Formation of porous Cu hydroxy double salt nanoflowers derived from metal-organic frameworks with efficient peroxidase-like activity for label-free detection of glucose

Recent Progress and Prospect of Metal-Organic Framework-Based Nanozymes in Biomedical Application

A nanozyme is a nanoscale material having enzyme-like properties. It exhibits several superior properties, including low preparation cost, robust catalytic activity, and long-term storage at ambient temperatures. Moreover, high stability enables repetitive use in multiple catalytic reactions. Hence, it is considered a potential replacement for natural enzymes. Enormous research interest in nanozymes in the past two decades has made it imperative to look for better enzyme-mimicking materials for biomedical applications. Given this, research on metal-organic frameworks (MOFs) as a potential nanozyme material has gained momentum. MOFs are advanced hybrid materials made of inorganic metal ions and organic ligands. Their distinct composition, adaptable pore size, structural diversity, and ease in the tunability of physicochemical properties enable MOFs to mimic enzyme-like activities and act as promising nanozyme candidates. This review aims to discuss recent advances in the development of MOF-based nanozymes (MOF-NZs) and highlight their applications in the field of biomedicine. Firstly, different enzyme-mimetic activities exhibited by MOFs are discussed, and insights are given into various strategies to achieve them. Modification and functionalization strategies are deliberated to obtain MOF-NZs with enhanced catalytic activity. Subsequently, applications of MOF-NZs in the biosensing and therapeutics domain are discussed. Finally, the review is concluded by giving insights into the challenges encountered with MOF-NZs and possible directions to overcome them in the future. With this review, we aim to encourage consolidated efforts across enzyme engineering, nanotechnology, materials science, and biomedicine disciplines to inspire exciting innovations in this emerging yet promising field.

Recent Development of Copper-Based Nanozymes for Biomedical Applications

Copper (Cu), an indispensable trace element within the human body, serving as an intrinsic constituent of numerous natural enzymes, carrying out vital biological functions. Furthermore, nanomaterials exhibiting enzyme-mimicking properties, commonly known as nanozymes, possess distinct advantages over their natural enzyme counterparts, including cost-effectiveness, enhanced stability, and adjustable performance. These advantageous attributes have captivated the attention of researchers, inspiring them to devise various Cu-based nanomaterials, such as copper oxide, Cu metal-organic framework, and CuS, and explore their potential in enzymatic catalysis. This comprehensive review encapsulates the most recent advancements in Cu-based nanozymes, illuminating their applications in the realm of biochemistry. Initially, it is delved into the emulation of typical enzyme types achieved by Cu-based nanomaterials. Subsequently, the latest breakthroughs concerning Cu-based nanozymes in biochemical sensing, bacterial inhibition, cancer therapy, and neurodegenerative diseases treatment is discussed. Within this segment, it is also explored the modulation of Cu-based nanozyme activity. Finally, a visionary outlook for the future development of Cu-based nanozymes is presented.

Adsorption of anionic dye from aqueous environment using surface-engineered Zn/Cu hydroxy double salt-based material: mechanistic, equilibrium and kinetic studies

Herein, ethylene glycol (EG)-modified Zn/Cu hydroxy double salts (HDS) were synthesized using a facile synthetic approach. The formation of layered structure and presence of EG in the interlayer region were confirmed using PXRD and FTIR techniques. Furthermore, XPS analysis was used to confirm presence of metal ions in synthesized HDS. The surface area and pore size diameter of the HDS was found to be 32.30 m2 g-1 and 2.22 nm, respectively, using BET. The role of HDS was evaluated for its potential application as a sorbent for Congo red (CR) dye uptake. Batch studies were conducted to examine the impact of key variables, i.e., pH, time, adsorbent dosage and dye concentration on adsorption efficiency of HDS. Linear-nonlinear isotherm and kinetic models were employed for detailed analysis of experimental data. Langmuir, Freundlich and Temkin isotherm models were subsequently utilized to fit equilibrium data, among which Langmuir demonstrated to be most accurate. The maximum monolayer adsorption capacity estimated using Langmuir model was computed to be 181.81 mg g-1. The kinetic data follows pseudo-second-order model having good R2 value (0.999). Additionally, thermodynamic study suggested spontaneous and endothermic nature of adsorption process having reusability up to 5 cycles with removal efficiency more than 85%.

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.

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.

Peroxidase catalytic activity of carbon nanoparticles for glutathione detection

Peroxidases are present widely in microorganisms and plants, and catalyze many reactions. However, the activity of natural peroxidases is susceptible to external conditions. We prepared carbon nanoparticles (CNPs) using an environmentally friendly and simple method. These CNPs were demonstrated to possess intrinsic peroxidase-like activity. CNPs could catalyze the reaction of a peroxidase substrate, 3,3,5,5-tetramethylbenzidine (TMB), in the presence of H2O2 to produce a blue solution at 652 nm. CNPs exhibited higher peroxidase activity than that of other carbon-based nanomaterials. Moreover, CNPs retained their high peroxidase activity after being reused several times. Glutathione (GSH) can change the blue color of oxidized TMB into a colorless hue at 652 nm. Based on this fact, qualitative and quantitative approaches were employed to detect GSH using a colorimetric method. This method showed a broad detection range (2.5-50 μM) with a limit of detection of 0.26 μM. This method was shown to be accurate for GSH detection in a cell culture medium compared with that using a commercial assay kit. Our findings could facilitate application of CNPs in biomedical areas.

Nanozymes in Point-of-Care Diagnosis: An Emerging Futuristic Approach for Biosensing

Nanomaterial-based artificial enzymes (or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes. Numerous advantages of nanozymes such as diverse enzyme-mimicking activities, low cost, high stability, robustness, unique surface chemistry, and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal, metal oxide, metal-organic framework-based nanozymes have been exploited for the development of biosensing systems, which present the potential for point-of-care analysis. To highlight recent progress in the field, in this review, more than 260 research articles are discussed systematically with suitable recent examples, elucidating the role of nanozymes to reinforce, miniaturize, and improve the performance of point-of-care diagnostics addressing the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical, colorimetric, fluorescent, and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However, basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size, shape, composition, surface charge, surface chemistry as well as external parameters such as pH or temperature, these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore, it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications.

Mesoporous Materials-Based Electrochemical Biosensors from Enzymatic to Nonenzymatic

Mesoporous materials have drawn more and more attention in the field of biosensors due to their high surface areas, large pore volumes, tunable pore sizes, as well as abundant frameworks. In this review, the progress on mesoporous materials-based biosensors from enzymatic to nonenzymatic are highlighted. First, recent advances on the application of mesoporous materials as supports to stabilize enzymes in enzymatic biosensing technology are summarized. Special emphasis is placed on the effect of pore size, pore structure, and surface functional groups of the support on the immobilization efficiency of enzymes and the biosensing performance. Then, the development of a nonenzymatic strategy that uses the intrinsic property of mesoporous materials (carbon, silica, metals, and composites) to mimic the behavior of enzymes for electrochemical sensing of some biomolecules is discussed. Finally, the challenges and perspective on the future development of biosensors based on mesoporous materials are proposed.

Novel hierarchical CuNiAl LDH nanotubes with excellent peroxidase-like activity for wide-range detection of glucose

Novel hierarchical CuNiAl layered double hydroxide (CuNiAl LDH) nanotubes were prepared with in situ transformation of Al₂O₃ produced using the atomic layer deposition (ALD) method. Based on the characterizations using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), CuNiAl LDH displays a typical nanotube-like structure consisting of uniform ultrathin nanoflakes. It is also confirmed that nitrate precursors play a crucial role in the formation of the LDH hierarchical structure. The unique hierarchical tube-like structure for CuNiAl LDH can supply more active sites and higher surface areas, leading to outstanding peroxidase mimicking property. The kinetic analyses indicate that the catalytic behavior of CuNiAl LDH follows classic Michaelis-Menten models and the affinity of CuNiAl LDH to the substrate is significantly higher than horseradish peroxidase. A simple and label-free method was developed for the colorimetric detection of glucose. As low as 2.9 μM of glucose can be detected with a broad linear range from 10 to 200 μM. The established method is also proved to be suitable for glucose detection in juice samples.

Metal–organic frameworks as photoluminescent biosensing platforms: mechanisms and applications

Recent progress of MOF-based photoluminescent platforms: a comprehensive overview of their applications in biosensing and underlying mechanisms.

Platinum (II)-doped graphitic carbon nitride with enhanced peroxidase-like activity for detection of glucose and H2O2

A platinum (II)-doped graphitic carbon nitride (Pt²⁺@g-C₃N₄) nanozyme was prepared in this work. Compared to g-C₃N₄, Pt²⁺@g-C₃N₄ shows enhanced peroxidase-like activity. According to DFT calculations and ESR measurements, the Pt on the surface of g-C₃N₄ accelerates the decomposition of H₂O₂ into OH and consequently accelerates TMB oxidation. Furthermore, as a proof of concept, the obtained Pt²⁺_2.30@g-C₃N₄ was applied in the detection of glucose with an LOD of 0.01 mM. The reproducibility and precision tests of the glucose detection method based on Pt²⁺_2.30@g-C₃N₄ show that this method is reliable and feasible for the detection of glucose.

Air-thermal processing of hierarchically porous metal-organic frameworks

Metal-organic frameworks (MOFs) show great potential for various applications. The functions of MOFs are closely related to their porous structures and lattice integrities. However, the generally existing guest solvent/linker molecules and crystalline defects will alter internal microstructures and microenvironments of MOFs. Meanwhile, although MOFs have tailorable pore structures within the range of microspores, the achievement of meso/macropores in MOFs is of scientific interest. Herein, a versatile air-thermal processing (ATP) strategy is reported to remove the residual molecules and incompletely coordinated linkers in MOFs. Through processing MOFs in confined space, the thermalized and pressurized air can assist the filling solvents and partially/totally uncoordinated linkers to overcome the energy barrier of escape, and then maximize MOF porosity. The obtained MOF materials with hierarchical micro/mesoporous structures display substantially improved adsorption capacities and selectivities. For example, CuBTC-A shows 36%, 72%, 22%, and 86% enhancements in surface area, pore volume, CO₂ uptake, and CO₂/N₂ selectivity, respectively. Moreover, by adjusting processing temperature, the ATP strategy is available for fabricating MOF materials with hierarchically micro/meso/macroporous superstructures under modulator/template-free conditions.

Nanoscale metal-organic frameworks in detecting cancer biomarkers

Following the efficient performance of metal-organic frameworks (MOFs) as recognition elements in gas sensors, biosensors based on MOFs are now being investigated to capture and quantify potential cancer biomarkers, such as circulating tumor cells (CTCs), nucleic acids and proteins. The current status of MOF-based biosensors in the detection of early stages of cancer is in its infancy, although it has significantly emerged since the beginning of this decade. That said, salient research has been conducted in the past five years to utilize the distinctive porous crystalline structure of MOFs for highly sensitive and selective detection of cancer biomarkers. In this pursual, MOFs designed with bimetallic assembly, doped with magnetic nanoparticles, coated with polymers, and even conjugated with peptides or oligonucleotides have shown promising outcomes in detecting CTCs, nucleic acids and proteins. In particular, aptamer-conjugated MOFs are able to perform at a lower limit of detection down to the femtomolar, implying their efficacy for the point of care testing in clinical trials. In this way, aptasensors based on aptamer-conjugated MOFs present a newer sub-branch, to be coined as a MOFTA sensor in the current review. Considering the emerging progress and promising outcomes of MOFTA sensors as well as a variety of MOF-based techniques of detecting cancer biomarkers, this review will highlight their significant advances and related aspects in the recent five years on the context of detecting CTCs, nucleic acids and proteins for the early-stage detection of cancer.

Fluorescence Method for the Detection of Protein Kinase Activity by Using a Zirconium-Based Metal-Organic Framework as an Affinity Probe

In cell-signaling pathways, protein kinases are critical and ubiquitous regulators. Abnormal kinase activity leads to many major diseases; therefore, simple and efficient methods for detecting protein kinases are in high demand. This study proposed a simple, rapid fluorescence-based sensor for protein kinase activity analysis, using the zirconium-based metal organic framework UiO-66 as a highly efficient affinity probe. UiO-66 has a large specific surface area, good stability, and a large number of Zr defect sites, which can efficiently identify phosphorylation sites. UiO-66 is an ideal nanoreactor that can efficiently enrich phosphorylated peptides. Under optimal experimental conditions, the increased fluorescence intensity was directly proportional to the protein kinase activity. The lower limit of detection was 0.00005 U·μL^-1. The assay could also be used for the screening of protein kinase inhibitors, could determine the activity of other kinds of kinases, and was universally applicable. This method was used for protein kinase activity detection in drug-stimulated MCF-7 cell lysates and demonstrated its potential applicability in kinase-related research.

High-activity Mo, S co-doped carbon quantum dot nanozyme-based cascade colorimetric biosensor for sensitive detection of cholesterol

Nanozymes have drawn considerable attention because of their lower cost, higher stability and convenient preparation compared to protein enzymes. In the present work, Mo, S co-doped carbon quantum dots (Mo-CQDs) as a peroxidase mimic were used to fabricate a cascade colorimetric biosensor to detect cholesterol. The Mo-CQDs possess a robust peroxidase-like activity, and they can easily catalyze 3,3,5,5-tetramethylbenzidine (TMB) to produce an oxidized TMB in the presence of H₂O₂. The Mo, S doping in the carbon quantum dots (CQDs) notably boosts the yield of CQDs and may facilitate the electron transfer between TMB and H₂O₂, which further enhances the catalytic activity of CQDs. The colorimetric biosensor based on Mo-CQDs and cholesterol oxidase exhibited excellent selectivity and high sensitivity for cholesterol in the range of 0.01-1.0 mM along with a detection limit as low as 7 μM. The total cholesterol concentration in the serum sample was measured with satisfactory results and read out by the naked eye, indicating the potential application in clinical diagnosis and portable test kits.

Label-free colorimetric detection of deoxyribonuclease I activity based on the DNA-enhanced peroxidase-like activity of MIL-53(Fe)

In this study, the effect of single-stranded DNA (ssDNA) on the intrinsic peroxidase-like activity of MIL-53(Fe) was investigated.

Melamine formaldehyde–metal organic gel interpenetrating polymer network derived intrinsic Fe–N-doped porous graphitic carbon electrocatalysts for oxygen reduction reaction

Melamine formaldehyde metal organic gel interpenetrating networks for heteroporous Fe–N-doped carbon.