Copper nanoclusters as peroxidase mimetics and their applications to H2O2 and glucose detection

Copper nanoclusters (Cu NCs) are found to possess intrinsic peroxidase-like activity for the first time. Similar to nature peroxidase, they can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine by H₂O₂ to produce a nice blue color reaction. Compared with horseradish peroxidase, Cu NCs exhibits higher activity near neutral pH, which is beneficial for biological applications. The increase in absorbance caused by the Cu NCs catalytic reaction allows the detection of H₂O₂ in the range of 10 μM to 1 mM with a detection limit of 10 μM. A colorimetric method for glucose detection was also developed by combining the Cu NCs catalytic reaction and the enzymatic oxidation of glucose with glucose oxidase. Taking into account the advantages of ultra-small size, good stability, and high biocompatibility in aqueous solutions, Cu NCs are expected to have potential applications in biotechnology and clinical diagnosis as enzymatic mimics.     

Native carbon nanodots as a fluorescent probe for assays based on the use of glucose oxidase or horseradish peroxidase

We report on a sensitive and selective fluorescent assay utilizing native carbon dots (CDs) as signal transducers. The optical probes 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) or 3,3′-diaminobenzidine (DAB) were employed as substrates of horseradish peroxidase (HRP). It was found that the corresponding oxidation products (ox-ABTS or ox-DAB) quench the fluorescence of CDs, mainly via photoinduced electron transfer in case of ox-ABTS, and via aggregation and inner filter effect in case of ox-DAB. By coupling with bienzyme (glucose oxidase and HRP)-mediated biocatalytic reactions, the method was applied to the determination of hydrogen peroxide and glucose. In case of ABTS as the substrate of HRP, a wide linear range (0.05 to 100 μM) and a very low detection limit (10 nM) for glucose were attained. The method was applied to the determination of glucose in human serum and the results were found to agree well with data provided by a local hospital.

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Graphical abstract In this work, a sensitive and selective fluorescent assay was developed for probing the enzymatic substrates of hydrogen peroxide and glucose which utilized native carbon dots (CDs) as signal transducer.

     

Carbon nanodots as fluorescence probes for rapid, sensitive, and label-free detection of Hg2+ and biothiols in complex matrices

In this work, unmodified carbon nanodots are demonstrated as novel and environmentally-friendly fluorescence probes for the sensing of Hg(2+) and biothiols with high sensitivity and selectivity.     

Aromatic derivatives and tellurium analogues of cyclic seleninate esters and spirodioxyselenuranes that act as glutathione peroxidase mimetics

[Reaction: see text]. Several novel organoselenium and tellurium compounds were prepared and evaluated as mimetics of the selenoenzyme glutathione peroxidase, which protects cells from oxidative stress by reducing harmful peroxides with the thiol glutathione. The compounds were tested for catalytic activity in a model system wherein tert-butyl hydroperoxide or hydrogen peroxide were reduced with benzyl thiol and the rate of the reaction was measured by monitoring the formation of dibenzyl disulfide. Thus, aromatic derivatives 19, 22, 24, and 25 proved to be inferior catalysts compared to the parent cyclic seleninate ester 14 and spirodioxyselenurane 16. In the case of 19 and 22, this was the result of their rapid conversion to the relatively inert selenenyl sulfides 31 and 32, respectively. In general, hydrogen peroxide was reduced faster than tert-butyl hydroperoxide in the presence of the selenium-based catalysts. The cyclic tellurinate ester 27 and spirodioxytellurane 29 proved to be superior catalysts to their selenium analogues 14 and 16, respectively, resulting in the fastest reaction rates by far of all of the compounds we have investigated to date. Oxidation of 29 with hydrogen peroxide produced the unusual and unexpected peroxide 33, in which two hypervalent octahedral tellurium moieties are joined by ether and peroxide bridges. The structure of 33 was confirmed by X-ray crystallography. Although 33 displayed strong catalytic activity when tested independently in the model system, its relatively slow formation from the oxidation of 29 rules out its intermediacy in the catalytic cycle of 29.     

Revisiting catechol derivatives as robust chromogenic hydrogen donors working in alkaline media for peroxidase mimetics

Colloidal noble metal-based nanoparticles are able to catalyze oxidation of chromogenic substrates by H₂O_2, similarly to peroxidases, even in basic media. However, lack of robust chromogens, which work in high pH impedes their real applications. Herein we demonstrate the applicability of selected catechol derivatives: bromopyrogallol red (BPR) and pyrogallol (PG) as chromogenic substrates for peroxidase-like activity assays, which are capable of working over wide range of pH, covering also basic values. Hyperbranched polyglycidol-stabilized gold nanoparticles (HBPG@AuNPs) were used as model enzyme mimetics. Efficiency of several methods of improving stability of substrates in alkaline media by means of selective suppression of their autoxidation by molecular oxygen was evaluated. In a framework of presented studies the impact of borate anion, applied as complexing agent for PG and BPR, on their stability and reactivity towards oxidation mediated by catalytic AuNPs was investigated. The key role of high concentration of hydrogen peroxide in elimination of non-catalytic oxidation of PG and improvement of optical properties of BPR in alkaline media containing borate was underlined. Described methods of peroxidase-like activity characterization with the use of BPR and PG can become universal tools for characterization of nanozymes, which gain various applications, among others, they are used as catalytic labels in bioassays and biosensors.     

Synthesis of tetrahydroisoquinoline-based pseudopeptides and their characterization as suitable reverse turn mimetics

New peptidomimetics containing the Tic moiety were synthesized in enantiomerically pure form and their conformational features were studied by NMR, IR, and molecular modeling techniques. The presence of a reverse turn conformation was observed in all the structures, suggesting the key role of the scaffold as reverse turn inducer. In particular, all the analyses led to the conclusion that a β-turn conformation is mostly stabilized in tetrapeptide mimetic 4b and in hexapeptide mimetics 5a,b. In the case of 5a,b, the C1 stereochemistry plays a central role in determining stable conformations, supporting the formation of a β-hairpin arrangement with a 14-membered intramolecular hydrogen bond ring only in 5b.     

Colorimetric quantification of galactose using a nanostructured multi-catalyst system entrapping galactose oxidase and magnetic nanoparticles as peroxidase mimetics

A colorimetric method for quantification of galactose, which utilizes a nanostructured multi-catalyst system consisting of Fe(3)O(4) magnetic nanoparticles (MNPs) and galactose oxidase (Gal Ox) simultaneously entrapped in large pore sized mesocellular silica, is described. Gal Ox, immobilized in a silica matrix, promotes reaction of galactose to generate H(2)O(2) that subsequently activates MNPs in silica mesopores to convert a colorimetric substrate into a colored product. By using this colorimetric method, galactose can be specifically detected. Along with excellent reusability via application of simple magnetic capturing, enhanced operational stability was achieved by employing a cross-linked enzyme aggregate (CLEA) method for Gal Ox immobilization. This protocol leads to effective prevention of enzyme leaching from the pores of mesocellular silica. The analytical utility of the new colorimetric biosensor was demonstrated by its use in diagnosing galactosemia, a genetic metabolic disorder characterized by the inability to utilize galactose, through analysis of clinical dried blood spot specimens. A microscale well-plate format was employed that possesses a multiplexing capability. The multi-catalyst system entrapping Gal Ox and MNPs represents a new approach for rapid, convenient, and cost-effective quantification of galactose in human blood and it holds promise as an alternative method for galactosemia diagnosis, replacing the laborious procedures that are currently in use.     

Magnetic carbon nitride nanocomposites as enhanced peroxidase mimetics for use in colorimetric bioassays,and their application to the determination of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

Graphite-like carbon nitride ? Fe₃O₄ magnetic nanocomposites were synthesized by a chemical co-precipitation method. The nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, FTIR spectroscopy, X-ray photoelectron spectroscopy and magnetization hysteresis loops. The nanocomposites exhibit enhanced peroxidase-like activity (compared to that of graphite-like carbon nitride or Fe₃O₄ NPs). More specifically, they are capable of catalyzing the oxidation of different peroxidase substrates (such as TMB, ABTS or OPD) by H₂O₂ to produce the typical color reactions (blue, green or orange). The nanocomposites retain their magnetic properties and can be separated by an external magnet. On the basis of these findings, a highly sensitive and selective method was applied to the determination of H₂O₂ and glucose (by using glucose oxidase). It was successfully applied to the determination of glucose in (spiked) human serum. Compared to other nanomaterial-based peroxidase mimetics, the one described here provides distinctly higher sensitivity for both H₂O₂ and glucose, with detection limits as low as 0.3 μM and 0.25 μM, respectively.

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Graphical abstract The magnetic carbon nitride nanocomposite exhibits enhanced peroxidase-like activity that is much larger than that of graphite-like carbon nitride or Fe₃O₄ NPs alone. This finding was applied to design a highly sensitive and selective colorimetric assay for H₂O₂ and glucose.

     

Aziridine ring opening as regio- and stereoselective access to O-glycosyl amino acids and their transformation into O-glycopeptide mimetics

Glycosyl amino acid mimetics of the typical GalNAc-(1→O)-Ser/Thr motif of O-glycopeptides were synthesised. Starting from galactose a 1,5-anhydro derivative could be obtained and regio- and stereoselectively coupled to serine- or threonine-derived aziridine compounds, respectively. The corresponding Fmoc derivatives could be used to prepare two 13-mer glycopeptides of the mucin MUC1 carrying instead of Ser-2 or Th-5, the corresponding O-glcycosyl amino acid mimetics.     

Iterative synthesis of spacered glycodendrons as oligomannoside mimetics and evaluation of their antiadhesive properties

Dendrimer chemistry is an attractive concept for mimicry of the highly branched character of the bioactive carbohydrates found as part of a cell's sugar coat, called the glycocalyx. Glycodendrimers have thus been used to study biological processes occurring on cell surfaces, such as bacterial adhesion. This paper details a new approach in glycodendrimer synthesis, in which a 3,6-diallylated carbohydrate is utilised as core molecule, hydroboration-oxidation is the activating step, and glycosylation with branched and unbranched sugar trichloroacetimidates is used for dendritic growth. To obtain pure dendritic pseudo-tri- and -heptasaccharides in good yields, radical addition of mercaptoethanol to peripheral double bonds was also evaluated with great success. A collection of six new hyperbranched glycodendrons was tested for their potential as inhibitors of type 1 fimbriae-mediated bacterial adhesion in an ELISA and the results were interpreted with regard to sugar valency and spacer characteristics.     

Substituent effects upon the catalytic activity of aromatic cyclic seleninate esters and spirodioxyselenuranes that act as glutathione peroxidase mimetics

Substituent effects were studied in a series of aromatic cyclic seleninate esters and spirodioxyselenuranes that function as mimetics of the antioxidant selenoenzyme glutathione peroxidase. The methoxy-substituted selenurane proved the most efficacious catalyst for the reduction of hydrogen peroxide with benzyl thiol, and the reaction rates were enhanced for both classes by electron-donating substituents. Hammett plots indicated rho = -0.45 and -3.1 for the seleninates and selenuranes, respectively, suggesting that oxidation at Se is the rate-determining step in their catalytic cycles.     

二氧化铈纳米微粒过氧化物酶活性及其在葡萄糖检测中的应用

合成了一种稳定和水溶性的聚丙烯酸修饰CeO2 NPs,利用动态光散射(DLS)、傅里叶变换红外光谱(FT-IR)和X射线光电子能谱(XPS)进行表征.结果表明,CeO2 NPs能够催化H2O2氧化3,3′,5,5′-四甲基联苯胺(TMB)发生显色反应,表现出过氧化物模拟酶催化活性.利用Raman和顺磁共振(EPR)光谱技术研究了其催化机理.基于CeO2 NPs催化TMB变色反应对H2O2浓度的依赖性和葡萄糖氧化酶能够催化溶解氧氧化葡萄糖产生H2O2的原理,构建了一种简单、灵敏、选择性高的测定血清中葡萄糖的检测方法.在优化条件下,测定葡萄糖的线性范围为0.5~10 mmol/L,检出限(3σ)为0.1 mmol/L.对1.0 mmol/L葡萄糖进行11次平行测定,其相对标准偏差为2.4%.该方法已成功用于血清样品中葡萄糖的测定.     

Spherical polyelectrolyte brushes as bio-platforms to integrate platinum nanozyme and glucose oxidase for colorimetric detection of glucose

The integration of nanozyme and natural enzyme for cascade reactions has attracted great attention due to their huge potential applications in detection, biomedicine, and catalysis. Here the novel cascade bio-platforms were fabricated by using spherical poly[(2-methacryloyloxyethyl)trimethyl ammonium chloride] (PMOTA) brushes (SPB) as nanoreactors to prepare platinum nanoparticles in situ and as nanocarriers to immobilize glucose oxidase (GOX). The generated Pt nanoparticles possess high stability and peroxidase-like properties, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate blue colored oxidized TMB (oxTMB). And the absorbed GOX can specifically catalyze the oxidation of glucose into gluconic acid and H₂O₂, while the produced H₂O₂ is subsequently catalyzed by the Pt nanozymes. Thus, the co-immobilized Pt nanozymes and GOX within SPB (SPB@Pt@GOX) acted as effective biosensors for colorimetric detection of glucose showing high selectivity and great feasibility. This work demonstrates a facile and general strategy to use SPB as bio-platforms to integrate nanozymes and natural enzymes for cascade reactions.     

Preparation of grain size controlled boron-doped diamond thin films and their applications in selective detection of glucose in basic solutions

Boron-doped diamond (BDD) thin films with different crystal grain sizes were prepared by controlling the reacting gas pressure using hot filament chemical vapor deposition (HFCVD). The morphologies and structures of the prepared diamond thin films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. The electrochemical responses of K₄Fe(CN)₆ on different BDD electrodes were investigated. The results suggested that electron transfer was faster at the boron-doped nanocrystalline diamond (BDND) thin film electrodes in comparison with that at other BDD thin film electrodes. The prepared BDD thin film electrodes without any modification were used to directly detect glucose in the basic solution. The results showed that the as-prepared BDD thin film electrodes exhibited good selectivity for detecting glucose in the presence of ascorbic acid (AA) and uric acid (UA). The higher sensitivity was observed on the BDND thin film grown on the boron-doped microcrystalline diamond (BDMD) thin film surface, and the linear response range, sensitivity and the low detection limit were 0.25–10 mM, 189.1 μA mmo^?1 cm^?2 and 25 μM (S/N=3) for glucose in the presence of AA and UA, respectively.     

Doughnut-shaped peptide nano-assemblies and their applications as nanoreactors

Doughnut-shaped nanoreactors, peptide nano-doughnuts, were self-assembled from peptides and organic Au salts. We demonstrated that monodisperse Au nanocrystals were synthesized inside the cavities of peptide nano-doughnuts by the reduction of Au ions and the size of the Au nanocrystal was controlled by the cavity dimension. The Au nanocrystals inside the nano-doughnuts were extracted by destroying the nano-doughnuts via long UV irradiation (>10 h). These features may allow the peptide nano-doughnuts to be applied in the fields of nanomaterial syntheses, controlled release systems, and drug delivery.     

Synthesis and catalytic evaluation of Fe3O4/MWCNTs nanozyme as recyclable peroxidase mimetics: Biochemical and physicochemical characterization

In this research, the nanocomposite of multiwalled carbon nanotubes and magnetic metal oxide nanoparticles (Fe₃O₄/MWCNTs), as enzyme mimetic, was synthesized using an in situ chemical reduction method. The structure, composition and morphology of the prepared Fe₃O₄/MWCNT nanocomposite materials were characterized using X‐ray diffraction, FT‐IR and scanning electron microscopy with energy dispersive X‐ray spectroscopy, respectively. The magnetic properties of the nanocomposite were investigated by the vibrating sample magnetometer. A colorimetric system involving nanozyme, phenol/4‐aminoantipyrine and H₂O₂ was utilized for the determination of peroxidase mimetic catalytic assay. The obtained results confirmed that the synthesis of Fe₃O₄/MWCNTs nanostructures was successful. It was found that Fe₃O₄/MWCNTs nanohybrid exhibited peroxidase‐like activity without any pH limitation. Colorimetric data demonstrated that the prepared nanocatalyst had higher catalytic activity toward H₂O₂ than MWCNTs. The kinetic parameters of the nanozyme, K_m and V_max, were estimated to be 8.3 mm and 1.4 mm min^?1, respectively. The Fe₃O₄/MWCNTs nanostructures were also successfully applied for glucose detection. In addition, peroxidase‐like activity of the nanozyme increased in the presence of butyl‐imidazolium bromide ionic liquid. These biomimetic catalysts have some advantages, such as simplicity, stability, reusability and cost effectiveness, which makes them great candidates to be used in various fields of biotechnology applications.     

Uncapped nanobranch-based CuS clews used as an efficient peroxidase mimic enable the visual detection of hydrogen peroxide and glucose with fast response

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 H₂O₂ 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 H₂O₂ 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.     

Chirospecific synthesis of spirocyclic beta-lactams and their characterization as potent type II beta-turn inducing peptide mimetics

[reaction: see text] Starting from natural proline, a practical chirospecific synthesis of spirocyclic beta-lactams of type 2 is described when a methylene moiety showing minimal steric demand is employed as a constraint element for adjusting the dihedral angle psi(i + 1). Employing the concept of self-reproduction of chirality, C-formylation of the oxazolidinone 5 afforded the key intermediate 7 taking advantage of an intermediate protection of the bridging element as a vinyl moiety. NMR- and IR-based conformational studies clearly indicated that spiro-beta-lactams of type 2 can serve as efficient beta-turn nucleators.