Peroxidase Mimic Research Articles

Iron, Nitrogen-Doped Carbon Aerogels for Fluorescent and Electrochemical Dual-Mode Detection of Glucose.

Due to their effective catalytic activity and maximum atom utilization, single metal atoms dispersed in carbon matrices have found diverse applications in electrocatalysis, photocatalysis, organic catalysis, and biosensing. Herein, iron is atomically dispersed into nitrogen-doped porous carbon aerogel by a facile pyrolysis procedure, and the resulting nanocomposite behaves both as a peroxidase mimic for the sensitive detection of glucose by fluorescence spectroscopy and as an effective catalyst for the electrochemical oxidation of glucose. The glucose concentration can be quantified within the millimolar to micromolar range with a limit of detection of 3.1 and 0.5 μM, respectively. Such a dual-functional detection platform also shows excellent reproducibility, stability, and selectivity, and the performance in glucose detection of clinical and artificial human body fluids is highly comparable to that of leading assays in recent studies and results from commercial sensors. Results from this study suggest that carbon aerogel-supported single atoms can be used as a dual-functional nanozyme for the construction of low-cost, high-performance dual-signal readout platforms for glucose detection.

Mn3O4–Au nanozymes as peroxidase mimic and the surface-enhanced Raman scattering nanosensor for the detection of hydrogen peroxide

The artificial enzyme-mimicking system using nanomaterials has attracted significant research interest in chemical and biological sensing for industrial and environmental applications. Mn3O4 nanostructure serves as an effective catalyst in oxidation and reduction reactions that mimic natural peroxidase enzymes. In this study, we synthesized Mn3O4–Au spindle nanocomposites (Mn3O4–Au SNCs) stabilized by L-cysteine using a simple hydrothermal reduction. The enzyme-mimicking peroxidase activity of these Mn3O4–Au SNCs with hydrogen peroxide (H2O2) was investigated in the presence of a chromogenic substrate, 3,3′,5,5′-tetramethylbenzidine that catalyzed reduction of H2O2 in water and milk giving rise to a blue color inferring the nanozyme activity of Mn3O4–Au SNCs. The exceptional enzyme-like catalytic activity of Mn3O4–Au SNC probes later proved to be excellent surface-enhanced Raman scattering (SERS) sensor nanoprobes for sensitive H2O2 detection over a wide concentration range from 0.005 to 10 μM. The developed Mn3O4–Au SERS sensor exhibited a lower detection limit (LoD) of 2 nM in water and 0.6 μM in spiked milk indicating sensitivity for H2O2 detection with excellent selectivity, reproducibility, and long-term stability. The developed Mn3O4–Au nanoprobes demonstrated unique combination of properties with visual and SERS methods for sensitively detecting H2O2 in food, overcoming limitations of existing H2O2 sensors. The developed SERS method using nanozymes potentially be extended to detecting a variety of other redox chemicals or explosives in industries, environments, and biomedical fields.

The Fabrication of Amino Acid Incorporated Nanoflowers with Intrinsic Peroxidase-like Activity and Its Application for Efficiently Determining Glutathione with TMB Radical Cation as Indicator.

The assessment of glutathione (GSH) levels is associated with early diagnostics and pathological analysis for various disorders. Among all kinds of techniques for detecting GSH, the colorimetric assay relying on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) catalyzed by many nanomaterials with peroxidase-like activity attracts increasing attention owing to its outstanding merits, such as high sensitivity and high selectivity. However, the aggregation between the nanomaterials severely hinders the entrance of TMB into the “active site” of these peroxidase mimics. To address this problem, the D-amino acid incorporated nanoflowers possessing peroxidase-like activity with a diameter of 10–15 μm, TMB and H2O2 were employed to establish the detection system for determining the level of glutathione. The larger diameter size of the hybrid nanoflowers substantially averts the aggregation between them. The results confirm that the hybrid nanoflowers detection system presents a low limit of detection, wide linear range, perfect selectivity, good storage stability and desired operational stability for the detection of GSH relying on the intrinsic peroxidase-like activity and favorable mechanical stability of the hybrid nanoflowers, indicating that the hybrid nanoflowers detection system has tremendous application potential in clinical diagnosis and treatment.

A dual-quenched ECL immunosensor for ultrasensitive detection of retinol binding protein 4 based on luminol@AuPt/ZIF-67 and MnO2@CNTs

BackgroundRetinol binding protein 4 (RBP4) has been regarded as an important serological biomarker for type 2 diabetes mellitus (T2DM). Hence, the construction of a highly sensitive detection method for RBP4 is the key to early prevention and multidisciplinary intervention of T2DM. In this work, a dual-quenched electrochemiluminescence (ECL) immunosensor has been fabricated for ultrasensitive detection of RBP4 by combining zeolitic imidazolate framework-67/AuPt-supported luminol (luminol@AuPt/ZIF-67) with MnO2 nanosheets-grown on carbon nanotubes (MnO2@CNTs).ResultsAuPt/ZIF-67 hybrids with high-efficiency peroxidase-like activity could provide multipoint binding sites for luminol and antibodies and significantly boost the amplified initial signal of the ECL immunosensor. Upon glutathione/H2O2 coreactants system, MnO2@CNTs composites could quench the initial signal by inhibiting mimic peroxidase activity of luminol@AuPt/ZIF-67. Moreover, the absorption spectrum of the MnO2@CNTs composites completely overlaps with the emission spectrum of luminol, which can further reduce initial signal by ECL resonance energy transfer (ECL-RET).ConclusionsBenefiting from the above-mentioned properties, the designed immunoassay sensitivity exhibited excellent sensitivity and relative stability for RBP4 detection range from 0.0001 to 100 ng mL−1 with a low detection limit of 43 fg mL−1. Therefore, our ECL immunosensor provides an alternative assaying strategy for early diagnosis of T2DM.Graphic abstract

Enzyme like-colorimetric sensing of H2O2 based on intrinsic peroxidase mimic activity of WS2 nanosheets anchored reduced graphene oxide

With the rapid advance of peroxidase mimic sensing nanomaterials have been reasonably considered as the alternates for natural enzymes due to their higher stability and cost-effectiveness. Herein, we proposed the synthesis of WS2 Nanosheets anchored reduced graphene oxide (rGO) for the peroxidase sensing of H2O2. The well-dispersed WS2 nanosheets anchored on rGOwith huge porosity of 18 nm in diameter were synthesized by facile one-pot hydrothermal method. The prepared catalysts show thegreater catalytic activity towards the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The obtained Michaelis-Menton constant possessed the stronger affinity of H2O2 and TMB by the WS2/rGO. The outstanding catalytic performance of the WS2/rGO is due to their unique mesoporous structure with the higher specific surface area and the synergetic effect of the rGO matrix. This colorimetric detection exhibits a lower detection limit of about 82 nM with a wide linear range. Michaelis-Menton constant and the rate of reaction was found to be 10.001 M and 0.9332 × 10−8 M s−1for H2O2 and 22.406 M and 0.9606 × 10−8 M s−1 for TMB. Also, the WS2/rGO exhibits higher selectivity among various interfering compounds. It exhibits a higher recovery in practical application towards the human urine sample with the standard deviation of±2. Thus, this present study built a favourable strategy for the development of colorimetric sensors towards H2O2 and it demonstrating its potential applications in various clinical applications.

Fluorescent MOF-based nanozymes for discrimination of phenylenediamine isomers and ratiometric sensing of o-phenylenediamine

Although peroxidase-like nanozymes have made great progress in bioanalysis, few current nanozyme-based biosensors are constructed for discriminating isomers of organic compounds. Herein, fluorescent metal-organic framework (MOF)-based nanozyme is utilized for phenylenediamine isomers discrimination and detection. NH2-MIL-101(Fe), as a member of Fe-based MOFs, functions as not only fluorescent indicator but also peroxidase mimics. In the presence of H2O2, NH2-MIL-101(Fe) can catalyze the oxidation of o-phenylenediamine (OPD) and p-phenylenediamine (PPD) into their corresponding oxidation products (OPDox and PPDox), which in turn quench its intrinsic fluorescence at 445 nm via inner filter effect (IFE). Differently, a new fluorescence peak at 574 nm is observed for OPDox. Thus, a ratiometric fluorescence method for the detection of OPD can be designed with the fluorescence intensity ratio F574/F445 as readout. This proposed strategy displays excellent discrimination ability for three phenylenediamines and may open new applications of MOFs in environmental science.

A visual cardiovascular biomarker detection strategy based on distance as readout by the coffee-ring effect on microfluidic paper

We first reported a novel visualized instrument-free signal conversion method on paper for cardiovascular biomarker detection based on the coffee-ring effect (CRE). Our strategy was based on the principle that cTnI was captured by DNA probe decorated detection antibody to form sandwich complex, which could hybridize with H1 probes to form G-quadruplex DNAzyme. As a peroxidase mimic, G-quadruplex DNAzyme could catalyze colorimetric reaction and generate colored products, which were converted to the end edge of the paper by evaporation-driven flow, forming a visible colored band. Hence, the resulted colored signals were converted to distance signal by CRE, so that the quantification of cTnI could be measured easily only by a ruler. Our results demonstrated that the length of the colored bands was proportional to the concentration of cTnI, with a limit of detection of 1.0 pg/mL. Furthermore, this strategy not only showed advanced performance to discriminate cTnI from complex samples but also exhibited high accuracy with standard method in real sample. Hence, these results demonstrated that this method established a promising equipment-free and visualized platform for detecting various kinds of genetic diseases and biomarkers, further promoting the development of point-of-care testing (POCT) in biomedicine.

Core–shell magnetic Fe3O4/CNC@MOF composites with peroxidase-like activity for colorimetric detection of phenol

Rapid and accurate detection of phenolic wastewater from industries has created global concern. Herein, core–shell magnetic cellulose nanocrystal supported MOF (Fe3O4/CNC@ZIF-8) with robust peroxidase-like activity was synthesized with tannic acid as modifier and bridge. The peroxidase-mimic catalytic activity of as-prepared Fe3O4/CNC@ZIF-8 was further investigated using o-phenylenediamine (OPD) as peroxidase substrates in the presence of H2O2. Moreover, the experimental conditions were optimized and the kinetic analysis results showed that Fe3O4/CNC@ZIF-8 had higher affinity towards both the substrate OPD and H2O2 than horseradish peroxidase (HRP). Finally, a phenol colorimetric assay with a linear range of 2–200 µM and a detection limit of 0.316 µM was constructed. The catalytic mechanism of Fe3O4/CNC@ZIF-8 with phenol was further investigated by fluorescence test and the generated ·OH was proved to act a crucial role to produce quinoid radicals. Additionally, the synthesized magnetic material had excellent stability and recyclability and ease to separation. These results suggest that the Fe3O4/CNC@ZIF-8 may be one of the promising candidates as peroxidase mimic for colorimetric detection of phenol.

Colorimetric Detection of Cholesterol Based on the Peroxidase‐Like Activity of Metal‐Organic Framework MIL‐101(Cr)

AbstractEfficient quantitative determination of cholesterol has important application value in drug testing and clinical diagnosis of cardiovascular diseases. In this work, a metal‐organic framework MIL‐101(Cr) (MIL=Materials of Institute Lavoisier) was synthesized and developed as a peroxidase mimic for colorimetric detection of cholesterol. Kinetic analysis indicated that the MIL‐101(Cr) nanoparticles showed a higher Vmax (2.27*10−7 MS−1) and a lower Km (0.07 mM) than the natural horseradish peroxidase (HRP). An effective colorimetric sensor has been proven to detect cholesterol. Based on the outstanding catalytic activity, the colorimetric sensor displayed a linear response for cholesterol in the concentration range from 1.1 μM to 22.9 μM and the detection limit as low as 0.86 μM. Furthermore, the proposed method based on MIL‐101(Cr) nanoparticles showed a favorable reproducibility and recovery. The sensor had been successfully applied to determine serum cholesterol level in mice and human, respectively.

Dual Targeting of Endoplasmic Reticulum by Redox-Deubiquitination Regulation for Cancer Therapy.

BackgroundRecently, nanocatalyst-induced endoplasmic reticulum (ER) stress for cancer therapy has been attracting considerable attention. However, cancer cells are often able to overcome ER stress-induced death by activating the unfolded protein response (UPR), making nanocatalytic monotherapy a poor defense against cancer progression.PurposeIn this study, to improve the nanocatalytic treatment efficacy, a phase change material (PCM) was used to encapsulate the upstream ER stress initiator, iron oxide nanoparticles (Fe3O4 NPs), and the downstream UPR modulator, PR-619. Subsequently, the tumor-homing peptide tLyP-1 was coupled to it to form tLyP-1/PR-619/Fe3O4@PCM (tPF@PCM) theranostic platform.Materials and MethodstPF@PCM was synthesized using nanoprecipitation and resolidification methods followed by the EDC/NHS cross-linking method. The targeting capacity of tPF@PCM was evaluated in vitro and in vivo using flow cytometry and magnetic resonance imaging, respectively. The therapeutic efficacy of tPF@PCM was investigated in a renal cell carcinoma mouse model. Moreover, we explored the synergistic anti-tumor mechanism by examining the intracellular reactive oxygen species (ROS), aggregated proteins, ER stress response levels, and type of cell death.ResultstPF@PCM had excellent tumor-targeting properties and exhibited satisfactory photothermal-enhanced tumor inhibition efficacy both in vitro and in vivo. Specifically, the phase transition temperature (45 °C) maintained using 808 nm laser irradiation significantly increased the release and catalytic activity of the peroxidase mimic Fe3O4 NPs. This strongly catalyzed the generation of hydroxyl radicals (•OH) via the Fenton reaction in the acidic tumor microenvironment. The redox imbalance subsequently resulted in an increase in the level of damaged proteins in the ER and initiated ER stress. Moreover, the pan-deubiquitinase inhibitor PR-619 blocked the “adaptive” UPR-mediated degradation of these damaged proteins, exacerbating the ER burden. Consequently, irremediable ER stress activated the “terminal” UPR, leading to apoptosis in cancer cells.ConclusionThis ER stress-exacerbating strategy effectively suppresses tumorigenesis, offering novel directions for advances in the treatment of conventional therapy-resistant cancers.

Label-free and dual-amplified electrochemical bioanalysis of MUC1 based on an inorganic-organic polymer hybrid mimic peroxidase (AuNPs@Cu7S4@Cu/Mn-AzoPPOP) and catalytic hairpin assembly

We constructed a label-free and dual-amplified electrochemical bioanalysis for ultrasensitive detection of mucin 1 (MUC1, a tumor biomarker for lung cancer, breast cancer, and ovarian cancer) based on an inorganic-organic polymer hybrid mimic peroxidase (AuNPs@Cu7S4@Cu/Mn-AzoPPOP) and catalytic hairpin assembly (CHA). The organic porous polymer (Cu/Mn-AzoPPOP) has a high surface area, which can load large amounts of Cu7S4 and Au nanopartibcles (AuNPs). The formed inorganic-organic nanocomposite (AuNPs@Cu7S4@Cu/Mn-AzoPPOP) can not only serve as an electrochemical probe but also possesses significantly enhanced peroxidase-like performance, compared with that of only Cu7S4 and only Cu/Mn-AzoPPOP. AuNPs@Cu7S4@Cu/Mn-AzoPPOP had high sensitivity towards the reduction of H2O2 by means of differential pulse voltammetry (DPV) and chronoamperometry (CA). Based on the specific recognition between MUC1 and aptamers and its following cyclic reuse by simple strand displacement of CHA, further electrochemical signal amplification was achieved. The fabricated biosensor displayed ultra-sensitivity and highly selectivity for MUC1 determination, ranging from 1 fg/mL to 10 pg/mL, with low detection limits of 0.72 fg/mL (DPV) and 0.82 fg/mL (CA), respectively. Additionally, the proposed biosensor could also retain good performance in spiked serum samples, which implied its great promise for application in biomedical fields.

Structural tuning of CTAB@MgFe2O4 nanocomposite as peroxidase mimic for H2O2 and glucose sensing

Natural enzymes have been used in food industry, biosensing and pharmaceuticals due to their high catalytic activity. Their catalytic potential is governed by the environmental conditions leading to their denaturation, thus increasing operational cost. Nanoparticles (NPs) as enzyme mimic is a thrust area of research. Magnesium ferrite nanoparticles (MgFe2O4 NPs) have gained focus of researchers due to good catalytic activity, stability and magnetic properties. Their catalytic activity can be enhanced by surface coating with suitable surfactant. In this work, CTAB (cetyl trimethyl ammonium bromide) coated MgFe2O4 NPs were prepared and evaluated as peroxidase mimics. The XRD pattern of MgFe2O4 NPs confirmed single-phase formation of spinel structure with cubic geometry. FT-IR studies confirmed the presence of CTAB along with MgFe2O4 NPs. Surface area, Particle size and magnetic character of the NPs were evaluated by Brunauer Emmett Teller analysis, Transmission Electron Microscope and Vibrating Sample Magnetometer respectively. CTAB coated ferrite NPs showed increased surface area and decreased particle size as compared to pristine NPs. CTAB@MgFe2O4 in w/w ratio (1:1) showed best peroxidase like activity towards o-dianisidine dihydrochloride and was influenced by pH, temperature and substrate concentration in solution. The synthesized CTAB@MgFe2O4 (1:1) based system could be used for colorimetric detection of H2O2 in the linear range of 20–300 μM with a detection limit of 10 μM and also for the detection for glucose in the range of 10–1000 μM with a detection limit of 5 μM.

Layer‐by‐Layer Electrodeposition of FTO/TiO2/CuxO/CeO2 (1 <x< 2) Photocatalysts with High Peroxidase‐Like Activity by Greatly Enhanced Singlet Oxygen Generation

AbstractInorganic nanomaterials have attracted much attention as enzyme mimics because of simple and stable spatial conformation of those artificially synthesized nanocatalysts. Cu2O, as an important kind of narrow band gap semiconductor, is identified as effective as visible‐light‐driven photocatalysts, which can catalyze decomposition of H2O2 into reactive oxygen species. Moreover, after forming CuxO/CeO2 hybrids, the strongly coupled interface between the two components will further improve their catalytic performance. In this paper, the authors try to construct FTO/TiO2/CuxO/CeO2 (1 < x < 2) nanohybrids with such a kind of active interface via a layer‐by‐layer electrodeposition strategy by aid of the following surface etching process. It is found that FTO/TiO2/CuxO/CeO2 exhibits good peroxidase mimic activity in the dark but much better performance under visible light irradiation (λ ≥ 420 nm) during catalytic oxidation of 3,3′,5,5′‐tetramethylbenzidine substrates in the presence of H2O2. Detailed characterizations disclose that the construction of TiO2/Cu2O pn‐heterojunctions do effectively accelerate separation of photogenerated carriers, and the formation of a highly active CuxO/CeO2 interface is synergistically favorable for selectively generating singlet oxygen to boost the catalytic performance of FTO/TiO2/CuxO/CeO2.

(Invited) Chemical Sensing Based on Metal-Carbon Nanocomposites

Detection of hydrogen peroxide is of great significance for clinical diagnosis and biomedical research. Ratiometric detection represents an effective method that is generally based on horseradish peroxidase. In this presentation, we will show that ruthenium ion-complexed carbon nitride (Ru−C3N4) nanosheets can be used as a peroxidase mimic and catalyze the conversion of o-phenylenediamine to fluorescent 2,3-diaminophenazine in the presence of H2O2. The produced 2,3- diaminophenazine also results in the apparent quenching of the Ru−C3N4 photoluminescence due to the inner filter effect. These unique characteristics can be exploited for the construction of an effective, peroxidase-free ratiometric fluorescence framework for the detection of H2O2 and glucose, which has also been used in the successful detection of glucose in human serum. Results from this study not only demonstrate a new peroxidase mimic but also provide a novel ratiometric fluorescence platform for the detection of H2O2 and metabolites involving reactions of H2O2 generation in the absence of horseradish peroxidase.

Nanozyme based on graphene oxide modified with Fe3O4, CuO, and cucurbit[6]uril for colorimetric determination of homocysteine.

A nanozyme based on graphene oxide modified with Fe3O4 NPs, CuO NPs, and cucurbit[6]uril has beensuccessfully fabricated by a simple sonochemical technique. By employing CB[6] as a specific binding pocket and Fe3O4@CuO-GO as a peroxidase mimic, this novel nanozyme (BN I) is equipped with molecular recognition ability and enhanced peroxidase-like activity. On the basis of the inhibition effect of homocysteine (Hcy) towards the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by BN I, a simple colorimetric method is established for the sensitive and selective determination of Hcy. This proposed method displays a good linear response in the range 5-200μM with a detection limit of 1.8μM. In thepractical assay of human plasma samples, the relative standard deviations (RSD) are lower than 11% and the recoveries are between 98.0 and 104.9%. In theassay of human urine samples, the RSD are below 9.0% and the recoveries range from 94.0 to 103.5%. Thecolorimetric method presentedoffers a convenient and accurate way for the determination of biomarkers in point-of-care testing (POCT).

Hierarchical mesoporous hollow Ce-MOF nanosphere as oxidase mimic for highly sensitive colorimetric detection of ascorbic acid

In this work, we firstly developed a new method for the synthesis of hierarchical mesoporous hollow Ce-MOF nanosphere templated by diblock copolymer. The hierarchical hollow mesoporous Ce-MOF nanosphere as the oxidase mimic shows highly catalytic chromogenic activity toward 3,3,5,5-tetramethylbenzidine (TMB) without the presence of H2O2, and it can be used as a substitute for peroxidase mimics and H2O2 system in the colorimetric reaction. Herein, we provide a new highly sensitive and selective colorimetric method for the detection of Ascorbic acid (AA). At the optimal pH (3.5), temperature (the room temperature), time (5 min) and TMB concentration (280 μM), the limit of detection (LOD) was 0.03 µM, the range of the detection was 8 to 56 µM.

Palygorskite@Co3O4 nanocomposites as efficient peroxidase mimics for colorimetric detection of H2O2 and ascorbic acid

Nanomaterials with intrinsic enzyme-like activities have attracted extensive research interest as promising alternatives to natural biological enzymes due to their advantages of low cost and high stability. Many artificial enzyme mimics have been successfully applied in the fields of sensing, environmental treatment, and oncotherapy. Herein, novel palygorskite@Co3O4 nanocomposites (Pal@Co3O4 NCs) were fabricated by modifying Pal with Co3O4 nanoparticles through a facile hydrothermal method. The obtained Pal@Co3O4 nanocomposites as nanozymes displayed enhanced peroxidase-like activity, which can catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to obtain colored products. Kinetic assay indicated that the Pal@Co3O4 peroxidase mimics showed a higher affinity towards TMB than that of natural horseradish peroxidase (HRP). Moreover, a sensitive and selective sensor for colorimetric determination of H2O2 and ascorbic acid (AA) was successfully constructed by using Pal@Co3O4 nanocomposites as peroxidase mimics. Furthermore, the proposed assay for sensing of AA in model samples was evaluated with satisfactory results, demonstrating the potential applications in complex biological systems.

Capsulation of AuNCs with AIE Effect into Metal–Organic Framework for the Marriage of a Fluorescence and Colorimetric Biosensor to Detect Organophosphorus Pesticides

Organophosphorus pesticides (OPs) can inhibit the activity of acetylcholinesterase (AChE) to induce neurological diseases. It is significant to exploit a rapid and sensitive strategy to monitor OPs. Here, a metal-organic framework (MOF) acted as a carrier to encapsulate AuNCs, which can limit the molecular motion of AuNCs, trigger the aggregation-induced emission (AIE) effect, and exhibit a strong fluorescence with a fluorescence lifetime and quantum yield of 6.83 μs and 4.63%, respectively. Then, the marriage of fluorescence and colorimetric signals was realized on the basis of the dual function of the enzymolysis product from AChE and choline oxidase (CHO) on AuNCs@ZIF-8. First, it can decompose ZIF-8 to weaken the restraint on AuNCs, and thus the fluorescence receded. Second, it can be used as a substrate for the peroxidase mimics of the released AuNCs to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) and a visible blue appeared. Thus, on the basis of the inhibition of AChE activity by OPs, a fluorescence-colorimetric dual-signal biosensor was established. In addition, colorimetric paper strips were exploited to realize a visual semiquantitative detection, and a smartphone APP was developed to make the visualization results more precise and realize real-time supervision of pesticide contamination.

Highly Sensitive Fluorescent Detection of Acetylcholine Based on the Enhanced Peroxidase-Like Activity of Histidine Coated Magnetic Nanoparticles.

Inspired by the active site structure of natural horseradish peroxidase having iron as a pivotal element with coordinated histidine residues, we have developed histidine coated magnetic nanoparticles (His@MNPs) with relatively uniform and small sizes (less than 10 nm) through one-pot heat treatment. In comparison to pristine MNPs and other amino acid coated MNPs, His@MNPs exhibited a considerably enhanced peroxidase-imitating activity, approaching 10-fold higher in catalytic reactions. With the high activity, His@MNPs then were exploited to detect the important neurotransmitter acetylcholine. By coupling choline oxidase and acetylcholine esterase with His@MNPs as peroxidase mimics, target choline and acetylcholine were successfully detected via fluorescent mode with high specificity and sensitivity with the limits of detection down to 200 and 100 nM, respectively. The diagnostic capability of the method is demonstrated by analyzing acetylcholine in human blood serum. This study thus demonstrates the potential of utilizing His@MNPs as peroxidase-mimicking nanozymes for detecting important biological and clinical targets with high sensitivity and reliability.

Facile and selective colorimetric assay of choline based on AuNPs-WS2QDs as a peroxidase mimic

In the current work, we have fabricated a paper test strip for visual assay of choline by using choline oxidase enzyme with H2O2 based on the oxidation product of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) catalyzed by gold nanoparticles decorated WS2 quantum dots (AuNPs-WS2QDs) to appear blue color product. Under a large range of temperature, pH and H2O2 concentration, AuNps-WS2QDs exhibit prominent peroxidase-like property. In the presence of oxygen, choline oxidized by choline oxidase which produces H2O2 is colorimetrically measured, at 652 nm. The blue color appears due to biochemical reactions between TMB and AuNps-WS2QDs were used as an indication for estimation of H2O2. The proposed scheme is applied for choline detection in concentration range of 1–150 μM in PBS with the 0.086 µM limit of detection. Color variation can be observed visually and this assay is selective, simple and quick. Further portable test kit was fabricated for choline detection in real samples i.e. serum and milk which shows an excellent response towards choline detection. The filter paper test strip changed color intensity based on the concentration of choline.