Adenine phosphate-Cu nanozyme with multienzyme mimicking activity for efficient degrading phenolic compounds and detection of hydrogen peroxide, epinephrine and glutathione

Cascade-enhanced based-polyoxometalates nanozyme for glutathione detection and tumor cell disruption

Nanozymes with biological enzyme activity show great promise in biochemical analysis and medicine, yet single-activity nanozymes were limited by low catalytic efficiency and strict catalytic environment requirements. Consequently, the development of nanozymes with multiple enzyme activities presents a significant challenge. In the work, a vanadium-capped polyoxometalates (POMs)-encapsulating metal-organic framework (MOF), [Cu12(Trz)8Cl][PMo12O40(VO)2], was synthesized via hydrothermal synthesis, which shows multiple enzyme activities concluding oxidase (OXD), peroxidase (POD) and catalase (CAT) activities. In the catalytic procedure, a fraction of H2O2 generated by the OXD is further subjected to the POD catalytic reaction and the remaining portion is transformed into O2 through the CAT activity, in turn, supplies the driving force for the OXD-like catalytic process. This cascade reaction, in conjunction with the transformation between Cu2+ and Cu+ within the material, engenders a structure analogous to an interlocking "gear", which augments the catalytic efficacy as well as the adaptability to intricate environmental conditions of the [Cu12(Trz)8Cl][PMo12O40(VO)2] enzyme. By capitalizing on this high catalytic efficiency, the rapid quantitative detection of glutathione (GSH) was established with the calculated limit of detection (LOD) 0.062 μM in the range of 5-60 μM. Surprisingly, the multi-enzymatic [Cu12(Trz)8Cl][PMo12O40(VO)2] can concurrently enhance the generation of reactive oxygen species (ROS) and the depletion of GSH in the tumor microenvironment (TME), thereby inducing tumor cell apoptosis. This research holds promising application prospects in the fields of biotechnology, clinical diagnosis, and tumor therapy.

Multifunctional nanozymes: Promising applications in clinical diagnosis and cancer treatment

Cancer remains one of the greatest challenges in modern medicine. Traditional chemotherapy drugs often cause severe side effects, including nausea, vomiting, diarrhea, neurotoxicity, liver damage, and nephrotoxicity. In addition to these adverse effects, high recurrence and metastasis rates following treatment pose significant challenges for clinicians. There is an urgent need for novel therapeutic strategies to improve cancer treatment outcomes. In this context, nanozymes-artificial enzyme mimetics-have attracted considerable attention due to their unique advantages, including potent tumor-killing effects, enhanced biocompatibility, and reduced toxicity. Notably, nanozymes can dynamically monitor tumors through imaging and tracing. The multifunctional nanozyme (MN) is a promising research focus, integrating multiple catalytic activities, signal enhancement, sensing capabilities, and diverse modifications within a single nanozyme system. MNs can selectively target tumor regions, facilitating synergistic effects with other cancer therapies while enabling real-time imaging and tumor tracking. In this review, we first categorize MNs based on their composition and structural characteristics. We then discuss the primary mechanisms by which MNs exert their anticancer effects. Additionally, we review three types of MN biosensors and four MN-based therapeutic approaches applied in cancer treatment. Finally, we highlight the current challenges in MN research and provide an outlook on future developments in this field.

Frontiers in laccase nanozymes-enabled colorimetric sensing: A review

In recent years, nanozyme-based analytics have become popular. Among these, laccase nanozyme-based colorimetric sensors have emerged as simple and rapid colorimetric detection methods for various analytes, effectively addressing natural enzymes' stability and high-cost limitations. Laccase nanozymes are nanomaterials that exhibit inherent laccase enzyme-like activity. They can oxidize phenolic compounds to generate a coloured product, independently or with a chromogenic agent. This chromogenic reaction provides the basis for developing simple and robust colorimetric assays for various analytes, enabling rapid and point-of-need analytical decision-making in food safety, clinical diagnostics, and environmental monitoring. This review article provides a concise overview of laccase nanozymes, including their classification and catalytic mechanisms. The article mainly discusses colorimetric and dual-mode detection methods and outlines various strategies to enhance the colorimetric sensing performance of laccase nanozymes. Additionally, the article highlights future research directions that could further improve laccase nanozyme-enabled colorimetric sensing. We hope this work will enhance the field's understanding and help future researchers identify gaps in developing simple, low-cost colorimetric sensors.

Pyrroloquinoline quinone exhibiting peroxidase-mimicking property for colorimetric assays

BACKGROUND

Small molecule mimics offer the advantages of easy preparation, good thermodynamic stability, and reproducible catalytic activity. However, most of the reported organic artificial mimics face challenges including low catalytic activity, oxidative self-destruction, and auto-aggregation into inactive dimers. Therefore, novel organic mimics with high catalytic activity as well as good thermal and environmental stability are highly desirable.

RESULTS

We found that pyrroloquinoline quinone (PQQ), a nutritionally important growth factor, displayed significant peroxidase-like activity to catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB) by H2O2. Its catalytic activity surpassed that of other organic small molecules reported previously, including fluorescein derivatives and adenosine/guanosine triphosphate. Based on the reduction of oxTMB by the enzymatically generated ascorbic acid (AA), the PQQ/TMB-based system was used to monitor alkaline phosphatase (ALP) activity with ascorbic acid 2-phosphate (AAP) as the substrate. This sensing system allowed for the determination of ALP with a detection limit of 1 mU/mL. Furthermore, we discovered that PQQ can coordinate with Cu2+ to form metal-organic nanoparticles. The building blocks of two active cofactors endowed the nanoparticles with impressive functionalities for biocatalytic applications. With Cu-PQQ nanoparticles as signal labels, colorimetric immunoassays of prostate specific antigen (PSA) were achieved with a lowest detectable concentration down to 0.1 pg/mL.

SIGNIFICANCE

This work is valuable for the design of novel biosensors by utilizing PQQ as an artificial enzyme because of its high catalytic activity, good stability, ease of storage, and simple chemical structure.

Cu3(HITP)2 with peroxidase- and ascorbic acid oxidase-like catalytic activity for fluorescence/chemiluminescence sensing of ascorbic acid

Nanomaterials with intrinsic enzyme mimicking activity have achieved widespread application. However, developing novel nanomaterials with multienzyme mimicry activity remains challenging. Herein, Cu3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) with ascorbic acid oxidase (AAO)- and peroxidase (POD)-like activity are successfully synthesized. Cu3(HITP)2 exhibits excellent AAO-like activity and can specifically catalyze the oxidation reaction of ascorbic acid (AA). Dehydroascorbic acid (DHAA) obtained from the oxidation of AA is allowed to react with nonfluorescent o-phenylenediamine (OPD) to form 3-(1,2-dihydrox-yethyl) furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission. Moreover, Cu3(HITP)2 is able to catalyze the chemiluminescence (CL) reaction of ABEI-H2O2 to generate a strong and glow-type emission based on its POD activity. Inspired by the multienzyme mimicry activity of Cu3(HITP)2, the simple and sensitive fluorescence and chemiluminescence sensing platforms are successfully constructed and applied for the detection of AA. The sensors show high sensitivity and excellent selectivity. We believe that this multienzyme mimicry activity nanomaterial not only can be used to construct the multiple-mode biosensing platform, but also enables the extensive applications in the fields of biomedicine, energy, and environment.

Construction of pyrimidine derivatives-copper enzyme mimics as colorimetric sensing elements for efficient detection of phenolic compounds and hydrogen peroxide

As concerns about environmental pollution grow, the rapid identification and quantification of pollutants have become increasingly vital. In this work, a series of pyrimidine derivatives-Cu enzyme mimics (Cytosine-Cu, Cytidine-Cu, and CMP-Cu) with laccase- and peroxidase-like activity were prepared through the coordination of Cu2+ with different pyrimidine derivatives (PDs). The PDs-Cu enzyme mimics contain high levels of Cu+ and N - Cu coordination structures, which provide sufficient catalytic sites for the substrates. Compared with natural enzymes and other nanozymes, PDs-Cu demonstrate superior substrate affinity, catalytic efficiency, stability, and resistance to interference. It was found that PDs-Cu enzyme mimics have different catalytic activities towards different phenolic compounds. Therefore, a three-channel colorimetric sensor array (CSA) was successfully developed utilizing PDs-Cu as the sensing elements. The CSA can accurately identify different phenolic compounds and their mixtures in seawater and simulated wastewater. Additionally, a colorimetric method for detecting H2O2 in eye drops was developed, featuring a detection range of 0.1-10.0 μM and a limit of quantification of 0.1 μM. This research not only provides a flexible protocol for regulating the catalytic activity of enzyme mimics, but also provides important inspiration for the development of methods for rapid identification and detection of contaminants in the environmental water.

A novel dual-ligand copper-based nanoflower for the colorimetric and fluorescence detection of 2,4-dichlorophenol, epinephrine and hydrogen peroxide

BACKGROUND

Nanozymes have the advantages of cost effective, simple synthesis, high durability and stability, and have been widely used in various fields. However, only a few nanomaterials with multiple enzyme-like activity have been reported, and most of the currently developed nanozymes are usually used in colorimetric or fluorescence analysis depending on a single colorimetric or fluorescence signal output. In this study, a copper-based dual-ligand biomimetic nanoflower (Cu-MN) was constructed, which demonstrated potential multiple enzyme-like activity, and was applied to the multi-mode detection of 2,4-dichlorophenol (2,4-DP), epinephrine (EP), and H2O2.

RESULTS

The laccase-like activity of Cu-MN can catalyze the conversion of 2,4-DP and EP, resulting in the formation of red and yellow-brown oxidation products with distinct UV absorption peaks at 510 nm and 485 nm, respectively. Furthermore, the fluorescence emission peak at 426 nm of Cu-MN can be dynamic quenched during substrate oxidation due to the fluorescence internal filtration effect (IFE). Therefore, a dual-mode analysis method was constructed to detect 2,4-DP and EP by fluorescence and ultraviolet colorimetry, which was successfully applied in natural lake water and rabbit plasma analysis, respectively. Furthermore, a colorimetric sensing strategy based on the peroxidase-like activity of Cu-MN was developed and successfully applied to the monitoring of H2O2 in hydrogen peroxide disinfectant. Additionally, the visualization analysis method was also established by RGB reading of the smartphone.

SIGNIFICANCE AND NOVELTY

In brief, inspired by the fluorescence characteristics of 2-aminoterephthallc acid and the imidazole group of 2-methylimidazole, a novel copper-based dual-ligand biomimetic nanoflower (Cu-MN) was prepared and used to establish multi-mode method for the detection of 2,4-DP, EP, and H2O2, which opens up new avenues for its applications in bioanalysis and environmental monitoring.

Non-pyrolytic synthesis of laccase-like iron based single-atom nanozymes for highly efficient dual-mode colorimetric and fluorescence detection of epinephrine

Single-atom nanozymes have garnered significant attention due to their exceptional atom utilization and ability to establish well-defined structure-activity relationships. However, conventional pyrolytic synthesis methods pose challenges such as high energy consumption and random local environments at the active sites, while achieving non-pyrolytic synthesis of single-atom nanozymes remains a formidable technical hurdle. The present study focuses on the synthesis of laccase-like iron-based single-atom nanozymes (Fe-SAzymes) using a non-pyrolysis method facilitated by microwave irradiation. Under low iron loading conditions, Fe-SAzymes exhibited significantly enhanced laccase activity (12.1 U/mg), surpassing that of laccase by 24-fold. Moreover, Fe-SAzymes demonstrated efficient catalytic oxidation of epinephrine (EP), enabling its colorimetric detection. Owing to the remarkable laccase activity of Fe-SAzymes, the conventional nanozymes EP detection time was reduced from 60 min to 20 min, with an impressive low detection limit as low as 2.95 μM. In addition, an ultra-sensitive fluorescence method for EP detection was developed using the internal filter effect of EP oxidation products and CDs combined with carbon dots probe. The detection limit of fluorescence method was only 0.39 μM. Therefore, an visual, fast, and highly sensitive dual-mode EP detection strategy has great potential in the clinical diagnostic industry.

Platinum-ruthenium-iron embedded in nitrogen-doped ordered mesoporous carbon for adrenaline electrochemical sensing study

A novel nitrogen-doped ordered mesoporous carbon (OMC) pore-embedded growth Pt-Ru-Fe nanoparticles (Pt1-Ru7.5-Fex@N-OMCs) composite was designed and synthesized for the first time. SBA-15 was used as a template, and dopamine was used as a carbon and nitrogen source and metal linking reagent. The oxidative self-polymerization reaction of dopamine was utilized to polymerize dopamine into two-dimensional ordered SBA-15 template pores. Iron porphyrin was introduced as an iron source at the same time as polymerization of dopamine, which was introduced inside and outside the pores using dopamine-metal linkage. Carbonization of polydopamine, nitrogen doping and iron nanoparticle formation were achieved by one-step calcination. Then the templates were etched to form Fex@N-OMCs, and finally the Pt1-Ru7.5-Fex@N-OMCs composites were stabilized by the successful introduction of platinum-ruthenium nanoparticles through the substitution reaction. The composite uniformly embeds the transition metal nanoparticles inside the OMC pores with high specific surface area, which limits the size of the metal nanoparticles inside the pores. At the same time, the metal nanoparticles are also loaded onto the surface of the OMCs, realizing the uniform loading of metal nanoparticles both inside and outside the pores. This enhances the active sites of the composite, promotes the mass transfer process inside and outside the pores, and greatly enhances the electrocatalytic performance of the catalyst. The material shows high electrocatalytic performance for adrenaline, which is characterized by a wide linear range, high sensitivity and low detection limit, and can realize the detection of actual samples.

Binary-amplifying electrochemiluminescence sensor for sensitive assay of catechol and luteolin based on HKUST-1 derived CuO nanoneedles as a novel luminophore

Herein, a highly novel and effective electrochemiluminescence (ECL) sensor based on metal-organic framework (MOF, HKUST-1) derived CuO nanoneedles (HKUST-1 derived CuO NNs), gold nanoparticles (AuNPs) and TiO2 was developed for ultrasensitive detection of catechol and luteolin. The HKUST-1 derived CuO NNs were employed as luminophore for the first time, which were successfully fabricated by using HKUST-1 as precursor. The results revealed that the HKUST-1 derived CuO NNs exhibit excellent ECL activity ascribed to its abundant active site and the high specific surface area, thus obviously promoting the separation and transfer of charge and further improving the current density of ECL sensor. To binary-amplify the signal of the ECL sensor, the AuNPs and TiO2 nano-materials with good biocompatibility, great electron transport efficiency and high catalytic activity were used as co-reaction accelerators in the ECL process. Dependent on the above brilliant strategy, the proposed ECL sensor achieved wide linear ranges from 3 × 10-9 - 1 × 10-4 M for catechol and 1 × 10-8 - 2 × 10-4 M for luteolin, with the detection limits of 1.5 × 10-9 M for catechol and 5.3 × 10-9 M for luteolin, respectively. Furthermore, the ECL sensor exhibited outstanding selectivity, repeatability, stability and obtained great feedback on determination of catechol and luteolin in actual samples. The method not only filled a gap in the ECL application of MOF-derived materials but also provided a novel sight for design other highly efficient luminescent materials.

Energy difference-driven ROS reduction for electrochemical tracking crop growth sensitized with electron-migration nanostructures

Aiming for sustainable crop productivity under changing climate conditions, it is essential to develop handy models for in-situ monitoring of reactive oxygen species (ROS). Herein, this work reports a simple electrochemical sensing toward hydrogen peroxide (H2O2) for tracking crop growth status sensitized with electron-migration nanostructure. To be specific, Cu-based metal-organic frameworks (MOFs) with high HOMO energy level are designed for H2O2 reduction on account of Cu(I)/Cu(II) redox switchability. Importantly, the sensing performance is improved by electrochemically reduced graphene oxide (GO) with ready to use feature. To overcome the shortcomings of traditional liquid electrolytes, conductive hydrogel as semi-solid electrolyte exhibits the adhesive property to the cut plant petiole surface. Benefitting from the preferred composite models and conductive hydrogel, the electrochemical sensing toward H2O2 with high sensitivity and good anti-interference against the coexistent molecules, well qualified for acquiring plant growth status.

Detection of Arsenic(V) by Fluorescence Sensing Based on Chlorin e6-Copper Ion

The high toxicity of arsenic (As) can cause irreversible harm to the environment and human health. In this study, the chlorin e6 (Ce6), which emits fluorescence in the infrared region, was introduced as the luminescence center, and the addition of copper ion (Cu2+) and As(V) provoked a regular change in fluorescence at 652 nm, whereas that of As(III) was 665 nm, which was used to optionally detect Cu2+, arsenic (As(III), and As(V)). The limit of detection (LOD) values were 0.212 μM, 0.089 ppm, and 1.375 ppb for Cu2+, As(III), and As(V), respectively. The developed method can be used to determine Cu2+ and arsenic in water and soil with good sensitivity and selectivity. The 1:1 stoichiometry of Ce6 with Cu2+ was obtained from the Job plot that was developed from UV-visible spectra. The binding constants for Cu2+ and As(V) were established to be 1.248 × 105 M-1 and 2.35 × 1012 M-2, respectively, using B-H (Benesi-Hildebrand) plots. Fluorescence lifetimes, B-H plots, FT-IR, and 1H-NMR were used to postulate the mechanism of Cu2+ fluorescence quenching and As(V) fluorescence restoration and the interactions of the two ions with the Ce6 molecule.

Colorimetric Sensors: Methods and Applications

Colorimetric sensors have attracted considerable attention in many sensing applications because of their specificity, high sensitivity, cost-effectiveness, ease of use, rapid analysis, simplicity of operation, and clear visibility to the naked eye [...].