Pt-Decorated Boron Nitride Nanosheets as Artificial Nanozyme for Detection of Dopamine

Two-Dimensional Nanomaterials With Enzyme-Like Properties for Biomedical Applications

Recently, remarkable progress has been made in nanozyme research due to the rapid development of nanomaterials. Two-dimensional nanomaterials such as metal nanosheets, graphene-based materials, transition metal oxides/dichalcogenides, etc., provide enhanced physical and chemical functionality owing to their ultrathin structures, high surface-to-volume ratios, and surface charges. They have also been found to have high catalytic activities in terms of natural enzymes such as peroxidase, oxidase, catalase, and superoxide dismutase. This review provides an overview of the recent progress of nanozymes based on two-dimensional nanomaterials, with an emphasis on their synthetic strategies, hybridization, catalytic properties, and biomedical applications. Finally, the future challenges and prospects for this research are discussed.

Degradation of polyvinyl chloride microplastics via an electro-Fenton-like system with a TiO2/graphite cathode

Nowadays, microplastic pollution has been brought into focus for its hazards to aquatic life. However, researches on the electrocatalytic treatment for efficient degradation of microplastics are still insufficient. Herein, an electro-Fenton like (EF-like) technology based on TiO₂/graphite (TiO₂/C) cathode was put forward to degrade polyvinyl chloride (PVC), a typical microplastic in water. It exhibited a remarkable performance on PVC degradation via cathodic reduction dechlorination and hydroxyl radical (OH) oxidation simultaneously. Besides, the effects of reaction temperature and initial PVC concentration were investigated. Under optimal conditions, the dechlorination efficiency of PVC reached 75 % after potentiostatic electrolysis at -0.7 V vs. Ag/AgCl for 6 h. The intermediate products were explored during the degradation of PVC microplastics. The surface morphologies and molecular weight of PVC changed accordingly. Based on these results, a possible degradation process for PVC was proposed. This work demonstrated that such a heterogeneous EF-like technology using TiO₂/C cathode was hopefully to provide an eco-friendly method for microplastic wastewater treatment.

Construct of Carbon Nanotube-Supported Fe2O3 Hybrid Nanozyme by Atomic Layer Deposition for Highly Efficient Dopamine Sensing

The Fe2O3 nanozyme has been identified as the most promising alternative for the Fe3O4 nanozyme due to its relatively low toxic risk and good chemical stability. However, its enzyme-like activity is relatively low enough to meet specific application requirements. Furthermore, previous synthesis approaches have difficulties in fabricating ultra-small Fe2O3 nanoparticles with tunable size and suffer from agglomeration problems. In this study, atomic layer deposition (ALD) was used to deposit Fe2O3 on surfaces of carbon nanotubes to form hybrid nanozymes (Fe2O3/CNTs). ALD enables the preparation of ultrafine Fe2O3 nanoparticles with precise size control <1 nm, while CNTs could be served as promising support for good dispersibility and as an effective activity activator. Hence, the formed Fe2O3/CNTs exhibit excellent peroxidase-like activity with a specific peroxidase activity of 24.5 U mg-1. A colorimetric method for sensing dopamine (DA) was established and presented good sensitivity with a limit of detection (LOD) as low as 0.11 μM. These results demonstrated that, in virtue of meticulous engineering methods like ALD, carbon nanomaterial-based hybrids can be developed as talented enzyme mimetic, thus paving a way for nanozyme design with desired activity and broadening their applications in biosensing and other fields.

In Situ Detection of Neurotransmitters from Stem Cell-Derived Neural Interface at the Single-Cell Level via Graphene-Hybrid SERS Nanobiosensing

In situ quantitative measurements of neurotransmitter activities can provide useful insights into the underlying mechanisms of stem cell differentiation, the formation of neuronal networks, and neurodegenerative diseases. Currently, neurotransmitter detection methods suffer from poor spatial resolution, nonspecific detection, and a lack of in situ analysis. To address this challenge, herein, we first developed a graphene oxide (GO)-hybrid nanosurface-enhanced Raman scattering (SERS) array to detect dopamine (DA) in a selective and sensitive manner. Using the GO-hybrid nano-SERS array, we successfully measured a wide range of DA concentrations (10^-4 to 10^-9 M) rapidly and reliably. Moreover, the measurement of DA from differentiating neural stem cells applies to the characterization of neuronal differentiation. Given the challenges of in situ detection of neurotransmitters at the single-cell level, our developed SERS-based detection method can represent a unique tool for investigating single-cell signaling pathways associated with DA, or other neurotransmitters, and their roles in neurological processes.

Platinum nanoparticle-deposited multi-walled carbon nanotubes as a NADH oxidase mimic: characterization and applications

The effective regeneration of bioactive NAD+ plays an important role in numerous dehydrogenase-dependent applications including biocatalysis and biosensing. However, this process usually suffers from high thermodynamic barrier, instability and high cost associated with natural enzymes. The emergence of nanomaterials with enzyme mimic characteristics has offered a potential alternative to many enzyme-catalyzed processes. Platinum nanoparticles (PtNPs), for example, have been extensively studied for their peroxidase- and oxidase-like activities. However, their behavior as a NADH oxidase mimic has barely been characterized in detail. Herein, we report a facile approach for preparing PtNP-deposited multi-walled carbon nanotubes (PtNPs@MWCNTs) as the nanozyme for NADH oxidation. Its enzymatic activity was investigated in depth, revealing that it is a NADH oxidase instead of a peroxidase and the catalytic process generates O2˙-, rather than OH˙ or 1O2, from dissolved O2. The recovery yield of bioactive NAD+ regeneration by the nanozyme could reach ∼100% with a total turnover number of ∼6000. Besides, it exhibited terrific electrochemical performance for NADH oxidation and sensing by greatly boosting the response and lowering the oxidation overpotential. It could also work on biomimetic cofactors with even higher activity. Finally, xylose dehydrogenase was immobilized with the nanozyme to constitute a hybrid bioelectrode for xylose sensing. The biosensor had a xylose detecting range of 5-400 μM with the limit of detection as low as 1 μM and can retain its performance after being reused several times. Our results suggest that the PtNPs@MWCNTs characterized as a NADH oxidase nanozyme hold great promise in the applications of biocatalysis and biosensing, which intensively deal with dehydrogenases and natural or biomimetic cofactors.

Recent Progress in the Study of Thermal Properties and Tribological Behaviors of Hexagonal Boron Nitride-Reinforced Composites

Ever-increasing significance of composite materials with high thermal conductivity, low thermal expansion coefficient and high optical bandgap over the last decade, have proved their indispensable roles in a wide range of applications. Hexagonal boron nitride (h-BN), a layered material having a high thermal conductivity along the planes and the band gap of 5.9 eV, has always been a promising candidate to provide superior heat transfer with minimal phonon scattering through the system. Hence, extensive researches have been devoted to improving the thermal conductivity of different matrices by using h-BN fillers. Apart from that, lubrication property of h-BN has also been extensively researched, demonstrating the effectivity of this layered structure in reduction of friction coefficient, increasing wear resistance and cost-effectivity of the process. Herein, an in-depth discussion of thermal and tribological properties of the reinforced composite by h-BN will be provided, focusing on the recent progress and future trends.

ZIF-67 as a Template Generating and Tuning "Raisin Pudding"-Type Nanozymes with Multiple Enzyme-like Activities: Toward Online Electrochemical Detection of 3,4-Dihydroxyphenylacetic Acid in Living Brains

Due to its unique structure and high porosity, metal-organic frameworks (MOFs) can act not only as nanozyme materials but also as carriers to encapsulate natural enzymes and thus have received extensive attention in recent years. However, a few research studies have been conducted to investigate MOF as a template to generate and tune nanozymes in the structure and performance. In this work, the "raisin pudding"-type ZIF-67/Cu_0.76Co_2.24O₄ nanospheres (ZIF-67/Cu_0.76Co_2.24O₄ NSs) were obtained by rationally regulating the weight ratio of ZIF-67 and Cu(NO₃)₂ in the synthesis process. Here, ZIF-67 not only acts as a template but also provides a cobalt source for the synthesis of cobalt copper oxide on the surface of ZIF-67/Cu_0.76Co_2.24O₄ NSs with multiple enzyme-like activities. The ZIF-67/Cu_0.76Co_2.24O₄ NSs can mimic four kinds of enzymes with peroxidase-like, glutathione peroxidase-like, superoxide dismutase-like, and laccase-like activities. Based on its laccase-like activity, an online electrochemical system for continuous monitoring of 3,4-dihydroxyphenylacetic acid with good linearity in the range of 0.5-20 μM and a detection limit of 0.15 μM was established. Furthermore, the alteration of DOPAC in the brain microdialysate before and after ischemia of the rats' brain was also successfully recorded. This work not only raises a new idea for the synthesis of nanozyme materials with multiple enzyme activities but also provides a new solution for the detection of neurotransmitters in living brains.

A pH-responsive colorimetric detection of human telomerase RNA based on a three-dimensional DNA amplifier

Human telomerase RNA (hTR), one of the essential components of telomerase, serves as a reverse template to add repeated segments of (TTAGGG)_n to the 3' end of telomere DNA for maintaining the length of telomere DNA, endowing cells indefinite proliferation capability. Expression level of hTR displays a close relationship with tumor grade. Inspired by the mechanism of urease hydrolyzing urea to release ammonia and elevate the pH value of the sample solution, we developed a facile and novel pH-responsive colorimetric strategy for hTR detection by incorporating catalyzed hairpin assembly (CHA) onto the magnetic beads (MBs). The CHA process was initiated by target hTR and recycled via toehold binding and branch migration, thereby abundant urease being anchored on the surface of MBs. After separated by an external magnetic field, the assembled urease catalyzed the hydrolysis of urea to release a large amount of ammonia, which gave rise to a remarkable pH signal. Thus, quantification of hTR was achieved by measuring the solution pH via a hand-held pH meter or visualizing the solution color with the assistance of the pH indicator phenol red. The proposed sensing platform exhibits excellent performance toward hTR with a detection limit as low as 41 pM and a remarkable sequence selectivity, being able to differentiate a single mismatch in the target DNA. The pH-responsive colorimetric sensing platform contributes to introducing pH-related portable strategies into the detections of numerous universal biomarkers such as nucleic acids and proteins.

Point-of-care assay for drunken driving with Pd@Pt core-shell nanoparticles-decorated ploy(vinyl alcohol) aerogel assisted by portable pressure meter

Alcohol abuse causes health problems and security accidents. A reliable and sensitive detection system for alcohol has been an instinctive demand in law enforcement and forensic. More efforts are demanded in developing new sensing strategy preferably with portable and non-invasive traits for the pushforward of point-of-care (POC) device popularization.

Methods: We developed a POC diagnosis system for alcohol assay with the aid of alcohol oxidase (AOX) pre-joining in the system as well as Pd@Pt core-shell nanoparticles (abbreviated to Pd@Pt) that were decorated on ploy(vinyl alcohol) aerogel with amphiphilicity. Biological samples like saliva and whole blood can be absorbed by the aerogel in a quick process, in which the analyte would go through a transformation from alcohol, H₂O₂, to a final production of O₂, causing an analyte dose-dependent signal change in the commercial portable pressure meter. The cascade reactions are readily catalyzed by AOX and Pd@Pt, of which the latter one possesses excellent peroxidase-like activity.

Results: Our design has smartness embodied in the aerogel circumvents the interference from methanol which is more ready to be catalyzed by AOX. Under the optimal conditions, the limit of detection for alcohol was 0.50 mM in saliva, and is able to distinguish the driving under the influence (DUI) (1.74 mM in saliva) and driving while impaired (DWI) (6.95 mM in saliva) in the national standard of China.

Conclusion: Our proof-of-concept study provides the possibility for the establishment of POC device for alcohol and other target detection, not only owing to the sensing qualification but also thanks to the architecture of such sensor that has great flexibility by replacing the AOX with glucose oxidase (GOX), thenceforth realizing the accurate detection of glucose in 0.5% whole blood sample. With the advantages of easy accessibility and anti-interference ability, our sensor exhibits great potential for quantitative diagnostics in biological system.

Electrodeposition-Assisted Rapid Preparation of Pt Nanocluster/3D Graphene Hybrid Nanozymes with Outstanding Multiple Oxidase-Like Activity for Distinguishing Colorimetric Determination of Dihydroxybenzene Isomers

Here, we demonstrate a facile bottom-up strategy to fabricate Pt nanoclusters (Pt NCs) grafted onto three-dimensional graphene foam (3D GF) assisted by cetyltrimethyl ammonium bromide (CTAB) using the electrodeposition method. The homogeneous grafting of Pt NC onto 3D GF is due to the formation of hemimicelles above some CTAB concentration. With the unique nanocluster structure and the high content of Pt⁰, the Pt NC/3D GF nanohybrid exhibits extremely high activity and shows higher reusability and stability. Apart from the intrinsic oxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate, the Pt NC/3D GF nanohybrid can act simultaneously as an effective polyphenol oxidase (PPO) mimic, such as tyrosinase, catechol oxidase, and laccase. More importantly, utilizing intrinsic catechol oxidase-like activity and the oxidase-like activity with TMB as the substrate of the nanohybrid, distinguishing colorimetric determination of dihydroxybenzene isomers (catechol and hydroquinone) is performed. Distinguishing colorimetric analysis of dihydroxybenzene isomers was first developed using nanozymes. The present work provides a simple bottom-up approach for the reasonable fabrication of various nanostructured nanozymes with excellent performance using the electrodeposition method assisted with surfactants.

Dual responsive magnetic Fe3O4-TiO2/graphene nanocomposite as an artificial nanozyme for the colorimetric detection and photodegradation of pesticide in an aqueous medium

The Fe₃O₄-TiO₂/reduced graphene oxide (Fe₃O₄-TiO₂/rGO) nanocomposite was successfully prepared by one step hydrothermal method and exhibit intrinsic peroxidase mimic activity and photocatalytic efficiency. The as-prepared nanomaterials were characterized by several analytical tools including XRD, HRTEM, FESEM, XPS, VSM, FT-IR, AFM, TGA and zeta potential analysis. The average particle size of Fe₃O₄ and TiO₂ NPs on the rGO nanosheets are found to be 9 ± 0.2 nm. The synthesized nanocomposite showed dual responsive including highly sensitive colorimetric detection of harmful atrazine pesticide in an aqueous medium as well as photocatalytic degradation of atrazine pesticide. The Fe₃O₄-TiO₂/rGO nanocomposite showed the efficient peroxidase-like catalytic activity throughout the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) as a peroxidase substrate to the blue-colored oxidized product (ox-TMB) in presence of H₂O₂. Based on this observation, the colorimetric detection technique is applied for the sensing of atrazine as model pesticides using TMB as a peroxidase substrate molecule and 2.98 μg/L of the limit of detection (LOD) was obtained in the linear range of 2-20 μg/L. Thus the proposed colorimetric sensing technique is simple and low cost for the real-time monitoring of the pesticides in an aqueous medium. Further, the Fe₃O₄-TiO₂/rGO nanocomposite was also successfully utilized towards efficient photocatalytic degradation of atrazine molecule (100 %) under irradiation of natural sunlight. Moreover, Fe₃O₄-TiO₂/rGO nanocomposite was successfully recycled for 10 times without a significant loss of its photocatalytic efficiency. This work delivers a new insight for the dual responsive of the Fe₃O₄-TiO₂/rGO nanocomposite as an artificial nanozyme for colorimetric sensing of the water pollutant and also removal of the water pollutant by simple photocatalytic degradation method under natural sunlight irradiation.

Promoting Active Sites in MOF-Derived Homobimetallic Hollow Nanocages as a High-Performance Multifunctional Nanozyme Catalyst for Biosensing and Organic Pollutant Degradation

Nanozymes are one of the ideal alternatives to natural enzymes for various applications. The rational design of nanozymes with improved catalytic activity stimulates increasing attention to address the low activity of current nanozymes. Here, we reported a general strategy to fabricate the Co-based homobimetallic hollow nanocages (HNCs) (C-CoM-HNC, M = Ni, Mn, Cu, and Zn) by ion-assistant solvothermal reaction and subsequent low-temperature calcination from metal-organic frameworks. The C-CoM-HNCs are featured with HNCs composed of interlaced nanosheets with homogeneous bimetallic oxide dispersion. The hierarchical structure and secondary metallic doping endow the C-CoM-HNC highly active sites. In particular, the Cu-doped C-CoCu-HNCs nanostructures exhibit superior performances over the other C-CoM-HNC as both the oxidase mimicking and peroxymonosulfate (PMS) activator. A sensitive bioassay for acetylcholinesterase (AChE) was established based on the excellent oxidase-like activity of C-CoCu-HNC, offering a linear detection range from 0.0001 to 1 mU/mL with an ultralow detection limit of 0.1 mU/L. As the PMS activator, the C-CoCu-HNC was applied for targeted organic pollutant (rhodamine B, RhB) degradation. A highly efficient RhB degradation was realized, along with good adaptability in a wide pH range and good reusability during the eight-cycle run. The results suggest that C-CoCu-HNC holds a practical potential for clinical diagnostics and pollution removal. Further density functional theory calculation reveals that Cu doping leads to a tighter connection and more negative adsorption energy for O₂/PMS, as well as an upshifted d-band center in the C-CoCu-HNCs nanostructures. These changes facilitated the adsorption of O₂/PMS on the C-CoCu-HNC surface for dissociation. This work not only offers a promising multifunctional nanozyme catalyst for clinical diagnostics and pollution removal but also gives some clues for the further development of novel nanozymes with high catalytic activities.

In situ formation and immobilization of gold nanoparticles on polydimethylsiloxane (PDMS) exhibiting catalase-mimetic activity

We used needles to prepare immobilized AuNPs on the surface of PDMS in situ with catalase-mimetic activity.

Tetrakis(4-aminophenyl) ethene-doped perylene microcrystals with strong electrochemiluminescence for biosensing applications

A facile and economic method for the inhibition of ACQ effect was developed by doping of non-planar moleculars ETTA into Pe MCs, which exhibited almost 10 times stronger ECL signal in aqueous phase compared to that of pure Pe MCs.

One-pot synthesis of luminol–gallium nanoassemblies and their peroxidase-mimetic activity for colorimetric detection of pyrophosphate

Luminol–Ga nanoassemblies exhibit peroxidase-mimetic activity. Colorimetric detection of PPi is developed owing to the formation of a complex between PPi and Ga³⁺.