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The sensitive and rapid detection of dopamine (DA) is of great significance for early diagnosis of related diseases. Current detection strategies of DA are time-consuming, expensive and inaccurate, while biosynthetic nanomaterials were considered highly stable and environment friendly, which were promising on colorimetric sensing. Thus, in this study, novel zinc phosphate hydrate nanosheets (SA@ZnPNS) biosynthesized by Shewanella algae were designed for the detection of DA. SA@ZnPNS showed high peroxidase-like activity which catalyzed the oxidation reaction of 3,3',5,5'-tetramethylbenzidine in the presence of H 2 O 2 . Results showed that the catalytic reaction of SA@ZnPNS followed Michaelis-Menton kinetics, and catalytic process conformed to ping-pong mechanism with chief active species of hydroxyl radicals. The colorimetric detection of DA in human serum samples was performed based on SA@ZnPNS peroxidase-like activity. The linear range of DA detection was 0.1-40 μM, and the detection limit was 0.083 μM. This study provided a simple and practical method for the detection of DA and expanded the application of biosynthesized nanoparticles to biosensing fields., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The peroxidase-like activity of MXene@Fe 3 O 4 nanocomposites and the relevant colorimetric application have been investigated for the first time. According to a kinetic study, MXene@Fe 3 O 4 nanocomposites displayed higher peroxidase activity than their individual components, and the catalytic process followed a ping-pong mechanism. The improved peroxidase-like activity of the MXene@Fe 3 O 4 nanocomposites was obtained due to the synergetic impact of the Fe 3 O 4 and MXene phases, the huge ion-accessible interface, and quick electron transfer channels in the nanocomposites. In the presence of hydrogen peroxide (H 2 O 2 ), the MXene@Fe 3 O 4 nanocomposites can catalyze the reaction of the colorless substrate 3, 3, 5, 5-tetramethylbenzidine (TMB) into oxidized TMB which revealed a blue color at 652 nm. After the introduction of glutathione (GSH), the blue color was gradually fading owing to the hydroxyl radical scavenging effect of glutathione. A colorimetric detection platform based on the peroxidase-like activity of the MXene@Fe 3 O 4 nanocomposites was developed for H 2 O 2 and GSH with a detection limit of 0.4 μM and 0.5 μM, respectively. The calibration plot for glutathione detection is calculated by absorbance difference at 652 nm, which ranged from 0.5 to 10 μM with a detection limit of 0.2 μM. The recoveries of GSH with different concentrations ranged from 93.76 to 108.50% and the relative standard deviation from 0.30 to 5.96%. This work significantly extends the application of MXene@Fe 3 O 4 nanocomposites in the construction of colorimetric sensors and reveals a satisfactory result in real sample analysis., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Iron-cobalt oxide nanosheets (FeCo-ONSs) were proved to have intrinsic peroxidase-like activity. Additionally, the peroxidase-like activity of FeCo-ONSs toward the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) was dramatically enhanced after heparin addition due to the stronger affinity toward TMB. Protamine combines with heparin, so the promotion of peroxidase-like activity of FeCo-ONSs with heparin was suppressed. With the addition of trypsin, protamine was hydrolyzed and the enhancement effect of catalytic activity of FeCo-ONSs was recovered. Based on above process, a sensitive colorimetric platform for trypsin activity determination was constructed through measuring the absorbance of produced oxTMB at 652 nm, providing a linear detection range of 5 to 500 ng/mL and a low detection limit of 2.8 ng/mL. The method was applied to trypsin determination in real samples (human urine sample and multienzyme tablet sample) with satisfactory results, illustrating the potential application of this biosensor., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The construction of enzyme mimics using protein protection layers possesses advantages of high biocompatibility and superior catalytic activity, which is desirable for biomedical applications including diseases diagnosis. Here, from E. coli expression system, recombinant protein of camel serum albumin (rCSA) from Camelus bactrianus was successfully obtained to encapsulate hemin via the self-assemble method without additional toxic organic reagents. As compared with that of horseradish peroxidase, the produced rCSA-hemin nanoparticles exhibited enhanced enzyme-mimicking activity and stability under harsh experimental conditions. Additionally, the steady-state kinetic analysis of rCSA-hemin in the solution revealed its higher affinity to the substrates. Therefore, a colorimetric detection method of H 2 O 2 and glucose was constructed with a linear range of 2.5-500 μM with an LOD of 2.39 and 2.42 μM, respectively, which was also applied for the determination of glucose in the serum samples with satisfying recovery ratio ranging from 101.1% to 112.1%. The constructed camel protein-derived nanozyme system of remarkable stability holds promising potentials for the versatile biomedical uses., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Hybrid nanoflowers consisting of graphitic carbon nitride (GCN) and copper were successfully constructed without the involvement of any biomolecule, by simply mixing them at room temperature to induce proper self-assembly to achieve a flower-like morphology. The resulting biomolecule-free GCN-copper hybrid nanoflowers (GCN-Cu NFs) exhibited an apparent peroxidase-mimicking activity, possibly owing to the synergistic effect from the coordination of GCN and copper, as well as their large surface area, which increased the number of catalytic reaction sites. The peroxidase-mimicking GCN-Cu NFs were then employed in the colorimetric determination of selected phenolic compounds hydroquinone (HQ), methylhydroquinone (MHQ), and catechol (CC). For samples without phenolic compounds, GCN-Cu NFs catalyzed the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H 2 O 2 , producing an intense blue color signal. Conversely, in the presence of phenolic compounds, the oxidation of TMB was inhibited, resulting in a significant reduction of the color signal. Using this strategy, HQ, MHQ, and CC were selectively and sensitively determined in a linear range up to 100 μM with detection limits down to 0.82, 0.27, and 0.36 μM, respectively. The practical utility of this assay system was also validated by using it to detect phenolic compounds spiked in tap water, yielding a good recovery of 97.1-108.9% and coefficient of variation below 3.0%, demonstrating the excellent reliability and reproducibility of this strategy. Colorimetric determination of phenolic compounds using peroxidase mimics based on biomolecule-free hybrid nanoflowers consisting of graphitic carbon nitride and copper., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The rapid and onsite detection of glyphosate herbicides in agricultural products is still a challenge. Herein, a novel colorimetric nanozyme sheet for the rapid detection of glyphosate has been successfully prepared through the physical adsorption of porous Co 3 O 4 nanoplates on a polyester fiber membrane. Glyphosate can specifically inhibit the peroxidase-mimicking catalytic activity of porous Co 3 O 4 nanoplates, thereby the visual detection of glyphosate can be realized by distinguishing the change in the color intensity of the established nanozyme sheet. The prepared nanozyme sheet has good sensitivity and selectivity, with a detection limit of 0.175 mg·kg -1 for glyphosate detection just by the naked eyes. It can effectively detect glyphosate within 10 min, and the color spots can maintain more than 20 min. The nanozyme sheet is not easily affected by the external environment in detection and storage. The merits of the nanozyme sheet facilitate its practical application in the large-scale preliminary screening of glyphosate residues in agricultural products.

In this work, we report the synthesis of Cu-Ag bimetallic nanopartiles and g-C 3 N 4 nanosheets decorated on zeolitic imidazolate framework-8 (ZIF-8) to form a Cu-Ag/g-C 3 N 4 /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-C 3 N 4 /ZIF hybrid has intrinsic peroxidaselike catalytic activity towards the oxidation of TMB in the presence of H 2 O 2 . The situ synthesis of Cu-Ag bimetallic nanopartiles on 2D support such as g-C 3 N 4 nanosheets would significantly enhance the peroxidaselike catalytic properties of individual Cu-Ag bimetallic nanopartiles and the g-C 3 N 4 nanosheets. After loading of Cu-Ag bimetallic nanopartiles and g-C 3 N 4 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 H 2 O 2 -generation reactions.

Novel and uniform Co 4 S 3 nanoparticles were synthesized through a two-step hydrothermal process and testified to possess intrinsic peroxidase (POx)-like activity for the first time. As a fresh POx mimic, we studied its catalytic properties, kinetic, and mechanism to catalyze the oxidation of 3, 3', 5, 5'-tetramethylbenzidine in the presence of H 2 O 2 . According to the experiments, the bactericidal mechanism is the same as that of simulated enzyme. Based on the ability of Co 4 S 3 inducing H 2 O 2 to express O 2 - , the bactericidal rate can be as high as 100%. Besides, using the POx-like activity of Co 4 S 3 , a new off-on sensor for H 2 O 2 and l-cysteine (l-Cys) detection is constructed. The sensor reveals a good wide linear response to H 2 O 2 in the 40-2000 µM with a detection limit of 18 µM, while l-Cys in the 20-100 mM with a detection limit of 10 mM. The proposed method also shows great stability, high selectivity, and excellent practicability., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Nanomaterials that exhibit enzyme-like activity (nanozymes) have attracted significant attention due to their potential for applications in analytical tests and in the biological field. In this study, an enzyme-like nanomaterial is developed by coupling Pt nanoparticles with WO 2.72 (Pt/WO 2.72 ). The resultant nanocomposite nanomaterial exhibits peroxidase activity and catalase activity. Moreover, owing to the presence of W 6+ and W 5+ in WO 2.72 , Pt/WO 2.72 nanoplates demonstrate promise as scavengers of hydroxyl radicals. The Pt/WO 2.72 composite nanoplates exhibit excellent peroxidase-like activity for the sensitive colorimetric detection of H 2 O 2 and blood glucose. These Pt/WO 2.72 nanoplates are thought to be a promising tool for broad potential applications in biomedicine, biotechnology, and environmental chemistry. Pt nanoparticles anchored WO 2.72 nanoplates (Pt/WO 2.72 ) as a multienzyme-like mimetics exhibits peroxidase activity and catalase activity. Furthermore, this composite can be acted scavengers of hydroxyl radicals.

Nanomaterials with enzyme-like activity have attracted much attention recently. Herein, we report the synthesis of a new type of 2D MXene-Ti 3 C 2 /CuS nanocomposites with peroxidase-like activity using a simple hydrothermal approach. Significantly, compared with the individual MXene-Ti 3 C 2 nanosheets or CuS nanoparticles, the MXene-Ti 3 C 2 /CuS nanocomposites show a synergistically enhanced peroxidase-like activity and can be used as an efficient mimetic peroxidase to catalyze the reaction of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2 ), causing a blue color change. Kinetic studies reveal that the MXene-Ti 3 C 2 /CuS nanocomposites have a higher catalytic activity to TMB than their single components, and the catalytic reaction follows the ping-pong mechanism. The MXene-Ti 3 C 2 /CuS nanocomposites are used for the colorimetric determination of cholesterol with a linear range of 10-100 μM and a limit of detection (LOD) of 1.9 μM. Our results show that the MXene-Ti 3 C 2 /CuS nanocomposites based colorimetric cholesterol biosensor is cost-effective, sensitive, and selective, which has potential application in H 2 O 2 and cholesterol detection and clinic medicine diagnostics., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Fluorescent eggshell membrane-templated gold nanoclusters (Au-ESM) can be obtained in a facile and low-cost manner in this study. The fluorescence of the Au-ESM may be significantly quenched by mercapto-compounds and peroxidase-like activity of Au-ESM could be regulated by the reaction process with glutathione. Moreover, the catalytic activity of the mimetic enzyme membrane could be modulated by immunoreactions. An immunoassay for colorimetric determination of staphylococcal enterotoxins B (SE-B) using colored gold nanoparticles was established based on the catalytic activity adjusted by the target molecules. This colorimetric assay can detect SE-B at the concentration range of 0.4-20 ng/mL and the limit of detection (LOD) is 0.12 ng/mL. As a practical application, the proposed colorimetric assay was further utilized to detect SE-B in food samples such as flour, corn and rice, requiring very low volume of sample and exhibiting great sensitivity and high accuracy, which provides promising platform for development of point-of-care diagnostic devices with biomedical and food safety applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In clinical diagnosis, monitoring of uric acid (UA) is generally realized by combining uricase with natural peroxidase. The use of bio-enzymes, however, shadows some highlights of these methods due to their vulnerable activities against environments. Herein, we report a novel biosensor for the natural enzyme-free colorimetric detection of UA by using CoP nanosheet arrays grown on Ni foam (NF) as a monolithic peroxidase mimic. The integrated nanozyme can be put into and taken out from reaction systems conveniently with only tweezers, making it possible for on-demand analysis. As demonstrated, the obtained CoP/NF exhibits outstanding peroxidase-like activity to trigger the oxidation reaction of colorless 3,3'5,5'-tetramethylbenzidine (TMB) to a blue product (TMBox) mediated by H 2 O 2 . It is found that the blue TMBox can be reduced to colorless TMB again by UA selectively, thus the presence of UA in solutions will suppress the color reaction of TMB. Based on this principle, an uricase-free biosensor is developed for the photometric determination of UA, providing a wide detection range of 1-200 μM and a limit of detection down to 1.0 μM. In addition, the fabricated biosensor can be applied for measuring UA in clinical samples with merits of simple operation and good reliability, exhibiting its great promise in clinical diagnosis., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this study, a novel colorimetric aptasensor was prepared by coupling trivalent peroxidase-mimic DNAzyme and magnetic nanoparticles for highly sensitive and selective detection of target proteins. A three G-quadruplex (G4) DNA-hemin complex was employed as the trivalent peroxidase-mimic DNAzyme, in which hemin assisted the G4-DNA to fold into a catalytic conformation and act as an enzyme. The design of the aptasensor includes magnetic nanoparticles (MNPs), complementary DNA (cDNA) modified with biotin, and a label-free single strand DNA (ssDNA) including the aptamer and trivalent peroxidase-mimic DNAzyme. The trivalent DNAzyme, which has the highest catalytic activity among multivalent DNAzymes, catalyzed the H 2 O 2 -mediated oxidation of ABTS. The colorless ABTS was oxidized to produce a blue-green product that can be clearly distinguished by the naked eye. The aptamer and trivalent peroxidase-mimic DNAzyme promote the specificity and sensitivity of this detection method, which can be generalized for other targets by simply replacing the corresponding aptamers. To demonstrate the feasible use of the aptasensor for target detection, a well-known tumor biomarker MUC1 was evaluated as the model target. The limits of detection were determined to be 5.08 and 5.60 nM in a linear range of 50-1000 nM in a buffer solution and 10% serum system, respectively. This colorimetric and label-free aptasensor with excellent sensitivity and strong anti-interference ability has potential application in disease diagnoses, prognosis tracking, and therapeutic evaluation., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Early diagnosis of diabetes yields significant clinical benefits. The serum level of 1,5‑anhydroglucitol (1,5‑AG) has been a new biochemical marker for postprandial hyperglycemia. In this study, a simple colorimetric method for 1,5‑AG detection has been designed based on highly efficient peroxidase mimetic activity of GQDs and enzyme-catalyzed reaction. By the catalytic action of pyranose oxidase (PROD), the 1,5‑AG was oxidized to 1,5‑anhydrofuctose and H 2 O 2 . The GQDs in the presence of H 2 O 2 exhibited highly efficient catalytic activity toward the oxidation of 3, 3', 5, 5'‑tetramethylbenzidine (TMB) to a blue colored product. The influence of relevant experimental variables was optimized. A linear relationship of optical signal with the concentration of 1,5‑AG in the range of 20.0-100.0μg/mL with the regression correlation coefficient of 0.9985 was obtained which could be monitored by colorimetry detection. The limit of detection (LOD) for 1,5‑AG detection was approximately 0.144μg/mL. All in all, the proposed 1,5‑AG detection system based on GQDs and PROD-catalyzed reaction showed better performances with simple operation, low-cost, higher selectivity., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Fabrication of core-shell nanostructured catalyst is a promising way for tuning its catalytic performance due to the highly active interface and rich redox properties. In this work, hierarchical Co 3 O 4 @NiO core-shell nanotubes are fabricated by the deposition of NiO shells via a chemical bath treatment using electrospun Co-C composite nanofibers as templates, followed by a calcination process in air. The as-prepared Co 3 O 4 @NiO core-shell nanotubes exhibit a uniform and novel hollow structure with Co 3 O 4 nanoparticles attached to the inner wall of NiO nanotubes and excellent catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H 2 O 2 . Due to the synergistic effect, the peroxidase-like activity of the Co 3 O 4 @NiO core-shell nanotubes is much higher than that of individual Co 3 O 4 and NiO components. Owing to the superior peroxidase-like activity, a simple and rapid colorimetric approach for the detection of dopamine with a detection limit of 1.21µM and excellent selectivity has been developed. It is anticipated that the prepared Co 3 O 4 @NiO core-shell nanotubes are promising materials applied for biomedical analysis and environmental monitoring., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A sensitive, rapid and label-free colorimetric aptasensor for sulfadimethoxine (SDM) detection was developed based on the tunable peroxidase-like activity of graphene/nickel@palladium nanoparticle (Gr/Ni@Pd) hybrids. The addition of the SDM aptamer could inhibit the peroxidase-like catalytic activity of the hybrids. However, the target SDM and aptamer could be triggered tightly and recover the catalytic activity of the Gr/Ni@Pd hybrids. Due to the peroxidase-like catalytic activity, Gr/Ni@Pd could catalyze the decomposition of H 2 O 2 with releasing hydroxyl radicals which further oxidized reagent 3, 3', 5, 5'-Tetramethylbenzidine (TMB) to oxTMB accompanied with a colorless-to-blue color change. The original color change could be applied to obtain quantitative detection of SDM, due to the relationship between the concentration of the target and the color difference. As a result, this approach performed a linear response for SDM from 1 to 500 ng/mL with a limit detection of 0.7 ng/mL (S/N = 3) under the optimized conditions and realized the detection of SDM in spiked lake water samples. Therefore, this colorimetric aptasensor was an alternative assay for SDM detection in real water. Moreover, with its design principle, this work might be applied to detecting other small molecule by employing appropriate aptamer., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Nanosized materials acting as substitutes of natural enzymes are currently attracting significant research due to their stable enzyme-like characteristics, but some flaws of these nanozymes, including their limited catalytic rate and efficiency, need to be remedied to enable their wider applications. In this work, we verify for the first time the catalytic behavior of uncapped nanobranch-based CuS clews as a peroxidase mimic. XRD, XPS, SEM, and TEM proofs demonstrate that high-purity CuS clews composed of intertwined wires with abundant nanodendrites outside are successfully produced via a facile one-pot hydrothermal synthesis approach, with thiourea as both the sulfion source and the structure-directing agent. The synthesized CuS can catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) by H 2 O 2 to trigger a visible color reaction with rapid response (reaching a maximum change within 5 min). The proposed CuS nanozyme exhibits preferable catalytic kinetics over natural horseradish peroxidase (HRP). This outstanding activity primarily results from the large surface area and rich sites exposed by the uncapped unique structure. Under optimized conditions, the fabricated sensing system provides linear absorbance (652 nm) changes in the H 2 O 2 concentration range of 0.2˜130 μM, with a detection limit of as low as 63 nM. When coupled with glucose oxidase (GOD), the system is demonstrated to be capable of monitoring glucose in blood samples with excellent performance., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this work, we find that the peroxidase-like activity of MoS2 nanoparticles (NPs) is dependent on the surface charge. Negatively charged sodium dodecyl sulfate modified MoS2 nanoparticles (SDS-MoS2 NPs) possess highly-efficient peroxidase-like activity. MoS2 NPs with intrinsic peroxidase-like activity were synthesized through a simple one-pot hydrothermal route. The peroxidase-like activities of different surfactants modified MoS2 NPs were discussed. Compared with bare MoS2 NPs and positively charged cetyltrimethyl ammonium bromide modified MoS2 NPs, SDS-MoS2 NPs have the best peroxidase-like activity. SDS-MoS2 NPs can efficiently catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue product. On basis of this, we have successfully established a novel platform for colorimetric detection of H2O2, and the detection limit is 0.32μM. Furthermore, the SDS-MoS2 NPs based platform can also be used for high sensitivity and selectivity detection of glucose with a wide linear range of 5.0-500μM by controlling the generation of H2O2 in the presence of glucose oxidase., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this paper, the highly intrinsic peroxidase-like catalytic activity of nitrogen-doped graphene quantum dots (N-GQDs) is revealed. This activity was greatly dependent on pH, temperature and H2O2 concentration. The experimental results showed that the stable N-GQDs could be used for the detection of H2O2 and glucose over a wide range of pH and temperature, offering a simple, highly selective and sensitive approach for their colorimetric sensing. The linearity between the analyte concentration and absorption ranged from 20 to 1170 μM for H2O2 and 25 to 375 μM for glucose with a detection limit of 5.3 μM for H2O2 and 16 μM for glucose. This assay was also successfully applied to the detection of glucose concentrations in diluted serum and fruit juice samples., (Copyright © 2015 Elsevier B.V. All rights reserved.)

As promising alternatives for natural enzymes, much attention has been paid to nanozymes. And our recent study showed that the medium acid sites on the support are the active sites for the adsorption and oxidation of the substrate. Thus, in this work, due to the abundance of medium acid sites, Al2O3 was chosen as the support to prepare Pt/Al2O3 nanozymes. Through the Pt/Al2O3 samples, we further proved that the distribution of the Pt clusters and the amount of the medium acid sites can significantly influence the peroxidase‐like activity. Then the Pt/Al2O3 sample was used for the detection of glucose. And as low as 0.96 μM glucose could be detected with a linear range from 5–60 μM via our method. This work showed the great potential applications of the easily prepared Pt/Al2O3 samples in varieties of simple, robust, and easy‐to‐make analytical approaches in the future. [ABSTRACT FROM AUTHOR]

Multifunctional N, Fe-doped carbon dots (N, Fe-CDs) were synthesized by the one-step hydrothermal method using ferric ammonium citrate and dicyandiamide as raw materials. The N, Fe-CDs exhibited peroxidase-like (POD) activity by catalyzing the oxidization of 3,3′,5,5′-tetramethylbenzidine (TMB) to the green oxidation state ox-TMB in the presence of hydrogen peroxide (H2O2). Subsequently, based on the POD activity of N, Fe-CDs, an efficient and sensitive colorimetric method for the detection of H2O2 and ascorbic acid (AA) was established with a limit of detection of 0.40 µM and 2.05 µM. The proposed detection method has been successfully applied to detect AA in fruit juice, vitamin C tablets, and human serum samples and has exhibited excellent application prospects in biotechnology and food fields. Furthermore, N, Fe-CDs also showed a protective effect on the cell damage caused by H2O2 and could be used as an antioxidant agent. [ABSTRACT FROM AUTHOR]

In this paper, Cu-BTC derived mesoporous CuS nanomaterial (m-CuS) was synthesized via a two-step process involving carbonization and sulfidation of Cu-BTC for colorimetric glutathione detection. The Cu-BTC was constructed by 1,3,5-benzenetri-carboxylic acid (H3BTC) and Cu2+ ions. The obtained m-CuS showed a large specific surface area (55.751 m2/g), pore volume (0.153 cm3/g), and pore diameter (15.380 nm). In addition, the synthesized m-CuS exhibited high peroxidase-like activity and could catalyze oxidation of the colorless substrate 3,3′,5,5′-tetramethylbenzidine to a blue product. Peroxidase-like activity mechanism studies using terephthalic acid as a fluorescent probe proved that m-CuS assists H2O2 decomposition to reactive oxygen species, which are responsible for TMB oxidation. However, the catalytic activity of m-CuS for the oxidation of TMB by H2O2 could be potently inhibited in the presence of glutathione. Based on this phenomenon, the colorimetric detection of glutathione was demonstrated with good selectivity and high sensitivity. The linear range was 1–20 μM and 20–300 μM with a detection limit of 0.1 μM. The m-CuS showing good stability and robust peroxidase catalytic activity was applied for the detection of glutathione in human urine samples. [ABSTRACT FROM AUTHOR]

[Display omitted] Herein, we present a novel microwave-assisted method for the synthesis of palladium nanoparticles (PdNPs) supported by Limonia acidissima Groff tree extract gum. The synthesized PdNPs were characterized using various analytical techniques, including FTIR, SEM, TEM, UV–visible, and powder XRD analyses. TEM and XRD analysis confirmed that the synthesized LAG-PdNPs are highly crystalline nature spherical shapes with an average size diameter of 7–9 nm. We employed these gum-capped PdNPs to investigate their peroxidase-like activity for colorimetric detection of hydrogen peroxide (H 2 O 2) and glucose. The oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 , catalyzed by PdNPs, produces oxidation products quantified at 652 nm using spectrophotometry. The catalytic activity of PdNPs was optimized with respect to temperature and pH. The developed method exhibited a linear range of detection from 1 to 50 µm, with detection limits of 0.35 µm for H 2 O 2 and 0.60 µm for glucose. [ABSTRACT FROM AUTHOR]

A novel and highly sensitive colorimetric DNA sensor for determination of miRNA-155 at attomolar levelsis presented that combines the peroxidase-like activity of copper nanoparticles (CuNPs) with the hybridization chain reaction (HCR). The utilization of CuNPs offers advantages such as strong interaction with double-stranded DNA, excellent molecular recognition, and mimic catalytic activity. Herein, a capture probe DNA (P1) was immobilized on carboxylated magnetic beads (MBs), allowing for amplified immobilization due to the 3D surface. Subsequently, the presence of the target microRNA-155 led to the formation of a sandwich structure (P2/microRNA-155/P1/MBs) when P2 was introduced to the modified P1/MBs. The HCR reaction was then triggered by adding H1 and H2 to create a super sandwich (H1/H2)n. Following this, Cu2+ ions were attracted to the negatively charged phosphate groups of the (H1/H2)n and reduced by ascorbic acid, resulting in the formation of CuNPs, which were embedded into the grooves of the (H1/H2)n. The peroxidase-like activity of CuNPs catalyzed the oxidation reaction of 3,3',5,5'-Tetramethylbenzidine (TMB), resulting in a distinct blue color measured at 630 nm. Under optimal conditions, the colorimetric biosensor exhibited a linear response to microRNA–155 concentrations ranging from 80 to 500 aM, with a detection limit of 22 aM, and discriminate against other microRNAs. It was also successfully applied to the determination of microRNA–155 levels in spiked human serum. [ABSTRACT FROM AUTHOR]

Designing unique nanomaterials for the selective sensing of biomolecules is of significant interest in the field of nanobiotechnology. In this work, we demonstrated the synthesis of ordered Cu nanoparticle‐functionalised mesoporous C3N5 that has unique peroxidase‐like nanozymatic activity for the ultrasensitive and selective detection of glucose and glutathione. A nano hard‐templating technique together with the in‐situ polymerisation and self‐assembly of Cu and high N‐containing CN precursor was adopted to introduce mesoporosity as well as high N and Cu content in mesoporous C3N5. Due to the ordered structure and highly dispersed Cu in the mesoporous C3N5, a large enhancement of the peroxidase mimetic activity in the oxidation of a redox dye in the presence of hydrogen peroxide could be obtained. Additionally, the optimised Cu‐functionalised mesoporous C3N5 exhibited excellent sensitivity to glutathione with a low detection limit of 2.0 ppm. The strong peroxidase activity of the Cu‐functionalised mesoporous C3N5 was also effectively used for the sensing of glucose with a detection limit of 0.4 mM through glucose oxidation with glucose oxidase. This unique Cu‐functionalised mesoporous C3N5 has the potential for detecting various molecules in the environment as well as for next‐generation glucose and glutathione diagnostic devices. [ABSTRACT FROM AUTHOR]

The proteolytic enzyme ficin exhibits peroxidase-like activity but it is low and insufficient for real applications. Herein, we developed ficin-copper hybrid nanoflowers and demonstrated that they have significantly enhanced peroxidase-like activity of over 6-fold higher than that of free ficin, with one of the lowest Km and highest kcat values among all reported ficin-based peroxidase-like nanozymes. This was most likely caused by the synergistic catalysis of co-existing ficin and crystalline copper phosphate within nanoflower matrices having a large surface area. The nanoflowers were easily prepared by incubating ficin and copper sulfate at ambient temperature, causing coordination interactions between ficin's amine/amide moieties and copper ions, followed by concomitant anisotropic growth of petals composed of copper phosphate crystals with ficin. When compared to free ficin and natural horseradish peroxidase, the resulting nanoflowers' affinity toward H2O2 was greatly increased, yielding Km values of half and one-tenth, respectively, as well as noticeably improved stability. The nanoflowers were then applied to colorimetric determination of biological thiols (biothiols), such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), based on their inhibition of nanoflowers' peroxidase-like activity, producing reduced color intensities as the concentration of biothiols increased. This strategy achieved highly sensitive colorimetric determinations of Cys, GSH, and Hcy after only 25-min incubation. Additionally, using this technique, biothiols in human serum were successfully determined with excellent precision, suggesting the potential application of this technology in clinical settings, particularly in point-of-care testing environments. [ABSTRACT FROM AUTHOR]

A highly sensitive and facile colorimetric assay is introduced for detecting biogenic gaseous H2S using peroxidase (POD)-like catalytic activity of silver core/gold shell nanoplates (Ag@Au NPls). H2S can react with Ag@Au NPls to form Ag2S or Au2S on their surface, which can reduce POD-like activity of Ag@Au NPls and consequently decrease the absorbance at 650 nm due to oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). For in situ and multiple detection of H2S, we utilized a microplate cover with 24 polydimethylsiloxane inner wells where Ag@Au NPls reacted with H2S gas followed by treatment with TMB/H2O2. As a result, the change in absorbance at 650 nm showed a linear relationship with the H2S concentration in the range 0.33 to 2.96 μM (0.36 absorbance/μM H2S in PBS, R2 = 0.994) with a limit of detection of 263 nM and a relative standard deviation of 4.4%. Finally, this assay could detect H2S released from Eikenella corrodens, used as a model bacterium, in a short time (20 min) or at a low number of bacteria (1 × 104 colony forming units/mL). Therefore, this assay is expected to be applied for the study of H2S signaling in bacterial physiology, as well as measure H2S production released from other oral bacteria that cause halitosis and oral diseases, leading to the subsequent diagnosis. [ABSTRACT FROM AUTHOR]

The simple and accurate monitoring of blood glucose level is of great significance for the prevention and control of diabetes. In this work, a magnetic nanozyme was fabricated based on loading nitrogen-doped carbon dots (N-CDs) on mesoporous Fe3O4 nanoparticles for the colorimetric detection of glucose in human serum. Mesoporous Fe3O4 nanoparticles were easily synthesized using a solvothermal method, and N-CDs were then prepared in situ and loaded on the Fe3O4 nanoparticles, leading to a magnetic N-CDs/Fe3O4 nanocomposite. The N-CDs/Fe3O4 nanocomposite exhibited good peroxidase-like activity and could catalyze the oxidation of the colorless enzyme substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to blue TMB oxide (ox-TMB) in the presence of hydrogen peroxide (H2O2). When the N-CDs/Fe3O4 nanozyme was combined with glucose oxidase (Gox), Gox catalyzed the oxidization of glucose, producing H2O2 and leading to the oxidation of TMB under the catalysis of the N-CDs/Fe3O4 nanozyme. Based on this mechanism, a colorimetric sensor was constructed for the sensitive detection of glucose. The linear range for glucose detection was from 1 to 180 μM, and the limit of detection (LOD) was 0.56 μM. The recovered nanozyme through magnetic separation showed good reusability. The visual detection of glucose was also realized by preparing an integrated agarose hydrogel containing the N-CDs/Fe3O4 nanozyme, glucose oxidase, and TMB. The colorimetric detection platform has an enormous potential for the convenient detection of metabolites. [ABSTRACT FROM AUTHOR]

A solid‐state method was used to derive a sulfur rich CuO‐carbon nitride core‐shell nano‐composite from a Cu‐organic hybrid. The synthesized material was characterized by XRD, morphology by SEM and TEM. Elemental analysis was investigated using EDS. The novel sulfur rich CuO‐carbon nitride core‐shell composite demonstrated as peroxidase activity for the oxidation of aminophenol isomers in the presence of H2O2. The oxidized products of o‐aminophenol (o‐AP) and p‐aminophenol (p‐AP) in phosphate buffer (PB, pH 7) showed strong absorption peaks at 435 and 475 nm, respectively in the UV‐Visible spectra. Whereas no oxidation reaction was observed for m‐aminophenol. Kinetic analysis of sulfur rich CuO‐graphitic carbon nitride revealed that the catalyst functioned by a ping‐pong mechanism for the oxidation of both o‐AP & p‐AP by hydrogen peroxide (H2O2). Based on KM values, substrate affinities were in the order o‐AP>H2O2>p‐AP. We further used this material for selective colorimetric detection of o‐AP and p‐AP in PB pH 7. The linear ranges obtained for o‐AP and p‐AP were 1–200 μM (LOD=1.5 μM, r2=0.99) and 10–500 μM (LOD=2.27 μM, r2=0.99), respectively. The developed analytical platform was used to detect these isomers in river water and p‐AP in artificial urine. [ABSTRACT FROM AUTHOR]

[Display omitted] • Peroxidase-mimicking crystalline colorimetric sensors were synthesized. • Sensors integrated dual active sites of polyoxoanions and coordination unsaturated Cu centers. • Sensors allowed sensitive colorimetric detection for phenol with low detection limit. • Sensors show high anti-interference ability and good applicability in real water samples. • Common phenolic species were well discriminated by using principal component analysis. Phenol and its derivatives represent a kind of significant hazards to both human health and the integrity of ecological systems. Exploring an efficient detection and discrimination approach for them is urgent. Herein, a kind of polyoxometalate-based peroxidase-mimicking crystalline colorimetric sensors were developed by integrating dual active sites of Keggin-type polyoxoanions and coordination unsaturated copper centers, for which the formulas are [Cu(dppeo) 3 ] 2 [Cu(dppeo) 2 (H 2 O)](dppeo) 0.75 [PMo 12 O 40 ] 2 ·9H 2 O (1), [Cu(dppeo) 2 (H 2 O)] 2 [SiW 12 O 40 ]·6H 2 O (2), [Cu(dppeo) 2 ] 3 [PW 12 O 40 ] 2 ·12H 2 O (3), (dppeo = 1,2-bis(diphenylphosphino)ethane dioxide). Structural analysis revealed that these compounds exhibit 0-D supramolecular architecture formed through the interplay of electrostatic forces and hydrogen bonding interactions between Keggin-type polyoxoanions and dppeo-chelated copper-organic cationic fragments. Sensors 1 – 3 exhibit favorable peroxidase-mimicking catalytic activities, which expedite the reaction involving phenol, 4-aminoantipyrine and hydrogen peroxide (H 2 O 2), resulting in a pronounced color change for indicating the target concentration levels. These crystalline sensors responded linearly to phenol concentration within 0.01–1.0 mM, affording low detection limits of 1.19, 1.59 and 3.78 μM for 1 – 3. These sensors demonstrate exceptional anti-interference capabilities and exhibit excellent applicability in real water samples, ensuring high recovery rates. By incorporating a colorimetric array with principal component analysis, the sensors effectively discriminate between common phenolic compounds. This research presents an innovative methodology for the design of crystalline sensor materials, paving the way for the detection and differentiation of phenolic pollutants within environmental applications. [ABSTRACT FROM AUTHOR]

Double-decker phthalocyanine Eu[Pc(SC 6 H 13) 8 ] 2 modified Cu/CuFe 2 O 4 nanocomposites (Eu[Pc(SC 6 H 13) 8 ] 2 /Cu/CFO) were successfully prepared by two-step hydrothermal method and characterized by XRD, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). For the first time, Eu[Pc(SC 6 H 13) 8 ] 2 /Cu/CFO with enhanced peroxidase-like activity is designed as peroxide mimic enzymes for the detection of N-acetylcysteine. The colorimetric platform showed a sensitive response to H 2 O 2 and N-acetylcysteine in the range of 2–9 mM and 5–30 μM with a limit of detection of 0.19 mM and 0.835 μM under optimal conditions. Furthermore, due to excellent sensitivity and selectivity, a sensor based on Eu[Pc(SC 6 H 13) 8 ] 2 /Cu/CFO can be used to detect N-acetylcysteine in serum, confirming the great practicability in sensing fields. • Double decker phthalocyanine modified Cu/CuFe 2 O 4 was firstly used as nanozymes. • First colorimetric platform for N-acetylcysteine detection. • N-acetylcysteine determination with a limit of detection of 0.835 μM. [ABSTRACT FROM AUTHOR]

Regulating the catalytic activity of nanozymes is significant for their applications in various fields. Here, we demonstrate a new strategy to achieve reversible regulation of the nanozyme's activity for sensing purpose. This strategy involves the use of zero-dimensional MoS2 quantum dots (MQDs) as the building blocks of nanozymes which display very weak peroxidase (POD)-like activity. Interestingly, such POD-like activity of the MQDs largely enhances in the presence of Fe3+ while diminishes with the addition of captopril thereafter. Further investigations identify the mechanism of Fe3+-mediated aggregation-induced enhancement of the POD-like activity and the inhibitory effect of captopril on the enhancement, which is highly dependent on their concentrations. Based on this finding, a colorimetric method for the detection of captopril is developed. This sensing approach exhibits the merits of simplicity, rapidness, reliability, and low cost, which has been successfully applied in quality control of captopril in pharmaceutical products. Moreover, the present sensing platform allows smartphone read-out, which has promising applications in point-of-care testing devices for clinical diagnosis and drug analysis.

The peroxidase-like activity of MXene@Fe3O4 nanocomposites and the relevant colorimetric application have been investigated for the first time. According to a kinetic study, MXene@Fe3O4 nanocomposites displayed higher peroxidase activity than their individual components, and the catalytic process followed a ping-pong mechanism. The improved peroxidase-like activity of the MXene@Fe3O4 nanocomposites was obtained due to the synergetic impact of the Fe3O4 and MXene phases, the huge ion-accessible interface, and quick electron transfer channels in the nanocomposites. In the presence of hydrogen peroxide (H2O2), the MXene@Fe3O4 nanocomposites can catalyze the reaction of the colorless substrate 3, 3, 5, 5-tetramethylbenzidine (TMB) into oxidized TMB which revealed a blue color at 652 nm. After the introduction of glutathione (GSH), the blue color was gradually fading owing to the hydroxyl radical scavenging effect of glutathione. A colorimetric detection platform based on the peroxidase-like activity of the MXene@Fe3O4 nanocomposites was developed for H2O2 and GSH with a detection limit of 0.4 μM and 0.5 μM, respectively. The calibration plot for glutathione detection is calculated by absorbance difference at 652 nm, which ranged from 0.5 to 10 μM with a detection limit of 0.2 μM. The recoveries of GSH with different concentrations ranged from 93.76 to 108.50% and the relative standard deviation from 0.30 to 5.96%. This work significantly extends the application of MXene@Fe3O4 nanocomposites in the construction of colorimetric sensors and reveals a satisfactory result in real sample analysis. [ABSTRACT FROM AUTHOR]

The peroxidase-like activity of MXene@Fe3O4 nanocomposites and the relevant colorimetric application have been investigated for the first time. According to a kinetic study, MXene@Fe3O4 nanocomposites displayed higher peroxidase activity than their individual components, and the catalytic process followed a ping-pong mechanism. The improved peroxidase-like activity of the MXene@Fe3O4 nanocomposites was obtained due to the synergetic impact of the Fe3O4 and MXene phases, the huge ion-accessible interface, and quick electron transfer channels in the nanocomposites. In the presence of hydrogen peroxide (H2O2), the MXene@Fe3O4 nanocomposites can catalyze the reaction of the colorless substrate 3, 3, 5, 5-tetramethylbenzidine (TMB) into oxidized TMB which revealed a blue color at 652 nm. After the introduction of glutathione (GSH), the blue color was gradually fading owing to the hydroxyl radical scavenging effect of glutathione. A colorimetric detection platform based on the peroxidase-like activity of the MXene@Fe3O4 nanocomposites was developed for H2O2 and GSH with a detection limit of 0.4 μM and 0.5 μM, respectively. The calibration plot for glutathione detection is calculated by absorbance difference at 652 nm, which ranged from 0.5 to 10 μM with a detection limit of 0.2 μM. The recoveries of GSH with different concentrations ranged from 93.76 to 108.50% and the relative standard deviation from 0.30 to 5.96%. This work significantly extends the application of MXene@Fe3O4 nanocomposites in the construction of colorimetric sensors and reveals a satisfactory result in real sample analysis. [ABSTRACT FROM AUTHOR]

Nanozymes are highly desired to overcome the shortcomings of natural enzymes, such as low stability, high cost and difficult storage during biosensing applications. Herein, by imitating the structure of natural enzymes, we propose a one-pot annealing process to synthesis imidazole-ring-modified graphitic carbon nitride (g-C3N4-Im) with enhanced peroxidase-like activity. g-C3N4-Im shows enhanced peroxidase-like activity by 46.5 times compared to unmodified g-C3N4. Furthermore, imidazole rings of g-C3N4-Im make it possible to anchor Cu(II) active sites on it to produce g-C3N4-Im-Cu, which shows a further increase in peroxidase-like activity by three times. It should be noted that the as-prepared g-C3N4-Im-Cu could show obvious peroxidase-like activity over a broad range of pH values and at a low temperature (5 °C). The ultrahigh peroxidase-like activity is attributed to the electronic effect of imidazole rings and the active sites of Cu(II) for ·OH production. Based on the enhanced peroxidase-like activity, a H2O2 and glucose biosensor was developed with a high sensitivity (limit of detection, 10 nM) and selectivity. Therefore, the biosensor shows potential for applications in diabetic diagnoses in clinical practice. [ABSTRACT FROM AUTHOR]

The generation of a mesoporous structure in platinum nanoparticles can effectively enhance physical and chemical properties. In this study, mesoporous platinum nanoparticles (MPNs) were synthesized by a soft template-mediated one-pot chemical method. To develop a mesoporous structure, Pluronic F-127 was employed. The Pluronic F-127 surfactant forms self-assembled micelles, and the micelles act as the pore-directing agents in the synthesis of nanoparticles. Scanning electron microscopy results revealed that the MPN had a uniform size of 70 nm on average and a distinct mesoporous structure. The development of a concave mesoporous structure on the surface of the MPNs can increase the surface area and facilitate the efficient transport of reactants. The synthesized MPNs exhibited peroxidase-like activity. Furthermore, the MPNs showed excellent catalytic efficiency compared to HRP, due to the high surface area derived from the presence of the mesoporous structure. The peroxidase-like MPNs were applied to the enzyme-linked immunosorbent assay (ELISA) of C-reactive protein (CRP). The MPN-based ELISA exhibited sensitive CRP detection in the range from 0.24 to 7.8 ng/mL with a detection limit of 0.13 ng/mL. Moreover, the recoveries of the CRP concentrations in spiked human serum were 98.6% and 102%. These results demonstrate that as a peroxidase mimic, the MPNs can replace the natural enzymes in conventional ELISA for sensitive CRP detection. [ABSTRACT FROM AUTHOR]

In this work, a new oxidase mimic Ce-MOF was synthesized for the detection of H2O2. The Ce-MOF nanosphere as the oxidase mimic shows the highly catalytic chromogenic activity toward 3,3,5,5-tetramethylbenzidine. It was used instead of peroxidase mimics and H2O2 system for the colorimetric reaction, and this work provides a new highly sensitive and selective colorimetric method for the detection of H2O2, the limit of detection was 10 µM, and the range of the detection was 4 to 16 mM. [ABSTRACT FROM AUTHOR]

A new coordination polymer (Ce-Fe-GMP) with excellent catalytic activity was prepared by a facile route, which was further applied to the detection of F− with high sensitivity and selectivity. The simple doping of Fe3+ into the coordination network can easily modulate the mixing ratio of Ce3+ and Ce4+ in the presence of H2O2, which can extremely improve the catalytic ability of Ce-Fe-GMP. Based on the synergistic effect, the Ce-Fe-GMP with dual-active sites shows better peroxidase activity than that of Ce-GMP. In addition, we found that F− can inhibit the peroxidase activity of Ce-Fe-GMP because of the coordination structure fragmentation and the regulation of Ce3+/Ce4+ ratio. Therefore, different concentrations of F− can be detected by the colorimetric reaction based on this mechanism. The absorption at 652 nm displays a good linear relationship versus the concentration of F− over the range 2.0 to 100.0 μM. Furthermore, F− in real mineral-mixed samples can be measured with satisfactory results. The colorimetric strategy based on the peroxidase activity of Ce-Fe-GMP is simple and low-cost, which shows the potential applications in the field of on-site environment measurement. [ABSTRACT FROM AUTHOR]

In this work, a new oxidase mimic Ce-MOF was synthesized for the detection of H2O2. The Ce-MOF nanosphere as the oxidase mimic shows the highly catalytic chromogenic activity toward 3,3,5,5-tetramethylbenzidine. It was used instead of peroxidase mimics and H2O2 system for the colorimetric reaction, and this work provides a new highly sensitive and selective colorimetric method for the detection of H2O2, the limit of detection was 10 µM, and the range of the detection was 4 to 16 mM. [ABSTRACT FROM AUTHOR]

Carbon dots (CD) generated from biomass were fabricated on g‐C3N4 to construct a metal‐free nanozyme with inherent peroxidase mimic functions. The formation of CD/g‐C3N4 was confirmed by different characterization techniques. The CD/g‐C3N4 displays distinct peroxidase mimic activities, as evidenced by the catalyzed oxidation of TMB (3,3',5,5', ‐tetramethylbenzidine) in the presence of H2O2, as well as color alteration from transparent to blue. The mechanistic analysis of peroxidase activity indicated that H2O2 was catalyzed by CD/g‐C3N4 to produce reactive oxygen species. In an acidic solution, the presence of Cr (VI) accelerates the breakdown of H2O2 to ⋅OH radicals thereby increasing the rate of TMB oxidation. Hence, a visual colorimetric sensor was developed for the purpose of detecting Cr(VI) with limits of detection (LOD) 0.31 μM, based on the accelerated electron transfer between TMB and H2O2 with the assistance of CD/g‐C3N4. [ABSTRACT FROM AUTHOR]

Though numerous nanomaterials with enzyme‐like activities have been utilized as probes and sensors for detecting biological molecules, it is still challenging to construct highly sensitive detectors for biomarkers using polymeric materials. Benefiting from the π‐d delocalization effect of electrons, excellent metal‐chelating property, high electron transferability, and good chemical stability of π‐conjugated phthalocyanine, the design of the copper phthalocyanine‐based conjugated polymer nanoparticles (Cu‐PcCP NPs) as a colorimetric sensor for a variety of biomarkers is reported. The Cu‐PcCP NPs are synthesized through a simple microwave‐assisted polymerization, and their chemical structures are thoroughly characterized. The colorimetric results of Cu‐PcCP NPs demonstrate excellent peroxidase‐like detecting activity and also great substrate selectivity than most of the reported Cu‐based nanomaterials. The Cu‐PcCP NPs can achieve a detection limit of 4.88 μM for the H2O2, 4.27 μM for the L‐cysteine, and 21.10 μM for the glucose via a cascade catalytic system, which shows comparable detecting sensitivity as that of many earlier reported enzyme‐like nanomaterials. Moreover, Cu‐PcCP NPs present remarkable resistance to harsh conditions, including high temperature, low pH, and excessive salts. These highly specific π‐conjugated copper‐phthalocyanine nanoparticles not only overcome the current limitation of polymeric material‐based sensors but also provide a new direction for designing next‐generation enzyme‐like nanomaterial‐based colorimetric biosensors. [ABSTRACT FROM AUTHOR]

The successful synthesis of ruthenium oxide/reduced graphene oxide (RuO2/rGO) heterostructures by one-pot hydrothermal method using graphene oxides and RuCl3 as precursors is reported. The heterostructures had high peroxidase-like (POD-like) activities, which catalyzes the oxidation of classical peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to create a blue colored reaction product. The catalytic activity was significantly enhanced by the synergistic effect between RuO2 nanoparticles and rGO. RuO2/rGO had a low Km of 0.068 mM and a high vmax of 1.228 × 10−7 M·s−1 towards TMB in the TMB-H2O2 catalytic oxidation system. In addition, the POD-like activity originating from the electron transfer mechanism was confirmed by cytochrome C (Cyt C) oxidation experiment. A colorimetric method based on RuO2/rGO heterostructures was developed with good sensitivity and selectivity for glucose detection with a limit of detection of 3.34 μM and a linear range of 0–1500 μM. The RuO2/rGO heterostructures have potential applications in the biomedical areas, such as biosensor and diagnostics. [ABSTRACT FROM AUTHOR]

[Display omitted] • PP-AgNZ was cost-effectively synthesized using catechin that was extracted from Piper pedicellatum leaves. • The peroxidase mimic activity of PP-AgNZ was established by taking TMB as the chromogenic substrate in the presence of H 2 O 2. • The blue hue by oxidized TMB was referenced in the colorimetric discrimination of nanomolar levels of CA, HQ, and RE in simple procedures. • The selectivity and sensitivity of the approach advocated for its applicability in water and soil samples with good recovery rates. Ag-Nanozyme (AgNZ) was fabricated by simple reduction method using Piper pedicellatum (PP) extract where catechin is the major constituent. The prepared PP-AgNZ acted as a nanozyme (NZ) that could catalyze the oxidation of TMB substrate in presence of H 2 O 2 leading to a color reaction at an optimal time of 30 min at 45 °C. The enzyme mimic activity of PP-AgNZ showed a significant K m value of 0.0636 mM for TMB. Dihydroxybenzene (DHB) isomers could interrupt the oxidation process of TMB leading to the fading of the blue color into distinct intensities each for CA, HQ, and RE. This study reports a simple preparation of NZ used for reliable colorimetric detection of trace amounts of DHB isomers employing very simple technique. The detection was achieved for a linear range of 10–270 nM for CA and RE and, 10–390 nM for HQ. The limit of detection was found to be very low i.e. 32.38 nM, 30.64 nM, and 37.5 nM for CA, HQ, and RE respectively. Further, the detection of HQ was also supported by smartphone-assisted sensing to show the accessibility and applicability of our approach. Our work also demonstrated its effectiveness when applied to real environmental samples, yielding remarkable recovery rates ranging from 91.4 % to 108.6 %. Thus, the synthesized PP-AgNZ stands out as a promising NZ for its applications in environmental chemistry. [ABSTRACT FROM AUTHOR]

• A simple template-free method was used to synthesize IMBO NCs. • Cr (III) inhibited the catalytic activity of IMBO NCs. • Cr (VI) enhanced the catalytic activity of IMBO NCs. • An IMBO-TMB colorimetric sensor was constructed to detect Cr (III) and Cr (VI). In recent years, most of the researches on nanozymes have focused on improving their catalytic activity and direct synthesis, but this task is still very complicated. Bimetallic oxides are particularly popular because of their mixed valence and special structure. In this study, iron-manganese bimetallic oxide nano-cubes (IMBO NCs) were prepared by a rapid and effective solvothermal synthesis technique, and showed excellent oxidase-like activity. The exposure of Cr(III) and Cr(VI) inhibited and enhanced the catalytic activity of IMBO NCs respectively. On this basis, a simple, economical and accurate colorimetric sensor was established by combining with 3,3′,5,5′-tetramethylbenzidine (TMB). Using oxidase activity instead of traditional peroxidase activity to detect Cr(III) and Cr(VI) greatly shortens the detection time. The method has also been successfully applied to the quantitative monitoring of Cr(III) and Cr(VI) in lake water. This study provides theoretical support for the effective design of bimetallic oxide nanozyme activity and can guide the development of accurate detection systems for the analysis of Cr(III) in food and Cr(VI) in environment. [ABSTRACT FROM AUTHOR]

Nanozyme are well-regarded for their ease of synthesis, cost-effectiveness, robust stability, and significant capacity to replicate the functional attributes of natural enzymes, all of which make them highly applicable in colorimetric detection assays. In this study, we synthesized ultra-small copper oxide nanozymes (USCuO) via a simple hydrothermal process. These USCuO exhibited considerable peroxidase-mimetic activity, effectively catalyzing the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) so as to produce a blue product. We observed that the presence of doxorubicin (DOX) could inhibit this process selectively and sensitively. Leveraging this inhibitory effect, we developed a novel colorimetric method for DOX detection characterized by its high selectivity and sensitivity with a detection range of 0.01 mM to 0.1 mM and a detection limit of 0.3 µM. We further applied this method to the determination of DOX levels in chicken and fish samples using the standard addition technique, and then evaluated its performance against that of conventional liquid phase detection methods. The results demonstrated that our newly established method enables the rapid and reliable detection of DOX in food samples, suggesting its potential utility in food safety monitoring. [Display omitted] • Ultra-small copper oxide nanozyme were synthesized using a one-pot hydrothermal method. • These nanozyme enable highly selective and sensitive colorimetric detection of DOX. • The methodology is suitable for DOX on-site analytical applications. [ABSTRACT FROM AUTHOR]

Regulating the catalytic activity of nanozymes is significant for their applications in various fields. Here, we demonstrate a new strategy to achieve reversible regulation of the nanozyme's activity for sensing purpose. This strategy involves the use of zero-dimensional MoS 2 quantum dots (MQDs) as the building blocks of nanozymes which display very weak peroxidase (POD)-like activity. Interestingly, such POD-like activity of the MQDs largely enhances in the presence of Fe3+ while diminishes with the addition of captopril thereafter. Further investigations identify the mechanism of Fe3+-mediated aggregation-induced enhancement of the POD-like activity and the inhibitory effect of captopril on the enhancement, which is highly dependent on their concentrations. Based on this finding, a colorimetric method for the detection of captopril is developed. This sensing approach exhibits the merits of simplicity, rapidness, reliability, and low cost, which has been successfully applied in quality control of captopril in pharmaceutical products. Moreover, the present sensing platform allows smartphone read-out, which has promising applications in point-of-care testing devices for clinical diagnosis and drug analysis. [Display omitted] • A new post-synthesis strategy is developed to achieve reversible regulation of nanozyme's activity. • Fe3+-mediated aggregation can enhance the peroxidase-like activity of MoS 2 quantum dots more than 10 times. • Quality control of captopril in pharmaceutical products is realized by manipulating nanozyme's catalytical activity. • This sensing approach allows smartphone read-out, which has promising applications in point-of-care testing. [ABSTRACT FROM AUTHOR]

A novel colorimetric/fluorescent dual-mode nanosensor for Hg2+ detection was constructed using expanded mesoporous silica (EMSN)-encapsulated ultrasmall platinum nanoclusters (EMSN@Pt NCs) with improved peroxidase-like and stable fluorescent activities. The sensing technique was based on the mechanism that the peroxidase mimetic activity and fluorescence intensity of EMSN@Pt NCs can be inhibited in the presence of Hg2+. In this sensing platform, a linear range of 5–50 nM with a detection limit of 1.78±0.38 nM and quantification limit of 5.93 nM was obtained via fluorescent analysis. A linear calibration curve from 0.25 to 200 nM with a detection limit of 8.25±0.51 nM and quantification limit of 27.47 nM was achieved via colorimetric analysis. The proposed dual-mode probe possesses excellent selectivity and reliability for Hg2+ detection, which can function as an efficient nanosensor for the quantitative determination of Hg2+ in Pueraria lobata. [ABSTRACT FROM AUTHOR]

Porous Au@Pt nanoparticles (NPs) with electron-rich Pt shells exhibited significantly enhanced peroxidase-like activity by changing the catalytic reaction path, which offered valuable opportunities to construct sensitive colorimetric biosensors, as exemplified by detection of spike 1 protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). [Display omitted] The development of colorimetric assays for rapid and accurate diagnosis of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is of practical importance for point-of-care (POC) testing. Here we report the colorimetric detection of spike (S1) protein of SARS-CoV-2 based on excellent peroxidase-like activity of Au@Pt nanoparticles, with merits of rapidness, easy operation, and high sensitivity. The Au@Pt NPs were fabricated by a facile seed-mediated growth approach, in which spherical Au NPs were premade as seeds, followed by the Pt growth on Au seeds, producing uniform, monodispersed and porous Au@Pt core–shell NPs. The as-obtained Au@Pt NPs showed a remarkable enhancement in the peroxidase-mimic catalysis, which well abided by the typical Michaelis-Menten theory. The enhanced catalysis of Au@Pt NPs was ascribed to the porous nanostructure and formed electron-rich Pt shells, which enabled the catalytic pathway to switch from hydroxyl radical generation to electron transfer process. On a basis of these findings, a colorimetric assay of spike (S1) protein of SARS-CoV-2 was established, with a linear detection range of 10–100 ng mL−1 of protein concentration and a low limit of detection (LOD) of 11 ng mL−1. The work presents a novel strategy for diagnosis of COVID-19 based on metallic nanozyme-catalysis. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) was widely applied as the bactericide and bleach agent in food industry due to its strong oxidation, whose residue had also posed a hazard to public health at the same time. Therefore, it was indispensable to establish a simple, highly effective and accurate method for the detection of H2O2 in foods. Herein, the MIL-88B-Fe metal–organic framework (MOF) was prepared by a facile solvothermal process and utilized as the peroxidase mimic for H2O2 detection. The resultant MIL-88B-Fe MOF exhibited an excellent peroxidase mimetic activity to effectively catalyse the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, generating a blue coloured product. Under the optimal testing conditions, the linear absorbance response is well correlated with the H2O2 concentration ranging from 10 to 100 μM with a detection limit of 0.60 μM. The catalytic kinetic assay suggested that the MIL-88B-Fe MOF possessed the higher affinity towards both the substrate TMB and H2O2 than horseradish peroxidase. Moreover, the MIL-88B-Fe MOF also displayed a high selectivity and anti-interference performance towards H2O2 detection. In addition, the peroxidase mimetic catalytic oxidation TMB mechanism over the MIL-88B-Fe MOF was clarified by the photoluminescence test. Benefitting from the sensitive response and good anti-interference capacity, this method was applied in real milk and beer samples for H2O2 detection and showed a favourable reproducibility and feasibility. These results indicated that the proposed method based on MIL-88B-Fe as peroxidase mimic might be a promising candidate for H2O2 detection in food field. [ABSTRACT FROM AUTHOR]

A practical colorimetric assay was developed for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). For this purpose, magnetic γ Fe2O3 nanoparticles were synthesized and used as a peroxidase-like mimic activity molecule. In the presence of γ Fe2O3 nanoparticles, the color change of H2O2 included 3,3′,5,5′-tetramethylbenzidine was monitored at the wavelength of 654 nm when spike protein interacted with angiotensin-converting enzyme 2 receptor. This oxidation-reduction reaction was examined both spectroscopically and by using electrochemical techniques. The experimental parameters were optimized and the analytical characteristics investigated. The developed assay was applied to real SARS-CoV-2 samples, and very good results that were in accordance with the real time polymerase chain reaction were obtained. [ABSTRACT FROM AUTHOR]