Oxidase Mimic Research Articles

In Situ Enzymatically Generated Photoswitchable Oxidase Mimetics and Their Application for Colorimetric Detection of Glucose Oxidase.

In this study, a simple and amplified colorimetric assay is developed for the detection of the enzymatic activity of glucose oxidase (GOx) based on in situ formation of a photoswitchable oxidase mimetic of PO43−-capped CdS quantum dots (QDs). GOx catalyzes the oxidation of 1-thio-β-d-glucose to give 1-thio-β-d-gluconic acid which spontaneously hydrolyzes to β-d-gluconic acid and H2S; the generated H2S instantly reacts with Cd2+ in the presence of Na3PO4 to give PO43−-stabilized CdS QDs in situ. Under visible-light (λ ≥ 400 nm) stimulation, the PO43−-capped CdS QDs are a new style of oxidase mimic derived by producing some active species, such as h+, •OH, O2•− and a little H2O2, which can oxidize the typical substrate (3,3,5,5-tetramethylbenzydine (TMB)) with a color change. Based on the GOx-triggered growth of the oxidase mimetics of PO43−-capped CdS QDs in situ, we developed a simple and amplified colorimetric assay to probe the enzymatic activity of GOx. The proposed method allowed the detection of the enzymatic activity of GOx over the range from 25 μg/L to 50 mg/L with a low detection limit of 6.6 μg/L. We believe the PO43−-capped CdS QDs generated in situ with photo-stimulated enzyme-mimicking activity may find wide potential applications in biosensors.

Polyacrylic acid-coated cerium oxide nanoparticles: An oxidase mimic applied for colorimetric assay to organophosphorus pesticides

It is important and urgent to develop reliable and highly sensitive methods that can provide on-site and rapid detection of extensively used organophosphorus pesticides (OPs) for their neurotoxicity. In this study, we developed a novel colorimetric assay for the detection of OPs based on polyacrylic acid-coated cerium oxide nanoparticles (PAA-CeO2) as an oxidase mimic and OPs as inhibitors to suppress the activity of acetylcholinesterase (AChE). Firstly, highly dispersed PAA-CeO2 was prepared in aqueous solution, which could catalyze the oxidation of TMB to produce a color reaction from colorless to blue. And the enzyme of AChE was used to catalyze the substrate of acetylthiocholine (ATCh) to produce thiocholine (TCh). As a thiol-containing compound with reducibility, TCh can decrease the oxidation of TMB catalyzed by PAA-CeO2. Upon incubated with OPs, the enzymatic activity of AChE was inhibited to produce less TCh, resulting in more TMB catalytically oxidized by PAA-CeO2 to show an increasing blue color. The two representative OPs, dichlorvos and methyl-paraoxon, were tested using our proposed assay. The novel assay showed notable color change in a concentration-dependent manner, and as low as 8.62 ppb dichlorvos and 26.73 ppb methyl-paraoxon can be readily detected. Therefore, taking advantage of such oxidase-like activity of PAA-CeO2, our proposed colorimetric assay can potentially be a screening tool for the precise and rapid evaluation of the neurotoxicity of a wealth of OPs.

Correction: Enhanced luminol–O2 chemiluminescence reaction by CuO nanoparticles as oxidase mimics and its application for determination of ceftazidime

Correction for ‘Enhanced luminol–O2 chemiluminescence reaction by CuO nanoparticles as oxidase mimics and its application for determination of ceftazidime’ by Mortaza Iranifam et al., Anal. Methods, 2016, 8, 3816–3823.

Enhanced luminol–O2 chemiluminescence reaction by CuO nanoparticles as oxidase mimics and its application for determination of ceftazidime

A cursory survey of the literature shows that although peroxidase-like activity is a well-known and well-applied property of CuO nanoparticles (CuO NPs), the oxidase-like activity of CuO NPs is a property that is somehow neglected to be incorporated in analytical applications.

Highly sensitive electrochemical sensing platform for lead ion based on synergetic catalysis of DNAzyme and Au–Pd porous bimetallic nanostructures

In this work, a sensitive and specific electrochemical biosensor for lead ion (Pb2+) detection was developed by coupling with synergetic catalysis of porous Au–Pd bimetallic nanoparticles and hemin/G-quadruplex-based DNAzyme. In the presence of target Pb2+, the substrate strand was cleaved and the enzyme strand was released. Subsequently, G-rich DNA-labeled Au–Pd bimetallic nanoparticle was linked with the released enzyme strand through the helper DNA. Upon addition of hemin, a large number of hemin/G-quadruplex-based DNAzyme molecules were formed on the electrode to serve as nicotinamide adenine dinucleotide hydrogen (NADH) oxidase and peroxidase mimics. DNAzyme could catalyzed the reduction of H2O2, generated from NADH in the presence of O2, to produce an electrochemical signal when using thionine as the electron mediator. Introduction of porors Au–Pd bimetallic nanoparticles could enhance the detectable signal and cause the increase in the sensitivity. Experimental results showed that the variations (∆I) in the cathodic peak currents of the biosensor were linearly dependent on target Pb2+ concentrations from 1.0pM to 100nM with a detection limit (LOD) of 0.34pM. The excellent performance of the sensing platform indicated its promising prospect as a valuable tool for simple and cost-effective Pb2+ detection in practical application.

Ligand-dependent oxidation of copper bound α-amino-isobutyric acid as 1-aminocyclopropane-1-carboxylic acid oxidase mimics

As a continuity of the [CuII(AIB)(bpy)(H2O)](ClO4)2-containing (1) ACCO (1-aminocyclopropane-1-carboxylate oxidase) model, two new copper(II)–amino acid complexes [CuII2(AIB)2(PBI)2(CH3OH)(ClO4)]ClO4 (2) and [CuII2(AIB)2(PBT)2(H2O)](ClO4)2·CH3OH (3) with a modified hetero-bidentate ligands (PBT=2-pyridin-2-yl-benzothiazole and PBI=2-pyridin-2-yl-1H-benzoimidazole) have been synthesized, characterized by various techniques including IR, UV–Vis, electrochemical and X-ray measurements, and investigated their reactivity toward H2O2 with respect to the redox behavior compare to 1.

Evaluation of the antioxidant activity of phenols and tannic acid determination with Mn3O4nano-octahedrons as an oxidase mimic

Mn3O4nano-octahedrons as an effective oxidase mimic for the preliminary assessment of phenols' antioxidant activity and visual determination of tannic acid were demonstrated.

PB@Co3O4 nanoparticles as both oxidase and peroxidase mimics and their application for colorimetric detection of glutathione

Co3O4-modified Prussian blue nanocubes (PB@Co3O4) were obtained by using a water-bath method and were found to exhibit both intrinsic oxidase-like and peroxidase-like activities.

Bifunctionalized mesoporous silica-supported gold nanoparticles: intrinsic oxidase and peroxidase catalytic activities for antibacterial applications.

Bifunctionalized mesoporous silica-supported gold nanoparticles as oxidase and peroxidase mimics for antibacterial applications are demonstrated. For the first time, these mesoporous silica-supported gold nanoparticles are applied as oxidase and peroxidase mimics. Taking advantage of their prominent enzyme activities, the MSN-AuNPs show excellent antibacterial properties against both Gram-negative and Gram-positive bacteria. Furthermore, MSN-AuNPs also exhibit outstanding performance in biofilm elimination .

Mercury(ii)-stimulated oxidase mimetic activity of silver nanoparticles as a sensitive and selective mercury(ii) sensor

Research on oxidase mimics is challenging but important. In this article, mercury(II) ion enabled citrate-capped silver nanoparticles (Cit–AgNPs) exhibit catalytic activity toward the oxidation of typical chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by dissolved oxygen under mild conditions, suggesting a new type of oxidase mimic. In addition, the oxidase-like activity of Cit–AgNPs was sensitive to the concentration of mercury(II) ions and selective towards mercury(II) ions among other metal ions. Based on this, a facile colorimetric mercury(II) ion sensor was developed. Hg2+ was reduced on the surface of Cit–AgNPs to form Hg–Ag alloys. The Hg–Ag alloys activated oxygen and generated superoxide anions, which oxidized TMB. This discovery indicates the potential of nanoparticles for efficient enzyme mimetics.

CoFe2O4 Nanoparticles as Oxidase Mimic-Mediated Chemiluminescence of Aqueous Luminol for Sulfite in White Wines

Recently, the intrinsic enzyme-like activity of nanoparticles (NPs) has become a growing area of interest. However, the analytical applications of the NP-based enzyme mimetic are mainly concentrated on their peroxidase-like activity; no attempts have been made to investigate the analytical applications based on the oxidase mimic activities of NPs. For the first time, we report that CoFe(2)O(4) NPs were found to possess intrinsic oxidase-like activity and could catalyze luminol oxidation by dissolved oxygen to produce intensified chemiluminescence (CL). The effect of sulfite on CoFe(2)O(4) NP oxidase mimic-mediated CL of aqueous luminol was investigated. It is very interesting that when adding sulfite to the luminol-CoFe(2)O(4) system, the role of sulfite in the luminol-CoFe(2)O(4) NP-sulfite system depends on its concentration. At a relatively low concentration level, sulfite presents an inhibition effect on the luminol-CoFe(2)O(4) NP system. However, it does have an enhancement effect at a higher concentration level. Investigations on the effect of the solution pH and luminol and CoFe(2)O(4) NP concentrations on the kinetic characteristics of the studied CL system in the presence of trace sulfite suggested that the enhancement and inhibition of the luminol-CoFe(2)O(4) NP-sulfite CL system also depended on the solution pH. It seems that the concentrations of luminol and CoFe(2)O(4) NPs did not influence the CL pathway. The possible mechanism of the luminol-CoFe(2)O(4) NP-sulfite CL system was also discussed. On this basis, a flow injection chemiluminescence method was established for the determination of trace sulfite in this study. Under the optimal conditions, the proposed system could respond down to 2.0 × 10(-8) M sulfite. The method has been applied to the determination of trace sulfite in white wine samples with satisfactory results. The results given by the proposed method are in good agreement with those given by the standard titration method.

BSA-templated MnO2 nanoparticles as both peroxidase and oxidase mimics

Inorganic nanomaterials that mimic enzymes are fascinating as they potentially have improved properties relative to native enzymes, such as greater resistance to extremes of pH and temperature and lower sensitivity to proteases. Although many artificial enzymes have been investigated, searching for highly-efficient and stable catalysts is still of great interest. In this paper, we first demonstrated that bovine serum albumin (BSA)-stabilized MnO(2) nanoparticles (NPs) exhibited highly peroxidase-, oxidase-, and catalase-like activities. The activities of the BSA-MnO(2) NPs were evaluated using the typical horseradish peroxidase (HRP) substrates o-phenylenediamine (OPD) and 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of either hydrogen peroxide or dissolved oxygen. These small-sized BSA-MnO(2) NPs with good dispersion, solubility and biocompatibility exhibited typical Michaelis-Menten kinetics and high affinity for H(2)O(2), OPD and TMB, indicating that BSA-MnO(2) NPs can be used as satisfactory enzyme mimics. Based on these findings, BSA-MnO(2) NPs were used as colorimetric immunoassay tags for the detection of goat anti-human IgG in place of HRP. The colorimetric immunoassay using BSA-MnO(2) NPs has the advantages of being fast, robust, inexpensive, easily prepared and with no HRP and H(2)O(2) being needed. These water-soluble BSA-MnO(2) NPs may have promising potential applications in biotechnology, bioassays, and biomedicine.

Formation of PdPt Alloy Nanodots on Gold Nanorods: Tuning Oxidase-like Activities via Composition

The island growth mode of Pt was employed to guide the forma-tion of PdPt alloy nanodots on gold nanorods (Au@PdPt NRs). Well-defined alloy nanodots, with tunable Pd/Pt ratios from 0.2 to 5, distribute homogeneously on the surface of the Au NR. Formation of nanodots shell leads to the red-shift and broadening of the longitudinal surface plasmon resonance (LSPR) band of the Au NRs. The Au@PdPt alloy NRs exhibit catalytic activity toward oxidation of often-used chromogenic substrates by dissolved oxygen under mild conditions, suggesting a new type of oxidase mimics. Composition dependence catalytic activity is observed for the oxidation of ascorbic acid (AA) and 3,3',5,5'-tetramethylbenzidine (TMB) and for the reduction of p-nitrophenol. For AA and TMB, catalytic activity enhances quickly at lower Pd/Pt ratios and tends to saturate at higher Pd/Pt ratios. For p-nitrophenol reduction, catalytic activity shows a nice linear relationship with Pd/Pt ratio owing to much higher catalytic activity of Pd. In conclusion, proper alloying of Pd and Pt presents an effective route to tailor the catalytic activity. Interesting, alloy nanodots can also catalyze the oxidation of Fe (II) to Fe (III) by dissolved oxygen. Thus, based on the competitive oxidation of TMB and Fe (II), selective detection of the latter can be achieved.

Screening of inhibitors for oxidase mimics of Au@Pt nanorods by catalytic oxidation of OPD

Nanostructured materials are a new class of enzyme mimics, the inhibitors of which have not been studied. Herein, we demonstrate the screening of inhibitors for Au@Pt nanorod (NR) oxidase mimics. In addition, based on the enzyme inhibition reaction, determination of "poisoning" inhibitors is demonstrated.

A flexible hydroxy-bridged dicopper complex as catechol oxidase mimic

The molecular structure of [Cu 2 (4′MeInd) 2 (MeOH)(μ-OH)]ClO 4 ·MeOH [4′MeIndH = 1,3-bis(4′-methyl-2-pyridylimino)isoindoline] was fully determined by IR, UV–Vis, and X-ray crystal analysis. With the flexible hydroxy-bridged isoindoline-containing dicopper complex has been shown that it does not maintain its dimeric nature when catalyzing catechol oxidase-like reaction. A flexible hydroxy-bridged dicopper complex with isoindoline ligand has prepared and characterized and shown that it does not maintain its dimeric nature when catalyzing catechol oxidase-like reaction.

Oxidation of Unactivated Primary Aliphatic Amines Catalyzed by an Electrogenerated 3,4‐Azaquinone Species: A Small‐Molecule Mimic of Amine Oxidases

High catalytic performance of the electrogenerated amine oxidase mimic 3,4-iminoquinone 1ox is observed under metal-free conditions in the chemoselective oxidation reaction of unactivated primary aliphatic amines.

Cu(II)-nitroxyl radicals as catalytic galactose oxidase mimics.

Results from Hammett correlation studies and primary kinetic isotope effects for the CuCl-TEMPO catalysed aerobic benzyl alcohol oxidations are inconsistent with an oxoammonium based mechanism. We postulate a copper-mediated dehydrogenation mechanism, in which TEMPO regenerates the active Cu(II)-species. This mechanism is analogous to that observed for Galactose Oxidase and mimics thereof.