The Fe-N-C Nanozyme with Both Accelerated and Inhibited Biocatalytic Activities Capable of Accessing Drug-Drug Interactions

Advances in total antioxidant capacity detection based on nanozyme

Nanozymes, a class of nanomaterials mimicking natural enzymatic functions, have gained significant attention due to their exceptional biocatalytic properties and wide-ranging applications in biosensing. The total antioxidant capacity (TAC) can serve as a crucial parameter for assessing food quality, guiding dietary choices, and monitoring health conditions. In recent years, various nanomaterials with peroxidase (POD)-like and oxidase (OXD)-like activity have been widely used for TAC determination. This review discusses the enzyme-mimicking catalytic activities of nanozymes related to TAC determination, the construction principles of nanozyme-based TAC sensors and systematically classifies the application of nanozyme sensors in TAC determination. Furthermore, the potential opportunities and challenges in the development of nanozyme-based sensors are evaluated, aiming to provide valuable insights for researchers in related fields.

Flower-like Ag-ZIF nanoparticles with petal-like structures as effective hot/cold-adapted oxidase mimic: Visual color tonality nitrite detection

This study presents the synthesis of novel flower-like silver-based zeolitic imidazolate frameworks (Ag-ZIFs) with petal-like nanosheet structures, exhibiting robust oxidase-like activity. These nanozymes catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) effectively across a wide temperature range (5 °C to 80 °C), making them suitable for thermophilic and cryogenic applications. Leveraging this strong oxidase activity, Ag-ZIFs@TMB system was used to design a conventional ratiometric colorimetric method for nitrite detection in water and food samples, alongside a color tonality-based visual detection mode. Nitrite concentrations ranging from 1.0 to 54.0 μM were quantified, achieving a detection limit of 0.06 μM. The ratiometric approach demonstrated enhanced sensitivity, lower detection limits, and superior resistance to interference compared to traditional single-absorbance methods. Furthermore, the smartphone-assisted or naked-eye detection mode enabled rapid, portable, and accurate analysis, offering practical applications in environmental monitoring and food safety. These results highlight the multifunctional potential of Ag-ZIFs in advanced sensing technologies.

Atomically Dispersed Metal Interfaces for Analytical Chemistry

ConspectusEngineering sensing interfaces with functional nanomaterials have aroused great interest in constructing novel analytical platforms. The good catalytic abilities and physicochemical properties allow functional nanomaterials to perform catalytic signal transductions and synergistically amplify biorecognition events for efficient target analysis. However, further boosting their catalytic performances poses grand challenges in achieving more sensitive and selective sample assays. Besides, nanomaterials with abundant atomic compositions and complex structural characteristics bring about more difficulties in understanding the underlying mechanism of signal amplification. Atomically dispersed metal catalysts (ADMCs), as an emerging class of heterogeneous catalysts, feature support-stabilized isolated metal catalytic sites, showing maximum metal utilization and a strong metal-support interfacial interaction. These unique structural characteristics are akin to those of homogeneous catalysts, which have well-defined coordination structures between metal sites with synthetic or biological ligands. By integrating the advantages of heterogeneous and homogeneous catalysts, ADMCs present superior catalytic activity and specificity relative to the nanoparticles formed by the nonuniform aggregation of active sites. ADMC-enabled sensing platforms have been demonstrated to realize advanced applications in various fields. Notably, the easily tunable coordination structures of ADMCs bring more opportunities to improve their catalytic performance, further moving toward efficient signal transduction ability. Besides, by leveraging their inherent physicochemical properties and various detection strategies, ADMC-enabled sensing interfaces not only achieve enhanced signal transductions but also show diversified output models. Such superior functions allow ADMC-enabled sensing platforms to access the goal of high-performance detection of trace targets and making significant progress in analytical chemistry.In this Account, we provide an overview of recent progress in atomically dispersed metal-involved interfaces in analytical chemistry. The engineering strategies focused on regulating metal centers, integrating multisite synergy, and tuning charge transport pathways are discussed to boost the catalytic activity and specificity of ADMCs as well as expand their multifunctionality. Combined with various transduction models, including colorimetry, electrochemistry, chemiluminescence, electrochemiluminescence, and photoelectrochemistry, ADMC-based sensors achieve efficient detection of diverse analytes. Specifically, the underlying mechanisms of signal transduction are highlighted. Finally, the perspective and challenges of the ADMC-enabled interface for analytical chemistry are further proposed. We hope that this Account will afford significant inspiration toward the design of ADMCs and the decoding of the improved sensing interfaces.

Dual FeCo single-atom nanozymes with specific oxidase-like activity for sensitive detection of aflatoxin B1

Single-atom nanozymes (SAzymes) with well-defined metal-nitrogen-carbon coordination structures are of great interest for the development of colorimetric biosensing. However, their catalytic efficiency and specificity is restricted due to the limited number of single metal atoms that can serve as catalytic centre. Therefore, the construction of SAzymes with high activity and specificity is vital but remains challenging. To address these issues, we prepared a bimetallic SAzymes with an independent iron and cobalt structure (FeCo/NC), and the oxidase-like activity was enhanced by >112.8% relative to Fe/NC. This preparation strategy increased the amount of single metal atoms loaded, resulting in a strong synergistic effect and proximity-orientation effects due to the unique structure of single Co and Fe atoms coexisting on graphene. The oxidase-mimicking activity of FeCo/NC was specifically enhanced by co doping, although the activities of peroxidase-, superoxide dismutase-, or catalase-like were not significantly affected. In light of these discoveries, as a symbol of the proof-of-concept, FeCo/NC-based colorimetric immunoassays were developed for sensitive detection of aflatoxin B1 (AFB1), achieving a linear range of 0.01-10 ng/mL and a detection limit of 0.005 ng/mL. This study provides a convenient strategy for promoting the catalytic activity and specificity of SAzymes, thereby enhancing their potential in biosensing.

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.

Cobalt Single-Atom Intercalation in Molybdenum Disulfide Enhances Piezocatalytic and Enzyodynamic Activities for Advanced Cancer Therapeutics

Piezoelectric semiconductor nanomaterials have attracted considerable interest in piezocatalytic tumor treatment. However, piezocatalytic therapy encounters obstacles such as suboptimal piezoelectric responses, rapid electron-hole recombination, inefficient energy harvesting, and the complexities of the tumor microenvironment. In this study, sulfur vacancy-engineered cobalt (Co) single-atom doped molybdenum disulfide (SA-Co@MoS2) nanoflowers are strategically designed, which exhibit enhanced piezoelectric effects. Specifically, the introduction of Co single atom not only induces lattice distortion and out-of-plane polarization but also leads to the formation of numerous sulfur vacancies. These changes collectively narrow the intrinsic bandgap of the material, facilitating effective separation and migration of charge carriers, and enabling efficient production of reactive oxygen species under ultrasound stimulation. Additionally, the SA-Co@MoS2 nanoflowers demonstrate improved enzymatic activity and exhibit glutathione depletion capabilities attributed to the mixed valence states of Co, intensifying oxidative stress in tumor cells, and leading to cell cycle arrest and apoptosis, while the inactivation of glutathione peroxidase 4 induces ferroptosis. Both in vitro and in vivo results indicate that SA-Co@MoS2 nanoflowers can significantly eliminate tumor cells. This study offers valuable insights into the exploration of single-atom doping-enhanced piezoelectric sonosensitizers for cancer treatment, potentially paving the way for advancements in the field of piezocatalytic synergistic enzyodynamic therapy.

Magnetic rod-shaped Mn-based MOF as a multi-functional and recyclable platform for dual-mode ratiometric-based nitrite detection

The development is shown of rod-shaped manganese-based metal-organic frameworks (Mn-MOFs) as hot- and cold-adapted oxidase-like nanozymes, with strong magnetic properties. These Mn-MOFs enable highly sensitive detection of nitrite ions, utilizing both convenient colorimetric ratio analysis and a visual instrument-free-based approach compatible with smartphone-based detection. The Mn-MOF showed multi-functional activity, such as cold/hot-adapted and magnetic oxidase-like activity, catalyzing the oxidation of chromogenic substrates 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB). Mn-MOF shows high oxidase activity with Vmax of 1.39 × 10-8 M/s and Km of 0.068 mM for TMB oxidation. Nitrite ions further react with oxTMB to form a yellow color via diazotization resulting in the ratiometric change in absorbance (A652/A461). The color ratio is also quantified through the naked eye and/or smartphone app by analyzing RGB values, providing a rapid, portable, and cost-effective method for on-site detection. When applying Mn-MOF for smartphone-based nitrite detection, it performs excellent detection, with a linear range of 5.0-55.0 µM and a limit of detection of 0.18 µM, superior to most of the oxidase nanozyme-based nitrite sensing platforms. The detection platforms develop sensing probes using a reusable nanozyme that enables highly sensitive and selective detection of nitrite, featuring a broad linear range and a low limit of detection.

Flower-like boron-doped zinc single-atom nanozymes for colorimetric sensing and smartphone-assisted detection of Cr(VI)

With the development of electronics, electroplating, printing, and dyeing industries, environmental pollution caused by hexavalent chromium (Cr(VI)) has become increasingly prominent. Skin contact with Cr (VI) can cause allergies or genetic defects, and inhalation can cause cancer, which is a lasting danger to the environment and the human body. Developing effective strategies to monitor Cr(VI) in environmental water or industrial wastewater can evaluate the degree of water pollution and risk warning, thus helping to prevent the spread of Cr(VI) pollution, promote the protection of water resources and the ecological environment, and ensure human safety and sustainable development. On the basis of the regulation of dopamine, boron-doped zinc single-atom nanozymes (Zn/B-NC SAzymes) with three-dimensional nanoflower morphology were controlled in this work. The introduction of B in Zn/B-NC SAzymes and the high metal loading of Zn (6.5 wt%) led to the formation of more active sites, resulting in the material showing excellent enzyme-like activity. H2O2 decomposed to generate superoxide radicals under the catalysis of Zn/B-NC SAzymes, which then oxidized the substrate 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxTMB. When Cr(VI) was introduced into the sensor system, the color of blue oxTMB is deepened, and the colorimetric method of Cr(VI) was constructed. The linear range is 0.2-40 μM, LOD is 59 nM, and the visual detection of Cr (VI) is performed with the aid of the smartphone. This work not only provides experimental and theoretical guidance for understanding the active centers of Zn-SAzymes and their catalytic processes, but also provides a promising and alternative detection strategy for the rapid and even visual on-site detection of Cr(VI) in aquatic environments, which is of great significance for the control of Cr(VI) pollution in the environment and industrial wastewater.

Ferrous Tungstate Nanomaterials with Excellent Enzyme-Mimicking Activity to Enhance Lateral Flow Immunoassay Sensitivity

Lateral flow immunochromatography (LFIA) with gold nanoparticles (AuNPs) is widely used in the biomedical field as a rapid and simple in vitro detection technique. However, the conventional AuNP-LFIA has limitations in sensitivity and detection range. In this study, nonprecious metal iron-based bimetallic FeWO4 nanomaterials with convenient and excellent enzyme-mimetic catalytic activities were synthesized by a one-pot hydrothermal method. Here, FeWO4 nanomaterials were combined with C-reactive protein (CRP) detection antibodies to form a novel signal-enhancing probe for the analysis of CRP. The probe further achieves significant signal amplification by catalyzing the oxidation reaction of 3-amino-9-ethylcarbazole in the LFIA assay, thereby improving the sensitivity and accuracy of the assay. The application of FeWO4-based LFIA improved the limit of detection of CRP to 19.38 ng/mL after catalytic amplification, which is approximately 30-fold lower than that of the conventional AuNP-LFIA method. In addition, the method demonstrated good stability and reproducibility, providing a promising and prospective strategy for the early diagnosis of inflammatory diseases.

Pine needle-derived oxidase-like Mn nanozymes: sustainable nanozyme, scalable synthesis, and visual and colorimetric nitrite detection

Manganese nanoparticles (Mn NPs) were successfully synthesized using a cost-effective and eco-friendly biogenic approach, with pinus brutia pine needles. The produced Mn NPs were thoroughly characterized using common spectroscopic and microscopic techniques. The Mn NPs exhibited remarkable oxidase-like activity, effectively catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidized form (oxTMB) over a broad temperature range. This robust catalytic performance highlights their versatility and stability under varying thermal conditions, making them suitable for diverse applications. Nitrite forms orange-yellow color via diazotization of the blue oxTMB. An image processing algorithm analyzes the image changes induced by addition of nitrite. Under optimized conditions, the visual-based platform demonstrated a broad linear response for NO₂⁻ detection, spanning 0.0-58.0 uM and the detection limit was 0.11 μM. The visual method demonstrated exceptional sensitivity and recovery for nitrite detection in food samples. Combining simplicity, cost-effectiveness, and eco-friendliness, this instrument-free approach ensures accurate, portable, and point-of-care nitrite detection, ideal for real-world food testing applications.

Engineering Dual Active Sites and Defect Structure in Nanozymes to Reprogram Jawbone Microenvironment for Osteoradionecrosis Therapy

Four to eight percent of patients with head and neck cancer will develop osteoradionecrosis of the jaw (ORNJ) after radiotherapy. Various radiation-induced tissue injuries are associated with reactive oxygen and nitrogen species (RONS) overproduction. Herein, Fe doping is used in VOx (Fe-VOx) nanozymes with multienzyme activities for ORNJ treatment via RONS scavenging. Fe doping can induce structure reconstruction of nanozymes with abundant defect production, including Fe substitution and oxygen vacancies (OVs), which markedly increased multiple enzyme-mimicking activity. Catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) enzyme-like performance of Fe-VOx can effectively reprogram jawbone microenvironment to restore mitochondrial dysfunction and enhance mitophagy. Moreover, the surface plasmon resonance (SPR) effect of Fe-VOx made it a good photothermal nanoagents for inhibiting jaw infection. Thus, this work demonstrated that Fe-VOx nanozymes can efficiently scavenge RONS, activate mitophagy, and inhibit bacteria, which is potential for ORNJ treatment.

Multifunctional MOF: Cold/hot adapted sustainable oxidase-like MOF nanozyme with ratiometric and color tonality for nitrite ions detection

Integrating multiple functionalities into a single entity is highly important, especially when a broad spectrum of application is required. In the present work, we synthesized a novel manganese-based MOF (denoted as UoZ-6) that functions as a cold/hot-adapted and recyclable oxidase nanozyme (Km 0.085 mM) further developed for ratiometric-based colorimetric and color tonality visual-mode detection of nitrite in water and food. Nitrite ions promote the diazotization process of the oxTMB product, resulting in a decay in the absorbance signal at 652 nm and the emergence of a new signal at 461 nm. The dual-absorbance ratiometric platform for nitrite ion detection functions effectively across a wide temperature range (0 °C to 100 °C), offering a linear detection range of 5-45 μM with a detection limit of 0.15 μM using visual-mode. This approach is sensitive, reliable, and selective, making it effective for detecting nitrite ions in processed meat and water.

Co-based carbon material as CYP3A4-like nanozyme with both biocatalytic activity and inhibition behaviors

Up to now, the biocatalytic activity of nanozymes has been extensively studied, while little research focus on their inhibitory behaviors. Here, Co-based carbon material (Co-DMOF) containing abundant carboxylic acid groups was prepared, with defects introduced by COx escape during pyrolysis to achieve controllable activity. As a result, Co-DMOF exhibited biocatalytic activity similar to cytochrome P450 3A4 (CYP3A4) in the metabolism of 1,4-Dihydropyridine (1,4-DHP, a calcium channel blocker). Excitingly, studies on IC50 and drug-drug interaction (DDI) suggested that Co-DMOF had similar inhibitory behaviors to CYP3A4. Moreover, Co-DMOF displayed excellent stability even under high temperature (100 °C), organic solvents, and a wide range of pH (4-9). Additionally, it can be reused for at least 7 times with only slight loss of activity. Therefore, Co-DMOF has great potential to become a low-cost alternative to CYP3A4 for drug dosage guideline, drug metabolism and DDI. This work provides more possibilities for expanding the CYP3A4-like nanozyme library.

Amino-Induced Modulation of Electronic State and Neighboring Site Distance through Second Shell Boosted Catecholase-Mimicking Activity of Electron-Rich Cu Center

Boosting the biomimetic catalytic activity of nanozyme is important for its potential application. One common strategy to achieve this goal mainly focused on manipulating the electronic state of metal site through the first coordination shell to modulate the adsorption/desorption strength of related reactant, intermediate and/or product, but remained challenging. Taking Cu-based catecholase-mimicking nanozyme for example, this work herein reports a different strategy involving amino-induced modulation of electronic state through the second shell to raise the electron density of Cu site, which further triggers the repulsion effect between neighboring geminal Cu centers to increase the Cu─Cu distance. The resulting nanozyme with electron-rich Cu site (DT-Cu) presents a lower work function and an upshifted d-band center in comparison with its counterpart (i.e., relatively electron-deficient TA-Cu), which promotes the electron transfer and enhances the adsorption strengths of Cu site for O2, catechol and H2O2 intermediate. The longer Cu─Cu distance of DT-Cu accelerated the O─O bond dissociation of H2O2 intermediate. This expedites the oxygen reduction process during catecholase-like catalysis, which together with the enhanced O2/H2O2/catechol adsorption corporately boosts the catecholase-like activity of DT-Cu.

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.

Inhibition effect of p-d orbital hybridized PtSn nanozymes for colorimetric sensor array of antioxidants

Rational design of peroxidase (POD)-like nanozymes with high activity and specificity still faces a great challenge. Besides, the investigations of nanozymes inhibitors commonly focus on inhibition efficiency, the interaction between nanozymes-involved catalytic reactions and inhibitors is rarely reported. In this work, we design a p-block metal Sn-doped Pt (p-d/PtSn) nanozymes with the selective enhancement of POD-like activity. The p-d orbital hybridization interaction between Pt and Sn can effectively optimize the electronic structure of PtSn nanozymes and thus selectively enhance POD-like activity. In addition, the antioxidants as nanozymes inhibitors can effectively inhibit the POD-like activity of p-d/PtSn nanozymes, which results in the fact that antioxidants absorbed on the p-d/PtSn surface can hinder the adsorption of hydrogen peroxide. The inhibition type (glutathione as a model molecule) is reversible mixed-inhibition with inhibition constants (Ki' and Ki) of 0.21 mM and 0.03 mM. Finally, based on the varying inhibition levels of antioxidant molecules, a colorimetric sensor array is constructed to distinguish and simultaneously detect five antioxidants. This work is expected to design highly active and specific nanozymes through p-d orbital hybrid engineering, and also provides insights into the interaction between nanozymes and inhibitors.

Regulating Reactive Oxygen Intermediates of Fe-N-C SAzyme via Second-Shell Coordination for Selective Aerobic Oxidation Reactions

Reactive oxygen species (ROS) regulation for single-atom nanozymes (SAzymes), e.g., Fe-N-C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe-N-C containing the same FeN4 but with tunable second-shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe-N-C sample, the second-shell sulfur functionalized Fe-N-C delivered a 2.4-fold increase of oxidase-like activity via the bound Fe=O intermediate. Conversely, free ROS (⋅O2 -) release was significantly reduced after functionalization, down to only 17 % of that observed for Fe-N-C. The detailed characterizations and theoretical calculations revealed that the second-shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe-N-Cs with different second-shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Rapid and Green Fabrication of Nanozyme with Geminal CuN3O Configuration for Efficient Catecholase-Mimicking

Fabrication of nanozyme with catecholase-like catalytic activity faces the great challenge of merging outstanding activity with low cost as well as simple, rapid, and low-energy-consumed production, restricting its industrial applications. Herein, an inexpensive yet robust nanozyme (i.e., DT-Cu) via simple one-step coordination between diaminotriazole (DT) and CuSO4 within 1 h in water at room temperature is constructed. The asymmetric dicopper site with CuN3O configuration for each copper as well as Cu─O bond length of ≈1.83 Å and Cu···Cu distance of ≈3.5 Å in DT-Cu resemble those in catechol oxidase (CO), which ensure its prominent intrinsic activity, outperforming most CO-mimicking nanozymes and artificial homogeneous catalysts. The use of inexpensive DT/CuSO4 in this one-pot strategy endows DT-Cu with only ≈20% cost of natural CO per activity unit. During catalysis, O2 experienced a 4e-dominated reduction process accompanied by the formation of 1O2 and H2O2 intermediates and the product of H2O. Benefiting from the low cost as well as the distinctive structure and superior intrinsic activity, DT-Cu presents potential applications ranging from biocatalysis to analytical detection of biomolecules such as epinephrine and beyond.

Metal-ligand dual-site single-atom nanozyme mimicking urate oxidase with high substrates specificity

In nature, coenzyme-independent oxidases have evolved in selective catalysis using isolated substrate-binding pockets. Single-atom nanozymes (SAzymes), an emerging type of non-protein artificial enzymes, are promising to simulate enzyme active centers, but owing to the lack of recognition sites, realizing substrate specificity is a formidable task. Here we report a metal-ligand dual-site SAzyme (Ni-DAB) that exhibited selectivity in uric acid (UA) oxidation. Ni-DAB mimics the dual-site catalytic mechanism of urate oxidase, in which the Ni metal center and the C atom in the ligand serve as the specific UA and O2 binding sites, respectively, characterized by synchrotron soft X-ray absorption spectroscopy, in situ near ambient pressure X-ray photoelectron spectroscopy, and isotope labeling. The theoretical calculations reveal the high catalytic specificity is derived from not only the delicate interaction between UA and the Ni center but also the complementary oxygen reduction at the beta C site in the ligand. As a potential application, a Ni-DAB-based biofuel cell using human urine is constructed. This work unlocks an approach of enzyme-like isolated dual sites in boosting the selectivity of non-protein artificial enzymes.

Novel Immunosensor Based on Metal Single-Atom Nanozymes with Enhanced Oxidase-Like Activity for Capsaicin Analysis in Spicy Food

Capsaicin (CAP) is a primary indicator for assessing the level of pungency. Herein, iron-based single-atom nanozymes (SAzymes) (Fe/NC) with exceptional oxidase-like activity were used to construct an immunosensor for CAP analysis. Fe/NC could imitate oxidase actions by transforming O2 to •O2- radicals in the absence of hydrogen peroxide (H2O2), which could avoid complex operations and unstable results. By regulating the Fe atom loads, an optimal Fe0.7/NC atom usage rate could improve the catalytic activity (Michaelis-Menten constant (Km) = 0.09 mM). Fe0.7/NC was integrated with goat antimouse IgG by facile mix incubation to develop a competitive enzyme-linked immunosorbent assay (ELISA). Our Fe0.7/NC immunosensing platform is anticipated to outperform the conventional ELISA in terms of stability and shelf life. The proposed immunosensor provided color responses across 0.01-1000 ng/mL CAP concentrations, with a detection limit of 0.046 ng/mL. Fe/NC may have potential as nanozymes for CAP detection in spicy foods, with promising applications in food biosensing.

Colorimetric and SERS dual-mode detection of GSH in human serum based on AuNPs@Cu-porphyrin MOF nanozyme

BACKGROUND

Rapid and accurate detection of glutathione content in human blood plays an important role in real-time tracking of related diseases. Currently, surface-enhanced Raman scattering/spectroscopy (SERS) combined with nanozyme material has been proven to have excellent properties in the detection applications compared to many other methods because of it combines the advantages of trace detection capability of SERS and efficient catalytic activity of nanozymes. However, there are still existing problems in real sample detection, and to achieve quantitative detection is still challenging.

RESULTS

In this study, gold nanoparticles (AuNPs) were synthesized in situ on the surface of two-dimensional Cu-porphyrin metal-organic framework (MOF) nanosheets to produce the AuNPs@Cu-porphyrin MOF nanozyme, which exhibited both oxidase-like activity and SERS detection ability. On one hand, the intrinsic oxidase-like activity of the nanozyme could be inhibited due to the chelation of glutathione (GSH) and Cu, which thus led to the visual color change of the solution. On the other hand, the abundant Raman "hot spots" at the nanogap generated by Au NPs and the internal standard (IS) signal provided by Cu-meso-tetra (4-carboxyphenyl) porphine (Cu-TCPP) MOF improved the sensitivity and quantitative accuracy of detection.

SIGNIFICANCE AND NOVELTY

A dual-mode signal output sensor based on the nanozyme was thus established, which could be used in the trace detection of GSH. Such a dual-mode sensor possesses excellent detection performance, with the advantage of both wide detection range from 1 to 300 μM in the colorimetric detection mode and high sensitivity with LOD of 5 nM in the SERS detection mode, and can be applied to GSH detection in actual serum samples with reliable results.

MOF-based Ag NPs/Co3O4 nanozyme for colorimetric detection of thiophanate-methyl based on analyte-enhanced sensing mechanism

Silver nanoparticles supported on metal-organic framework (ZIF-67)-derived Co3O4 nanostructures (Ag NPs/Co3O4) were synthesized via a facile in situ reduction strategy. The resulting materials exhibited pH-switchable peroxidase/catalase-like catalytic activity. Ag NP doping greatly enhanced the catalytic activity of Ag NPs/Co3O4 towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation and H2O2 decomposition which were 59 times (A652 of oxTMB) and 3 times (A240 of H2O2) higher than that of ZIF-67, respectively. Excitingly, thiophanate-methyl (TM) further enhanced the peroxidase-like activity of Ag NPs/Co3O4 nanozyme due to the formation of Ag(I) species in TM-Ag NPs/Co3O4 and generation of more radicals resulting from strong interaction between Ag NPs and TM. The TM-Ag NPs/Co3O4 nanozyme exhibited lower Km and higher Vmax values towards H2O2 when compared with Ag NPs/Co3O4 nanozyme. A simple, bioelement-free colorimetric TM detection method based on Ag NPs/Co3O4 nanozyme via analyte-enhanced sensing strategy was successfully established with high sensitivity and selectivity. Our study demonstrated that hybrid noble metal NPs/MOF-based nanozyme can be a class of promising artificial nanozyme in environmental and food safety applications.

Mated-Atom Nanozymes with Efficient Assisted NAD+ Replenishment for Skin Regeneration

Excessive accumulation of reduced nicotinamide adenine dinucleotide (NADH) within biological organisms is closely associated with many diseases. It remains a challenge to efficiently convert superfluous and detrimental NADH to NAD+. NADH oxidase (NOX) is a crucial oxidoreductase that catalyzes the oxidation of NADH to NAD+. Herein, M1M2 (Mi=V/Mn/Fe/Co/Cu/Mo/Rh/Ru/Pd, i = 1 or 2) mated-atom nanozymes (MANs) are designed by mimicking natural enzymes with polymetallic active centers. Excitingly, RhCo MAN possesses excellent and sustainable NOX-like activity, with Km-NADH (16.11 μM) being lower than that of NOX-mimics reported so far. Thus, RhCo MAN can significantly promote the regeneration of NAD+ and regulate macrophage polarization toward the M2 phenotype through down-regulation of TLR4 expression, which may help to recover skin regeneration. However, RhRu MAN with peroxidase-like activity and RhMn MAN with superoxide dismutase-like activity exhibit little modulating effects on eczema. This work provides a new strategy to inhibit skin inflammation and promote skin regeneration.

Spatial engineering of single-atom Fe adjacent to Cu-assisted nanozymes for biomimetic O2 activation

The precise design of single-atom nanozymes (SAzymes) and understanding of their biocatalytic mechanisms hold great promise for developing ideal bio-enzyme substitutes. While considerable efforts have been directed towards mimicking partial bio-inspired structures, the integration of heterogeneous SAzymes configurations and homogeneous enzyme-like mechanism remains an enormous challenge. Here, we show a spatial engineering strategy to fabricate dual-sites SAzymes with atomic Fe active center and adjacent Cu sites. Compared to planar Fe-Cu dual-atomic sites, vertically stacked Fe-Cu geometry in FePc@2D-Cu-N-C possesses highly optimized scaffolds, favorable substrate affinity, and fast electron transfer. These characteristics of FePc@2D-Cu-N-C SAzyme induces biomimetic O2 activation through homogenous enzymatic pathway, resembling functional and mechanistic similarity to natural cytochrome c oxidase. Furthermore, it presents an appealing alternative of cytochrome P450 3A4 for drug metabolism and drug-drug interaction. These findings are expected to deepen the fundamental understanding of atomic-level design in next-generation bio-inspired nanozymes.

Synthesis of Spherical Mn2O3 Nanozymes from Different Green Precursors for their Innovative Applications in Catalytic Properties and Bioactivity

Here, spherical Mn2O3 nanozymes were synthesized via a one-step green method using different green precursors, and their physicochemical properties and biological activities were monitored with various green precursors. Powder X-ray diffraction (PXRD) was performed to determine the crystalline properties and phases involved in the formation of cubic Mn2O3 nanozymes. The synthesized nanozymes were spherical and examined by SEM and FESEM studies. All of the samples synthesized using different green precursors exhibited different sizes but similar spherical shapes. Moreover, all green-synthesized nanozymes catalyzed the oxidation reaction of the chromogenic substrate 3,3'5,5' tetramethylbenzidine (TMB) in the absence of H2O2, and A2 (lemon-mediated Mn2O3 nanozymes), which the followed Michaelis-Menten kinetics, showed the best activity. Therefore, A2 (lemon-mediated nanozyme) showed oxidase-mimicking activity with distinct Km and Vmax values calculated by the Lineweaver-Burk plot. Furthermore, the current nanozymes demonstrated a significant ability to kill both Gram-negative and Gram-positive bacteria as well as effectively destroy biofilms under physiological conditions. Moreover, the green-mediated nanozymes also displayed ROS-scavenging activity. Our nanozymes exhibited scavenging activity toward OH and O2-• radicals and metal chelation activity, which were investigated colorimetrically. Therefore, these nanozymes might be used as effective antibacterial agents and also for the consumption of reactive oxygen species.

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.

Biosystem-Inspired Engineering of Nanozymes for Biomedical Applications

Nanozymes with intrinsic enzyme-mimicking activities have shown great potential to become surrogates of natural enzymes in many fields by virtue of their advantages of high catalytic stability, ease of functionalization, and low cost. However, due to the lack of predictable descriptors, most of the nanozymes reported in the past have been obtained mainly through trial-and-error strategies, and the catalytic efficacy, substrate specificity, as well as practical application effect under physiological conditions, are far inferior to that of natural enzymes. To optimize the catalytic efficacies and functions of nanozymes in biomedical settings, recent studies have introduced biosystem-inspired strategies into nanozyme design. In this review, recent advances in the engineering of biosystem-inspired nanozymes by leveraging the refined catalytic structure of natural enzymes, simulating the behavior changes of natural enzymes in the catalytic process, and mimicking the specific biological processes or living organisms, are introduced. Furthermore, the currently involved biomedical applications of biosystem-inspired nanozymes are summarized. More importantly, the current opportunities and challenges of the design and application of biosystem-inspired nanozymes are discussed. It is hoped that the studies of nanozymes based on bioinspired strategies will be beneficial for constructing the new generation of nanozymes and broadening their biomedical applications.

Iron-doped carbon nitride with enhanced peroxidase-like activity for smartphone-based colorimetric assay of total antioxidant capacity

The facile detection of total antioxidant capacity (TAC) is limited by in-situ analysis, because it usually requires complex laboratory equipments. Here, a colorimetric assay for TAC detection is developed based on the peroxidase-like activity of iron-doped carbon nitride (Fe/NC) and the smartphone platform. The peroxidase-like activity of carbon nitride is greatly improved by the introduction of Fe atoms, and the active sites turn to Fe-Nx coordination groups in the Fe/NC. The inhibition mechanism of the chromogenic reaction for different kinds of antioxidants is also studied. The colorimetric assay is fabricated by the relationship of absorbance-color-antioxidant content and applied successfully to the TAC detection of several fruit juicesand commercial beverages. This work not only provides a promising approach for convenient in-situ TAC assay without the use of large instruments, but also expands the application of nanozymes in nutritional value assessment of foods.

Single-atom nanozymes with peroxidase-like activity: A review

Single-atom nanozymes (SANs) are nanomaterials-based nanozymes with atomically dispersed enzyme-like active sites. SANs offer improved as well as tunable catalytic activity. The creation of extremely effective SANs and their potential uses have piqued researchers' curiosity due to their advantages of cheap cost, variable catalytic activity, high stability, and large-scale production. Furthermore, SANs with uniformly distributed active centers and definite coordination structures offer a distinctive opportunity to investigate the structure-activity correlation and control the geometric and electrical features of metal centers. SANs have been extensively explored in photo-, thermal-, and electro-catalysis. However, SANs suffer from the following disadvantages, such as efficiency, non-mimicking of the 3-D complexity of natural enzymes, limited and narrow range of artificial SANs, and biosafety aspects. Among a quite limited range of artificial SANs, the peroxidase action of SANs has attracted significant research attention in the last five years with the aim of producing reactive oxygen species for use in cancer therapy, and water treatment among many other applications. In this review, we explore the recent progress of different SANs as peroxidase mimics, the role of the metal center in enzymatic activity, possible prospects, and underlying limitations in real-time applications.

Cobalt-Nitrogen Co-Doped Carbon as Highly Efficient Oxidase Mimics for Colorimetric Assay of Nitrite

Transition metal-N-doped carbon has been demonstrated to mimic natural enzyme activity; in this study, cobalt-nitrogen co-doped carbon (Co-N-C) nanomaterial was developed, and it could be an oxidase mimic. Firstly, Co-N-C with oxidase-like activity boosts the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to produce the oxidized TMB (oxTMB). And the aromatic primary amino group of oxTMB reacts with nitrite (NO₂^-) to form diazo groups. Based on this background, we developed a cascade system of a Co-N-C-catalyzed oxidation reaction and a diazotization reaction for nitrite determination. The low detection limit (0.039 μM) indicates that Co-N-C is superior compared with the vast majority of previously reported nitrite assays. This study not only provides a novel nanozyme with sufficiently dispersed active sites, but it also further applies it to the determination of nitrite, which is expected to expand the application of nanozymes in colorimetric analysis.

Cascade nanozymatic network mimicking cells with selective and linear perception of H2O2

A single stimulus leading to multiple responses is an essential function of many biological networks, which enable complex life activities. However, it is challenging to duplicate a similar chemical reaction network (CRN) using non-living chemicals, aiming at the disclosure of the origin of life. Herein, we report a nanozyme-based CRN with feedback and feedforward functions for the first time. It demonstrates multiple responses at different modes and intensities upon a single H₂O₂ stimulus. In the two-electron cascade oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), the endogenous product H₂O₂ competitively inhibited substrates in the first one-electron oxidation reaction on a single-atom nanozyme (Co-N-CNTs) and strikingly accelerated the second one-electron oxidation reaction under a micellar nanozyme. As a proof-of-concept, we further confined the nanozymatic network to a microfluidic chip as a simplified artificial cell. It exhibited remarkable selectivity and linearity in the perception of H₂O₂ stimulus against more than 20 interferences in a wide range of concentrations (0.01-100 mM) and offered an instructive platform for studying primordial life-like processes.

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.

Single-Atom Fe Nanozyme with Enhanced Oxidase-like Activity for the Colorimetric Detection of Ascorbic Acid and Glutathione

Single-atom nanozymes (SAzymes) have drawn ever-increasing attention due to their maximum atom utilization efficiency and enhanced enzyme-like activity. Herein, a facile pyrolysis strategy is reported for the synthesis of the iron-nitrogen-carbon (Fe-N-C) SAzyme using ferrocene trapped within porous zeolitic imidazolate framework-8 (ZIF-8@Fc) as a precursor. The as-prepared Fe-N-C SAzyme exhibited exceptional oxidase-mimicking activity, catalytically oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with high affinity (K_m) and fast reaction rate (V_max). Taking advantage of this property, we designed two colorimetric sensing assays based on different interaction modes between small molecules and Fe active sites. Firstly, utilizing the reduction activity of ascorbic acid (AA) toward oxidized TMB (TMBox), a colorimetric bioassay for AA detection was established, which exhibited a good linear range of detection from 0.1 to 2 μM and a detection limit as low as 0.1 μM. Additionally, based on the inhibition of nanozyme activity by the thiols of glutathione (GSH), a colorimetric biosensor for GSH detection was constructed, showing a linear response over a concentration range of 1-10 μM, with a detection limit of 1.3 μM. This work provides a promising strategy for rationally designing oxidase-like SAzymes and broadening their application in biosensing.

Platinum-Nickel Nanoparticles with Enhanced Oxidase-like Activity for Total Antioxidant Capacity Bioassay

While great progress in nanozyme-enabled analytical chemistry has been made, most current nanozyme-based biosensing platforms are based on peroxidase-like nanozymes. However, peroxidase-like nanozymes with multienzymatic activities can influence the detection sensitivity and accuracy, while the use of unstable hydrogen peroxide (H₂O₂) in a peroxidase-like catalytic reaction may result in the reproducibility challenge of sensing signals. We envision that constructing biosensing systems by using oxidase-like nanozymes can address these limitations. Herein, we reported that platinum-nickel nanoparticles (Pt-Ni NPs) with Pt-rich shells and Ni-rich cores possessed high oxidase-like catalytic efficiency, exhibiting a 2.18-fold higher maximal reaction velocity (v_max) than initial pure Pt NPs. The oxidase-like Pt-Ni NPs were applied to develop a colorimetric assay for the determination of total antioxidant capacity (TAC). The antioxidant levels of four bioactive small molecules, two antioxidant nanomaterials, and three cells were successfully measured. Our work not only provides new insights for preparing highly active oxidase-like nanozymes but also manifests their applications for TAC analysis.

A Molybdenum Disulfide Nanozyme with Charge-Enhanced Activity for Ultrasound-Mediated Cascade-Catalytic Tumor Ferroptosis

The deficient catalytic activity of nanozymes and insufficient endogenous H₂ O₂ in the tumor microenvironment (TME) are major obstacles for nanozyme-mediated catalytic tumor therapy. Since electron transfer is the basic essence of catalysis-mediated redox reactions, we explored the contributing factors of enzymatic activity based on positive and negative charges, which are experimentally and theoretically demonstrated to enhance the peroxidase (POD)-like activity of a MoS₂ nanozyme. Hence, an acidic tumor microenvironment-responsive and ultrasound-mediated cascade nanocatalyst (BTO/MoS₂ @CA) is presented that is made from few-layer MoS₂ nanosheets grown on the surface of piezoelectric tetragonal barium titanate (T-BTO) and modified with pH-responsive cinnamaldehyde (CA). The integration of pH-responsive CA-mediated H₂ O₂ self-supply, ultrasound-mediated charge-enhanced enzymatic activity, and glutathione (GSH) depletion enables out-of-balance redox homeostasis, leading to effective tumor ferroptosis with minimal side effects.

Activity Regulating Strategies of Nanozymes for Biomedical Applications

On accounts of the advantages of inherent high stability, ease of preparation and superior catalytic activities, nanozymes have attracted tremendous potential in diverse biomedical applications as alternatives to natural enzymes. Optimizing the activity of nanozymes is significant for widening and boosting the applications into practical level. As the research of the catalytic activity regulation strategies of nanozymes is boosting, it is essential to timely review, summarize, and analyze the advances in structure-activity relationships for further inspiring ingenious research into this prosperous area. Herein, the activity regulation methods of nanozymes in the recent 5 years are systematically summarized, including size and morphology, doping, vacancy, surface modification, and hybridization, followed by a discussion of the latest biomedical applications consisting of biosensing, antibacterial, and tumor therapy. Finally, the challenges and opportunities in this rapidly developing field is presented for inspiring more and more research into this infant yet promising area.

Cobalt Single-Atom Nanozyme Co-Administration with Ascorbic Acid Enables Redox Imbalance for Tumor Catalytic Ablation

The elevated antioxidant defense system in cancer cells can lead to resistance to treatments involving ROS. Breaking the redox balance of the cell system through a "open up the source and regulate the flow" strategy can inhibit the growth of cancer cells and thus design a cancer treatment strategy. Here, cobalt single atom-supported N-doped carbon nanozymes (Co SA-N/C) were synthesized via a simple sacrificial template method, which can mimic the properties of ascorbate oxidase and glutathione oxidase effectively. The synthesized Co SA-N/C can induce the generation of active oxygen by accelerating the oxidation of ascorbic acid (AA) and destroy the endogenous active oxygen scavenging system by consuming the main antioxidant, glutathione (GSH). In-depth in vitro and in vivo investigations indicate that compared with solo therapy, Co SA-N/C together with AA can significantly enhance the anti-tumor efficiency by simultaneously elevating oxidative stress and consuming the overexpressed glutathione (GSH) through the redox reaction catalyzed by Co SA-N/C. This work provides a promising route for developing nanozyme-guided and ascorbate-based antitumor agents.

Molecular insights of nanozymes from design to catalytic mechanism

Emerging as cost-effective potential alternatives to natural enzymes, nanozymes have attracted increasing interest in broad fields. To exploit the in-depth potential of nanozymes, rational structural engineering and explicit catalytic mechanisms at the molecular scale are required. Recently, impressive progress has been made in mimicking the characteristics of natural enzymes by constructing metal active sites, binding pockets, scaffolds, and delicate allosteric regulation. Ingenious in-depth studies have been conducted with advances in structural characterization and theoretical calculations, unveiling the "black box" of nanozyme-catalytic mechanisms. This review introduces the state-of-art synthesis strategies by learning from the natural enzyme counterparts and summarizes the general overview of the nanozyme mechanism with a particular emphasis on the adsorbed intermediates and descriptors that predict the nanozyme activity The emerging activity assessment methodology that illustrates the relationship between electrochemical oxygen reduction and enzymatic oxygen reduction is discussed with up-to-date advances Future opportunities and challenges are presented in the end to spark more profound work and attract more researchers from various backgrounds to the flourishing field of nanozymes.

Intrinsic Light-Activated Oxidase Mimicking Activity of Conductive Polyaniline Nanofibers: A Class of Metal-Free Nanozyme

In recent decades, studies have focused on inorganic nanozymes to overcome the intrinsic drawbacks of bioenzymes due to the demands of improving the reaction conditions and lack of robustness to harsh environmental factors. Many biochemical reactions catalyzed by enzymes require light activation. Light-activated nanozymes have distinct advantages, including being regulated by light stimuli, activating the molecular oxygen to produce reactive oxygen species (ROS) without interfering supplementary oxidants, and often showing a synergistic effect to catalyze some challenging reactions. Only a few studies have been done on this connection. Therefore, it is still a big challenge to develop a nanozyme regulated by light activation. Herein, we uncovered the light-activated oxidase mimicking activity of a conducting polymer polyaniline nanofibers (PANI-NFs). PANI-NFs exhibit intrinsic light-activated brilliant oxidase-like activity, can catalyze the colorless tetramethyl benzidine (TMB) to produce a blue product TMBox, and have a distinct K_m = 0.087 mM and a high V_max = 2.32 μM min^-1 value, measured by using Hanes-Woolf kinetics. We also report the light-activated oxidase activity of some other renowned carbocatalysts graphene oxide and graphitic carbon nitride and compare them with PANI-NFs. This type of property shown by the conductive polymer is amazing. The density functional theory is used to verify the stability and the mode of adsorption of the PANI NFs-TMB composite, which corroborates the experimental results. Furthermore, the current nanozyme demonstrated a significant ability to kill both Gram-negative and Gram-positive bacteria as well as effectively destroy biofilms under physiological conditions. We believe that this work provides the motivation to create a link between optoelectronics and biological activity in the near future.

Oxidase-like ZnCoFe Three-Atom Nanozyme as a Colorimetric Platform for Ascorbic Acid Sensing

Great enthusiasm in single-atom catalysts for various catalytic reactions continues to heat up. However, the poor activity of the existing single/dual-metal-atom catalysts does not meet the actual requirement. In this scenario, the precise design of triple-metal-atom catalysts is vital but still challenging. Here, a triple-atom site catalyst of FeCoZn catalyst coordinated with S and N, which is doped in the carbon matrix (named FeCoZn-TAC/SNC), is designed. The FeCoZn catalyst can mimic the activity of oxidase by activating O₂ into ^•O₂^- radicals by virtue of its atomically dispersed metal active sites. Employing this characteristic, triple-atom catalysts can become a great driving force for the development of novel biosensors featuring adequate sensitivity. First, the property of FeCoZn catalyst as an oxidase-like nanozyme was explored. The obtained FeCoZn-TAC/SNC shows remarkably enhanced catalytic performance than that of FeCoZn-TAC/NC and single/dual-atom site catalysts (FeZn, CoZn, FeCo-DAC/NC and Fe, Zn, Co-SAC/NC) because of trimetallic sites, demonstrating the synergistic effect. Further, the utility of the oxidase-like FeCoZn-TAC/SNC in biosensor field is evaluated by the colorimetric sensing of ascorbic acid. The nanozyme sensor shows a wide concentration range from 0.01 to 90 μM and an excellent detection limit of 6.24 nM. The applicability of the nanozyme sensor in biologically relevant detection was further proved in serum. The implementation of TAC in colorimetric detection holds vast promise for further development of biomedical research and clinical diagnosis.

Fully-Exposed Pd Cluster Catalyst: An Excellent Catalytic Antibacterial Nanomaterial

Exploring antibacterial nanomaterials with excellent catalytic antibacterial properties has always been a hot research topic. However, the construction of nanomaterials with robust antibacterial activity at the atomic level remains a great challenge. Here a fully-exposed Pd cluster atomically-dispersed on nanodiamond-graphene (Pd_n /ND@G) with excellent catalytic antibacterial properties is reported. The fully-exposed Pd cluster nanozyme provides atomically-dispersed Pd cluster sites that facilitate the activation of oxygen. Notably, the oxidase-like catalytic performance of the fully-exposed Pd cluster nanozyme is much higher than that of Pd single-atom oxidase mimic, Pd nanoparticles oxidase mimic and even the previously reported palladium-based oxidase mimics. Under the density functional theory (DFT) calculations, the Pd cluster sites can efficiently catalyze the decomposition of oxygen to generate reactive oxygen species, resulting in strong antibacterial properties. This research provides a valuable insight to the design of novel oxidase mimic and antibacterial nanomaterial.