Atomic engineering of single-atom nanozymes for enzyme-like catalysis

Enzyme mimics, especially nanozymes, play a crucial role in replacing natural enzymes for diverse applications related to bioanalysis, therapeutics and other enzyme-like catalysis. Nanozymes are catalytic nanomaterials with enzyme-like properties, which currently face formidable challenges with respect to their intricate structure, properties and mechanism in comparison with enzymes. The latest emergence of single-atom nanozymes (SAzymes) undoubtedly promoted the nanozyme technologies to the atomic level and provided new opportunities to break through their inherent limitations. In this perspective, we discuss key aspects of SAzymes, including the advantages of the single-site structure, and the derived synergetic enhancements of enzyme-like activity, catalytic selectivity and the mechanism, as well as the superiority in biological and catalytic applications, and then highlight challenges that SAzymes face and provide relevant guidelines from our point of view for the rational design and extensive applications of SAzymes, so that SAzyme may achieve its full potential as the next-generation nanozyme.

Single-atom nanozymes with definite active centers, high catalytic activities and enzyme-like selectivities promote the nanozyme research entering a new period of atomic level.     

5-Fluorouracil-containing inorganic iron oxide/platinum nanozymes with dual drug delivery and enzyme-like activity for the treatment of breast cancer

Intrinsic enzyme-mimic activity of inorganic nanoparticles has been widely used for nanozymatic anticancer and antibacterial treatment. However, the relatively low peroxidase-mimic activity (PMA) and catalse-mimic activity (CMA) of nanozymes in tumor microenvironment has hampered their potential application in the cancer therapy. Therefore, in this study, we aimed to fabricate platinum (Pt) nanozymes dispersed on the surface of iron oxide (Fe₃O₄) nanosphere that, in addition to boosting the PMA and CMA, resulted in the formation of a pH-sensitive nano-platform for drug delivery in breast cancer therapy. After development of Fe₃O₄ nanospheres containing Pt nanozymes and loading 5-fluorouracil (abbreviated as: Fe₃O₄/Pt-FLU@PEG nanospheres), the physicochemical properties of the nanospheres were examined by electron microscopy, dynamic light scattering, zeta potential, X-ray diffraction, thermogravimetric, BET surface, and PMA/CMA analyses. Then, the cytotoxicity of the Fe₃O₄/Pt-FLU@PEG nanospheres against 4T1 cells was investigated by the cell counting kit-8 assay and flow cytometry. Also, the anticancer effect of fabricated nanoplatform was assessed in mouse bearing 4T1 cancer tumors, in vivo. The results showed that the Fe₃O₄/Pt-FLU@PEG nanospheres provide a platform for optimal FLU loading, continuous pH-sensitive drug release, and potential PMA and CMA to increase the level of ROS and O₂, respectively. Cytotoxicity outputs showed that the Fe₃O₄/Pt-FLU@PEG nanospheres mitigate the proliferation of 4T1 cancer cells mediated by apoptosis and intracellular generation of reactive oxygen species (ROS). Furthermore, in vivo assays indicated a significant reduction in tumor size and overcoming tumor hypoxia. Overall, we believe that the developed nanospheres with dual enzyme-mimic activity and pH-sensitive drug delivery can be used for ROS/chemotherapy double-modality antitumor therapy.     

Enhanced oxidase-like activity of g-C3N4 nanosheets supported Pd nanosheets for ratiometric fluorescence detection of acetylcholinesterase activity and its inhibitor

The undesirable enzymatic activity of nanozymes under near neutral p H condition and the traditional single signal output always restrict the analytical application of nanozyme-based biosensors.Herein,graphitic carbon nitride nanosheets supported palladium nanosheets composite （Pd/g-C₃N₄） with both oxidase-like activity and fluorescent property is synthesized.Notably,Pd/g-C₃N₄exhibits enhanced oxidase-like activity compared to Pd NSs under p H 7.4.By c...     

单原子铂纳米酶的简便构建及其类过氧化物酶活性

采用浸渍吸附法,以多孔碳纳米笼(CNC)作为载体,简便构建了单原子铂/CNC(SA-Pt/CNC)纳米酶。通过透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)和X射线光电子能谱(XPS)深入解析了SA-Pt/CNC的微观结构。酶活性测试表明,SA-Pt/CNC表现出优异的类过氧化物酶活性,能高效催化过氧化氢氧化各种底物分子。     

Modification and application of Fe3O4 nanozymes in analytical chemistry: A review

In recent years, Fe₃O₄ nanomaterials have received much attention in analytical chemistry due to their excellent magnetic and peroxidase-like activity. As the catalytic characteristics of Fe₃O₄ nanomaterials is similar to those of horseradish peroxidase (HRP), Fe₃O₄ nanomaterials are also used as peroxidase mimics and have achieved a certain development in many fields based on latest research results. To improve the stability and catalytic ability of simple Fe₃O₄ nanomaterials, various modification strategies of Fe₃O₄ nanomaterials have been developed. The recent advances of these strategies have been presented and discussed. In addition, this paper introduces the application of Fe₃O₄ nanozymes in the detection of food and industrial pollutants, as well as in the field of biosafety.     

Reversible covalent inhibition of a protein target

Electron-deficient Michael acceptors can be used in reversible addition/elimination reactions with thiols. These electrophiles were used to convert a known irreversible kinase inhibitor into a covalent and reversible inhibitor. Such an approach might provide high-affinity binders with increased selectivity without the toxicological risks associated with irreversible protein modifications.     

Bimetallic AuRu aerogel with enzyme-like activity for colorimetric detection of Fe2+ and glucose

Aerogels have become a hot topic of research due to their extremely low density and special interconnected structure as well as their enzyme-like activity. The development of new multifunctional nano-enzyme aerogels with high activity and good stability is still a considerable challenge. In this paper, AuRu aerogels with peroxidase and oxidase activities were synthesized using a simple one-step method and successfully used to construct colorimetric sensors for the detection of Fe²⁺ and glucose based on their enzyme-like activities. Furthermore, we are fortunate to find that AuRu aerogels have good photothermal properties. This suggests that AuRu aerogels can be used not only for in vitro testing but also for promising applications such as disease treatment.     

Reversible electrochemical detection of nonelectroactive polyions

Selective extraction principles for the recognition of nonelectroactive polyions such as heparin and protamine exist, but the high ionic valency renders the extraction process irreversible. A response principle for the reversible detection of such polyions is proposed here. The extraction of the polyionic analyte to the membrane and its subsequent back-extraction is now controlled electrochemically. The principle is established with a protamine electrode, and excellent stability and reproducibility are demonstrated. This method has important implications for the design of chemical recognition principles for polyionic analytes.     

单原子催化剂M1/FeOx(M=Pt,Fe)的理论研究:CO氧化反应

负载型纳米贵金属催化剂是用于多相催化反应的重要的催化剂之一,也是各国催化科学与技术研发的重点,其工业应用也越来越广泛.理论和实验的研究结果均表明,当载体表面的金属粒子尺寸减小至亚纳米级乃至更小的低配位、不饱和的原子团簇时,它们常常成为诱发催化反应的活性中心,呈现更高的催化活性和选择性.将负载的金属尺寸由纳米量级减小至分散的金属团簇甚至单原子而使每个原子成为反应的活性位点已成为研究的重点.最近,由张涛等首次合成的单原子催化剂(SAC)Pt1/FeOx引起了国内外催化及表面科学工作者的极大关注.单原子催化剂作为连接均相催化剂和多相催化剂的桥梁,不仅具有非均相催化剂的稳定、易于与反应体系分离、易表征等优点,而且具有均相催化剂活性中心结构均一、活性中心原子利用率百分之百等优点.一方面,单原子催化剂给多相催化领域注入了新的活力,另一方面也更有利于运用量子与计算化学的研究方法建立与实验相匹配的理论模型并从原子水平上进一步理解多相催化反应的微观作用机理.实验和理论的研究结果表明,其它单原子催化剂如Ir1/FeOx,Au1/FeOx和Ni1/FeOx催化CO氧化反应表现出不同的活性.然而,底物FeOx中的Fe同样是第VIII族中的3d过渡金属,却在低温下对CO氧化反应没有催化活性.我们围绕这一问题,重点研究了底物FeOx在负载单原子Pt1前后催化CO氧化的反应机理和活性,解释了单原子催化剂Pt1/FeOx相比于底物FeOx为何具有如此高的催化活性的原因.我们采用Vienna Ab-initio Simulation Package(VASP)从头算模拟软件和密度泛函理论(DFT)的广义梯度近似(GGA)进行了理论计算.其中,选择PBE泛函描述体系的交换关联相互作用,用投影缀加波(PAW)赝势基组方法描述体系中的电子和离子实之间的相互作用,对Fe原子采用了DFT+U方法进行d电子强相关校正,并使用Dimer计算方法搜寻反应过渡态.研究结果表明,底物FeOx中氧空位的再生伴随第二个CO2分子从催化剂表面脱附的过程需要较高的活化势垒(1.09 eV),这一过程是整个CO氧化反应的决速步.与此相比较,Pt1/FeOx催化剂中,由于Pt原子代替了表面Fe原子,导致电子结构及性质的显著变化,有利于CO的活化、氧化和CO2的脱附.我们从电子能量态密度(DOS)和Bader电荷分析及模型分子团簇的轨道相互作用的角度进一步分析了两种催化剂存在差异的本质;揭示了单原子催化剂Pt1/FeOx中Pt1和底物FeOx之间的相互作用的机理及催化剂表面Pt单原子在催化反应过程中的关键作用.     

Ensemble of single-atom catalysis and defect engineering in Cu1/CeO2 nanozymes for tumor therapy

As a class of nanomaterials with natural enzyme-like characteristics, nanozymes have shown their great potential in various applications. Reducible metal oxides featured with defect structures, and single-atom catalysts with isolated metal sites are regarded as two of the most promising nanozymes. However, the strategies to construct highly performed nanozymes by combining these advantages are rarely reported. Herein, we report the coordination-unsaturated single-atomic Cu species supported on s...     

非贵金属单原子催化剂的进展与展望

由于良好的催化活性和稳定性,贵金属催化剂已经被广泛应用于各种异相催化反应中,但是贵金属的稀有性和高成本无法满足未来日益增长的催化需求.2011年,张涛课题组成功地制备了高效、稳定的铂单原子催化剂.高效的单原子催化剂利用单个活性位点作为催化活性中心,可能会成为连接同相催化和异相催化的桥梁.然而从经济适用的长远角度考虑,将非贵金属催化剂缩小到原子尺度是否也会展现出优良的催化活性;是否有潜力替代目前已被广泛应用的贵金属催化剂?虽然现阶段非贵金属催化剂的催化性能仍无法达到贵金属催化剂的标准,但是已有相关研究从理论和实验上报道了非贵金属单原子催化剂及其优异的性能表明了其在未来发展中极其重要,因而,可以预见这两个疑问的答案都是肯定的.单原子概念的出现不仅为提高贵金属的催化性能及成本的降低指明了方向,同时也为制备具有高催化活性、甚至可与贵金属催化剂相媲美的非贵金属催化剂提供了可能性.我们在上述背景下,阐述了对单原子的概念日益加深的机制认知,并从理论和实验上概述了非贵金属单原子催化剂近期的发展情况,指出了目前的在单原子催化剂领域需要解决的一些问题,最后,针对研究现状,我们对未来单原子的发展提出了相应的展望.单原子催化剂具有较高的表面能,因而,如何寻找合适的基体与单原子相互作用,进而,使基体材料像一只手一样稳固地"抓紧"单原子,因而,降低其高表面能则是发挥优良催化性能的基础.强金属–基体相互作用(SMSI)不仅可以将单原子限制在基体表面,亦会影响整个催化过程.目前应用于单原子催化剂的基体种类很多,如金属氧化物、金属以及其他材料,而对SMSI认知则主要分两大类,一类是源自于基体表面的结构缺陷,另一类是源于其电子缺陷.从目前的发展状况来看SMSI机制仍有很多疑惑尚未解决,例如对电子转移影响的认知等.理论研究表明,在某些反应中非贵金属单原子展示出可替代贵金属的催化性质.比如,在一氧化碳优先反应(PROX)中,单原子钴和钛展示出的催化性能可与贵金属相媲美;理论计算同样证明单原子镍在一氧化碳还原中的催化活性比单原子铱优秀,甚至与单原子铂类似.大量的实验进展也报道了非贵金属单原子同样能在其他反应中展现出优异的性能,如氧析出反应(OER)、氢析出反应(HER)和氧还原反应(ORR).对于单原子催化剂,还有很多问题需要我们去解决,例如基体对于催化过程的具体影响、非贵金属的电子结构对于其催化性能的影响,以及单原子在基体上产生相互作用的位点等问题.纵然有许多问题需要更加深入的研究,但是单原子概念的出现,使得非贵金属催化剂材料取代传统贵金属催化剂成为了可能.     

Tandem catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural over a Ni3Fe intermetallic supported Pt single-atom site catalyst

Single-atom site catalysts (SACs) have been used in multitudinous reactions delivering ultrahigh atom utilization and enhanced performance, but it is challenging for one single atom site to catalyze an intricate tandem reaction needing different reactive sites. Herein, we report a robust SAC with dual reactive sites of isolated Pt single atoms and the Ni₃Fe intermetallic support (Pt₁/Ni₃Fe IMC) for tandem catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural (5-HMF). It delivers a high catalytic performance with 99.0% 5-HMF conversion in 30 min and a 2, 5-dimethylfuran (DMF) yield of 98.1% in 90 min at a low reaction temperature of 160 °C, as well as good recyclability. These results place Pt₁/Ni₃Fe IMC among the most active catalysts for the 5-HMF hydrodeoxygenation reaction reported to date. Rational control experiments and first-principles calculations confirm that Pt₁/Ni₃Fe IMC can readily facilitate the hydrodeoxygenation reaction by a tandem mechanism, where the single Pt site accounts for C O group hydrogenation and the Ni₃Fe interface promotes the C–OH bond cleavage. This interfacial tandem catalysis over the Pt single-atom site and Ni₃Fe IMC support may develop new opportunities for the rational structural design of SACs applied in other heterogeneous tandem reactions.

A robust Pt₁/Ni₃Fe single-atom site catalyst was designed for the tandem catalysis of 5-hydroxymethylfurfural hydrodeoxygenation to DMF, where Pt atoms catalyze the C O group hydrogenation and Ni₃Fe interface accounts for the C–OH bond rupture.     

Ultrasensitive endonuclease activity and inhibition detection using gold nanoparticle-enhanced fluorescence polarization

We have developed a highly sensitive and selective fluorescence polarization assay method based on the specificity of the DNA cleavage reaction with the enhancement of gold nanoparticles (AuNPs) for assaying endonuclease activity and inhibition. This assay can detect EcoRI endonuclease down to 5.0×10(-4) U mL(-1) with a detection range from 5.0×10(-4) to 10 U mL(-1).     

A label-free and sensitive fluorescent assay for one step detection of protein kinase activity and inhibition

In this paper, a label-free, highly sensitive and simple assay for one step detection of protein kinase (PKA) activity and inhibition that avoids the fluorescent dye process has been established. The detection was based on the fluorescence (FL) quenching of peptide-Ag nanoclusters (Ag NCs) caused by antibody modified Au nanoparticles (anti-Au NPs) via fluorescence resonance energy transfer (FRET). With PKA and adenosine 5′-triphosphate (ATP) introduced, the substrate peptide of Ag NCs could react with PKA via targeted phosphorylation, and followed by the linking interactions between peptide-Ag NCs and anti-Au NPs. According to the fluorescence quenching of Ag NCs, the activity of protein kinase can be facilely monitored in the range of 0.1–2000 mU/μL with high sensitivity. The detection limit for PKA is 0.039 mU/μL. We further explored the inhibitory effect of H-89 for protein kinase activity. The developed method was also applied to the investigation of drug-induced PKA activation in HeLa cells, which provides a promising means for screening of kinase-related drugs and the clinical diagnosis of disease.     

Multifunctional design of single-atom catalysts for multistep reactions

With the merits of high atom utilization, low cost, unique and tunable microstructures, as well as the particular catalytic behaviors, single-atom catalysts(SACs) have gained worldwide interest and achieved great advancements in heterogeneous catalysis recently. However, catalyzing an intricate multistep reaction is usually challenging for one single-atom center, in which case multiple catalytic sites are needed. In this review, the experimental and computational advances in the construction str...     

Homogeneous time-resolved fluorescence assays for the detection of activity and inhibition of phosphatase enzymes employing phosphorescently labeled peptide substrates

A rapid, homogenous, antibody-free assay for phosphatase enzymes was developed using the phosphorescent platinum (II)-coproporphyrin label (PtCP) and time-resolved fluorescent detection. An internally quenched decameric peptide substrate containing a phospho-tyrosine residue, labeled with PtCP-maleimide and dabcyl-NHS at its termini was designed. Phosphatase catalysed dephosphorylation of the substrate resulted in a minor increase in PtCP signal, while subsequent cleavage by chymotrypsin at the dephosphorylated Tyr-Leu site provided a 3.5 fold enhancement of PtCP phosphorescence. This phosphorescence phosphatase enhancement assay was optimized to a 96 well plate format with detection on a commercial TR-F plate reader, and applied to measure the activity and inhibition of alkaline phosphatase, recombinant human CD45, and tyrosine phosphatases in Jurkat cell lysates within 40 min. Parameters of these enzymatic reactions such as K_m's, limits of detection (L.O.D's) and IC₅₀ values for the non-specific inhibitor sodium orthovanadate were also determined.     

Atom-level interfacial synergy of single-atom site catalysts for electrocatalysis

Single-atom site catalysts(SACs)have made great achievements due to their nearly 100%atomic utilization and uniform active sites.Regulating the surrounding environment of active sites,including electron structure and coordination environment via atom-level interface regulation,to design and construct an advanced SACs is of great significance for boosting electrocatalytic reactions.In this review,we systemically summarized the fundamental understandings and intrinsic mechanisms of SACs for electrocatalytic applications based on the interface site regulations.We elaborated the several different regulation strategies of SACs to demonstrate their ascendancy in electrocatalytic applications.Firstly,the interfacial electronic interaction was presented to reveal the electron transfer behavior of active sites.Secondly,the different coordination structures of metal active center coordinated with two or three non-metal elements were also summarized.In addition,other atom-level interfaces of SACs,including metal atom–atom interface,metal atom-X-atom interface(X:non-metal element),metal atom-particle interface,were highlighted and the corresponding promoting effect towards electrocatalysis was disclosed.Finally,we outlooked the limitations,perspectives and challenges of SACs based on atomic interface regulation.     

电解水金属单原子催化剂的研究进展

氢能因其能量密度高、清洁无污染等特点,作为替代化石燃料的能源载体得到了广泛的研究.如何清洁高效地制备氢气受到了大量研究者的关注.当前,以化石能源的热反应所得副产氢气是主要来源.然而,采用该类方法不仅不能摆脱化石能源的使用以及温室气体的排放,还会造成生产氢气的纯度不高,碳氧化物杂质浓度过高的问题,严重影响氢气的后续使用.采用可再生能源(太阳能、风能等)所产富余电,进行电解水制氢,产生的氢气不含碳氧化合物杂质,纯度很高,可以真正实现碳的零排放,被认为是未来氢气来源的重要方式.目前,电解水制氢在制氢市场的所占份额较小,而造成这样局面的主要因素是该过程中的高能耗问题.为了降低能耗,开发高效催化剂加速两个电极上的电解反应的动力学尤为重要.近年,金属单原子催化剂(SACs)因其独特的结构,在很多研究中被用作电解水催化剂,进而开发出大量高性能的金属单原子电解水催化剂.本文综述了近年SACs在电解水催化方面的应用.首先,针对电解水反应本身,总结了阴阳极两侧的电极反应机制以及影响电极催化性能的关键吸附中间物种;然后,根据载体的不同,即合金、碳以及其它化合物将SACs分为三类,总结了相关电解水催化研究现状,并且针对不同类型SACs目前的发展情况,提出了它们各自存在的问题.其次,进一步总结了影响SACs电解水催化活性的因素,提出了四种决定SACs催化性能的影响因子,分别为金属原子的固有元素性质、配位环境、几何结构和负载量;同时讨论了这四类影响因素对SACs催化活性的影响机制,总结了调控各类影响因素的方法,为SACs的设计提出了一些建议.最后,展望了SACs在电解水催化中的应用,探讨了SACs在催化剂设计及催化机制研究方面的问题,提出了SACs在电解水催化中的未来发展方向.     

Reversible fluorescent probe for highly selective and sensitive detection of mercapto biomolecules

A coumarin-derived complex, Hg(2)L(2), was reported as a highly sensitive and selective probe for the detection of mercapto biomolecules in aqueous solution. The addition of Cys to a 99% aqueous solution of Hg(2)L(2) resulted in rapid and remarkable fluorescence OFF-ON (emission at 525 nm) due to the ligand-exchange reaction of Cys with L coordinated to Hg(2+). The increased fluorescence can be completely quenched by Hg(2+) and recovered again by the subsequent addition of Cys. Such a fluorescence OFF-ON circle can be repeated at least 10 times by the alterative addition of Cys and Hg(2+) to the solution of Hg(2)L(2), indicating that it can be used as a convertible and reversible probe for the detection of Cys. The interconversion of Hg(2)L(2) and L via the decomplexation/complexation by the modulation of Cys/Hg(2+) was definitely verified from their crystal structures. Other competitive amino acids without a thiol group cannot induce any fluorescence changes, implying that Hg(2)L(2) can selectively determine mercapto biomolecules. Using confocal fluorescence imaging, L/Hg(2)L(2) as a pair of reversible probes can be further applied to track and monitor the self-detoxification process of Hg(2+) ions in SYS5 cells.