N-Doped Carbon Nanotubes Supported Fe-Mn Dual-Single-Atoms Nanozyme with Synergistically Enhanced Peroxidase Activity for Sensitive Colorimetric Detection of Acetylcholinesterase and Its Inhibitor

Ultra-trace Ag doped carbon quantum dots with peroxidase-like activity for the colorimetric detection of glucose

Carbon quantum dots (CQDs) have significant applications in nanozymes. However, previous studies have not elucidated the structure-activity relationship and enzyme mechanism. In this study, we employed a one-step microwave method to synthesize ultra-trace Ag-doped carbon quantum dots (Ag-CQDs). In the presence of hydrogen peroxide (H2O2), we used the oxidative coupling reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to evaluate the intrinsic peroxidase-like activity, kinetics, and mechanism of Ag-CQDs. The trace amount of doped Ag (1.64 %) facilitated electron transfer from the CQDs interior to the surface. The electron transfer triggered the peroxide activity of CQDs, producing hydroxyl radical (·OH), which oxidized the colorless TMB to blue-colored TMB (oxTMB). By coupling with glucose oxidase (GOx), the Ag-CQDs/H2O2/TMB system has been used for colorimetric glucose determination. The system demonstrated a low detection limit (0.17 µM), wide linear range (0.5-5.5 µM), and satisfactory results when fruit juice was analyzed. This study reports a feasible method for the colorimetric detection of glucose by synthesizing ultra-trace Ag-doped carbon quantum dots with peroxidase-mimicking activity.

Tumor microenvironment activated mussel-inspired hollow mesoporous nanotheranostic for enhanced synergistic photodynamic/chemodynamic therapy

Anti-tumor therapies reliant on reactive oxygen species (ROS) as primary therapeutic agents face challenges due to a limited oxygen substrate. Photodynamic therapy (PDT) is particularly hindered by inherent hypoxia, while chemodynamic therapy (CDT) encounters obstacles from insufficient endogenous hydrogen peroxide (H2O2) levels. In this study, we engineered biodegradable tumor microenvironment (TME)-activated hollow mesoporous MnO2-based nanotheranostic agents, designated as HAMnO2A. This construct entails loading artemisinin (ART) into the cavity and surface modification with a mussel-inspired polymer ligand, namely hyaluronic acid-linked poly(ethylene glycol)-diethylenetriamine-conjugated (3,4-dihydroxyphenyl) acetic acid, and the photosensitizer Chlorin e6 (mPEG-HA-Dien-(Dhpa/Ce6)), facilitating dual-modal imaging-guided PDT/CDT synergistic therapy. In vitro experimentation revealed that HAMnO2A exhibited ideal physiological stability and enhanced cellular uptake capability via CD44-mediated endocytosis. Additionally, it was demonstrated that accelerated endo-lysosomal escape through the pH-dependent protonation of Dien. Within the acidic and highly glutathione (GSH)-rich TME, the active component of HAMnO2A, MnO2, underwent decomposition, liberating oxygen and releasing both Mn2+ and ART. This process alleviates hypoxia within the tumor region and initiates a Fenton-like reaction through the combination of ART and Mn2+, thereby enhancing the effectiveness of PDT and CDT by generating increased singlet oxygen (1O2) and hydroxyl radicals (•OH). Moreover, the presence of Mn2+ ions enabled the activation of T1-weighted magnetic resonance imaging. In vivo findings further validated that HAMnO2A displayed meaningful tumor-targeting capabilities, prolonged circulation time in the bloodstream, and outstanding efficacy in restraining tumor growth while inducing minimal damage to normal tissues. Hence, this nanoplatform serves as an efficient all-in-one solution by facilitating the integration of multiple functions, ultimately enhancing the effectiveness of tumor theranostics.

Direct detection of acetylcholinesterase by Fe(HCOO)2.6(OH)0.3. H2O nanosheets with oxidase-like activity on a smartphone platform

Monitoring acetylcholinesterase (AChE) is crucial in clinical diagnosis and drug screening. Traditional methods for detecting AChE usually require the addition of intermediates like acetylthiocholine, which complicates the detection process and introduces interference risks. Herein, we develop a direct colorimetric assay based on alkaline iron formate nanosheets (Fe(HCOO)2.6(OH)0.3·H2O NSs, Fef NSs) for the detection of AChE without any intermediates. The as-prepared Fef NSs exhibit oxidase-like activity, catalyzing the generation of O2·-, 1O2 and ·OH, which leads to a color change from colorless to blue when exposed to 3,3',5,5'-tetramethylbenzidine. AChE directly inhibits the oxidase-like activity of Fef NSs, resulting in a hindered color reaction, enabling the detection of AChE. The biosensor has a linear detection range of 0.1-30 mU/mL, with a minimum detection limit of 0.0083 mU/mL (S/N = 3), representing a 100-fold improvement in detection sensitivity over the traditional Ellman's method. Satisfactory results were obtained when analyzing real AChE samples. Attractively, a method for the quantitative detection of AChE by a smartphone is established based on the Fef NSs. This method enables instant acquisition of AChE concentrations, achieving real-time visualized detection.

Critical role of zero-valent iron in the efficient activation of H2O2 for 4-CP degradation by bimetallic peroxidase-like

Peroxidase-like based on double transition metals have higher catalytic activity and are considered to have great potential for application in the field of pollutant degradation. First, in this paper, a novel Fe0-doped three-dimensional porous Fe0@FeMn-NC-like peroxidase was synthesized by a simple one-step thermal reduction method. The doping of manganese was able to reduce part of the iron in Fe-Mn binary oxides to Fe0 at high temperatures. In addition, Fe0@FeMn-NC has excellent peroxidase-like mimetic activity, and thus, it was used for the rapid degradation of p-chlorophenol (4-CP). During the degradation process, Fe0 was able to rapidly replenish the constantly depleted Fe2+ in the reaction system and brought in a large number of additional electrons. The ineffective decomposition of H2O2 due to the use of H2O2 as an electron donor in the reduction reactions from Fe3+ to Fe2+ and from Mn3+ to Mn2+ was avoided. Finally, based on the experimental results of LC-MS and combined with theoretical calculations, the degradation process of 4-CP was rationally analyzed, in which the intermediates were mainly p-chloro-catechol, p-chloro resorcinol, and p-benzoquinone. Fe0@FeMn-NC nano-enzymes have excellent catalytic activity as well as structural stability and perform well in the treatment of simulated wastewater containing a variety of phenolic pollutants as well as real chemical wastewater. It provides some insights and methods for the application of peroxidase-like enzymes in the degradation of organic pollutants.

A cost-effective, "mix & act" G-quadruplex/Cu (II) metal-nanozyme-based ratiometric fluorescent platform for highly sensitive and selective cysteine/bleomycin detection and multilevel contrary logic computing

Versatile nanozymes with fascinating catalytic properties provide inspiring and effective options for biosensing and pharmaceutical analysis. Herein, we report the first nanozyme-based ratiometric fluorescent platform for cysteine (Cys) and bleomycin (BLM) detection by harnessing the cost-effective and "mix & act" G-quadruplex/Cu(II) (G4/Cu) metal-nanozyme with satisfactory peroxidase-like activity, which was fully proven by circular dichroism (CD), electron paramagnetic resonance (EPR) spectra and reactive oxygen species (ROS) scavenging experiments. Based on the catalytic oxidation of G4/Cu metal-nanozyme toward two fluorescent substrates (Amplex Ultrared, AU; Scopoletin, Sc) with opposite responses in the presence of H2O2, and the specific interaction between Cu2+ and targets, we achieved the highly sensitive detection of Cys and BLM. Through recording the fluorescence changes of AU (emission at 590 nm, F590) and Sc (emission at 465 nm, F465), we obtained good linear relationships between ratiometric fluorescence values (F590/F465) and variable contents of targets, resulting in the competitive LODs of Cys (6.7 nM) and BLM (10 nM), respectively. Moreover, this platform presented high selectivity (without the need for masking agent) and acceptable performance in human serum samples. Furthermore, a library of DNA contrary logic pairs (CLPs) and multilevel concatenated circuits were fabricated based on the reverse dual-output of the above platform, enriching the building blocks of biocomputing. This work not only enlightened the design of affordable, "mix & act" type nanozyme-based ratiometric biosensors with high reliability, but also facilitated the pluralistic application of nucleic acid-templated nanozymes to innovative biocomputing.

Natural Enzyme-Inspired Design of the Single-Atom Cu Nanozyme as Dual-Enzyme Mimics for Distinguishing Total Antioxidant Capacity and the Ascorbic Acid Level

Although various oxidase mimetic or peroxidase (POD) mimetic nanozymes have been extensively studied, their poor substrate selectivity significantly inhibits their practical applications. Nanozymes with specific biomolecules as substrates, especially ascorbic acid oxidase (AAO) mimetic nanozymes with ascorbic acid (AA) as a substrate, have scarcely been studied. Herein, inspired by the multi-Cu atom sites and the redox electron transfer pathway of Cu2+/Cu+ in the natural AAO, atomically dispersed Cu sites immobilized on N-doped porous carbon (Cu-N/C) are artificially designed to simulate the function of natural AAO. Compared with their natural counterparts, the Cu-N/C catalysts exhibited higher catalytic efficiency and superior stability. Combined theoretical calculation and experimental characterizations reveal that the Cu-N/C nanozymes could catalyze the AA oxidation through a 2e- oxygen reduction pathway with H2O2 as the product. Moreover, the Cu-N/C nanozymes also possess high POD activity. As a proof-of-concept application, Cu-N/C can simultaneously realize AA detection in fluorescent mode based on its AAO activity and total antioxidant capacity detection in colorimetric mode utilizing its POD activity.

Fe-Ni dual-single atoms nanozyme with high peroxidase-like activity for sensitive colorimetric and fluorometric dual-mode detection of cholesterol

Cholesterol is widely existed in nerve myelin sheath and various membrane structures, whose abnormal level would deteriorate human cells or even cause diseases. Herein, Fe-Ni dual-single-atom nanozyme was efficiently incorporated into N-doped carbon nanosheets (FeNi DSAs/N-CSs) by a simple calcination method. Its nanozyme activity and catalytic mechanism were investigated in details. The FeNi DSAs/N-CSs nanozyme showed superior peroxidase-like property, which was applied for the dual-mode determination of hydrogen peroxide (H2O2) and cholesterol. The colorimetric/fluorometric assays of H2O2 displayed the linear ranges of 1-50 mM and 5-40 mM with low limits of detection of 0.45 mM and 3.33 mM, respectively. In parallel, there exhibited the linear ranges of 0.5-5.0 mM and 0.25-5.0 mM for the colorimetric/fluorometric analysis of cholesterol, coupled with the limits of detection down to 0.19 mM and 0.044 mM, respectively. This work provided a rapid, cost-effectiveness and simple colorimetric/fluorometric method for sensitive dual-mode detection of cholesterol in human serum samples.

High Peroxidase-Mimicking Metal-Organic Frameworks Decorated with Platinum Nanozymes for the Colorimetric Detection of Acetylcholine Chloride and Organophosphorus Pesticides via Enzyme Cascade Reaction

The sensitive detection of acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) is very important for the protection of human health. Herein, a hybrid material, Pt NPs/Fe-MOF, consisting of a metal-organic framework (MIL-88B-NH2, Fe-MOF) decorated with platinum nanoparticles (Pt NPs), was prepared first and exhibited remarkably improved and excellent peroxidase-mimicking activity compared to the Fe-MOF material resulting from the synergistic catalysis effect between Fe-MOF and Pt NPs, which can effectively catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to generate a blue product (oxidized TMB, oxTMB). Interestingly, in the presence of AChE and acetylcholinesterase, the peroxidase-mimicking activity from Pt NPs/Fe-MOF was inhibited obviously, and thus, a colorimetric sensing platform for AChE can be constructed; more importantly, after the addition of OPs, this nanozyme activity can be recovered, inducing the further successful construction of a sensitive colorimetric sensing platform for OPs. The related sensing mechanism and condition optimization were studied, and the as-prepared Pt NPs/Fe-MOF nanozyme-based colorimetric method for AChE and OP detection displayed superior analytical performances with wide linearities and low detection limits. Furthermore, the designed method offers satisfactory real application ability. We expect the as-proposed Pt NPs/Fe-MOF nanozyme-based colorimetric sensing platform for AChE and OPs via the enzyme cascade reaction to show great potential application.