Intrinsic Peroxidase-like Catalytic Activity Research Articles

Pathogen-Activated Macrophage Membrane Encapsulated CeO2-TCPP Nanozyme with Targeted and Photo-Enhanced Antibacterial Therapy.

Nanozymes with peroxidase-mimic activity have recently emerged as effective strategies for eliminating infections. However, challenges in enhancing catalytic activities and the ability to target bacteria have hindered the broader application of nanozymes in bacterial infections. Herein, a novel nanozyme based on mesoporous CeO2 nanosphere and meso-tetra(4-carboxyphenyl)porphine (TCPP) encapsulated within pathogen-activated macrophage membranes, demonstrates photodynamic capability coupled with photo-enhanced chemodynamic therapy for selective and efficient antibacterial application against infected wounds. Interestingly, the expression of Toll-like receptors accordingly upregulates when macrophages are co-cultured with specific bacteria, thereby facilitating to recognition of the pathogen-associated molecular patterns originating from bacteria. The CeO2 not only serve as carriers for TCPP, but also exhibit intrinsic peroxidase-like catalytic activity. Consequently, Staphylococcus aureus (S. aureus)-activated macrophage membrane-coated CeO2-TCPP (S-MM@CeO2-TCPP) generated singlet oxygen, and simultaneously promoted photo-enhanced chemodynamic therapy, significantly boosting reactive oxygen species (ROS) to effectively eliminate bacteria. S-MM@CeO2-TCPP specifically targeted S. aureus via Toll-like receptor, thereby directly disrupting bacterial structural integrity to eradicate S. aureus in vitro and relieve bacteria-induced inflammation to accelerate infected wound healing in vivo. By selectively targeting specific bacteria and effectively killing pathogens, such strategy provides a more efficient and reliable alternative for precise elimination of pathogens and inflammation alleviation in microorganism-infected wounds.

A peroxidase-like single-atom Fe-N5 active site for effective killing human lung adenocarcinoma cells

Single-atom catalyst (SAC) is one of the newest catalysts, and attracts people’s wide attention in cancer therapy based on their characteristics of maximum specific catalytic activity and high stability. We designed and synthesized a Fe-N decorated graphene nanosheet (Fe-N5/GN SAC) with the coordination number of five. Through enzymology and theoretical calculations, the Fe-N5/GN SAC has outstanding intrinsic peroxidase-like catalytic activity due to single-atom Fe site with five-N-coordination structure. We explored its potential on lung cancer therapy, and found that it could kill human lung adenocarcinoma cells (A549) by decomposing hydrogen peroxide (H2O2) into toxic reactive oxygen species (ROS) under acidic microenvironment in three-dimensional (3D) lung cancer cell model. Our study demonstrates a promising application of SAC with highly efficient single-atom catalytic sites for cancer treatment.

A dual-readout sandwich immunoassay based on biocatalytic perovskite nanocrystals for detection of prostate specific antigen

Nanozymes have been regarded as an excellent alternative for natural enzymes because of their high stability, low cost, and high activity. However, their use in disease diagnosis is still challenging, since the complex biological samples foul the nanozymes’ surface and generate interference signals, thereby compromising the performance of nanozyme-based assays. Here, we report a dual-readout, CsPbBr3 NCs-based sandwich immunoassay for the detection of prostate specific antigen (PSA). Thanks to their excellent fluorescence and intrinsic peroxidase-like catalytic activity, the designed phospholipid-coated CsPbBr3 NCs (PL-CsPbBr3 NCs) served as an attractive dual signal generator (fluorescent and colorimetric), which is hardly achieved by other nanozymes. The Michaelis-Menten constant (KM) values of PL-CsPbBr3 NCs for H2O2 and tetramethylbenzidine are 2.85 mM and 1.42 mM, respectively. Meanwhile, the lipid shell around CsPbBr3 NCs not only greatly improves their aqueous stability, but also helps them resist the unspecific adsorption of biological impurities. Thus, the proposed dual-readout immunoassay enables precise, cost-effective, and anti-jamming detection of PSA in real serum samples with a low detection limit of 0.29 ng mL-1 (colorimetric) and 0.081 ng mL-1 (fluorescence). This enhanced immunoassay opens new insights for the application of perovskites in bioanalysis, especially for protein assay, holding great potential for disease diagnosis.

DNA-Engineered iron-based metal-organic framework bio-interface for rapid visual determination of exosomes

In this study, a rapid, low-cost and facile method for detecting exosomes was developed by engineering DNA ligands on the surface of an iron-based metal–organic framework (Fe-MOF). Aptamers of exosomal transmembrane CD63 protein (CD63-aptamers) were utilized as both the optically active layer and the exosome-specific recognition element to engineer an Fe-MOF bio-interface for high-efficiency regulation of the catalytic behavior of Fe-MOF toward the chromogenic substrate. The effective enhancement of the intrinsic peroxidase-like catalytic activity was confirmed via the self-assembly of CD63-aptamers on the surface of Fe-MOF. The specific binding of exosomes with CD63-aptamers altered the conformation of DNA ligands on the surface of Fe-MOF, contributing to sensitive variation in Fe-MOF catalytic activity. This directly produced a distinct color change and enabled the visual detection of exosomes. Via one-step “mixing-and-detection”, the Fe-MOF bio-interface exhibited excellent performance in quantitative analysis of exosomes derived from human breast cancer cell lines ranging from 1.1 × 105 to 2.2 × 107 particles/μL with a detection limit of 5.2 × 104 particles/μL. The expression of exosomal CD63 proteins originated from three types of cancer cell lines, including breast cancer, gastric cancer and lung cancer cell lines, was differentiated within only 17 min. Furthermore, the method was successfully applied to the identification of exosomes in serum samples, suggesting its potential in clinical analysis as a valuable tool for the rapid, convenient and economical testing of exosomes.

A reusable colorimetric assay based on mixed valence state Ce-MOF@Pt nanoparticles for highly sensitive detection of visfatin

In this work, a colorimetric assay for visfatin detection is described. The mixed valence state Ce-MOF (MVCM) modified by platinum nanoparticles (Pt NPs) is used as a novel catalyst. MVCM exhibits excellent intrinsic peroxidase-like catalytic activity due to the spontaneous recycling of the Ce(III)/Ce(IV) system. Pt NPs serve not only as a carrier of the –NH2-modified single strand DNA (S1) but also as a synergistic catalyst of MVCM. The capture probe (S2) attached to the streptavidin-modified magnetic beads (Mag-SA) could combine with the aptamer to form the Mag-SA/S2/aptamer complex. When in the presence of the target visfatin, aptamer specifically combines with the visfatin, which induces the release of Mag-SA/S2 from the Mag-SA/S2/aptamer complex. At this time, the MVCM@Pt/S1 complex connects with the released Mag-SA/S2, which quickly catalyzes the 3,3,3′,3′-tetramethylbenzidine (TMB), leading to a color change. Under optimal conditions, the absorbance increases linearly when the concentration ranges from 1 ng mL−1 to 100 ng mL−1, and the detection limit is as low as 0.11 ng mL−1. Furthermore, Mag-SA/S2 can be reused at least five times by using the uracil-DNA glycosylase (UDG) and an external magnetic field. The proposed method shows satisfying reproducibility, stability, specificity, and sensitivity, and it was successfully applied to detect visfatin in spiked human serum samples. Thus, it has great potential for clinical research, detection, and catalytic applications.

A Colorimetric Assay for the Detection of Glucose and H2O2 Based on Cu-Ag/g-C3N4/ZIF Hybrids with Superior Peroxidase Mimetic Activity.

In this work, we report the synthesis of Cu-Ag bimetallic nanopartiles and g-C3N4 nanosheets decorated on zeolitic imidazolate framework-8 (ZIF-8) to form a Cu-Ag/g-C3N4/ZIF hybrid. The hybrid was synthesized and characterized by Transmission electron microscopy (TEM), Fourier transformed infrared (FTIR), the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Cu-Ag/g-C3N4/ZIF hybrid has intrinsic peroxidaselike catalytic activity towards the oxidation of TMB in the presence of H2O2. The situ synthesis of Cu-Ag bimetallic nanopartiles on 2D support such as g-C3N4 nanosheets would significantly enhance the peroxidaselike catalytic properties of individual Cu-Ag bimetallic nanopartiles and the g-C3N4 nanosheets. After loading of Cu-Ag bimetallic nanopartiles and g-C3N4 nanosheets on the ZIF-8, the hybrids exhibited superior peroxidaselike catalytic activity and good recyclability. Then, this method was applied for detecting glucose in human serum, owing the significant potential for detection of metabolites with H2O2-generation reactions.

Facile synthesis of large-area ultrathin two-dimensional supramolecular nanosheets in water

Synthesizing large-area ultrathin two-dimensional (2D) nanostructures in aqueous media has received considerable increasing attention but remains a big challenge. Herein, we report a facile method for the synthesis of two unprecedented large-area ultrathin 2D supramolecular nanosheets via ionic self-assembly in water. Upon consideration of electrostatic interaction and repulsive effect, deprotonated tetrakis(4-carboxyphenyl)porphyrin (TCPP) or Fe(III) tetra(4-carboxyphenyl)porphine chloride (TCPP(Fe)) as connection vertex and protonated bis(2-dimethylaminoethyl) ether (BDMAEE) unit as bridging edge connect with each other to form few-layer 2D nanosheet with a thickness of ~ 1.8–1.9 nm, while the lateral size can close to one hundred micrometers. Moreover, the well-dispersed 2D TCPP(Fe)-BDMAEE with heme-like active center displays intrinsic peroxidase-like catalytic activity, which can be used to detect hydrogen peroxide. The present facile strategy highlights new opportunities in constructing large-area ultrathin 2D supramolecular nanomaterials and paves the avenue to expand their potential applications.

Hemin-Bridged MOF Interface with Double Amplification of G-Quadruplex Payload and DNAzyme Catalysis: Ultrasensitive Lasting Chemiluminescence MicroRNA Imaging.

Here, we report a double-amplified sensing platform for ultrasensitive chemiluminescence (CL) miRNA detection in real patients' blood in which a hemin-bridged metal-organic framework (MOF) is employed as a functional interface to boost the payload and catalysis of G-quadruplex (G4) DNAzymes. Hemin is here used as the organic ligand for the MOF synthesis, which endows the MOF with an intrinsic peroxidase-like catalytic activity. Most importantly, the MOF surface provides a large amount of binding sites for polymeric G4 DNAzymes that are produced by miRNA-triggered rolling circle amplification reactions, and meanwhile, the interfaced G4 DNAzymes on MOFs (G4/MOFzymes) display an about 100-fold higher catalytic activity than those in solution. By using the G4/MOFzyme catalysts in the luminol/H2O2 CL system, the amplification detection of two acute myocardial infarction (AMI)-related miRNAs (low to 1 fM seen with naked eyes) is achieved in human serum with a smartphone as a portable imaging detector, which provides a facile methodology for point-of-care (POC) diagnosis of AMI. Compared with previous smartphone-based counterparts not requiring sophisticated equipment, this new facile methodology shows both 6 orders of magnitude higher sensitivity and an ∼50-fold longer duration for CL miRNA imaging. These unique features allow our developed G4/MOFzymes to be further employed as a novel luminescent ink for printing commonly used patterns.

Hydrogel-based artificial enzyme for combating bacteria and accelerating wound healing

Artificial enzymes have provided great antimicrobial activity to combat wound infection. However, the lack of tissue repair capability compromised their treatment effect. Therefore, development of novel artificial enzyme concurrently with the excellent antibacterial activity and the property of promoting wound healing are required. Here, we demonstrated the hydrogel-based artificial enzyme composed of copper and amino acids possessed intrinsic peroxidase-like catalytic activity, which could combat wound pathogen effectively and accelerate wound healing by stimulating angiogenesis and collagen deposition. Furthermore, the system possesses good biocompatibility for practical application. The synergic effect of the hydrogel-based artificial enzyme promises the system as a new paradigm in bacteria-infected wound healing therapy.

High peroxidase-like activity realized by facile synthesis of FeS2 nanoparticles for sensitive colorimetric detection of H2O2 and glutathione

In the last decades, enzyme mimics have been regarded as strong substitutes to natural enzymes. The construction of biosensors based on these enzyme mimics with competitive catalytic activity and substrate specificity has attracted a lot of research interest. Herein, for the first time, we investigated the capability of nanoscale FeS2 to serve as enzyme mimics. Then, a facile and effective biosensor is fabricated based on its intrinsic peroxidase-like catalytic activity. In the presence of H2O2, FeS2 nanoparticles (NPs) possess high peroxidase-like activity to 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, which can be ascribed to the generation of hydroxyl radicals (·OH) from the H2O2 decomposition catalyzed by FeS2 NPs. As for TMB, the resulting Michaelis−Menten constant (Km) value of FeS2 NPs is found to be about 12 times lower than that of natural horseradish peroxidase (HRP), highlighting the superiority of FeS2 NPs. Based on these intriguing observations, a reliable colorimetric method is then developed for detection of H2O2 and glutathione (GSH) by a simple mix-and-detect strategy. The detection limits of H2O2 and GSH are as low as 0.91 μM and 0.15 μM (3σ/slope), respectively. Moreover, FeS2 NPs can also catalyse the photoluminescence (PL) substrate terephthalic acid (TA) under the assistance of H2O2. This work remarkably extends the utilization of FeS2 NPs in the construction of colorimetric and PL biosensors in the fields of biosensing, environmental monitoring, and medical diagnosis.

Bifunctionalized novel Co-V MMO nanowires: Intrinsic oxidase and peroxidase like catalytic activities for antibacterial application

The development of effective and low-cost enzyme-like nanomaterials for killing bacteria is essential for human health and environmental protection. We report the synthesis of novel Co-V mixed metal oxide (MMO) nanowires composited of Co3V2O8 uniform dispersing among Co3O4 by calcining Co6(CO3)2(OH)8·H2O@Co3V2O8 nanowires in air. Co-V MMO nanowires can possess intrinsic oxidase-like and peroxidase-like catalytic activity. When the Co/V molar ratio is 3 and the calcination temperature is 400 °C, Co-V MMOs have superior activity. Utilizing this unique bifunctional activity, an antibacterial system combining Co-V MMOs with a low level of H2O2 has been put forward. The activity originates from their ability to catalyze the generation of O2―, which hydrolyze to HO2. Thus, the intracellular reactive oxygen species level can be enhanced and toxicity of high level H2O2 can be avoided. This work would be indicative to construct Co-V MMOs in the application of new energy and environmental catalysis.

Graphene-supported biomimetic catalysts with synergistic effect of adsorption and degradation for efficient dye capture and removal

Design and development of iron porphyrin-based artificial enzymes system have been attracting a lot of attention. Herein, without any toxic reductant and harsh processing, we present a facile one-pot method to fabricate bifunctional catalytic nanocomposites consisting of graphene and hemin by using vitamin C as a mild reduction reagent. The presence of graphene helps the formation of a high degree of highly active and stable hemin on the graphene surface in a monomeric form through their π−π stacking interaction. As a result, such nanocomposites possess a superior adsorption capacity and intrinsic peroxidase-like catalytic activity. Moreover, by the combination of their dye adsorption ability, RGO-hemin nanocomposites can serve as a suitable candidate for efficient capture and removal of dyes via a synergistic effect. Our findings may pave the way to apply graphene-supported artificial enzymes in a variety of fields, such as environmental chemistry, bionics, medicine, and biotechnology

Nitrogen-doped graphene quantum dots (N-GQDs) perturb redox-sensitive system via the selective inhibition of antioxidant enzyme activities in zebrafish

Graphene quantum dots (GQDs) are well-known for its potential applications for bioimaging, biosensor, and drug carrier in biomedicine. GQDs are well characteristic of intrinsic peroxidase-like catalytic activity, which is proven effective in scavenging the free radicals, such assuperoxide anion, hydrogen peroxide, and hydroxyl radical. GQDs are also well praised for its low in vivo and in vitro toxicity. Here, we found that nitrogen-doped GQDs (N-GQDs) can strongly disturb redox-sensitive system via the selective inhibition of endogenous antioxidant enzyme activities in zebrafish. The enzyme activities or transcription levels of a battery of hemoproteins including catalase (CAT), superoxide dismutase (SOD), respiratory chain complex I, complex Ⅲ, hemoglobin (Hb), and myeloperoxidase (MPO), were significantly suppressed by N-GQDs. We also found that N-GQDs activated the cytochrome P450 monooxygenase (e.g. cyp1a) and the associated aryl-hydrocarbon receptor repressors (ahrr1 and ahrr2) in zebrafish embryos. Compared to the ultrasmall graphene oxide (USGO), N-GQDs exhibited stronger fluorescent permeability and tissue-specific bio-accumulative effects. Taken together, our findings highlighted that exposure to N-GQDs can disrupt endogenous antioxidant enzyme activities, possibly via the competitive inhibition of electron transfer process. Our results in this study provided solid data for biosafety evaluations of various types of GQDs, and created an alert for the future biomedical applications of N-GQDs.

Germanium nanoparticles: Intrinsic peroxidase-like catalytic activity and its biosensing application

In recent years, germanium nanoparticles (Ge NPs) have attracted considerable research attention because of its excellent electrical and optical properties. However, it is mainly applied in the field of solar cells, photodetectors and photothermal therapy. Actually, Ge NPs have the advantages of low toxicity and excellent biocompatibility, which means that they have great potential in biosensing applications. However, there are few related reports. In this paper, we discovered that Ge NPs have the intrinsic peroxidase-like catalytic activity and can significantly accelerate the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by H2O2 for the first time. Compared with natural enzyme (horseradish peroxidase, HRP), Ge NPs maintain higher catalytic stability after treatment at different pH, temperature and ionic strength. Furthermore, a Ge NPs-based colorimetric platform was established for the first time to detect biomolecules with favourable sensitivity and selectivity, such as uric acid, glucose and choline. This work finds the new property of Ge NPs and extends its application in biosensing.

MOF-808: A Metal-Organic Framework with Intrinsic Peroxidase-Like Catalytic Activity at Neutral pH for Colorimetric Biosensing.

Natural enzyme mimetics with high catalytic activity at nearly neutral pH values are highly desired for their applications in biological systems. Herein for the first time a stable MOF, namely MOF-808, has been shown to possess high intrinsic peroxidase-like catalytic activity under acidic, neutral, and alkaline conditions. As a novel peroxidase mimetic, MOF-808 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine when H2O2 serves as oxidant, accompanied by a significant color variation in the solution. The catalytic activity and the color variation were greatly dependent on H2O2 concentration, and thus MOF-808 can be applied to the colorimetric sensing of H2O2. The H2O2 detection limit is 4.5 μM, and the linear range is 10 μM to 15 mM. In view of the significant inhibition effect produced by ascorbic acid, a facile and sensitive approach for colorimetric sensing of ascorbic acid was successfully established. The AA detection limit is 15 μM, and the linear range is 30-1030 μM. Further investigation found that the catalytic activity of MOF-808 could be mainly ascribed to the Zr-OH(OH2) groups. Such active Zr-OH(OH2) groups can be effectively shielded by gluconic acid, and subsequently the catalytic activity of MOF-808 was significantly suppressed. With these findings, a facile and selective colorimetric assay for glucose sensing has been successfully explored via combination of the glucose oxidation with the TMB oxidation. The glucose detection limit is 5.7 μM, and the linear range is 5.7-1700 μM. MOF-808 is one of the best colorimetric biosensors among the peroxidase mimics reported for H2O2, AA, and glucose detection.

Facile visual colorimetric sensor based on iron carbide nanoparticles encapsulated in porous nitrogen-rich graphene

Herein, via one-step pyrolysis of glucose, dicyandiamide (DCDA) and Fe containing metal–organic framework (Fe-MOF), small Fe3C nanoparticles were in-situ decorated in 3D porous network of N-rich graphene (NGr). The Fe-MOF served as size regulating precursor, layered g-C3N4 (derived from pyrolysis of DCDA) acted as not only a template to guide the growth of small Fe3C nanoparticles, but also the carbon source for 3D porous NGr network. The intrinsic peroxidase-like catalytic activity of Fe3C/NGr was unpredictably discovered, by taking the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) with H2O2 as a protocol. Fast and distinguished color change, improved stability in exposure to extreme H2O2 concentration and high temperature were obtained. The Michaelis–Menten kinetics was investigated. The detection of glucose was accomplished over a wide concentration range of 2.0~500.0μM with a detection limit lower than most of other similar systems. The reliability of the present sensor was further evaluated by practical monitoring glucose in diluted serum samples. Low cost and simple preparation, fast and distinguished color change, high tolerance to extreme H2O2 concentration and high temperature, endow Fe3C/NGr as one of the promising materials for fast visual colorimetry.

Sandwich-like electrochemiluminescence aptasensor based on dual quenching effect from hemin-graphene nanosheet and enzymatic biocatalytic precipitation for sensitive detection of carcinoembryonic antigen

A new and simple sandwich-like electrochemiluminescence (ECL) aptasensor for carcinoembryonic antigen (CEA) assay was fabricated based on the dual quenching effect from hemin-graphene (H-rGO) nanosheet and enzymatic biocatalytic precipitation (BCP) on the Au-CdS nanocomposites-based ECL system. In this aptasensor platform, flower-like spherical Au-CdS nanocomposites were used as ECL luminophores and exhibit a strong ECL signal. The rGO nanosheet was used as a supporter to immobilize hemin molecules via π-π stacking interactions. Due to the steric hindrance and quenching effect of rGO, the ECL intensity decreased by the construction of the sandwich “CEA aptamer I (NH2-DNA)-CEA-aptamer II” (H-rGO-aptamer II) mode. In the process of BCP, the ECL intensity further decreased because the hemin with intrinsic peroxidase-like catalytic activity could oxidize the 4-chloro-1-naphthol (4-CN) to produce an insoluble precipitation on the sensor. Using this dual quenching strategy, the prepared aptasensor exhibits a linear range from 0.8pg/mL to 4ng/mL and a detection limit of 0.28pg/mL. This ECL aptasensor has simple design and undemanding in operation and was utilized to determine the content of CEA in complex samples with recoveries of 95.0% to 115.8%. Moreover, no any chemical modification of aptamer was required, suggesting that the proposed ECL aptasensor could be applied for the detection of diverse proteins just by altering the aptamer sequence.

5-Carboxyfluorescein: intrinsic peroxidase-like catalytic activity and its application in the biomimetic synthesis of polyaniline nanoplatelets.

5-Carboxyfluorescein is verified to possess intrinsic peroxidase-like catalytic activity and can serve as a robust artificial peroxidase for the biomimetic synthesis of polyaniline nanoplatelets under harsh conditions. Our work discloses the potential of using this small molecule as a peroxidase surrogate for the biomimetic synthesis of nanostructured polymers.

Protein-Directed Synthesis of Bifunctional Adsorbent-Catalytic Hemin-Graphene Nanosheets for Highly Efficient Removal of Dye Pollutants via Synergistic Adsorption and Degradation.

Herein, for the first time, we report a "green", one-pot reduction/decoration method for the synthesis of bifunctional adsorbent-catalytic hemin-graphene nanosheets by using a common available protein (bovine serum albumin, BSA) as both a reductant and a stabilizer. Our prepared nanosheets are highly stable and possess intrinsic peroxidase-like catalytic activity due to the decoration of BSA and hemin. Furthermore, benefiting from the combined advantages of graphene and BSA, these nanosheets are able to efficiently adsorb dye pollutants from aqueous solution. More importantly, due to their adsorption and catalytic ability, these adsorbent-catalytic nanosheets can be applied to highly efficient dye removal via synergistic adsorption and degradation. Specifically, our catalysts can easily bring organic dyes to their surface by adsorption, and then activate H2O2 to generate hydroxyl radicals, leading to the degradation of the dyes. Such catalytic mechanism of our as-prepared nanosheets was analogous to that of natural enzymes, in which the extremely high catalytic efficiency is largely dependent upon their ability to bring substrates in close proximity to the active sites of enzymes. Our finding may open new potential applications of hemin-graphene hybrid nanosheets in environmental chemistry, biotechnology, and medicine.

Colorimetric visualization of Cu2+ based on Cu2+-catalyzed reaction and the signal amplification induced by K+-aptamer-Cu2+ complex

In this work, we report an ultrasensitive colorimetric sensing strategy for Cu2+ based on the Cu2+ catalyzed TMB-H2O2 reaction, and the signal amplification induced by aptamer-K+-Cu2+ complex. It is demonstrated that Cu2+ exhibits an intrinsic peroxidase-like catalytic activity. Thus, we utilize the catalytic activity of Cu2+ to TMB-H2O2 reaction for direct colorimetric visualization of Cu2+ for the first time. The limit of detection (LOD) is 2.6μM. To further improve the sensitivity of Cu2+ detection, we utilized G-quadruplex-Cu2+ metalloenzyme complex formed by K+, G-rich DNA, and Cu2+ to amplify colorimetric signal of TMB-H2O2 reaction. The LOD is as low as 0.076μM, which is 34-fold lower than that of only Cu2+-catalyzed TMB-H2O2 system (2.6μM). The LOD shows excellent potential for monitoring ultralow levels of Cu2+ in water samples.