Bifunctional oxidase-peroxidase inorganic nanozyme catalytic cascade for wastewater remediation

Self-Cascade of the Cu/Ce-MOF-808 Nanozyme for One-Step Colorimetric Sensing

Natural enzyme cascades, including the same and different kinds of enzymes, have been widely used in biosensing. However, it is still a challenge for nanozymes, the mimics of natural enzymes, to achieve biosensing with different types of enzyme-like activities based on cascade reactions, such as hydrolase and oxidoreductase. Considering the characteristics of the multienzyme-like activity of some nanozymes, as a proof of concept, this study demonstrates a Cu/Ce-MOF-808 nanozyme as a self-cascade catalyst with hydrolase-like and catechol oxidase-like activities. Taking organophosphorus pesticides as an example, we constructed a self-cascade catalytic reaction for the one-step colorimetric detection of isocarbophos. Specifically, the hydrolase-like activity of Cu/Ce-MOF-808 can hydrolyze isocarbophos to produce colorless isopropyl salicylate, which is further oxidized by the catechol oxidase-like activity of Cu/Ce-MOF-808 and complexed with 4-aminoantipyrine (4-AAP) to produce red quinoneimine under neutral conditions with illumination. Thus, a colorimetric strategy for sensitive isocarbophos analysis is developed, with a linear range of 0.90-400.00 μg·mL-1 and a detection limit of 0.42 μg·mL-1. This research presents a new approach to the design and synthesis of nanozymes and has great application potential in the field of nanozyme cascade biosensing.

Covalent Coupling-Regulated rGO/VN Nanocomposite Enabling Nitrogen Defects to Remarkably Boost the Peroxidase-Like Catalytic Efficiency for the Ultrasensitive Colorimetric Assay of Uric Acid

It remains challenging to rationally design superior nanozymes and understand the underlying mechanism. Herein, a facile covalent coupling-modulated nitrogen defect is reported for significantly boosting peroxidase (POD)-like activity. Vanadium nitride (VN) nanoparticles are grown on graphene oxide (GO) via C-N bonding to form VN/rGO nanocomposites by varying with the VOx/GO ratio. The initial increasing GO amount enables formation of the C-N bond, dramatically boosting POD-like activity. Nevertheless, with a higher GO amount, the nitrogen defects decrease due to forming mainly V2O3. The defect-rich VN/rGO nanocomposite with 20 wt % GO (VG-2) exhibits the best catalytic efficiency (Vmax/Km = 0.0187 s-1), which is 778-fold higher than that of natural horseradish peroxidase. Theoretical calculations and structure characterization reveal that the rich-N defects originate from VN covalent binding onto rGO with an rich-electron structure, impeding VN agglomeration, which greatly reduces the energy barrier of the rate-determining step of the catalytic reaction. Finally, coupling urate oxidase with VG-2 as an enzyme cascade, an ultrasensitive and selective colorimetric detection was developed for uric acid (UA), one of the indicators of kidney function or gout attacks, with a linear detection ranging 1-100 μM and 0.1-2.5 mM with a limit of detection of 0.24 μM UA (S/N = 3). The proposed method was applicable to detecting UA in human serum samples satisfactorily. This work could inspire more effective insights into designing other robust nanozymes through covalent coupling for a variety of biochemical analysis and biocatalysis applications.

Co-based Nanozymatic Profiling: Advances Spanning Chemistry, Biomedical, and Environmental Sciences

Nanozymes, next-generation enzyme-mimicking nanomaterials, have entered an era of rational design; among them, Co-based nanozymes have emerged as captivating players over times. Co-based nanozymes have been developed and have garnered significant attention over the past five years. Their extraordinary properties, including regulatable enzymatic activity, stability, and multifunctionality stemming from magnetic properties, photothermal conversion effects, cavitation effects, and relaxation efficiency, have made Co-based nanozymes a rising star. This review presents the first comprehensive profiling of the Co-based nanozymes in the chemistry, biology, and environmental sciences. The review begins by scrutinizing the various synthetic methods employed for Co-based nanozyme fabrication, such as template and sol-gel methods, highlighting their distinctive merits from a chemical standpoint. Furthermore, a detailed exploration of their wide-ranging applications in biosensing and biomedical therapeutics, as well as their contributions to environmental monitoring and remediation is provided. Notably, drawing inspiration from state-of-the-art techniques such as omics, a comprehensive analysis of Co-based nanozymes is undertaken, employing analogous statistical methodologies to provide valuable guidance. To conclude, a comprehensive outlook on the challenges and prospects for Co-based nanozymes is presented, spanning from microscopic physicochemical mechanisms to macroscopic clinical translational applications.

Increased Range of Catalytic Activities of Immobilized Compared to Colloidal Gold Nanoparticles

Gold nanoparticles (AuNPs) can be described as nanozymes, species that are able to mimic the catalytic activities of several enzymes, such as oxidase/peroxidase, reductase, or catalase. Most studies in the literature focus on the colloidal suspension of AuNPs, and it is obvious that their immobilization could open the doors to new applications thanks to their increased stability in this state. This work aimed to investigate the behavior of surfaces covered by immobilized AuNPs (iAuNPs). Citrate-stabilized AuNPs (AuNPs-cit) were synthesized and immobilized on glass slides using a simple dip coating method. The resulting iAuNPs were characterized (surface plasmon resonance, microscopy, quantification of immobilized AuNPs), and their multi-enzymatic-like activities (oxidase-, peroxidase-, and catalase-like activity) were evaluated. The comparison of their activities versus AuNPs-cit highlighted their added value, especially the preservation of their activity in some reaction media, and their ease of reuse. The huge potential of iAuNPs for heterogeneous catalysis was then applied to the degradation of two model molecules of hospital pollutants: metronidazole and methylene blue.

Bioengineered Carboxymethylcellulose-Peptide Hybrid Nanozyme Cascade for Targeted Intracellular Biocatalytic-Magnetothermal Therapy of Brain Cancer Cells

Glioblastoma remains the most lethal form of brain cancer, where hybrid nanomaterials biofunctionalized with polysaccharide peptides offer disruptive strategies relying on passive/active targeting and multimodal therapy for killing cancer cells. Thus, in this research, we report for the first time the rational design and synthesis of novel hybrid colloidal nanostructures composed of gold nanoparticles stabilized by trisodium citrate (AuNP@TSC) as the oxidase-like nanozyme, coupled with cobalt-doped superparamagnetic iron oxide nanoparticles stabilized by carboxymethylcellulose ligands (Co-MION@CMC) as the peroxidase-like nanozyme. They formed inorganic-inorganic dual-nanozyme systems functionalized by a carboxymethylcellulose biopolymer organic shell, which can trigger a biocatalytic cascade reaction in the cancer tumor microenvironment for the combination of magnetothermal-chemodynamic therapy. These nanoassemblies were produced through a green aqueous process under mild conditions and chemically biofunctionalized with integrin-targeting peptide (iRDG), creating bioengineered nanocarriers. The results demonstrated that the oxidase-like nanozyme (AuNP) was produced with a crystalline face-centered cubic nanostructure, spherical morphology (diameter = 16 ± 3 nm), zeta potential (ZP) of -50 ± 5 mV, and hydrodynamic diameter (DH) of 15 ± 1 nm. The peroxide-like nanostructure (POD, Co-MION@CMC) contained an inorganic crystalline core of magnetite and had a uniform spherical shape (2R = 7 ± 1 nm) which, summed to the contribution of the CMC shell, rendered a hydrodynamic diameter of 45 ± 4 nm and a negative surface charge (ZP = -41 ± 5 mV). Upon coupling both nanozymes, water-dispersible colloidal supramolecular vesicle-like organic-inorganic nanostructures were produced (AuNP//Co-MION@CMC, ZP = -45 ± 4 mV and DH = 28 ± 3 nm). They confirmed dual-nanozyme cascade biocatalytic activity targeted by polymer-peptide conjugates (AuNP//Co-MION@CMC_iRGD, ZP = -29 ± 3 mV and DH = 60 ± 4 nm) to kill brain cancer cells (i.e., bioenergy "starvation" by glucose deprivation and oxidative stress through reactive oxygen species generation), which was boosted by the magneto-hyperthermotherapy effect when submitted to the alternating magnetic field (i.e., induced local thermal stress by "nanoheaters"). This groundwork offers a wide avenue of opportunities to develop innovative theranostic nanoplatforms with multiple integrated functionalities for fighting cancer and reducing the harsh side effects of conventional chemotherapy.

Nanozymes with Multiple Activities: Prospects in Analytical Sensing

Given the superiorities in catalytic stability, production cost and performance tunability over natural bio-enzymes, artificial nanomaterials featuring enzyme-like characteristics (nanozymes) have drawn extensive attention from the academic community in the past decade. With these merits, they are intensively tested for sensing, biomedicine and environmental engineering. Especially in the analytical sensing field, enzyme mimics have found wide use for biochemical detection, environmental monitoring and food analysis. More fascinatingly, rational design enables one fabrication of enzyme-like materials with versatile activities, which show great promise for further advancement of the nanozyme-involved biochemical sensing field. To understand the progress in such an exciting field, here we offer a review of nanozymes with multiple catalytic activities and their analytical application prospects. The main types of enzyme-mimetic activities are first introduced, followed by a summary of current strategies that can be employed to design multi-activity nanozymes. In particular, typical materials with at least two enzyme-like activities are reviewed. Finally, opportunities for multi-activity nanozymes applied in the sensing field are discussed, and potential challenges are also presented, to better guide the development of analytical methods and sensors using nanozymes with different catalytic features.