米酶高效催化功能,而且使纳米酶比天然酶稳定,易于规模化生产。另外,纳米酶独特的多酶活性将为设计廉价、稳定、各种各样全新的催化级联反应提供功能分子。纳米酶是多学科交叉融合的典范,2022年被IUPAC评为十大化学新兴技术。在全球从事化学、酶学、材料学、生物学、医学、理论计算等多领域科学家的共同推进下,如今纳米酶已经成为新的研究热点。我国科学家在这一新兴领域一直发挥着引领作用,解析了纳米酶的构-效关系,将其催化活性提高了约1万倍,实现了超越天然酶的理性设计,创造了全球首个纳米酶产品,出版了纳米酶学英文专著,发布纳米酶术语及中国/国际标准化。更可喜的是,纳...     

Reversible Electrochemical Modulation of a Catalytic Nanosystem

A catalytic system based on monolayer‐functionalized gold nanoparticles (Au NPs) that can be electrochemically modulated and reversibly activated is reported. The catalytic activity relies on the presence of metal ions (Cd²⁺ and Cu²⁺), which can be complexed by the nanoparticle‐bound monolayer. This activates the system towards the catalytic cleavage of 2‐hydroxypropyl‐p‐nitrophenyl phosphate (HPNPP), which can be monitored by UV/Vis spectroscopy. It is shown that Cu²⁺ metal ions can be delivered to the system by applying an oxidative potential to an electrode on which Cu⁰ was deposited. By exploiting the different affinity of Cd²⁺ and Cu²⁺ ions for the monolayer, it was also possible to upregulate the catalytic activity after releasing Cu²⁺ from an electrode into a solution containing Cd²⁺. Finally, it is shown that the activity of this supramolecular nanosystem can be reversibly switched on or off by oxidizing/reducing Cu/Cu²⁺ ions under controlled conditions.     

Self‐Assembly of Multi‐nanozymes to Mimic an Intracellular Antioxidant Defense System

In this work, for the first time, we constructed a novel multi‐nanozymes cooperative platform to mimic intracellular antioxidant enzyme‐based defense system. V₂O₅ nanowire served as a glutathione peroxidase (GPx) mimic while MnO₂ nanoparticle was used to mimic superoxide dismutase (SOD) and catalase (CAT). Dopamine was used as a linker to achieve the assembling of the nanomaterials. The obtained V₂O₅@pDA@MnO₂ nanocomposite could serve as one multi‐nanozyme model to mimic intracellular antioxidant enzyme‐based defense procedure in which, for example SOD, CAT, and GPx co‐participate. In addition, through assembling with dopamine, the hybrid nanocomposites provided synergistic antioxidative effect. Importantly, both in vitro and in vivo experiments demonstrated that our biocompatible system exhibited excellent intracellular reactive oxygen species (ROS) removal ability to protect cell components against oxidative stress, showing its potential application in inflammation therapy.     

Protocell Communication through the Eyes of Synthetic Organic Chemists

The bottom-up fabrication of synthetic cells (protocells) from molecules and materials, is a major challenge of modern chemistry. A significant breakthrough has been the engineering of protocells capable of chemical communication using bio-derived molecules and ex situ stabilised cell machineries. These, however, suffer from short shelf-lives, high costs, and require mild aqueous conditions. In this Concept Article we analyse the chemistry at the heart of protocell communication to highlight new opportunities for synthetic chemists in protocell engineering. Specifically, we (i) categorise the main bio-derived chemical communication machineries in enzyme cascades, DNA strand displacement, and gene-mediated communication; (ii) review the chemistries of these signal transduction machineries; and (iii) introduce new types of bio-inspired, fully synthetic artificial enzymes to replace their natural counterparts. Developing protocells that incorporate synthetic analogues of bio-derived signal transduction machineries will improve the robustness, stability, and versatility of protocells, and broaden their applications to highly strategic fields such as photocatalysis and fine chemicals production.     

The Most Active Oxidase-Mimicking Mn2O3 Nanozyme for Biosensor Signal Generation

Oxidase-mimicking nanozymes are more desirable than peroxidase-mimicking ones since H₂O₂ can be omitted. However, only a few nanomaterials are known for oxidase-like activities. In this work, we compared the activity of Mn₂O₃, Mn₃O₄ and MnO₂ and found that Mn₂O₃ had the highest oxidase activity. Interestingly, the activity of Mn₂O₃ was even inhibited by H₂O₂. The oxidase-like activity of Mn₂O₃ was not much affected by the presence of proteins such as bovine serum albumin (BSA), but the physisorption of antibodies to Mn₂O₃ was not strong enough to withstand the displacement by BSA. We then treated Mn₂O₃ with 3-aminopropyltriethoxysilane to graft an amine group, which was used to conjugate antibodies using glutaraldehyde as a crosslinker. A one-step indirect competitive ELISA (icELISA) was developed for the detection of isocarbophos, and an IC₅₀ of 261.7 ng/mL was obtained, comparable with the results of the standard two-step assay using horseradish peroxidase (HRP)-labeled antibodies. This assay has the advantage of significant timesaving for rapid detection of large amounts of samples. This work has discovered a highly efficient oxidase-mimicking nanozyme useful for various nano- and analytical applications.     

Multienzyme-Mimetic Activity of Gold/Cerium Oxide Nanozyme

Redox-active nanozymes offer low-cost controlled synthesis, high stability, and tunable catalytic properties over natural enzymes, which have attracted wide attention in the field of disease diagnosis and treatment. However, the improvement of catalytic activity remains an important challenge for nanozymes. Herein, the Au/CeO₂ nanozymes is developed to achieve enhanced multiple enzyme-mimetic activity. The Au/CeO₂ nanozymes at 5% doping possess best peroxidase-like activity with threefold higher catalytic rate than CeO₂. For catalase-mimic catalysis, the Au/CeO₂ nanozymes at 5% doping also exhibited a 1.5-fold enhanced reaction rate higher than pure CeO₂. The superoxide dismutase (SOD)-like capacity of Au/CeO₂ nanozymes is proportional to Au content. The Au/CeO₂ nanozymes at 10% doping show optimal SOD-like capacity of 60.2 U mg⁻¹. In vitro experiments validate the regulation ability of intracellular oxidative stress and inflammation. Au/CeO₂ nanozymes can reduce lipopolysaccharide- or H₂O₂-induced oxidative damage by scavenging excess ROS in nerve cell. Therefore, Au/CeO₂ can be used as a promising antioxidant in disease treatment, and the study offers general guidelines for achieving enhanced biocatalytic property through atomic doping.