Ngo Xuan Dinh

This study integrates DFT calculations with experimental results to elucidate the effect of Ni substitution within the ZnCo ₂ O ₄ spinel lattice on its electronic structure, active sites, and electrochemical response toward Pb( ii ).

Mn substitution in ZnCo ₂ O ₄ tuned redox properties and enhanced oxidase-like activity. Mn–O–Co centers promoted O ₂ activation and electron transfer. A colorimetric platform reliably detected ascorbic acid in juice, proving cation tuning for nanozymes.

In this study, MnCo ₂ O ₄ is successfully synthesized via a one-pot microwave-assisted hydrothermal method and uniformly integrated into the g framework. The resulting MnCo ₂ O ₄ @g composites are designed for the sensitive and selective detection of the antibiotic CAP and toxic Pb ²⁺ heavy metal ions in aqueous media, respectively. Structural and surface characteristics of the materials are analyzed using spectroscopic techniques, confirming their superior physicochemical properties, particularly those of the MnCo ₂ O ₄ @g composites. The MnCo ₂ O ₄ @g/SPE demonstrates enhanced electrochemical characteristics, including lower charge-transfer resistance ( R _ct = 1688 Ω and Δ E _p = 190 mV), a larger electrochemically active surface area (0.1708 cm ² ), and increased density of surface-active sites. Electrochemical sensing studies reveal efficient cathodic reduction of CAP and anodic oxidation of Pb ²⁺ at MnCo ₂ O ₄ @g-based sensor. The as-developed sensor exhibits favorable electron-transfer kinetics toward the redox processes of both analytes, corresponding to the following regression equations: I _pc (μA) = 0.006 ν (mV s ⁻¹ ) + 1.529 ( R ² = 0.997) for CAP and I _pa (μA) = 3.16 ν ^1/2 (mV s ⁻¹ ) ^1/2 –2.045 ( R ² = 0.998) for Pb ²⁺ . It achieves wide linear detection ranges (0.25–50 μM for CAP, 0.5–1000 ppb for Pb ²⁺ ), low LOD of 0.2 μM for CAP and 1.07 ppb for Pb ²⁺ ), and high sensitivities (1.3 μA•μM ⁻¹ •cm ⁻² for CAP, 0.24 μA•ppb ⁻¹ •cm ⁻² for Pb ²⁺ ).

Fe doping induces a synergistic enhancement of electronic conductivity and electrocatalytic activity in Gd ₂ O ₃ nanoparticles, enabling highly sensitive electrochemical detection of chloramphenicol in real pharmaceutical and milk samples.

This work presents a rapid synthesis of ZnO/ZnCo ₂ O ₄ heterojunctions with unique two dimensional (2D) nanostructure for the enhancement of electrochemical sensing of ofloxacin in water.

The adjustment of active metal ion centers and electronic structures for boosting the electrocatalytic activity of spinel oxide nanostructures is considered an efficient strategy for developing the advanced high-performance electrochemical sensors. Here, ZnCo ₂ O ₄ (ZCO-NPs) and Co ₃ O ₄ nanoparticles with a tendency to self-assembly into 1D nanostructure were prepared by a one-pot microwave-assisted hydrothermal method, and evaluated the electrochemical sensing performance towards small dopamine (DA) molecule in biofluid samples. The physicochemical properties were systematically studied by combining experiments and density functional theory (DFT) calculation. The DFT calculation results indicate the ZnCo ₂ O ₄ possesses the strongest affinity for dopamine amongst all three tested biomolecules (ascorbic acid, dopamine, uric acid), while Co ₃ O ₄ shows a higher affinity for ascorbic acid. Benefiting from the adjustment of surface catalyst centers and electronic structures induced by Zn substitution, the ZCO-NPs/SPE exhibited an approximate 36.6-fold increased electrochemical sensitivity towards DA than that of Co ₃ O ₄ -NPs. The ZCO-NPs-based electrochemical sensors also displayed outstanding performance in detection of DA with a detection limit as low as 56 nM, and reaching an electrochemical sensitivity of 5.2 μAμM ⁻¹ cm ⁻² . This work provides an innovative strategy based on reliable theoretical and experimental basis for the electronic structural regulation of spinel oxide nanostructures for ultrasensitive electrochemical sensing of small molecules.

Co-MnO₂ nanoparticles with oxygen vacancies and Mn/Co redox couples exhibit enhanced oxidase-mimicking activity. This highlights Co ion-doping as an effective strategy for performance improvement in nanozymes for colorimetric assays.