Effect of Morphology of ϵ‐MnO2on Hydrogen Peroxide Sensing

Morphology Effect of One-Dimensional MnO2 Nanostructures on Heteroatom-Doped Carbon Dot-Based Biosensors for Selective Detection of Glutathione

Structural versatility of MnO₂ nanostructures plays a significant role in biosensing applications. So, we have prepared simple and selective "turn-off-on" sensing probes for the detection of glutathione (GSH), based on nitrogen, sulfur codoped carbon dots (N, S-Cdots) and different morphologies of one-dimensional (1-D) MnO₂ nanostructures. N, S-Cdots with a high fluorescence quantum yield (73.42%) were prepared by a green approach through high-temperature pyrolysis in just 5 min. The different morphologies of 1-D MnO₂ nanostructures (nanowires with varying aspect ratios and nanorods) were synthesized through a hydrothermal method by varying the reaction period (8, 10, and 12 h). MnO₂ nanowires prepared at 8 h showed a high specific surface area (34 m² g^-1) with a large aspect ratio. They showed significant fluorescence quenching, Stern-Volmer constants, and binding constants in the presence of N, S-Cdots. Further, ultraviolet-visible absorption, zeta potential, and time decay studies showed that the quenching mechanism of the developed sensing system was the inner filter effect, which was further confirmed by using the Parker equation. The N, S-Cdots-MnO₂ nanowire (with a high aspect ratio) sensing system showed the best limit of detection, i.e., 28.5 μM for GSH. This fast, simple, eco-friendly, and cost-effective sensing system can be further used for real-time biosensing and bioimaging application.

3D carbonized wood-based integrated electrochemical immunosensor for ultrasensitive detection of procalcitonin antigen

This work presents a novel 3D carbonized wood-based integrated electrochemical immunosensor for ultrasensitive detection of procalcitonin (PCT) antigen at picogram level, achieving a wide linear detection range for PCT concentrations range from 0.05 to 90 pg mL^-1 with a low detection limit of 0.014 pg mL^-1 (S/N = 3), outperforming the previous reports. 3D carbonized wood as a new immunosensor matrix is used for electrochemical PCT biosensing, improving the stability of electrode and overcoming the disadvantages of traditional glassy carbon electrode (GCE). It obtained an excellent detection result, due to it has abundant mutual crisscross microchannels that promote the reactants and electrons transfer, greatly amplify the current signal. This novel sandwich-type electrochemical immunosensor is composed of 3D carbonized wood, carboxylic multi-walled carbon nanotube (cMWCNT), Au@Co₃O₄ core-shell nanosphere and Au/single layer nitrogen-doped graphene (Au/SL-NG), when it is applied for PCT detection in real clinical samples, it exhibits high accuracy same as enzyme-linked immunosorbent assay (ELISA) method.

Studies on the Morphology Effect on Catalytic Ability of a Single MnO2 Catalyst Particle with a Solid Nanopipette

Investigating the catalytic ability of an individual catalyst particle helps to understand heterogeneity and can provide new insights into the synthesis of high-efficiency catalysts. Solid-state nanopores have become a promising tool for detecting single molecules/particles due to their high temporal and spatial resolution. Here, we report a nanopore-based strategy for the evaluation and comparison of a single MnO₂ catalyst particle with different morphologies by monitoring the generated O₂ bubbles from the catalytic decomposition of H₂O₂. The finite element simulation was introduced to account for the flow velocity and bubble-induced current variation in the nanopore. In particular, the differences in catalytic ability of spherical and cubic MnO₂ have been studied by calculating the production rate and volume of O₂. It demonstrates that the shape of a single MnO₂ catalyst particle has a significant effect on its catalytic activity indeed.

Morphology-Dependent Performance of MnO2 Nanostructure-Carbon Dot-Based Biosensors for the Detection of Glutathione

Herein, we develop a facile, sensitive, and selective fluorescent nanosensor for the detection of glutathione (GSH). In this protocol, carbon dots (Cdots) with a fairly high quantum yield were synthesized by a microwave-assisted pyrolysis technique. Moreover, different shapes of the MnO₂ nanostructure were also prepared by the hydrothermal technique. A comparative photophysical study of different morphology-dependent Cdots@MnO₂ nanostructure-based biosensors was explored, which showed different results for the quenching values of ("turn-off") fluorescence intensity, quantum yields, electron transfer rate, and average lifetime. The structure, property, and performance of nanomaterials are interdependent. Therefore, the different shapes of MnO₂, that is, nanoflowers (NFs), nanorods (NRs), and a mixture of NFs/NRs was prepared by the hydrothermal method owing to different specific surface areas (23-69 m² g^-1) which put the impact on their sensing activity. It was observed that the variation in the different photophysical parameters of fluorescent Cdots such as quantum yield (Φ), average lifetime values [τ_av (ns)], radiative (k_r) rate constant, nonradiative (k_nr) rate constant, rate of electron transfer (k_ET), the efficiency of electron transfer (Φ_EET), FRET efficiency (E), and Förster distance (R₀) were dependent on the different shapes of the MnO₂ nanostructure. These results indicate that the transfer of energy occurs between the Cdots and different shapes of MnO₂ nanostructures based on fluorescence resonance energy transfer at different charge-transfer rates. The recovery rate ("turn-on") of fluorescence of Cdots with the addition of GSH was obtained best for the NF structure by conversion of MnO₂ to Mn²⁺, and the limit of detection was obtained as ∼19 μM for GSH. The developed sensing probes were rapid, easy, cheap, and eco-friendly for the determination of GSH.

A ferrocene-linked metal-covalent organic polymer as a peroxidase-enzyme mimic for dual channel detection of hydrogen peroxide

A novel ferrocene-linked metal-covalent organic polymer (MCOP-NFC) was synthesized through the Claisen-Schmidt condensation reaction of 1,1'-diacetyl ferrocene and tris(4-formylphenyl)amine. MCOP-NFC acts as a highly efficient artificial enzyme for mimicking peroxidase, and shows good stability in harsh chemical environments including strong bases and acids, and boiling water. Based on the peroxidase-like activity of MCOP-NFC, a highly sensitive dual channel detection method for hydrogen peroxide was developed. For the colorimetric detection strategy, the limit of detection (LOD) reached 2.1 μM, while the limit of detection was found to be as low as 0.08 μM based on the electrochemical detection channel. This study offers a new strategy for the development of an enzyme mimetic on the basis of the covalent assembly of nanostructures, and the proposed electrochemical-colorimetric sensor for H₂O₂ detection has great potential for applications in biology and biomedicine.