Colorimetric Determination Of Hydrogen Peroxide Research Articles

Synthetization and Characterization of Zinc Oxide Nanoparticles by X- Ray Diffractometry (XRD), Fourier Transforms, Infra-Red Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Antibacterial Activity Test

Purpose: Nanomaterials with their derivable potentials offer wide obtain ability and have recently aroused much attention for biomedical applications. Nowadays, nanomaterials-based colorimetric sensing is a quickly emerging field of sensing applications. Nanomaterials are considered as the main component of colorimetric determination of hydrogen peroxide to replace the natural enzyme-based sensors because of some associated intrinsic drawbacks. Considering the advantageous properties of ionic liquid (IL) for various applications, significant attention has been made to the use of ionic liquid stabilized metal NPs which may serve as a regulator to enhance the catalytic performance of the metal nanoparticles in the different IL reaction medium. 
 Methodology: The peroxidase-like activity of IL coated metal NPs (IL-MNPs) have been considered for the catalytic oxidation reaction of chromogenic substrate 3,3,5,5- tetramethylbenzidine (TMB) in the presence of H2O2 at an estimated wavelength of 652 nm.
 Results: The synthesized metal nanoparticles (Ag) were produced using a chemical reduction method. Various characterization techniques like FTIR, UV-Visible spread Reflectance Spectroscopy [UV-VIS DRS], were employed, which verified the structure, nano-size and successful combination of metal dopant ion into the samples. The molecular structure of ionic liquid with varying cations was produced and confirmed by 1H-NMR spectroscopy. The ionic liquid was coated on metal nanoparticles to enhance their conductivity. 
 Unique Contribution to Theory, Practice and Policy: Optimized reaction conditions like pH, temperature and catalyst dosage affect catalytic activity and color sensing properties. The coating of [Min] Ac on Ag achieved low detection limits and colorimetric detection of [Pyr] based Ag.

Silver nanoparticles@metal-organic framework as peroxidase mimics for colorimetric determination of hydrogen peroxide and blood glucose

• A colorimetric strategy for sensitive detection of H 2 O 2 and glucose has been developed. • A broad dynamic response range for glucose in the range from 0.5 to 50 μM with a limit of detection of 0.23 μM. • The proposed method can be used to monitor glucose in human serum samples. As a major origin of energy for cellular activity and intermediates product of metabolism, glucose plays a significant role in biological activity. Thus, it is relatively vital to explore a sensitive and accurate approach to monitor blood glucose. Herein, a colorimetric biosensor for sensitive, rapid, and reliable monitoring of blood glucose was successfully established. In this sensing system, a nanocomposite of silver nanoparticles (AgNPs) depositing on the MIL-101 (Fe) surface (AgNPs@MOF) was employed as an excellent peroxidase mimic. Glucose could be effectively catalyzed by glucose oxidase (GOx) to produce hydrogen peroxide (H 2 O 2 ) and gluconic acid. Afterward, the AgNPs@MOF nanozyme catalyzed the oxidation of the colorless material TMB into the blue product oxTMB by H 2 O 2 , causing a noticeable change in absorbance at 652 nm. A colorimetric glucose measurement platform was proposed with preferable simplicity and high sensitivity using GOx and AgNPs@MOF nanozyme that with peroxidase-mimicking activity. The limit of detection of the established biosensor was down to 0.17 μM for H 2 O 2 and 0.23 μM for glucose. More importantly, as a result of the application of this biosensor with human blood samples, glucose levels could be monitored with high accuracy, which indicated that this approach had great potential for diabetes therapy. A colorimetric biosensor for sensitive, rapid, and reliable monitoring of blood glucose was successfully established. In this sensing system, a nanocomposite of silver nanoparticles (AgNPs) depositing on the MIL-101 (Fe) surface (AgNPs@MOF) was employed as an excellent peroxidase mimic. Glucose could be effectively catalyzed by glucose oxidase (GOx) to produce hydrogen peroxide (H 2 O 2 ) and gluconic acid. Afterward, the AgNPs@MOF nanozyme catalyzed the oxidation of the colorless material TMB into the blue product oxTMB by H 2 O 2 , causing a noticeable change in absorbance at 652 nm.

PtS2 nanosheets as a peroxidase-mimicking nanozyme for colorimetric determination of hydrogen peroxide and glucose.

Using an ultrasonication-assisted liquid exfoliation method, we have synthesized PtS2 nanosheets with good reproducibility. Herein, intrinsic peroxidase-like activity was for the first time demonstrated for PtS2 nanosheets, which can catalyze H2O2 oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate a colored solution. The catalytic mechanism of PtS2 nanosheets was investigated, which indicated that acceleration ofthe electron transfer between TMB and H2O2 was the main reason for the peroxidase-like activity of PtS2 nanosheets. Based on these observations, we exploited PtS2 nanosheets integrated into dopamine-functionalized hyaluronic acid (HA-DA) hydrogel microspheres by droplet microfluidics to construct PtS2 nanosheet- and PtS2@HA-DA microsphere-based sensors for highly sensitive determination of H2O2. When coupled with glucose oxidase, we further developed two glucose sensors based on the above two methods. Among them, the linearity of the PtS2 nanosheet-based spectrophotometry was in the range of 0.5 to 150μM and the limit of detection as low as 0.20μM. The linearity of the microsphere-based colorimetry was in the range 200 to 12,000μM with a detection limit of 29.95μM. Both of the glucose sensors can be applied to the determination of glucose in human serum with reliable results and reproducibility.

Colorimetric determination of hydrogen peroxide based on the robust peroxidase-like activities of flower-like YVO4 microstructures

In this study, yttrium vanadate (YVO4) flower-like microstructures assembled by quadrangular prisms (YVFPs) were prepared through a facile hydrothermal method, which were developed as a novel nanoenzyme to determine hydrogen peroxide (H2O2) for the first time. In the presence of H2O2, YVFPs exhibited a highly efficient peroxidase-like activity in catalyzing the oxidation the typical peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB). Colorless TMB would be turned into oxidized TMB with a visible blue color and UV–visible absorption peak at 652 nm. The catalytic reaction mechanism was proposed according to the kinetics experiments and active species capture tests, indicating that·O2- radicals played a key role in the peroxidase mimetic reaction. Besides, YVFPs showed a superior affinity to TMB compared with the natural enzyme horse radish peroxidase with a lower Km value. Taking advantage of the strong peroxidase-like activity of YVFPs, a simple, rapid, sensitive, and visual platform was successfully established for colorimetric detection of H2O2. The YVFPs-based colorimetric system possessed good selectivity, stability and reusability with a wider linear range from 0.5 μM to 50 μM and a lower detection limit as low as 0.126 μM towards H2O2 determination. Moreover, the feasibility of this convenient method was further validated by assaying residual H2O2 in milk and contact lens solutions. This work not only provides a novel artificial biomimetic catalyst with efficient catalytic abilities, but also opens up a new potential application field of YVO4 materials in clinical diagnosis, food safety and biomedicine.

UV-assisted one-pot synthesis of bimetallic Ag-Pt decorated reduced graphene oxide for colorimetric determination of hydrogen peroxide.

Bimetallic Ag-Pt nanoparticles decorated on the surface of reduced graphene oxide (Ag-Pt/rGO) were designed and selected as a nanozyme for the assay ofhydrogen peroxide. The nanocomposites were prepared through a one-pot reduction of potassium chloroplatinate, silver nitrate, and graphene oxide under ultraviolet irradiation without using any extra chemical reducing agents or surfactants. The successful formation of Ag-Pt/rGO nanocomposites was confirmed by transmission electron microscopy, energy disperse spectroscopy mapping, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. Significantly, Ag-Pt/rGO nanocomposites possessed excellent peroxidase-like activity toward the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine to form a blue product in the presence of hydrogen peroxide. Steady-state kinetics studies suggested that Ag-Pt/rGO nanocomposites had high affinity to hydrogen peroxide. Based on these properties, a convenient and sensitive method for the colorimetric determination of hydrogen peroxide was developed. Under optimal conditions, the absorbance at 652nm increases linearly in the 10-100μM and 100μM-1mM ranges of hydrogen peroxide concentration, and the detection limit is 0.9μM (S/N = 3). The method was successfully applied to the determination of hydrogen peroxide in real water samples. Graphical abstract Ag-Pt/rGO nanocomposites were prepared by a one-pot UV irradiation method and used as a novel nanozyme for colorimetric determination of H2O2.

Microwave-assisted synthesis of carbon dots as reductant and stabilizer for silver nanoparticles with enhanced-peroxidase like activity for colorimetric determination of hydrogen peroxide and glucose.

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 5min at 700W. 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 1.4nm. Photoexcitation of theCDs with a UV lamp of 365nm results inblue fluorescence. The absorption spectra of the CDs show a peak at 205nm along the wide shoulder absorption band. On incorporation ofthe Ag nanoparticles into the CDs matrix, the color of the CDs turns into yellow and an additional absorbance peak at 408nm 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 the0.1-100μMconcentration 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- 600μM. The detection limits for H2O2 and glucose are 9nM and 10nM, 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 dilutedblood plasma. Graphical abstractSchematic representation of microwave-assisted synthesis of AgNP@CDs with enhanced-peroxidase like activity for colorimetric determination of hydrogen peroxide and glucose.

Cerium(III)-doped MoS2 nanosheets with expanded interlayer spacing and peroxidase-mimicking properties for colorimetric determination of hydrogen peroxide.

Molybdenum disulfide (MoS2) nanosheets (NSs) with an 8.1Å interlayer spacing were heavily loaded with cerium(III) ions by a one-step hydrothermal method. The material thus obtained has a strong peroxidase-like (POx-like) activity. The introduction of the large Ce(III) ion enlarges the interlayer distance of MoS2NSs. It also supports shuttling and transport of substrate, intermediates and electrons. It also increases the specific surface of MoS2. Thisresults in a larger number of active sites, accelerates the contact between substrate and catalytic surface, and improves the kinetics of the catalytic reaction. The nanomaterial catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide (H2O2 ) to give a blue-green product with an absorption maximum at 652nm. The assay has a linear response in the 1-50μM H2O2 concentration range and a 0.47μM limit of detection. The colorimetric method was applied to real milk samples, and high recoveries (98.4%-108.0%) and repeatability were obtained. Graphical abstractMolybdenum disulfide nanosheets loaded with cerium(III)catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) by hydrogen peroxide to give a blue-green product with an absorption maximum at 652 nm.

Smartphone colorimetric determination of hydrogen peroxide in real samples based on B, N, and S co-doped carbon dots probe.

In this paper, we report the use of a smartphone and B, N, and S co-doped carbon dots (BNS-CDs) as a promising peroxidase mimic to quantify hydrogen peroxide (H2O2). The synthesized BNS-CDs exhibited excellent peroxidase-like activity to catalyze the reaction of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) with H2O2 to generate a blue oxide product (ox-TMB) with maximum absorption at 652nm. Steady-state kinetic analysis demonstrated that the BNS-CDs showed much higher affinity than natural horseradish peroxidase (HRP) for H2O2 due to their small size and larger specific surface area. A smartphone colorimetric readout device was employed to record the RGB (red green blue) value of the ox-TMB solution via the Android application Color Grab for quantitative detection. A good linear relationship (R2 = 0.9970) between the H2O2 concentration and |R-Rblank| value was obtained in the range of 3-30μM with a limit of detection (LOD) of 0.8μM. The current method was successfully applied to determine H2O2 in mouthwash and milk with recoveries of 92.70-108.30%. The developed assay is a promising portable detection platform for H2O2 with good sensitivity and selectivity, simple operation, fast response, and low cost. Graphical abstract.

Nitrogen- and sulfur-doped carbon dots as peroxidase mimetics: colorimetric determination of hydrogen peroxide and glutathione, and fluorimetric determination of lead(II).

Fluorescent carbon dots co-doped with nitrogen and sulfur (N/S CDs) were prepared and found to display viable peroxidase mimicking activity. They have a blue fluorescence (with excitation/emission maxima at 340/456nm) with a quantum yield of 35%. The N/S CDs catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, and this leads to the appearance of a blue solution with a absorption maximum at 654nm. A colorimetric method was developed for the determination of H2O2 that has a 1.75μM detection limit and a linear response in the 10-5 to 10-4M concentration range. The method can be extended to the enzymatic determination of glutathione with a 0.26μM detection limit and a working rangefrom 0.20 to 100μM. In addition, the CDs respond to lead(II) which is a quencher of the blue fluorescence at 456nm, with a detectionlimit of 11μM and a working range up to 100μM. Simultaneously, the color changes can be visually detected with absorbance signal changes from 10 to 100μM with limit of 3.9μM. A multiple detection system was worked out that allows monitoring of H2O2 and glutathione successively, and of lead(II). Graphical abstract (A) Schematic representation of the nitrogen & sulphur doped carbon dots with blue fluorescence, (B) the peroxidase-like activity in colorimetric detecting of H2O2 and GSH and (C) the illustration for the application of Pb2+ detection with fluorescence and colorimetric method.

Fe/C magnetic nanocubes with enhanced peroxidase mimetic activity for colorimetric determination of hydrogen peroxide and glucose.

Iron-carbon (Fe/C) magnetic nanocubes were synthesized by direct pyrolysis of Prussian blue nanocubes under an inert gas atmosphere. They are shown to possess intrinsic peroxidase mimicking activity to catalyze the oxidation of peroxidase substrate N,N-diethyl-p-phenylenediamine sulfate salt to form a purple colored product in the presence of H2O2. The values for Km and Vmax are 74μM and 46nmols-1, respectively. Steady-state kinetic analysis also indicates that the catalysis reaction follows a ping-pong mechanism. Based on these findings, an ultrasensitive colorimetric H2O2 assay was worked. Absorbance (best value measured at 550nm) increases linearly in the 10nM to 0.2mM H2O2 concentration range, and the limit of detection is 1.5nM. The method was also applied to the quantification of glucose, which is oxidized by glucose oxidase in the coexistence of H2O2. The response covers the 0.1 to 500μM glucose concentration range, and the limit of detection is 16nM. The method was applied to the determination of H2O2 in rainwater samples. The glucose assay was used to analyze serum samples, and satisfactory results were obtained.Other attractive features include good chemical activity, low cost, easy storage, and high catalytic efficiency. Graphical abstract Schematic presentation of converting Prussian blue nanoparticles into Fe/C magnetic nanocubes by a pyrolysis technique and the use of glucose oxidase and Fe/C magnetic nanocubes to establish a one-step spectrophotometric method for the determination of glucose and hydrogen peroxide.

Perylene diimide-functionalized CeO2 nanocomposite as a peroxidase mimic for colorimetric determination of hydrogen peroxide and glutathione.

A novel perylene diimide (PDI) functionalized CeO2 nanocomposite (NC) was successfully fabricated via one-pot hydrothermal method. Compared with pure CeO2 nanoparticles (CeO2 NPs), the NC catalyst presents more Ce3+ and active oxygen species and exhibits a higher peroxidase mimicking activity towards the oxidation 3,3',5,5'-tetramethylbenzidine by H2O2 to form a blue product with an absorption maximum at 652nm. The composite catalyst shows high sensitivity and selectivity toward H2O2 determination in the range of 20 to 80μM with a limit of detection (LOD) of 2.59μM. Based on the colorimetric method, a sensitive method for detecting the reduced glutathione (GSH) was also established over arrange of 1~4μM with a LOD of 0.92μM. Electron spin resonance (ESR) experiments suggest that the active radicals during the catalytic processes are •OH and •O2-. A possible synergistic catalytic mechanism is discussed. Graphical abstract Schematic presentation of the possible catalytic mechanism for colorimetric determination of hydrogen peroxide and glutathione based on the peroxidase-like activity perylene-diimide (PDI) functionalized CeO2 nanocomposite.

In situ growth of PtMn nanoparticles on Layered Double Hydroxide for colorimetric determination of hydrogen peroxide

In this report, Platinum manganese nanoparticles (PtMn NPs) were attached onto Layered Double Hydroxide (LDH) via a facile in-situ growth strategy. Based on the prepared nanoparticles, a novel colorimetric sensor for fast and sensitive determination of H2O2 was established. The established colorimetric sensing platform exhibited perfect peroxidase-like activities confirmed by oxidating 4, 4’-Bi-2, 6-xylidine (TMB) with H2O2. The sensing platform was pH and temperature-dependent.

Carbondots on V2O5 nanowires are a viable peroxidase mimic for colorimetric determination of hydrogen peroxide and glucose.

A nanocomposite was hydrothermally prepared from C-dots and V2O5 nanowires, and characterized by TEM, FTIR and XRD. Due to the synergistic effects between C-dots and V2O5 nanowires, the nanocomposite is found to possess peroxidase-mimicking activity. This finding was exploited to design colorimetric methods for determination of H2O2 and glucose (via glucose oxidase) by using of 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. The C-dot/V2O5 nanocomposite catalyzes hydrogen peroxide to oxidize TMB and the resultant product, i.e., TMB* produces a blue color in the solution. Also for glucose determination, at first glucose reacts with dissolved oxygen in the presence of glucose oxidase and generates H2O2. Then, produced H2O2 was monitored by theC-dot/V2O5 nanozyme in the presence of TMB. Intensity of the blue color in the solution at wavelength of 650nm is an indication of H2O2 or glucose concentration. The response to H2O2 is linear in the 0.5-520μM concentration ranges, and that for glucose from 0.7μM to 300μM. Graphical abstract Schematic presentation of peroxidase mimicking activity of C-dot/V2O5 nanocomposite and its application as sensitive colorimetric H2O2/glucose assay by using of 3,3',5,5'-tetramethylbenzidine (TMB) as chromogenic substrate to induce a typical blue color reaction.

Colorimetric Determination Of Hydrogen Peroxide Based on Localized Surface Plasmon Resonance of Silver Nanoprisms Using a Microchannel Chip

Silver nanoprisms (AgNPrs) have unique optical phenomena due to their localized surface plasmon resonance that results in the extinction of light from the visible to the near-infrared spectral region. In this study, we propose the colorimetric determination of silver nanoprisms in microchannels using a smartphone camera. Image acquisition was performed by capturing an image of the colloidal solution of the silver nanoprisms in the microchannel using the transmitted light. Red, green, and blue chromaticity levels were extracted from the recorded images for further quantification of the silver nanoprisms. This technique was employed for the detection and colorimetric determination of hydrogen peroxide (H2O2). Good linearity between the change in the green chromaticity level and concentration of hydrogen peroxide was observed for values from 10 to 300 μM with an R2 value of 0.9670. We anticipate that the developed methodology for the quantification of silver nanoprisms and hydrogen peroxide by monitoring the change in color in the images of transmitted light will enhance the development of simple, rapid, and reliable detection systems for quality control in the production of silver nanoprisms as well as in chemical sensor applications.

Etched PtCu nanowires as a peroxidase mimic for colorimetric determination of hydrogen peroxide

Etched PtCu nanowires (NWs) were synthesized by a hydrothermal reaction and chemical etching process. The NWs are shown to be viable peroxidase (POx) mimics capable of catalyzing the oxidation of the substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to form a blue-green coloration. The mechanism of catalysis was investigated and the results demonstrated that H2O2 is decomposed to form hydroxyl radicals which oxidize TMB in the presence of the NWs. Under optimized conditions, a steady-state kinetic analysis revealed that the NWs possess a stronger affinity for H2O2 and TMB compared to the enzyme horseradish POx. Based on the high POx-like activity, a colorimetric assay for H2O2 was established. Absorbance at 652 nm increases linearly in the 0.1-300 μM H2O2 concentration range, and the detection limit is 0.06 μM (at S/N = 3). The assay was successfully applied to the determination of H2O2 in (spiked) milk and contact lens solution. Furthermore, a highly sensitive test strip was designed which represents a low cost and fast alternative for the visual determination of H2O2. Graphical Abstract Schematic presentation of the colorimetric detection of H2O2. PtCu nanowires (PtCu NWs) can catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by H2O2 to produce blue-green oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB). Based on the color change, test strips were designed for H2O2 detection.

Synthesis of PB@FePt hybrid nanoparticles with peroxidase-mimicking activity for colorimetric determination of hydrogen peroxide in living cells

The rapid determination of H2O2 is important in a series of areas, such as bioanalysis, food safety and clinical diagnosis.

A 3-dimensional C/CeO2 hollow nanostructure framework as a peroxidase mimetic, and its application to the colorimetric determination of hydrogen peroxide.

Various3-dimensional C/CeO2 hollow nanostructure frameworks (3D C/CeO2 HNFs) were synthesized by using a polymer blowing process that is accelerated by adding a certain amount of cerium nitrate. Polyvinylpyrrolidone was used as the polymer. The resulting HNFs were characterized by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The HNFs possess a large specific surface area, and the CeO2 nanocrystals consist of a single phase. The HNFs display intrinsic peroxidase-like activity and can catalyze the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine in the presence of H2O2 to produce a blue product. The method was applied to the quantification of H2O2 with a 5.2 nM detection limit. The analytical range is from 10nM to 1μM. Graphical abstract Schematic of the preparation of a3-dimensional C/CeO2 hollow nanostructure framework by a polyvinylpyrrolidone-blowing process accelerated by Ce(NO3)3. They were applied to H2O2 detection by catalyzing the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) to the oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) to produce blue-color reaction.

In-situ synthesis of Cu2O[sbnd]Au nanocomposites as nanozyme for colorimetric determination of hydrogen peroxide

In this paper, gold nanoparticles-doped Cu2O cubes (Cu2OAu nanocomposites) with peroxide-like character were readily prepared through a simple two-step method and were used for sensitive readout of H2O2 with color variation for the first time. By changing reaction temperature and feed rate, Cu2O nanocrystals with very small size were obtained and were then used to prepare Cu2OAu nanocomposites. HR-TEM, SEM, and XRD were used to characterize their morphology and size. The results revealed that the as-prepared Cu2OAu nanocomposites displayed rough cube morphology, with Cu2O cube, ca. 85 nm in size, filled with 8 nm spheres. In the presence of H2O2, 3,3,5′,5′-tetramethyl benzidine (TMB) was catalyzed by Cu2OAu nanocomposites and generated color changes, which was employed to detect H2O2. By comparison with Cu2O nanocrystals with different sizes, Cu2OAu nanocomposites exhibited highest peroxide-like activity, which relies heavily on the pH and temperature in the reaction systems and satisfies with the Michaelis-Menten kinetics. Based on these findings, a colorimetric method was developed to detect H2O2 over a range between 0.4 μM and 1000 μM. This platform extends a great prospect in the field of clinical diagnosis, food safety, and environmental monitoring.

Intrinsic peroxidase-like activity of rhodium nanoparticles, and their application to the colorimetric determination of hydrogen peroxide and glucose.

The intrinsic peroxidase-like activity of rhodium nanoparticles (RhNPs) and their use as catalytic labels for sensitive colorimetric assays is presented. RhNPs catalyze the oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue reaction product with a maximum absorbance at 652nm. Kinetic studies show catalysis to follow Michaelis-Menten kinetics and a "ping-pong" mechanism. The calculated kinetic parameters indicate high affinity of RhNPs for both the substrate TMB and H2O2. In fact, they are better than other peroxidase mimicking nanomaterials and even the natural enzyme horseradish peroxidase. On the other hand, RhNPs exhibit no reactivity towards saccharides, thiols, amino acids and ascorbic acid. Based on these findings, a sensitive and selective colorimetric method was worked out for the determination of H2O2 in real samples with a linear response in the 1-100μM concentration range. By employing glucose oxidase, the glucose assay has a linear range that covers the 5 to 125μM glucose concentration range. The detection limits are <0.75μM for both species. The methods were applied to the determination of H2O2 in spiked pharmaceutical formulations, and of glucose in soft drinks and blood plasma. Figures of merit include (a) good accuracy (with errors of <6%), (b) high recoveries (96.5-103.7%), and (c) satisfactory reproducibility (<6.3%). Graphical abstract Rhodium nanoparticles catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue reaction product.Theeffect is exploited in photometricassays for hydrogen peroxide and glucose.

Application of enzyme-like activity of Fe-doped ZnS QDs for colorimetric determination of hydrogen peroxide

ABSTRACTFe-doped ZnS quantum dots (QDs) were synthesised using a hydrothermal method. Then, the peroxidase-like catalytic activity of these materials was investigated using the study of the oxidation of colourless peroxidase substrate, 3,3′,5,5′-tetramethylbenzidine, in the presence of H2O2 to produce a blue product. Finally, these new materials were used for determination of H2O2 aqueous samples. The obtained linear range and limit of detection for determination of H2O2 were 4.1–98 and 3.06 µg L−1, respectively. As a result, Fe-doped ZnS QDs could be used for inexpensive and highly sensitive and simple determination of H2O2 in aqueous samples.