Reversible inhibition of the oxidase-like activity of Fe single-atom nanozymes for drug detection

Inhibition effect-involved colorimetric sensor array based on PtBi aerogel nanozymes for discrimination of antioxidants

Nanozymes, as superior alternatives to natural enzymes, frequently employ the inhibition effect in turn-off sensors for analyte detection. However, limited attention has been paid to the inhibition mechanisms between analytes and nanozymes, limiting advancements in nanozyme-based sensing. Benefiting from the synergistic effects between three-dimensional network structure of aerogel and ligand effect triggered electronic regulation, Pt100Bi2 aerogel nanozymes (Pt100Bi2 ANs) exhibit superior peroxidase-like activity (293.48 U/mg). We found that antioxidants are able to inhibit the peroxidase-like activity of Pt100Bi2 ANs. The inhibition type (gallic acid as model) is reversible mixed-inhibition with the inhibition constants (Ki and Ki') of 0.213 mM and 0.108 mM. The inhibition effect-involved colorimetric sensor arrays were developed to overcome the "lock-key" limitation of traditional sensors, enabling distinguish five antioxidants via principal component analysis, with detection limit below 2 μM. This work provides new perspective on the inhibition mechanisms of nanozymes and optimization strategies for high-performance nanozyme-based sensors.

Fe-N-C oxidase-mimicking nanozymes for discrimination of antioxidants and detection of Hg2

Single-atom nanozymes (SAzymes) with high atom utilization efficiency and well-defined coordination structures have been extensively studied. However, research on the use of the enzyme-like activity of SAzymes for the detection and discrimination of antioxidants remains relatively limited. Herein, synthesized Fe-N-C SAzymes (FeN4) display excellent oxidase-like activity with a maximum reaction rate of 1.083 × 10-7 M s-1, which is 40.85 times higher than that for NC nanozymes. Experimental studies and density functional theory (DFT) calculations revealed that the high catalytic performance arises from the efficient absorption and activation of O2 at highly exposed Fe sites. Based on the different inhibitory effects of ascorbic acid (AA), glutathione (GSH), and cysteine (Cys), a colorimetric sensor array for identifying antioxidants was developed. AA, GSH, and Cys were effectively distinguished through linear discriminant analysis (LDA). Moreover, a colorimetric platform for the rapid detection of trace Hg2+ was successfully presented, taking advantage of the strong binding ability between -SH of Cys and Hg2+, and achieving an impressive limit of detection (LOD) of 9.29 nM. This work not only provides a novel concept for distinguishing antioxidants but also expands the application of nanozymes in heavy metal ion detection.

Highly accessible Fe-N-C single-atom nanozymes with enhanced oxidase-like activity for smartphone-assisted colorimetric detection of uric acid

Fe-N-C single-atom nanozymes (SANzymes), which exhibit the properties of well-defined atomic structures and carefully controlled coordination environments, have become a hot research topic in biomedical fields. Unfortunately, the lower accessibility and intrinsic activity of the FeN4 sites severely limit their enzyme-like activity. Here, a densely exposed surface FeN4 structure was constructed on layered nitrogen-doped hierarchical porous carbon support through two steps of pyrolysis strategy. Using a honeycomb porous carbon support, the Fe-N-C catalyst boasted a high specific surface area with numerous Fe anchoring sites and was equipped with efficiently accessible active FeN4 structures. The Fe edge effect could modulate the electronic structure of individual Fe atoms, thereby boosting the intrinsic oxidase-like activity of the FeN4 molecules. As a result, Fe-N-C SANzymes were efficiently able to catalyze O2 with 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate, achieving higher catalytic kinetic values than previously reported SANzymes. The colorimetric sensor using Fe-N-C SANzymes further detected uric acid (UA) with a wide detection range and a low detection limit. Then the visual sensing of the colorimetric system allowed the smartphone to identify colors by HSV patterns and obtain quantitative analysis. Moreover, the developed Fe-N-C colorimetric method showed satisfactory results in clinical samples, and proved to be a simple-operated and reliable method for detection of UA. This work not only highlights the advantages of the rationally designed edge effect of iron single atoms, but also presents the promising applicability of single-atom nanozymes in clinical diagnosis and related fields.

Second coordination sphere regulates nanozyme inhibition to assist early drug discovery

Early drug discovery is a time- and cost-consuming task requiring enzymes. Although nanozymes with metal sites akin to metallocofactors display similar activities, the lack of proximal amino acids hinders them from more adequately mimicking enzymes for drug discovery purposes. Hence, the rational design of the nanozyme second coordination sphere is desirable yet remains challenging. Herein, we report a nanozyme featuring atomically dispersed Cu-N4 sites with proximal hydroxyl groups (CuNC-OH). Experimental and theoretical results reveal that Cu-N4 site and hydroxyl respectively behave as cofactor and amino acid of the enzymatic pocket to interact with adsorbates, regulating nanozyme activity and inhibition. This mechanism involving dual sites is similar to that of thyroid peroxidases, which enables specific inhibition of CuNC-OH by antithyroid drugs. Based on these findings, a nanozyme-assisted drug discovery kit is established to analyze inhibition features of thyroid peroxidase inhibitors and screen out promising antithyroid drugs with a significant cost reduction compared with traditional enzyme kits.

MOF scaffold for anchoring platinum-nickel nanoparticles with enhanced oxidase-like activity to improve lateral flow immunoassay diagnosis

Noble metal nanoparticles have attracted tremendous attention as the promising signal reporters for catalytic-colorimetric lateral flow immunoassay (LFIA). However, it remains great challenges for improving their stability and catalytic activity. Herein, first, a kind of porphyrinic based metal-organic framework (MOF) was used as a carrier for loading platinum (Pt) nanoparticles to avoid its aggregation. Moreover, nickel (Ni) atoms were dopped into Pt nanoparticles to adjust crystal structure, thus greatly improving catalytic activity. The resulting MOF@PtNi nanocomposite showed enhanced colorimetric signal brightness and excellent oxidase-like activity, which can improve sensitivity via amplifying the color signal. The catalytic mechanism was further studied by scavenger and electron paramagnetic resonance analysis. Furthermore, integrated with the competitive immunization LFIA platform, the high sensitivity colorimetric detection of human immunoglobulin G was realized with a detection limit of 0.378 ng/mL and 0.269 ng/mL for pre- and post-catalytic detection, respectively. In addition, this MOF@PtNi based catalytic-colorimetric LFIA was used for detection of clinical serum samples and the results agreed well with that measured by the standard method. Therefore, this study helps open up the application of proposed catalytic-colorimetric nanocomposite in the ultrasensitive LFIA for point-of-care diseases diagnosis.

Research progress and applications of iron-based nanozymes in colorimetric sensing of agricultural pollutants

Natural enzymes are highly valued for their efficient specificity and catalytic activity. However, their poor stability, environmental sensitivity, and costly preparation restrict their practical applications. Nanozymes are nanomaterials with superior catalytic properties that compensate for natural enzyme deficiencies. As one of the earliest developed nanozymes, iron-based nanozymes have diverse morphological structures and different simulated catalytic properties, showing promising potential for agricultural pollutant sensing. Compared with traditional detection methods, the colorimetric method based on nanozymes has the characteristics of simplicity, rapidity, and visualization, which can be used for immediate and rapid on-site detection. In this review, the catalytic types of iron-based nanozymes, such as peroxidase-like, oxidase-like, catalase-like, and superoxide dismutase-like activities, and the corresponding catalytic mechanisms are presented. The classification of iron-based nanozymes based on various structures is then discussed. Furthermore, this review focuses on the current status of iron-based nanozymes for the colorimetric detection of common agricultural pollutants, including heavy metal ions, nonmetal ions, pesticides, and pharmaceutical and personal care products. Finally, the current research status and development direction of iron-based nanozymes in sensing applications are summarized and prospected.

Versatile laccase-mimicking enzyme for dye decolorization and tetracyclines identification upon a colorimetric array sensor

In this study, the laccase-mimicking enzyme MnO2/Cu-BDC-His was synthesized by a facile procedure, and was applied in tetracycline antibiotics (TCs) identification and dye degradation. The MnO2/Cu-BDC-His nanozymes effectively recognized phenolic hydroxyl groups in TCs and catalyzed the generation of colored oxidation products with different characteristic absorbance peaks at 350 nm, 525 nm and 600 nm. Different TCs mixtures produced different absorbance intensities at the above wavelengths and exhibited cross-color responses. Consequently, a colorimetric array sensor for the simultaneous identification and detection of TCs with wavelength as the sensing element was established. Unlike the traditional "lock-and-key" detection mode, the array sensor enabled simultaneous multi-analyte detection and identification, which achieved the identification and quantification of mixed TCs in the range of 5-200 µM, providing a premise for its application in lake and soil water. Additionally, the MnO2/Cu-BDC-His nanozymes were also applied in colored dyes decolorization. Therefore, MnO2/Cu-BDC-His nanozymes provided a promising application in environmental monitoring.

Nanozymes with Modulable Inhibition Transfer Pathways for Thiol and Cell Identification

The elementary mechanism and site studies of nanozyme-based inhibition reactions are ambiguous and urgently require advanced nanozymes as mediators to elucidate the inhibition effect. To this end, we develop a class of nanozymes featuring single Cu-N catalytic configurations and B-O sites as binding configurations on a porous nitrogen-doped carbon substrate (B6/CuSA) for inducing modulable inhibition transfer at the atomic level. The full redistribution of electrons across the Cu-N sites, induced by B-O sites incorporation, yields B6/CuSA with enhanced peroxidase-like activity versus CuSA. More importantly, CuSA with single Cu-N sites features in cysteine binding and expresses a competitive inhibition through coordination bonds, with an inhibition constant of 0.048 mM. Benefiting from the modulable binding way in nanozymes, B6/CuSA possesses mixed binding approaches for cysteine through noncovalent bonds and delivers a record-mixed inhibition interaction with a competitive inhibition constant of 0.054 mM and a noncompetitive inhibition constant of 0.71 mM. Based on the modulable inhibition of B6/CuSA and CuSA, a multichannel sensor array accomplishes the detection of various cancer cells, normal cells, and thiols. The design principle of this work is endowed with guidelines for the preliminary inhibition mechanism evaluation of massive potential thiols, cell discrimination, and disease prediction.

A Colorimetric and Fluorescent Dual-Mode Sensor Based on a Smartphone-Assisted Laccase-like Nanoenzyme for the Detection of Tetracycline Antibiotics

A copper-based nanoenzyme (Cu-BL) co-modified by L-L-lysine and 2-2-amino terephthalic acid has laccase-like activity and fluorescence characteristics. Based on this, a colorimetric and fluorescent dual-mode sensor was developed to visually and quantitatively detect tetracycline antibiotics (TCs), including tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC). In the colorimetric detection system, TCs can inhibit the generation of singlet oxygen (1O2) and weaken the ability of 2,4-dichlorophenol (2,4-DP) to be oxidized into pink-colored quinone substances. The linear ranges are 0.5-80 μM, 1-80 μM, and 0.25-80 μM, and the detection limits are 0.27 μM, 0.22 μM, and 0.26μM, respectively. In addition, due to the inner filter effect, tetracycline antibiotics can interact with Cu-BL, and with the increase in tetracycline antibiotic concentration, the fluorescence intensity will decrease. In addition, the smartphone sensing platform is combined with the colorimetric signal for the rapid and visual quantitative detection of tetracycline antibiotics. Generally speaking, the colorimetric/fluorescence dual-mode sensor demonstrates good stability, high specificity, and strong anti-interference capabilities, highlighting its practical application potential. This work is expected to offer novel insights for the development of multifunctional nanoenzymes and the integration of a multi-mode sensing platform.

Single-atom Fe nanozymes with excellent oxidase-like and laccase-like activity for colorimetric detection of ascorbic acid and hydroquinone

Although traditional Fe-based nanozymes have shown great potential, generally only a small proportion of the Fe atoms on the catalyst's surface are used. Herein, we synthesized single-atom Fe on N-doped graphene nanosheets (Fe-CNG) with high atom utilization efficiency and a unique coordination structure. Active oxygen species including superoxide radicals (O2•-) and singlet oxygen (1O2) were efficiently generated from the interaction of the Fe-CNG with dissolved oxygen in acidic conditions. The Fe-CNG nanozymes were found to display enhanced oxidase-like and laccase-like activity, with Vmax of 2.07 × 10-7 M∙S-1 and 4.54 × 10-8 M∙S-1 and Km of 0.324 mM and 0.082 mM, respectively, which is mainly due to Fe active centers coordinating with O and N atoms simultaneously. The oxidase-like performance of the Fe-CNG can be effectively inhibited by ascorbic acid (AA) or hydroquinone (HQ), which can directly obstruct the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Therefore, a direct and sensitive colorimetric method for the detection of AA and HQ activity was established, which exhibited good linear detection and limit of detection (LOD) of 0.048 μM and 0.025 μM, respectively. Moreover, a colorimetric method based on the Fe-CNG catalyst was fabricated for detecting the concentration of AA in vitamin C. Therefore, this work offers a new method for preparing a single-atom catalyst (SAC) nanozyme and a promising strategy for detecting AA and HQ.

A high oxidase-like activity, bimetallic single-atom nanozyme FeCe/NC prepared by FeCe-ZIF-8 approach for sensing tannic acid in tea

To improve the activity of single-atom nanozymes (SAzymes) for applications in food analysis, a new bimetal SAzyme FeCe/NC was developed. Its oxidase-like activity is 40% higher than that of single metal SAzyme Fe/NC. Based on a series of characterization investigations, the catalytic mechanism is that it directly catalyzed O2 to generate •OH, O2 •-and 1O2. It could directly catalyze oxidation 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxTMB, thereunder, a FeCe/NC SAzyme-TMB colorimetric method for the detection of tannic acid (TA) was constructed after the optimization of catalytic conditions. The method has a high R2 of 0.995, a low limit of detection (LOD) of 0.26 μmol/L, and high stability. The detection performance was validated by the real samples (tea). Therefore, the prepared bimetallic SAzyme FeCe/NC can be applied for TA detection without the addition of H2O2, and will have broad applications in the areas of food, feed, and life science.

S-Doping Regulated Iron Spin States in Fe-N-C Single-Atom Material for Enhanced Peroxidase-Mimicking Activity at Neutral pH

Designing biomimetic nanomaterials with peroxidase (POD)-like activity at neutral pH remains a significant challenge. An S-doping strategy is developed to afford an iron single-atom nanomaterial (Fe1@CN-S) with high POD-like activity under neutral conditions. To the best of knowledge, there is the first example on the achievement of excellent POD-like activity under neutral conditions by regulating the active site structure. S-doping not only promotes the dissociation of the N─H bond in 3,3″,5,5″-tetramethylbenzidine (TMB), but also facilitates the desorption of OH* by the transformation of iron species' spin states from middle-spin (MS FeII) to low-spin (LS FeII). Meanwhile, LS FeII sites typically have more unfilled d orbitals, thereby exhibiting stronger interactions with H2O2 than MS FeII, which can enhance POD-like activity. Finally, a one-pot visual detection of glucose at pH 7 is performed, demonstrating the best selectivity and sensitivity than previous reports.

Bioorthogonal Cu Single-Atom Nanozyme for Synergistic Nanocatalytic Therapy, Photothermal Therapy, Cuproptosis and Immunotherapy

Single-atom nanozymes (SAzymes) with atomically dispersed active sites are potential substitutes for natural enzymes. A systematic study of its multiple functions can in-depth understand SAzymes's nature, which remains elusive. Here, we develop a novel ultrafast synthesis of sputtered SAzymes by in situ bombarding-embedding technique. Using this method, sputtered copper (Cu) SAzymes (CuSA) is developed with unreported unique planar Cu-C3 coordinated configuration. To enhance the tumor-specific targeting, we employ a bioorthogonal approach to engineer CuSA, denoted as CuSACO. CuSACO not only exhibits minimal off-target toxicity but also possesses exceptional ultrahigh catalase-, oxidase-, peroxidase-like multienzyme activities, resulting in reactive oxygen species (ROS) storm generation for effective tumor destruction. Surprisingly, CuSACO can release Cu ions in the presence of glutathione (GSH) to induce cuproptosis, enhancing the tumor treatment efficacy. Notably, CuSACO's remarkable photothermal properties enables precise photothermal therapy (PTT) on tumors. This, combined with nanozyme catalytic activities, cuproptosis and immunotherapy, efficiently inhibiting the growth of orthotopic breast tumors and gliomas, and lung metastasis. Our research highlights the potential of CuSACO as an innovative strategy to utilize multiple mechanism to enhance tumor therapeutic efficacy, broadening the exploration and development of enzyme-like behavior and physiological mechanism of action of SAzymes.

Fiber Optic LSPR Sensing AFM1 in Milk with Enhanced Sensitivity by the Hot Spot Effect Based on Nanogap Construction

The detection of the amount of aflatoxin M1 (AFM1) in milk is crucial for food safety. Here, we utilize a fiber optic (FO) localized surface plasmon resonance (LSPR) biosensor by constructing gold nanoparticle (AuNP) multimers, in which the nanogaps amplified the LSPR signal by the hot spot effect, and achieved a highly sensitive detection of f AFM1. Through the optimization of parameter conditions for the fabrication of the sensor and detection system, a high performance result from the FO LSPR biosensor was obtained, and the method for AFM1 detection was established, with a wide detection range of 0.05-100 ng/mL and a low limit of detection (LOD) of 0.04 ng/mL, and it has been successfully validated with the actual sample milk. Therefore, it is a good strategy to fabricate highly sensitive FO LSPR sensors for detecting AFM1 by constructing AuNP multimers, and this approach is suitable for developing other biosensors.

Green synthesis of iron-doped graphene quantum dots: an efficient nanozyme for glucose sensing

Single-atom nanozymes with well-defined atomic structures and electronic coordination environments can effectively mimic the functions of natural enzymes. However, the costly and intricate preparation processes have hindered further exploration and application of these single-atom nanozymes. In this study, we presented a synthesis technique for creating Fe-N central single-atom doped graphene quantum dot (FeN/GQDs) nanozymes using a one-step solvothermal process, where individual iron atoms form strong bonds with graphene quantum dots through nitrogen coordination. Unlike previous studies, this method significantly simplifies the synthesis conditions for single-atom nanozymes, eliminating the need for high temperatures and employing environmentally friendly precursors derived from pineapple (ananas comosus) leaves. The resulting FeN/GQDs exhibited peroxidase-like catalytic activity and kinetics comparable to that of natural enzymes, efficiently converting H2O2 into hydroxyl radical species. Leveraging their excellent peroxide-like activity, FeN/GQDs nanozymes have been successfully applied to construct a colorimetric biosensor system characterized by remarkably high sensitivity for glucose detection. This achievement demonstrated a promising approach to designing single-atom nanozymes with both facile synthesis procedures and high catalytic activity, offering potential applications in wearable sensors and personalized health monitoring.

Construction and Application of Nanozyme Sensor Arrays

Compared with traditional "lock-key mode" biosensors, a sensor array consists of a series of sensing elements based on intermolecular interactions (typically hydrogen bonds, van der Waals forces, and electrostatic interactions). At the same time, sensor arrays also have the advantages of fast response, high sensitivity, low energy consumption, low cost, rich output signals, and imageability, which have attracted widespread attention from researchers. Nanozymes are nanomaterials which own enzyme-like properties. Because of the adjustable activity, high stability, and cost effectiveness of nanozymes, they are potential candidates for construction of sensor arrays to output different signals from analytes through the chemoresponse of colorants, which solves the shortcomings of traditional sensors that they cannot support multiple detection and lack universality. Recently, a sensor array based on nanozymes as nonspecific recognition receptors has attracted much more attention from researchers and has been applied to precise recognition of proteins, bacteria, and heavy metals. In this perspective, attention is given to nanozymes and the regulation of their enzyme-like activity. Particularly, the building principles and methods for sensor arrays based on nanozymes are analyzed, and the applications are summarized. Finally, the approaches to overcome the challenges and perspectives are also presented and analyzed for facilitating further research and development of nanozyme sensor arrays. This perspective should be helpful for gaining insight into research ideas within the field of nanozyme sensor arrays.

Atomic Engineering of Single-Atom Nanozymes for Biomedical Applications

Single-atom nanozymes (SAzymes) showcase not only uniformly dispersed active sites but also meticulously engineered coordination structures. These intricate architectures bestow upon them an exceptional catalytic prowess, thereby captivating numerous minds and heralding a new era of possibilities in the biomedical landscape. Tuning the microstructure of SAzymes on the atomic scale is a key factor in designing targeted SAzymes with desirable functions. This review first discusses and summarizes three strategies for designing SAzymes and their impact on reactivity in biocatalysis. The effects of choices of carrier, different synthesis methods, coordination modulation of first/second shell, and the type and number of metal active centers on the enzyme-like catalytic activity are unraveled. Next, a first attempt is made to summarize the biological applications of SAzymes in tumor therapy, biosensing, antimicrobial, anti-inflammatory, and other biological applications from different mechanisms. Finally, how SAzymes are designed and regulated for further realization of diverse biological applications is reviewed and prospected. It is envisaged that the comprehensive review presented within this exegesis will furnish novel perspectives and profound revelations regarding the biomedical applications of SAzymes.

Current Advances on the Single-Atom Nanozyme and Its Bioapplications

Nanozymes, a class of nanomaterials mimicking the function of enzymes, have aroused much attention as the candidate in diverse fields with the arbitrarily tunable features owing to the diversity of crystalline nanostructures, composition, and surface configurations. However, the uncertainty of their active sites and the lower intrinsic deficiencies of nanomaterial-initiated catalysis compared with the natural enzymes promote the pursuing of alternatives by imitating the biological active centers. Single-atom nanozymes (SAzymes) maximize the atom utilization with the well-defined structure, providing an important bridge to investigate mechanism and the relationship between structure and catalytic activity. They have risen as the new burgeoning alternative to the natural enzyme from in vitro bioanalytical tool to in vivo therapy owing to the flexible atomic engineering structure. Here, focus is mainly on the three parts. First, a detailed overview of single-atom catalyst synthesis strategies including bottom-up and top-down approaches is given. Then, according to the structural feature of single-atom nanocatalysts, the influence factors such as central metal atom, coordination number, heteroatom doping, and the metal-support interaction are discussed and the representative biological applications (including antibacterial/antiviral performance, cancer therapy, and biosensing) are highlighted. In the end, the future perspective and challenge facing are demonstrated.

Axially Coordinated Gold Nanoclusters Tailoring Fe-N-C Nanozymes for Enhanced Oxidase-Like Specificity and Activity

Metal-organic frameworks (MOF) derived nitrogen-doped carbon-supported monodisperse Fe (Fe-N-C) catalysts are intensively studied, but great challenges remain in understanding the relationship between the coordination structure and the performance of Fe-N-C nanozymes. Herein, a novel nanocluster ligand-bridging strategy is proposed for constructing Fe-S1 N4 structures with axially coordinated S and Au nanoclusters on ZIF-8 derived Fe-N-C (labeled Aux /Fe-S1 N4 -C). The axial Au nanoclusters facilitate electron transfer to Fe active sites, utilizing the bridging ligand S as a medium, thereby enhancing the oxygen adsorption capacity of composite nanozymes. Compared to Fe-N-C, Aux /Fe-S1 N4 -C exhibits high oxidase-like specificity and activity, and holds great potential for detecting acetylcholinesterase activity with a detection limit of 5.1 µU mL-1 , surpassing most reported nanozymes.

Simple enzyme-free detection of uric acid by an in situ fluorescence and colorimetric method based on Co-PBA with high oxidase activity

In this work, we prepared a simple and low-cost cobalt-doped Prussian blue analog (Co-PBA), which can directly oxidize 10-acetyl-3,7-dihydroxyphenoxazine and 3,3',5,5'-tetramethylbenzidine (TMB) to produce resorufin (ox-AR) with high fluorescent quantum yield and ox-TMB with blue color, respectively, without the need for unstable H2O2. Using the Michaelis-Menten curve and Lineweaver-Burk equation, the Michaelis-Menten constant of Co-PBA and the substrate TMB was found to be 0.033 mM, which was much lower than horseradish peroxidase and other reported nanozymes, showing satisfactory substrate affinity. Uric acid (UA) can cause erosion of the Co-PBA structure, and it significantly reduces the catalytic activity of Co-PBA, resulting in the decrease of the fluorescence emission signal of ox-AR and the absorption signal of ox-TMB. Based on this, a simple, sensitive, and fast fluorescence/colorimetric dual-mode uric acid detection platform was established. The detection range for UA by fluorescence method is 0.625-40 μM, and the detection limit (LOD, S/N = 3) is as low as 0.389 μM. The detection system was applied to serum samples with good recovery and can be used for field detection of UA in biological samples under different environments to meet different needs.

Perspectives for the Role of Single-Atom Nanozymes in Assisting Food Safety Inspection and Food Nutrition Evaluation

Single-atom nanozymes (SAzymes) have been greatly developed for rapid detection, owing to their rich active sites and excellent catalytic activity. Although several excellent reviews concentrating on SAzymes have been reported, they mainly focused on advanced synthesis, sensing mechanisms, and biomedical applications. To date, few reviews elaborate on the promising applications of SAzymes in food safety inspection and food nutrition evaluation. In this paper, we systematically reviewed the enzyme-like activity of SAzymes and the catalytic mechanism, in addition to recent research advances of SAzymes in the domain of food safety inspection and food nutrition evaluation in the past few years. Furthermore, current challenges hampering practical applications of SAzymes in food assay are summarized and analyzed, and possible research areas focusing on SAzyme-based sensors in rapid food testing are also proposed.

Diatomic iron nanozyme with lipoxidase-like activity for efficient inactivation of enveloped virus

Enveloped viruses encased within a lipid bilayer membrane are highly contagious and can cause many infectious diseases like influenza and COVID-19, thus calling for effective prevention and inactivation strategies. Here, we develop a diatomic iron nanozyme with lipoxidase-like (LOX-like) activity for the inactivation of enveloped virus. The diatomic iron sites can destruct the viral envelope via lipid peroxidation, thus displaying non-specific virucidal property. In contrast, natural LOX exhibits low antiviral performance, manifesting the advantage of nanozyme over the natural enzyme. Theoretical studies suggest that the Fe-O-Fe motif can match well the energy levels of Fe2 minority β-spin d orbitals and pentadiene moiety π* orbitals, and thus significantly lower the activation barrier of cis,cis-1,4-pentadiene moiety in the vesicle membrane. We showcase that the diatomic iron nanozyme can be incorporated into air purifier to disinfect airborne flu virus. The present strategy promises a future application in comprehensive biosecurity control.

Specific detection of fungicide thiophanate-methyl: A smartphone colorimetric sensor based on target-regulated oxidase-like activity of copper-doped carbon nanozyme

Nanozyme-based colorimetric assays have shown great potential in the rapid and sensitive determination of pesticide residue in environment. However, the non-specific enzyme inhibition makes the assays generally lack of selectivity. In this study, we proposed a colorimetric sensing platform for the specific detection of the agricultural fungicide thiophanate-methyl (TM) based on its distinctive inhibitory effect on the nanozyme activity. Since TM contains the symmetric ethylenediamine- and bisthiourea-like groups, it displays strong affinity to the metal site, leading to a loss of the catalytic activity. Accordingly, a Cu-doped carbon nanozyme with excellent oxidase-like properties was designed, and the oxidation process of chromogenic substrate is promoted by Cu-induced generation of reactive oxygen species. Interestingly, the nanozyme activity can be directly and strongly restrained by TM, rather than other probably coexistent pesticides. Consequently, the as-proposed analytical method exhibits specific response toward TM and good linear relationship in the range of 0.2-15 μg mL-1 with a low limit of detection of 0.04 μg mL-1 (S/N = 3). Besides, a smartphone-assisted rapid detection was achieved through identifying the RGB value of the chromogenic system. This work provides a new nanozyme inhibition strategy for the specific detection of TM in environmental sample.

Nanozymatic Biofuel Cell-Enabled Self-Powered Sensing System for a Sensitive Immunoassay

Self-powered sensing system (SPSS) integrating the enzymatic biofuel cell and biosensing platform has attracted tremendous interest. However, natural enzymes suffer from the intrinsic drawbacks of enzymes and enzymatic proteins. Nanozymes with enzyme-like activities are the ideal alternatives to enzymes, and it is greatly challenging to explore high-performance nanozymatic biofuel cell for SPSS. Herein, the advanced nanozymatic biofuel cell-enabled SPSS is developed for the sensitive detection of the prostate-specific antigen (PSA), where Ir single atoms supported by nitrogen-doped carbon and Au nanozymes serve as the cathode and anode, respectively. Based on the excellent electrochemical activity and stability, the resultant nanozymatic biofuel cell exhibits a higher power output and open-circuit potential than the Pt/C-based counterpart, which is beneficial for the application of SPSS. As a proof of concept, the nanozymatic biofuel cell-enabled SPSS shows a wide detection range of 0.2-500 ng mL-1 with a detection limit of 62 pg mL-1 for PSA, which provides new insight into broadening the application scenarios of nanozymes.

Dimensionality Engineering of Single-Atom Nanozyme for Efficient Peroxidase-Mimicking

In nature, enzymatic reactions occur in well-functioning catalytic pockets, where substrates bind and react by properly arranging the catalytic sites and amino acids in a three-dimensional (3D) space. Single-atom nanozymes (SAzymes) are a new type of nanozymes with active sites similar to those of natural metalloenzymes. However, the catalytic centers in current SAzymes are two-dimensional (2D) architectures and the lack of collaborative substrate-binding features limits their catalytic activity. Herein, we report a dimensionality engineering strategy to convert conventional 2D Fe-N-4 centers into 3D structures by integrating oxidized sulfur functionalities onto the carbon plane. Our results suggest that oxidized sulfur functionalities could serve as binding sites for assisting substrate orientation and facilitating the desorption of H₂O, resulting in an outstanding specific activity of up to 119.77 U mg^-1, which is 6.8 times higher than that of conventional FeN₄C SAzymes. This study paves the way for the rational design of highly active single-atom nanozymes.

Research Progress in Iron-Based Nanozymes: Catalytic Mechanisms, Classification, and Biomedical Applications

Natural enzymes are crucial in biological systems and widely used in biology and medicine, but their disadvantages, such as insufficient stability and high-cost, have limited their wide application. Since Fe₃O₄ nanoparticles were found to show peroxidase-like activity, researchers have designed and developed a growing number of nanozymes that mimic the activity of natural enzymes. Nanozymes can compensate for the defects of natural enzymes and show higher stability with lower cost. Iron, a nontoxic and low-cost transition metal, has been used to synthesize a variety of iron-based nanozymes with unique structural and physicochemical properties to obtain different enzymes mimicking catalytic properties. In this perspective, catalytic mechanisms, activity modulation, and their recent research progress in sensing, tumor therapy, and antibacterial and anti-inflammatory applications are systematically presented. The challenges and perspectives on the development of iron-based nanozymes are also analyzed and discussed.

Air-Derived Inhibitor of Nanozymes

Nanozymes are functional nanomaterials with enzyme-mimicking activities, which have found wide applications in various fields. Investigation on nanozyme inhibitors not only helps to apply nanozymes in a controlled manner but also deepens our insight into the catalysis mechanism. Herein, we report an inorganic ion inhibitor, HCO₃^-, which can significantly inhibit the alkaline phosphatase-mimicking activities of Ce₆ cluster-based metal-organic framework (Ce-MOF) nanozymes. The inhibition of adsorption of the negatively charged fluorescence sodium on Ce₆ clusters in Ce-MOF nanoparticles (NPs) by HCO₃^- proves that HCO₃^- ions occupy and deactivate Ce₆ clusters (i.e., catalytic active sites), leading to the activity inhibition of Ce-MOF nanozymes. Tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer is widely employed as the alkaline reaction medium. HCO₃^- ions can be formed in Tris-HCl buffer through adsorption of CO₂ in the air during storage in a sealed tube, which significantly inhibits the activity of Ce-MOF nanozymes. To our knowledge, this study is the first to demonstrate an air-derived inhibitor of nanozymes.

Mineral-Enhanced Manganese Ferrite with Multiple Enzyme-Mimicking Activities for Visual Detection of Disease Markers

Local geometric configurations of metal cations in inorganic enzyme mimics determine their catalytic behaviors, while their optimization remains challenging. Herein, kaolinite, a naturally layered clay mineral, achieves the optimization of cationic geometric configuration in manganese ferrite. We demonstrate that the exfoliated kaolinite induces the formation of defective manganese ferrite and makes more iron cations fill into the octahedral sites, significantly enhancing the multiple enzyme-mimicking activities. The steady-state kinetic assay results show that the catalytic constant of composites toward 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂ are more than 7.4- and 5.7-fold higher than manganese ferrite, respectively. Furthermore, density functional theory (DFT) calculations reveal that the outstanding enzyme-mimicking activity of composites is attributed to the optimized iron cation geometry configuration, which has a higher affinity and activation ability toward H₂O₂ and lowers the energy barrier of key intermediate formation. As a proof of concept, the novel structure with multiple enzyme-mimicking activities amplifies the colorimetric signal, realizing the ultrasensitive visual detection of disease marker acid phosphatase (ACP), with a detection limit of 0.25 mU/mL. Our findings provide a novel strategy for the rational design of enzyme mimics and an in-depth investigation of their enzyme-mimicking properties.

Colorimetric identification of multiple terpenoids based on bimetallic FeCu/NPCs nanozymes

Nanozymes have been relatively well explored, and bimetal-doped nanozymes have attracted much exploration due to their superior catalytic activity. We developed bimetallic FeCu/NPCs and Cu/NPCs nanozymes, which have good catalytic properties due to the coordination of Fe and Cu with N and P. The nanozymes acted as sensing elements in a cascade reaction system to effectively recognize seven terpenoids, including menthol (Men), paeoniflorin (Pae), camphor (Cam), paclitaxel (Pac), andrographolide (Andro), ginkgolide A (Gin A), and piperone (Pip). Terpenoids act as inhibitors of acetylcholinesterase (AChE) and reduce the hydrolysis of acetylcholine (ATCh), providing insight into establishing a simple and distinct assay for terpenoids. Notably, the sensor array distinguished seven terpenoids with concentrations as low as 10 ng/mL and achieved high-precision detection of mixed samples with different molar ratios and 21 unknown samples. Finally, the sensor array successfully distinguished and identified multiple terpenoids in herbal samples.

Electrochemical biomimetic enzyme cascade amplification combined with target-induced DNA walker for detection of thrombin

Fe-N-doped carbon nanomaterials (Fe-N/CMs) were designed as a novel biomimetic enzyme with excellent peroxidase-like activity to achieve high-efficient enzyme cascade catalytic amplification with the aid of glucose oxidase (GOx), which was further combined with target-induced DNA walker amplification to develop a sensitive electrochemical biosensor for thrombin detection. Impressively, massive output DNA was transformed from small amounts of target thrombin by highly effective DNA walker amplification as protein-converting strategy, which could then induce the immobilization of functionalized nanozyme on the electrode surface to achieve the high-efficient electrochemical biomimetic enzyme cascade amplification. As a result, an amplified enzyme cascade catalytic signal was measured for thrombin detection ranging from 0.01 pM to 1 nM with a low detection limit of 3 fM. Importantly, the new biomimetic enzyme cascade reaction coupled the advantages of natural enzyme and nanozyme, which paved an avenue to construct varied artificial multienzymes amplification systems for biosensing, bioanalysis, and disease diagnosis applications.

Peroxidase-Mimicking Hierarchically Organized Gold Particles for Glucose Detection

In this work, we synthesize a series of hierarchically organized gold nanoparticles (Au HOPs-X) with peroxidase (POD)-like catalytic activity by the in situ reduction of Au-thiolate hierarchically organized particles (Au HOPs). The initial Au HOPs show little POD-like catalytic activity. However, after the reduction of the particles, the Au HOPs-X showed enhanced POD-like catalytic activity, where X represents the reduction degree of Au HOPs. The reasons are as follows: (1) the Au-thiolate complexes on the surface of the Au HOPs-X were reduced into Au nanoparticles, and the active Au⁰ content increases with the increase of the reduction degree; (2) the specific surface area of Au HOPs-X becomes larger. Based on this, the Au HOPs-10 with the highest catalytic activity were combined with glucose oxidase to obtain a standard curve as a function of glucose concentrations. The color of the solutions was captured by mobile phone photos to determine their saturation, and the rapid detection of glucose was achieved through the standard curve of glucose concentration and saturation determined in this study.

Single-atom nanozymes: From bench to bedside

Single-atom nanozymes (SANs) are the new emerging catalytic nanomaterials with enzyme-mimetic activities, which have many extraordinary merits, such as low-cost preparation, maximum atom utilization, ideal catalytic activity, and optimized selectivity. With these advantages, SANs have received extensive research attention in the fields of chemistry, energy conversion, and environmental purification. Recently, a growing number of studies have shown the great promise of SANs in biological applications. In this article, we present the most recent developments of SANs in anti-infective treatment, cancer diagnosis and therapy, biosensing, and antioxidative therapy. This text is expected to better guide the readers to understand the current state and future clinical possibilities of SANs in medical applications.

Plasmonic/magnetic nanoarchitectures: From controllable design to biosensing and bioelectronic interfaces

Controllable design of the nanocrystal-assembled plasmonic/magnetic nanoarchitectures (P/MNAs) inspires abundant methodologies to enhance light-matter interactions and control magnetic-induced effects by means of fine-tuning the morphology and ordered packing of noble metallic or magnetic building blocks. The burgeoning development of multifunctional nanoarchitectures has opened up broad range of interdisciplinary applications including biosensing, in vitro diagnostic devices, point-of-care (POC) platforms, and soft bioelectronics. By taking advantage of their customizability and efficient conjugation with capping biomolecules, various nanoarchitectures have been integrated into high-performance biosensors with remarkable sensitivity and versatility, enabling key features that combined multiplexed detection, ease-of-use and miniaturization. In this review, we provide an overview of the representative developments of nanoarchitectures that being built by plasmonic and magnetic nanoparticles over recent decades. The design principles and key mechanisms for signal amplification and quantitative sensitivity have been explored. We highlight the structure-function programmability and prospects of addressing the main limitations for conventional biosensing strategies in terms of accurate selectivity, sensitivity, throughput, and optoelectronic integration. State-of-the-art strategies to achieve affordable and field-deployable POC devices for early multiplexed detection of infectious diseases such as COVID-19 has been covered in this review. Finally, we discuss the urgent yet challenging issues in nanoarchitectures design and related biosensing application, such as large-scale fabrication and integration with portable devices, and provide perspectives and suggestions on developing smart biosensors that connecting the materials science and biomedical engineering for personal health monitoring.

Tuning iron spin states in single-atom nanozymes enables efficient peroxidase mimicking

The large-scale application of nanozymes remains a significant challenge owing to their unsatisfactory catalytic performances. Featuring a unique electronic structure and coordination environment, single-atom nanozymes provide great opportunities to vividly mimic the specific metal catalytic center of natural enzymes and achieve superior enzyme-like activity. In this study, the spin state engineering of Fe single-atom nanozymes (FeNC) is employed to enhance their peroxidase-like activity. Pd nanoclusters (PdNC) are introduced into FeNC, whose electron-withdrawing properties rearrange the spin electron occupation in Fe(ii) of FeNC-PdNC from low spin to medium spin, facilitating the heterolysis of H2O2 and timely desorption of H2O. The spin-rearranged FeNC-PdNC exhibits greater H2O2 activation activity and rapid reaction kinetics compared to those of FeNC. As a proof of concept, FeNC-PdNC is used in the immunosorbent assay for the colorimetric detection of prostate-specific antigen and achieves an ultralow detection limit of 0.38 pg mL-1. Our spin-state engineering strategy provides a fundamental understanding of the catalytic mechanism of nanozymes and facilitates the design of advanced enzyme mimics.

Recent progress in single-atom nanozymes research

Single-atom nanozyme (SAzyme) is the hot topic of the current nanozyme research. Its intrinsic properties, such as high activity, stability, and low cost, present great substitutes to natural enzymes. Moreover, its fundamental characteristics, i.e., maximized atom utilizations and well-defined geometric and electronic structures, lead to higher catalytic activities and specificity than traditional nanozymes. SAzymes have been applied in many biomedical areas, such as anti-tumor therapy, biosensing, antibiosis, and anti-oxidation therapy. Here, we will discuss a series of representative examples of SAzymes categorized by their biomedical applications in this review. In the end, we will address the future opportunities and challenges SAzymes facing in their designs and applications.

Exploring gabosine and chlorogentisyl alcohol derivatives from a marine-derived fungus as EcGUS inhibitors with informatic assisted approaches

β-Glucuronidase catalyzes the cleavage of glucuronosyl-O-bonds, whose inhibitors reduce the level of toxic substances present in the intestine caused by anti-cancer and anti-inflammatory therapies. Herein, we presented a new tool, Bioactive Fractions Filtering Platform (BFFP), which is able to reliably discern active candidate node from crude extracts. The source code for the BFFP is available on GitHub (https://github.com/BioGavin/msbff). With the assistant of BFFP, 25 gabosine and chlorogentisyl alcohol derivatives including 19 new compounds were isolated from a marine-derived fungus Epicoccum sp. GST-5. Compounds 7, 9-15 possessed an unusual hybrid skeleton of gabosine and chlorogentisyl alcohol units. Compounds 9-12, 16 and 17 possessed a novel three-membered spiral ring skeleton with one/two gabosine and one/two chlorogentisyl alcohol units. Compound 25 represented new gabosine-derived skeleton possessing an unusual 6/6/6/5/6 condensed ring system. All isolates were evaluated for in vitro E. coli β-glucuronidase (EcGUS) inhibitory activity. 14 Compounds demonstrated superior inhibitory activity (IC₅₀ = 0.24-4.61 μM) to that of standard d-saccharic acid 1,4-lactone (DSL, IC₅₀ = 56.74 ± 4.01 μM). Compounds with chlorogentisyl alcohol moiety, such as 17 (IC₅₀ = 0.24 ± 0.02 μM) and 1 (IC₅₀ = 0.74 ± 0.03 μM), exhibited the most potent inhibitory activity. Furthermore, literature based QSAR profiling by applying PCA and OPLS analysis was carried out to analyze the features of compounds against EcGUS, revealing that the introduction of substituents able to form polar interactions with binding sites of receptor would lead to more active structures.