Convenient and sensitive colorimetric detection of melamine in dairy products based on Cu(ii)-H2O2-3,3′,5,5′-tetramethylbenzidine system

The illegal adulteration of melamine in dairy products for false protein content increase is a strong hazard to human health. Herein, a simple and sensitive colorimetric method was developed for the quantification of melamine in dairy products based on a Cu²⁺-hydrogen peroxide (H₂O₂)-3,3′,5,5′-tetramethylbenzidine (TMB) system. In this strategy, Cu²⁺ exhibits peroxidase-like activity and can catalyze the oxidation of TMB to oxidized TMB (oxTMB) in the presence of H₂O₂ with a blue colour change of the solution. However, the presence of melamine quickly interacts with H₂O₂ leading to the consumption of H₂O₂ and thus strongly hinders the oxidation of TMB. Under the optimal conditions, the absorbance change of oxTMB has a linear response to the concentration of melamine from 1 to 100 μM with a detection limit of 0.5 μM for melamine. The proposed method has many merits including more simplicity, good selectivity, and more cost-effectiveness without using any nanomaterials. The method was further successfully applied to detect melamine in dairy products including milk and infant formula powder.

Convenient and sensitive colorimetric detection of melamine in dairy products based on a Cu(ii)-H₂O₂-3,3′,5,5′-tetramethylbenzidine system was reported.     

A nano-sized Cu-MOF with high peroxidase-like activity and its potential application in colorimetric detection of H2O2 and glucose

Peroxidase widely exists in nature and can be applied for the diagnosis and detection of H₂O₂, glucose, ascorbic acid and other aspects. However, the natural peroxidase has low stability and its catalytic efficiency is easily affected by external conditions. In this work, a copper-based metal–organic framework (Cu-MOF) was prepared by hydrothermal method, and characterized by means of XRD, SEM, FT-IR and EDS. The synthesized Cu-MOF material showed high peroxidase-like activity and could be utilized to catalyze the oxidation of o-phenylenediamine (OPDA) and 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂. The steady-state kinetics experiments of the oxidation of OPDA and TMB catalyzed by Cu-MOF were performed, and the kinetic parameters were obtained by linear least-squares fitting to Lineweaver–Burk plot. The results indicated that the affinity of Cu-MOF towards TMB and OPDA was close to that of the natural horseradish peroxidase (HRP). The as-prepared Cu-MOF can be applied for colorimetric detection of H₂O₂ and glucose with wide linear ranges of 5 to 300 μM and 50 to 500 μM for H₂O₂ and glucose, respectively. Furthermore, the specificity of detection of glucose was compared with other sugar species interference such as sucrose, lactose and maltose. In addition, the detection of ascorbic acid and sodium thiosulfate was also performed upon the inhibition of TMB oxidation. Based on the high catalytic activity, affinity and wide linear range, the as-prepared Cu-MOF may be used for artificial enzyme mimics in the fields of catalysis, biosensors, medicines and food industry.

A Cu-MOF with high peroxidase-like activity was prepared and could be used for colorimetric detection of H₂O₂ and glucose with high selectivity and good linear range (50–500 μM).     

Colorimetric detection of hydrogen peroxide and glucose by exploiting the peroxidase-like activity of papain

Papain, a natural plant protease that exists in the latex of Carica papaya, catalyzes the hydrolysis of peptide, ester and amide bonds. In this work, we found that papain displayed peroxidase-like activity and catalyzed the oxidation of 3,3′,5′,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂. This results in the formation of a blue colored product with an absorption maximum at 652 nm. The effects of experimental parameters including pH and reaction temperature on catalytic activity of papain were investigated. The increase of absorbance induced by the catalytic effect of papain offers accurate detection of H₂O₂ in the range of 5.00–90.0 μM, along with a detection limit of 2.10 μM. A facile colorimetric method for glucose detection was also proposed by combining the glucose oxidase (GOx)-catalyzed glucose oxidation and papain-catalyzed TMB oxidation, which exhibited a linear response in the range of 0.05–0.50 mM with a detection limit of 0.025 mM. The method proposed here displayed excellent selectivity, indicating that common coexisting substances (urea, uric acid, ascorbic acid, maltose, lactose and fructose) in urine did not interfere with detection of glucose. More importantly, the suggested method was successfully used to precisely detect the glucose concentration in human urine samples with recoveries over 96.0%.

We reported a simple colorimetric method for the detection of glucose based on GOx-catalyzed glucose oxidation and papain-catalyzed TMB oxidation.     

Highly efficient reduction of 4-nitrophenolate to 4-aminophenolate by Au/γ-Fe2O3@HAP magnetic composites

In this article, the catalyst Au/γ-Fe₂O₃@hydroxyapatite (Au/γ-Fe₂O₃@HAP) consisting of Au nanoparticles supported on the core–shell structure γ-Fe₂O₃@HAP was prepared through a deposition–precipitation method. The catalyst was characterized by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, N₂ adsorption–desorption and atomic absorption spectrometry. The as-prepared Au/γ-Fe₂O₃@HAP exhibited excellent performance for the reduction of 4-nitrophenolate (4-NP) to 4-aminophenolate (4-AP) in the presence of NaBH₄ at room temperature. Thermodynamic and kinetic data on the reduction of 4-NP to 4-AP catalyzed by the as-prepared catalyst were studied. The as-prepared catalyst could be easily separated by a magnet and recycled 6 times with over 92% conversion of 4-NP to 4-AP. In addition, the as-prepared catalyst showed excellent catalytic performance on other nitrophenolates. The TOF value of this work on the reduction of 4-NP to 4-AP was 241.3 h⁻¹. Au/γ-Fe₂O₃@HAP might have a promising potential application on the production of 4-AP and its derivatives.

In this article, the catalyst Au/γ-Fe₂O₃@hydroxyapatite (Au/γ-Fe₂O₃@HAP) consisting of Au nanoparticles supported on the core–shell structure γ-Fe₂O₃@HAP was prepared through a deposition–precipitation method.     

Colorimetric determination of ascorbic acid based on carbon quantum dots as peroxidase mimetic enzyme

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm. Interestingly, the ox-TMB could be further reduced by ascorbic acid (AA) leading to fading of the blue color and an absorbance decrease. Thus, a convenient and sensitive colorimetric method for detection of AA using CQDs as peroxidase mimics was established. Several factors, such as acidity, temperature, incubating time, and TMB concentration, which might influence the response of the analysis signal, were optimized. The results showed that the decrease of absorbance (ΔA) was in good linear agreement with AA concentration in the range of 1.0–105 μM, with a low detection limit of 0.14 μM. The feasibility of this method was also investigated in commercial beverages with the 94.3–110.0% recovery.

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm.     

The remarkable performance of a single iridium atom supported on hematite for methane activation: a density functional theory study

Methane is the major component of natural gas, and it significantly contributes to global warming. In this study, we investigated methane activation on the α-Fe₂O₃(110) surface and M/α-Fe₂O₃(110) surfaces (M = Ag, Ir, Cu, or Co) using the density-functional theory (DFT) + U method. Our study shows that the Ir/α-Fe₂O₃(110) surface is a more effective catalyst for C–H bond activation than other catalyst surfaces. We have applied electron density difference (EDD), density of states (DOS), and Bader charge calculations to confirm the cooperative CH⋯O and agostic interactions between CH₄ and the Ir/α-Fe₂O₃(110) surface. To further modify the reactivity of the Ir/α-Fe₂O₃(110) surface towards methane activation, we conducted a study of the effect of oxygen vacancy (O_V) on C–H activation and CH₄ dehydrogenation. In the comparison of pristine α-Fe₂O₃(110), Ir/α-Fe₂O₃(110), and Ir/α-Fe₂O₃(110)–O_V surfaces, the Ir/α-Fe₂O₃(110)–O_V surface is the best in terms of CH₄ adsorption energy and C–H bond elongation, whereas the Ir/α-Fe₂O₃(110) surface catalyst has the lowest C–H bond activation barrier for the CH₄ molecule. The calculations indicate that the Ir/α-Fe₂O₃(110)–O_V surface could be a candidate catalyst for CH₄ dehydrogenation reactions.

The Fe₂O₃(110)–O_V surface is the best in terms of CH₄ adsorption energy and C–H bond elongation. Therfore, the Ir/α-Fe₂O₃(110)–O_V surface could be a candidate catalyst for CH₄ dehydrogenation reaction.     

Mesoporous anodic α-Fe2O3 interferometer for organic vapor sensing application

In this work, we reported the utilization of mesoporous α-Fe₂O₃ films as optical sensors for detecting organic vapors. The mesoporous α-Fe₂O₃ thin films, which exhibited obvious Fabry–Perot interference fringes in the reflectance spectrum, were successfully fabricated through electrochemical anodization of Fe foils. Through monitoring the optical thickness of the interference fringes, three typical organic species with different vapor pressures and polarities (hexane, acetone and isopropanol) were applied as probes to evaluate the sensitivity of the α-Fe₂O₃ based interferometric sensor. The experiment results showed that the as-synthesized mesoporous α-Fe₂O₃ interferometer displayed high reversibility and stability for the three organic vapors, and were especially sensitive to isopropanol, with a detection limit of about 65 ppmv. Moreover, the photocatalytic properties of α-Fe₂O₃ under visible light are beneficial for degradation of dodecane vapor residues in the nano-pores and refreshment of the sensor, demonstrating good self-cleaning properties of the α-Fe₂O₃-based interferometric sensor.

Mesoporous α-Fe₂O₃ interferometers with well-resolved optical fringes can display high sensitivity to organic vapors.     

α-Fe2O3 hollow meso–microspheres grown on graphene sheets function as a promising counter electrode in dye-sensitized solar cells

Although nanoparticles, nanorods, and nanosheets of α-Fe₂O₃ on graphene sheets have been synthesized, it remains a challenge to grow 3D α-Fe₂O₃ nanomaterials with more sophisticated compositions and structures on the graphene sheets. Herein, we demonstrate a facile solvothermal route under controlled conditions to successfully fabricate 3D α-Fe₂O₃ hollow meso–microspheres on the graphene sheets (α-Fe₂O₃/RGO HMM). Attributed to the combination of the catalytic features of α-Fe₂O₃ hollow meso–microspheres and the high conductivity of graphene, α-Fe₂O₃/RGO HMM exhibited promising electrocatalytic performance as a counter electrode in dye-sensitized solar cells (DSSCs). The DSSCs fabricated with α-Fe₂O₃ HMM displayed high power conversion efficiency of 7.28%, which is comparable with that of Pt (7.71%).

Although nanoparticles, nanorods, and nanosheets of α-Fe₂O₃ on graphene sheets have been synthesized, it remains a challenge to grow 3D α-Fe₂O₃ nanomaterials with more sophisticated compositions and structures on the graphene sheets.     

Magnetic hyperthermia with ε-Fe2O3 nanoparticles

Biocompatibility restrictions have limited the use of magnetic nanoparticles for magnetic hyperthermia therapy to iron oxides, namely magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃). However, there is yet another magnetic iron oxide phase that has not been considered so far, in spite of its unique magnetic properties: ε-Fe₂O₃. Indeed, whereas Fe₃O₄ and γ-Fe₂O₃ have a relatively low magnetic coercivity, ε-Fe₂O₃ exhibits a giant coercivity. In this report, the heating power of ε-Fe₂O₃ nanoparticles in comparison with γ-Fe₂O₃ nanoparticles of similar size (∼20 nm) was measured in a wide range of field frequencies and amplitudes, in uncoated and polymer-coated samples. It was found that ε-Fe₂O₃ nanoparticles primarily heat in the low-frequency regime (20–100 kHz) in media whose viscosity is similar to that of cell cytoplasm. In contrast, γ-Fe₂O₃ nanoparticles heat more effectively in the high frequency range (400–900 kHz). Cell culture experiments exhibited no toxicity in a wide range of nanoparticle concentrations and a high internalization rate. In conclusion, the performance of ε-Fe₂O₃ nanoparticles is slightly inferior to that of γ-Fe₂O₃ nanoparticles in human magnetic hyperthermia applications. However, these ε-Fe₂O₃ nanoparticles open the way for switchable magnetic heating owing to their distinct response to frequency.

ε-Fe₂O₃ is a magnetic iron(iii) oxide with a giant coercivity. Its potential in hyperthermia applications has been evaluated in comparison with γ-Fe₂O₃ over a wide range of field frequencies and amplitudes.     

Crystal growth control of rod-shaped ε-Fe2O3 nanocrystals

Herein we report crystal growth control of rod-shaped ε-Fe₂O₃ nanocrystals by developing a synthesis based on the sol–gel technique using β-FeO(OH) as a seed in the presence of a barium cation. ε-Fe₂O₃ nanocrystals are obtained over a wide calcination temperature range between 800 °C and 1000 °C. A low calcination temperature (800 °C) provides an almost cubic rectangular-shaped ε-Fe₂O₃ nanocrystal with an aspect ratio of 1.4, whereas a high calcination temperature (1000 °C) provides an elongated rod-shaped ε-Fe₂O₃ nanocrystal with an aspect ratio of 3.3. Such systematic anisotropic growth of ε-Fe₂O₃ is achieved due to the wide calcination temperature in the presence of barium cations. The surface energy and the anisotropic adsorption of barium on the surface of ε-Fe₂O₃ can explain the anisotropic crystal growth of rod-shaped ε-Fe₂O₃ along the crystallographic a-axis. The present work may provide important knowledge about how to control the anisotropic crystal shape of nanomaterials.

Crystal growth control of rod-shaped ε-Fe₂O₃ nanocrystals is achieved by a synthesis based on the sol–gel technique.     

Novel magnetic g-C3N4/α-Fe2O3/Fe3O4 composite for the very effective visible-light-Fenton degradation of Orange II

A novel magnetic heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst was successfully synthesized through a simple hydrothermal method. The structure, morphology, and optical properties of the catalyst were characterized. The photocatalytic activity of the heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst for the photo-Fenton degradation of Orange II in the presence of H₂O₂ irradiated with visible light (λ > 420 nm) at neutral pH was evaluated. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ photocatalyst was found to be an excellent catalyst for the degradation of Orange II and offers great advantages over the traditional Fenton system (Fe(ii/iii)/H₂O₂). The results indicated that successfully combining monodispersed Fe₃O₄ nanoparticles and g-C₃N₄/α-Fe₂O₃ enhanced light harvesting, retarded photogenerated electron–hole recombination, and significantly enhanced the photocatalytic activity of the system. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ (30%) sample gave the highest degradation rate constant, 0.091 min⁻¹, which was almost 4.01 times higher than the degradation rate constant for α-Fe₂O₃ and 2.65 times higher than the degradation rate constant for g-C₃N₄/α-Fe₂O₃ under the same conditions. A reasonable mechanism for catalysis by the g-C₃N₄/α-Fe₂O₃/Fe₃O₄ composite was developed. The g-C₃N₄/α-Fe₂O₃/Fe₃O₄ composite was found to be stable and recyclable, meaning it has great potential for use as a photo-Fenton catalyst for effectively degrading organic pollutants in wastewater.

A novel magnetic heterogeneous g-C₃N₄/α-Fe₂O₃/Fe₃O₄ catalyst was firstly synthesized and exhibited very effective visible-light-Fenton degradation of Orange II at neutral pH.     

Mesoporous MnFe2O4 magnetic nanoparticles as a peroxidase mimic for the colorimetric detection of urine glucose

Mesoporous MnFe₂O₄ magnetic nanoparticles (mMnFe₂O₄ MNPs) were prepared with a one-step synthesis method and characterized to possess intrinsic peroxidase-like activity, and had obvious advantages over other peroxidase nanozymes in terms of high catalytic affinity, high stability, mono-dispersion, easy preparation, and quick separation. The mMnFe₂O₄ MNPs were used as a colorimetric sensor for indirect sensing of urine glucose based on the sensing principle that H₂O₂ can be produced from glucose oxidation catalyzed by glucose oxidase (GOx), and under the catalysis of the mMnFe₂O₄ MNPs nanozyme, H₂O₂ can oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a blue color in a few minutes. This sensor is simple, cheap, sensitive, and specific to glucose detection with a detection limit of 0.7 μM, suggesting its potential for on-site glucose detection.

Schematic illustration of glucose detection with glucose oxidase (GOx) and mMnFe₂O₄ MNPs-catalyzed system.     

A highly selective and sensitive H2S sensor at low temperatures based on Cr-doped α-Fe2O3 nanoparticles

Cr-doped α-Fe₂O₃ nanoparticles were synthesized by a low-cost and environmentally friendly hydrothermal route. Their gas sensing properties were investigated and the sensor showed high sensitivity and selectivity to H₂S gas. Different Cr doping levels from 0 to 8.0 wt% were studied, and the sensor of 4.0 wt% Cr-doped α-Fe₂O₃ showed the largest response, with a response of 213 to 50 ppm H₂S at 100 °C. The incorporation of Cr ions within α-Fe₂O₃ nanocrystals increases the specific surface area, and promotes the oxidation of H₂S and oxygen adsorption in the air. Thus, the doping of Cr into α-Fe₂O₃ nanostructures would be a promising method for designing and fabricating high performance H₂S gas sensors.

Cr-doped α-Fe₂O₃ nanoparticles were synthesized by one-step hydrothermal reaction and showed high sensitivity and selectivity to H₂S at low temperature.     

A three-dimensional electrochemical oxidation system with α-Fe2O3/PAC as the particle electrode for ammonium nitrogen wastewater treatment

A three-dimensional particle electrode loaded with α-Fe₂O₃ on powdered activated carbon (PAC) (α-Fe₂O₃/PAC) was synthesized by the microwave method for removing ammonium nitrogen from wastewater in a three-dimensional electrode system. The α-Fe₂O₃/PAC electrode was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of the added α-Fe₂O₃/PAC on the removal of ammonium nitrogen from simulated wastewater was studied by changing the cell voltage, particle dosage, and particle electrode synthesis conditions. Simulated experiments were also carried out on different pollutants under the best experimental conditions and the actual domestic sewage was tested. The results show that the optimal synthesis conditions of the particle electrode are as follows: the ratio of PAC to anhydrous FeCl₃ is 1 : 2, and the microwave power is 1000 W for 60 s. After 20 min of electrolysis at 20 V, the ammonium nitrogen removal rate can reach 95.30%.

A microwave method was used to synthesis α-Fe₂O₃/PAC 3D particle electrode rapidly which can remove NH₄⁺–N from wastewater.     

Preparation of Ag3PO4/α-Fe2O3 hybrid powders and their visible light catalytic performances

The inefficiency of conventional photocatalytic treatment for removing rhodamine B is posing potential risks to ecological environments. Here, we construct a highly efficient photocatalyst consisting of Ag₃PO₄ and α-Fe₂O₃ hybrid powders for the treatment of rhodamine B. Ag₃PO₄ nanoparticles (nanoparticles, about 50 nm) are uniformly dispersed on the surface of α-Fe₂O₃ microcrystals (hexagonal sheet, about 1.5 μm). The Ag₃PO₄-deposited uniformity on the α-Fe₂O₃ surface first increased, then decreased on increasing the hybrid ratio of Ag₃PO₄ to α-Fe₂O₃. When the hybrid ratio of Ag₃PO₄ to α-Fe₂O₃ is 1 : 2, the distribution of Ag₃PO₄ particles on the sheet α-Fe₂O₃ is more uniform with excellent Ag₃PO₄/α-Fe₂O₃ interface performance. The catalytic degradation efficiency of hybrids with the introduction of Ag₃PO₄ nanoparticles on the α-Fe₂O₃ surface reached 95%. More importantly, the hybrid material exhibits superior photocatalytic stability. Ag₃PO₄/α-Fe₂O₃ hybrids have good reusability, and the photocatalytic efficiency could still reach 72% after four reuses. The excellent photocatalytic activity of the as-prepared hybrids can be attributed to the heterostructure between Ag₃PO₄ and α-Fe₂O_3, which can effectively inhibit the photoelectron–hole recombination and broaden the visible light response range.

We construct a highly efficient photocatalyst consisting of Ag₃PO₄ and α-Fe₂O₃ hybrid powders for the treatment of rhodamine B. The catalytic degradation efficiency reached 95% after 10 min.     

Cu@Au(Ag)/Pt nanocomposite as peroxidase mimic and application of Cu@Au/Pt in colorimetric detection of glucose and l-cysteine

Nanomaterial-based artificial peroxidase has attracted extensive interests due to their distinct advantages over natural counterpart. Cu@Au/Pt and Cu@Ag/Pt nanocomposite with rambutan-like structure were prepared and discovered to function like peroxidase, which was illustrated by catalyzing the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) accompanied with a blue color change. Steady-state investigation indicates that the catalytic kinetics of Cu@Au/Pt and Cu@Ag/Pt all followed typical Michaelis–Menten behaviors and Cu@Au/Pt showed a strong affinity for H₂O₂, while Cu@Ag/Pt showed strong affinity for TMB. The color change and absorbance intensity strongly depend on the concentration of H₂O₂, thus the direct determination of H₂O₂ and indirect detection of glucose were demonstrated using Cu@Au/Pt with a detection limit of 1.5 μM and 6 μM, respectively. What is more important, the method was applied for detection of glucose in 50% fetal bovine serum with a detection limit of 80 μM, which is much lower than the lowest glucose content in blood for diabetes (7 mM). Moreover, the Cu@Au/Pt nanocomposite were also successfully applied for sensing l-cysteine because of the inhibition effect. Considering the good peroxidase-like activity and novel structure, Cu@Au(Ag)/Pt is expected to have a wide range of applications in bioassays and biocatalysis.

Cu@Au(Ag)/Pt nanocomposite possess good peroxidase-like activity and can be used for detection of glucose and l-cysteine.     

Ultrasensitive detection of uric acid in serum of patients with gout by a new assay based on Pt@Ag nanoflowers

A ultrasensitive assay for the determination of uric acid (UA) based on Pt@Ag nanoflowers (Pt@Ag NFs) was constructed. H₂O₂ was formed by the reaction of uricase and UA and produced the hydroxyl radical (˙OH). The system was catalyzed by Pt@Ag NFs to change the color of 3,3′,5,5′-tetramethylbenzidine (TMB) from colorless to blue, and the morphology and chemical properties of Pt@Ag NFs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. Under the optimized conditions, a linear relationship between the absorbance and UA concentration was in the range of 0.5–150 μM (R² = 0.995) with a limit of detection of 0.3 μM (S/N = 3). The method can be applied to detection of UA in actual samples with satisfactory results. The proposed assay was successfully applied to the detection of UA in human serum with recoveries over 96.8%. Thus, these results imply that the UA assay provides an effective tool in fast clinical analysis of gout.

A ultrasensitive assay for the determination of uric acid (UA) based on Pt@Ag nanoflowers (Pt@Ag NFs) was constructed.     

Target-induced activation of DNAzyme for highly sensitive colorimetric detection of bleomycin via DNA scission

In this work, a label-free and sensitive colorimetric sensing strategy for the detection of bleomycin (BLM) was developed on the basis of BLM-mediated activation of G-quadruplex DNAzyme via DNA strand scission. A G-quadruplex based hairpin probe (G4HP) containing the scission site (5′-GT-3′) of BLM at the loop region and guanine (G)-rich sequences at its 5′-end was employed in this protocol. In the presence of BLM, it may cleave the 5′-GT-3′ site of the hairpin probe with Fe(ii) as a cofactor, releasing the G-tetrads DNA fragment, which may further bind hemin to form a catalytic G-quadruplex-hemin DNAzyme. The resultant G-quadruplex DNAzyme has notable peroxidase-like activity, which effectively catalyzes the oxidation of 2,2′-azino-bis(3-ethylbenzothiozoline-6-sulfonic acid) (ABTS) by H₂O₂ to produce the blue-green-colored free-radical cation (ABTS^·+). Therefore, the detection of BLM can be achieved by observing the color transition with the naked eye or measuring the absorbance at a wavelength of 420 nm using a UV-Vis spectrophotometer. Attributing to the specific BLM-induced DNA strand scission and the effective locking of G-tetrads in the stem of the G4HP, the colorimetric sensing strategy exhibits high sensitivity and selectivity for detection of BLM in human serum samples, which might hold great promise for BLM assay in biomedical and clinical research.

A label-free and sensitive colorimetric strategy for bleomycin detection was developed based on target-induced activation of DNAzyme via DNA scission.     

Efficient electrocatalyst of α-Fe2O3 nanorings for oxygen evolution reaction in acidic conditions

Large-scale application of sustainable energy devices urgently requires cost-effective electrocatalysts to overcome the sluggish kinetics related to the oxygen evolution reaction (OER) under acidic conditions. Here, we first report the highly efficient electrocatalytic characteristics of α-Fe₂O₃ nanorings (NRs), which exhibits prominent OER electrocatalytic activity with lower overpotential of 1.43 V at 10 mA cm⁻² and great stability in 1 M HCl, surpassing the start-of-the art Ir/C electrocatalyst. The significantly optimized OER activity of the α-Fe₂O₃ NRs mainly attributes to the synergistic effect of the excellent electrical conductivity and a large effective active surface because of their unique nanoring structure, disordered surface, and the dynamic stability of α-Fe₂O₃ NRs in acidic conditions.

α-Fe₂O₃ NRs is obtained for OER with lower small overpotential and great stability in 1 M HCl, surpassing Ir/C electrocatalyst.     

Molecular imprinting on PtPd nanoflowers for selective recognition and determination of hydrogen peroxide and glucose

PtPd nanoflowers (PtPd NFs) exhibit intrinsic peroxidase-like activity as nanozymes, but the nanozymes lack substrate specificity and have low catalytic activity. Herein, a molecularly imprinted nanogel on PtPd NFs was prepared by using 3,3′,5,5′-tetramethylbenzidine (TMB) as the template through the aqueous precipitation polymerization method. After the TMB was washed out, many substrate binding pockets were retained in the PtPd NFs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) were employed to characterize the molecularly imprinted polymer (MIP) PtPd nanoflowers (T-MIP-PtPd NFs). The obtained T-MIP-PtPd NFs exhibited enhanced catalytic activity and specific recognition for TMB. Compared with PtPd NFs, T-MIP-PtPd NFs showed a linear range from 0.01–5000 μM and a detection limit of 0.005 μM toward the detection of H₂O₂. Glucose can also be sensitively detected through cascade reaction by the T-MIP-PtPd NFs and glucose oxidase. Therefore, molecular imprinting on nanozymes technology shows promising application in biocatalysis and sensing fields.

PtPd nanoflowers (PtPd NFs) exhibit intrinsic peroxidase-like activity as nanozymes, but the nanozymes lack substrate specificity and have low catalytic activity.