Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 67
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Bioelectrochemistry ; 140: 107829, 2021 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-33964612

RESUMO

Ginkgo biloba is a dioecious plant. Male ginkgoes are mainly used in landscaping, while females are mainly used for fruit production. However, sex identification of ginkgo is a difficult task, especially at the seedling stage. In this work, we present for the first time the use of electrochemical techniques for the identification of ginkgo sex based on the differences in peroxides within male and female ginkgos. Graphene was used to concentrate peroxides in ginkgo extract, thereby improving electrochemical signal sensitivity. The electrochemical reduction of hydrogen peroxide catalyzed by peroxidase was used as a prob for sex determination in ginkgo. This electrochemical identification technique can be used not only for the analysis of adult ginkgo, but also successfully for the analysis of tissue culture seedlings and live seedlings. This electrochemical sensor has excellent discrimination ability due to the difference in peroxidase content in the leaves and petiole of ginkgo of different sexes. This electrochemical sensor allows for a rapid identification of the sex of ginkgo and has a very strong potential for field analysis.

2.
ACS Nano ; 2021 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-33734662

RESUMO

The rapid development of integrated circuits and electronic devices creates a strong demand for highly thermally conductive yet electrically insulating composites to efficiently solve "hot spot" problems during device operation. On the basis of these considerations, hexagonal boron nitride nanosheets (BNNS) have been regarded as promising fillers to fabricate polymer matrix composites. However, so far an efficient approach to prepare ultrahigh-aspect-ratio BNNS with large lateral size while maintaining an atomically thin nature is still lacking, seriously restricting further improvement of the thermal conductivity for BNNS/polymer composites. Here, a rapid and high-yield method based on a microfluidization technique is developed to obtain exfoliated BNNS with a record high aspect ratio of ≈1500 and a low degree of defects. A foldable and electrically insulating film made of such a BNNS and poly(vinyl alcohol) (PVA) matrix through filtration exhibits an in-plane thermal conductivity of 67.6 W m-1 K-1 at a BNNS loading of 83 wt %, leading to a record high value of thermal conductivity enhancement (≈35 500). The composite film then acts as a heat spreader for heat dissipation of high-power LED modules and shows superior cooling efficiency compared to commercial flexible copper clad laminate. Our findings provide a practical route to produce electrically insulating polymer composites with high thermal conductivity for thermal management applications in modern electronic devices.

3.
Sensors (Basel) ; 21(4)2021 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-33572293

RESUMO

Chloramphenicol (CAP) is a harmful compound associated with human hematopathy and neuritis, which was widely used as a broad-spectrum antibacterial agent in agriculture and aquaculture. Therefore, it is significant to detect CAP in aquatic environments. In this work, carbon nanotubes/silver nanowires (CNTs/AgNWs) composite electrodes were fabricated as the CAP sensor. Distinguished from in situ growing or chemical bonding noble metal nanomaterials on carbon, this CNTs/AgNWs composite was formed by simple solution blending. It was demonstrated that CNTs and AgNWs both contributed to the redox reaction of CAP in dynamics, and AgNWs was beneficial in thermodynamics as well. The proposed electrochemical sensor displayed a low detection limit of up to 0.08 µM and broad linear range of 0.1-100 µM for CAP. In addition, the CNTs/AgNWs electrodes exhibited good performance characteristics of repeatability and reproducibility, and proved suitable for CAP analysis in real water samples.


Assuntos
Cloranfenicol , Nanotubos de Carbono , Nanofios , Cloranfenicol/análise , Técnicas Eletroquímicas , Eletrodos , Humanos , Reprodutibilidade dos Testes , Prata
4.
Micromachines (Basel) ; 11(11)2020 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-33138269

RESUMO

An electrochemical voltammogram recording method for plant variety identification is proposed. Electrochemical voltammograms of Vistula, Andromeda, Danuta, Armandii 'Apple Blossom,' Proteus, Hagley Hybrid, Violet Elizabeth, Kiri Te Kanawa, Regina, and Veronica's Choice were recorded using leaf extracts with two solvents under buffer solutions. The voltametric data recorded under different conditions were derived as scatter plots, 2D density patterns, and hot maps for variety identification. In addition, the voltametric data were further used for genetic relationship studies. The dendrogram deduced from the voltammograms was used as evidence for relationship study. The dendrogram deduced from voltametric data suggested the Andromeda, Danuta, Proteus, Regina, and Hagley Hybrid were closely related, while Violet Elizabeth and Veronica's Choice were closely related. In addition, Vistula and Armandii 'Apple Blossom' could be considered outliers among the varieties.

5.
Research (Wash D C) ; 2020: 4093732, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32613198

RESUMO

In this work, 3D highly electrically conductive cellulose nanofibers (CNF)/Ti3C2Tx MXene aerogels (CTA) with aligned porous structures are fabricated by directional freezing followed by freeze-drying technique, and the thermally annealed CTA (TCTA)/epoxy nanocomposites are then fabricated by thermal annealing of CTA, subsequent vacuum-assisted impregnation and curing method. Results show that TCTA/epoxy nanocomposites possess 3D highly conductive networks with ultralow percolation threshold of 0.20 vol% Ti3C2Tx. When the volume fraction of Ti3C2Tx is 1.38 vol%, the electrical conductivity (σ), electromagnetic interference shielding effectiveness (EMI SE), and SE divided by thickness (SE/d) values of the TCTA/epoxy nanocomposites reach 1672 S m-1, 74 dB, and 37 dB mm-1, respectively, which are almost the highest values compared to those of polymer nanocomposites reported previously at the same filler content. In addition, compared to those of the samples without Ti3C2Tx, the storage modulus and heat-resistance index of TCTA/epoxy nanocomposites are enhanced to 9792.5 MPa and 310.7°C, increased by 62% and 6.9°C, respectively, presenting outstanding mechanical properties and thermal stabilities. The fabricated lightweight, easy-to-process, and shapeable TCTA/epoxy nanocomposites with superior EMI SE values, excellent mechanical properties, and thermal stabilities greatly broaden the applications of MXene-based polymer composites in the field of EMI shielding.

6.
Biosens Bioelectron ; 159: 112212, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32364933

RESUMO

A biosensor has been developed based on disposable screen-printed electrode for recording the electrochemical fingerprint of plant leaf tissue. A thin layer of polydopamine functionalized graphene sheets was coated on the plant tissue modified electrode for signal enhancement. The voltammetric data recorded under different buffer solutions can be derived as patterns for species identification. As the distribution of electrochemical active compounds in plants is controlled by genes, these fingerprints can reflect differences at the genetic level between species. Therefore, the electrochemical fingerprint of plant tissues can be used for phylogenetic research without qualitative analysis. 19 species of Amaryllidaceae including A. africanus, Clivia miniata, Clivia nobilis, Crinum firmifolium, Crinum latifolium, Crinum moorei, Curculiga gracilis, Cyrtanthus breviflorus, Habranthus robustus, Haemanthus albiflos, Haemathus multiflorus, Hippeastrum rutilum, Hymenocallis littoralis, Leucojum aestivum, Sprekelia formosissima, Tulbaghia violacea, Zephyranthes grandiflora, Zephyranthes macrosiphon and Zephyranthes minima have been selected deliberately. The dendrogram deduced from the electrochemical fingerprint was compared with the molecular phylogenetics. The results indicate the electrochemical fingerprint-based phylogenetic study is a persuasive methodology for plant phylogenetic analysis.

7.
Mikrochim Acta ; 187(6): 361, 2020 05 29.
Artigo em Inglês | MEDLINE | ID: mdl-32468206

RESUMO

A magnetic bead (MB)-based sandwich biorecognition reactions is combined with a gold nanoprobe-induced homogenous synthesis of molybdophosphate to develop a novel bioassay method for the electrochemical detection of the tumor biomarker of carcinoembryonic antigen (CEA). The nanoprobe is prepared through the specific loading of numerous alkaline phosphatase (ALP)-functionalized gold nanoparticles (Au NPs) on a double-stranded DNA (dsDNA) produced by the CEA aptamer-triggered hybridization chain reaction (HCR). Both the large amounts of PO43- produced by the ALP catalytic hydrolysis of pyrophosphate and the phosphate backbones of dsDNA can react with the added MoO42- to generate electroactive molybdophosphates. So, the gold nanoprobe was used for signal tracing of the sandwich bioassay of CEA at a constructed antibody-functionalized MB platform. The sensitive electrochemical measurement of molybdophosphate produced from the quantitatively captured nanoprobes at a carbon nanotube-modified electrode (measured at about 0.12 V vs. Ag/AgCl, 3 M KCl) enabled the convenient signal transduction of the method. Due to the dually enhanced synthesis of molybdophosphate by the HCR and multi-enzyme Au NP nanotags, this method shows a wide linear range from 0.05 pg mL-1 to 10 ng mL-1 along with a low detection limit of 0.027 pg mL-1. In addition, the MB-based biorecognition reaction and the homogeneous synthesis of molybdophosphate are much convenient in manipulations. These excellent performances decide the extensive application potentials of the method. Graphical abstract A magnetic bead-based bioassay method was simply developed for the electrochemical detection of carcinoembryonic antigen. The dually enhanced homogenous synthesis of molybdophosphate by hybridization chain reaction (HCR) and enzyme nanotags and the sensitive electrochemical measurement of molybdophosphate at a carbon nanotube (CNT)-electrode enable ultrasensitive signal transduction of the method.

8.
Analyst ; 145(8): 3073-3080, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32142088

RESUMO

Herein we combine the sandwich immunoreaction at a vertically aligned single-walled carbon nanotube (SWCNT)-based immunosensor and the enzymatically catalytic deposition of gold nanoparticles (Au NPs) by a gold nanoprobe to develop a novel electrochemical immunosensing method. The vertically arranged nanostructure was prepared through the covalent linking of terminally carboxylated SWCNTs at an aryldiazonium-modified electrode. It not only provides an excellent platform for the high density immobilization of antibodies to obtain the immunosensor but also serves as useful molecular wires to accelerate electron transfer during the electrochemical immunosensing process. Meanwhile, the enzymatic reaction of the nanoprobe prepared by surface functionalization of the nanocarrier of Au NPs by high-content glucoamylases can catalyze the deposition of a large number of Au NPs at the immunosensor. The electrochemical stripping analysis of these nanoparticles enabled the convenient signal transduction of the method. Due to the sensitive gold stripping analysis at the vertically aligned SWCNTs and the multi-enzyme signal amplification of the nanoprobe, the electrochemical signal response was greatly enhanced. Thus, the method can be used for the ultrasensitive detection of the tumor biomarker of carcinoembryonic antigen in a wide linear range of 5 orders of magnitude with a low detection limit of 0.48 pg mL-1. Considering its obvious performance superiorities, this immunosensing method exhibits an extensive prospect for practical applications.

9.
Artigo em Inglês | MEDLINE | ID: mdl-32164392

RESUMO

Located in the subtropics, Taiwan is one of the major epidemic areas for dengue fever, with severe epidemics occurring in recent years. Dengue fever has become a serious health threat to Taiwan's residents and a potentially serious economic cost to society. This study recruited 730 random participants and adopted the contingent valuation method to understand the factors influencing the populace's willingness to pay (WTP) to reduce the health risk of dengue fever. The results show that high-income women with children and people with higher preventive perceptions and behavior are more willing to invest in preventive measures against dengue fever. In the evaluation of WTP for preventive treatment for health risks, each person was willing to pay on average NT$751 annually to lower psychological health risks, NT$793 annually to lower the risk of illness, and NT$1086 annually to lower the risk of death.


Assuntos
Dengue , Serviços de Saúde , Criança , Dengue/economia , Dengue/prevenção & controle , Feminino , Serviços de Saúde/economia , Humanos , Renda , Masculino , Risco Ajustado/economia , Risco Ajustado/estatística & dados numéricos , Taiwan , Valor da Vida
10.
Front Chem ; 8: 92, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32211371

RESUMO

The rapid identification of sex has potential uses involving dioecious commercial plants. In this work, we first propose a rapid electrochemical analysis method for plant sex determination using the signal difference generated by the electrochemically active substances in plant tissue. Polydopamine-functionalized graphene was wrapped around plant tissue. The introduction of polydopamine-functionalized graphene could solve the problem of the instability of plant tissue immobilization and enhance the electrochemical signals from plant tissue. Taxus × media, Dioscorea zingiberensis, and Dioscorea bulbifera were deliberately selected as dioecious plant models due to their pharmaceutical applications. The sex of the plant was not obvious after simply comparing the electrochemical voltammograms. Scatter patterns and 3D surface patterns were generated based on the voltammograms recorded after different solvent extractions. Sex determination was successfully achieved by pattern recognition.

11.
Adv Sci (Weinh) ; 7(4): 1903239, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-32099768

RESUMO

Friction and wear remain the primary modes for energy dissipation in moving mechanical components. Superlubricity is highly desirable for energy saving and environmental benefits. Macroscale superlubricity was previously performed under special environments or on curved nanoscale surfaces. Nevertheless, macroscale superlubricity has not yet been demonstrated under ambient conditions on macroscale surfaces, except in humid air produced by purging water vapor into a tribometer chamber. In this study, a tribological system is fabricated using a graphene-coated plate (GCP), graphene-coated microsphere (GCS), and graphene-coated ball (GCB). The friction coefficient of 0.006 is achieved in air under 35 mN at a sliding speed of 0.2 mm s-1 for 1200 s in the developed GCB/GCS/GCP system. To the best of the knowledge, for the first time, macroscale superlubricity on macroscale surfaces under ambient conditions is reported. The mechanism of macroscale superlubricity is due to the combination of exfoliated graphene flakes and the swinging and sliding of the GCS, which is demonstrated by the experimental measurements, ab initio, and molecular dynamics simulations. These findings help to bridge macroscale superlubricity to real world applications, potentially dramatically contributing to energy savings and reducing the emission of carbon dioxide to the environment.

12.
Materials (Basel) ; 13(3)2020 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-32046259

RESUMO

In this work, a Ni/graphene (Ni/G) electrode was designed and fabricated by plasma-enhanced chemical vapor deposition (PECVD) for the ultrasensitive recognition of d- and l-phenylalanine. Through a single-step PECVD process, the Ni/G electrode can achieve better hydrophilicity and larger catalytic surface area, which is beneficial for the electrochemical recognition of bio-objects. After surface modification with ß-cyclodextrin, the Ni/G electrode can distinguish d-phenylalanine from l-phenylalanine according to a 0.09 V peak shift in differential pulse voltammetry tests. Moreover, this Ni/G electrode achieved a detection limit as low as 1 nM and a wide linear range from 1 nM to 10 mM toward l-phenylalanine, with great storage stability and working stability.

13.
Nanoscale ; 12(6): 3795-3802, 2020 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-31994570

RESUMO

As a new family of two-dimensional materials, MXenes have attracted increasing attention in recent years due to their widespread potential applications. In contrast to early transition metals in convention, here we expand the M element of MXene to the rare earth element lutetium. Based on the first-principles density functional calculations, the bare lutetium-based carbide MXene Lu2C is determined to be stabilized in the T-type configuration. Furthermore, both fluorine and hydroxyl terminated configurations are found to be semiconductors, and their band gaps are suitable for use in semiconductors and visible and near-infrared optical devices. The Lu2C(OH)2 configuration shows a direct band gap and possesses an ultralow work function of 1.4 eV. Both Lu2CT2 (T = F, OH) MXenes exhibit high carrier mobilities. Particularly, the electron mobility of the Lu2C(OH)2 MXene is found to be anisotropic at room temperature, with values as high as 95.19 × 103 and 217.1 × 103 cm2 V-1·s-1 in the zigzag and armchair directions, respectively, which makes Lu2C(OH)2 a promising material for nanodevices. Based on these predicted properties, our work widens the range of MXene materials and their applications in semiconducting devices.

14.
ACS Omega ; 5(2): 1170-1177, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31984274

RESUMO

Polymer composites with excellent thermal conductivity and superior mechanical strength are in high demand in the electrical engineering systems. However, achieving superior thermal conductivity and mechanical properties simultaneously at high loading of fillers will still be a challenging issue. In this work, a facile method was proposed to prepare the epoxy composite with carbon fibers (CFs) and alumina (Al2O3). This CF and Al2O3 hybrid structure can effectively reduce the interfacial thermal resistance between the matrix and the CFs. The thermal conductivity of epoxy composite with 6.4 wt % CFs and 74 wt % Al2O3 hybrid filler reaches 3.84 W/(m K), which is increasing by 2096% compared with that of pure epoxy. Meanwhile, the epoxy composite still retains outstanding thermal stability and mechanical performance at high filler loading. A cost-effective avenue to prepare highly thermally conductive and superior mechanical properties of polymer-based composites may enable some prospective application in advanced thermal management.

15.
Bioelectrochemistry ; 133: 107455, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31978859

RESUMO

Voltammetric scan can record the profile of electrochemical active substances in plant tissues. Because the distribution of chemical components in plants is controlled by genes, these profiles can reflect differences at the genetic level in different species. In this study, the voltammetric scan was applied to the investigation of macrophanerophytes taxonomy. All species of Chimonanthus with two exotaxa were deliberately selected due to their controversial infrageneric relationship. Electrode surface modification was excluded in this work to improve the convenience and accuracy of the fingerprint recording process. The dendrogram deduced from the electrochemical fingerprint data suggests that Ch. Zhejiangensis and Ch. grammatus are two groups of Ch. nitens, which may be only the ecotype of Ch. nitens, rather than independent taxonomic species. The small variations between the three species may be due to environmental factors and cannot be used for species formation. In addition, Ch. campanulatus and Ch. Praecox were clustered together with a close relationship.

16.
Nanotechnology ; 31(11): 115502, 2020 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-31778981

RESUMO

Surface modification is a simple and effective means to promote the sensing performance of metal oxide semiconductor-based gas sensors. Marigold-shaped ZnO nanoflowers are fabricated via a simple precipitation reaction and subsequently catalytically modified with RuO2 on the surface through an ethylene glycol solvothermal treatment. The experimental results have proven that a very low content of Ru on the surface of ZnO exists in an oxidized state. However, the gas response of the sensor based on RuO2-modified ZnO is remarkably improved by 17 times to 100 ppm acetone with the decrease of optimal operating temperature from 219 °C-172 °C and reduction in recovery time from 79-52 s. The sensing enhancement mechanism of surface modification can be attributed to the formation of massive small heterostructure between p-type RuO2 ultrasmall nanoparticles and n-type ZnO as well as the catalytic effect of Ru4+ and a rougher surface.

17.
Materials (Basel) ; 13(1)2019 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-31861814

RESUMO

Much attention has been paid to graphite flakes/copper (GFs/Cu) composites for thermal management due to their remarkable thermal properties. Most studies focus on the interface interaction between GFs and Cu in composites. However, controlling the orientation of GFs still remains a challenge. Herein, we report a reliable method to ensure consistent orientation of GFs in the composites. Firstly, the disorder GFs were well arranged on the surface of copper foil by tape casting process in the casting machine. Then highly aligned GFs/Cu composites were fabricated by hot pressing process in a vacuum hot-pressing furnace, with the volume fraction of graphite from 30% to 70%. The SEM images show that the obtained GFs/Cu composites presented a layer-by-layer structure or network structure with a different content of GFs. The thermal conductivity of GFs/Cu composites exhibited an extreme anisotropy due to the highly aligned GFs. The ultrahigh thermal conductivity of GFs/Cu composites with 70 vol% GFs reached 741 W/(m·K), while through-plane thermal conductivity was just 42 W/(m·K). The alignment of GFs and interfacial thermal resistance were deeply analyzed and a thermal conductivity model for GFs/Cu composites was established. Our work provides a new idea to significantly enhance the thermal transportation performance of GFs/Cu composites by well controlled alignment of GFs in Cu matrix.

18.
Nanomaterials (Basel) ; 9(11)2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31703273

RESUMO

The nitrogen-vacancy (NV) color center in chemical vapor deposition (CVD) diamond has been widely investigated in quantum information and quantum biosensors due to its excellent photon emission stability and long spin coherence time. However, the temperature dependence of the energy level of NV color centers in diamond is different from other semiconductors with the same diamond cubic structure for the high Debye temperature and very small thermal expansion coefficient of diamond. In this work, a diamond sensor for temperature measurement with high precision was fabricated based on the investigation of the energy level shifts of NV centers by Raman and photoluminescence (PL) spectra. The results show that the intensity and linewidth of the zero-phonon line of NV centers highly depend on the environmental temperature, and the energy level shifts of NV centers in diamond follow the modified Varshni model very well, a model which is better than the traditional version. Accordingly, the NV color center shows the ability in temperature measurement with a high accuracy of up to 98%. The high dependence of NV centers on environmental temperature shows the possibility of temperature monitoring of NV center-based quantum sensors in biosystems.

19.
ACS Appl Mater Interfaces ; 11(47): 44700-44707, 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31670938

RESUMO

With the minimization and higher power of electronic devices, materials with effective heat dissipation and high electrical insulation have attracted relentless interest. Especially, highly thermally conductive, highly electrically insulating but low filler content of polymer-based composites are desirable. Herein, a facile and eco-friendly cotton candy-templated method (CTM) to construct three-dimensional heat transport pathways inside epoxy resin is reported. The fabricated Al2O3/epoxy composites with enhanced heat transport capability feature a 15-fold increase in thermal conductivity at a filler content of 36.2 vol % compared to pristine epoxy. Moreover, the remarkable thermal conductive property has excellent stability over a wide range of temperature before and after heating and cooling cycles. Meanwhile, the CTM composite still retain highly electrical insulation. The cotton candy-templated method proposed in this work is a new avenue for the preparation of three-dimensional heat transport pathways within polymer-based composites for microelectronic packaging and electrical engineering systems.

20.
ACS Nano ; 13(10): 11561-11571, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31550125

RESUMO

Along with the technology evolution for dense integration of high-power, high-frequency devices in electronics, the accompanying interfacial heat transfer problem leads to urgent demands for advanced thermal interface materials (TIMs) with both high through-plane thermal conductivity and good compressibility. Most metals have satisfactory thermal conductivity but relatively high compressive modulus, and soft silicones are typically thermal insulators (0.3 W m-1 K-1). Currently, it is a great challenge to develop a soft material with the thermal conductivity up to metal level for TIM application. This study solves this problem by constructing a graphene-based microstructure composed of mainly vertical graphene and a thin cap of horizontal graphene layers on both the top and bottom sides through a mechanical machining process to manipulate the stacked architecture of conventional graphene paper. The resultant graphene monolith has an ultrahigh through-plane thermal conductivity of 143 W m-1 K-1, exceeding that of many metals, and a low compressive modulus of 0.87 MPa, comparable to that of silicones. In the actual TIM performance measurement, the system cooling efficiency with our graphene monolith as TIM is 3 times as high as that of the state-of-the-art commercial TIM, demonstrating the superior ability to solve the interfacial heat transfer issues in electronic systems.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...