Colorimetric array sensor based on bimetallic nitrogen-doped carbon-based nanozyme material to detect multiple antioxidants.

Copper-cobalt bimetallic nitrogen-doped carbon-based nanoenzymatic materials (CuCo@NC) were synthesized using a one-step pyrolysis process. A three-channel colorimetric sensor array was constructed for the detection of seven antioxidants, including cysteine (Cys), uric acid (UA), tea polyphenols (TP), lysine (Lys), ascorbic acid (AA), glutathione (GSH), and dopamine (DA). CuCo@NC with peroxidase activity was used to catalyze the oxidation of TMB by H2O2 at three different ratios of metal sites. The ability of various antioxidants to reduce the oxidation products of TMB (ox TMB) varied, leading to distinct absorbance changes. Linear discriminant analysis (LDA) results showed that the sensor array was capable of detecting seven antioxidants in buffer and serum samples. It could successfully discriminate antioxidants with a minimum concentration of 10 nM. Thus, multifunctional sensor arrays based on CuCo@NC bimetallic nanoenzymes not only offer a promising strategy for identifying various antioxidants but also expand their applications in medical diagnostics and environmental analysis of food.

Colorimetric and electrochemical dual-mode uric acid determination utilizing peroxidase-mimicking activity of CoCu bimetallic nanoclusters.

We present the preparation of CoCu bimetallic nanoclusters (Co@Cu-BNCs) by a hydrothermal and one-step pyrolysis method to build a colorimetric and electrochemical dual-mode sensing platform for uric acid (UA) detection. In the presence of H2O2, Co@Cu-BNCs with peroxidase-mimicking activity may convert colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxidized TMB (oxTMB). However, due to the inhibitory effect of uric acid (UA) on the oxidation process of TMB, the characteristic absorption peak intensity of oxTMB decreased when UA was added into a mixed solution. In this approach, a colorimetric assay platform for the detection of UA was demonstrated, with a linear range of 0.1-195 µM and a low limit of detection of 0.06 µM (S/N ratio of 3). In addition, an even wider detection range is achieved in the electrochemical method, due to the pronounced electrocatalytic activity of Co@Cu-BNCs. The surface of the glassy carbon electrode was modified with Co@Cu-BNCs to build an electrochemical sensor for detecting UA. The sensor achieves a wider linear range from 2 to 1000 µM and a limit of detection of 0.61 µM (S/N ratio of 3). Moreover, the detection of UA in a human serum sample showed satisfactory results. The results proved that the colorimetric and electrochemical dual-mode detection platform was sensitive, convenient and accurate.

In situ green synthesis of the nanocomposites of MnO2/graphene as an oxidase mimic for sensitive colorimetric and electrochemical dual-mode biosensing.

Herein we report the colorimetry and an electrochemical for the determination of dopamine (DA) by using MnO2 nanoparticles and graphene nanosheets composite (MnO2@G) that display oxidase mimicking property. MnO2@G could directly oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB) without extra oxidants such as H2O2. Nevertheless, the presence of DA will inhibit the TMB oxidation due to the presence of the competitive reaction of MnO2@G and DA, giving a product color change from blue to colorless. A colorimetric assay for detect the concentration of DA was worked out according to this finding. Response is linear in the 0.1 to 15 µM DA concentration range, and the detection limit is 0.14 µM. Wider detection range is achieved in an electrochemical method which is due to the pronounced electrocatalytic activity of MnO2@G. The MnO2@G was modified on the surface of the glassy carbon electrode in order to fabricate one type electrochemical sensor. The sensor achieves a wide detection two linear ranges from 0.4 to 70 µM, with the detection limit of 1.16 µM. The detection of DA in real serum sample proved that the nanozyme based on MnO2@G could be developed into a colorimetry and electrochemical dual-readout sensing platform.

Preparation of Elastic Macroporous Graphene Aerogel Based on Pickering Emulsion Method and Combination with ETPU for High Performance Piezoresistive Sensors.

High-performance pressure sensors provide the necessary conditions for smart shoe applications. In this paper, the elastic Macroporous Graphene Aerogel (MGA) was synthesized via the modified Hummers' method, and it was further combined with Expanded-Thermoplastic polyurethane (ETPU) particles to assemble MGA-ETPU flexible sensors. The MGA-ETPU has a low apparent density (3.02 mg/cm3), high conductivity (0.024 S/cm) and fast response time (50 ms). The MGA-ETPU has a large linear sensing range (0-10 kPa) and consists of two linear regions: the low-pressure region (0 to 8 kPa) and the high-pressure region (8 to 10 kPa), with sensitivities of 0.08 kPa-1, and 0.246 kPa-1, respectively. Mechanical test results show that the MGA-ETPU sensor showed 19% reduction in maximum stress after 400 loading-unloading compression cycles at 40% strain. Electrical performance tests showed that the resistance of MGA-ETPU sensor decreased by 12.5% when subjected to sudden compression at 82% strain and returned to its original state within 0.05 s. Compared to existing flexible sensors, the MGA-ETPU sensors offer excellent performance and several distinct advantages, including ease of fabrication, high sensitivity, fast response time, and good flexibility. These remarkable features make them ideally suited as flexible pressure sensors for smart shoes.

[Finite element contact stress analysis of simulating teeth with wedge-shaped defects in the cervical region].

PURPOSE: To study the distribution of stress of simulating teeth with wedge-shaped defects in the cervical region. METHODS: The models of anisotropic enamel of the mandibular first premolar and the opposite maxillary first premolar crown were created. A defect was introduced into the model of mandibular premolar in the buccal cervical region along the enamelo-dentinal junction. The stress distribution in the cervical region of the mandibular premolar was investigated with regard to different loading conditions simulating working, nonworking and vertical micromotions. In each case, the stroke was applied to the mandibular premolars in a stepping procedure using nonlinear contact analysis. RESULTS: The stresses were concentrated in the defect of the enamel and dentin at the enamelo-dentinal junction(EDJ) in the condition of different loading, especially in the condition of simulating lateral excursion on one contact. CONCLUSION: Undermined cervical EDJ had a significant effect on the stress distribution in the buccal cervical region.

[Finite element contact stress analysis of simulating teeth with wedge shaped defects in the cervical region].

OBJECTIVE: To study the distribution of stress of simulating teeth with wedge shaped defects in the cervical region. METHODS: The models of anisotropic enamel of the mandibular first premolar and the opposite maxillary first premolar crown were created. A defect was introduced into the model of mandibular premolar in the buccal cervical region along the enamelo-dentinal junction (DEJ). The stress distribution in the cervical region of the mandibular premolar was investigated considering lateral condition simulating working micromotions. In this case, the stroke was applied to the maxillary first mandibular in a stepping procedure using nonlinear contact analysis. RESULTS: The stresses were concentrated in the defect of the enamel and dentin at the DEJ in the condition of lateral loading. As the defect length increased in size, the peak maximum principal stress (MPS) value and the magnitude of the stress field along the DEJ both increased. CONCLUSION: Undermined cervical DEJ had a significant effect on the stress distribution in the buccal cervical region.

[The ultraviolet absorption spectra of pyrazoles and 1-carboxamidepyrazoles and their application].

The ultraviolet absorption spectra of pyrazoles and 1-carboxamidepyrazoles were studied. The results indicated that substitution in the 3 or the 5 position it leads to a bathochromic shift of the position of the maximum absorption by about 3-4 nm, whereas in the 4 position leads to a much larger bathochromic shift (> 10 nm). The introduction of carboxamide causes a bathochromic shift of the position of the maximum absorption by about 20-26 nm. Its also leads to an increase in molar extinction coefficient by about 2-3 times. So UV methods were established for determining the contents of pyrazoles and their derivations. Using these methods, the content of 3,4-dimethylpyrazole phosphate (DMPP) in stabilized urea was determined to be 1.15% of urea-N, the hydrolytic half lives of 1-carboxamide-3-methylpyrazole (CMP) in water solution at 20, 25 and 30 degrees C were 48, 30 and 18 h, respectively, and the extraction percentage of nitrification inhibitor 3-methylpyrazole phosphate (MPP) in 3 soils by 3 different extractants were ranged from 63.2% to 89.2%.