Bimetallic Fe/Mn metal-organic-frameworks and Au nanoparticles anchored carbon nanotubes as a peroxidase-like detection platform with increased active sites and enhanced electron transfer

Bimetallic MOF-derived three-dimensional nanoflowers PdCoOx as peroxidase mimic activity for determining total antioxidant capacity

Bimetallic MOF derivatives have shown excellent performance as nano-enzymes in the field of catalysis. Herein, PdCo oxide nanoflowers with three-dimensional flower were prepared by a simple pyrolysis method on a precursor of bimetallic PdCo-MOF. PdCoOx showed excellent peroxidase mimic activity, which could significantly promote the oxidation of TMB by H2O2. Compared with CoOx, the peroxidase mimic activity of the optimized PdCoOx-300 increased by 2.41-fold. PdCoOx-300 has high affinity for TMB and H2O2 with Km values of 0.16 mM and 2.11 mM, which are only 57.03% and 36.87% of HRP, respectively. The highly specific peroxidase mimic activity is conducive to the sensitive detection of H2O2, glucose and ascorbic acid with limit of detection of 10, 100 and 10 nM, respectively. Furthermore, the total antioxidant capacity in the actual beverage samples was conducted, which showed good anti-interference ability and recovery rate.

Coupling metal organic frameworks nanozyme with carbon nanotubes on the gradient porous hollow fiber membrane for nonenzymatic electrochemical H2O2 detection

In this paper, we present a gradient porous hollow fiber structure integrated the signal transduction within a microspace, serving as a platform for cellular metabolism monitoring. We developed a nonenzymatic electrochemical electrode by coupling carbon nanotubes (CNT) and metal organic frameworks (MOF) nanozyme on three-dimensional (3D) gradient porous hollow fiber membrane (GPF) for in-situ detection of cell released hydrogen peroxide (H2O2). The GPF was used as a substrate for cell culture as well as the supporting matrix of the working electrode. The ultrasonically coupled CNT@MOF composite was immobilized on the outer surface of the GPF by means of pressure filtration. Notably, the MOF, acting as a peroxidase mimic, exhibits superior stability compared to traditional horseradish peroxidase. The incorporation of CNT not only provided sufficient specific surface area to improve the uniform distribution of MOF nanozyme, but also formed 3D conductive network. This network efficiently facilitates the electrons transfer during the catalytic process of the MOF, addressing the inherent poor conductivity of MOFs. The GPF-CNT@MOF nonenzymatic bioelectrode demonstrated excellent electrocatalytic performance including rapid response, satisfactory sensing selectivity, and attractive stability, which enabled the development of a robust in-situ cellular metabolic monitoring platform.

Unique three-dimensional ordered macroporous dealloyed gold-silver electrochemical sensing platforms for ultrasensitive mercury(II) monitoring

To address the requirement of ultra-sensitive detection of trace mercury(II) (Hg2+) ions in the environment and food, we developed an electrochemical biosensor with super-sensitivity, extremely high selectivity, and reusability. This biosensor comprised two signal amplification components: a three-dimensional macroporous dealloyed (3DOMD) Au-Ag thin-film electrode and a multifunctional encoded Au@Pt nanocage (APNC). As a platform for immobilized capture DNA (cDNA), a 3DOMD Au-Ag thin film prepared by a dealloying method with an active surface area 4.8 times higher than that of 3D macroporous gold films generated by cyclic voltammetry (CV) with sulfuric acid was capable of increasing the sensing surface area while also strengthening the electron transport capacity of the sensing substrate due to its multilayered multi-porous framework. In the presence of Hg2+, probe DNA (pDNA) could be hybridized with the mismatched capture DNA (cDNA) through stable thymine-Hg2+-thymine (T-Hg2+-T) linkages, connecting thionine-APNC to the electrode surface and utilizing the large specific surface area to accomplish highly sensitive detection of Hg2+. With an extremely low Hg2+ detection limit of 2 pM and a detection range from 0.01 to 1000 nM, this technique opened up a new avenue for the ultrasensitive detection of a wider range of heavy metal ions or biomolecules.

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 advances in the colorimetric and fluorescence analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials

Nanomaterials with enzyme-like activity have been widely used in the construction of colorimetric and fluorescence sensors due to their advantages of cost-effectiveness, high stability, good biocompatibility, and ease of modification. Furthermore, the colorimetric and fluorescence sensors, which are effective approaches for detecting bioactive small-molecule compounds, have been extensively explored due to their simple operation and high sensitivity. Recent significant researches have focused on designing various sensors based on nanozymes with peroxidase- and oxidase-like activity for the colorimetric and fluorescence analysis of different analytes. In this review, recent developments (from 2018 to present) in the colorimetric and fluorescent analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials were summarized. In addition, the challenges and design strategies in developing colorimetric and fluorescent assays with high performance and specific sensing were discussed.

Metal-organic framework composite Mn/Fe-MOF@Pd with peroxidase-like activities for sensitive colorimetric detection of hydroquinone

The construction of highly sensitive detection methods for hydroquinone (HQ) in environment and cosmetics is of great significance for environmental protection and human health. In this work, a novel detection method for HQ was successfully developed by constructing a metal-organic framework mimic enzyme colorimetric sensor (Mn/Fe-MOF@Pd1.0) with excellent peroxidase-like activity, which was synthesized by doping manganese ions into Fe-MOF by introducing bimetallic active centers, thereby improving the peroxidase-like activity of Fe-MOF, and the acid resistance and stability of Mn/Fe-MOF were improved by supporting palladium (Pd NPs). It is proven that Mn/Fe-MOF@Pd1.0 promoted the decomposition of hydrogen peroxide (H2O2) to generate active species, therefore, oxidized chromogenic substrate discoloration. On this basis, the detection of HQ based on the Mn/Fe-MOF@Pd1.0 colorimetric sensor was constructed, in which the limit of detection (LOD) was 0.09 μM in the linear range of 0.3-30 μM. Furthermore, Mn/Fe-MOF@Pd1.0 was successfully used for detecting HQ in hydroquinone whitening cream and actual water samples. The successful synthesis of Mn/Fe-MOF@Pd1.0 may provide new insights for further study of the enzyme-like activity of metal-organic framework composites, and the constructed facile and sensitive sensor system could broaden the application prospects of HQ detection.

Carbon nanotubes: a powerful bridge for conductivity and flexibility in electrochemical glucose sensors

The utilization of nanomaterials in the biosensor field has garnered substantial attention in recent years. Initially, the emphasis was on enhancing the sensor current rather than material interactions. However, carbon nanotubes (CNTs) have gained prominence in glucose sensors due to their high aspect ratio, remarkable chemical stability, and notable optical and electronic attributes. The diverse nanostructures and metal surface designs of CNTs, coupled with their exceptional physical and chemical properties, have led to diverse applications in electrochemical glucose sensor research. Substantial progress has been achieved, particularly in constructing flexible interfaces based on CNTs. This review focuses on CNT-based sensor design, manufacturing advancements, material synergy effects, and minimally invasive/noninvasive glucose monitoring devices. The review also discusses the trend toward simultaneous detection of multiple markers in glucose sensors and the pivotal role played by CNTs in this trend. Furthermore, the latest applications of CNTs in electrochemical glucose sensors are explored, accompanied by an overview of the current status, challenges, and future prospects of CNT-based sensors and their potential applications.

Recent advances in metal-organic framework/carbon nanotube nanocomposites for developing analytical applications

Nanoscience shows promise for scientific advancement in many sectors, such as biology, energy, materials, environment, and manufacturing. Nanocomposites are mixtures of two or more materials, one of which is nanosized particles. The composites are expected to show combined features resulting in general enhancements in their physical and chemical properties. Metal-organic frameworks (MOFs) are coordination polymers that have attracted attention from researchers in recent years due to their porosity and controllable functionality. Another example of interesting nanomaterials is carbon nanotubes (CNTs) which are also known for their mechanical and thermal properties. Incorporation of both these materials into a nanocomposite has shown an enhancement in properties and conquered challenges in the defects of construction. This mini-review sheds light on the recent synthetic approaches and characterization of MOF-CNT nanocomposites in order to access porous selective nanocomposites that can improve analyte detection in environmental matrixes and biological systems. A summary of the chemical composition of nanocomposites, analytes in the target, and analytical techniques used is provided.

A novel electrochemical aptasensor for ultrasensitive detection of herbicide prometryn based on its highly specific aptamer and Ag@Au nanoflowers

Herbicide prometryn has become a common pollutant in aquatic environments and caused adverse impacts on ecosystems. This study developed an ultrasensitive electrochemical aptasensor for prometryn based on its highly affinitive and specific aptamer and Ag@Au nanoflowers (Ag@AuNFs) for signal amplification. Firstly, this study improved the Capture-SELEX strategy to screen aptamers and obtained aptamer P60-1, which had a high affinity (Kd: 23 nM) and could distinguish prometryn from its structural analogues. Moreover, the typical stem-loop structure in aptamer P60-1 was found to be the binding pocket for prometryn. Subsequently, an electrochemical aptasensor for prometryn was established using multiwalled carbon nanotubes and reduced graphene oxide as electrode substrate, Ag@Au NFs as signal amplification element, and aptamer P60-1 as recognition element. The aptasensor had a detection range of 0.16-500 ng/mL and a detection limit of 60 pg/mL, which was much lower than those of existing detection methods. The aptasensor had high stability and good repeatability, and could specifically detecting prometryn. Furthermore, the utility of the aptasensor was validated by measuring prometryn in environmental and biological components. Therefore, this study provides a robust and ultrasensitive aptasensor for accurate detection for prometryn pollution.

G-/C-rich ssDNA-based Fe and Cu/Fe nanoclusters with peroxidase-like activity for intracellular ROS production and cytotoxicity applications

Five G-/C-rich single-stranded DNA (ssDNA) with different sequences and lengths were templated to prepare the DNA-Cu, DNA-Fe, and bimetallic DNA-Cu/M nanoclusters (NCs). The peroxidase-like activities of these nanomaterials were studied using H₂O₂ and 3,3',5,5''-tetramethylbenzidine (TMB) as the reaction substrates in HAc-NaAc buffer. It was found that T30-G2-Fe NCs and T30-G2-Cu/Fe NCs, with a size of about 2 nm, exhibit similar and the strongest enzyme-like activity under optimal conditions. Both NCs possess a similarly high affinity to substrates, and the Michaelis-Menten constant (K_m) values to TMB and H₂O₂ are about 11 and 2-3 times lower than those of natural horseradish peroxidase (HRP), respectively. The activity of both nanozymes decreases to about 70% after being kept for one week in pH 4.0 buffer at 4 °C, which is comparable with HRP. Hydroxyl radicals (•OH) are the main reactive oxygen species (ROS) produced in the catalytic reaction. Moreover, both NCs can facilitate in situ generation of ROS in HeLa cells using endogenous H₂O₂. MTT assays indicate that the T30-G2-Cu/Fe NCs exhibit the strong selective cytotoxicity to HeLa cells over HL-7702 cells. The cellular viability is about 70% and 50% after incubating with 0.6 M NCs for 24 h without or with 2 mM H₂O₂, respectively. The current study shows that the T30-G2-Cu/Fe NCs have the potential for chemical dynamic treatment (CDT).

Peroxidase-like activity of hollow sphere-like FeS2/SC boosted by synergistic action of defects and S-C bonding

Pyrite FeS₂ has been applied as a peroxidase due to its easy preparation and low cost. However, the low peroxidase-like (POD) activity limited its wide application. A hollow sphere-like composite (FeS₂/SC-5.3%) composed of pyrite FeS₂ and sulfur-doped hollow sphere-shaped carbon was synthesized by a facile solvothermal method, where the S-doped carbon was in situ formed during FeS₂ formation. The synergistic action such as the defects at the carbon surface and the formation of S-C bonding improved the nanozyme activity. The S-C bonding was a bridge between the carbon and the Fe atom in FeS₂, which enhanced the electron transfer between the Fe atom and the carbon and accelerated the conversion from Fe³⁺ to Fe²⁺. The optimum experimental conditions were obtained by the response surface methodology (RSM). The POD-like activity of FeS₂/SC-5.3% was significantly improved compared to that of FeS₂. The Michaelis-Menten constant (K_m) of FeS₂/SC-5.3% is 80 times lower than that of horseradish peroxidase (HRP, natural enzyme). FeS₂/SC-5.3% can be used to detect cysteine (Cys) with a limit of detection (LOD) as small as 0.061 μM at room temperature in only 1 min.

Sandwich photoelectrochemical biosensing of concanavalin A based on CdS/AuNPs/NiO Z-scheme heterojunction and lectin-sugar binding

A CdS/AuNPs/NiO Z-scheme heterojunction was prepared on a fluorine-doped tin oxide (FTO) electrode by hydrothermal synthesis of NiO on FTO, electrodeposition of AuNPs on NiO/FTO electrode and then cast-coating of CdS quantum dots. The CdS/AuNPs/NiO/FTO electrode gave a notably increased photocurrent versus NiO/FTO, CdS/FTO, AuNPs/NiO/FTO, CdS/AuNPs/FTO and CdS/NiO/FTO electrodes. The CdS/AuNPs/NiO/FTO electrode was further cast-coated with chitosan to immobilize d-mannose by Schiff base reaction, and concanavalin A (ConA) and then horseradish peroxidase (HRP) were captured on the electrode surface by lectin-sugar binding. 4-Chloro-1-naphthol (4-CN) was oxidized to form an insoluble precipitate catalyzed by HRP in the presence of H₂O₂, and the presence of precipitate on the photoelectrode inhibited the photocurrent in the presence of holes scavenger ascorbic acid. The relevant electrodes were characterized by electrochemistry, quartz crystal microbalance (QCM), UV-vis spectrophotometry, scanning electron microscopy/energy dispersive spectroscopy, and transmission electron microscopy. The QCM revealed that the collection efficiency (η) of the 4-CN-electrooxidation precipitate on the electrode can be as high as 91.8%. Under the optimal conditions, the decline of photocurrent responded linearly to the common logarithm of ConA concentration from 50 pM to 500 nM, with a limit of detection of 17 pM (S/N = 3). Satisfactory results were obtained in the detection of real soybean samples.

Synthesis of Fe2O3/Mn2O3 Nanocomposites and Impregnated Porous Silicates for Dye Removal: Insights into Treatment Mechanisms

Fe2O3/Mn2O3 nanocomposites and impregnated porous silicates (Fe2O3/Mn2O3@SiO2 [FMS]) were prepared and investigated as catalytic adsorbents. The catalysts were applied for cationic and anionic dye pollutants in the adsorption, Fenton reaction, and photocatalysis processes at a pH of 7. Fe2O3/Mn2O3 nanoparticles (FM-NPs) were prepared using the co-precipitation method and were impregnated in SiO2 by the sol–gel process. The synthesized materials were characterized using various sophisticated techniques. Results indicated that the impregnation of bi-metallic NPs in SiO2 increased the surface area, and the function of the adsorbent also improved. FMS showed a significant adsorption effect, with 79.2% rhodamine B removal within 15 min. Fenton and photocatalyst reaction showed removal rates of 85.3% and 97.9%, respectively, indicating that negatively charged porous silicate attracts cationic pollutants. In the case of the anionic pollutant, Congo red, the adsorption reaction of FMS did not occur, and the removal rate of the photocatalyst reaction was 79%, indicating the repulsive force between the negatively charged silica and the anionic dye. Simultaneously, bi-metal-bonded FM-NPs facilitated the photocatalytic reaction, reducing the recombination of electron-hole pairs. This study provides new insights into the synthesis of FM-NPs and FMS as photocatalytic adsorbents and their photocatalytic mechanisms based on reaction conditions and contaminant characteristics. The developed materials have potential applications for environmental mitigation.

Morphology Control Strategy of Bimetallic MOF Nanosheets for Upgrading the Sensitivity of Noninvasive Glucose Detection

The precise measurement of glucose level is significant for the health management of the human body. However, the existing sensitive materials and detection methods for glucose are less satisfying for practical applications. Herein, an ultrathin reticular two-dimensional nanosheets array composed of trimesic acid (H₃BTC)-based bimetal metal-organic frameworks (MOFs) and carbon cloth (CC), which is constructed through a morphology control strategy, is reported for glucose sensing. Meanwhile, this nonmoving sweat glucose sensor based on a NiCo-BTC/CC electrode has been successfully prepared by a screen printing method. Benefiting from the regular and ultrathin nanosheets array, the NiCo-BTC/CC electrode has an excellent sensitivity of 2701.29 μA mM^-1 cm^-2, which is about 2.4 times that of its unregulated counterpart (1127.85 μA mM^-1 cm^-2) in the linear range 5-205 μM. In addition, an ultralow detection limit (0.09 μM, S/N = 3) and good selectivity of NiCo-BTC/CC were also obtained. The high sensitivity of the glucose sensor based on NiCo-BTC/CC electrode is 0.174 μA μM^-1 (50-1000 μM). Remarkably, the preciously designed sensor is used to detect glucose concentration in sweat with a noninvasive mode, and the results are basically consistent with those of a commercial glucose device with an invasive mode. This research exhibits potential methodology for the morphology design of bimetallic MOFs nanosheets to achieve a high accuracy rate and noninvasive and timeless measurement of a glucose sensor.

Flower-like ZIF-8 enhance the peroxidase-like activity of nanoenzymes at neutral pH for detection of heparin and protamine

The peroxide-like catalytic activity of gold nanoclusters (Au-NCs) is very low under physiological conditions (pH 7.4), which greatly limits its biological detection applications. A new nanoenzyme platform was constructed by self-assembly of Au-NCs and ZIF-8/CQDs. It was found that heparin can significantly promote the peroxidase-like activity of Au-NCs on the nanoenzyme platform at pH 7.4. In the presence of H₂O₂, the catalytic activity of Au-NCs on the nanoenzyme platform for TMB increased nearly 50 times. Based on this phenomenon, a colorimetric method was developed to determine heparin in the range of 0.0185-9.25 U/mL, with a detection limit of 0.0027 U/mL. When protamine is introduced, heparin and protamine take the lead in specific binding due to antagonism, which makes heparin unable to adsorb on the surface of ZIF-8/CQDS, thus inhibiting the enhancement of the catalytic activity of Au-NCs. Based on this phenomenon, a colorimetric method was developed to determine protamine in the range of 0.01-0.5 μg/mL, with a detection limit of 0.003 μg/mL. Therefore, this method provides a new idea for the visual detection of heparin and protamine under physiological conditions.

Explaining chemical clues of metal organic framework-nanozyme nano-/micro-motors in targeted treatment of cancers: benchmarks and challenges

Nowadays, nano-/micro-motors are considered as powerful tools in different areas ranging from cleaning all types of contaminants, to development of Targeted drug delivery systems and diagnostic activities. Therefore, the development and application of nano-/micro-motors based on metal-organic frameworks with nanozyme activity (abbreviated as: MOF-NZs) in biomedical activities have received much interest recently. Therefore, after investigating the catalytic properties and applications of MOF-NZs in the treatment of cancer, this study intends to point out their key role in the production of biocompatible nano-/micro-motors. Since reducing the toxicity of MOF-NZ nano-/micro-motors can pave the way for medical activities, this article examines the methods of making biocompatible nanomotors to address the benefits and drawbacks of the required propellants. In the following, an analysis of the amplified directional motion of MOF-NZ nano-/micro-motors under physiological conditions is presented, which can improve the motor behaviors in the propulsion function, conductivity, targeting, drug release, and possible elimination. Meanwhile, by explaining the use of MOF-NZ nano-/micro-motors in the treatment of cancer through the possible synergy of nanomotors with different therapies, it was revealed that MOF-NZ nano-/micro-motors can be effective in the treatment of cancer. Ultimately, by analyzing the potential challenges of MOF-NZ nano-/micro-motors in the treatment of cancers, we hope to encourage researchers to develop MOF-NZs-based nanomotors, in addition to opening up new ideas to address ongoing problems.

Carbon Nanomaterials (CNMs) and Enzymes: From Nanozymes to CNM-Enzyme Conjugates and Biodegradation

Carbon nanomaterials (CNMs) and enzymes differ significantly in terms of their physico-chemical properties-their handling and characterization require very different specialized skills. Therefore, their combination is not trivial. Numerous studies exist at the interface between these two components-especially in the area of sensing-but also involving biofuel cells, biocatalysis, and even biomedical applications including innovative therapeutic approaches and theranostics. Finally, enzymes that are capable of biodegrading CNMs have been identified, and they may play an important role in controlling the environmental fate of these structures after their use. CNMs' widespread use has created more and more opportunities for their entry into the environment, and thus it becomes increasingly important to understand how to biodegrade them. In this concise review, we will cover the progress made in the last five years on this exciting topic, focusing on the applications, and concluding with future perspectives on research combining carbon nanomaterials and enzymes.

Enzyme-mimicking capacities of carbon-dots nanozymes: Properties, catalytic mechanism, and applications - A review

Nanozymes, novel engineered nanomaterial-based artificial enzymes, have been developed to overcome intrinsic drawbacks exist in natural enzymes including high-cost storage, structural instability, and chemical sensitivity. More recently, carbon dots (CDs) have received significant attention due to their biocompatibility, high catalytic activity, and simple surface functionalization, thus emerging as possible alternatives for biomedical and environmental applications. In this review, we analyze methods and precursors used to synthesize CDs with enzyme-mimicking behaviors. In addition, approaches such as doping or constructing hybrid nanozymes are included as possible strategies to enhance the catalytic performance of CDs. Recent studies have reported CDs that mimic different oxidoreductases, exhibiting peroxidase-, catalase-, oxidase/laccase-, and superoxide dismutase-like activities. Therefore, this review presents a detailed discussion of the mechanism, recent advances, and application for each oxidoreductase-like activity reported on nanozymes based on CDs nanomaterials. Finally, current challenges faced in the successful translation of CDs to potential applications are addressed to suggest research directions.

Carbon Nanotube Based Metal-Organic Framework Hybrids From Fundamentals Toward Applications

Metal-organic frameworks (MOFs) materials constructed by the coordination chemistry of metal ions and organic ligands are important members of the crystalline materials family. Owing to their exceptional properties, for example, high porosity, tunable pore size, and large surface area, MOFs have been applied in several fields such as gas or liquid adsorbents, sensors, batteries, and supercapacitors. However, poor conductivity and low stability hamper their potential applications in several attractive fields such as energy and gas storage. The integration of MOFs with carbon nanotubes (CNTs), a well-established carbon allotrope that exhibits high conductivity and stability, has been proposed as an efficient strategy to overcome such limitations. By combining the advantages of MOFs and CNTs, a wide variety of composites can be prepared with properties superior to their parent materials. This review provides a comprehensive summary of the preparation of CNT@MOF composites and focuses on their recent applications in several important fields, such as water purification, gas storage and separation, sensing, electrocatalysis, and energy storage (supercapacitors and batteries). Future challenges and prospects for CNT@MOF composites are also discussed.

Delineating the Role of Tailored Gold Nanostructures at the Biointerface

Gold (Au) has emerged as a superior element, because of its widespread applications in electronic and medical fields. The desirable physical, chemical, optical, and inherent enzyme-like properties of Au are efficiently exploited for detection, diagnostic, and therapeutic purposes. Au offers a unique advantage of fabricating gold nanostructures (GNS) having exact physical, chemical, optical, and enzyme-like properties required for the specific biomedical application. In this Review, the emerging trend of GNS for various biomedical applications is highlighted. Some notable structural and chemical modifications achieved for the detection of biomolecules, pathogens, diagnosis of diseases, and therapeutic applications are discussed in brief. The limitations of GNS during biomedical usage are highlighted and the way forward to overcome these limitations are discussed.

Pt Nanoparticles Anchored on NH2-MIL-101 with Efficient Peroxidase-Like Activity for Colorimetric Detection of Dopamine

Dopamine (DA) is an important catecholamine neurotransmitter that plays a highly relevant role in regulating the central nervous system, and abnormal DA content can cause many immune-related diseases. Hence, it is of significance to sensitively and specifically identify DA for clinical medicine. In this work, Pt/NH2-MIL-101 hybrid nanozymes with bimetallic catalytic centers were fabricated by forming coordinate bonds between Pt nanoparticles (Pt NPs) and –NH2 on metal–organic frameworks (MOF). The catalytic activity of Pt/NH2-MIL-101 was increased by 1.5 times via enlarging the exposure of more active sites and improving the activity of the active sites through the strategy of forming bimetallic catalytic centers. In the presence of DA, competing with 3, 3′, 5, 5′-tetramethylbenzidine (TMB) for the generated hydroxyl radicals (•OH), the blue oxidation state TMB (Ox-TMB) is reduced to colorless TMB, showing dramatic color changes. The Pt/NH2-MIL-101-based colorimetric assay enables the sensitive and robust detection of DA molecules with a detection limit of only 0.42 μM and has an observable potential in clinical applications.

A 3D electrochemical biosensor based on Super-Aligned Carbon NanoTube array for point-of-care uric acid monitoring

Uric acid analysis is extremely important for gout prognosis, diagnosis and treatment. Previous technologies either lack specificity or exhibit poor performance, and thus could not meet the need of Point-of-Care (POC) uric acid monitoring. Here we present for the first time, a novel electrochemical biosensor based on 3D Super-Aligned Carbon NanoTube (SACNT) array to facilitate POC uric acid monitoring. The working electrode of the biosensor is composed of an orderly 3D SACNT array immobilized with uricase through a precipitation and crosslinking procedure. Such biosensor possesses a higher enzyme density, significantly larger contact area with reactants and could maintain the intact SACNT structure and its excellent conductivity after modification. The developed 3D SACNT array electrochemical biosensor benefits from high specific surface area, high electro-catalytic activity and large contact area with analytes, and demonstrates high sensitivity of 518.8 μA/(mM⋅cm²), wide linear range of 100-1000 μM and low limit of detection of 1 μM for uric acid. Dynamic uric acid monitoring has been achieved using the presented biosensor. And the obtained results in serum samples had no significant difference compared with those obtained using the FDA-approved electrochemical analyzer (Paired T-test, p > 0.05). These demonstrated that the technology can potentially be applied in POC monitoring of other biomolecules to improve prognosis, diagnosis and treatment outcomes of metabolic diseases.

Facile synthesis of Cu-CuFe2O4 nanozymes for sensitive assay of H2O2 and GSH

Artificial enzymes have drawn substantial research interest from the scientific community due to their advantages over natural enzymes. However, majority of artificial enzymes exhibit low affinity towards H2O2, which means that a high H2O2 concentration is needed for the oxidation of a substrate such as 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxTMB. With this concern, Cu-CuFe2O4 was facilely synthesized, wherein, Cu0 accelerates the redox capacity of Cu-CuFe2O4 as well as the electron transfer between CuFe2O4 and H2O2. These materials induce excellent activity as a peroxidase. Cu-CuFe2O4 shows high affinity towards H2O2 with lower Michaelis-Menten constant (Km) than the reported values for ferrites and Horseradish enzyme (HRP). Moreover, it took only 5 min to detect hydrogen peroxide (H2O2) and glutathione (GSH) through a colorimetric assay using Cu-CuFe2O4. Compared with CuFe2O4, the limit of detection (LOD) is about 90-fold lower for H2O2 using Cu-CuFe2O4. In addition, Cu-CuFe2O4 shows high stability as a nanozyme. Thus, the mechanism of the peroxidase-like nanozyme Cu-CuFe2O4 is proposed.

A simple enzymeless approach for Paraoxon determination using imidazole-functionalized carbon nanotubes

This work describes the application of a glassy carbon electrode (GCE) modified with imidazole functionalized carbon nanotubes (CNT-H-IMZ) for Paraoxon (PX) determination in samples of commercial, fresh and 100% orange juice. Homemade multi-walled CNTs were treated according to the Hummers procedure to oxidize graphite and later chemically functionalized with imidazole groups. Modified electrodes with CNT-H-IMZ presented a high peak current of PX reduction and an electrocatalytic effect in comparison to the other electrodes. This behavior was associated with the synergistic contribution of IMZ and CNT that increases the electrochemical activity of PX. Repeatability and reproducibility studies showed that the relative peak current values did not show significant differences between them, less than 10%, and it was possible to define that the diffusional process is the mechanism that limits the electrode mass transport. After the optimization of parameters inherent to the methodology and the voltammetric technique, the proposed device presented a linear region of 1.0 to 16.0 μM^-1 (R² = 0.99), presenting LOD and LOQ as 120 and 400 nM^-1, respectively. The method proposed was successfully applied to PX determination in spiked samples.