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1.
J Am Chem Soc ; 2020 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-32207939

RESUMO

Here we propose a strategy of radical oxidation reaction for the high-efficiency production of graphene oxide (GO). GO plays important roles in the sustainable development of energy and the environment, taking advantages of oxygen-containing functional groups for good dispersibility and assembly. Compared with Hummers' method, electrochemical exfoliation of graphite is considered facile and green, although the oxidation is fairly low. To synthesize GO with better crystallinity and higher oxidation degree, we present a photosynergetic electrochemical method. By using oxalate anions as the intercalation ions and co-reactant, the interfacial concentration of hydroxyl radicals generated during electrochemical exfoliation was promoted, and the oxidation degree was comparable with that of GO prepared by Hummers' method. In addition, the crystallinity was improved with fewer layers and larger size. Moreover, the aniline coassembled GO membrane was selectively permeable to water molecules by the hydrogen-bond interaction, but it was impermeable to Na+, K+, and Mg2+, due to the electrostatic interactions. Thus, it has a prospective application to water desalination and purification. This work opens a novel approach to the direct functionalization of graphene during the electroexfoliation processes and to the subsequent assembly of the functionalized graphene.

2.
Chem Sci ; 10(23): 5893-5897, 2019 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-31360393

RESUMO

Here we report photoelectric-effect-enhanced interfacial charge transfer reactions. The electrochemical corrosion rate of n-type gallium arsenide (n-GaAs) induced by the contact potential at platinum (Pt) and GaAs boundaries can be accelerated by the photoelectric effect of n-GaAs. When a GaAs wafer is illuminated with a xenon light source, the electrons in the valence band of GaAs will be excited to the conduction band and then move to the Pt boundaries due to the different work functions of the two materials. This results in an enhanced contact electric field as well as an enlarged Pt/GaAs contact potential. Consequently, in the presence of electrolyte solution, the polarizations of both the Pt/solution interface and the GaAs/solution interface at the Pt/GaAs/solution 3-phase boundary are enhanced. If the accumulated electrons on the Pt side are removed by electron acceptors in the solution, anodic corrosion of GaAs will be accelerated strictly along the Pt/GaAs/solution 3-phase boundary. This photo-enhanced electrochemical phenomenon can increase the corrosion rate of GaAs and accelerate the process of electrochemical nanoimprint lithography (ECNL) on GaAs. The method opens an innovative, highly efficient, low-cost nanoimprint technique performed directly on semiconductors, and it has prospective applications in the semiconductor industry.

3.
Talanta ; 200: 177-185, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31036171

RESUMO

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (µPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DµPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions.


Assuntos
Automação , Papel , Troponina I/análise , Colorimetria/economia , Colorimetria/instrumentação , Técnicas Eletroquímicas/economia , Técnicas Eletroquímicas/instrumentação , Técnicas Analíticas Microfluídicas/economia , Técnicas Analíticas Microfluídicas/instrumentação
4.
Nanoscale ; 9(22): 7476-7482, 2017 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-28530294

RESUMO

The functional three dimensional micro-nanostructures (3D-MNS) play crucial roles in integrated and miniaturized systems because of the excellent physical, mechanical, electric and optical properties. Nanoimprint lithography (NIL) has been versatile in the fabrication of 3D-MNS by pressing thermoplastic and photocuring resists into the imprint mold. However, direct nanoimprint on the semiconductor wafer still remains a great challenge. On the other hand, considered as a competitive fabrication method for erect high-aspect 3D-MNS, metal assisted chemical etching (MacEtch) can remove the semiconductor by spontaneous corrosion reaction at the metal/semiconductor/electrolyte 3-phase interface. Moreover, it was difficult for MacEtch to fabricate multilevel or continuously curved 3D-MNS. The question of the consequences of NIL meeting the MacEtch is yet to be answered. By employing a platinum (Pt) metalized imprint mode, we demonstrated that using electrochemical nanoimprint lithography (ECNL) it was possible to fabricate not only erect 3D-MNS, but also complex 3D-MNS with multilevel stages with continuously curved surface profiles on a gallium arsenide (GaAs) wafer. A concave microlens array with an average diameter of 58.4 µm and height of 1.5 µm was obtained on a ∼1 cm2-area GaAs wafer. An 8-phase microlens array was fabricated with a minimum stage of 57 nm and machining accuracy of 2 nm, presenting an excellent optical diffraction property. Inheriting all the advantages of both NIL and MacEtch, ECNL has prospective applications in the micro/nano-fabrications of semiconductors.

5.
Chem Sci ; 8(3): 2407-2412, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28451347

RESUMO

Although metal assisted chemical etching (MacEtch) has emerged as a versatile micro-nanofabrication method for semiconductors, the chemical mechanism remains ambiguous in terms of both thermodynamics and kinetics. Here we demonstrate an innovative phenomenon, i.e., the contact electrification between platinum (Pt) and an n-type gallium arsenide (100) wafer (n-GaAs) can induce interfacial redox reactions. Because of their different work functions, when the Pt electrode comes into contact with n-GaAs, electrons will move from n-GaAs to Pt and form a contact electric field at the Pt/n-GaAs junction until their electron Fermi levels (EF) become equal. In the presence of an electrolyte, the potential of the Pt/electrolyte interface will shift due to the contact electricity and induce the spontaneous reduction of MnO4- anions on the Pt surface. Because the equilibrium of contact electrification is disturbed, electrons will transfer from n-GaAs to Pt through the tunneling effect. Thus, the accumulated positive holes at the n-GaAs/electrolyte interface make n-GaAs dissolve anodically along the Pt/n-GaAs/electrolyte 3-phase interface. Based on this principle, we developed a direct electrochemical nanoimprint lithography method applicable to crystalline semiconductors.

6.
Chem Soc Rev ; 46(5): 1526-1544, 2017 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-28168253

RESUMO

Micro/nano-machining (MNM) is becoming the cutting-edge of high-tech manufacturing because of the increasing industrial demand for supersmooth surfaces and functional three-dimensional micro/nano-structures (3D-MNS) in ultra-large scale integrated circuits, microelectromechanical systems, miniaturized total analysis systems, precision optics, and so on. Taking advantage of no tool wear, no surface stress, environmental friendliness, simple operation, and low cost, electrochemical micro/nano-machining (EC-MNM) has an irreplaceable role in MNM. This comprehensive review presents the state-of-art of EC-MNM techniques for direct writing, surface planarization and polishing, and 3D-MNS fabrications. The key point of EC-MNM is to confine electrochemical reactions at the micro/nano-meter scale. This review will bring together various solutions to "confined reaction" ranging from electrochemical principles through technical characteristics to relevant applications.

7.
Faraday Discuss ; 193: 133-139, 2016 12 12.
Artigo em Inglês | MEDLINE | ID: mdl-27711893

RESUMO

Due to a high turnover coefficient, redox enzymes can serve as current amplifiers which make it possible to explore their catalytic mechanism by electrochemistry at the level of single molecules. On modified nanoelectrodes, the voltammetric behavior of a horseradish peroxidase (HRP) catalyzed hydroperoxide reduction no longer presents a continuous current response, but a staircase current response. Furthermore, single catalytic incidents were captured through a collision mode at a constant potential, from which the turnover number of HRP can be figured out statistically. In addition, the catalytic behavior is dynamic which may be caused by the orientation status of HRP on the surface of the electrode. This modified nanoelectrode methodology provides an electrochemical approach to investigate the single-molecule catalysis of redox enzymes.


Assuntos
Eletrodos , Peroxidase do Rábano Silvestre/metabolismo , Nanotecnologia , Técnicas Biossensoriais , Catálise , Eletroquímica , Peróxido de Hidrogênio , Oxirredução
8.
Acc Chem Res ; 49(11): 2596-2604, 2016 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-27668827

RESUMO

In the past several decades, electrochemical machining (ECM) has enjoyed the reputation of a powerful technique in the manufacturing industry. Conventional ECM methods can be classified as electrolytic machining and electroforming: the former is based on anodic dissolution and the latter is based on cathodic deposition of metallic materials. Strikingly, ECM possesses several advantages over mechanical machining, such as high removal rate, the capability of making complex three-dimensional structures, and the practicability for difficult-to-cut materials. Additionally, ECM avoids tool wear and thermal or mechanical stress on machining surfaces. Thus, ECM is widely used for various industrial applications in the fields of aerospace, automobiles, electronics, etc. Nowadays, miniaturization and integration of functional components are becoming significant in ultralarge scale integration (ULSI) circuits, microelectromechanical systems (MEMS), and miniaturized total analysis systems (µ-TAS). As predicted by Moore's law, the feature size of interconnectors in ULSI circuits are down to several nanometers. In this Account, we present our perseverant research in the last two decades on how to "confine" the ECM processes to occur at micrometer or even nanometer scale, that is, to ensure ECM with nanoscale accuracy. We have been developing the confined etchant layer technique (CELT) to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductor materials since 1992. In general, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) feeding the tool electrode to etch the workpiece. Scavengers, which can react with the etchant, are usually adopted to form a confined etchant layer. Through the subsequent homogeneous reaction between the scavenger and the photo- or electrogenerated etchant in the electrolyte solution, the diffusion distance of the etchant is confined to micro- or nanometer scale, which ensures the nanoscale accuracy of electrochemical machining. To focus on the "confinement" of chemical etching reactions, external physical-field modulations have recently been introduced into CELT by introducing various factors such as light field, force field, hydrodynamics, and so on. Meanwhile, kinetic investigations of the confined chemical etching (CCE) systems are established based on the finite element analysis and simulations. Based on the obtained kinetic parameters, the machining accuracy is tunable and well controlled. CELT is now applicable for 1D milling, 2D polishing, and 3D microfabrication with an accuracy at nanometer scale. CELT not only inherits all the advantages of electrochemical machining but also provides advantages over photolithography and nanoimprint for its applicability to different functional materials without involving any photocuring and thermoplastic resists. Although there are some technical problems, for example, mass transfer and balance, which need to be solved, CELT has shown its prospective competitiveness in electrochemical micromachining, especially in the semiconductor industry.

9.
Chem Sci ; 7(1): 697-701, 2016 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-28791112

RESUMO

Can isotropic wet chemical etching be controlled with a spatial resolution at the nanometer scale, especially, for the repetitive microfabrication of hierarchical 3D µ-nanostructures on the continuously curved surface of functional materials? We present an innovative wet chemical etching method called "electrochemical buckling microfabrication": first, a constant contact force is applied to generate a hierarchical 3D µ-nanostructure on a mold electrode surface through a buckling effect; then, the etchant is electrogenerated on-site and confined close to the mold electrode surface; finally, the buckled hierarchical 3D µ-nanostructures are transferred onto the surface of a Ga x In1-x P coated GaAs wafer through WCE. The concave microlens, with a Fresnel structure, has an enhanced photoluminescence at 630 nm. Comparing with energy beam direct writing techniques and nanoimprint lithography, this method provides an electrochemical microfabrication pathway for the semiconductor industry, with low cost and high throughput.

10.
Chem Commun (Camb) ; 51(100): 17700-3, 2015 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-26489368

RESUMO

We report synergetic effect enhanced photoelectrocatalysis, in which Fe(3+) and Br(-) are used as the acceptors of photogenerated charges on TiO2 nanoparticles. The kinetic rate of interfacial charge transfer is promoted from (4.0 ± 0.5) × 10(-4) cm s(-1) (TiO2/(O2, Br(-))) to (1.5 ± 0.5) × 10(-3) cm s(-1) (TiO2/(Fe(3+), Br(-))). The synergetic effect provides a valuable approach to the design of photoelectrocatalytic systems.


Assuntos
Bromo/química , Processos Fotoquímicos , Titânio/efeitos da radiação , Brometos/química , Catálise , Técnicas Eletroquímicas , Eletrodos , Compostos Férricos/química , Química Verde , Cinética , Luz , Nanopartículas , Oxirredução , Oxigênio/química , Titânio/química
11.
Chem Sci ; 6(11): 6091-6096, 2015 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-28717449

RESUMO

Here we emphasise the importance of the dielectric environment on the electron transfer behavior in interfacial electrochemical systems. Through doping cobalt hexacyanide (Co(CN)63-) into single microcrystals of sodium chloride (NaCl), for the first time, we obtained the direct electrochemical behavior of Co(CN)63- which is hardly ever obtained in either aqueous or conventional nonaqueous solutions. DFT calculations elucidate that, as the Co(CN)63- anions occupy the lattice units of NaCl65- in the NaCl microcrystal, the redox energy barrier of Co(CN)63-/4- is decreased dramatically due to the low dielectric constant of NaCl. Meanwhile, the low-spin Co(CN)64- anions are stabilized in the lattices of the NaCl microcrystal. The results also show that the NaCl microcrystal is a potential solvent for solid-state electrochemistry at ambient temperature.

12.
Anal Chem ; 86(24): 11972-6, 2014 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-25417799

RESUMO

Solar energy is the most abundant nature resource and plays important roles in the sustainable developments of energy and environment. Scanning photoelectrochemical microscopy provides a high-throughput screening method by introducing the combinatorial technique to prepare the substrate with photoelectrochemical catalyst array. However, the signal/noise (S/N) ratio suffers from the background current of indium-tin oxide or fluorine-doped tin oxide itself, including a transient charge-discharge current of electric double layer and a steady-state photocatalytic current. Here we adopt a facile microfabrication method to isolate the substrate area other than the catalyst array from not only the electrolyte solution but also the light illumination. Consequently, the imaging quality has been promoted dramatically due to suppressed background current. This method provides a high S/N ratio screening method, which will be valuable for the high-throughput optimization of the photoelectrocatalytic system.

13.
J Int Med Res ; 41(5): 1570-6, 2013 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-24097828

RESUMO

OBJECTIVE: To test the proof-of-principle that genetically-engineered mesenchymal stem cells (MSCs) transfected with the human hyperpolarization-activated cyclic nucleotide-gated channel 1 (hHCN1) gene can be modified to become cardiac pacemaker cells. METHODS: MSCs were transfected with the hHCN1 gene using lentiviral-based transfection. The expressed pacemaker current (I(f)) in hHCN1-transfected MSCs was recorded using whole-cell patch-clamp analysis. The effect of the hHCN1-transfected MSCs on cardiomyocyte excitability was determined by coculturing the MSCs with neonatal rabbit ventricular myocytes (NRVM). The spontaneous action potentials of the NRVM were recorded by whole-cell current-clamp analysis. RESULTS: A high level time- and voltage-dependent inward hyperpolarization current that was inhibited by 4 mM caesium chloride was detected in hHCN1-transfected MSCs, suggesting that the HCN1 proteins acted as I(f) channels in MSCs. The mean ± SE beating frequency in NRVMs cocultured with control MSCs transfected with the pcDNA3 plasmid control was 82 ± 8 beats/min (n = 5) compared with 129 ± 11 beats/min (n = 5) in NRVMs cocultured with hHCN1-transfected MSCs. CONCLUSIONS: Genetically-engineered MSCs transfected with the hHCN1 gene can be modified to become cardiac pacemaker cells.


Assuntos
Engenharia Celular/métodos , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/genética , Células-Tronco Mesenquimais/fisiologia , Miócitos Cardíacos/fisiologia , Canais de Potássio/genética , Potenciais de Ação , Animais , Animais Recém-Nascidos , Césio/farmacologia , Cloretos/farmacologia , Técnicas de Cocultura , Expressão Gênica , Vetores Genéticos , Ventrículos do Coração/citologia , Ventrículos do Coração/efeitos dos fármacos , Humanos , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/metabolismo , Lentivirus/genética , Células-Tronco Mesenquimais/citologia , Células-Tronco Mesenquimais/efeitos dos fármacos , Miócitos Cardíacos/citologia , Miócitos Cardíacos/efeitos dos fármacos , Técnicas de Patch-Clamp , Plasmídeos , Canais de Potássio/metabolismo , Coelhos , Transfecção
14.
Anal Chem ; 85(3): 1322-6, 2013 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-23289726

RESUMO

Substrate leveling is an essential but neglected instrumental technique of scanning electrochemical microscopy (SECM). In this technical note, we provide an effective substrate leveling method based on the current feedback mode of SECM. By using an air-bearing rotary stage as the supporter of an electrolytic cell, the current feedback presents a periodic waveform signal, which can be used to characterize the levelness of the substrate. Tuning the adjusting screws of the tilt stage, substrate leveling can be completed in minutes by observing the decreased current amplitude. The obtained high-quality SECM feedback curves and images prove that this leveling technique is valuable in not only SECM studies but also electrochemical machining.

15.
Faraday Discuss ; 164: 189-97, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24466665

RESUMO

The confined etchant layertechnique (CELT) has been proved an effective electrochemical microfabrication method since its first publication at Faraday Discussions in 1992. Recently, we have developed CELT as an electrochemical mechanical micromachining (ECMM) method by replacing the cutting tool used in conventional mechanical machining with an electrode, which can perform lathing, planing and polishing. Through the coupling between the electrochemically induced chemical etching processes and mechanical motion, ECMM can also obtain a regular surface in one step. Taking advantage of CELT, machining tolerance and surface roughness can reach micro- or nano-meter scale.

17.
Chin Med J (Engl) ; 123(12): 1571-6, 2010 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-20819514

RESUMO

BACKGROUND: Extensive research toward creating a biological pacemaker by enhancement of inward depolarizing current has been performed. However, studies have mainly focused on inducing spontaneous activity and have not adequately addressed ways to improve pacemaker function. In this study we attempted to improve pacemaker function by altering connexin expression in rat mesenchymal stem cells (MSCs) to a phenotype similar to native sinus node pacemaker cells. METHODS: To generate a biological pacemaker, MSCs were transduced with a cardiac pacemaker gene-hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4), via transfection with a lentiviral vector. Funny current (I(f)) in HCN4(+) MSCs was recorded by voltage-clamp. Overexpression of connexin 45 (gene Gja7) in MSCs was achieved by transfection with the plasmid pDsRED2-N1-Gja7-RFP. Double-immunolabelling with anti-connexin 43 and anti-connexin 45 antibodies were used to identify the gap junction channels. The effects of the genetically modified MSCs on cardiomyocyte excitability were determined in MSCs cocultured with neonatal rat ventricular myocytes. Spontaneous action potentials of neonatal rat ventricular myocytes were recorded by current-clamp. RESULTS: High level time- and voltage-dependent inward hyperpolarization current that was sensitive to 4 mmol/L Cs(+) was detected in HCN4(+) MSCs, confirming that HCN4 acted as I(f) channels in MSCs. Connexin 43 and connexin 45 were simultaneously detected in CX45(+) MSCs. Beating frequency was (82 +/- 8) beats per minute (n = 5) in myocytes cocultured with non-transfected control MSCs, versus (129 +/- 11) beats per minute (n = 5) in myocytes cocultured with HCN4(+) MSCs. Myocytes cocultured with MSCs cotransfected with HCN4 and connexin 45 had the highest beating frequency at (147 +/- 9) beats per minute (n = 5). CONCLUSION: These findings demonstrate that overexpression of connexin 45 and subsequent formation of heteromeric connexin 45/connexin 43 gap junction channels in HCN4 expressing MSCs can improve their function as cardiac biological pacemakers in vitro.


Assuntos
Relógios Biológicos/fisiologia , Conexinas/metabolismo , Células-Tronco Mesenquimais/citologia , Células-Tronco Mesenquimais/fisiologia , Animais , Animais Recém-Nascidos , Células Cultivadas , Conexinas/genética , Eletrofisiologia , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização , Células-Tronco Mesenquimais/metabolismo , Miócitos Cardíacos/citologia , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/fisiologia , Canais de Potássio/genética , Canais de Potássio/metabolismo , Ratos , Ratos Sprague-Dawley , Reação em Cadeia da Polimerase Via Transcriptase Reversa
18.
Med Hypotheses ; 69(5): 1093-7, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17449188

RESUMO

Pacemaker cells differ from common cardiomyocytes for the presence of a spontaneous depolarization process during the diastolic phase of the cardiac cycle, which is due to the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel genes, providing the presence of an inward current. With this in mind, we embarked on a study to test proof-of-principle if genetically engineered mesenchymal stem cells (MSCs) transfected with HCN2 genes can be modified to be cardiac pacemaker cells. In addition to expressing an anticipated high level of hHCN2 gene, MSCs transfected with HCN2 genes by LentiV in our study also expressed characteristic hHCN2 protein, the I(f)-like current and were capable of increasing the spontaneous beating rate of cocultured cardiac myocytes. Control MSCs did not exert these effects. Thus, the electrical effects of the MSCs transfected with the hHCN2 gene were similar to the effects of overexpression of the same gene in the myocytes in vitro system. For stable genetic modification, we used the self-inactivating HIV1-based lentiviral vector (LentiV) for transgene delivery in our study, which can integrate transgene into the host genome. This unique property makes LentiV ideal for modifying MSCs, which allows persistent transgene expression. With these findings, we hypothesize that genetically engineered MSCs transfected with HCN2 genes by LentiV can be modified to be cardiac pacemaker cells.


Assuntos
Relógios Biológicos/fisiologia , Canais Iônicos/metabolismo , Células-Tronco Mesenquimais/citologia , Células-Tronco Mesenquimais/fisiologia , Miócitos Cardíacos/citologia , Miócitos Cardíacos/fisiologia , Engenharia Tecidual/métodos , Animais , Diferenciação Celular , Células Cultivadas , Melhoramento Genético/métodos , Vetores Genéticos/genética , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização , Canais Iônicos/genética , Lentivirus/genética , Coelhos
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