Silver nanoparticles loaded carbon-magnetic nanocomposites: A nanozyme for colorimetric detection of dopamine

Dopamine (DA) is catecholamine neurotransmitters that play an important role in the central nervous system. In recent years people started to intentionally add DA to animal feed to enhance muscle development and increase their profit margin. Human consumption of the residual DA from animal tissues has been reported to be associated with the development of such diseases as Parkinson's disease, epilepsy, senile dementia, and schizophrenia and pose serious human health risks. These require development of rapid, cheap, and sensitive methods for detection of DA from animal tissue. Compared to other techniques that require access to expensive instruments, skilled human power, and tiresome routine procedures, colorimetric methods provide cheap and reliable options for detection of DA. Here we report a colorimetric method based on the peroxidase-mimic activity of Fe3O4@C@AgNPs for the detection of DA. A simple wet chemical method was employed to synthesize AgNPs on hydrophilic carbon coated Fe3O4. The produced nanocomposites were characterized by transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), and surface-enhanced Raman spectroscopy (SERS). The detection of DA was done based on inhibition of the peroxidase-like activity of Fe3O4@C@AgNPs using 3, 3', 5, 5'-tetramethylbenzidine (TMB) as a substrate. In the presence of DA, however, the peroxidase-like activity started to decrease. The decrease in activity was concentration dependent showing a linear relationship in the range of 0.5-80 µM. In this linear range, the limit of detection (LOD) was computed and found to be as low as 0.12 µM. Therefore, we propose that the peroxidase-like activity of Fe3O4@C@AgNPs could be used for quantitative detection of DA from different samples.

Copper oxide nanosheets as an effective nanozyme with haloperoxidase-like activity for the colorimetric detection of H2O2 and glucose

Copper oxide nanosheets (CuO NSs) have been successfully obtained by exploiting an effective one-step approach of sugar-blowing method followed by calcination. The nanosheets were characterized by several techniques like X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Impressively, CuO NSs display haloperoxidase (HPO) like catalytic activity which catalyses the oxidation of chloride ions by H2O2 giving rise to reactive chlorine species (RCS). A sensitive and selective colorimetric sensor was then demonstrated via the oxidation of chromogenic substrate 3,3',5,5'- tetramethylbenzidine (TMB) by the novel nanoenzyme CuO NSs through the generation of RCS for H2O2 and glucose detection with limit of detection of 109 nM and 21 nM in the linear ranges of 4.6 µM to 769 µM and 0.22 µM to 19.57 µM respectively. Additionally, the methodology is validated for the analysis of glucose in real samples.

Nanozyme-based colorimetric sensor arrays coupling with smartphone for discrimination and "segmentation-extraction-regression" deep learning assisted quantification of flavonoids

Achieving rapid, cost effective, and intelligent identification and quantification of flavonoids is challenging. For fast and uncomplicated flavonoid determination, a sensing platform of smartphone-coupled colorimetric sensor arrays (electronic noses) was developed, relying on the differential competitive inhibition of hesperidin, nobiletin, and tangeretin on the oxidation reactions of nanozymes with a 3,3',5,5'-tetramethylbenzidine substrate. First, density functional theory calculations predicted the enhanced peroxidase-like activities of CeO2 nanozymes after doping with Mn, Co, and Fe, which was then confirmed by experiments. The self-designed mobile application, Quick Viewer, enabled a rapid evaluation of the red, green, and blue values of colorimetric images using a multi-hole parallel acquisition strategy. The sensor array based on three channels of CeMn, CeFe, and CeCo was able to discriminate between different flavonoids from various categories, concentrations, mixtures, and the various storage durations of flavonoid-rich Citri Reticulatae Pericarpium through a linear discriminant analysis. Furthermore, the integration of a "segmentation-extraction-regression" deep learning algorithm enabled single-hole images to be obtained by segmenting from a 3 × 4 sensing array to augment the featured information of array images. The MobileNetV3-small neural network was trained on 37,488 single-well images and achieved an excellent predictive capability for flavonoid concentrations (R2 = 0.97). Finally, MobileNetV3-small was integrated into a smartphone as an application (Intelligent Analysis Master), to achieve the one-click output of three concentrations. This study developed an innovative approach for the qualitative and simultaneous multi-ingredient quantitative analysis of flavonoids.

Colorimetric sensor array for identifying antioxidants based on pyrolysis-free synthesis of Fe-N/C single-atom nanozymes

Iron-anchored nitrogen/doped carbon single-atom nanozymes (Fe-N/C), which possess homogeneous active sites and adjustable catalytic environment, represent an exemplary model for investigating the structure-function relationship and catalytic activity. However, the development of pyrolysis-free synthesis technique for Fe-N/C with adjustable enzyme-mimicking activity still presents a significant challenge. Herein, Fe-N/C anchored three carrier morphologies were created via a pyrolysis-free approach by covalent organic polymers. The peroxidase-like activity of these Fe-N/C nanozymes was regulated via the pores of the anchored carrier, resulting in varying electron transfer efficiency due to disparities in contact efficacy between substrates and catalytic sites within diverse microenvironments. Additionally, a colorimetric sensor array for identifying antioxidants was developed: (1) the Fe-N/C catalytically oxidized two substrates TMB and ABTS, respectively; (2) the development of a colorimetric sensor array utilizing oxTMB and oxABTS as sensing channels enabled accurate discrimination of antioxidants such as ascorbic acid (AsA), glutathione (GSH), cysteine (Cys), gallic acid (GA), and caffeic acid (CA). Subsequently, the sensor array underwent rigorous testing to validate its performance, including assessment of antioxidant mixtures and individual antioxidants at varying concentrations, as well as target antioxidants and interfering substances. In general, the present study offered valuable insights into the active origin and rational design of nanozyme materials, and highlighting their potential applications in food analysis.

Phosphatase-mimicking Zr@PDA nanozyme with excellent dispersion stability for the detection of fructose 1,6-diphosphate

Zr4+-doped polydopamine (Zr@PDA) nanozyme with phosphatase-like activity was synthesized by a one-pot hydrothermal method for the first time. Compared with previous representative phosphatase-mimicking nanozymes (i.e., CeO2 NPs, ZrO2 NPs and UiO-66), Zr@PDA not only exhibited higher dispersion stability in water, but also higher catalytical efficiency. Kcat/Km of Zr@PDA is 35 and 12 times that of UiO-66 and ZrO2 NPs, respectively, which would endow the Zr@PDA-based analytical methods with high sensitivity. As a demonstration, a novel colorimetric method based on Zr@PDA nanozyme was developed for sensitive detection of the drug fructose 1,6-diphosphate. The linear range is 1-15 μM with a detection limit as low as 0.38 μM.

Dual-enhanced enzyme cascade hybrid hydrogel for the construction of optical biosensor

The biomimetic enzyme cascade system plays a key role in biosensing as a sophisticated signal transduction and amplification strategy. However, constructing a regulated enzyme cascade sensing system remains challenging due to the mismatch of multiple enzyme activities and poor stability. Herein, we design an efficient dual-enhanced enzyme cascade hybrid system (UFD-DEC) containing DNA-controlled nanozymes (Fe-cdDNA) and enzyme (urease) via combining the electrostatic contact effect with the hydrogel-directed confinement effect. Precise modulation of Fe-cdDNA nanozyme by DNA offers a means to control its catalytic efficiency. This regulated UFD-DEC system accelerates the reaction rate and provides remarkable stability compared with the free enzyme system. Benefiting from the plasticity properties of hydrogels, a "lab-in-a-tube" platform was constructed by encapsulating UFD-DEC in a microcentrifuge tube. Such a UFD-DEC-based hydrogel tube exhibits sufficient adaptability to profile urea when used in conjunction with a smartphone-assisted image processing algorithm, which on-site delivers urea information with a detection limit of 0.12 mmol L-1. This customizable and inexpensive miniaturized biosensor platform for monitoring urea may facilitate point-of-care testing applications.

Ultrasensitive analyses of zearalenone in grain samples with a catalytic oxidation platform involving gold nanomaterials

Zearalenone (ZEN) contamination in cereals poses a serious threat to human and animal health, yet existing rapid test methods still suffer from poor stability and low sensitivity. The studied sensor reduces inspection time while enabling applications for on-site grain inspection. Specifically, a ZEN detector that can sensitively detect ZEN content in grains was developed. Ion implantation is an effective method for modifying screen-printed electrodes (SPEs). Gold nanoparticles (AuNPs; 5-10 nm) were uniformly implanted using screen-printed electrodes as a catalytic oxidation medium to generate an electrochemical sensor. The surface structure of the modified electrode was characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. The results showed that differential pulse voltammetry had good linear electrochemical response to ZEN at 10 ng/kg to 10 mg/kg, with a detection limit of 1.1 ng/kg. We used AuNP-SPE sensors to detect ZEN in grain samples such as maize and oats.

High-performance colorimetric sensor based on PtRu bimetallic nanozyme for xanthine analysis

The identification and quantification of xanthine are crucial for assessing the freshness and quality of food products, particularly in the seafood industry. Herein, a new approach was developed, involving the in-situ controllable growth of Pt91Ru9 nanoparticles on graphitic carbon nitride to yield Pt91Ru9@C3N4 catalytic materials. By integrating Pt91Ru9@C3N4 with the xanthine/xanthine oxidase (XOD) enzyme catalytic system, a nanozyme-enzyme tandem platform was obtained for the quantification analysis of xanthine. Under the catalytic oxidation of xanthine by XOD in the presence O2, H2O2 was generated. Upon the addition of peroxidase-like activity of Pt91Ru9@C3N4, H2O2 can be decomposed into •OH and 1O2, which can further catalyze the oxidation of TMB to its oxidation product oxTMB with an absorption peak at 652 nm. This smartphone-assisted portable colorimetric sensor for visual monitoring xanthine with a low detection limit of 8.92 nmol L-1, and successfully applied to detect xanthine in grass carp and serum samples.

Nano-architectonics of Pt single-atoms and differently-sized nanoparticles supported by manganese-oxide nanosheets and impact on catalytic and anti-biofilm activities

Hybrid-nanozymes are promising in various applications, but comprehensive comparison of hybrid-nanozymes composed of single-atoms or nanoparticles on the same support has never been made. Here, manganese-oxide nanosheets were loaded with Pt-single-atoms or differently-sized nanoparticles and their oxidase- and-peroxidase activities compared. High-resolution Transmission-Electron-Microscopy and corresponding Fast Fourier Transform imaging showed that Pt-nanoparticles (1.5 nm diameter) had no clear (111) crystal-planes, while larger nanoparticles had clear (111) crystal-planes. X-ray Photo-electron Spectroscopy demonstrated that unloaded nanosheets were composed of MnO2 with a high number of oxygen vacancies (Vo/Mn 0.4). Loading with 7.0 nm Pt-nanoparticles induced a change to Mn2O3, while loading with 1.5 nm nanoparticles increased the number of vacancies (Vo/Mn 1.2). Nanosheets loaded with 3.0 nm Pt-nanoparticles possessed similarly high catalytic activities as Pt-single-atoms. However, loading with 1.5 nm or 7.0 nm Pt-nanoparticles yielded lower catalytic activities. A model is proposed explaining the low catalytic activity of under- and over-sized Pt-nanoparticles as compared with intermediately-sized (3.0 nm) Pt-nanoparticles and single-atoms. Herewith, catalytic activities of hybrid-nanozymes composed of single-atoms and intermediately-sized nanoparticles are put a par, as confirmed here with respect to bacterial biofilm eradication. This conclusion facilitates a balanced choice between using Pt-single-atoms or nanoparticles in further development and application of hybrid-nanozymes.

Visual and photoelectrochemical analysis of antibiotic resistance genes enabled by surface-engineered ZIF-8@Au cascade nanozymes

The aggravation of antibiotic resistance genes (ARGs) in the environment has posed a significant global health crisis. Accurate evaluation of ARGs levels in a facile manner is a pressing issue for environmental surveillance. Here, we demonstrate a unique dumbbell-shaped cascade nanozyme for visual/photoelectrochemical (PEC) dual-mode detection of ARGs. Gold nanoparticles (AuNPs) with tunable exposed facets are controllably anchored onto ZIF-8 dodecahedrons, exhibiting glucose oxidase (GOx)-like (ZIF-8@Au/G) and peroxidase (POD)-like (ZIF-8@Au/P) activities. Upon the occurrence of ARGs, an asymmetric cascade-amplified "dumbbell" configuration is spontaneously generated via target-induced DNA hybridization, comprising GOx-like ZIF-8@Au/G with capture DNA on one side and POD-like ZIF-8@Au/P with signal DNA on the opposite side. Such a cascade nano-system can efficiently oxidize colorless 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) into its green oxidation state and synergistically decompose H2O2, realizing colorimetric/PEC dual-mode ARGs detection with a detection limit of 0.112 nM. The applicability of the present bioassay is validated through measuring ARGs in real sludge samples. This work suggests the possibility to rationally design task-specific nanozymes and develop target-responsive nano-cascade assays for environmental monitoring.

Construction of the fluorescence sensing platform with a bifunctional Cu@MOF nanozyme for determination of alkaline phosphatase and its inhibitor

In this work, a novel and sensitive fluorescence sensing system for alkaline phosphatase (ALP) was constructed using a bifunctional copper metal-organic framework (Cu@MOF) nanozyme, which had excellent oxidase-mimetic activity and fluorescence properties. Owing to the presence of 2-amino-1,4-benzenedicarboxylic acid (1,4-BDC-NH2) ligand, Cu@MOF displays excellent fluorescence performance at 444 nm. Additionally, Cu2+ endows the oxidase-like activity of Cu@MOF, which could trigger p-phenylenediamine (PPD) to be oxidized to a brown product (PPDox) and quench the photoluminescence of Cu@MOF through the inner filtration effect (IFE). As the preferential affinity of ATP for Cu2+, the catalytic activity of Cu@MOF was significantly reduced once ATP was added, thus PPD could not be oxidized and fluorescence was recovered. In the presence of ALP, ATP was hydrolyzed to adenosine and Pi, which allowed Cu@MOF to regain its catalytic activity and continued to catalyze the generation of PPDox. The fluorescence of Cu@MOF was therefore weakened once again. The ALP activity was directly proportional to the degree of decrease in fluorescence intensity. Thus, this novel fluorescence sensing strategy had a linear range of 0.5-60 U/L and the limit of detection was 0.14 U/L. The established sensing method could also be used to for ALP inhibitors screening, and achieved satisfactory results in determining the level of ALP activity in human serum.

Inhibition effect of p-d orbital hybridized PtSn nanozymes for colorimetric sensor array of antioxidants

Rational design of peroxidase (POD)-like nanozymes with high activity and specificity still faces a great challenge. Besides, the investigations of nanozymes inhibitors commonly focus on inhibition efficiency, the interaction between nanozymes-involved catalytic reactions and inhibitors is rarely reported. In this work, we design a p-block metal Sn-doped Pt (p-d/PtSn) nanozymes with the selective enhancement of POD-like activity. The p-d orbital hybridization interaction between Pt and Sn can effectively optimize the electronic structure of PtSn nanozymes and thus selectively enhance POD-like activity. In addition, the antioxidants as nanozymes inhibitors can effectively inhibit the POD-like activity of p-d/PtSn nanozymes, which results in the fact that antioxidants absorbed on the p-d/PtSn surface can hinder the adsorption of hydrogen peroxide. The inhibition type (glutathione as a model molecule) is reversible mixed-inhibition with inhibition constants (Ki' and Ki) of 0.21 mM and 0.03 mM. Finally, based on the varying inhibition levels of antioxidant molecules, a colorimetric sensor array is constructed to distinguish and simultaneously detect five antioxidants. This work is expected to design highly active and specific nanozymes through p-d orbital hybrid engineering, and also provides insights into the interaction between nanozymes and inhibitors.

Two-dimensional β-MnOOH nanosheets with high oxidase-mimetic activity for smartphone-based colorimetric sensing

Manganese (Mn) is a versatile transition element with diverse oxidation states and significant biological importance. Mn-based nanozymes have emerged as promising catalysts in various applications. However, the direct use of manganese oxides as oxidase mimics remains limited and requires further improvement. In this study, we focus on hydroxylated manganese (MnOOH), specifically the layered form β-MnOOH which exhibits unique electronic and structural characteristics. The two-dimensional β-MnOOH nanosheets were synthesized through a hydrothermal approach and showed remarkable oxidase-like activity. These nanosheets effectively converted the oxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB), into its oxidized form by initiating the conversion of dissolved oxygen into ·O2-, 1O2 and ·OH. However, in the presence of L-cysteine (L-Cys), the catalytic activity of β-MnOOH was significantly inhibited, enabling highly sensitive detection of L-Cys. This sensing strategy was successfully applied for smartphone-based L-Cys assay, offering potential utility in the diagnosis of Cys-related diseases. The exploration of layered β-MnOOH nanosheets as highly active oxidase mimics opens up new possibilities for catalytic and biomedical applications.

Multi-mechanism antitumor/antibacterial effects of Cu-EGCG self-assembling nanocomposite in tumor nanotherapy and drug-resistant bacterial wound infections

Chemotherapy and surgery stand as primary cancer treatments, yet the unique traits of the tumor microenvironment hinder their effectiveness. The natural compound epigallocatechin gallate (EGCG) possesses potent anti-tumor and antibacterial traits. However, the tumor's adaptability to chemotherapy due to its acidic pH and elevated glutathione (GSH) levels, coupled with the challenges posed by drug-resistant bacterial infections post-surgery, impede treatment outcomes. To address these challenges, researchers strive to explore innovative treatment strategies, such as multimodal combination therapy. This study successfully synthesized Cu-EGCG, a metal-polyphenol network, and detailly characterized it by using synchrotron radiation and high-resolution mass spectrometry (HRMS). Through chemodynamic therapy (CDT), photothermal therapy (PTT), and photodynamic therapy (PDT), Cu-EGCG showed robust antitumor and antibacterial effects. Cu+ in Cu-EGCG actively participates in a Fenton-like reaction, generating hydroxyl radicals (·OH) upon exposure to hydrogen peroxide (H2O2) and converting to Cu2+. This Cu2+ interacts with GSH, weakening the oxidative stress response of bacteria and tumor cells. Density functional theory (DFT) calculations verified Cu-EGCG's efficient GSH consumption during its reaction with GSH. Additionally, Cu-EGCG exhibited outstanding photothermal conversion when exposed to 808 nm near-infrared (NIR) radiation and produced singlet oxygen (1O2) upon laser irradiation. In both mouse tumor and wound models, Cu-EGCG showcased remarkable antitumor and antibacterial properties.

Engineering a two-dimensional metal-carbon nanozyme-based portable paper-based colorimetric chip for onsite and visual analysis of pyrophosphate

Sensitive and accurate analysis of pyrophosphate (PPi) is of great importance for preventing health hazard in environment. Nevertheless, most of sensors focus on sensitivity and selectivity, but practicality is also a significant quota. How to reconciling sensitivity, selectivity and practicability in one single sensor is desirable but remains challenging. Here, we created a novel metal-carbon nanozyme V2O5@C with two-dimensional (2D) morphology and high yet exclusive peroxidase (POD)-like activity via a glucose and NH4NO4-co-directed avenue, and further showed its application in constructing a portable and disposable paper-based analytical chip (PA-chip) for rapid, visual and onsite analysis of PPi. PPi etched V2O5 to prevent the decomposition of H2O2 into ·OH, resulting in weakened POD-like activity. In comparison with PPi deficiency, colorless TMB couldn't be oxidized into oxidized TMB with a dropped absorption at 652 nm. Therefore, obviously shallowed blue color on PA-chip surface was recorded, and demonstrated a negative relationship with PPi dosage, enabling rapid and visual detection of PPi with a limit of detection of 2.6 nM. This study demonstrated the burgeoning applications of nanozymes with POD-like activity in construction of PA-chips for PPi and will quicken the advancement of practical sensors, guaranteeing environmental safety.

Glutathione‑iron hybrid nanozyme-based colorimetric sensor for specific and stable detection of thiram pesticide on fruit juices

Given the potential dangers of thiram to food safety, constructing a facile sensor is significantly critical. Herein, we presented a colorimetric sensor based on glutathione‑iron hybrid (GSH-Fe) nanozyme for specific and stable detection of thiram. The GSH-Fe nanozyme exhibits good peroxidase-mimicking activity with comparable Michaelis constant (Km = 0.551 mM) to the natural enzyme. Thiram pesticides can specifically limit the catalytic activity of GSH-Fe nanozyme via surface passivation, causing the change of colorimetric signal. It is worth mentioning that the platform was used to prepare a portable hydrogel kit for rapid qualitative monitoring of thiram. Coupling with an image-processing algorithm, the colorimetric image of the hydrogel reactor is converted into the data information for accurate quantification of thiram with a detection limit of 0.3 μg mL-1. The sensing system has good selectivity and high stability, with recovery rates in fruit juice samples ranging from 92.4% to 106.9%.

Regulating Reactive Oxygen Intermediates of Fe-N-C SAzyme via Second-Shell Coordination for Selective Aerobic Oxidation Reactions

Reactive oxygen species (ROS) regulation for single-atom nanozymes (SAzymes), e.g., Fe-N-C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe-N-C containing the same FeN4 but with tunable second-shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe-N-C sample, the second-shell sulfur functionalized Fe-N-C delivered a 2.4-fold increase of oxidase-like activity via the bound Fe=O intermediate. Conversely, free ROS (⋅O2 -) release was significantly reduced after functionalization, down to only 17 % of that observed for Fe-N-C. The detailed characterizations and theoretical calculations revealed that the second-shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe-N-Cs with different second-shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Vanadium-Based Metal-Organic Frameworks with Peroxidase-like Activity as a Colorimetric Sensing Platform for Direct Detection of Organophosphorus Pesticides

Colorimetry based on the bioenzyme inhibition strategy holds promising application prospects in the field of organophosphorus pesticide (OPs) detection. However, overcoming the challenges of the high cost and low stability of bioenzymes remains crucial. In this study, we successfully synthesized a peroxidase vanadium-based metal-organic framework (MOF) nanozyme named MIL-88B(V) and employed its mediated bioenzyme-free colorimetric strategy for direct OPs detection. The experimental results demonstrated that MIL-88B(V) exhibited a remarkable affinity and a remarkable catalytic rate. When the OPs target is added, it can be anchored on the MOF surface through a V-O-P bond, effectively inhibiting the MOF's activity. Subsequently, leveraging the advantages of smartphones such as convenience, speed, and sensitivity, we developed a paper sensor integrated into a smartphone for efficient OPs detection. The as-designed nanozyme-based colorimetric assay and paper sensor presented herein offer notable advantages, including affordability, speed, stability, wide adaptability, low cost, and accuracy in detecting OPs, thus providing a versatile and promising analytical approach for real sample analysis and allowing new applications of V-based MOF nanozymes.

Mechanism of the antimicrobial activity induced by phosphatase inhibitor sodium ortho-vanadate

The present study describes a novel antimicrobial mechanism based on Sodium Orthovanadate (SOV), an alkaline phosphatase inhibitor. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed to examine the surface morphologies of the test organism, Escherichia coli (E. coli), during various antibacterial phases. Our results indicated that SOV kills bacteria by attacking cell wall growth and development, leaving E. coli's outer membrane intact. Our antimicrobial test indicated that the MIC of SOV for both E. coli and Lactococcus lactis (L. lactis) is 40 μM. A combination of quantum mechanical calculations and vibrational spectroscopy revealed that divanadate from SOV strongly coordinates with Ca2+ and Mg2+, which are the activity centers for the phosphatase that regulates bacterial cell wall synthesis. The current study is the first to propose the antibacterial mechanism caused by SOV attacking cell wall.

Mn-based Prussian blue analogues: Multifunctional nanozymes for hydrogen peroxide detection and photothermal therapy of tumors

Nanozymes have the advantages of simple synthesis, high stability, low cost and easy recycling, and can be applied in many fields including molecular detection, disease diagnosis and cancer therapy. However, most of the current nanozymes suffer from the defects of low catalytic activity and single function, which limits their sensing sensitivity and multifunctional applications. The development of highly active and multifunctional nanozymes is an important way to realize multidisciplinary applications. In this work, Mn-based Prussian blue analogues (Mn-PBA) and their derived double-shelled nanoboxes (DSNBs) are synthesized by co-precipitation method. The nanobox structure of DSNBs formed by etching Mn-PBA with tannic acid endows Mn-PBA DSNBs with better peroxidase-like activity than Mn-PBA. A colorimetric method for the rapid and sensitive determination of H2O2 is developed using Mn-PBA DSNBs-1.5 as a sensor with a detection limit as low as 0.62 μM. Moreover, Mn-PBA DSNBs-2 has excellent photothermal conversion ability, which can be applied to the photothermal therapy of tumors to inhibit the proliferation of tumor cells without damaging other tissues and organs. This study provides a new idea for the rational design of nanozymes and the expansion of their multi-functional applications in various fields.

Expression of chiral molecular and supramolecular structure on enantioselective catalytic activity

Understanding the structure-function relationships encoded on chiral catalysts is important for investigating the fundamental principles of catalytic enantioselectivity. Herein, the synthesis and self-assembly of naphthalene substituted bis-l/d-histidine amphiphiles (bis-l/d-NapHis) in DMF/water solution mixture is reported. The resulting supramolecular assemblies featuring well-defined P/M nanoribbons (NRs). With combination of the (P/M)-NR and metal ion catalytic centers (Mn+ = Co2+, Cu2+, Fe3+), the (P)-NR-Mn+ as chiral supramolecular catalysts show catalytic preference to 3,4-dihydroxy-S-phenylalanine (S-DOPA) oxidation while the (M)-NR-Mn+ show enantioselective bias to R-DOPA oxidation. In contrast, their monomeric counterparts bis-l/d-NapHis-Mn+ display an inverse and dramatically lower catalytic selectivity in the R/S-DOPA oxidation. Among them, the Co2+-coordinated supramolecular nanostructures show the highest catalytic efficiency and enantioselectivity (select factor up to 2.70), while the Fe3+-coordinated monomeric ones show nearly racemic products. Analysis of the kinetic results suggests that the synergistic effect between metal ions and the chiral supramolecular NRs can significantly regulate the enantioselective catalytic activity, while the metal ion-mediated monomeric bis-l/d-NapHis were less active. The studies on association constants and activation energies reveal the difference in catalytic efficiency and enantioselectivity resulting from the different energy barriers and binding affinities existed between the chiral molecular/supramolecular structures and R/S-DOPA enantiomers. This work clarifies the correlation between chiral molecular/supramolecular structures and enantioselective catalytic activity, shedding new light on the rational design of chiral catalysts with outstanding enantioselectivity.

A facile and on-site sensing strategy for phenolic compounds based on a novel nanozyme with high polyphenol oxidase-like activity

Phenolic compounds (PCs) are diverse in nature and undergo complex migration and transformations in the environment, making it challenging to use techniques such as chromatography and other traditional methods to determine the concentration of PCs by separation, individual monitoring and subsequent addition. To address this issue, a facile and on-site strategy was developed to measure the concentration of PCs using a novel nanozyme with polyphenol oxidase-like activity. First, the nanozyme was designed by coordinating the asymmetric ligand nicotinic acid with copper to mimic the structure of mononuclear and trinuclear copper clusters of natural laccases. Subsequently, by introducing 2-mercaptonicotinic acid to regulate the valence state of copper, the composite nanozyme CuNA10S was obtained with significantly enhanced activity. Interestingly, CuNA10S was shown to have a broad substrate spectrum capable of catalyzing common PCs. Building upon the superior performance of this nanozyme, a method was developed to determine the concentration of PCs. To enable rapid on-site sensing, we designed and prepared CuNA10S-based test strips and developed a tailored smartphone sensing platform. Using paper strip sensors combined with a smartphone sensing platform with RGB streamlined the sensing process, facilitating rapid on-site analysis of PCs within a range of 0-100 μM. Our method offers a solution for the quick screening of phenolic wastewater at contaminated sites, allowing sensitive and quick monitoring of PCs without the need for standard samples. This significantly simplifies the monitoring procedure compared to more cumbersome large-scale instrumental methods.

Prussian Blue-Derived Nanocomposite Synergized with Calcium Overload for Three-Mode ROS Outbreak Generation to Enhance Oncotherapy

Calcium overload can lead to tumor cell death. However, because of the powerful calcium channel excretory system within tumor cells, simplistic calcium overloads do not allow for an effective antitumor therapy. Hence, the nanoparticles are created with polyethylene glycol (PEG) donor-modified calcium phosphate (CaP)-coated, manganese-doped hollow mesopores Prussian blue (MMPB) encapsulating glucose oxidase (GOx), called GOx@MMPB@CaP-PEG (GMCP). GMCP with a three-mode enhancement of intratumor reactive oxygen species (ROS) levels is designed to increase the efficiency of the intracellular calcium overload in tumor cells to enhance its anticancer efficacy. The released exogenous Ca2+ and the production of cytotoxic ROS resulting from the perfect circulation of the three-mode ROS outbreak generation that Fenton/Fenton-like reaction and consumption of glutathione from Fe2+/Fe3+and Mn2+/Mn3+ circle, and amelioration of hypoxia from MMPB-guided and GOx-mediated starvation therapy. Photothermal efficacy-induced heat generation owing to MMPB accelerates the above reactions. Furthermore, abundant ROS contribute to damage to mitochondria, and the calcium channels of efflux Ca2+ are inhibited, resulting in a calcium overload. Calcium overload further increases ROS levels and promotes apoptosis of tumor cells to achieve excellent therapy.

Wide temperature adaptive oxidase-like based on mesoporous manganese based metal-organic framework for detecting total antioxidant capacity

Overcoming the intense variation of enzymatic activity among different temperatures is very critical in catalytic medicine and catalytic biology. Here, Mn-based metal-organic framework-based wide-temperature-adaptive mesoporous artificial enzymes (Mn-TMA-MOF) were designed and synthesized. The oxidase-like Mn-TMA-MOF showed excellent catalytic activity at 0-50 °C and avoided the activity loss and instability due to temperature variation that occurred. The excellent oxidase-like properties of Mn-TMA-MOF with wide temperature adaptativeness are mainly ascribed to the mixed oxidized state (Mn3+/Mn2+) and high substrate affinity (Km = 0.034 mM) of Mn. Moreover, the mesopore-micropores two-level structure of Mn-TMA-MOF provides a large space and surface area for enzyme catalysis. Based on the stability of Mn-TMA-MOF, we developed a colorimetric sensor that can detect total antioxidant capacity in fruits with a limit of detection up to 0.59 μM.

An aptasensor for chloramphenicol determination based on dual signal output of photoelectrochemistry and colorimetry

In the present work, we developed an aptasensor to determine chloramphenicol (CAP) based on the dual signal output of photoelectrochemistry (PEC) and colorimetry. The Fe3+-doped porous tungsten trioxide was prepared by sol-gel method and coated on the ITO conductive glass to form ITO/p-W(Fe)O3. After assembling the captured DNA (cDNA) and the aptamer of CAP (apt) successively, the constructed ITO/p-W(Fe)O3-cDNA/apt aptasensor exhibited excellent photocurrent response under visible light irradiation in the presence of glucose, which provided the feasibility for PEC measurement with high sensitivity. In the presence of CAP, the apt left the ITO/p-W(Fe)O3 surface and AuNPs linked on the probe DNA would be assembled on it, which led to the decrease of photocurrent. Thanks to the oxidase-mimic catalytic performance of AuNPs and the recycling catalytic hydrolysis by exonuclease I, the measurement signal of the aptasensor could be amplified significantly, and the photocurrent decrease of the aptasensor was linearly related to the concentration of CAP in the range of 1.0 pM-10.0 nM and low detection limit was 0.36 pM. Meanwhile, the H2O2 produced from catalytic oxidation of glucose could oxidize TMB to blue oxTMB under HRP catalysis, which absorbance at 652 nm was linearly related to the concentration of CAP in the range of 5.0 pM-10.0 nM and low detection limit was 1.72 pM. Therefore, an aptasensor that determine CAP in real samples was successfully constructed with good precision of the relative standard deviation less than 5.7 % for PEC method and 7.3 % for colorimetric method, which can meet the analysis needs in different scenarios.

Nanozyme-catalyzed and zwitterion-modified swabs based for the detection of Listeria monocytogenes in complex matrices

In recent years, nanozymes have been widely used in the field of biosensing and food safety testing due to their advantages of low cost, high stability, easy modification and adjustable catalytic activity. However, how to reduce the signal interference generated by reducing substances, macromolecules and colored substances in the food matrix in nanozymes-based colorimetric sensing is still a major challenge. In this paper, using Listeria monocytogenes as a model analyte, sodium sulfonyl methacrylate (SBMA) polymers were modified onto cotton swabs by photothermal polymerization and combined with Listeria monocytogenes-specific aptamer (Apt1) to prepare swabs that can specifically capture and isolate Listeria monocytogenes from complex matrices (SBMA/Apt1 cotton swab). In addition, in combination with the inhibitory effect of the aptamer (Apt2) on the oxidase activity of Mn3O4 NPs, a colorimetric biosensor based on nanozymes that can quantitatively, sensitively, and specifically identify Listeria monocytogenes in food products was constructed. The results showed that the colorimetric signal of the method was linear with the concentration of Listeria monocytogenes in the range of 2.83-2.83 × 105 CFU/mL, and the limit of detection was 2.64 CFU/mL, which can be used for the detection of Listeria monocytogenes in complex environments and food samples.

Nanoparticles constructed from natural polyphenols are used in acute kidney injury

Acute kidney injury (AKI) is a severe clinical syndrome characterized by rapid deterioration of renal function caused by a variety of pathogeneses. Natural polyphenols have been considered to have potential in the treatment of AKI due to their powerful antioxidant and anti-inflammatory activities, but their low bioavailability in vivo limits their efficacy. Polyphenol nanoparticles based on a nano-delivery system show good effects in reducing kidney injury, improving renal function and promoting renal tissue repair, and brings new hope and possibility for the treatment of AKI. This review provides an overview of the common characteristics, treatments, and associated adverse effects of AKI. The classification and bioavailability of polyphenols as well as their therapeutic role in AKI and potential possible effects are outlined. The potential therapeutic effects of polyphenol-based nanoparticles on AKI and the underlying mechanisms are discussed.

Plasmonic and nanozyme dual-channel-based logic judgment for enhancing gold nanoparticle based colorimetric Hg2+ ion sensing performance

An AND logic gate-based Hg2+ ion colorimetric assay was constructed using the plasmonic and nanozyme dual signal channels of gold nanoparticles (AuNPs). This assay increased the judgment criteria for the identification of Hg2+ ions and effectively improved the accuracy of Hg2+ ion detection.

Synthesis of Mo-Pt/CeO2 Dual Single-Atom Nanozyme for Multifunctional Biochemical Detection Applications

Elaborated structural modulation of Pt-based artificial nanozymes can efficiently improve their catalytic activity and expand their applications in clinical diagnosis and biochemical sensing. Herein, a highly efficient dual-site peroxidase mimic composed of highly dispersed Pt and Mo atoms is reported. The obtained Mo-Pt/CeO2 exhibits exceptional peroxidase-like catalytic activity, with a Vmax as high as 34.16 × 10-8 m s-1, which is 37.5 times higher than that of the single-site counterpart. Mechanism studies suggest that the Mo atoms can not only serve as adsorption and activation sites for the H2O2 substrate but also regulate the charge density of Pt centers to promote the generation ability of •OH. As a result, the synergistic effect between the dual active sites significantly improves the catalytic efficiency. Significantly, the application of the Mo-Pt/CeO2 catalyst's excellent peroxidase-like activity is extended to various biochemical detection applications, including the trace detection of glucose and cysteine, as well as the assessment of antioxidants' antioxidant capacity. This work reveals the great potential of rational design dual-site active centers for constructing high-performance artificial nanozymes.

Nitrogen Vacancy Modulation of Tungsten Nitride Peroxidase-Mimetic Activity for Bacterial Infection Therapy

Bacterial infections claim millions of lives every year, with the escalating menace of microbial antibiotic resistance compounding this global crisis. Nanozymes, poised as prospective substitutes for antibiotics, present a significant frontier in antibacterial therapy, yet their precise enzymatic origins remain elusive. With the continuous development of nanozymes, the applications of elemental N-modulated nanozymes have spanned multiple fields, including sensing and detection, infection therapy, cancer treatment, and pollutant degradation. The introduction of nitrogen into nanozymes not only broadens their application range but also holds significant importance for the design of catalysts in biomedical research. The synergistic interplay between W and N induces pivotal alterations in electronic configurations, endowing tungsten nitride (WN) with a peroxidase-like functionality. Furthermore, the introduction of N vacancies augments the nanozyme activity, thus amplifying the catalytic potential of WN nanostructures. Rigorous theoretical modeling and empirical validation corroborate the genesis of the enzyme activity. The meticulously engineered WN nanoflower architecture exhibits an exceptional ability in traversing bacterial surfaces, exerting potent bactericidal effects through direct physical interactions. Additionally, the topological intricacies of these nanostructures facilitate precise targeting of generated radicals on bacterial surfaces, culminating in exceptional bactericidal efficacy against both Gram-negative and Gram-positive bacterial strains along with notable inhibition of bacterial biofilm formation. Importantly, assessments using a skin infection model underscore the proficiency of WN nanoflowers in effectively clearing bacterial infections and fostering wound healing. This pioneering research illuminates the realm of pseudoenzyme activity and bacterial capture-killing strategies, promising a fertile ground for the development of innovative, high-performance artificial peroxidases.

Development of Nanozymatic Characteristics in Metal-Doped Oxide Nanomaterials

Nanozymes are nanoscale materials that exhibit enzymatic-like activity, combining the benefits of nanomaterials with biocatalytic effects. The addition of metals to nanomaterials can enhance their nanozyme activity by mimicking the active sites of enzymes, providing structural support and promoting redox activity. In this study, nanostructured oxide and silicate-phosphate nanomaterials with varying manganese and copper additions were characterized. The objective was to assess the influence of metal modifications (Mn and Cu) on the acquisition of the nanozymatic activity by selected nanomaterials. An increase in manganese content in each material enhanced proteolytic activity (from 20 to 40 mUnit/mg for BG-Mn), while higher copper addition in glassy materials increased activity by 40%. Glassy materials exhibited approximately twice the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid radical activity (around 40 μmol/mL) compared to that of oxide materials. The proteolytic and antioxidant activities discussed in the study can be considered indicators for evaluating the enzymatic properties of the nanomaterials. Observations conducted on nanomaterials may aid in the development of materials with enhanced catalytic efficiency and a wide range of applications.

Biomimetic engineering of a neuroinflammation-targeted MOF nanozyme scaffolded with photo-trigger released CO for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is one of the most fatal and irreversible neurodegenerative diseases, which causes a huge emotional and financial burden on families and society. Despite the progress made with recent clinical use of inhibitors of acetylcholinesterase and amyloid-β (Aβ) antibodies, the curative effects of AD treatment remain unsatisfactory, which is probably due to the complexity of pathogenesis and the multiplicity of therapeutic targets. Thus, modulating complex pathological networks could be an alternative approach to treat AD. Here, a neutrophil membrane-coated MOF nanozyme (denoted as Neu-MOF/Fla) is biomimetically engineered to disturb the malignant Aβ deposition-inflammation cycle and ameliorate the pathological network for effective AD treatment. Neu-MOF/Fla could recognize the pathological inflammatory signals of AD, and deliver the photo-triggered anti-inflammatory CO and MOF based hydrolytic nanozymes to the lesion area of the brain in a spontaneous manner. Based on the in vitro and in vivo studies, Neu-MOF/Fla significantly suppresses neuroinflammation, mitigates the Aβ burden, beneficially modulates the pro-inflammatory microglial phenotypes and improves the cognitive defects of AD mice models. Our work presents a good example for developing biomimetic multifunctional nanotherapeutics against AD by means of amelioration of multiple symptoms and improvement of cognitive defects.

Au-modified ceria nanozyme prevents and treats hypoxia-induced pulmonary hypertension with greatly improved enzymatic activity and safety

BACKGROUND

Despite recent advances the prognosis of pulmonary hypertension remains poor and warrants novel therapeutic options. Extensive studies, including ours, have revealed that hypoxia-induced pulmonary hypertension is associated with high oxidative stress. Cerium oxide nanozyme or nanoparticles (CeNPs) have displayed catalytic activity mimicking both catalase and superoxide dismutase functions and have been widely used as an anti-oxidative stress approach. However, whether CeNPs can attenuate hypoxia-induced pulmonary vascular oxidative stress and pulmonary hypertension is unknown.

RESULTS

In this study, we designed a new ceria nanozyme or nanoparticle (AuCeNPs) exhibiting enhanced enzyme activity. The AuCeNPs significantly blunted the increase of reactive oxygen species and intracellular calcium concentration while limiting proliferation of pulmonary artery smooth muscle cells and pulmonary vasoconstriction in a model of hypoxia-induced pulmonary hypertension. In addition, the inhalation of nebulized AuCeNPs, but not CeNPs, not only prevented but also blunted hypoxia-induced pulmonary hypertension in rats. The benefits of AuCeNPs were associated with limited increase of intracellular calcium concentration as well as enhancement of extracellular calcium-sensing receptor (CaSR) activity and expression in rat pulmonary artery smooth muscle cells. Nebulised AuCeNPs showed a favorable safety profile, systemic arterial pressure, liver and kidney function, plasma Ca2+ level, and blood biochemical parameters were not affected.

CONCLUSION

We conclude that AuCeNPs is an improved reactive oxygen species scavenger that effectively prevents and treats hypoxia-induced pulmonary hypertension.

Artificial Bacteriophages for Treating Oral Infectious Disease via Localized Bacterial Capture and Enhanced Catalytic Sterilization

With the rapid emergence of antibiotic-resistant pathogens, nanomaterial-assisted catalytic sterilization has been well developed to combat pathogenic bacteria by elevating the level of reactive oxygen species including hydroxyl radical (·OH). Although promising, the ultra-short lifetime and limited diffusion distance of ·OH severely limit their practical antibacterial usage. Herein, the rational design and preparation of novel virus-like copper silicate hollow spheres (CSHSs) are reported, as well as their applications as robust artificial bacteriophages for localized bacterial capture and enhanced catalytic sterilization in the treatment of oral infectious diseases. During the whole process of capture and killing, CSHSs can efficiently capture bacteria via shortening the distance between bacteria and CSHSs, produce massive ·OH around bacteria, and further iinducing the admirable effect of bacterial inhibition. By using mucosal infection and periodontitis as typical oral infectious diseases, it is easily found that the bacterial populations around lesions in animals after antibacterial treatment fall sharply, as well as the well-developed nanosystem can decrease the inflammatory reaction and promote the hard or soft tissue repair. Together, the high Fenton-like catalytic activity, strong bacterial affinity, excellent antibacterial activity, and overall safety of the nanoplatform promise its great therapeutic potential for further catalytic bacterial disinfection.

A Non-Metallic Nanozyme Ameliorates Pulmonary Hypertension Through Inhibiting ROS/TGF-β1 Signaling

Pulmonary hypertension (PH) is a life-threatening cardiovascular disease with a lack of effective treatment options. Nanozymes, though promising for PH therapy, pose safety risks due to their metallic nature. Here, a non-metallic nanozyme is reported for the treatment of monocrotaline (MCT)-induced PH with a therapeutic mechanism involving the ROS/TGF-β1 signaling. The synthesized melanin-polyvinylpyrrolidone-polyethylene glycol (MPP) nanoparticles showcase ultra-small size, excellent water solubility, high biocompatibility, and remarkable antioxidant capacity. The MPP nanoparticles are capable of effectively eliminating ROS in isolated pulmonary artery smooth muscle cells (PASMCs) from PH rats, and significantly reduce PASMC proliferation and migration. In vivo results from a PH model demonstrate that MPP nanoparticles significantly increase pulmonary artery acceleration time, decrease wall thickening and PCNA expression in lung tissues, as evidenced by echocardiograpy, histology and immunoblot analysis. Additionally, MPP nanoparticles treatment improve running capacity, decrease Fulton index, and attenuate right ventricular fibrosis in MCT-PH rats by using treadmill test, picrosirius red, and trichrome Masson staining. Further transcriptomic and biochemical analyses reveal that inhibiting ROS-driven activation of TGF-β1 in the PA is the mechanism by which MPP nanoparticles exert their therapeutic effect. This study provides a novel approach for treating PH with non-metallic nanozymes based on a well-understood mechanism.

Smart Bioorthogonal Nanozymes: From Rational Design to Appropriate Bioapplications

Bioorthogonal chemistry has provided an elaborate arsenal to manipulate native biological processes in living systems. As the great advancement of nanotechnology in recent years, bioorthogonal nanozymes are innovated to tackle the challenges that emerged in practical biomedical applications. Bioorthogonal nanozymes are uniquely positioned owing to their advantages of high customizability and tunability, as well as good adaptability to biological systems, which bring exciting opportunities for biomedical applications. More intriguingly, the great advancement in nanotechnology offers an exciting opportunity for innovating bioorthogonal catalytic materials. In this comprehensive review, the significant progresses of bioorthogonal nanozymes are discussed with both spatiotemporal controllability and high performance in living systems, and highlight their design principles and recent rapid applications. The remaining challenges and future perspectives are then outlined along this thriving field. It is expected that this review will inspire and promote the design of novel bioorthogonal nanozymes, and facilitate their clinical translation.

Computer-aided nanodrug discovery: recent progress and future prospects

Nanodrugs, which utilise nanomaterials in disease prevention and therapy, have attracted considerable interest since their initial conceptualisation in the 1990s. Substantial efforts have been made to develop nanodrugs for overcoming the limitations of conventional drugs, such as low targeting efficacy, high dosage and toxicity, and potential drug resistance. Despite the significant progress that has been made in nanodrug discovery, the precise design or screening of nanomaterials with desired biomedical functions prior to experimentation remains a significant challenge. This is particularly the case with regard to personalised precision nanodrugs, which require the simultaneous optimisation of the structures, compositions, and surface functionalities of nanodrugs. The development of powerful computer clusters and algorithms has made it possible to overcome this challenge through in silico methods, which provide a comprehensive understanding of the medical functions of nanodrugs in relation to their physicochemical properties. In addition, machine learning techniques have been widely employed in nanodrug research, significantly accelerating the understanding of bio-nano interactions and the development of nanodrugs. This review will present a summary of the computational advances in nanodrug discovery, focusing on the understanding of how the key interfacial interactions, namely, surface adsorption, supramolecular recognition, surface catalysis, and chemical conversion, affect the therapeutic efficacy of nanodrugs. Furthermore, this review will discuss the challenges and opportunities in computer-aided nanodrug discovery, with particular emphasis on the integrated "computation + machine learning + experimentation" strategy that can potentially accelerate the discovery of precision nanodrugs.

Preparation of hollow double-layer Pt@CeO2 nanospheres as oxidase mimetics for the colorimetric-fluorescent-SERS triple-mode detection of glutathione in serum

Glutathione (GSH) is an essential antioxidant in the human body, but its detection is difficult due to the interference of complex components in serum. Herein, hollow double-layer Pt@CeO2 nanospheres were developed as oxidase mimetics, and the light-assisted oxidase mimetics effects were found. The oxidase activity was enhanced significantly by utilizing the synergistic effect of Schottky junction and the localized surface plasmon resonance (LSPR) of Pt under UV light. A novel GSH colorimetric-fluorescent-SERS sensing platform was established, with the sensing performance notably boosted by using the light-assisted oxidase mimetics effects. This platform boasts an exceptionally low detection limit (LOD) of 0.084 μM, while the detection time was shortened from 10 min to just 2 min. The anti-interference detection with high recovery rate (96.84%-107.4 %) in real serum made it be promising for practical application.

Optimizing the standardized assays for determining the catalytic activity and kinetics of peroxidase-like nanozymes

Nanozymes are nanomaterials with enzyme-like catalytic properties. They are attractive reagents because they do not have the same limitations of natural enzymes (e.g., high cost, low stability and difficult storage). To test, optimize and compare nanozymes, it is important to establish fundamental principles and systematic standards to fully characterize their catalytic performance. Our 2018 protocol describes how to characterize the catalytic activity and kinetics of peroxidase nanozymes, the most widely used type of nanozyme. This approach was based on Michaelis-Menten enzyme kinetics and is now updated to take into account the unique physicochemical properties of nanomaterials that determine the catalytic kinetics of nanozymes. The updated procedure describes how to determine the number of active sites as well as other physicochemical properties such as surface area, shape and size. It also outlines how to calculate the hydroxyl adsorption energy from the crystal structure using the density functional theory method. The calculations now incorporate these measurements and computations to better characterize the catalytic kinetics of peroxidase nanozymes that have different shapes, sizes and compositions. This updated protocol better describes the catalytic performance of nanozymes and benefits the development of nanozyme research since further nanozyme development requires precise control of activity by engineering the electronic, geometric structure and atomic configuration of the catalytic sites of nanozymes. The characterization of the catalytic activity of peroxidase nanozymes and the evaluation of their kinetics can be performed in 4 h. The procedure is suitable for users with expertise in nano- and materials technology.

A colorimetric sensor for rapid discrimination of tea polyphenols and tea authentication based on Rh-decorated Pd nanocubes with high peroxidase-like activity

The rapid development of nanozymes has offered substantial opportunities for the fields of biomedicine, chemical sensing, and food safety. Among these applications, multichannel sensors, with the capability of simultaneously detecting multiple target analytes, hold promise for the practical application of nanozymes in chemical sensing with high detection efficiency. In this study, Rh-decorated Pd nanocubes (Pd-Rh nanocubes) with significantly enhanced peroxidase-like activity are synthesized through the mediation of underpotential deposition (UPD) and subsequently employed to develop a multichannel colorimetric sensor for discriminating tea polyphenols (TPs) and tea authentication. Based on a single reactive unit of efficient catalytic oxidation of 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB), the nanozyme-based multichannel colorimetric sensor responds to each analyte in as short as 1 min. With the aid of principal component analysis (PCA) and hierarchical cluster analysis (HCA), various TPs and types of tea can be accurately identified. This work not only provides a new type of simply structured and highly active nanozymes but also develops a concise and rapid multichannel sensor for practical application in tea authentication and quality inspection.

Emerging Nanomaterials as Versatile Nanozymes: A New Dimension in Biomedical Research

The enzyme-mimicking nature of versatile nanomaterials proposes a new class of materials categorized as nano-enzymes, ornanozymes. They are artificial enzymes fabricated by functionalizing nanomaterials to generate active sites that can mimic enzyme-like functions. Materials extend from metals and oxides to inorganic nanoparticles possessing intrinsic enzyme-like properties. High cost, low stability, difficulty in separation, reusability, and storage issues of natural enzymes can be well addressed by nanozymes. Since 2007, more than 100 nanozymes have been reported that mimic enzymes like peroxidase, oxidase, catalase, protease, nuclease, hydrolase, superoxide dismutase, etc. In addition, several nanozymes can also exhibit multi-enzyme properties. Vast applications have been reported by exploiting the chemical, optical, and physiochemical properties offered by nanozymes. This review focuses on the reported nanozymes fabricated from a variety of materials along with their enzyme-mimicking activity involving tuning of materials such as metal nanoparticles (NPs), metal-oxide NPs, metal-organic framework (MOF), covalent organic framework (COF), and carbon-based NPs. Furthermore, diverse applications of nanozymes in biomedical research are discussed in detail.

Broad-spectrum degradation of fluoroquinolone antibiotics by Hemin-His-Fe nanozymes with peroxidase-like activity

Fluoroquinolones are a widely used class of antibiotics, with a large variety, which are frequently monitored in the aqueous environment, threatening ecological and human health. To date, effective degradation of fluoroquinolone antibiotics remains a major challenge. Focused on the broad-spectrum degradation of fluoroquinolone antibiotics, a novel biomimetic peroxidase nanozyme named Hemin-His-Fe (HHF)-peroxidase nanozyme was synthesized through a green and rapid "one-pot" method involving hemin, Fmoc-L-His and Fe2+ as precursors. After systematic optimization of the reaction conditions, fluoroquinolone antibiotics can be degraded by the HHF-peroxidase nanozyme when supplemented with H2O2 in acidic environments. Through validation and analysis, it was proved that the generated strong oxidative hydroxyl radicals are the main active species in the degradation process. In addition, it was verified that this method shows great universal applicability in real water samples.

Nanozyme-Enabled Biomedical Diagnosis: Advances, Trends, and Challenges

As nanoscale materials with the function of catalyzing substrates through enzymatic kinetics, nanozymes are regarded as potential alternatives to natural enzymes. Compared to protein-based enzymes, nanozymes exhibit attractive characteristics of low preparation cost, robust activity, flexible performance adjustment, and versatile functionalization. These advantages endow them with wide use from biochemical sensing and environmental remediation to medical theranostics. Especially in biomedical diagnosis, the feature of catalytic signal amplification provided by nanozymes makes them function as emerging labels for the detection of biomarkers and diseases, with rapid developments observed in recent years. To provide a comprehensive overview of recent progress made in this dynamic field, here an overview of biomedical diagnosis enabled by nanozymes is provided. This review first summarizes the synthesis of nanozyme materials and then discusses the main strategies applied to enhance their catalytic activity and specificity. Subsequently, representative utilization of nanozymes combined with biological elements in disease diagnosis is reviewed, including the detection of biomarkers related to metabolic, cardiovascular, nervous, and digestive diseases as well as cancers. Finally, some development trends in nanozyme-enabled biomedical diagnosis are highlighted, and corresponding challenges are also pointed out, aiming to inspire future efforts to further advance this promising field.

Atom-pair engineering of single-atom nanozyme for boosting peroxidase-like activity

Constructing atom-pair engineering and improving the activity of metal single-atom nanozyme (SAzyme) is significant but challenging. Herein, we design the atom-pair engineering of Zn-SA/CNCl SAzyme by simultaneously constructing Zn-N4 sites as catalytic sites and Zn-N4Cl1 sites as catalytic regulator. The Zn-N4Cl1 catalytic regulators effectively boost the peroxidase-like activities of Zn-N4 catalytic sites, resulting in a 346-fold, 1496-fold, and 133-fold increase in the maximal reaction velocity, the catalytic constant and the catalytic efficiency, compared to Zn-SA/CN SAzyme without the Zn-N4Cl1 catalytic regulator. The Zn-SA/CNCl SAzyme with excellent peroxidase-like activity effectively inhibits tumor cell growth in vitro and in vivo. The density functional theory (DFT) calculations reveal that the Zn-N4Cl1 catalytic regulators facilitate the adsorption of *H2O2 and re-exposure of Zn-N4 catalytic sites, and thus improve the reaction rate. This work provides a rational and effective strategy for improving the peroxidase-like activity of metal SAzyme by atom-pair engineering.

Neutrophil membrane-derived nanoparticles protect traumatic brain injury via inhibiting calcium overload and scavenging ROS

The secondary injury is more serious after traumatic brain injury (TBI) compared with primary injury. Release of excessive reactive oxygen species (ROS) and Ca2+ influx at the damaged site trigger the secondary injury. Herein, a neutrophil-like cell membrane-functionalized nanoparticle was developed to prevent ROS-associated secondary injury. NCM@MP was composed of three parts: (1) Differentiated neutrophil-like cell membrane (NCM) was synthesized, with inflammation-responsive ability to achieve effective targeting and to increase the retention time of Mn3O4 and nimodipine (MP) in deep injury brain tissue via C-X-C chemokine receptor type 4, integrin beta 1 and macrophage antigen-1. (2) Nimodipine was used to inhibit Ca2+ influx, eliminating the ROS at source. (3) Mn3O4 further eradicated the existing ROS. In addition, NCM@MP also exhibited desirable properties for T1 enhanced imaging and low toxicity which may serve as promising multifunctional nanoplatforms for precise therapies. In our study, NCM@MP obviously alleviated oxidative stress response, reduced neuroinflammation, protected blood-brain barrier integrity, relieved brain edema, promoted the regeneration of neurons, and improved the cognition of TBI mice. This study provides a promising TBI management to relieve the secondary spread of damage.

PdMoPtCoNi High Entropy Nanoalloy with d Electron Self-Complementation-Induced Multisite Synergistic Effect for Efficient Nanozyme Catalysis

Engineering multimetallic nanocatalysts with the entropy-mediated strategy to reduce reaction activation energy is regarded as an innovative and effective approach to facilitate efficient heterogeneous catalysis. Accordingly, conformational entropy-driven high-entropy alloys (HEAs) are emerging as a promising candidate to settle the catalytic efficiency limitations of nanozymes, attributed to their versatile active site compositions and synergistic effects. As proof of the high-entropy nanozymes (HEzymes) concept, elaborate PdMoPtCoNi HEA nanowires (NWs) with abundant active sites and tuned electronic structures, exhibiting peroxidase-mimicking activity comparable to that of natural horseradish peroxidase are reported. Density functional theory calculations demonstrate that the enhanced electron abundance of HEA NWs near the Fermi level (EF) is facilitated via the self-complementation effect among the diverse transition metal sites, thereby boosting the electron transfer efficiency at the catalytic interface through the cocktail effect. Subsequently, the HEzymes are integrated with a portable electronic device that utilizes Internet of Things-driven signal conversion and wireless transmission functions for point-of-care diagnosis to validate their applicability in digital biosensing of urinary biomarkers. The proposed HEzymes underscore significant potential in enhancing nanozymes catalysis through tunable electronic structures and synergistic effects, paving the way for reformative advancements in nano-bio analysis.

Deep convolutional neural network-based 3D fluorescence sensor array for sugar identification in serum based on the oxidase-mimicking property of CuO nanoparticles

Developing sensor arrays capturing comprehensive fluorescence (FL) spectra from a single probe is crucial for understanding sugar structures with very high similarity in biofluids. Therefore, the analysis of highly similar sugar' structures in biofluids based on the entire FL of a single nanozyme probe needs more concern, which makes the development of novel alternative approaches highly wanted for biomedical and other applications. Herein, a well-designed deep learning model with intrinsic information of 3D FL of CuO nanoparticles (NPs)' oxidase-like activity was developed to classify and predict the concentration of a group of sugars with very similar chemical structures in different media. The findings presented that the overall accuracy of the developed model in classifying the nine selected sugars was (99-100 %), which prompted us to transfer the developed model to predict the concentration of the selected sugars at a concentration range of (1-100 μM). The transferred model also gave excellent results (R2 = 97-100 %). Therefore, the model was extended to other more complex applications, namely the identification of mixtures of sugars in serum and the detection of polysaccharides in different media such as serum and lake water. Notably, LOD for fructose was determined at 4.23 nM, marking a 120-fold decrease compared to previous studies. Our developed model was also compared with other deep learning-based models, and the results have demonstrated remarkable progress. Moreover, the identification of other possible coexisting interference substances in lake water samples was considered. This work marks a significant advancement, opening avenues for the widespread application of sensor arrays integrating nanozymes and deep learning techniques in biomedical and other diverse fields.

Applications of Metals and Metal Compounds in Improving the Sensitivity of Microfluidic Biosensors - A Review

The enhancement of detection sensitivity in microfluidic sensors has been a continuously explored field. Initially, many strategies for sensitivity improvement involved introducing enzyme cascade reactions, but enzyme-based reactions posed challenges in terms of cost, stability, and storage. Therefore, there is an urgent need to explore enzyme-free cascade amplification methods, which are crucial for expanding the application range and improving detection stability. Metal or metal compound nanomaterials have gained great attention in the exploitation of microfluidic sensors due to their ease of preparation, storage, and lower cost. The unique physical properties of metallic nanomaterials, including surface plasmon resonance, surface-enhanced Raman scattering, metal-enhanced fluorescence, and surface-enhanced infrared absorption, contribute significantly to enhancing detection capabilities. The metal-based catalytic nanomaterials, exemplified by Fe3O4 nanoparticles and metal-organic frameworks, are considered viable alternatives to biological enzymes due to their excellent performance. Herein, we provide a detailed overview of the applications of metals and metal compounds in improving the sensitivity of microfluidic biosensors. This review not only highlights the current developments but also critically analyzes the challenges encountered in this field. Furthermore, it outlines potential directions for future research, contributing to the ongoing development of microfluidic biosensors with improved detection sensitivity.

In Situ Defect Engineering of Fe-MIL for Self-Enhanced Peroxidase-Like Activity

Defect engineering is an effective strategy to enhance the enzyme-like activity of nanozymes. However, previous efforts have primarily focused on introducing defects via de novo synthesis and post-synthetic treatment, overlooking the dynamic evolution of defects during the catalytic process involving highly reactive oxygen species. Herein, a defect-engineered metal-organic framework (MOF) nanozyme with mixed linkers is reported. Over twofold peroxidase (POD)-like activity enhancement compared with unmodified nanozyme highlights the critical role of in situ defect formation in enhancing the catalytic performance of nanozyme. Experimental results reveal that highly active hydroxyl radical (•OH) generated in the catalytic process etches the 2,5-dihydroxyterephthalic acid ligands, contributing to electronic structure modulation of metal sites and enlarged pore sizes in the framework. The self-enhanced POD-like activity induced by in situ defect engineering promotes the generation of •OH, holding promise in colorimetric sensing for detecting dichlorvos. Utilizing smartphone photography for RGB value extraction, the resultant sensing platform achieves the detection for dichlorvos ranging from 5 to 300 ng mL-1 with a low detection limit of 2.06 ng mL-1. This pioneering work in creating in situ defects in MOFs to improve catalytic activity offers a novel perspective on traditional defect engineering.

Immobilizing DNase in ternary AuAgCu hydrogels to accelerate biofilm disruption for synergistically enhanced therapy of MRSA infections

Bacterial biofilm-related infections have become a significant global concern in public health and economy. Extracellular DNA (eDNA) is regarded as one of the key elements of extracellular polymeric substances (EPS) in bacterial biofilm, providing robust support to maintain the stability of bacterial biofilms for fighting against environmental stresses (such as antibiotics, reactive oxygen species (ROS), and hyperthermia). In this study, ternary AuAgCu hydrogels nanozyme with porous network structures were utilized for the immobilization of DNase (AuAgCu@DNase hydrogels) to realize enhanced biofilm decomposition and antibacterial therapy of MRSA. The prepared AuAgCu@DNase hydrogels can efficiently hydrolyze eDNA in biofilms so that the generated ROS and hyperthermia by laser irradiation can permeate into the interior of the biofilm to achieve deep sterilization. The typical interface interactions between AuAgCu hydrogels and DNase and the excellent photothermal-boost peroxidase-like performances of AuAgCu hydrogels take responsibility for the enhanced antibacterial activity. In the MRSA-infected wounds model, the in vivo antibacterial results revealed that the AuAgCu@DNase hydrogels possess excellent drug-resistant bacteria-killing performance with superb biocompatibility. Meanwhile, the pathological analysis of collagen deposition and fibroblast proliferation of wounds demonstrate highly satisfactory wound healing. This work offers an innovative path for developing nanozyme-enzyme antibacterial composites against drug-resistant bacteria and their biofilms.