Ti3C2Tx MXene-derived TiO2/C-QDs as oxidase mimics for the efficient diagnosis of glutathione in human serum.

Nanozyme-based colorimetry was suggested to be a rapid method for biomarker (e.g. glutathione) detection, but this method suffers from lack of efficiency and low-toxicity nanozymes till now. Herein, quantum dots of TiO2 loaded on carbon (TiO2/C-QDs) oxidase-like nanozymes were prepared via a hydrothermal treatment of tiny and few-layered Ti3C2Tx MXene nanosheets, which possess abundant thermodynamic metastable Ti atoms on MXene margins as raw materials for the preparation of TiO2/C-QDs. The oxygen vacancy in TiO2 on the surface of the carbon matrix can facilitate O2 adsorption in the solution and generate reactive oxygen species (ROS), thereby quickly oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidized form (TMBox) in the absence of H2O2. After adding glutathione (GSH), TMBox was able to be restored to TMB, which resulted in a corresponding decrease in the UV-vis absorbance value at 652 nm. Furthermore, this assay possesses good selectivity, excellent specificity and high sensitivity (limit of detection: 0.2 µM), which made it possible to efficiently detect GSH in complex biological samples such as human serum.

VO x Quantum Dots with Multienzyme-Mimic Activities and the Application in Constructing a Three-Dimensional (3D) Coordinate System for Accurate Discrimination of the Hydrogen Peroxide over a Broad Concentration Range.

The construction of efficient nanozyme with multienzyme activities in a simple way is vital for the wide biological and chemical applications. Generally, the mimic enzyme activities depend on their sizes, surface states, and materials types. Quantum dots (QDs), one type of zero-dimensional nanomaterials, are much appealing due to their abundant catalytically active surface deficiency. The vanadium oxide (VO x) is one special transition metal oxides possessing different valence states. Inspired by these views, we synthesized VO xQDs herein via a one-pot top-down ethanol-thermal method using bulk VO2 as the precursor. The VO xQDs showed not only oxidase- and peroxidase-like activities in ethanol as the main background solution (ethanol-BGS), but also exhibited additional superoxide dismutase mimetic activity in phosphate buffer solution. Furthermore, the TMB-VO xQDs system in the ethanol-BGS produced three distinct colors in the presence of hydrogen peroxide (H2O2) at three different concentration gradients (10-90 µM, 0.1-10 mM, and 20-100 mM). Accordingly, we constructed a three-dimensional (3D) coordinate system (3D-CS) by using the three variables: the initial velocities, the maximum absorption values and the visual colors of the enzymatic reaction system. As a result, the rapid detection of H2O2 can be achieved while effectively avoiding the faked appearance due to the inhibition effects to the enzymatic system at too high H2O2 concentration. The applicability of the VO xQDs based 3D-CS was further proved via the facile and accurate H2O2 assays in three different practical samples.

Ultra-efficient electromagnetic wave absorption with ethanol-thermally treated two-dimensional Nb2CTx nanosheets.

Nb2CTx, an emerging type of MXene, should be a promising electromagnetic wave (EMW) absorbing material to overcome the EMW pollution nowadays due to its unique layered structure and extremely thin monolayer thickness, but was lack of systematic study till now. Meanwhile, Nb2CTx nanosheets obtained upon HF etching of Nb2AlC MAX was unfortunately found with limited absorption performance due to its mainly dielectric loss mechanism herein. Therefore, the Nb2CTx nanosheets were further treated with solvothermal strategy in various solvents. As a result, the absorption performance of the as-treated Nb2CTx nanosheets could be significantly improved, while the ones in ethanol showed much more superior absorption capability, especially in the low-frequency band (2.0-4.0 GHz). The minimum reflection loss value could reach -52.2 dB at 3.93 GHz with the thickness of only 2.90 mm, indicating more than 99.999% EMW was absorbed. These should be due to the multi-loss mechanism including dielectric, interfacial, and multiple reflection ones resulting from the enlarged interlayer spacing, and increased surface functional groups on the Nb2CTx nanosheets upon the ethanol-based solvothermal treatment.

Solvent-regulated preparation of well-intercalated Ti3C2Tx MXene nanosheets and application for highly effective electromagnetic wave absorption.

MXene-derived nanostructures provide the possibility of meeting the requirements of strong absorption, thin thickness and flexible layer for electromagnetic (EM) wave absorption. However, exploration of pure and well-intercalated MXene nanosheets for efficient EM wave absorption is still in the nascent stages. Herein, Ti3C2Tx nanosheets with solvent-manipulated properties were achieved via ultrasonication-solvothermal treatment of bulk Ti3C2Tx in different solvents including dimethylformamide (DMF), ethanol, and dimethyl sulfoxide (DMSO), respectively, because of their combined influences of molecular size, oxidation capability, and boiling point. Especially, it was found that a larger layer space and less oxidation effects on the Ti3C2Tx nanosheets were observed upon solvothermal treatment in DMF than those in ethanol or DMSO treatment. As a result, the DMF-treated Ti3C2Tx nanosheets can be used as highly effective dielectric materials for EM wave absorption. The reflection loss value reached -41.9 dB (more than 99.99%) at 13.4 GHz with the sample thickness of only 1.1 mm. Characterization techniques including scanning electron microscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and density functional theory calculation were used to elaborate the possible mechanisms.

Molybdenum oxide quantum dots prepared via a one-step stirring strategy and their application as fluorescent probes for pyrophosphate sensing and efficient antibacterial materials.

MoOx quantum dots (QDs) were prepared using a one-step stirring treatment of molybdenum trioxide (MoO3) powder in dimethyl sulfoxide (DMSO). Besides their highly sensitive label-free metal ion and pyrophosphate sensing, the antibacterial activity of the as-prepared MoOx QDs was discovered for the first time.

One-Step Synthesis of Fluorescent Boron Nitride Quantum Dots via a Hydrothermal Strategy Using Melamine as Nitrogen Source for the Detection of Ferric Ions.

A facile and effective approach for the preparation of functionalized born nitride quantum dots (BNQDs) with blue fluorescence was explored by the hydrothermal treatment of the mixture of boric acid and melamine at 200 °C for 15 h. The as-prepared BNQDs were characterized by transmission electron microscopy (TEM), high-resolution TEM, atomic force microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and fluorescence spectroscopy. The single layered BNQDs with the average size of 3 nm showed a blue light emission under the illumination of the UV light. The BNQDs could be easily dispersed in an aqueous medium and applied as fluorescent probes for selective detection of Fe3+ with remarkable selectivity and sensitivity (the lowest detection limit was 0.3 µM). The fluorescence fiber imaging demonstrated that the as-prepared quantum dots could be used as a valuable fluorchrome. Therefore, the BNQDs could be envisioned for potential applications in many fields such as biocompatible staining, fluorescent probes, and biological labeling.