Search

Nanozymes are nanomaterials with intrinsic enzyme-mimic activity, but their large-scale application is generally limited by their low catalytic activity. Herein, we demonstrated that highly exposed Cu active sites on two-dimensional (2D) nitrogen-doped carbon (Cux/NC) can serve as efficient peroxidase-like (POD) catalysts with high atomic utilization. Specially, the uniformly distributed Cu active sites could react with H2O2to produce singlet oxygen (1O2) under acidic conditions, which can efficiently oxidizes colorless 3,3′, 5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB). Among various Cux/NC nanozymes studied, the Cu0.14/NC exhibited smaller maximum catalytic velocities (Vmax) and Menten constant (Km) for TMB and H2O2. Benefiting from the highly active peroxidase-like activity, the Cu0.14/NC nanozyme could be successfully applied for the hydroquinone (HQ) and ascorbic acid (AA) detection applications through the inhibitory effect of HQ and AA. More interestingly, α-glucosidase (α-Glu) detection sensing platform could be constructed based on HQ as a signal transmitter, with the detection range ranging from 0 to 12 U/L and the minimum detection limit being 0.68 U/L. This work provides not only an idea for the rational design of highly exposed Cu active sites but also fabricate an effective detection sensing platform for HQ, AA, and α-Glu detection.

Concerns regarding human health and food safety have generated interest in developing simple, accurate, and cost-effective strategies for evaluating organophosphorus pesticide (OP) residues. In this study, nitrogen-doped carbon dots (N-CDs) were synthesized from a common low-cost precursor via a simple pyrolysis process. The fluorescence of the N-CDs can be suppressed by p-nitrophenol, which is the hydrolysis product of the p-nitrophenyl phosphate salt catalyzed by alkaline phosphatase (ALP). A fluorescent turn-on assay for the inhibitory effect of glyphosate was developed with a low detection limit and wide linear range. Moreover, the feasibility of visualizing OPs in vegetables was demonstrated by the fluorescence imaging of glyphosate on cabbage leaves. This research not only offers a facile method for the synthesis of highly fluorescent CDs but also inspires the development of effective multi-mode sensing platforms that include fluorescent testing and imaging for monitoring pesticide residues.

Although various oxidase mimetic or peroxidase (POD) mimetic nanozymes have been extensively studied, their poor substrate selectivity significantly inhibits their practical applications. Nanozymes with specific biomolecules as substrates, especially ascorbic acid oxidase (AAO) mimetic nanozymes with ascorbic acid (AA) as a substrate, have scarcely been studied. Herein, inspired by the multi-Cu atom sites and the redox electron transfer pathway of Cu2+/Cu+in the natural AAO, atomically dispersed Cu sites immobilized on N-doped porous carbon (Cu-N/C) are artificially designed to simulate the function of natural AAO. Compared with their natural counterparts, the Cu-N/C catalysts exhibited higher catalytic efficiency and superior stability. Combined theoretical calculation and experimental characterizations reveal that the Cu-N/C nanozymes could catalyze the AA oxidation through a 2e–oxygen reduction pathway with H2O2as the product. Moreover, the Cu-N/C nanozymes also possess high POD activity. As a proof-of-concept application, Cu-N/C can simultaneously realize AA detection in fluorescent mode based on its AAO activity and total antioxidant capacity detection in colorimetric mode utilizing its POD activity.

One-step single-spinneret electrospinning synthesis of 1D fibrous hierarchical structure can not only prevent the agglomeration or restacking of fibers or particles and enlarge surface active area but also promote the directional migration of electrons in materials and achieve effective regulation of resistances. Herein, tunable SnO2and SnO2/ZnO fibrous hierarchical structures with in situ growth of monodisperse spherical-like particles on surface provide a new sight for adjusting component distribution, surface absorption and chemical reaction, electronic transmission path, and electron transfer efficiency. Compared with SnO2porous fibers and SnO2hierarchical structures, the optimal SnO2/ZnO sensors exhibit superior gas-sensing response value of 366–100 ppm ethanol at 260 °C as well as excellent gas selectivity and long-term stability, in which the enhanced gas-sensing mechanism is primarily derived from multilevel effective heterojunctions with unique interface electronic effects. Especially, these SnO2-based sensors can achieve favorable linear relationship of the response and gas concentration for sensitive trace detection in cosmetics for the first time, providing a new strategy to design composite materials for quantitative analysis of volatiles in the cosmetics evaluation process.

Morphology-tunable C–N/SnO2-based hierarchical microspheres with good gas sensitivity for triethylamine (TEA) have been fabricated via facile electrospinning and a subsequent calcination process. The reaction temperature and modifying calcining technology played a dominant role for the morphological evolution from precursor fibers to microspherical shapes and the formation of C–N-decorated SnO2phase composition. C–N/SnO2/ZnO composites with tunable crystallinity, microstructure, and gas-sensing performance were strictly dependent on the added amount of Zn element. Fascinatingly, the constructed C–N/SnO2/ZnO/Au composites can not only precisely regulate the crystal size, dispersion status, loading position, and content of Au nanoparticles but also display excellent gas-sensing properties with ultrasensitivity and high selectivity under various temperature detections. The response of C–N/SnO2/ZnO/Au composites can reach up to approximately 1970, calculated to be 121.6 and 23.6 times for 50 ppm TEA molecules at optimal conditions compared with C–N/SnO2and C–N/SnO2/ZnO microspheres, respectively, actually representing the highest response value at high temperatures reported to date. The superior long-aging stability of sensing behaviors and phase structures can be also observed after 1 month. More importantly, novel C–N/SnO2/ZnO/Au sensors were employed for availably detecting low-concentration volatiles released from the storage procedure of fishes at 80 °C, indicating the practical application in chemical detectors and biosensors at low temperature. The novel gas-sensing mechanisms derived primarily from the combination of phase compositions, morphologies, and unique surface/interface transfer processes of C–N/SnO2/ZnO/Au composites are presented and investigated in detail, which will contribute to the design and development of other semiconductor-based composite sensors.