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1.
Angew Chem Int Ed Engl ; 63(4): e202314528, 2024 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-38037863

RESUMO

Porous solids often contain complex pore networks with pores of various sizes. Tracking individual fluorescent probes as they diffuse through porous materials can be used to characterize pore networks at tens of nanometers resolution. However, understanding the motion behavior of fluorescent probes in confinement is crucial to reliably derive pore network properties. Here, we introduce well-defined lithography-made model pores developed to study probe behavior in confinement. We investigated the influence of probe-host interactions on diffusion and trapping of confined single-emitter quantum-dot probes. Using the pH-responsiveness of the probes, we were able to largely suppress trapping at the pore walls. This enabled us to define experimental conditions for mapping of the accessible pore space of a one-dimensional pore array as well as a real-life polymerization-catalyst-support particle.

2.
Small ; 19(49): e2302939, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-37496086

RESUMO

Microbubble generation and manipulation play critical roles in diverse applications such as microfluidic mixing, pumping, and microrobot propulsion. However, existing methods are typically limited to lateral movements on customized substrates or rely on specific liquids with particular properties or designed concentration gradients, thereby hindering their practical applications. To address this challenge, this paper presents a method that enables robust vertical manipulation of microbubbles. By focusing a resonant laser on hydrophilic silica-coated gold nanoparticle arrays immersed in water, plasmonic microbubbles are generated and detach from the substrates immediately upon cessation of laser irradiation. Using simple laser pulse control, it can achieve an adjustable size and frequency of bubble bouncing, which is governed by the movement of the three-phase contact line during surface wetting. Furthermore, it demonstrates that rising bubbles can be pulled back by laser irradiation induced thermal Marangoni flow, which is verified by particle image velocimetry measurements and numerical simulations. This study provides novel insights into flexible bubble manipulation and integration in microfluidics, with significant implications for various applications including mixing, drug delivery, and the development of soft actuators.

3.
Electrophoresis ; 39(3): 496-503, 2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29193178

RESUMO

Combining high-resolution imaging and electrophysiological recordings is key for various types of experimentation on lipid bilayers and ion channels. Here, we propose an integrated biosensing platform consisting of a microfluidic cartridge and a dedicated chip-holder to conduct such dual measurements on suspended lipid bilayers, in a user-friendly manner. To illustrate the potential of the integrated platform, we characterize lipid bilayers in terms of thickness and fluidity while simultaneously monitoring single ion channel currents. For that purpose, POPC lipid bilayers are supplemented with a fluorescently-tagged phospholipid (NBD-PE, 1% mol) for Fluorescence Recovery After Photobleaching (FRAP) measurements and a model ion channel (gramicidin, 1 nM). These combined measurements reveal that NBD-PE has no effect on the lipid bilayer thickness while gramicidin induces thinning of the membrane. Furthermore, the presence of gramicidin does not alter the lipid bilayer fluidity. Surprisingly, in lipid bilayers supplemented with both probes, a reduction in gramicidin open probability and lifetime is observed compared to lipid bilayers with gramicidin only, suggesting an influence of NBD-PE on the gramicidin ion function. Altogether, our proposed microfluidic biosensing platform in combination with the herein presented multi-parametric measurement scheme paves the way to explore the interdependent relationship between lipid bilayer properties and ion channel function.


Assuntos
Técnicas Biossensoriais/instrumentação , Canais Iônicos/química , Bicamadas Lipídicas/química , Técnicas Analíticas Microfluídicas/instrumentação , Microscopia Confocal/instrumentação , Corantes Fluorescentes/química , Gramicidina/química , Dispositivos Lab-On-A-Chip , Fosfatidilcolinas/química , Fosfatidiletanolaminas/química
4.
Anal Chem ; 88(18): 9190-8, 2016 09 20.
Artigo em Inglês | MEDLINE | ID: mdl-27563730

RESUMO

Specific electrochemical cleavage of peptide bonds at the C-terminal side of tyrosine and tryptophan generates peptides amenable to liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for protein identification. To this end we developed a microfluidic electrochemical cell of 160 nL volume that combines a cell geometry optimized for a high electrochemical conversion efficiency (>95%) with an integrated boron doped diamond (BDD) working electrode offering a wide potential window in aqueous solution and reduced adsorption of peptides and proteins. Efficient cleavage of the proteins bovine insulin and chicken egg white lysozyme was observed at 4 out of 4 and 7 out of 9 of the predicted cleavage sites, respectively. Chicken egg white lysozyme was identified based on 5 electrochemically generated peptides using a proteomics database searching algorithm. These results show that electrochemical peptide bond cleavage in a microfluidic cell is a novel, fully instrumental approach toward protein analysis and eventually proteomics studies in conjunction with mass spectrometry.

5.
Biomacromolecules ; 16(12): 3802-10, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26558488

RESUMO

To date, optical lithography has been extensively used for in situ patterning of hydrogel structures in a scale range from hundreds of microns to a few millimeters. The two main limitations which prevent smaller feature sizes of hydrogel structures are (1) the upper glass layer of a microchip maintains a large spacing (typically 525 µm) between the photomask and hydrogel precursor, leading to diffraction of UV light at the edges of mask patterns, (2) diffusion of free radicals and monomers results in irregular polymerization near the illumination interface. In this work, we present a simple approach to enable the use of optical lithography to fabricate hydrogel arrays with a minimum feature size of 4 µm inside closed microchips. To achieve this, we combined two different techniques. First, the upper glass layer of the microchip was thinned by mechanical polishing to reduce the spacing between the photomask and hydrogel precursor, and thereby the diffraction of UV light at the edges of mask patterns. The polishing process reduces the upper layer thickness from ∼525 to ∼100 µm, and the mean surface roughness from 20 to 3 nm. Second, we developed an intermittent illumination technique consisting of short illumination periods followed by relatively longer dark periods, which decrease the diffusion of monomers. Combination of these two methods allows for fabrication of 0.4 × 10(6) sub-10 µm sized hydrogel patterns over large areas (cm(2)) with high reproducibility (∼98.5% patterning success). The patterning method is tested with two different types of photopolymerizing hydrogels: polyacrylamide and polyethylene glycol diacrylate. This method enables in situ fabrication of well-defined hydrogel patterns and presents a simple approach to fabricate 3-D hydrogel matrices for biomolecule separation, biosensing, tissue engineering, and immobilized protein microarray applications.


Assuntos
Resinas Acrílicas/química , Hidrogéis/química , Microtecnologia/métodos , Polietilenoglicóis/química , Técnicas Biossensoriais , Radicais Livres/química , Vidro/química , Microtecnologia/instrumentação , Processos Fotoquímicos , Análise Serial de Proteínas , Reprodutibilidade dos Testes , Raios Ultravioleta
6.
Small ; 9(7): 1076-85, 2013 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-23139010

RESUMO

A microfluidic platform is reported for various experimentation schemes on cell membrane models and membrane proteins using a combination of electrical and optical measurements, including confocal microscopy. Bilayer lipid membranes (BLMs) are prepared in the device upon spontaneous and instantaneous thinning of the lipid solution in a 100-µm dry-etched aperture in a 12.5-µm thick Teflon foil. Using this quasi-automated approach, a remarkable 100% membrane formation yield is reached (including reflushing in 4% of the cases), and BLMs are stable for up to 36 h. Furthermore, the potential of this platform is demonstrated for (i) the in-depth characterization of BLMs comprising both synthetic and natural lipids (1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and L-α-phosphatidylcholine (L-α-PC)/cholesterol, respectively) in terms of seal resistance, capacitance, surface area, specific capacitance, and membrane hydrophobic thickness; (ii) confocal microscopy imaging of phase separation in sphingomyelin/L-α-PC/cholesterol ternary membranes; (iii) electrical measurements of individual nanopores (α-hemolysin, gramicidin); and (iv) indirect assessment of the alteration of membrane properties upon exposure to chemical stimuli using the natural nanopore gramicidin as a sensor.


Assuntos
Bicamadas Lipídicas/química , Membranas Artificiais , Microfluídica/métodos , Colesterol/química , Microscopia Confocal , Fosfatidilcolinas/química
7.
Microsyst Nanoeng ; 9: 39, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37007606

RESUMO

The particles of heterogeneous catalysts differ greatly in size, morphology, and most importantly, in activity. Studying these catalyst particles in batch typically results in ensemble averages, without any information at the level of individual catalyst particles. To date, the study of individual catalyst particles has been rewarding but is still rather slow and often cumbersome1. Furthermore, these valuable in-depth studies at the single particle level lack statistical relevance. Here, we report the development of a droplet microreactor for high-throughput fluorescence-based measurements of the acidities of individual particles in fluid catalytic cracking (FCC) equilibrium catalysts (ECAT). This method combines systematic screening of single catalyst particles with statistical relevance. An oligomerization reaction of 4-methoxystyrene, catalyzed by the Brønsted acid sites inside the zeolite domains of the ECAT particles, was performed on-chip at 95 °C. The fluorescence signal generated by the reaction products inside the ECAT particles was detected near the outlet of the microreactor. The high-throughput acidity screening platform was capable of detecting ~1000 catalyst particles at a rate of 1 catalyst particle every 2.4 s. The number of detected catalyst particles was representative of the overall catalyst particle population with a confidence level of 95%. The measured fluorescence intensities showed a clear acidity distribution among the catalyst particles, with the majority (96.1%) showing acidity levels belonging to old, deactivated catalyst particles and a minority (3.9%) exhibiting high acidity levels. The latter are potentially of high interest, as they reveal interesting new physicochemical properties indicating why the particles were still highly acidic and reactive.

8.
Nano Lett ; 11(6): 2334-41, 2011 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-21526845

RESUMO

Nanoscale ISFET (ion sensitive field-effect transistor) pH sensors are presented that produce the well-known sub-nernstian pH-response for silicon dioxide (SiO(2)) surfaces and near ideal nernstian sensitivity for alumina (Al(2)O(3)) surfaces. Titration experiments of SiO(2) surfaces resulted in a varying pH sensitivity ∼20 mV/pH for pH near 2 and >45 mV/pH for pH > 5. Measured pH responses from titrations of thin (15 nm) atomic layer deposited (ALD) alumina (Al(2)O(3)) surfaces on the nanoISFETs resulted in near ideal nernstian pH sensitivity of 57.8 ± 1.2 mV/pH (pH range: 2-10; T = 22 °C) and temperature sensitivity of 0.19 mV/pH °C (22 °C ≤ T ≤ 40 °C). A comprehensive analytical model of the nanoISFET sensor, which is based on the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) model, accompanies the experimental results and an extracted ΔpK ≈ 1.5 from the measured responses further supports the near ideal nernstian pH sensitivity.


Assuntos
Óxido de Alumínio/química , Nanoestruturas/química , Dióxido de Silício/química , Transistores Eletrônicos , Eletrodos , Concentração de Íons de Hidrogênio , Propriedades de Superfície
9.
Electrophoresis ; 32(22): 3094-100, 2011 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22025223

RESUMO

We report a PDMS microfluidic platform for parallel single-cell analysis (PaSCAl) as a powerful tool to decipher the heterogeneity found in cell populations. Cells are trapped individually in dedicated pockets, and thereafter, a number of invasive or non-invasive analysis schemes are performed. First, we report single-cell trapping in a fast (2-5 min) and reproducible manner with a single-cell capture yield of 85% using two cell lines (P3x63Ag8 and MCF-7), employing a protocol which is scalable and easily amenable to automation. Following this, a mixed population of P3x63Ag8 and MCF-7 cells is stained in situ using the nucleic acid probe (Hoechst) and a phycoerythrin-labeled monoclonal antibody directed at EpCAM present on the surface of the breast cancer cells MCF-7 and absent on the myeloma cells P3x63Ag8 to illustrate the potential of the device to analyze cell population heterogeneity. Next, cells are porated in situ using chemicals in a reversible (digitonin) or irreversible way (lithium dodecyl sulfate). This is visualized by the transportation of fluorescent dyes through the membrane (propidium iodide and calcein). Finally, an electrical protocol is developed for combined cell permeabilization and electroosmotic flow (EOF)-based extraction of the cell content. It is validated here using calcein-loaded cells and visualized through the progressive recovery of calcein in the side channels, indicating successful retrieval of individual cell content.


Assuntos
Técnicas Analíticas Microfluídicas/instrumentação , Análise de Célula Única/instrumentação , Análise de Célula Única/métodos , Animais , Linhagem Celular Tumoral , Permeabilidade da Membrana Celular , Eletro-Osmose , Fluoresceínas/química , Corantes Fluorescentes , Humanos , Espaço Intracelular/química , Camundongos , Reprodutibilidade dos Testes
10.
Electrophoresis ; 32(18): 2402-9, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-21922490

RESUMO

The electrokinetic transport behavior of λ-DNA (48 kbp) in 20 nm-high fused-silica nanoslits in the presence of short-chain PVP is investigated. Mobility and video data show a number of phenomena that are typical of DNA transport through gels or polymer solutions, thus indicative of rigid migration obstacles in the DNA pathway. Calculations show that a several nanometer thin layer of wall-adsorbed PVP ('nano-gel') can provide such a rigid obstacle matrix to the DNA. Such ultrathin wall-adsorbed polymer layers represent a new type of matrix for electrokinetic DNA separation.


Assuntos
DNA Viral/química , Eletroforese/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Adsorção , Bacteriófago lambda/química , Bacteriófago lambda/genética , DNA Viral/análise , Eletroforese/métodos , Técnicas Analíticas Microfluídicas/métodos , Polímeros , Dióxido de Silício/química , Estatísticas não Paramétricas
11.
Nanotechnology ; 22(49): 494013, 2011 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-22101733

RESUMO

We report a high-throughput clog-free microfluidic deoxyribonucleic acid (DNA) fragmentation chip that is based on hydrodynamic shearing. Salmon sperm DNA has been reproducibly fragmented down to ∼ 5k bp fragment lengths by applying low hydraulic pressures (≤1 bar) across micromachined constrictions positioned in larger microfluidic channels that create point-sink flow with large velocity gradients near the constriction entrance. Long constrictions (100 µm) produce shorter fragment lengths compared to shorter constrictions (10 µm), while increasing the hydrodynamic pressure requirement. Sample recirculation (10 ×) in short constrictions reduces the mean fragment length and fragment length variation, and improves yield compared to single-pass experiments without increasing the hydrodynamic pressure.


Assuntos
Fragmentação do DNA , DNA/genética , Genômica/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Análise de Sequência com Séries de Oligonucleotídeos/instrumentação , Animais , DNA/análise , Desenho de Equipamento , Hidrodinâmica , Salmão
12.
Lab Chip ; 10(8): 986-90, 2010 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-20358104

RESUMO

We present an electrokinetic label-free biomolecular screening chip (Glass/PDMS) to screen up to 10 samples simultaneously using surface plasmon resonance imaging (iSPR). This approach reduces the duration of an experiment when compared to conventional experimental methods. This new device offers a high degree of parallelization not only for analyte samples, but also for multiplex analyte interactions where up to 90 ligands are immobilized on the sensing surface. The proof of concept has been demonstrated with well-known biomolecular interactant pairs. The new chip can be used for high throughput screening applications and kinetics parameter extraction, simultaneously, of interactant-protein complex formation.


Assuntos
Eletrônica/instrumentação , Imunoensaio/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Mapeamento de Interação de Proteínas/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Cinética , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Coloração e Rotulagem
13.
Lab Chip ; 10(11): 1410-6, 2010 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-20480106

RESUMO

Handling microorganisms in high throughput and their deployment into miniaturized platforms presents significant challenges. Contact printing can be used to create dense arrays of viable microorganisms. Such "living arrays", potentially with multiple identical replicates, are useful in the selection of improved industrial microorganisms, screening antimicrobials, clinical diagnostics, strain storage, and for research into microbial genetics. A high throughput method to print microorganisms at high density was devised, employing a microscope and a stamp with a massive array of PDMS pins. Viable bacteria (Lactobacillus plantarum, Esherichia coli), yeast (Candida albicans) and fungal spores (Aspergillus fumigatus) were deposited onto porous aluminium oxide (PAO) using arrays of pins with areas from 5 x 5 to 20 x 20 microm. Printing onto PAO with up to 8100 pins of 20 x 20 microm area with 3 replicates was achieved. Printing with up to 200 pins onto PAO culture chips (divided into 40 x 40 microm culture areas) allowed inoculation followed by effective segregation of microcolonies during outgrowth. Additionally, it was possible to print mixtures of C. albicans and spores of A. fumigatus with a degree of selectivity by capture onto a chemically modified PAO surface. High resolution printing of microorganisms within segregated compartments and on functionalized PAO surfaces has significant advantages over what is possible on semi-solid surfaces such as agar.


Assuntos
Óxido de Alumínio/química , Fenômenos Fisiológicos Bacterianos , Bioensaio/instrumentação , Fungos/fisiologia , Análise em Microsséries/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Nanoestruturas/química , Desenho de Equipamento , Análise de Falha de Equipamento , Teste de Materiais , Miniaturização , Nanoestruturas/ultraestrutura , Porosidade , Propriedades de Superfície
14.
Proc Natl Acad Sci U S A ; 104(46): 18217-22, 2007 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-17989237

RESUMO

A miniaturized, disposable microbial culture chip has been fabricated by microengineering a highly porous ceramic sheet with up to one million growth compartments. This versatile culture format, with discrete compartments as small as 7 x 7 mum, allowed the growth of segregated microbial samples at an unprecedented density. The chip has been used for four complementary applications in microbiology. (i) As a fast viable counting system that showed a dynamic range of over 10,000, a low degree of bias, and a high culturing efficiency. (ii) In high-throughput screening, with the recovery of 1 fluorescent microcolony in 10,000. (iii) In screening for an enzyme-based, nondominant phenotype by the targeted recovery of Escherichia coli transformed with the plasmid pUC18, based on expression of the lacZ reporter gene without antibiotic-resistance selection. The ease of rapid, successive changes in the environment of the organisms on the chip, needed for detection of beta-galactosidase activity, highlights an advantageous feature that was also used to screen a metagenomic library for the same activity. (iv) In high-throughput screening of >200,000 isolates from Rhine water based on metabolism of a fluorogenic organophosphate compound, resulting in the recovery of 22 microcolonies with the desired phenotype. These isolates were predicted, on the basis of rRNA sequence, to include six new species. These four applications suggest that the potential for such simple, readily manufactured chips to impact microbial culture is extensive and may facilitate the full automation and multiplexing of microbial culturing, screening, counting, and selection.


Assuntos
Candida albicans/crescimento & desenvolvimento , Escherichia coli/crescimento & desenvolvimento , Lactobacillus/crescimento & desenvolvimento , Candida albicans/ultraestrutura , Meios de Cultura , Escherichia coli/ultraestrutura , Lactobacillus/ultraestrutura , Microscopia Eletrônica de Varredura
15.
Lab Chip ; 20(21): 3938-3947, 2020 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-32975255

RESUMO

Chromatographic columns are suffering from Taylor-Aris dispersion, especially for slowly diffusing molecules such as proteins. Since downscaling the channel size to reduce Taylor-Aris dispersion meets fundamental pressure limitations, new strategies are needed to further improve chromatography beyond its current limits. In this work we demonstrate a method to reduce Taylor-Aris dispersion by lateral mixing in a newly designed silicon AC-electroosmotic flow mixer. We obtained a reduction in κaris by a factor of three in a 40 µm × 20 µm microchannel, corresponding to a plate height gain of 2 to 3 under unretained conditions at low to high Pe values. We also demonstrate an improvement of a reverse-phase chromatographic separation of coumarins.

16.
Lab Chip ; 9(11): 1511-6, 2009 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-19458856

RESUMO

The current paper describes the development and characterization of a pillar array chip that is constructed out of a sandwich of cyclo olefin polymer (COP) sheets. The silicon master of a 5 cm long pillar array was embossed into the COP, yielding 4.3 microm deep pillars of 15.3 microm diameter with an external porosity of 43 % and a well designed sidewall region to avoid side wall induced band broadening. A closed channel configuration was obtained by pressure assisted thermal bonding to a non-processed COP lid. Injection of coumarin dye plugs and detection with a fluorescence microscope showed very close agreement of this channel configuration to theoretical expectations in terms of band broadening. This agreement is due to the low taper, the optimized sidewall region and the excellent bonding quality between the two polymer sheets, even at the pillar area. Under non-retained conditions (pure methanol as mobile phase), plate heights as low as 4 microm were obtained. Under retained conditions, using the native hydrophobic properties of the COP channel (in 70/30 v/v water/methanol mixture as mobile phase), a minimum plate height of 6 microm was obtained. A 4 component separation was successfully achieved, demonstrating that COP is a cheap and efficient alternative for silicon and silica based liquid chromatography formats.

17.
Lab Chip ; 19(6): 1054-1059, 2019 03 13.
Artigo em Inglês | MEDLINE | ID: mdl-30768116

RESUMO

In this work, a new method to track particles in microfluidic channels is presented. Particle position tracking in microfluidic systems is crucial to characterize sorting systems or to improve the analysis of cells in impedance flow cytometry studies. By developing an electric field gradient in a two parallel electrode array the position of the particles can be tracked in one axis by impedance analysis. This method can track the particle's position at lower frequencies and measure the conductivity of the system at higher frequencies. A 3-D simulation was performed showing particle position detection and conductivity analysis. To experimentally validate the technique, a microfluidic chip that develops a gradient in the electric field was fabricated and used to detect the position of polystyrene particles in one axis and measure their conductivity at low and high frequencies, respectively.

18.
Lab Chip ; 19(8): 1332-1343, 2019 04 09.
Artigo em Inglês | MEDLINE | ID: mdl-30869670

RESUMO

Measuring biomolecule concentrations in the brain of living animals, in real time, is a challenging task, especially when detailed information at high temporal resolution is also required. Traditionally, microdialysis probes are used that generally have sampling areas in the order of about 1 mm2, and provide information on concentrations with a temporal resolution of at least several minutes. In this paper, we present a novel miniaturized push-pull perfusion sampling probe that uses an array of small 3 µm-wide sampling channels to sample neurotransmitters at a typical recovery rate of 61%, with a reduced risk of clogging. The added feature to segment the dialysate inside the probe into small water-in-decane droplets enables the detection of concentrations with a temporal resolution of a few seconds. Here we used the probe for in vivo recordings of neurotransmitter glutamate released upon electrical stimulation in the brain of a mouse to demonstrate the feasibility of the probe for real-time neurochemical brain analysis.


Assuntos
Dispositivos Lab-On-A-Chip , Neurotransmissores/metabolismo , Animais , Desenho de Equipamento , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Fenômenos Ópticos
19.
J Phys Chem C Nanomater Interfaces ; 123(38): 23586-23593, 2019 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-31583035

RESUMO

Under continuous laser irradiation, noble metal nanoparticles immersed in water can quickly heat up, leading to the nucleation of so-called plasmonic bubbles. In this work, we want to further understand the bubble nucleation and growth mechanism. In particular, we quantitatively study the effect of the amount of dissolved air on the bubble nucleation and growth dynamics, both for the initial giant bubble, which forms shortly after switching on the laser and is mainly composed of vapor, and for the final life phase of the bubble, during which it mainly contains air expelled from water. We found that the bubble nucleation temperature depends on the gas concentration: the higher the gas concentration, the lower the bubble nucleation temperature. Also, the long-term diffusion-dominated bubble growth is governed by the gas concentration. The radius of the bubbles grows as R(t) ∝ t 1/3 for air-equilibrated and air-oversaturated water. In contrast, in partially degassed water, the growth is much slower since, even for the highest temperature we achieve, the water remains undersaturated.

20.
Nanoscale ; 11(25): 12152-12160, 2019 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-31194202

RESUMO

We report a robust and high-yield fabrication method for wafer-scale patterning of high-quality arrays of dense gold nanogaps, combining displacement Talbot lithography based shrink-etching with dry etching, wet etching, and thin film deposition techniques. By using the self-sharpening of <111>-oriented silicon crystal planes during the wet etching process, silicon structures with extremely smooth nanogaps are obtained. Subsequent conformal deposition of a silicon nitride layer and a gold layer results in dense arrays of narrow gold nanogaps. Using this method, we successfully fabricate high-quality Au nanogaps down to 10 nm over full wafer areas. Moreover, the gap spacing can be tuned by changing the thickness of deposited Au layers. Since the roughness of the template is minimized by the crystallographic etching of silicon, the roughness of the gold nanogaps depends almost exclusively on the roughness of the sputtered gold layers. Additionally, our fabricated Au nanogaps show a significant enhancement of surface-enhanced Raman scattering (SERS) signals of benzenethiol molecules chemisorbed on the structure surface, at an average enhancement factor up to 1.5 × 106.

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