Facile synthesis of laccase mimic Cu/H3BTC MOF for efficient dye degradation and detection of phenolic pollutants

Enhancing the Catalytic Activity of Laccase@Copper-Metal-Organic Framework Nanofractal Microspheres: Synergistic Contribution of the Mass Transfer and Electron Transfer Pathway

Metal-organic frameworks (MOFs) are limited by small pores and buried active sites, and their enzyme-like catalytic activity is still very low. Herein, laccase was employed as the organic component to construct laccase@Cu3(BTC)2 nanofractal microspheres. During the preparation process, laccase adsorbed Cu2+ by electrostatic attractive interaction, then combined with Cu2+ by coordination interaction, and finally induced the in situ growth of H3BTC2 in multiple directions by electrostatic repulsion. Interestingly, electrostatic repulsion was tuned efficiently by adjusting the Cu2+ concentration to obtain laccase@Cu3(BTC)2 nanofractal microspheres (nanosheet microspheres, nanorod microspheres, and nanoneedle microspheres). Laccase@Cu3(BTC)2 nanorod microspheres exhibited the highest catalytic efficiency, which was 14-fold higher than that of smooth microspheres. The mechanism of the improvement of catalytic activity in the degradation of BPA was proposed for the first time. The enhanced catalytic activity depended on the adsorption effect of the nanorod framework and dual cycle synergistic catalysis of Cu+/Cu2+ active sites, which accelerated substrate diffusion and electron transfer. The catalytic mechanism of enzyme@MOF nanofractal microspheres not only deepens our understanding of enzyme and MOF synergistic catalysis but also provides new insights into the design of catalysts.

Recent Progress on Conversion of Lignocellulosic Biomass by MOF-Immobilized Enzyme

The enzyme catalysis conversion of lignocellulosic biomass into valuable chemicals and fuels showed a bright outlook for replacing fossil resources. However, the high cost and easy deactivation of free enzymes restrict the conversion process. Immobilization of enzymes in metal-organic frameworks (MOFs) is one of the most promising strategies due to MOF materials' tunable building units, multiple pore structures, and excellent biocompatibility. Also, MOFs are ideal support materials and could enhance the stability and reusability of enzymes. In this paper, recent progress on the conversion of cellulose, hemicellulose, and lignin by MOF-immobilized enzymes is extensively reviewed. This paper focuses on the immobilized enzyme performances and enzymatic mechanism. Finally, the challenges of the conversion of lignocellulosic biomass by MOF-immobilized enzyme are discussed.

Nanozyme as detector and remediator to environmental pollutants: between current situation and future prospective

The term "nanozyme" refers to a nanomaterial possessing enzymatic capabilities, and in recent years, the field of nanozymes has experienced rapid advancement. Nanozymes offer distinct advantages over natural enzymes, including ease of production, cost-effectiveness, prolonged storage capabilities, and exceptional environmental stability. In this review, we provide a concise overview of various common applications of nanozymes, encompassing the detection and removal of pollutants such as pathogens, toxic ions, pesticides, phenols, organic contaminants, air pollution, and antibiotic residues. Furthermore, our focus is directed towards the potential challenges and future developments within the realm of nanozymes. The burgeoning applications of nanozymes in bioscience and technology have kindled significant interest in research in this domain, and it is anticipated that nanozymes will soon become a topic of explosive discussion.

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.

Rapid colorimetric sensor for ultrasensitive and highly selective detection of Fumonisin B1 in cereal based on laccase-mimicking activity of silver phosphate nanoparticles

Ag3PO4 nanoparticles (NPs) was prepared through a facile coprecipitation method, and was first found to have excellent laccase-mimicking catalytic activity. The study confirms that Fumonisin B1 (FB1) can effectively hinder the production of superoxide anion (O2-) between Ag3PO4 NPs and dissolved oxygen, and further inhibit laccase-mimicking activity of Ag3PO4 NPs. Thus, a novel rapid colorimetric sensor for FB1 analysis in cereal was first established using laccase-mimicking activity as sensing signal. The absorbance variation of sensing solution is directly related to the amount of FB1, and the color change is further combined with smartphone for quantitively analysis of FB1. The limit of detection (LOD) of the sensor is determined as low as 1.73 μg·L-1, which is far lower than the maximum residue limits (MRLs) of FB1 set by European Commission and US Food and Drug Administration (FDA). The average recovery of 87.8-104.5% for FB1 detection was obtained in cereal.

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.

Immobilization of purified enzyme EreB in metalorganic framework (MOF) mesopores for erythromycin degradation

Erythromycin, a commonly used macrolide antibiotic, plays a crucial role in both human medicine and animal husbandry. However, its abuse has led to residual presence in the environment, with problems such as the emergence of resistant bacteria and enrichment of resistance genes. These issues pose significant risks to human health. Thus far, there are no effective, environmentally friendly methods to manage this problem. Enzymes can specifically degrade erythromycin without causing other problems, but their unrecyclability and environmental vulnerability hinder large-scale application. Enzyme immobilization may help to solve these problems. This study used Cu-BTC, a synthetic metal-organic framework, to immobilize the erythromycin-degrading enzyme EreB. The loading temperature and enzyme quantity were optimized. The Cu-BTC and EreB@Cu-BTC were characterized by various methods to confirm the preparation of Cu-BTC and immobilization of EreB. The maximum enzyme loading capacity was 66.5 mg g-1. In terms of enzymatic properties, immobilized EreB had improved heat (25-45 °C) and alkaline (6.5-10) tolerance, along with greater affinity between the enzyme and its substrate; Km decreased from 438.49 to 372.30 mM. Recycling was also achieved; after 10 cycles, 57.12% of the enzyme activity was maintained. After composite degradation, the antibacterial activity of erythromycin-containing wastewater was examined; the results showed that the novel composite could completely inactivate erythromycin. In summary, Cu-BTC was an ideal carrier for immobilization of the enzyme EreB, and the EreB@Cu-BTC composite has good prospects for the treatment of erythromycin-containing wastewater.

Bacterial Nanocellulose/Copper as a Robust Laccase-Mimicking Bionanozyme for Catalytic Oxidation of Phenolic Pollutants

Industrial effluents containing phenolic compounds are a major public health concern and thus require effective and robust remediation technologies. Although laccase-like nanozymes are generally recognized as being catalytically efficient in oxidizing phenols, their support materials often lack resilience in harsh environments. Herein, bacterial nanocellulose (BNC) was introduced as a sustainable, strong, biocompatible, and environmentally friendly biopolymer for the synthesis of a laccase-like nanozyme (BNC/Cu). A native bacterial strain that produces nanocellulose was isolated from black tea broth fermented for 1 month. The isolate that produced BNC was identified as Bacillus sp. strain T15, and it can metabolize hexoses, sucrose, and less expensive substrates, such as molasses. Further, BNC/Cu nanozyme was synthesized using the in situ reduction of copper on the BNC. Characterization of the nanozyme by scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed the presence of the copper nanoparticles dispersed in the layered sheets of BNC. The laccase-mimetic activity was assessed using the chromogenic redox reaction between 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP) with characteristic absorption at 510 nm. Remarkably, BNC/Cu has 50.69% higher catalytic activity than the pristine Cu NPs, indicating that BNC served as an effective biomatrix to disperse Cu NPs. Also, the bionanozyme showed the highest specificity toward 2,4-DP with a Km of 0.187 mM, which was lower than that of natural laccase. The bionanozyme retained catalytic activity across a wider temperature range with optimum activity at 85 °C, maintaining 38% laccase activity after 11 days and 46.77% activity after the fourth cycle. The BNC/Cu bionanozyme could efficiently oxidize more than 70% of 1,4-dichlorophenol and phenol in 5 h. Thereby, the BNC/Cu bionanozyme is described here as having an efficient ability to mimic laccase in the oxidation of phenolic compounds that are commonly released into the environment by industry.

Copper nanoparticles embedded fungal chitosan as a rational and sustainable bionanozyme with robust laccase activity for catalytic oxidation of phenolic pollutants

Despite their potential for oxidation of persistent environmental pollutants, the development of rational and sustainable laccase nanozymes with efficient catalytic performance remains a challenge. Herein, fungal-produced chitosan-copper (CsCu) is proposed as a rational and sustainable bionanozyme with intrinsic laccase activity. The CsCu nanozyme was prepared by in situ reduction of copper on chitosan extracted from Irpex sp. isolate AWK2 a native fungus, from traditional fermented foods, yielding a low molecular weight chitosan with a 70% degree of deacetylation. Characterizations of the nanozyme using SEM-EDX, XRD, and XPS confirmed the presence of a multi-oxidation state copper on the chitosan matrix which is consistent with the composition of natural laccase. The laccase memetic activity was investigated using 2,4-DP as a substrate which oxidized to form a reddish-pink color with 4-AP (λmax = 510 nm). The CsCu nanozyme showed 38% higher laccase activity than the pristine Cu NPs at pH 9, indicating enhanced activity in the presence of chitosan structure. Further, CsCu showed significant stability in harsh conditions and exhibited a lower Km (0.26 mM) which is competitive with that reported for natural laccase. Notably, the nanozyme converted 92% of different phenolic substrates in 5 h, signifying a robust performance for environmental remediation purposes.

A bioinspired copper-based coordination polymer for the detection of pheochromocytoma biomarkers

Oxidase-mimicking (catechol oxidase/laccase) nanozymes provide outstanding specificity in the detection of epinephrine (Epi) for the assessment of pheochromocytoma; however, epinephrine (Epi) and norepinephrine (NE) co-existing in the same systems will reduce the selectivity of the biosensor. In the current study, we synthesized copper-based coordination polymer (Cu-CP) nanozymes capable of accelerating the oxidation of Epi with high specificity. Furthermore, the Cu-CP is able to detect Epi over a wide linear range of 0.5-100 μM with a low detection limit of 0.36 μM while providing excellent stability and recyclability. Furthermore, we employed colorimetric and fluorescence signals for sequential detection of the coexistence of Epi and NE for use in tracking the treatment outcomes of patients with pheochromocytoma. Experiments using artificial urine further confirmed the efficacy of the proposed system.

Application of Nanozymes in Environmental Monitoring, Management, and Protection

Nanozymes are nanomaterials with enzyme-like activity, possessing the unique properties of nanomaterials and natural enzyme-like catalytic functions. Nanozymes are catalytically active, stable, tunable, recyclable, and versatile. Therefore, increasing attention has been paid in the fields of environmental science and life sciences. In this review, we focused on the most recent applications of nanozymes for environmental monitoring, environmental management, and environmental protection. We firstly introduce the tuning catalytic activity of nanozymes according to some crucial factors such as size and shape, composition and doping, and surface coating. Then, the application of nanozymes in environmental fields are introduced in detail. Nanozymes can not only be used to detect inorganic ions, molecules, organics, and foodborne pathogenic bacteria but are also involved in the degradation of phenolic compounds, dyes, and antibiotics. The capability of nanozymes was also reported for assisting air purification, constructing biofuel cells, and application in marine antibacterial fouling removal. Finally, the current challenges and future trends of nanozymes toward environmental fields are proposed and discussed.

Bioinspired Coassembly of Copper Ions and Nicotinamide Adenine Dinucleotides for Single-Site Nanozyme with Dual Catalytic Functions

Nanozymes can imitate the catalytic properties of natural enzymes while overcoming the limitations of natural enzymes such as high cost, poor robustness, and difficulty in recycling. However, rational design and facile preparation of nanozymes are still in demand. Inspired by the chemical structure of laccase, we report an amorphous metal-organic coordination nanocomposite named CuNAD, which is composed of copper ions and nicotinamide adenine dinucleotide (NAD⁺) via a simple coordinating coassembly process. As a single-site nanozyme, CuNAD exhibits excellent robustness under extreme conditions, significantly stronger catalytic activity for phenolic compounds, and 4.02-fold higher sensitivity for epinephrine detection than laccase. Furthermore, by breaking through the functional constraints of laccase, CuNAD is also able to activate H₂O₂ at neutral pH, benefiting a one-step chromogenic detection platform for cholesterol. This facile approach demonstrates the potential to develop single-site nanozymes by biomimicking natural enzymes and may boost more insights into the structure-function relationship of nanozymes.

Immobilization of Lipase in Cu-BTC MOF with Enhanced Catalytic Performance for Resolution of N-hydroxymethyl Vince Lactam

Metal-organic frameworks (MOFs) can be used as the immobilization carriers to protect the physicochemical properties of enzymes and improve their catalytic performance. Herein, we report an in situ co-precipitation method to immobilize lipase from Candida sp. 99-125 in Cu-BTC MOF (BTC = 1, 3, 5-benzene tricarboxylic acid, H₃BTC). Characterizations of the immobilized lipase (lipase@Cu-BTC) have confirmed the entrapment of lipase molecules in Cu-BTC MOF. The immobilized lipase has been successfully applied for resolving N-hydroxymethyl vince lactam (N-HMVL) and its catalytic activity is five times that of native enzyme. More importantly, we found that Cu-BTC MOF can afford powerful protection for enzyme in nearly dry organic solvent and endow the immobilized lipase with excellent reusability and storage stability. Our present study may widen the application of immobilized enzyme with MOF as the immobilized carrier.

Green carbon-carbon homocoupling of terminal alkynes by a silica supported Cu(II)-hydrazone coordination compound

A Cu(II) complex, [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH (1), was obtained by the reaction of Cu(NO₃)₂·3H₂O and H2L in methanol solvent (H2L is (E)-4-amino-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide). H2L and compound 1 were characterized by various spectroscopic analyses and the molecular structure of [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH was determined by single-crystal X-ray analysis. The results indicated the product is a mononuclear Cu(II) complex and contains a free NH₂ functional group on the structure of the ligand. [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH was used for the preparation of a heterogeneous catalyst by supporting it on functionalized silica gel. The heterogeneous catalyst (Si-Cu) was prepared by an amidification reaction of [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH with functionalized silica gel. The resulting silica-supported catalyst (Si-Cu) was characterized by TGA, FT-IR, EPR, DRS, EDS, XRD, SEM and XPS analyses. Si-Cu was employed in a carbon-carbon coupling reaction and the effects of the amount of Si-Cu and temperature were investigated in the catalytic coupling. The structure of one of the products of the catalytic reactions (C₁₆H₂₂O₂, CP1) was determined by single-crystal X-ray analysis, which proved the formation of a C-C bond and the production of di-acetylene by homocoupling of terminal alkyne. This catalytic system is stable and it can be reused for a coupling reaction without a significant change in its catalytic activity.

Laccase-mimicking Mn-Cu hybrid nanoflowers for paper-based visual detection of phenolic neurotransmitters and rapid degradation of dyes

Background

Laccase-based biosensors are efficient for detecting phenolic compounds. However, the instability and high cost of laccases have hindered their practical utilization.

Results

In this study, we developed hierarchical manganese dioxide–copper phosphate hybrid nanoflowers (H–Mn–Cu NFs) as excellent laccase-mimicking nanozymes. To synthesize the H–Mn–Cu NFs, manganese dioxide nanoflowers (MnO₂ NFs) were first synthesized by rapidly reducing potassium permanganate using citric acid. The MnO₂ NFs were then functionalized with amine groups, followed by incubation with copper sulfate for three days at room temperature to drive the coordination interaction between the amine moieties and copper ions and to induce anisotropic growth of the petals composed of copper phosphate crystals, consequently yielding H–Mn–Cu NFs. Compared with those of free laccase, at the same mass concentration, H–Mn–Cu NFs exhibited lower K_m (~ 85%) and considerably higher V_max (~ 400%), as well as significantly enhanced stability in the ranges of pH, temperature, ionic strength, and incubation periods evaluated. H–Mn–Cu NFs also catalyzed the decolorization of diverse dyes considerably faster than the free laccase. Based on these advantageous features, a paper microfluidic device incorporating H–Mn–Cu NFs was constructed for the convenient visual detection of phenolic neurotransmitters, including dopamine and epinephrine. The device enabled rapid and sensitive quantification of target neurotransmitters using an image acquired using a smartphone.

Conclusions

These results clearly show that H–Mn–Cu NFs could be potential candidates to replace natural laccases for a wide range of applications in biosensing, environmental protection, and biotechnology.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01560-0.

Layer-by-layer coating of MIL-100(Fe) on a cotton fabric for purification of water-soluble dyes by the combined effect of adsorption and photocatalytic degradation

Efforts have been made for sustainable development of adsorbents to purify organic contaminants from wastewater. In this study, a MIL-100(Fe) based textile that acts as a reusable adsorbent and photocatalytic agent was developed by synthesizing MIL-100(Fe) onto a cotton fabric by the layer-by-layer (LBL) process using water-based solutions. As the number of LBL cycles increased, the add-on's of MIL-100(Fe) showed a drastic increase up to 8 cycles, then showed gradual increases with further treatments. The overall adsorption performance was enhanced with the increased MIL-100(Fe) add-on's, but the specific adsorption efficiency per unit mass of MIL-100(Fe) was reduced as the LBL cycles increased, implying the reduced average adsorption efficiency with a thicker coating. To examine the reusability of the adsorbent, desorption efficiency of RhB was measured. The desorption after the first-time adsorption was not efficient due to the strong binding inside the pores. For the later cycles of adsorption–desorption, desorption occurred more efficiently, probably because RhB molecules were adhered mostly at the outer surface of the MOF layer. Simultaneously, MIL-100(Fe)@cotton demonstrated the photocatalytic degradation performance against RhB in the presence of H₂O₂ by the Fenton reaction. With the combined effect of adsorption and photodegradation, the developed fabric attained 96% removal efficiency for RhB dissolved in water. This study demonstrates an environmentally responsible process of developing a MIL-100(Fe) coated fabric that is readily available for effective removal of organic foulants in water. This fabrication method can be applied as a scalable manufacturing of metal–organic framework-based photocatalytic adsorbent textiles.

A MIL-100(Fe)-based water purifying textile that functions by dual action of adsorption and photocatalytic activity is designed via a layer-by-layer process without using toxic organic solvents.

Design of laccase-metal-organic framework hybrid constructs for biocatalytic removal of textile dyes

This study aims to present a simple and effective carrier matrix to immobilize laccase as opposed to complex and tedious immobilization processes and also to use it in the removal of textile dyes. For this purpose, Cobalt (Co) and Copper (Cu) based metal-organic frameworks (MOFs) were prepared and laccase was immobilized on two different MOFs via encapsulation. The characterization outcomes showed that laccase was well immobilized into MOF supports. Optimum pH and temperature were found for Lac/Co-MOF (pH 4.5 at 50 °C) and Lac/Cu-MOF (pH 5.0 at 50 °C). The Km (0.03 mM) and Vmax (97.4 μmol/min) values of Lac/Cu-MOF were lower than those of Lac/Co-MOF (Km = 0.13 mM, Vmax = 230.7 μmol/min). The immobilized laccases showed good reusability as well as improved resistance to temperature denaturation and high storage stability. For instance, the Lac/Co-MOF and Lac/Cu-MOF retained more than 58% activity after 4 weeks of storage at room temperature. Meanwhile, Lac/Co-MOF and Lac/Cu-MOF maintained 56.5% and 55.8% of their initial activity, respectively, after 12 reuse cycles. Moreover, thermal deactivation kinetic studies of immobilized laccases displayed lower k value, higher t_1/2, and enhancement of thermodynamic parameters, which means better thermostability. Finally, the decolorization activities for the Lac/Co-MOF were 78% and 61% at the 5th cycle for Reactive Blue 171 and Reactive Blue 198, respectively. In conclusion, it can be inferred that the MOFs are more sustainable and beneficial support for laccase immobilization and they can be efficient for removing textile dyes from industrial wastes.

Degradation and Detection of Endocrine Disruptors by Laccase-Mimetic Polyoxometalates

Endocrine disruptors are newly identified water contaminants and immediately caught worldwide concern. An effort has been made to degrade endocrine disruptors in the water body by relying on laccase-assisted approaches, including laccase-mediated catalytic systems, immobilized laccase catalytic systems, and nano-catalytic systems based on atypical protein enzymes. Analogous to laccases, polyoxometalates (POMs) have a similar size as these enzymes. They are also capable of using oxygen as an electron acceptor, which could assist the removal of endocrine disruptors in water. This perspective begins with a brief introduction to endocrine disruptors and laccases, summarizes current approaches employing laccases, and focuses on the nano-catalytic systems that mimic the function of laccases. Among the inorganic nanoparticles, POMs meet the design requirements and are easy for large-scale production. The catalytic performance of POMs in water treatment is highlighted, and an example of using polyoxovanadates for endocrine disruptor degradation is given at the end of this perspective. Exploring laccase-mimetic POMs will give key insights into the degradation of emergent water contaminants.

Facile synthesis of Cu N-lauroyl sarcosinate nanozymes with laccase-mimicking activity and identification of toxicity effects for C. elegans

Toxicity assessment of Caenorhabditis elegans Cu-Ls Nz with laccase-like activity.

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.

A novel selective detection method for sulfide in food systems based on the GMP-Cu nanozyme with laccase activity

A selective and sensitive colorimetric strategy for sulfide analysis was developed using GMP-Cu nanozymes with a laccase-like activity. This research discovered for the first time that sulfide could significantly enhance the catalytic activity of the GMP-Cu nanozymes by about 3.5 folds. The enhanced laccase activities duo to two reasons. First, Cu²⁺ in GMP-Cu nanozymes was reduced to Cu⁺. The other reason was the formation of Cu-S bond which was beneficial to accelerate the electron transfer rate to improve catalytic activity. Therefore, this method showed an excellent selectivity for sulfide. And it had a linear relationship in the sulfide concentration range of 0-220 μmol/L with a detection limit of 0.67 μmol/L. Furthermore, the proposed method was successfully applied to examine sulfide in the food systems. This new method may be used in sulfide detection to improve food quality and safety.

Enzyme immobilization on metal organic frameworks: Laccase from Aspergillus sp. is better adapted to ZIF-zni rather than Fe-BTC

Laccase from Aspergillus sp. (LC) was immobilized within Fe-BTC and ZIF-zni metal organic frameworks through a one-pot synthesis carried out under mild conditions (room temperature and aqueous solution). The Fe-BTC, ZIF-zni MOFs, and the LC@Fe-BTC, LC@ZIF-zni immobilized LC samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The kinetic parameters (K_M and V_max) and the specific activity of the free and immobilized laccase were determined. Immobilized LCs resulted in a lower specific activity compared with that of the free LC (7.7 µmol min^-1 mg^-1). However, LC@ZIF-zni was almost 10 times more active than LC@Fe-BTC (1.32 µmol min^-1 mg^-1 vs 0.17 µmol min^-1 mg^-1) and only 5.8 times less active than free LC. The effect of enzyme loading showed that LC@Fe-BTC had an optimal loading of 45.2 mg g^-1, at higher enzyme loadings the specific activity decreased. In contrast, the specific activity of LC@ZIF-zni increased linearly over the loading range investigated. The storage stability of LC@Fe-BTC was low with a significant decrease in activity after 5 days, while LC@ZIF retained up to 50% of its original activity after 30 days storage. The difference in activity and stability between LC@Fe-BTC and LC@ZIF-zni is likely due to release of Fe³⁺ and the low stability of Fe-BTC MOF. Together, these results indicate that ZIF-zni is a superior support for the immobilization of laccase.

Recyclable laccase by coprecipitation with aciduric Cu-based MOFs for bisphenol A degradation in an aqueous environment

Copper-based MOF (Cu-PABA) was selected to immobilize laccase (Lac) at optimum pH because of its favorable acid resistance. Cu-PABA@Lac biocomposites were synthesized in situ by the one-step method under moderate conditions (water environment and normal temperature and pressure). Cu-PABA@Lac had great potential to maintain stability due to the protection of the Cu-PABA shell and reasonable conformational changes. In addition, Cu-PABA@Lac could be used repeatedly by centrifugation, as confirmed in the degradation experiment of bisphenol A (BPA). Because of the synergistic effect of copper ions between laccase and Cu-PABA, the K_m value decreased (from 0.0024 to 0.0014 mM); therefore, the affinity between laccase and guaiacol was enhanced. In conclusion, the system provides a choice for immobilized acid-resistant enzymes and a solution for environmental BPA degradation.

Facile Fabrication of a Novel Copper Nanozyme for Efficient Dye Degradation

In this study, a novel copper nanozyme (CNZ) was synthesized by a mild way and characterized by scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR). The as-fabricated CNZ exhibited typical peroxidase activity toward 2, 2'-azinodi-(3-ethylbenzthiazoline)-6-sulfonate. We successfully applied CNZ for the degradation of methyl orange pollutants. Under the optimum conditions (pH, 3.0; T, 60 °C; H2O2 concentration, 200 mM; dosage of CNZ, 8 mg), 93% of the degradation rate could be obtained in less than 10 min. Furthermore, the nanozyme exhibited excellent reusability and storage stability. All these experimental results suggested that CNZ is a powerful catalyst for industrial wastewater treatment.

Hollow MnFeO oxide derived from MOF@MOF with multiple enzyme-like activities for multifunction colorimetric assay of biomolecules and Hg2

In this work, a new type of hollow MnFeO oxide derived obtained from the metal-organic framework (MOF)@MOF was designed and proposed, which has intrinsic activity of mimicking enzymes of oxidase and peroxidase by adjustment pH values. Based on the colorimetric reaction and the hindrance of the oxidase-like activity in the presence of L-cysteine (Cys), as well as the recovery of oxidase-like activity due to the specific complexation of Cys and mercury (II) ions (Hg²⁺), a new type of colorimetric transmission platform for Cys and Hg²⁺ detection with wide linear ranges of 1-25 μM for Cys and 0.1-15 μM for Hg²⁺ has been developed. Besides, a better colorimetric sensing platform for detecting H₂O₂ was established with linear ranges of 1-60 μM and 60-300 μM based on generating hydroxyl radicals (·OH). Furthermore, the hollow MnFeO oxide has high stability, excellent selectivity with good activity over a long period of time. Surprisingly, the proposed method for Cys, Hg²⁺ and H₂O₂ estimation can also be used in actual samples. These characteristics lay a foundation for further investigation about the catalytic activity of the hollow MnFeO oxide nanomaterials and make it show broad prospects in the field of biosensing and catalysis.

Synthesis, Catalytic Properties and Application in Biosensorics of Nanozymes and Electronanocatalysts: A Review

The current review is devoted to nanozymes, i.e., nanostructured artificial enzymes which mimic the catalytic properties of natural enzymes. Use of the term "nanozyme" in the literature as indicating an enzyme is not always justified. For example, it is used inappropriately for nanomaterials bound with electrodes that possess catalytic activity only when applying an electric potential. If the enzyme-like activity of such a material is not proven in solution (without applying the potential), such a catalyst should be named an "electronanocatalyst", not a nanozyme. This paper presents a review of the classification of the nanozymes, their advantages vs. natural enzymes, and potential practical applications. Special attention is paid to nanozyme synthesis methods (hydrothermal and solvothermal, chemical reduction, sol-gel method, co-precipitation, polymerization/polycondensation, electrochemical deposition). The catalytic performance of nanozymes is characterized, a critical point of view on catalytic parameters of nanozymes described in scientific papers is presented and typical mistakes are analyzed. The central part of the review relates to characterization of nanozymes which mimic natural enzymes with analytical importance ("nanoperoxidase", "nanooxidases", "nanolaccase") and their use in the construction of electro-chemical (bio)sensors ("nanosensors").

An effective in-situ method for laccase immobilization: Excellent activity, effective antibiotic removal rate and low potential ecological risk for degradation products

In this study, we used a simple in-situ biomineralization method to immobilize Bacillus subtilis (B. subtilis)-derived laccase into the copper-Trimesic acid framework (Cu-BTC), and the synthesized Laccase@Cu-BTC particles were used to degrade tetracycline and ampicillin. Compared with free laccase, the Laccase@Cu-BTC showed 16.5-fold of activity recovery, higher thermo-tolerant performance, more excellent acid-proof ability and reusability. Without any mediators, Laccase@Cu-BTC displayed high degradation efficiency (nearly 100%) for tetracycline and ampicillin in some actual water. The degradation mechanism and proposed degradation pathways of tetracycline and ampicillin were discussed technically. Besides, bacteriostatic assay and survival test of Escherichia coli (E. coli) and B. subtilis confirmed the loss of antibiotic activity for tetracycline and ampicillin, as well as the low ecotoxicity of the degradation products. Our research demonstrates that Laccase@Cu-BTC has excellent performance in the effective removal of antibiotics and the detoxification of degradation products, which make it a promising candidate for environmental recovery.

Introducing a flexible tetracarboxylic acid linker into functional coordination polymers: synthesis, structural traits, and photocatalytic dye degradation

2,3′,4,4′-Diphenyl ether tetracarboxylic acid was explored as a novel flexible linker for assembling new metal(ii) coordination polymers with notable structural, topological and catalytic features.

Cu/H3BTC MOF as a potential antibacterial therapeutic agent against Staphylococcus aureus and Escherichia coli

The objective of this study was to design a more effective antibacterial agent to overcome the problem of fast-growing bacterial resistance.