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A dual-recognition strategy is reported to construct a one-step washing and highly efficient signal-transduction tag system for high-sensitivity colorimetric detection of Staphylococcus aureus (S. aureus). The porous (gold core)@(platinum shell) nanozymes (Au@PtNEs) as the signal labels show highly efficient peroxidase mimetic activity and are robust. For the sake of simplicity the detection involved the use of a vancomycin-immobilized magnetic bead (MB) and aptamer-functionalized Au@PtNEs for dual-recognition detection in the presence of S. aureus. In addition, we designed a magnetic plate to fit the 96-well microplate to ensure consistent magnetic properties of each well, which can quickly remove unreacted Au@PtNEs and sample matrix while avoiding tedious washing steps. Subsequently, Au@PtNEs catalyze hydrogen peroxide (H2O2) to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) generating a color signal. Finally, the developed Au@PtNEs-based dual-recognition washing-free colorimetric assay displayed a response in the range of S. aureus of 5 × 101–5 × 105 CFU/mL, and the detection limit was 40 CFU/mL within 1.5 h. In addition, S. aureus-fortified samples were analyzed to further evaluate the performance of the proposed method, which yielded average recoveries ranging from 93.66 to 112.44% and coefficients of variation (CVs) within the range 2.72–9.01%. These results furnish a novel horizon for the exploitation of a different mode of recognition and inexpensive enzyme-free assay platforms as an alternative to traditional enzyme-based immunoassays for the detection of other Gram-positive pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Bimetallic Pt/Ag nanoparticles (Pt/Ag NPs) were synthesized using 3-hydroxyphenyl-boronic acid as the reducing and stabilizing agent by a simple, one-step hydrothermal method. The bimetallic Pt/Ag NPs were demonstrated to possess intrinsic peroxidase mimetic catalytic activity for the luminol/H2O2 reaction to generate chemiluminescence (CL). The catalytic properties of the bimetallic Pt/Ag NPs were thoroughly investigated. The results showed that the combination of Pt and Ag greatly enhanced the chemiluminescence which is attributed to their synergy. Moreover, the prepared bimetallic Pt/Ag NPs exhibited superior peroxidase mimetic activity to horseradish peroxidase and were stable under a wide range of pH values and temperatures. Using the bimetallic Pt/Ag NPs as the catalyst, a novel chemiluminescence sensor was developed for the determination of glucose with a linear range from 1 to 500 µM and a detection limit of 0.35 µM. The developed method was successfully employed to determine glucose in human serum with satisfactory results. Bimetallic Pt/Ag NPs with peroxidase mimetic catalytic activity have promising applications for determination of glucose in clinical samples. [ABSTRACT FROM AUTHOR]

Purpose: Reactive oxygen species (ROS) are practically essential in radiotherapy to damage cancer cells; however, they are always inadequate for some malignant entities. Here, we designed a biodegradable mesoporous silica decorated with hemin and glucose oxidase (GOD@Hemin-MSN) to generate a chemodynamic therapy in order to enhance the killing capacity of radiotherapy. Methods: Mesoporous silica, as an outstanding drug carrier, can deliver hemin and glucose oxidase to the tumor site. With high level of metabolism activity, cancer cells are abundant in glucose, which can be oxidized into H2O2 by glucose oxidase (GOD) on site. The generated H2O2 is subsequently converted into intracellular ROS, especially hydroxyl radical within the tumor microenvironment, by hemin, which has mimetic peroxidase properties. By this means, the ROS can be supplemented or enriched to facilitate the killing of tumor cells. Results: The chemodynamic therapy induced by GOD@Hemin-MSN produced quantities of ROS, which compensated for their inadequacy as a result of radiotherapy, and exhibited remarkable antitumor efficacy, with a tumor inhibition rate of 91.5% in A549 tumor-bearing mice. Conclusion: This work has validated GOD@Hemin-MSN as a radiosensitizer in chemodynamic therapy, which showed biocompatibility and potential for translational application. [ABSTRACT FROM AUTHOR]

PurposeReactive oxygen species (ROS) are practically essential in radiotherapy to damage cancer cells; however, they are always inadequate for some malignant entities. Here, we designed a biodegradable mesoporous silica decorated with hemin and glucose oxidase (GOD@Hemin-MSN) to generate a chemodynamic therapy in order to enhance the killing capacity of radiotherapy.MethodsMesoporous silica, as an outstanding drug carrier, can deliver hemin and glucose oxidase to the tumor site. With high level of metabolism activity, cancer cells are abundant in glucose, which can be oxidized into H2O2 by glucose oxidase (GOD) on site. The generated H2O2 is subsequently converted into intracellular ROS, especially hydroxyl radical within the tumor microenvironment, by hemin, which has mimetic peroxidase properties. By this means, the ROS can be supplemented or enriched to facilitate the killing of tumor cells.ResultsThe chemodynamic therapy induced by GOD@Hemin-MSN produced quantities of ROS, which compensated for their inadequacy as a result of radiotherapy, and exhibited remarkable antitumor efficacy, with a tumor inhibition rate of 91.5% in A549 tumor-bearing mice.ConclusionThis work has validated GOD@Hemin-MSN as a radiosensitizer in chemodynamic therapy, which showed biocompatibility and potential for translational application.

Fe3O4-brominated graphene (Fe3O4-GBR) nanocomposites were synthesized via an in situ method using the precursors FeSO4.7H2O and GBR in different (1:1, 1:2, 2:1, 1:5, 1:10, 1:20, and 5:1) weight ratios at pH 11.5. The Fe3O4-GBR (1:5) nanocomposite in combination with H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB) showed swift and superior intrinsic peroxidase mimetic enzyme activity compared with the other Fe3O4-GBR composites, GBR and Fe3O4, as observed by colorimetry. It was characterized using high-resolution scanning electron microscopy (HRSEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Its catalytic activity was optimized by varying different parameters, and the optimum conditions for peroxidase mimetic activity were observed using 100 μL Fe3O4-GBR (1 mg/mL), 50 μL TMB (1 mg/mL), and 200 μL H2O2(1 mM) in 400 μL of acetate buffer of pH 2.3 at 30 °C temperature. Kinetic analysis has revealed the Michaelis–Menten kinetic behavior of peroxidase activity with Michaelis–Menten constants (Km) and maximum initial velocities (Vmax) of 0.082 mM and 14.1 nMs−1 respectively, for H2O2 and 0.086 mM and 5.1 nMs−1, respectively for TMB. The limit of detection and linear range were found to be 49.6 μM and 100–880 μM, respectively, for H2O2 and 41.9 μM and 47.6–952.3 μM, respectively, for cholesterol. On this basis, a simple, swift, sensitive, selective, and reproducible colorimetric assay to detect cholesterol levels in blood serum samples using Fe3O4-GBR nanocomposite has been developed. Thus, Fe3O4-GBR composite as compared to Fe3O4 and GBR has shown better peroxidase mimicking activity for biosensing. [ABSTRACT FROM AUTHOR]

For the first time the enzyme mimic activity of iron oxychloride (FeOCl) nanosheets has been studied. The intrinsic peroxidase-mimetic activity of the nanosheets in the presence of H2O2 was approved by the efficient oxidation of tetramethylbenzidine (TMB). The Michaelis–Menten constant of the nanosheets toward TMB was about six times lower than that of natural horseradish peroxidase. The superiority of the nanosheets’ catalytic property ascribes to their H2O2 activation ability. Based on the inhibition of the nanozymes’ catalytic reaction, an assay was developed for the quantitative measurement of glutathione (GSH) and cysteine (Cys). The linear range for both biomolecules was over the range of 3–33 μM. The LOD values (3σ/slope) for GSH and Cys were 2.23 μM and 2.76 μM, respectively. Importantly, we succeeded in colorimetric discrimination of GSH and Cys kinetically. We achieved high selectivity toward GSH and Cys. This work extends the feasibility of using FeOCl as nanozymes to construct biosensors, colorimetric probes for medical diagnosis, and nanozyme-based cancer therapy. [ABSTRACT FROM AUTHOR]

A Fe‐porphyrin covalent organic framework (Fe‐PorCOF) was prepared through a postmodification strategy and characterized using different techniques. Fe‐PorCOF exhibits an inherent peroxidase/oxidase mimetic catalytic activity and sharply accelerates chemiluminescence (CL) reactions between luminol and hydrogen peroxide (H2O2) or dissolved oxygen (O2) under alkaline conditions. The catalytic role was attributed to a significant increase in production of reactive oxygen species. Using the imminent peroxidase mimetic catalytic activity of Fe‐PorCOF, a new CL method was developed for determination of H2O2 over a linear range from 0.01 to 10.0 μmol·L−1 and with a limit of detection of 5.3 nmol·L−1. The combination of the peroxidase mimetic catalytic activity of Fe‐PorCOF with the catalytic activity of glucose oxidase on glucose oxidation presents a sensitive CL method for glucose assay. The linear range and the detection limit for glucose were 0.05–8.0 μmol·L−1 and 4.0 nmol·L−1, respectively. The practicability of this method was assessed by determination of glucose in human sera. As a peroxidase/oxidase mimetic, Fe‐PorCOF is easy to prepare and exhibits good catalytic efficiency in the luminol reaction. We believe that this strategy will promote the development of a CL field with functional COFs as a catalyst. [ABSTRACT FROM AUTHOR]

This article presents a novel peroxidase mimetic by doping S atoms into reduced graphene oxide (rGO), which was synthesized through a facile hydrothermal reaction without any templates or surfactants. The peroxidase-like activity of S-doped rGO (S-rGO) is greatly boosted compared with the pristine rGO, demonstrating the peroxidase-like active sites are dominantly originated in sulfur-containing groups. The steady-state kinetic studies further indicate that S-rGO obeys the typical Michaelis-Menten curves and has a much smaller Michaelis constant (Km) for hydrogen peroxide (H2O2) and 3, 3′, 5, 5′-tetramethylbenzidine (TMB). In view of the outstanding performance of S-rGO as a peroxidase mimetic, an efficient and sensitive colorimetric detection platform for H2O2 and glucose has been successfully established. The linear detection for H2O2 is obtained in a range of 0.1–1 μM with an extremely lower detection limit of 0.042 μM, and glucose can be measured in a linear range of 1–100 μM, giving a detection limit of 0.38 μM. This study not only provides a new avenue for the reasonable design of heteroatom-doped carbon-based nanomaterials but also offers meaningful reference for detecting the important biomolecules in biotechnology. [ABSTRACT FROM AUTHOR]

In order to monitor and respond rapidly to outbreaks of food-borne pathogens, establishing rapid and sensitive detection methods is becoming increasingly urgent. In this work, through the synthesis of copper-based metal-organic framework nanoparticles (Cu-MOF NPs) and functionalized with aptamers, we developed a colorimetric protocol to detect Escherichia coli. In a typical experimental procedure, aptamer 1 was immobilized onto microplate to act as capture probes. Cu-MOF NPs were synthesized and functionalized with streptavidin and biotinylated aptamer 2 to form the signal probes. In the presence of E. coli, aptamers on both capture and signal probes bind with E. coli and form a sandwich-type complex. The Cu-MOF NPs enable to catalyze the colorless peroxidase substrate to yield a colorimetric output signal. This peroxidase-like mimics-based colorimetric aptasensor showed a rapid and sensitive quantification of E. coli in the concentration range of 16~1.6 × 106 cfu/mL with a limit of quantitation (LOQ) of 16 cfu/mL and limit of detection (LOD) of 2 cfu/mL. The application of the developed assay for colorimetric measuring of milk samples was evaluated with satisfactory results. The developed Cu-MOF NPs-assisted visual method can be expected as a powerful alternative and promising tool for foodborne pathogen detection and control. [ABSTRACT FROM AUTHOR]

The development of high-efficiency peroxidase mimetics is highly desirable in view of high cost and low stability of natural enzymes. From the perspective of mimicking active site microenvironment at low cost, we herein report a novel histidine-functionalized graphene quantum dot (His-GQD)/hemin complex, which exhibits the highest catalytic rate for the peroxidase-based chromogenic reaction among the hemin-containing mimetics reported so far. Also, our peroxidase mimetic shows excellent tolerance to strongly acidic conditions and can function in a wide temperature range. Lineweaver-Burk plots and comprehensive electron paramagnetic resonance analysis reveal a ping-pong type catalytic mechanism for this mimetic. In addition, His-GQD/hemin demonstrates high efficiency and accuracy in detecting H2O2 and blood glucose. Our work provides an effective design of artificial enzymes for practical applications. [ABSTRACT FROM AUTHOR]

A carbon silver nano-assembly was prepared from silver nanoparticles and carbon dots (AgNP@CD). It was used to quantify hydrogen peroxide and glucose by UV-visible spectroscopy. Banana peels were used to prepare the CDs by a microwave-assisted method. The CDs can be prepared within 5 min at 700 W. They act as (a) substrate, (b) stabilizer, and (c) reductant to convert silver ions to AgNPs. The nano-assembly was characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy, and transmission electron microscopy. The CDs have a particle size of 1.4 nm. Photoexcitation of the CDs with a UV lamp of 365 nm results in blue fluorescence. The absorption spectra of the CDs show a peak at 205 nm along the wide shoulder absorption band. On incorporation of the Ag nanoparticles into the CDs matrix, the color of the CDs turns into yellow and an additional absorbance peak at 408 nm appears. FTIR spectroscopy shows that different functional groups are present on the CDs. They are responsible for the stabilization of the AgNPs. On exposure to H2O2, the color of the nano-assembly disappears gradually. Hence, the assembly can be used as a colorimetric indicator probe for H2O2 with a linear response in the 0.1-100 μM concentration range. It can also be applied to the determination of glucose by using glucose oxidase which causes the formation of H2O2 from glucose. The linear response ranges from 1- 600 μM. The detection limits for H2O2 and glucose are 9 nM and 10 nM, respectively. In our perception, this is the lowest detection limit reported so far. The AgNP@CD nano-assembly does not respond to saccharides, maltose, fructose, and lactose. It can be used to quantify glucose in diluted blood plasma. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 7 S 8 NSs with peroxidase-like activity was prepared by hydrothermal method. • A colorimetric and fluorescence dual-signal method was developed for determining glucose. • The method exhibited excellent sensitivity and high selectivity. Fe 7 S 8 nanosheets (Fe 7 S 8 NSs) was prepared from ferrous sulfate and thiourea, showing peroxidase-like activity and enabling the oxidation of o-phenylenediamine (OPD) in the presence of H 2 O 2 to produce 2,3-diaminophenol (DAP) with strong absorption and fluorescence peaks at 450 and 560 nm, respectively. Furthermore, both the level of absorbance at 450 nm (A 450) and the intensity of fluorescence at 560 nm (F 560) depended on the concentration of H 2 O 2. As a result, a dual response (colorimetry and fluorescence) method for the assay of H 2 O 2 was established. Due to the fact that H 2 O 2 can be produced from glucose oxidase catalyzed glucose oxidation, A 450 and F 560 were further used for indirect determination of glucose. The results indicated that the absorbance and fluorescence responses were closely related to glucose concentration in the range of 1.0–100 μM and 1.0––70 μM with the detection limit of 0.83 and 0.52 μM, respectively. To verify its practicality, the method has been used for determining glucose in human serum samples with recoveries ranging from 92.2 to 106.2 %, suggesting its promising potential applications. [ABSTRACT FROM AUTHOR]

Nanomaterial-mediated cancer therapeutics is a fast developing field and has been utilized in potential clinical applications. However, most effective therapies, such as photodynamic therapy (PDT) and radio therapy (RT), are strongly oxygen-dependent, which hinders their practical applications. Later on, several strategies were developed to overcome tumor hypoxia, such as oxygen carrier nanomaterials and oxygen generated nanomaterials. Among these, oxygen species generation on nanozymes, especially catalase (CAT) mimetic nanozymes, convert endogenous hydrogen peroxide (H2O2) to oxygen (O2) and peroxidase (POD) mimetic nanozymes converts endogenous H2O2 to water (H2O) and reactive oxygen species (ROS) in a hypoxic tumor microenvironment is a fascinating approach. The present review provides a detailed examination of past, present and future perspectives of POD mimetic nanozymes for effective oxygen-dependent cancer phototherapeutics.

Prussian blue analogs (PBAs) are well-known artificial enzymes with peroxidase (PO)-like activity. PBAs have a high potential for applications in scientific investigations, industry, ecology and medicine. Being stable and both catalytically and electrochemically active, PBAs are promising in the construction of biosensors and biofuel cells. The “green” synthesis of PO-like PBAs using oxido-reductase flavocytochrome b2 is described in this study. When immobilized on graphite electrodes (GEs), the obtained green-synthesized PBAs or hexacyanoferrates (gHCFs) of transition and noble metals produced amperometric signals in response to H2O2. HCFs of copper, iron, palladium and other metals were synthesized and characterized by structure, size, catalytic properties and electro-mediator activities. The gCuHCF, as the most effective PO mimetic with a flower-like micro/nano superstructure, was used as an H2O2-sensitive platform for the development of a glucose oxidase (GO)-based biosensor. The GO/gCuHCF/GE biosensor exhibited high sensitivity (710 A M−1m−2), a broad linear range and good selectivity when tested on real samples of fruit juices. We propose that the gCuHCF and other gHCFs synthesized via enzymes may be used as artificial POs in amperometric oxidase-based (bio)sensors.

A facile synthesis of polydopamine/Prussian blue (PDA/PB) nanocomposites was proposed by anchoring PB on the surface of PDA to eliminate the intrinsic color interference of PB for colorimetric detection. As expected, the as-obtained PDA/PB exhibited excellent peroxidase-like activity and could trigger the color reaction of several substrates. A glutathione (GSH) colorimetric assay was further established by incorporating the PDA/PB peroxidase mimic with GSH. Prussian blue (PB) nanoparticles are good candidates as peroxidase mimics for electrochemical biosensors due to their excellent catalytic activity and facile synthesis. However, they are rarely used in colorimetric sensing because of their aggregation in aqueous solution and intrinsic color interference. In this report, we developed a facile one-step approach to fabricate polydopamine/Prussian blue (PDA/PB) nanocomposites by anchoring highly dispersed PB nanoparticles on the surface of PDA nanospheres. As expected, the as-obtained PDA/PB nanocomposites have good dispersion in water and the intrinsic color interference is efficiently avoided. Moreover, the PDA/PB nanocomposites exhibited excellent peroxidase-like activity and could trigger the color reaction of several substrates including 3,3′,5,5′-tetramethylbenzidine (TMB), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and o-phenylenediamine (OPD) in the presence of H 2 O 2. Based on the inhibiting effect of glutathione (GSH) on TMB oxidation, a simple colorimetric assay for the detection of GSH was proposed. This assay has a linear concentration range from 0.5 to 20 μM and a limit of detection of 0.160 μM. Taken together, this approach provides a simple, rapid, sensitive and selective method for the quantification of GSH and may shed light on the colorimetric sensing for medical diagnosis and environmental monitoring. [ABSTRACT FROM AUTHOR]

Porous nanomaterials with superior peroxidase mimetic activity (nanozyme) at room temperature have gained increasing attention as potential alternatives to natural peroxidase enzymes. Herein, we report the application of porous iron oxide nanoflakes (IONFs), synthesized using the combination of solvothermal method and high‐temperature calcination as peroxidase nanozyme for the oxidation of 3,3′,5,5′‐tetramethylbenzidine (TMB) in the presence of H2O2. The four IONF catalysts possess porous structures with a wide pore size distribution between 2–30 nm and high specific surface areas around to 200 m2 g−1. The increase of calcination temperature of the IONFs from 250 °C to 400 °C resulted in a gradual decrease in their specific surface area and Michaelis‐Menten constant (Km) for TMB oxidation. The optimum IONF sample showed a much lower Km at 0.24 mM (towards TMB) compared to natural enzyme horseradish peroxidase (HRP) at 0.434 mM, revealing the promising potential of the as‐prepared IONFs as alternatives to HRP for biosensing applications. Porous iron oxide nanoflakes show high peroxidase mimetic activity towards the oxidation of TMB at room temperature compared to natural enzyme horseradish peroxidase. [ABSTRACT FROM AUTHOR]

Constructing hollow mesoporous nanostructures for dispersing catalytically active sites has attracted growing interest. Here, for the first time, Co 3 O 4 hollow nanocages (Co 3 O 4 HNCs) derived from ZIF-67 were prepared for loading iron nanoparticles (FeNPs), resulting in FeNPs@Co 3 O 4 hollow nanocages (FeNPs@Co 3 O 4 HNCs). FeNPs@Co 3 O 4 HNCs were characterized by SEM, TEM, XRD, XPS and FT-IR. The FeNPs@Co 3 O 4 HNCs composites could catalyze the oxidation of TMB into blue product by H 2 O 2 , showing better peroxidase-like activity than FeNPs and Co 3 O 4 HNCs. Notably, kinetic studies indicated that FeNPs@Co 3 O 4 HNCs behaved an excellent affinity to H 2 O 2 with K m value of 0.019 mM, which was 195 times lower than that of HRP. On this basis, a facile colorimetric biosensing method was established to detect glucose. The linear range was 0.5–30 μM, and the limit of detection was 0.05 μM. The proposed sensor was successfully used to determine glucose in human serum samples. The highly catalytic performance of FeNPs@Co 3 O 4 HNCs is attributed to its porous hollow structure, which is beneficial for dispersion of in situ formed FeNPs and for reducing the agglomeration. Further, the FeNPs@Co 3 O 4 HNCs catalysts with porous character provide an essential way to expose active sites as far as possible to the substrate and increase the catalytic active sites. [ABSTRACT FROM AUTHOR]

In this study, we describe a novel peroxidase-like activity of Co-aminoclay [CoAC] present at pH ~5.0 and its application to fluorescent biosensor for the determination of H2O2 and glucose. It is synthesized with aminoclays (ACs) entrapping cationic metals such as Fe, Cu, Al, Co., Ce, Ni, Mn, and Zn to find enzyme mimicking ACs by sol–gel ambient conditions. Through the screening of catalytic activities by the typical colorimetric reaction employing 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)diammonium salt (ABTS) as a substrate with or without H2O2, Fe, Cu, and CoACs are found to exhibit peroxidase-like activity, as well as oxidase-like activity was observed from Ce and MnACs. Among them, CoAC shows exceptionally high peroxidase-like activity, presumably due to its ability to induce electron transfer between substrates and H2O2. CoAC is then used to catalyze the oxidation of Amplex® UltraRed (AUR) into a fluorescent end product, which enables a sensitive fluorescent detection of H2O2. Moreover, a highly sensitive and selective glucose biosensing strategy is developed, based on enzyme cascade reaction between glucose oxidase (GOx) and CoAC. Using this strategy, a highly linear fluorescence enhancement is verified when the concentration of glucose is increased in a wide range from 10 μM to 1 mM with a lower detection limit of 5 μM. The practical diagnostic capability of the assay system is also verified by its use to detect glucose in human blood serum. Based on these results, it is anticipated that CoAC can serve as potent peroxidase mimetics for the detection of clinically important target molecules. [ABSTRACT FROM AUTHOR]

Encapsulating metal nanoparticles (NPs) into carbon materials is a promising strategy for the fabrication of nanozymes with high activity. Here, for the first time, the proof-of-concept is demonstrated by fabricating CoNPs embedded in NH 2 -MIL-88(Fe) MOFs-derived magnetic carbon (MC) through in situ reduction of cobalt precursors by NaBH 4 . The obtained CoNPs/MC was characterized by TEM, SEM, XPS, XRD, Raman spectrum, and FT-IR. The CoNPs/MC exhibits much higher peroxidase-like activity than pure CoNPs and magnetic carbon. The high peroxidase-like activity of the CoNPs/MC is attributed to the decomposition of H 2 O 2 to generate OH and O 2 − radicals, resulting in TMB color reaction. Also, CoNPs/MC is robust in a wide range of pH and temperature, indicating a promising peroxidase-like candidate. On this basis, a colorimetric assay was developed by combining glucose oxidase with CoNPs/MC for glucose biosensing. The linear range for glucose detection is from 0.25 to 30 μM with a lower detection limit of 156 nM. The CoNPs/MC-based colorimetric method has been successfully used to assay the content of glucose in real biological samples such as human serums. Our work reveals the high potential of encapsulating metal NPs into carbon materials for the fabrication of nanozymes with stable and high activity. [ABSTRACT FROM AUTHOR]

Tb 2 (MoO 4 ) 3 nanostructures are demonstrated for the first time to have an intrinsic peroxidase-like activity. Tb 2 (MoO 4 ) 3 nanoplates could efficiently catalyse the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate a blue dye (with an absorbance maximum at 652 nm) in the presence of H 2 O 2 . Based on the highly efficient catalytic of Tb 2 (MoO 4 ) 3 nanoplates, a novel system for optical determination of H 2 O 2 and glucose was successfully established under optimized conditions. The assay had 0.0.08 μM and 0.1 μM detection limit for H 2 O 2 and glucose, respectively. In our opinion, this enzyme mimetic has a potential to use in other oxidase based assays. [ABSTRACT FROM AUTHOR]

In present study, we highlight one-step electrochemical synthesis of nearly uniform size (~ 5 nm) of graphene quantum dots (E-GQDs) from wood charcoal and their further application as a peroxidase enzyme mimetic. The structural and optical properties of as-synthesized E-GQDs were probed by TEM, AFM, and spectroscopic techniques. Peroxidase enzyme mimetic potential of E-GQDs were examined for colorimetric detection of H 2 O 2 and glucose. E-GQDs allowed a rapid and sensitive detection of glucose with a detection limit of 0.006 mM for dynamic response range of 0.01–0.6 mM. The calculated higher value of V max (7.2 × 10 −7 M s −1 ) along with lower K m (0.012 mM) corroborate enhanced the peroxidase-like activity of E-GQDs. Study introduces a cheap and widely available raw material for the electrochemical synthesis of graphene quantum dots with commendable enzyme mimetic activity which may have a huge impact in developing calorimetric bioanalysis systems. [ABSTRACT FROM AUTHOR]

The effect of acetone on 3-aminopropyltrimethoxysilane (3-APTMS) mediated synthesis of gold nanoparticles (AuNPs) in polar protic, polar aprotic and non polar solvents specifically water, acetone and chloroform has been studied. The findings revealed that acetone promotes the formation of siloxane polymer in chloroform and acetone solvents, but not in water, while AuNPs are formed in all cases. The bifunctional nature of 3-APTMS [NH 2 (CH 2 ) 3 Si(OMe) 3 ] controls the formation of siloxane polymer through hydrolysis and condensation of trimethoxysilyl group whereas the amine moieties are likely to form imine linkage, which are involved in the synthesis of gold nanoparticles. The siloxane polymer with imine linkage can be formed both in absence and the presence of gold precursor (i.e. HAuCl 4 ). Accordingly, siloxane-gold nanoparticles can be made in different morphology, through control over the process, in three ways; (i) all precursors (Au 3+ , 3-APTMS and acetone) mixed simultaneously yielding [(siloxane-Au sim )], (ii) polymer made first followed by sequential reduction of Au 3+ in homogenous suspension forming (Au-siloxane homo ) seq and (iii) polymer made into thin film followed by sequential reduction of Au 3+ in the heterogeneous system yielding (Au-siloxane hetero ) seq . The AuNPs produced with the use of water as solvent is different from the three described above as discrete spherical AuNPs are formed as [(AuNPs) water ] and in this case siloxane polymer is not formed. The results based on AFM and SEM characterizations revealed porous morphology of NPs fabricated in chloroform/acetone, due to the formation of siloxane polymer, and non-porous morphology for the same in water. The “(Au-siloxane hetero ) seq ” efficiently promote the reduction of p-nitrophenol with good operational stability, justifying its interest for heterogeneous catalysis. On the other hand, (siloxane-Au sim ) and (Au-siloxane homo ) seq can be also deposited onto glassy carbon surfaces to yield polymer modified electrodes for subsequent electroanalytical applications. The cyclic voltammetry response of such modified electrodes to a redox probe (i.e., Fe(CN) 6 3 −/4 − ) was characteristic of diffusion controlled and thin-layer electrochemical behaviour respectively as a function of non-porous and porous nature of the polymer. The as made nanomaterial shows excellent biocatalyst for dopamine sensing based on peroxidase mimetic activity. The typical result on dopamine sensing is reported. [ABSTRACT FROM AUTHOR]

One-pot solvothermal treatment of Co(NO3)2·6H2O, H2L (5-(3-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl) isophthalic acid), and 4,4′-bipyridine (4,4′-bipy) in H2O/DMF (V/V = 1 : 1) yielded a cobalt-organic chain, [Co(L)(O)(H2O)2]n·1.25nH2O (1). Compound 1 as raw materials was calcined to obtain Co3O4, which could be confirmed by PXRD and SEM. Via the modification, Co3O4@SiO2-NH2 and Co3O4@SiO2-NH2-FA samples could be obtained. Compared to Co3O4@SiO2-NH2, Co3O4@SiO2-NH2-FA seems to have better peroxidase-mimetic properties. UV–vis results showed that optimal conditions of peroxidase-mimetic experiments were at 50°C in sodium acetate-acetic acid buffer (pH 3.6, 0.2 M), when the concentration of tetramethylbenzidine (TMB) was 0.2 mM. A concentration-dependent manner was shown between the concentration of glucose and absorbance in the measurement experiments for glucose. [ABSTRACT FROM AUTHOR]

Herein, via one-step pyrolysis of glucose, dicyandiamide (DCDA) and Fe containing metal–organic framework (Fe-MOF), small Fe 3 C nanoparticles were in-situ decorated in 3D porous network of N-rich graphene (NGr). The Fe-MOF served as size regulating precursor, layered g-C 3 N 4 (derived from pyrolysis of DCDA) acted as not only a template to guide the growth of small Fe 3 C nanoparticles, but also the carbon source for 3D porous NGr network. The intrinsic peroxidase-like catalytic activity of Fe 3 C/NGr was unpredictably discovered, by taking the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) with H 2 O 2 as a protocol. Fast and distinguished color change, improved stability in exposure to extreme H 2 O 2 concentration and high temperature were obtained. The Michaelis–Menten kinetics was investigated. The detection of glucose was accomplished over a wide concentration range of 2.0~500.0 μM 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 H 2 O 2 concentration and high temperature, endow Fe 3 C/NGr as one of the promising materials for fast visual colorimetry. [ABSTRACT FROM AUTHOR]

The well-dispersed Co 3 O 4 nanoparticles-decorated crumpled graphene microsphere (CGM) was successfully prepared by aerosol-assisted frying self-assembly and annealing process. It is found that the obtained Co 3 O 4 /CGM nanohybrid possessed enhanced intrinsic peroxidase-like activity and could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine by H 2 O 2 to produce a typical blue product. But the presence of ascorbic acid could induce the reduction of oxTMB to TMB, resulting in a significant blue color fading. Therefore, a simple, sensitive and selective colorimetric method to detect ascorbic acid was established with a good linear relationship (30–140 μM) and a low detection limit of 0.19 μM. Meanwhile, the selectivity, stability and repeatability were acceptable. It is also a facile route to fabricate nanoparticles/CGM as high-performance enzyme mimetic for colorimetric biosensing. [ABSTRACT FROM AUTHOR]

In this paper, a novel, convenient and sensitive colorimetric assay for acetylcholinesterase (AChE) activity and its inhibitor screening is successfully proposed based on the peroxidase-like activity of Prussian blue nanocubes (PB NCs). PB NCs can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 to develop a blue color and an absorption peak centered at 652 nm. AChE mediates the hydrolysis of acetylthiocholine (ATCh) to yield a reducing agent thiocholine (TCh) that cause the reduction of oxidized TMB and it can also chelate with Fe 3+ , both of which result in a blue color fading and a decrease of the absorbance. The generation of TCh is inhibited and the absorbance intensity is recovered after the introduction of AChE inhibitor. Consequently, the assay is also utilized in AChE inhibitor screening. The PB NCs-H 2 O 2 -TMB based platform is highly sensitive for AChE activity sensing with a low detection limit of 0.04 mU/mL. In addition, this assay has great potential in discriminatively determining AChE over other enzymes. The proposed method is fairly novel, simple and sensitive, which may pave the way for the detection of other hydrolytic enzyme activities with properly selected substrates. [ABSTRACT FROM AUTHOR]

Flexible biomimetic sensors have encountered a bottleneck of sensitivity and durability, as the sensors must directly work within complex body fluid with ultra-trace biomarkers. In this work, a wearable electrochemical sensor on a modified silk fibroin substrate is developed using gold nanoparticles hosted into N-doped porous carbonizated silk fibroin (AuNPs@CSF) as active materials. Taking advantage of the inherent biocompatibility and flexibility of CSF, and the high stability and enzyme-like catalytic activity of AuNPs, AuNPs@CSF-based sensor exhibits durable stability and superior sensitivity to monitor H 2 O 2 released from cancer cell (4T1) and glucose in sweat. The detection limits for H 2 O 2 and glucose are low to be 1.88 μM and 23 μM respectively, and the sensor can be applied in succession within 30 days at room temperature. Further, physical cross-linking of polyurethane (PU) with SF well matches with the skin tissue mechanically and provides a flexible, robust and stable electrode-tissue interface. AuNPs@CSF is applied successfully for wearable electrochemical monitoring of glucose in human sweat.The present AuNPs@CSF will possess a potential application in clinical diagnosing of H 2 O 2 - or glucose-related diseases in future. [ABSTRACT FROM AUTHOR]

In this study, we describe a novel peroxidase-like activity of Co-aminoclay [CoAC] present at pH ~5.0 and its application to fluorescent biosensor for the determination of H2O2 and glucose. It is synthesized with aminoclays (ACs) entrapping cationic metals such as Fe, Cu, Al, Co., Ce, Ni, Mn, and Zn to find enzyme mimicking ACs by sol–gel ambient conditions. Through the screening of catalytic activities by the typical colorimetric reaction employing 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)diammonium salt (ABTS) as a substrate with or without H2O2, Fe, Cu, and CoACs are found to exhibit peroxidase-like activity, as well as oxidase-like activity was observed from Ce and MnACs. Among them, CoAC shows exceptionally high peroxidase-like activity, presumably due to its ability to induce electron transfer between substrates and H2O2. CoAC is then used to catalyze the oxidation of Amplex® UltraRed (AUR) into a fluorescent end product, which enables a sensitive fluorescent detection of H2O2. Moreover, a highly sensitive and selective glucose biosensing strategy is developed, based on enzyme cascade reaction between glucose oxidase (GOx) and CoAC. Using this strategy, a highly linear fluorescence enhancement is verified when the concentration of glucose is increased in a wide range from 10 μM to 1 mM with a lower detection limit of 5 μM. The practical diagnostic capability of the assay system is also verified by its use to detect glucose in human blood serum. Based on these results, it is anticipated that CoAC can serve as potent peroxidase mimetics for the detection of clinically important target molecules.

In this work, we developed a highly sensitive and simple colorimetric method for glucose detection using poly(styrene sulfonate)/Pt-modified graphene nanosheets (PSS-GN-Pt) as peroxidase mimetics. First, in the presence of glucose, H 2 O 2 was generated as the main by-product of glucose oxidase (GOx)-catalyzed reaction. Then, the obtained H 2 O 2 triggered the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate blue color with the aid of PSS-GN-Pt nanocomposites as peroxidase mimetics. Via this method, as low as 9.28 × 10 −8 M glucose could be detected with a linear range from 2 × 10 −7 M to 1 × 10 −3 M. Besides absorbency measuring, the visual detection of glucose by naked eyes could also be realized very easily through the observable color changing from colorless to blue. In addition, this strategy was further used to determine the concentrations of glucose both in injection and serum samples with satisfying results. This proposed nanosystem holds great potential for diabetes mellitus research and can be easily expanded to the detection of various H 2 O 2 -involved analytes. [ABSTRACT FROM AUTHOR]

Three ferrites of type MFeO (where M is bivalent Fe, Co or Mn) dispersed on multi-walled carbon nanotubes (MWCNTs) were prepared by a coprecipitation method. Their electrocatalytic properties toward the reduction of HO at pH 7.4 were systematically compared. Catalytic reduction rates at an applied potential of −0.4 V (vs. Ag/AgCl) and pseudo Michaelis-Menten constants show the electrocatalytic ability to follows the order FeO > CoFeO > MnFeO. This diversity is attributed to the differences in the M(II) used and its occupancy on the lattice surface. The sensitivities are 120.98 ± 0.15, 48.45 ± 0.23 and 32.25 ± 0.27 μA cm mM, and the limits of detection are 0.98, 2.59 and 5.64 μM of HO (at an S/N ratio of 3). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We report herein the synthesis of water soluble Prussian blue nanoparticles (PBNPs) from single precursor potassium hexacynoferrate. It has been found that potassium hexacyanoferrate undergo rapid conversion into water soluble PBNPs in the presence of tetrahydrofuran (THF) and hydrogen peroxide (H 2 O 2 ) at 60 °C. The nanomaterial having average size to the order of 38 nm is highly stable as homogeneous suspension for longer period (>3 months). The as synthesized PBNPs is characterized by UV–vis spectroscopy, Fourier Transformation Infrared Spectroscopy (FT-IR), X-ray diffraction analysis (XRD), Energy dispersive spectroscopy (EDS), Transmission electron microscopy (TEM), and cyclic voltammetry. The PBNPs displays both homogeneous and heterogeneous catalysis having potentiality for H 2 O 2 sensing generated through glucose oxidase catalyzed oxidation of glucose. The Michaelis–Menten constant (K m ) and the maximal reaction velocity (V max ) for H 2 O 2 analysis are found to be 0.49 mM and 6.03 × 10 −7 M s −1 justifying the use of nanomaterial as perfect peroxidase replacement. The sensitivity and detection limit of H 2 O 2 analysis is found to the order of 156.5 μA mM −1 cm −2 and 50 nM respectively. [ABSTRACT FROM AUTHOR]

The luminescent carbon dots with peroxidase mimicking property had attracted considerable attention in biomedical field. In this work, iron-doped carbon dots (Fe-CDs) were prepared by one-pot hydrothermal method with 5, 10, 15, 20-tetra (4-borate phenyl)-21H, 23H-porphyrin Fe (II) (Fe-TBPP) as precursor. The obtained Fe-CDs emitted intense blue luminescence under ultraviolet light irradiation. Moreover, the Fe-CDs exhibited remarkable peroxidase mimicking property, which can efficiently catalyze the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) into blue ox-TMB in the presence of hydrogen peroxide (H 2 O 2 ). More importantly, the emission of Fe-CDs could be gradually quenched with the addition of H 2 O 2 . Based on these phenomena, a new optical dual-mode (colorimetric and fluorometric) method for the detection of H 2 O 2 and glucose was successfully established. The detection limits of glucose were calculated to be 3.86 and 7.27 μM (S/N = 3) respectively based on the colorimetric and fluorometric methods. Furthermore, we combined this dual-mode detection method with smartphone imaging. The colorimetric and fluorescent images were collected by recognition software of smartphone, which were then transformed into the corresponding HSL values for quantitative determination of glucose. Finally, the dual-mode approach based on Fe-CDs was used for the detection of glucose content in human serum, demonstrating the potential application of carbon dots in the biological area., 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.)

In the present study, we manifest that traditionally used gold nanoparticles when supported on molybdenum disulfide nanoribbons matrix (MoS 2 NRs–Au NPs) show synergistically enhanced intrinsic peroxidase like catalytic activity and can catalyze the oxidation of 3,3′,5,5′ tetramethyl benzidine by H 2 O 2 to produce a highly sensitive blue shade product depending on level of free cholesterol, when tested on complex system of human serum. Further the system attests appreciable kinetics, owing to K m value as low as 0.015 mM and better loading capacity ( V max =6.7×10 −6 M s −1 ). Additionally, the proposed system is stable for weeks with ability to perform appreciably in wide pH (3–6) and temperature range (25–60 °C). Utilizing this potential, the present work proposes a cholesterol detection color wheel which is used along with cost effective cholesterol detection strips fabricated out of proposed MoS 2 NRs–Au NPs system for quick and reliable detection of free cholesterol using unaided eye. [ABSTRACT FROM AUTHOR]

In the present study, we report graphene quantum dots (GQDs), an enzyme mimetic of horse radish peroxidase (HRP), for unprecedented detection of free cholesterol. Synthesized directly from graphite using simple and quick one step wet chemical method, these GQDs in the presence of H 2 O 2 exhibit highly efficient catalytic activity toward the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) to produce a blue colored product. The proposed detection system based on GQDs allows wide range (0.02–0.6 mM) of cholesterol sensing with a detection limit as low as 0.006 mM. Further, higher V max (7.3 × 10 −6 M s −1 ) along with lower K m (0.01 mM) attest enhanced peroxidase like catalytic activity and better binding affinity of cholesterol oxidase (ChOx) to cholesterol resulting in good biosensor stability and resistance to environmental interferences. The proposed method without the use of sophisticated instruments perceives the cholesterol using naked eye with blue color compound formation. The potential of the method to be applied on field is shown by the proposed cholesterol measuring color wheel, where the shades of color are related to actual levels of cholesterol in the sample. [ABSTRACT FROM AUTHOR]

Magnetic polymer particles with different surface functionalizations were prepared by a simple one-pot solvothermal method and characterized as peroxidase mimetics. The fluorescence enhancement obtained by attaching a β-cyclodextrin polymer (P β-CD ) to the surfaces of Fe 3 O 4 magnetic microspheres (Fe 3 O 4 MMs) to generate a Fe 3 O 4 /P β-CD composite allowed the rapid, sensitive and selective analysis of glucose. The catalytic activity of the Fe 3 O 4 /P β-CD composite was evaluated with regard to the effects of catalyst particle size and species, pH value, level of catalyst, benzoic acid concentration and reaction time. Detection limits of 0.015 μM for H 2 O 2 and 0.03 μM for glucose were determined when measuring at the 10-min mark. The presence of other saccharides, ion species, amino acids and proteins, had little effect on the results, and this technique was found to allow the analysis of glucose in human serum with high accuracy. The reusability of the Fe 3 O 4 /P β-CD composite was also investigated after 10 successive runs. A possible mechanism is proposed in which Fe 3 O 4 plays a significant role in inducing fluorescence and P β-CD enhances the fluorescence signal, acting as both a stabilizer and a phase transfer agent. [ABSTRACT FROM AUTHOR]

In this work, gold nanoparticles (AuNPs) assembled on the surface of iron based metal–organic frameworks (MOFs), Fe-MIL-88, are facilely prepared through electrostatic interactions using polyethyleneimine (PEI) molecules as linker. The resulting hybrid materials possess synergetic peroxidase-like activity. Because iron based metal–organic frameworks, Fe-MIL-88, exhibits highly peroxidase-like activity, and AuNPs has the distinct adsorption property to single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The peroxidase-like activity of Au@Fe-MIL-88 exhibit excellent switchable in response to specific DNA, ssDNA is easily adsorbed on the surface of the Au@Fe-MIL-88 hybrids, resulting in the reduce of the peroxidase-like activity of the hybrids. While it is recovered by the addition of target DNA, and the recovery degree is proportional to the target DNA concentration over the range of 30–150 nM with a detection limit of 11.4 nM. Based on these unique properties, we develop a label-free colorimetric method for DNA hybridization detection. In control experiment, base-mismatched DNA cannot induce recovery of the peroxidase-like activity. This detection method is simple, cheap, rapid and colorimetric. [ABSTRACT FROM AUTHOR]

A novel bacterial strain containing biogenic magnetic nanoparticles (BMNPs) was isolated from the sediments of Songhua River in Harbin, China, and was identified as Burkholderia sp. YN01. Extracted BMNPs from YN01 were characterized as pure face-centered cubic FeO with an average size of 80 nm through transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The hysteresis parameters of the BMNP samples such as B and B and ratios M/M were deduced as 35.6 mT, 43.2 mT, and 0.47, respectively, indicating that the BMNPs exhibit a ferromagnetic behavior. This is the first report concerning on biogenic FeO NPs produced in Burkholderia genus. Significantly, the BMNPs were proved to possess intrinsic peroxidase-like activity that could catalyze the oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of HO. Kinetic analysis indicates that the catalytic behavior is in accord with typical Michaelis-Menten kinetics and follows ping-pong mechanism. The catalytic constants ( K) were 6.5 × 10 s and 0.78 × 10 s with HO and TMB as substrate, respectively, which was higher than that of horseradish peroxidase (HRP). Electron spin resonance (ESR) spectroscopy experiments showed that the BMNPs could catalyze HO to produce hydroxyl radicals. The origin of peroxidase-like activity is also associated with their ability to transfer electron between electrode and HO according to an electrochemical study. As a novel peroxidase mimetic, the BMNPs were employed to offer a simple, sensitive, and selective colorimetric method for HO and glucose determination, and the BMNPs could efficiently catalyze the degradation of phenol and Congo red dye. [ABSTRACT FROM AUTHOR]

Enzyme mimetics have recently attracted considerable interest because of their high stability and low cost. We developed a general H2O2-involved fluorescence system using Fe3O4 magnetic microspheres as peroxidase mimetics and benzoic acid (BA) as indicator. Glucose and p-nitrophenol were used as models to determine the characteristics and effectiveness of the system. Glucose oxidase hydrolyzes glucose, in the presence of oxygen, to H2O2 followed by the activation of Fe3O4 MMs, resulting in the catalyzed oxidation of benzoic acid. Glucose can be determined by the quantitative fluorescence production. p-Nitrophenol is determined as model compounds which competes with benzoic acid for H2O2 resulting in the decreased catalytic oxidation of benzoic acid with the Fe3O4 MMs. The detection limit of the Fe3O4/H2O2/BA system is 0.008 μM for H2O2, 0.025 μM for glucose and 0.05 μM for p-nitrophenol. Furthermore, the system had high sensitivity, good selectivity and was capable of sensing glucose in human serum and p-nitrophenol in water samples. The proposed system has great potential in the chemical/biological sensing of a variety of analytes associated with reactions that produce or consume H2O2. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of Pd-WO3-SiO2-PB nanocomposite. [•] Peroxidase mimetic ability of the WO3. [ • ] Pd-WO 3 -SiO 2 -PB nanocomposite shows excellent electrocatalytic ability for biomedical applications. [•] Pd-WO3-SiO2-PB nanocomposite shows better immobilzation matrix for enzyme. [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel process for the synthesis of water dispersible Prussian blue nanoparticles (PBNPs). [•] Tetrahydrofuran hydroperoxide precisely convert single precursors K3[Fe(CN)6] into PBNPs. [•] PBNPs show both homogeneous and heterogeneous catalysis. [•] Colorimetric determination of GSH based on competitive reaction of o-dianisidine and GSH with H2O2 catalyzed by PBNPs. [•] PBNPs show electrocatalytic reduction of lipid hydroperoxides with better selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel dual signal amplification strategy was proposed based on hollow platinum nanoparticles decorated Fe3O4 nanoparticles (HPtNPs-Fe3O4) and glucose oxidase (GOD) for sensitive detection of α-1-fetoprotein (AFP). In such system, HPtNPs-Fe3O4 couples with glucose oxidase to form a pseudobienzymatic system because both HPtNPs and Fe3O4 nanoparticles (NPs) have peroxidase-like catalytic activity and this peroxidase mimetic is more stable and economical than natural peroxidases. With the employment of bovine serum albumin (BSA), the biocompatibility, stability and water solubility of Fe3O4 NPs was further enhanced. The BSA functionalized Fe3O4 NPs provided lysine groups to immobilized HPtNPs, antibodies and GOD, which further amplified the detection signal. The results show that the sensor exhibited attractive redox electrochemical activity and high catalysis activity when detected in the working buffer containing 3.6mM D-glucose. The electrochemical immunosensor exhibited a linear range of 0.01–60ng/mL with a low detection limit of 1.6pg/mL. [Copyright &y& Elsevier]

Abstract: In this article, for the first time, two-dimensional hybrid mesoporous Fe2O3–graphene (mFe2O3–G) nanostructures were developed as a peroxidase mimetic with catalytic activities superior to those of mFe2O3, G, and previously reported Fe-based peroxidase mimetics. The high-surface-area mFe2O3 not only offers a large number of catalytically active sites, but also facilitates the diffusion of 3,3,5,5-tetramethylbenzidine (TMB) and H2O2 toward G surface. On the other hand, G is π-rich and thus favors the adsorption and enrichment of TMB within these pores. These synergistic effects lead to highly improved catalytic performances. Based on these findings, a simple, rapid, and highly sensitive and selective optical detector of glucose has been developed and demonstrated in buffer solution with a pretty low detection limit of 0.5μM. In addition, this nanosensor is reusable and can also be used for glucose detection in diluted serum. [Copyright &y& Elsevier]

The development of a high-efficiency and stable heterogeneous catalyst has great significance for the recycling treatment of printing and dyeing wastewater. The flower-like Cu 9 S 8 with super large macroporous (d = 133.78 nm) was prepared using porous CuO that was synthesized by the sacrificial template method. The peroxidase mimics activity of flower-like Cu 9 S 8 was determined by catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with H 2 O 2. The kinetic constants (K m = 0.449 mM) displayed that the flower-like Cu 9 S 8 showed excellent affinity to H 2 O 2 , which was 8 times lower than that of horseradish peroxidase (HRP). The results of degradation experiments on different kinds of organic dyes showed that the Cu 9 S 8 had a wide application range in the degradation of different dyes with the degradation rate over 98%, and the removal rate of total organic carbon reached 78.2%. The flower-like Cu 9 S 8 can be a candidate catalyzer in the field of printing and dyeing wastewater treatment due to its high catalytic cycle stability and wide pH application range (3.0–8.0). [Display omitted] • The large pore size flower-like Cu 9 S 8 (d = 133.78 nm) was prepared by the sacrificial template method. • The affinity of flower-like Cu 9 S 8 to H 2 O 2 is 8 times higher than that of HRP (K m = 0.449 mM). • Flower-like Cu 9 S 8 has a strong universality for organic dyes, and the TOC removal rate reaches 78.2%. [ABSTRACT FROM AUTHOR]

Highlights: [•] The well-dispersed Co3O4 NPs on rGO surfaces were successfully synthesized. [•] The as-obtained Co3O4/rGO nanocomposites exhibit an effective peroxidase-like activity. [•] They can catalyze the oxidation of TMB by H2O2 to produce an intensified blue reaction. [•] The Co3O4/rGO-based colorimetric and visual biosensing of glucose was developed. [ABSTRACT FROM AUTHOR]

Abstract: We prepared a new positively-charged gold nanoparticle ((+)AuNPs)–single-walled carbon nanotubes (SWNTs) nanohybrids. The results showed that small (+)AuNPs dispersed uniformly on the surface of SWNTs. Importantly the resulting nanohybrids exhibited fascinating peroxidase-like activity, which can catalyze oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) by H2O2 to develop a blue color in aqueous solution. Furthermore, single-stranded DNA (ss-DNA) can resist salt-induced (+)AuNPs–SWNTs nanohybrids aggregation, whereas double-stranded DNA (ds-DNA) can not inhibit salt-induced nanohybrids aggregation. Based on these unique properties of the (+)AuNPs–SWNTs nanohybrids, we developed a label-free colorimetric method for DNA hybridization detection. The response to target DNA concentration was linear in the range of 0.025–0.5μM with a detection limit of 2nM (3σ). Based on the specific recognition of aptamer, the method can be extended to detect non-nucleic acid targets such as cocaine. The present limit of detection for cocaine is 2nM. The method offers the advantages of simple, cheap, rapid and sensitive. [Copyright &y& Elsevier]