Hydrogen peroxide (H 2 O 2 ) is an eminent biomarker in pathogenesis; a selective, highly sensitive real-time detection of H 2 O 2 released from live cells has drawn a significant research interest in bioanalytical chemistry. Binary transition-metal oxides (BTMOs) displayed a recognizable benefit in enhancing the sensitivity of H 2 O 2 detection; although the reported BTMObased H 2 O 2 sensor's detection limit is still insufficient, it is not appropriate for in situ profiling of trace amounts of cellular H 2 O 2 . In this paper, we describe an efficient, reliable electrochemical biosensor based on Mn 2 CuO 4 (MCO) microspheres to assay cellular H 2 O 2 . The Mn 2 CuO 4 microspheres were prepared through a superficial solvothermal method. It is obvious from impedance studies, introduction of manganese into copper oxide lattice significantly improved the ionic conductivity, which is beneficial for the electrochemical sensing process. Thanks to the distinct microsphere structure and excellent synergy, MCO-modified electrode exhibited excellent nonenzymatic electrochemical behavior toward H 2 O 2 sensing. The MCO-modified electrode delivered a broad working range (36 nM to 9.3 mM) and an appreciable detection limit (13 nM), with high selectivity toward H 2 O 2 . To prove its practicality, the developed sensor was applied in the detection of cellular H 2 O 2 released by RAW 264.7 cells in presence of CHAPS. These results label the possible appliance of the sensor in clinical analysis and pathophysiology. Thus, BTMOs are evolving as a promising candidate in designing catalytic matrices for biosensor applications. KEYWORDS: reactive oxygen species (ROS), H 2 O 2 , manganese copper oxide, electrocatalysis, electrochemical sensor

Herein, we report the preparation of novel spinel-type CuCo2O4 nanoplates (CCO NPs) through a cost-effective, soft-template (citrate)-assisted method, followed by low-temperature calcination. In the synthesis process, the metal cations such as Cu2+ and Co2+ can react with citrate molecules via coordination interaction to form the CuCo-citrate at elevated temperature. During the calcination process at 500 °C, the citrate molecules were eliminated from the CuCo-citrate precursor via simple organic species, and thus, spinel-type CuCo2O4 nanoplates were formed successfully. Surface morphology, crystalline nature, and phase purity of as-synthesized CCO NPs were assessed by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). As-synthesized CuCo2O4 nanoplates were used to construct a sensitive and reliable enzyme-free electrochemical sensor of acetylcholine (ACh) that shows a meaningful limit of detection (30 nM) with broad dynamic range (0.2–3500 μM) covering the clinical range of ACh. Furthermore, the developed ACh sensor delivered long-term durability and good reproducibility. The point-of-care utility of the ACh sensor was demonstrated in spiked blood serum samples with acceptable recovery rates. The present work demonstrates a facile synthesis method with an extensive potential toward the preparation of binary transition metal oxides (BTMOs) for divergent electrocatalytic applications.

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Exploring rapid, highly sensitive, cost-effective assay platforms to diagnose neurotransmitters is crucial in clinical biology. We propose a Cu@Cu2O nanospheres embedded B and N co-doped mesoporous carbon (BNDC) nanoelectrocatalyst to assay dopamine (DA) and acetylcholine (ACh). The Cu@Cu2O-BNDC catalyst has been prepared through a single step polymerization, followed by a carbonization. TEM results revealed that Cu@Cu2O nanoparticles appeared as nanospheres (size = 30 ± 5) entrapped on the mesoporous BNDC. Further, the catalyst possesses a specific surface area of 1025 m2 g–1 along with a pore size of 4 nm offers enormous active surface area for electrochemical sensing applications. The Cu@Cu2O-BNDC catalyst was employed in electrochemical sensing of DA and ACh in a working range of 0.004–542 μM and 0.3–2602 μM, and detection limits of 0.5 nM and 17 nM, respectively. The practicality of the developed sensor has been assessed via DA (pH 7) and ACh (0.1 M NaOH) spiked in human blood serum samples, and satisfactory recovery was obtained. On top of this, the proposed synthetic protocol of the catalyst can be a versatile route to achieve heteroatom doped carbon nanomaterials possessing an enormous surface area and desirable morphology.

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