'Laccase-like' properties of coral-like silver citrate micro-structures for the degradation and determination of phenolic pollutants and adrenaline

A stable colorimetric biosensor for highly selective detection of malathion residue in food based on aptamer-regulated laccase-mimic activity

Malathion causes a serious threat to human health due to its widespread use in the environment. Herein, a novel and stable smartphone-integrated colorimetric biosensor for malathion detection is firstly established based on aptamer-enhanced laccase-mimicking activity. The results indicate that the M17-F aptamer can increase the affinity of Ag2O nanoparticles to the substrate 2,4-dichlorophenol and enhance their laccase-mimicking activity. Thus, abundant semiquinone radicals are produced in the catalytic system, which are combined with chromogenic agent to generate dark red products. The corresponding RGB values for the colour change of the solution can be easily obtained using smartphones, which is used for the rapid detection of malathion. The established biosensor for malathion has a limit of detection as low as 5.85 nmol·L-1, and displays good selectivity for other competitive pesticides. Moreover, further studies have verified the applicability of the biosensor in actual samples, indicating that it may have the potential for application in malathion detection in food.

Nanozyme-Inhibited SERS Multichannel Paper-Based Sensor Array for the Quantification and Identification of Biothiols and Cancer Cells Based on Three Ag-Based Nanomaterials

Biothiols play essential roles in maintaining normal physiological functions, resisting oxidative stress, and protecting cell health. Establishing an effective and reliable sensor array for the accurate quantification and discrimination of diverse biothiols is extremely meaningful. In this work, Ag/Mn3O4, Ag3PO4, and Ag3Cit with excellent oxidase-mimetic activity and surface-enhanced Raman scattering (SERS)-enhanced features have been prepared and loaded onto Whatman filter paper (WFP) to build SERS paper chips as three sensing channels, which can induce 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to SERS-active reporters (TMBox) and concurrently generate prominent SERS signals. Nevertheless, the addition of biothiols can suppress conversion from TMB to TMBox, which can cause the reduction of the SERS signal from TMBox. Interestingly, each SERS sensing channel can generate different TMBox signals' variations due to differences in the oxidative inhibition abilities of diverse biothiols and exclusive properties of each paper chip, which can be plotted as specific fingerprint patterns of each biothiol and further translated into intuitive two-dimensional (2D) clustering profiles through linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA) techniques for precise identification of these six biothiols with the minimum concentration of 1 μM. More importantly, this SERS sensor array is exploited for the precise quantification of intracellular glutathione (GSH), and can differentiate between normal and cancer cells based on different intracellular GSH contents and even identify different types of tumor cells, demonstrating its powerful application prospects in disease diagnosis.

Patterned Au@Ag nanoarrays with electrically stimulated laccase-mimicking activity for dual-mode detection of epinephrine

Epinephrine (EP) is a crucial neurotransmitter in the central nervous system. However, an abnormal level of EP in biological fluids can lead to various diseases. Therefore, it is essential to rapidly and accurately detect EP content. Herein, electrically stimulated patterned Au@Ag nanoarrays with laccase-mimicking activity were designed for the dual-mode detection of EP concentration. The patterned Au@Ag nanoarrays exhibit excellent electrochemical properties and electrically stimulated laccase-mimicking activity. They provide sensitive electrochemical responses for detecting EP content. Simultaneously, the Au@Ag nanoarrays can catalyze the oxidation of EP, enabling its detection through a colorimetric process. This dual-mode approach achieves the detection of EP content over a wide linear range of 0.5-200 μM, with a low detection limit of 0.152 μM. Furthermore, the utility of these nanoarrays for sensing EP in human serum was evaluated. This work provides a convenient method using patterned nanozyme array for the visible, rapid and accurate detection of EP content. It provides the important implication for the development of portable and reliable on-site analytical instruments.

Boosting the LAC-like activity of tetrapeptide capped copper nanoparticle-based nanozymes for colorimetric determination of adrenaline

Enzymatic activity is important for a variety of technological applications, but the limited stability and complex structures of enzymes often limit their use. Therefore, designing powerful nanomaterial catalysts that are more stable and have higher catalytic activity than natural catalysts has been the pursuit of biotechnology. Here, inspired by electron transfer and the active site of laccase (LAC), four types of copper particles with LAC-like activity were synthesized using a simple hydrothermal method. Copper particles coated with the L-phenylalanine (F)-L-phenylalanine (F)-L-cysteine (C)-L-histidine (H) tetrapeptide exhibited higher LAC-like activity compared to those coated with a CH dipeptide, C, and H. This enhancement could be attributed to the higher structural homology and amino acid composition similarity with the natural LAC active center. The FFCH@CuNP nanozyme was employed for adrenaline detection, and it demonstrated outstanding activity, stability, and recyclability. Additionally, a method for the quantitative detection of adrenaline was established using a smartphone based on the FFCH@CuNP nanozymes. And the FFCH@CuNPs exhibited excellent sensitivity and specificity to adrenaline in a saliva-based test. Therefore, this work provides a reasonable pathway for the design of catalysts for future biotechnological and industrial applications.

A dual-functional single-atom Fe nanozyme-based sensitive colorimetric sensor for tannins quantification in brandy

Traditional methods of tannins detection suffer from complex pretreatment, long detection time, and limited sensitivity. Modern techniques like liquid chromatography require expertise, involve tedious result processing, and lack effective data visualization. Therefore, there is a need for an alternative detection method that simplifies pretreatment and detection steps, reduces analysis time, and provides visualized results. In this study, a novel colorimetric sensor based on single-atom Fe nanozyme (Fe@CN-20) was developed for tannins detection. Fe@CN-20 exhibited laccase-like and oxidase-like activities, enabling simultaneous oxidation of tannins and a substrate called TMB. Tannins competed with TMB, allowing quantification of tannins content. The Fe@CN-20/TMB system provided a detection range of 5-100 mg/L tannic acid, with a detection limit of 0.13 mg/L (S/N = 3). Analysis time was approximately 30 min. The platform successfully quantified tannins in brandy, showing less than 5% deviation compared to the standard method. The sensor was simple, sensitive, rapid, and provided strong visualization.

Biomimetic Electrochemical Sensor Based on Single-Atom Nickel Laccase Nanoenzyme for Quercetin Detection

Laccase, a member of the copper oxidase family, has been used as a green catalyst in the environmental and biochemical industries. However, laccase nanoenzymes are limited to materials with copper as the active site, and noncopper laccase nanoenzymes have been scarcely reported. In this study, inspired by the multiple copper active sites of natural laccase and the redox Cu2+/Cu+ electron transfer pathway, a novel nitrogen/nickel single-atom nanoenzyme (N/Ni SAE) with high laccase-like activity was prepared by inducing Ni and dopamine precipitation through a controllable water/ethanol interface reaction. Compared with that of laccase, the laccase activity simulated by N/Ni SAE exhibited excellent stability and reusability. The N/Ni SAE exhibited a higher efficiency toward the degradation of 2,4-dichlorophenol, hydroquinone, bisphenol A, and p-aminobenzene. In addition, a sensitive electrochemical biosensor was constructed by leveraging the laccase-like activity of N/Ni SAE; this sensor offered unique advantages in terms of catalytic activity, selectivity, stability, and repeatability. Its detection ranges for quercetin were 0.01-0.1 and 1.0-100 μM, and the detection limit was 3.4 nM. It was also successfully used for the quantitative detection of quercetin in fruit juices. Therefore, the single-atom biomimetic nanoenzymes prepared in this study promote the development of a new electrochemical strategy for the detection of various bioactive molecules and show great potential for practical applications.

Design of bifunctional ultrathin MnO2 nanofilm with laccase-like activity for sensing environmental pollutants containing phenol groups

Laccase-catalyzed oxidative reactions are increasingly examined as a reliable approach to environmental analysis and remediation, and it is urgent to widen metal category to compensate huge gap in the number of studies on copper- and non-copper laccase mimics. Herein, two-dimensional ultrathin MnO2 nanofilm (Mn-uNF) was designed via a chemical deposition and alkali etching process. Similar to Cu-laccase, Mn-uNF can oxidize phenols via a one-electron-transfer reaction of Mn(III) and accelerate the MnIII/MnIV state cycle through an unconventional oxygen reduction process. The excellent laccase-like performance of Mn-uNF can be ascribed to the abundant atomically dispersed Vo-assisted Mn(III) and surface -OH species, which was confirmed by characterizations and DFT calculation. Further, a facile dual-function colorimetric platform was designed for array sensing of o-, m-, and p-dihydroxybenzene isomers and one-step discrimination of tetracyclines containing phenol groups. These findings provide reasonable guidance for the design of a nanozyme with active Mn sites as a new family member of highly efficient copper-free laccase mimics.

Metal-organic frameworks for enzyme immobilization and nanozymes: A laccase-focused review

Laccases are natural catalysts with remarkable catalytic activity. However, their application is limited by their lack of stability. Metal-organic frameworks (MOFs) have emerged as a promising alternative for enzyme immobilization. Enzymes can be immobilized in MOFs via two approaches: postsynthetic immobilization and in situ immobilization. In postsynthetic immobilization, an enzyme is embedded after MOF formation by covalent interactions or adsorption. In contrast, in in situ immobilization, a MOF is formed in the presence of an enzyme. Additionally, MOFs have exhibited intrinsic enzyme-like activity. These materials, known as nanozymes when they have the ability to replace enzymes in certain catalytic processes, have multiple key advantages, such as low cost, easy preparation, and large surface areas. This review presents a general overview of the most recent advances in both enzyme@MOF biocatalysts and MOF-based nanozymes in different applications, with a focus on laccase, which is one of the most widely investigated enzymes with excellent industrial potential.

Carbon-coated copper nanocrystals with enhanced peroxidase-like activity for sensitive colorimetric determination of 2,4-dinitrophenylhydrazine

Carbon-coated copper nanocrystals (CuNCs) with peroxidase-like activity were hydrothermally prepared by using copper acetate, citric acid (CA) and histidine (His) as the precursors. Various shaped CuNCs, including urchin-like, slab-like and spherical appearance were facilely prepared by addition of different amount of NaNO2 in the precursor solutions. When 3,3',5,5'-tetramethylbenzidine (TMB) was used as the substrate, the CuNCs with urchin-like appearance have greatest peroxidase-like activity and their Michaelis-Menten constant (Km) and the maximum rate constant (νmax) are respectively 8.8 and 1.2 times higher than that obtained from horseradish peroxidase (HRP). The production of reactive oxygen species (ROS) was confirmed by radical quenching and electron spin resonance (ESR) tests. Subsequent studies have found that the CuNCs catalyzed color reaction of TMB can be selectively quenched by the environmental pollutant 2,4-dinitrophenylhydrazine (2,4-DNPH). Thus a new colorimetric method for the determination of 2,4-DNPH with a linear range of 0.60-20 µM was developed and a limit of detection (LOD) as low as 0.166 µM was achieved. The results obtained not only reveal the tunability of the peroxidase-like activity of Cu-based nanomaterials, but also provide a new method for the sensitive determination of environmental contaminate.

Selective sensing of catechol based on a fluorescent nanozyme with catechol oxidase activity

Nanozymes, an unusual category of nanomaterials possessing enzymatic properties, and have generated considerable interest regarding their application feasibilities on several important fronts. In the present work, an innovative sensing device for catechol was established ground on a fluorescent nanozyme (Cu-BDC-NH2) that exhibited catechol oxidase activity. The fluorescent nanozyme combines both functions of catechol recognition and response signal output, and can realize the sensing of catechol without the addition of other chromogenic agents. In the existence of Cu-BDC-NH2, catechol can be oxidized efficiently to produce quinones or polymers with strong electron absorption capacity, which immediately results in efficient fluorescence quenching of Cu-BDC-NH2. However, other common phenolic compounds, such as phenol, the other two diphenols (hydroquinone and resorcinol), phloroglucinol, and chlorophenol, do not result in efficient fluorescence quenching of Cu-BDC-NH2. The method shows a nice linear relationship between catechol concentration prep the fluorescence intensity of Cu-BDC-NH2 in the scope of 0-10 μM, with a detection limit of 0.997 μM. The detection of catechol in actual water samples has also achieved the satisfactory consequences, which provides a new strategy for the convenient and selective detection of catechol.

Tris-Copper Nanozyme as a Novel Laccase Mimic for the Detection and Degradation of Phenolic Compounds

Phenolic compounds are one of the main organic pollutants in the environment that can seriously affect ecosystems, even at very low concentrations. Due to the resistance of phenolic compounds to microorganisms, conventional biological treatment methods face challenges in effectively addressing this pollution problem. In this study, a novel laccase mimic (Tris-Cu nanozyme) is prepared using a simple and rapid synthesis strategy based on the coordination of copper ions and amino groups in Tris(hydroxymethyl)aminomethane (Tris). It is found that the Tris-Cu nanozyme exhibits good catalytic activity against a variety of phenolic compounds, the Km, Vmax and Kcat are determined to be 0.18 mM, 15.62 μM·min-1 and 1.57 × 107 min-1 using 2,4-dichlorophenol (2,4-DP) as the substrate, respectively. Then, based on the laccase-like activity of the Tris-Cu nanozyme, a novel colorimetric method for 2,4-DP (the limit of detection (LOD) = 2.4 μM, S/N = 3) detection in the range of 10-400 μM was established, and its accuracy was verified by analyzing tap and lake water samples. In addition, the Tris-Cu nanozyme shows excellent removal abilities for six phenolic compounds in experiments. The removal percentages for 2,4-DP, 2-chlorophenol (2-CP), phenol, resorcinol, 2,6-dimethoxyphenol (2,6-DOP), and bisphenol A (BPA) are 100%, 100%, 100%, 100%, 87%, and 81% at 1 h, respectively. In the simulated effluent, the Tris-Cu nanozyme maintains its efficient catalytic activity towards 2,4-DP, with a degradation percentage of 76.36% at 7 min and a reaction rate constant (k0) of 0.2304 min-1. Therefore, this metal-organic complex shows promise for applications in the monitoring and degrading of environmental pollutants.

Nucleic acid-functionalized nanozymes and their applications

Nanozymes are inorganic, organic and metal-organic framework nanoparticles that reveal catalytic functions by emulating native enzyme activities. Recently, these nanozymes have attracted growing scientific interest, finding diverse analytical and medical applications. However, the catalytic activities and functions of nanozymes are limited, due to the lack of substrate binding sites that concentrate on the substrate at the catalytic site (molarity effect), introduce substrate specificity and allow functional complexity of the catalysts (cascaded, switchable and cooperative catalysis). The modification of nanozymes with functional nucleic acids provides means to overcome these limitations and engineer nucleic acid/nanozyme hybrids for diverse applications. This is exemplified with the synthesis of aptananozymes, which are supramolecular aptamer-modified nanozymes. Aptananozymes exhibit combined specific binding and catalytic properties that drive diverse chemical transformations, revealing enhanced catalytic activities, as compared to the separated nanozyme/aptamer constituents. Relationships of structure-catalytic functions in the aptananozyme constructs are demonstrated. In addition, modification of nanozymes exhibiting multimodal catalytic functions with aptamers allows the engineering of nanozyme-based bioreactors for cascaded catalysis. Also, the functionalization of reactive oxygen species (ROS)-generating nanozymes with cancer cell-recognizing aptamers yields aptananozymes for targeted chemodynamic treatment of cancer cells and cancer tumors elicited in mice. Finally, nucleic acid-modified enzyme (glucose oxidase)-loaded metal-organic framework nanoparticles yield switchable biocatalytic nanozymes that drive the ON/OFF biocatalyzed oxidation of Amplex Red, dopamine or the generation of chemiluminescence. Herein, future challenges of the topic are addressed.

Construction of bacterial laccase displayed on the microbial surface for ultrasensitive biosensing of phenolic pollutants with nanohybrids-enhanced performance

Although bacterial laccase (BLac) has many advantages including short fermentation period and adaptable activity to wide temperature and pH ranges, it is of challenge and significance to apply BLac to the biosensors, due to the intracellular secretion and poor electron transfer efficiency of BLac. Here, cell surface-displayed BLac (CSDBLac) was successfully constructed as whole-cell biocatalyst through microbial surface display technology, eliminating the mass transfer restriction and laborious purification steps. Meanwhile, MXenes/polyetherimide-multiwalled carbon nanotubes (MXenes/PEI-MWCNTs) nanohybrids were designed to immobilize CSDBLac and improve their electrochemical activity. Then, an electrochemical biosensor was successfully constructed to detect common phenolic pollutants (catechol and hydroquinone) by the co-immobilization of CSDBLac and MXenes/PEI-MWCNTs nanohybrids onto a glassy carbon electrode. Subsequently, it was successfully applied to the water samples assay with good reliability and repeatability. This work innovatively used BLac and nanohybrid as the core elements of biosensor, which not only effectively solved the application bottleneck of BLac on biosensors, but also dramatically promote the electro transfer efficiency between whole-cell biocatalyst and electrode. This method is of profound meanings for significantly improving the performance of phenolic biosensors and other biosensors from the origin.

One stone, two birds: A Cu-S cluster as a laccase-mimicking nanozyme and sulfite activator for phenol remediation in marine environments

Phenols are infamous pollutants in marine environments and present a grave danger to human health, which makes their efficient detection and removal serious issues. Colorimetry is a simple method for detecting phenols in water because phenols can be oxidized by natural laccase and generate a brown product. However, high cost and poor stability impede the wide-spread implementation of natural laccase in phenol detection. To reverse this adverse situation, a nanoscale Cu-S cluster, Cu₄(MPPM)₄ (Cu₄S₄, MPPM = 2-mercapto-5-n-propylpyrimidine), is synthesized. As a stable and inexpensive nanozyme, Cu₄S₄ shows excellent laccase-mimicking activity and prompts the oxidation of phenols. This characteristic makes Cu₄S₄ a perfect option for phenol detection with colorimetry. In addition, Cu₄S₄ also exhibits sulfite activation properties. It can degrade phenols and other pollutants with advanced oxidation processes (AOPs). Theoretical calculations show good laccase-mimicking and sulfite activation properties originating from appropriate interactions between Cu₄S₄ and substrates. We anticipate that the phenol detection and degradation characteristics of Cu₄S₄ make it a promising material to be used for practical phenol remediation in water environments.

Supramolecular assembly of benzophenone alanine and copper presents high laccase-like activity for the degradation of phenolic pollutants

Laccases are multicopper oxidases of significant importance for the degradation of phenolic pollutants. Because of the inherent defects of natural laccases in practical applications, herein, we discovered highly effective and non-cytotoxic laccase-like metallo-nanofibers based on the supramolecular assembly of single unnatural amino acid, benzophenone-alanine (BpA), in combination with copper ions. Structural analysis revealed that the catalytic BpA-Cu nanofibers possess a Cu(I)-Cu(II) electron transfer system similar to that in natural laccase. Our BpA-Cu nanofibers exhibit 4 times higher substrate affinity and 24% higher catalytic efficiency than the well-known high-performance industrialized laccase (Novozym 51003) in 2,4-dichlorophenol degradation. In addition, the BpA-Cu nanofibers were demonstrated to be stable (>75% residual activity) in long-term storage at a wide range of pH, ionic strength, temperature, ethanol, and water sample, and to be readily recovered for pollutant degradation, keeping 83% of the laccase activity after 10 catalytic recycles. Remarkably, the nanofibers displayed a wide substrate spectrum, detecting and degrading a variety of phenolic pollutants with high activity than other laccase mimics reported in the literature. Furthermore, the biocompatibility of the material was proved with cultured cells. These findings demonstrated the potential of BpA-Cu nanofibers in mimicking laccases for environmental remediation.

Nanozyme-based pollutant sensing and environmental treatment: Trends, challenges, and perspectives

Nanozymes are defined as nanomaterials exhibiting enzyme-like properties, and they possess both catalytic functions and nanomaterial's unique physicochemical characteristics. Due to the excellent stability and improved catalytic activity in comparison to natural enzymes, nanozymes have established a wide base for applications in environmental pollutants monitoring and remediation. Nanozymes have been applied in the detection of heavy metal ions, molecules, and organic compounds, both quantitatively and qualitatively. Additionally, within the natural environment, nanozymes can be employed for the degradation of organic and persistent pollutants such as antibiotics, phenols, and textile dyes. Further, the potential sphere of applications for nanozymes traverses from indoor air purification to anti-biofouling agents, and even they show promise in combatting pathogenic bacteria. However, nanozymes may have inherent toxicity, which can restrict their widespread utility. Thus, it is important to evaluate and monitor the interaction and transformation of nanozymes towards biosphere damage when employed within the natural environment in a cradle-to-grave manner, to assure their utmost safety. In this context, various studies have concluded that the green synthesis of nanozymes can efficiently overcome the toxicity limitations in real life applications, and nanozymes can be well utilized in the sensing and degradation of several toxic pollutants including metal ions, pesticides, and chemical warfare agents. In this seminal review, we have explored the great potential of nanozymes, whilst addressing a range of concerns, which have often been overlooked and currently restrict widespread applications and commercialization of nanozymes.

Aptamer-Functionalized Ce4+-Ion-Modified C-Dots: Peroxidase Mimicking Aptananozymes for the Oxidation of Dopamine and Cytotoxic Effects toward Cancer Cells

Aptamer-functionalized Ce⁴⁺-ion-modified C-dots act as catalytic hybrid systems, aptananozymes, catalyzing the H₂O₂ oxidation of dopamine. A series of aptananozymes functionalized with different configurations of the dopamine binding aptamer, DBA, are introduced. All aptananozymes reveal substantially enhanced catalytic activities as compared to the separated Ce⁴⁺-ion-modified C-dots and aptamer constituents, and structure-catalytic functions between the structure and binding modes of the aptamers linked to the C-dots are demonstrated. The enhanced catalytic functions of the aptananozymes are attributed to the aptamer-induced concentration of the reaction substrates in spatial proximity to the Ce⁴⁺-ion-modified C-dots catalytic sites. The oxidation processes driven by the Ce⁴⁺-ion-modified C-dots involve the formation of reactive oxygen species (^•OH radicals). Accordingly, Ce⁴⁺-ion-modified C-dots with the AS1411 aptamer or MUC1 aptamer, recognizing specific biomarkers associated with cancer cells, are employed as targeted catalytic agents for chemodynamic treatment of cancer cells. Treatment of MDA-MB-231 breast cancer cells and MCF-10A epithelial breast cells, as control, with the AS1411 aptamer- or MUC1 aptamer-modified Ce⁴⁺-ion-modified C-dots reveals selective cytotoxicity toward the cancer cells. In vivo experiments reveal that the aptamer-functionalized nanoparticles inhibit MDA-MB-231 tumor growth.

Aptamer-Modified Au Nanoparticles: Functional Nanozyme Bioreactors for Cascaded Catalysis and Catalysts for Chemodynamic Treatment of Cancer Cells

Polyadenine-stabilized Au nanoparticles (pA-AuNPs) reveal dual nanozyme catalytic activities toward the H₂O₂-mediated oxidation of dopamine to aminochrome and toward the aerobic oxidation of glucose to gluconic acid and H₂O₂. The conjugation of a dopamine-binding aptamer (DBA) to the pA-AuNPs yields aptananozyme structures catalyzing simultaneously the H₂O₂-mediated oxidation of dopamine to aminochrome through the aerobic oxidation of glucose. A set of aptananozymes consisting of DBA conjugated through the 5'- or 3'-end directly or spacer bridges to pA-AuNPs were synthesized. The set of aptananozymes revealed enhanced catalytic activities toward the H₂O₂-catalyzed oxidation of dopamine to dopachrome, as compared to the separated pA-AuNPs and DBA constituents, and structure-function relationships within the series of aptananozymes were demonstrated. The enhanced catalytic function of the aptananozymes was attributed to the concentration of the dopamine at the catalytic interfaces by means of aptamer-dopamine complexes. The dual catalytic activities of aptananozymes were further applied to design bioreactors catalyzing the effective aerobic oxidation of dopamine in the presence of glucose. Mechanistic studies demonstrated that the aptananozymes generate reactive oxygen species. Accordingly, the AS1411 aptamer, recognizing the nucleolin receptor associated with cancer cells, was conjugated to the pA-AuNPs, yielding a nanozyme for the chemodynamic treatment of cancer cells. The AS1411 aptamer targets the aptananozyme to the cancer cells and facilitates the selective permeation of the nanozyme into the cells. Selective cytotoxicity toward MDA-MB-231 breast cancer cells (ca. 70% cell death) as compared to MCF-10A epithelial cells (ca. 2% cell death) is demonstrated.

Lighting Up Agricultural Sustainability in the New Era through Nanozymology: An Overview of Classifications and Their Agricultural Applications

With the concept of sustainable agriculture receiving increasing attention from humankind, nanozymes, nanomaterials with enzyme-like activity but higher environmental endurance and longer-term stability than natural enzymes, have enabled agricultural technologies to be reformative, economic, and portable. Benefiting from their multiple catalytic activities and renewable nanocharacteristics, nanozymes can shine in agricultural scenarios using enzyme engineering and nanoscience, acting as sustainable toolboxes to improve agricultural production and reduce the risk to agricultural systems. Herein, we comprehensively discuss the classifications of nanozymes applied in current agriculture, including peroxidase-like, oxidase-like, catalase-like, superoxide dismutase-like, and laccase-like nanozymes, as well as their biocatalytic mechanisms. Especially, different applications of nanozymes in agriculture are deeply reviewed, covering crop protection and nutrition, agroenvironmental remediation and monitoring, and agroproduct quality monitoring. Finally, the challenges faced by nanozymes in agricultural applications are proposed, and we expect that our review can further enhance agricultural sustainability through nanozymology.

A novel Apt-SERS platform for the determination of cardiac troponin I based on coral-like silver-modified magnetic substrate and BCA method

As a kind of acute cardiovascular disease, acute myocardial infarction (AMI) endangers human's life and fitness seriously. The detection of cardiac troponin I (cTnI), a biomarker of AMI, is the key to early medical prognosis and treatment. Surface-enhanced Raman spectroscopy is viewed to be an effective approach for detection of low-concentration substances, and aptamers are regarded to be effective fragments to recognize proteins specifically. In this work, a magnetic nanoparticle substrate coated with coral-like nano-silver was prepared, and the aptamer-modified substrate Fe₃O₄@PEI/Ag NC-Apt was used as magnetic capture probe. Combined with BCA method and SERS detection technology, an Apt-SERS platform was successfully constructed and used for high sensitivity quantitative detection of protein. Taking cTnI as the target, the detection range of the proposed Apt-SERS platform was 0.001-100 ng mL^-1, and the estimated detection of limit (LOD) was 0.23 pg mL^-1. The recovery and relative standard deviations (RSD) of spiked experiment in human serum samples were 92-106% and 3.8-10.1%, respectively. The platform combining BCA method and SERS provides a high sensitivity and good reproducibility method for cTnI detection, which offers a new method for the specific detection and analysis of proteins.

Enhanced laccase production by mutagenized Myrothecium verrucaria using corn stover as a carbon source and its potential in the degradation of 2-chlorophen

Chlorophenols are widely used in industry and are known environmental pollutants. The degradation of chlorophenols is important for environmental remediation. In this study, we evaluated the biodegradation of 2-chlorophenol using crude laccase produced by Myrothecium verrucaria. Atmospheric and room temperature plasma technology was used to increase laccase production. The culture conditions of the M-6 mutant were optimized. Our results showed that corn stover could replace glucose as a carbon source and promote laccase production. The maximum laccase activity of 30.08 U/mL was achieved after optimization, which was a 19.04-fold increase. The biodegradation rate of 2-chlorophenol using crude laccase was 97.13%, a positive correlation was determined between laccase activity and degradation rate. The toxicity of 2-CP was substantially reduced after degradation by laccase solution. Our findings show the feasibility of the use of corn stover in laccase production by M. verrucaria mutant and the subsequent biodegradation of 2-chlorophenol using crude laccase.

An efficient differential sensing strategy for phenolic pollutants based on the nanozyme with polyphenol oxidase activity

To realize the efficient differential sensing of phenolic pollutants in sewage, a novel sensing strategy was successfully developed based on one nanozyme (GMP-Cu) with polyphenol oxidase activity. Phenolic pollutants can be oxidized by GMP-Cu, and the oxidation products reacts subsequently with 4-aminoantipyrine to produce a quinone-imine compound. The absorption spectra of final quinone-imine products resulted from different phenolic pollutants showed obvious differences, which were due to the interaction difference between GMP-Cu and phenolic pollutants, as well as the different molecular structures of the quinone-imine products from different phenolic pollutants. Based on the difference of absorption spectra, a novel differential sensing strategy was developed. The genetic algorithm was used to select the characteristic wavelengths at different enzymatic reaction times, HCA and PLS-DA algorithms were utilized for the discriminant sensing of seven representative phenolic pollutants, including hydroquinone, resorcinol, catechol, resorcinol, phenol, p-chlorophenol, and 2,4-dichlorophenol. Scientific wavelength selection algorithm and recognition algorithm resulted in the successful identification of phenolic pollutants in sewage with a discriminant accuracy of 100%, and differentiation of the phenolic pollutants regardless of their concentration. These results indicate that sensing strategy can be used as an effective tool for the efficient identification and differentiation of phenolic pollutants in sewage.

Bioinspired laccase-mimicking catalyst for on-site monitoring of thiram in paper-based colorimetric platform

A long-standing goal has been to create artificial enzymes with natural enzyme-like catalytic activity. Herein, a laccase-mimicking catalyst (GSH-Cu) is designed by simulating the copper active sites and spatial amino acid microenvironment of natural enzymes. In particular, the engineered GSH-Cu shows a catalytic function that conforms to Michaelis-Menten kinetics of natural laccase. The high catalytic activity of GSH-Cu can be easily inhibited by thiram through surface passivation to produce copper nanoparticles. We demonstrate that the developed GSH-Cu with high stability and recyclability can be used to fabricate effective colorimetric sensor for sensitive detection of thiram. The resulting absorption intensity can be employed to quantify thiram in the range of 2.5-250 ng mL^-1, which meets the detection requirement in fruit. Bestowed with the feasibility analysis of colorimetric output, a portable platform is designed by integrating GSH-Cu based test paper with a conventional smartphone for conveniently on-site quantified thiram. The proposed strategy about engineering enzyme-mimicking catalysts with excellent catalytic performance will open avenues for boosting the sensing application.

Heparin-enhanced peroxidase-like activity of iron-cobalt oxide nanosheets for sensitive colorimetric detection of trypsin

Iron-cobalt oxide nanosheets (FeCo-ONSs) were proved to have intrinsic peroxidase-like activity. Additionally, the peroxidase-like activity of FeCo-ONSs toward the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) was dramatically enhanced after heparin addition due to the stronger affinity toward TMB. Protamine combines with heparin, so the promotion of peroxidase-like activity of FeCo-ONSs with heparin was suppressed. With the addition of trypsin, protamine was hydrolyzed and the enhancement effect of catalytic activity of FeCo-ONSs was recovered. Based on above process, a sensitive colorimetric platform for trypsin activity determination was constructed through measuring the absorbance of produced oxTMB at 652 nm, providing a linear detection range of 5 to 500 ng/mL and a low detection limit of 2.8 ng/mL. The method was applied to trypsin determination in real samples (human urine sample and multienzyme tablet sample) with satisfactory results, illustrating the potential application of this biosensor.

Iron single-atom anchored N-doped carbon as a 'laccase-like' nanozyme for the degradation and detection of phenolic pollutants and adrenaline

To solve the inherent defects of laccase, the first iron single-atom anchored N-doped carbon material (Fe₁@CN-20) as a laccase mimic was disclosed. The FeN₄ structure of this material can well mimic the catalytic activity of laccase. Although Fe₁@CN-20 has a lower metal content (2.9 wt%) than any previously reported laccase mimics, it exhibits kinetic constants comparable to those of laccase, as its K_m (Michaelis constant) and V_max (maximum rate) are 0.070 mM and 2.25 µM/min respectively, which are similar to those of laccase (0.078 mM, 2.49 µM/min). This catalyst displays excellent stability even under extreme pH (2-9), high temperature (100 °C), strong ionic strength (500 mM of NaCl), high ethanol concentration (volume ratio 40%) and long storage time (2 months). Additionally, it can be reused for at least 7 times with only a slight loss in activity. Therefore, this material has a much lower price and better stability and recyclability than laccase, which has been applied in the detection and degradation of a series of phenolic compounds. In the detection of adrenaline, Fe₁@CN-20 achieved a detection limit of 1.3 µM, indicating it is more sensitive than laccase (3.9 µM).

Catalytic antimicrobial therapy using nanozymes

Nanozymes are nanomaterials with enzyme-like characteristics, which catalyze the conversion of enzyme substrates and follow enzymatic kinetics under physiological conditions. As a new generation of artificial enzymes, nanozymes provide alternative approaches for those upon enzymatic catalysis. Compared with natural enzymes, nanozymes have the advantages of simple preparation, good stability and low cost, which makes nanozymes promising for application in many fields, such as antimicrobial infection treatment. Many studies have reported that nanozymes are capable of killing a number of pathogenic bacteria with resistance, fungi as well as viruses, and have shown great curative effects for diseases caused by these pathogens. Herein, we summarize the application of nanozymes for antibacterial, antiviral, and antifungal therapies and outline the issues needing resolution in the future. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Current research progress on laccase-like nanomaterials

The first systematic review of the progress of research on the types and applications of laccase-like activity of nanomaterials is reported.

Enhancement of laccase production from a newly isolated Trichoderma harzianum S7113 using submerged fermentation: Optimization of production medium via central composite design and its application for hydroquinone degradation

Trichoderma harzianum S7113 as an efficient fungal isolate for laccase production was identified using the 18S rRNA sequencing. T. harzianum S7113 attained its maximal laccase production level on the 14^th day of static incubation at 28 °C and pH 5.0 using the inoculum size of 5 discs (14 mm), according to the one factor per time (OFT) method. The most appropriate carbon, organic and inorganic nitrogen sources to promote maximal laccase synthesis were glucose (15 g/L), beef extract (5 g/L), and ammonium chloride (4 g/L), respectively. Results of Response Surface Methodology (RSM) revealed that glucose, meat extract, and ammonium chloride concentrations of 17.54, 7.17, and 4.36 g/L respectively, at a pH value of 6.74 are the favorite conditions for high titer production. The ANOVA analysis highlighted an excellent match between the actual experimental results and the model predicted laccase production levels. The biodegradation of hydroquinone (HQ) by T. harzianum S7113 laccase was most efficient in the pH range of 5.0 to 6.5. The increase in laccase concentration led to a significant increase in the HQ conversion to get a biodegradation rate of 92 ± 2.6% with a laccase concentration of 0.75 U/mL after 3 h of reaction.

Enzyme (Single and Multiple) and Nanozyme Biosensors: Recent Developments and Their Novel Applications in the Water-Food-Health Nexus

The use of sensors in critical areas for human development such as water, food, and health has increased in recent decades. When the sensor uses biological recognition, it is known as a biosensor. Nowadays, the development of biosensors has been increased due to the need for reliable, fast, and sensitive techniques for the detection of multiple analytes. In recent years, with the advancement in nanotechnology within biocatalysis, enzyme-based biosensors have been emerging as reliable, sensitive, and selectively tools. A wide variety of enzyme biosensors has been developed by detecting multiple analytes. In this way, together with technological advances in areas such as biotechnology and materials sciences, different modalities of biosensors have been developed, such as bi-enzymatic biosensors and nanozyme biosensors. Furthermore, the use of more than one enzyme within the same detection system leads to bi-enzymatic biosensors or multi-enzyme sensors. The development and synthesis of new materials with enzyme-like properties have been growing, giving rise to nanozymes, considered a promising tool in the biosensor field due to their multiple advantages. In this review, general views and a comparison describing the advantages and disadvantages of each enzyme-based biosensor modality, their possible trends and the principal reported applications will be presented.

Cu2+-modified MOF as laccase-mimicking material for colorimetric determination and discrimination of phenolic compounds with 4-aminoantipyrine

Based on the laccase-mimicking activity of Cu²⁺-modified University of Oslo (UiO) metal-organic framework (UiO-67-Cu²⁺), we developed a colorimetric sensor array for distinguishing a series of phenols with different number and position of substituted hydroxyl group (-OH) and different substituent group on the benzene ring, including phenol, catechol, quinol, resorcinol, pyrogallol, phloroglucinol, o-chlorophenol, o-aminophenol, and o-nitrophenol. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of phenolic compounds were obtained by theoretical calculation. The results show that the lower the LUMO energy level, the easier the chromogenic reaction occurs. The UiO-67-Cu²⁺-catalyzed phenol chromogenic reaction showed a good linearity in the range from 0.1 to 200 μM with limit of detection approximately 61 nM. Through the detection of phenol in tap water and river water, the recovery rate and RSD (n = 3) were calculated as 94.1~103% and 1.0~3.3, respectively, showing good recovery, reliable results, and outstanding stability. Therefore, the proposed colorimetric sensor array will have a great potential for the detection of phenols in the environment. Schematic presentation of a simple and sensitive colorimetric strategy based on the laccase-mimicking activity of Cu²⁺-modified UiO-type metal-organic framework (MOFs, Uio-67-Cu²⁺) to distinguish phenols with analogous structures.