A Simple and Low-Cost Electrochemical Immunosensor for Ultrasensitive Determination of Calreticulin Biomarker in Human Serum

An early on time detection of breast cancer significantly affects the treatment process and outcome. Herein, a new label-free impedimetric biosensor is developed to determine the lowest change in the level of calreticulin (CALR), which is a new biomarker of breast carcinoma. The proposed immunosensor is fabricated by using reduced graphene oxide/amino substituted polypyrrole polymer (rGO-PPyNH₂) nanocomposite modified disposable electrode. The anti-CALR antibodies are first attached on the rGO-PPyNH₂ nanocomposite coated electrode through glutaraldehyde crosslinking; the CALR antigens are then immobilized with the addition of CALR antigens to form an immunocomplex on the sensing surface. This immunocomplex induces considerably larger interfacial electron transport resistance (R_ct). The variation in the R_ct has a linear relationship with CALR level in the detection range of 0.025 to 75 pg mL⁻¹, with a detection limit of 10.4 fg mL⁻¹. The suggested biosensor shows high selectivity to CALR, good storage stability (at least 5 weeks) and suitable reproducibility results as shown in quality control chart. The designed immunosensor is utilized to analyze CALR levels in human sera with satisfying results. This immunosensor provides a novel way for the clinical determination of CALR and other cancer biological markers.     

Magnetic Fe3O4@Au composite-enhanced surface plasmon resonance for ultrasensitive detection of magnetic nanoparticle-enriched α-fetoprotein

Small molecules or analytes present at low concentrations are difficult to detect directly using conventional surface plasmon resonance (SPR) techniques because only small changes in the refractive index of the medium are typically induced by the binding of these analytes. Here, we present an amplification technique using core–shell Fe₃O₄@Au magnetic nanoparticles (MNPs) for an SPR bioassay. To evaluate this amplification effect, a novel SPR sensor based on a sandwich immunoassay was developed to detect α-fetoprotein (AFP) by immobilizing a primary AFP antibody (Ab₁) on the surface of a 3-mercapto-1-propanesulfonate/chitosan-ferrocene/Au NP (MPS/CS-Fc/Au NP) film employing Fe₃O₄@Au–AFP secondary antibody conjugates (Fe₃O₄@Au–Ab₂) as the amplification reagent. The stepwise fabrication of the biosensor was characterized using UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. A calibration curve of Fe₃O₄@Au–Ab₂ conjugates amplification for AFP detection was obtained to yield a correlation in the range of 1.0–200.0 ng mL⁻¹ with a detection limit of 0.65 ng mL⁻¹, and a significant increase in sensitivity was therefore afforded through the use of Fe₃O₄@Au–Ab₂ conjugates as an amplifier. This magnetic separation and amplification strategy has great potential for the detection of other biomolecules of interest with low interference and high sensitivity by changing the antibody label used in the Fe₃O₄@Au–antibody conjugates.     

A Novel Amperometric Glucose Biosensor Based on Fe3O4-Chitosan-β-Cyclodextrin/MWCNTs Nanobiocomposite

A novel enzymatic biosensing platform toward glucose is achieved with nanocomposite of magnetic nanoparticles (Fe₃O₄−CS−CD) and multi-walled carbon nanotubes (MWCNTs). The synergistic effect of chitosan, β-cyclodextrin and MWCNTs can facilitate electron transfer between enzyme and electrode based on the promoting results of the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The new biosensors exhibited direct electron transfer (DET) from enzyme to electrode after glucose oxidase (GOx) was immobilized on the modified electrode with the nanocomposite. Consequently, the enzymatic glucose biosensor displayed a considerably wide linear range (40 μM to 1.04 mM) with a high sensitivity of 23.59 μA mM⁻¹cm⁻², low detection limit of 19.30 μM, good selectivity, reproducibility and repeatability for detecting glucose. In addition, the current response still retained at 93.4 % after 25 days. Furthermore, the practical application of glucose biosensor was test in human serum samples with satisfactory accuracy, demonstrating promising and practical potential in biomedical diagnostics.     

A 2D cadmium metal–organic framework: Synthesis,structure and luminescence sensing for chromate,permanganate, cupric,silver and ferric

A multi-responsive Cd metal–organic framework {[Cd (ttpe)(H₂O)(ip)]•4H₂O•DMAC}_n ( 1•4H ₂ O•DMAC ) was synthesized using hydrothermal method (ttpe = 1,1,2,2-tetra(4-(1H-1,2,4-triazol-1-yl)phenyl)ethylene, ip = isophthalate, DMAC = N,N-dimethylacetamide), and characterized. 1 exhibits a 2D (4,4) network. The luminescent sensing experimrnts showed that 1•4H ₂ O•DMAC as a new MOF luminescent sensor can detect Cr₂O₇²⁻, CrO₄²⁻, MnO₄⁻, Cu²⁺, Ag⁺ and Fe³⁺ in aqueous solution with simultaneously high efficiency and high sensitivity. The quenching constants K_sv for Cr₂O₇²⁻, CrO₄²⁻, MnO₄⁻, Cu²⁺, Ag⁺ and Fe³⁺ are 4.231 × 10⁴ M⁻¹, 2.471 × 10⁴ M⁻¹, 6.459 × 10³ M⁻¹, 7.617 × 10³ M⁻¹, 1.563 × 10⁴ M⁻¹ and 3.574 × 10⁴ M⁻¹, respectively. The detection limits are 0.094 μM for Cr₂O₇²⁻, 0.108 μM for CrO₄^{2 −} , 0.346 μM for MnO₄⁻, 0.302 μM for Cu²⁺, 0.221 μM for Ag ⁺ , and 0.100 μM for Fe³⁺. 1•4H ₂ O•DMAC exhibits high photocatalytic efficiency for degradation of methylene blue under visible light irradiation.     

Ultrasensitive electrochemical immunosensors for multiplexed determination using mesoporous platinum nanoparticles as nonenzymatic labels

An ultrasensitive multiplexed immunoassay method was developed at a disposable immunosensor array using mesoporous platinum nanoparticles (M-Pt NPs) as nonenzymatic labels. M-Pt NPs were prepared by ultrasonic method and employed to label the secondary antibody (Ab₂) for signal amplification. The immunosensor array was constructed by covalently immobilizing capture antibody (Ab₁) on graphene modified screen printed carbon electrodes (SPECs). After the sandwich-type immunoreactions, the M-Pt-Ab₂ was bound to immunosensor surface to catalyze the electro-reduction of H₂O₂ reaction, which produced detectable signals for readout of analytes. Using breast cancer related panel of tumor markers (CA125, CA153 and CEA) as model analytes, this method showed wide linear ranges of over 4 orders of magnitude with the detection limits of 0.002 U mL⁻¹, 0.001 U mL⁻¹ and 7.0 pg mL⁻¹ for CA125, CA153 and CEA, respectively. The disposable immunosensor array possessed excellent clinical value in cancer screening as well as convenient point of care diagnostics.     

Fe3O4 Nanorods-RGO-ionic Liquid Nanocomposite Based Electrochemical Sensor for Aflatoxin B1 in Ground Paprika

A novel and sensitive method for the determination of aflatoxin B1 (AFA−B1) in ground paprika using a methyltrioctylammonium chloride ionic liquid (IL), iron oxide nanorods (Fe₃O₄ nanorods) and reduced graphene oxide (RGO) fabricated glassy carbon electrode (GCE) was developed. The synthesized nanoparticles, nanocomposites and modified electrode surfaces were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA/DSC) and x-ray diffraction (XRD) analyses. Moreover, the electrochemical performance of the developed sensor was determined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results demonstrate that the sensitivity of AFA−B1 is significantly enhanced on RGO-Fe₃O₄ nanorods-IL-GCE in comparison with bare GCE, RGO-GCE and RGO-Fe₃O₄ nanorods-GCE. The redox peak currents of AFA−B1 exhibited good linear relationship with its concentration in the range from 0.02 to 0.33 ng mL⁻¹ with detection limit of (LOD) 0.03 ng mL⁻¹ and limit of quantification (LOQ) 0.36 ng mL⁻¹ respectively (S/N=3). In addition, the fabricated electrode showed good stability and reproducibility. The proposed technique was effectively applied to identify the AFA−B1 in real ground paprika samples with acceptable results.     

A Prostate Specific Antigen Immunosensor Based on Biotinylated‐Antibody/Cyclodextrin Inclusion Complex: Fabrication and Electrochemical Studies

Immobilization of biomolecules with a proper orientation is considered as a basis for diverse biotechnological applications. Herein, we report a host‐guest inclusion complexation between β‐cyclodextrin (β‐CD) and biotin as a versatile approach for the immobilization of biomolecules. As a practical application, a sandwich‐type electrochemical immunosensor was designed for the determination of prostate specific antigen (PSA). The immunosensor was fabricated by in situ electropolymerization of poly(N‐acetylaniline) onto a rGO‐modified Pt electrode. Then, β‐CD was covalently grafted onto the over‐oxidized polymer backbone. For improving the efficiency of the assay, AuNPs were casted on the polymeric film, on the surface of which thionine (TH) as an electron mediator was covalently immobilized. Using a host‐guest inclusion complexation between β‐CD and biotin, a β‐CD/biotin‐Ab₁/PSA/Ab₂‐horseradish peroxidase (HRP) sandwich was formed on the electrode surface. The analytical signal was produced via electrochemical reduction of TH_ox, generated by biocatalytic oxidation of the TH_red in the presence of HRP/H₂O₂. Under optimal conditions, the proposed sensor responded linearly to PSA in the range from 10.0 pg mL⁻¹ to 25.0 ng mL⁻¹, with a low detection limit of 6.7 pg mL⁻¹ (S/N=3). Kinetic parameters of the interaction of β‐CD with Ab₁ were also investigated. Finally, the applicability of the immunosensor was successfully investigated for the detection of PSA in human serum samples.     

A novel, ultra sensible biosensor built by layer-by-layer covalent attachment of a receptor for diagnosis of tumor growth

In the presented research, a novel, ultra sensitive biosensor for the impedimetric detection of vascular endothelial growth factor (VEGF) is introduced. The human vascular endothelial growth factor receptor 1 (VEGF-R1, Flt-1) was used as a biorecognition element for the first time. The immobilization of VEGF-R1 on glassy carbon electrodes was carried out using layer-by-layer covalent attachment of VEGF-R1. The electrochemical properties of the layers constructed on the electrodes were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The differences in electron transfer resistance (R_et) between the working solution and the biosensor surface, recorded by the redox probe K₃[Fe(CN)₆]/K₄[Fe(CN)₆], confirmed the binding of VEGF to VEGF-R1. The new biosensor allowed a detection limit of 100 fg mL⁻¹ with a linear range of 100–600 fg mL⁻¹ to be obtained. The biosensor also exhibited good repeatability (with a correlation coefficient of 1.95%), and reproducibility.     

Calcium Carbonate–Gold Nanocluster Hybrid Spheres: Synthesis and Versatile Application in Immunoassays

Fluorescent gold nanoclusters (AuNCs) were incorporated into porous calcium carbonate spheres through electrostatic interaction. The resulting CaCO₃/AuNCs hybrid material exhibited interesting properties, such as porous structure, excellent biocompatibility, good water solubility, and degradability. These properties make the CaCO₃/AuNCs hybrid material a promising template to assemble horseradish peroxidase/antibody conjugates (HRP‐Ab₂). By using CaCO₃/AuNCs/HRP‐Ab₂ bioconjugates as probes, a versatile immunosensor was developed for fluorescent and electrochemical detection of the cancer biomarker neuron‐specific enolase (NSE). The detection limits of the sensor were 2.0 and 0.1 pg mL^?1 for fluorescent and electrochemical detection, respectively. The immunosensor shows high sensitivity and offers an alternative strategy for the detection of other proteins and DNA.     

Aptamer-functionalized Ti3C2-MXene Nanosheets with One-step Potentiometric Detection of Programmed Death-ligand 1

This communication describes a simple sensitive one-step potentiometric aptasensing method for quantitative detection of a referenced therapeutic biomarker (programmed death-ligand 1, PD−L1). The aptasensor is constructed by modifying PD−L1-specific aptamer on Ti₃C₂-MXene nanosheets-functionalized electrode. Introduction of PD−L1 induces the specific reaction between PD−L1 and aptamer, thereby resulting in the change of spatial structures. The surface electric potential of modified electrode is shifted upon addition of PD−L1 proteins before and after the reaction of aptamer with the analyte. Interestingly, potentiometric aptamer with Ti₃C₂-MXene nanosheets can achieve a higher sensitivity and a lower detection limit toward target PD−L1 relative to aptamer-modified electrode. Experimental results indicated that the linear range and detection limit of using Ti₃C₂-MXene nanosheets were 0.01–100 ng mL⁻¹ and 7.8 pg mL⁻¹ PD−L1, respectively. Meanwhile, the specificity, reproducibility, storing stability and accuracy of potentiometric aptasensor are acceptable for the screening of PD−L1 in human serum samples.     

Synthesis,Characterisation of Novel Polyaniline Nanomaterials and Application in Amperometric Biosensors

Summary: Anthracene sulfonic acid doped polyaniline nanomaterials were prepared through the chemical oxidative polymerisation process. Ammonium peroxydisulfate (APS) was employed as oxidant. Scanning electron microscopy (SEM) results show the resultant polyaniline (PANi) materials exhibited nanofibrillar morphology with diameter sizes less than 300 nm. Using the nanofibrillar PANI, amperometric biosensors for H₂O₂ and erythromycin were constructed through the drop-coating technique. Anthracene sulfonic acid (ASA) doped PANi and the test enzymes horseradish peroxidase, (HRP), or cytochrome P₄₅₀ 3A4, (CYP₄₅₀3A4) were mixed in phosphate buffer solution before drop coating onto the electrode. The resultant biosensors displayed typical Michaelis-Menten behaviour. The apparent Michaelis-Menten constant obtained was 0.18 ± 0.01 mM and 0.80 ± 0.02 µM L⁻¹ for the peroxide and erythromycin biosensor respectively. The sensitivity for the peroxide sensor was 3.3 × 10⁻³ A · cm⁻² · mM⁻¹, and the detection limit was found to be 1.2 × 10⁻² mM respectively. Similarly, the sensitivity for the erythromycin sensor was in the same order at 1.57 × 10⁻³ A · cm⁻² · mM⁻¹ and detection limit was found to be 7.58 × 10⁻² µM.     

Enzyme-catalyzed silver deposition on irregular-shaped gold nanoparticles for electrochemical immunoassay of alpha-fetoprotein

A new and disposable electrochemical immunosensor was designed for detection of alpha-fetoprotein (AFP), as a model analyte, with sensitivity enhancement based on enzyme-catalyzed silver deposition onto irregular-shaped gold nanoparticles (ISGNPs). The assay was carried out with a sandwich-type immunoassay protocol by using ISGNP-labeled anti-AFP antibodies conjugated with alkaline phosphatase (ALP–Ab₂) as detection antibodies. The enzymatically catalytic deposition of silver on the electrode could be measured by stripping analysis in KCl solution due to the Ag/AgCl solid-state voltammetric process. Several labeling protocols including spherical gold nanoparticle-labeled ALP–Ab₂ and ISGNP-labeled ALP–Ab₂ were investigated for determination of AFP, and improved analytical properties were achieved with the ISGNP labeling. With the ISGNP labeling method, the effects of incubation time and incubation temperature for antigen-antibody reaction, and deposition time of silver on the current responses of the electrochemical immunosensors were also monitored. Under optimal conditions, the electrochemical immunosensor exhibited a wide dynamic range from 0.01 ng mL⁻¹ to 200 ng mL⁻¹ with a detection limit of 5.0 pg mL⁻¹ AFP. The immunosensor displayed a good stability and acceptable reproducibility and accuracy. No significant differences at the 95% confidence level were encountered in the analysis of 10 clinical serum samples between the developed immunoassay and the commercially available electrochemiluminescent method for determination of AFP.     

A sensitive DNA biosensor based on the distance dependent quenching of Silica@Ru(bpy)32+-chitosan-GO electrochemiluminescence by Ferrocene@Gold nanoparticles

A sensitive electrochemiluminescence (ECL) biosensor for the specific DNA sequence of hepatitis C virus (HCV) was developed based on the efficient quenching effect of the ferrocene cluster functionalized gold nanoparticles (Fc@AuNPs) on the ECL of electrodeposited silica@Ru(bpy)₃²⁺-chitosan-graphene oxide nanocomposite (SiO₂@Ru−CS−GO). Graphene oxide (GO) can accelerate electron transfer rate, thus improving the ECL of Ru(bpy)₃²⁺ on electrode surface. The molecular beacons (MB) was fixed to SiO₂@Ru−CS−GO by glutaraldehyde (GA) using the Schiff reaction between amino groups of chitosan (CS) and MB. The ECL of SiO₂@Ru−CS−GO was depressed greatly by the Fc@AuNPs labelled at the end of MB, then, a stronger ECL was observed when the distance between Fc@AuNPs and SiO₂@Ru−CS−GO increased after the hybridization of target DNA with MB. Under optimum conditions, the restored ECL intensity increased linearly with the target DNA concentration in the range of 1.0×10⁻¹⁶∼1.0×10⁻¹⁰ mol ⋅ L⁻¹, and the limit of detection (LOD) is 1.4×10⁻¹⁷ mol ⋅ L⁻¹. The proposed method exhibits acceptable stability and reproducibility. In general, the constructed HCV biosensor can be used for the sensitive detection of HCV in human serum, suggesting potential application prospects in bioanalysis.     

Coordination-Induced N−H Bond Splitting of Ammonia and Primary Amine of CuI−MOFs

We report a porous three-dimensional anionic tetrazolium based Cu^I−MOF 1 , which is capable of cleaving the N−H bond of ammonia and primary amine, as well as the O−H bond of H₂O along with spontaneous H₂ evolution. In the gas-solid phase reaction of 1 with ammonia and water vapor, Cu^I−MOF 1 was gradually oxidized to NH₂−Cu^II−MOF and OH−Cu^II−MOF, through single-crystal-to-single-crystal (SCSC) structural transformations, which was confirmed by XPS, PXRD and X-ray single-crystal diffraction. Density functional theory (DFT) demonstrated that Cu^I−MOF could lower N−H bond dissociation free energy of ammonia through coordination-induced bond weakening and promote H₂ evolution by the reduction potential of 1 . To our knowledge, this is the first example of MOFs that activate ammonia and amine in gas-solid manner.     

Naked-eye detection of Cu (II) and Fe (III) based on a Schiff Base Ruthenium complex with nicotinohydrazide

A cyclometalated ruthenium (II) complex 1 [(Ru (Phen)₂(Pbznh)]⁺ PF₆⁻ (Phen = 1,10-phenanthroline and Pbznh = N-(4-(pyridine-2-yl)benzylidene) nicotinohydrazide) with nicotinohydrazide as a functional group was synthesized and characterized. Changes of its absorption spectra and color induced by Cu²⁺ and Fe³⁺ were systematic investigated. The results demonstrated that complex 1 could be served as a colorimetric probe to fast, selective and sensitive detection of Cu²⁺ and Fe³⁺ both in acetonitrile and filter paper based strips. Upon addition of Cu²⁺ and Fe³⁺ to solution of probe 1 , solution color changed from pink to colorless and light yellow respectively, and their corresponding detection limit were calculated to be 3.26 × 10⁻⁸ M and 3.12 × 10⁻⁷ M. Moreover, color of test papers with 1 changed from pink to colorless/yellow when Cu²⁺/Fe³⁺ were dropwise added. Therefore, it can be used as a desirable ‘naked-eye’ indicator candidate for Cu²⁺ and Fe³⁺.     

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2S Electrodes for Lithium-Ion Batteries

Owing to their high specific capacity and abundant reserve, Cu_xS compounds are promising electrode materials for lithium-ion batteries (LIBs). Carbon compositing could stabilize the Cu_xS structure and repress capacity fading during the electrochemical cycling, but the corresponding Li⁺ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu₂S was synthesized by CuS co-precipitation and thermal reduction with polyelectrolytes. High-temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu₂S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X-ray absorption spectroscopy. The N-doped carbon-composited Cu₂S (Cu₂S/C) exhibits an initial discharge capacity of 425 mAh g⁻¹ at 0.1 A g⁻¹, with a higher, long-term capacity of 523 mAh g⁻¹ at 0.1 A g⁻¹ after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g⁻¹ after 200 cycles. Multiple-scan cyclic voltammetry proves that extra Li⁺ storage can mainly be ascribed to the contribution of the capacitive storage.     

A Carbon-Negative Hydrogen Production Strategy: CO2 Selective Capture with H2 Production

We reported a strategy of carbon-negative H₂ production in which CO₂ capture was coupled with H₂ evolution at ambient temperature and pressure. For this purpose, carbonate-type Cu_xMg_yFe_z layered double hydroxide (LDH) was preciously constructed, and then a photocatalysis reaction of interlayer CO₃²⁻ reduction with glycerol oxidation was performed as driving force to induce the electron storage on LDH layers. With the participation of pre-stored electrons, CO₂ was captured to recover interlayer CO₃²⁻ in presence of H₂O, accompanied with equivalent H₂ production. During photocatalysis reaction, Cu_0.6Mg_1.4Fe₁ exhibited a decent CO evolution amount of 1.63 mmol g⁻¹ and dihydroxyacetone yield of 3.81 mmol g⁻¹. In carbon-negative H₂ production process, it showed an exciting CO₂ capture quantity of 1.61 mmol g⁻¹ and H₂ yield of 1.44 mmol g⁻¹. Besides, this system possessed stable operation capability under simulated flu gas condition with negligible performance loss, exhibiting application prospect.     

Development of a Bacterial Enzyme-Based Biosensor for the Detection and Quantification of Selenate

An enzymatic biosensor has been developed for the determination of selenate (SeO₄²⁻), in which selenate reductase (SeR) is chemically attached to a gold disk electrode by lipoic acid N-hydroxysuccinimide ester as linker, allowing the catalytic reduction of the SeO₄²⁻ to SeO₃²⁻. Modification of the gold electrode was characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and electrochemistry. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were performed in different buffers for selenate determination. Under optimum conditions, the calibration curve was linear over the range 7.0–3900.0 μg L⁻¹ with limits of detection and quantification of 4.97 and 15.56 μg L⁻¹, respectively. The possible interference of the relevant oxyanions SO₄²⁻, NO₃⁻, NO₂⁻, PO₄³⁻ and AsO₄³⁻ in the determination of SeO₄²⁻ was studied. Finally, the proposed biosensor was used to determine SeO₄²⁻ with recovery between 95.2 and 102.4 % in different real water samples.     

An Electrochemical ATP Biosensor with Enzymes Entrapped within a PEDOT Film

This paper reports on the electrochemical behavior of an ATP biosensor that utilizes glucose oxidase (GOx) and hexokinase (Hex) immobilized within the electroactive polymer, polyethylenedioxythiophene (PEDOT). This biosensor design detects ATP indirectly at 0.85 V vs. Ag/AgCl based on the oxidation current for enzymatically generated H₂O₂, and at −0.20 V; a potential at which improved analyte selectivity is achieved. The detection figures of merit at both detection potentials are a response time of 15±1 s, an experimental detection limit of 10.0±0.2 μmol L⁻¹ (S/N=3), and a sensitivity in the range of 100–500 mA M⁻¹cm⁻².     

Selective Four-Electron Reduction of Oxygen by a Nonheme Heterobimetallic CuFe Complex

We report herein the first nonheme CuFe oxygen reduction catalyst ([Cu^II(bpbp)(μ-OAc)₂Fe^III]²⁺, CuFe−OAc ), which serves as a functional model of cytochrome c oxidase and can catalyze oxygen reduction to water with a turnover frequency of 2.4×10³ s⁻¹ and selectivity of 96.0 % in the presence of Et₃NH⁺. This performance significantly outcompetes its homobimetallic analogues (2.7 s⁻¹ of CuCu−OAc with %H₂O₂ selectivity of 98.9 %, and inactive of FeFe−OAc ) under the same conditions. Structure-activity relationship studies, in combination with density functional theory calculation, show that the CuFe center efficiently mediates O−O bond cleavage via a Cu^II(μ-η¹ : η²-O₂)Fe^III peroxo intermediate in which the peroxo ligand possesses distinctive coordinating and electronic character. Our work sheds light on the nature of Cu/Fe heterobimetallic cooperation in oxygen reduction catalysis and demonstrates the potential of this synergistic effect in the design of nonheme oxygen reduction catalysts.