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1.
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Generating gas/liquid/liquid three-phase microdispersed systems in double T-junctions microfluidic device 总被引:1,自引:0,他引:1
This article describes the generation of microdispersed bubbles and droplets in a double T-junctions microfluidic device to
form immiscible gas/liquid/liquid three-phase flowing systems. Segmented gas plugs are controllably prepared in water at the
first T-junction to form gas/liquid two-phase fluid with the perpendicular flow cutting method. Then using this two-phase
fluid as the cross-shearing fluid for the oil phase at the second T-junction, the gas/liquid/liquid three-phase flowing systems
are prepared. Interestingly, it is found that the break-up of the oil droplets is mainly dominated by the cutting effect of
the gas/liquid interface or the pressure drop across the emerging droplet, but independent with the viscous shearing effect
of the continuous phase, even at the capillary number (Ca = u
wμw/γow) higher than 0.01. The size laws and the distributions of the bubbles and droplets are investigated carefully, and a mathematical
model has been developed to relating the operating conditions with the dispersed sizes. 相似文献
3.
We demonstrate fluorescent liquid-core/liquid-cladding (L
2) waveguides focused in three-dimensional (3-D) space based on a 3-D hydrodynamic focusing technique. In the proposed system,
the core and vertical cladding streams are passed through a curved 90° corner in a microfluidic channel, leading to the formation
of a pair of counter rotating vortices known as the Dean vortex. As a result, the core fluid is completely confined within
the cladding fluid and does not touch the top and bottom poly(dimethylsiloxane) (PDMS) surfaces of the microfluidic channel.
Because the core stream was not in contact with the PDMS channel, whose refractive index contrast and optical smoothness with
the core fluid are lower than that between the core and the cladding fluids, the 3-D focused L
2 waveguide exhibited a higher captured fraction (η) and lower propagation loss when compared to conventional two-dimensional
(2-D) focused L
2 waveguides. Because the proposed 3-D focused L
2 waveguides can be generated in planar PDMS microfluidic devices, such optofluidic waveguides can be integrated with precise
alignment together with other in-plane microfluidic and optical components to achieve micro-total analysis systems (μ-TAS). 相似文献
4.
Liang Li Qiang Fu Christopher A. Kors Lance Stewart Peter Nollert Philip D. Laible Rustem F. Ismagilov 《Microfluidics and nanofluidics》2010,8(6):789-798
This article presents a plug-based microfluidic system to dispense nanoliter-volume plugs of lipidic cubic phase (LCP) material
and subsequently merge the LCP plugs with aqueous plugs. This system was validated by crystallizing membrane proteins in lipidic
mesophases, including LCP. This system allows for accurate dispensing of LCP material in nanoliter volumes, prevents inadvertent
phase transitions that may occur due to dehydration by enclosing LCP in plugs, and is compatible with the traditional method
of forming LCP material using a membrane protein sample, as shown by the successful crystallization of bacteriorhodopsin from
Halobacterium salinarum. Conditions for the formation of LCP plugs were characterized and presented in a phase diagram. This system was also implemented
using two different methods of introducing the membrane protein: (1) the traditional method of generating the LCP material
using a membrane protein sample and (2) post LCP-formation incorporation (PLI), which involves making LCP material without
protein, adding the membrane protein sample externally to the LCP material, and allowing the protein to diffuse into the LCP
material or into other lipidic mesophases that may result from phase transitions. Crystals of bacterial photosynthetic reaction
centers from Rhodobacter sphaeroides and Blastochloris viridis were obtained using PLI. The plug-based, LCP-assisted microfluidic system, combined with the PLI method for introducing membrane
protein into LCP, should be useful for minimizing consumption of samples and broadening the screening of parameter space in
membrane protein crystallization. 相似文献
5.
Cheng-Che Chung I-Fang Cheng Chi-Chang Lin Hsien-Chang Chang 《Microfluidics and nanofluidics》2011,10(2):311-319
We studied an imaging-based technique for the rapid quantification of bio-particles in a dielectrophoretic (DEP) microfluidic
chip. Label-free particles could be successively sorted and trapped in a continuous flow manner under the applied alternating
current (AC) conditions. Both 2 and 3 μm polystyrene beads at a concentration of 1.0 × 107 particles ml−1 could be rapidly quantified within 5 min in our DEP system. Capturing efficiencies higher than 95% could be 2 μm polystyrene
beads with a linear flow speed, applied voltage and frequency of 0.89 mm s−1, 20 Vp-p and 5 MHz. Yeast cells (Candida glabrata and Candida albicans) could also be captured even at a lower concentration of 2.5 × 105 cells ml−1. Images of aggregative particles taken from the designed trapping area were further processed based on the intensity of relative
greyscale followed by correction of the particle numbers. The imaging-based quantification method showed higher agreement
than that of the conventional counting chamber method and proved the stability and feasibility of our AC DEP system. 相似文献
6.
This paper develops novel polymer transformers using thermally actuated shape memory polymer (SMP) materials. This paper applies
SMPs with thermally induced shape memory effect to the proposed novel polymer transformers as on-chip microfluidic vacuum
generators. In this type of SMPs, the morphology of the materials changes when the temperature of materials reaches its glass
transition temperature (T
g). The structure of the polymer transformer can be pre-programmed to define its functions, which the structure is reset to
the temporary shape, using shape memory effects. When subjected to heat, the polymer transformer returns to its pre-memory
morphology. The morphological change can produce a vacuum generation function in microfluidic channels. Vacuum pressure is
generated to suck liquids into the microfluidic chip from fluidic inlets and drive liquids in the microchannel due to the
morphological change of the polymer transformer. This study adopts a new smart polymer with high shape memory effects to achieve
fluid movement using an on-chip vacuum generation source. Experimental measurements show that the polymer transformer, which
uses SMP with a T
g of 40°C, can deform 310 μm (recover to the permanent shape from the temporary shape) within 40 s at 65°C. The polymer transformer
with an effective cavity volume of 155 μl achieved negative pressures of −0.98 psi. The maximum negative up to −1.8 psi can
be achieved with an effective cavity volume of 268 μl. A maximum flow rate of 24 μl/min was produced in the microfluidic chip
with a 180 mm long channel using this technique. The response times of the polymer transformers presented here are within
36 s for driving liquids to the end of the detection chamber. The proposed design has the advantages of compact size, ease
of fabrication and integration, ease of actuation, and on-demand negative pressure generation. Thus, this design is suitable
for disposable biochips that need two liquid samples control. The polymer transformer presented in this study is applicable
to numerous disposable microfluidic biochips. 相似文献
7.
Daniel Mark Patrick Weber Sascha Lutz Maximilian Focke Roland Zengerle Felix von Stetten 《Microfluidics and nanofluidics》2011,10(6):1279-1288
We present a new method for aliquoting liquids on the centrifugal microfluidic platform. Aliquoting is an essential unit operation
to perform multiple parallel assays (“geometric multiplexing”) from one individual sample, such as genotyping by real-time
polymerase chain reactions (PCR), or homogeneous immunoassay panels. Our method is a two-stage process with an initial metering
phase and a subsequent transport phase initiated by switching a centrifugo-pneumatic valve. The method enables aliquoting
liquids into completely separated reaction cavities. It includes precise metering that is independent on the volume of pre-stored
reagents in the receiving cavities. It further excludes any cross-contamination between the receiving cavities. We characterized
the performance for prototypes fabricated by three different technologies: micro-milling, thermoforming of foils, and injection
molding. An initial volume of ~90 μl was split into 8 aliquots of 10 μl volume each plus a waste reservoir on a thermoformed
foil disk resulting in a coefficient of variation (CV) of the metered volumes of 3.6%. A similar volume of ~105 μl was split
into 16 aliquots of 6 μl volume each on micro-milled and injection-molded disks and the corresponding CVs were 2.8 and 2.2%,
respectively. Thus, the compatibility of the novel aliquoting structure to the aforementioned prototyping and production technologies
is demonstrated. Additionally, the important question of achievable volume precision of the aliquoting structure with respect
to the production tolerances inherent to each of these production technologies is addressed experimentally and theoretically.
The new method is amenable to low cost mass production, since it does not require any post-replication surface modifications
like hydrophobic patches. 相似文献
8.
For further understanding the dispersion process in the T-shaped microfluidic device, a double-pore T-shaped microchannel
was designed and tested with octane/water system to form monodispersed plugs and droplets in this work. The liquid–liquid
two-phase flow patterns were investigated and it was found that only short plugs, relative length L/w < 1.4, were produced. Additionally, the droplets flow was realized at phase ratios (F
C
/F
D) just higher than 0.5, which is much smaller than that in the single-pore T-shaped microchannels. A repulsed effect between
the initial droplets was observed in the droplet formation process and the periodic fluctuation flow of the dispersed phase
was discussed by analyzing the resistances. Besides, the effect of the two-phase flow rates on the plug length and the droplet
diameter was investigated. Considering the mutual effect of the initial droplets and the equilibrium between the shearing
force with the interfacial tension, phase ratio and Ca number were introduced into the semi-empirical models to present the plug and droplet sizes at different operating conditions. 相似文献
9.
10.
Hayat Abdulla Yusuf Sara J. Baldock Peter R. Fielden Nick J. Goddard Stephan Mohr Bernard J. Treves Brown 《Microfluidics and nanofluidics》2010,8(5):587-598
This paper presents a mathematical and experimental study of the effect of inlet concentration (and therefore viscosity) of
glycerol solutions on the performance of a microfluidic network. This was achieved with analytical modelling, implemented
in MATLAB, and optical measurement of the entire concentration distribution of the network. A mathematical proposal to improve
the linearity of the outlet profile is also implemented and successfully verified experimentally. The concentration gradients
of a two inlet–six outlet (2–6) microfluidic network device were obtained with inlet solutions of 10–40 wt% glycerol and flow
rates of up to 5 μl/s per inlet. The mathematical model developed gave a good agreement with the experimental results obtained.
‘S’ shaped outlet profiles were obtained for the four glycerol cases studied and the closest results to the model were achieved
at an optimised flow rate of 1μl/s for 10 wt% glycerol, 5 μl/s for both 20 and 30 wt% glycerol and 1.5 μl/s for 40 wt% glycerol.
The linearity of the outlet profiles for the 20, 30 and 40 wt% inlet glycerol experiments were improved from R
2 of 0.977, 0.946 and 0.966, respectively (before linearisation) to their new values of 0.997, 0.995 and 0.974, respectively
(after the linearisation). This was performed by application of the mathematical model, at controlled inlet flow rate ratios
of 0.77, 0.63 and 0.52 with respect to the viscous inlet, for 20, 30 and 40 wt% glycerol experiments, again with very good
agreement of the outlet performance between the experimental and the mathematical results. 相似文献
11.
Goran T. Vladisavljevi? Isao Kobayashi Mitsutoshi Nakajima 《Microfluidics and nanofluidics》2011,10(6):1199-1209
Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d
3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel
plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel
consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth
of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with
decreasing dispersed phase viscosity and ranged from over 120 L m−2 h−1 for soybean oil to 2,700 L m−2 h−1 for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing
viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall
throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached
100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean
oil and the poorest for n-tetradecane. 相似文献
12.
Evaporation is of great importance when dealing with microfluidic devices with open air/liquid interfaces due to the large
surface-to-volume ratio. For devices utilizing a thermal reaction (TR) reservoir to perform a series of biological and chemical
reactions, excessive heat-induced microfluidic evaporation can quickly lead to reaction reservoir dry out and failure of the
overall device. In this study, we present a simple, novel method to decrease heat-induced fluid evaporation within microfluidic
systems, which is termed as heat-mediated diffusion-limited (HMDL) method. This method does not need complicated thermal isolation
to reduce the interfacial temperature, or external pure water to be added continuously to the TR chamber to compensate for
evaporation loss. The principle of the HMDL method is to make use of the evaporated reaction content to increase the vapor
concentration in the diffusion channel. The experimental results have shown that the relative evaporation loss (V
loss/V
ini) based on the HMDL method is not only dependent on the HMDL and TR region’s temperatures (T
HMDL and T
TR), but also on the HMDL and TR’s channel geometries. Using the U-shaped uniform channel with a diameter of 200 μm, the V
loss/V
ini within 60 min is low to 5% (T
HMDL = 105°C, T
TR = 95°C). The HMDL method can be used to design open microfluidic systems for nucleic acid amplification and analysis such
as isothermal amplification and PCR thermocycling amplification, and a PCR process has been demonstrated by amplifying a 135-bp
fragment from Listeria monocytogenes genomic DNA. 相似文献
13.
14.
The use of two-phase flow in lab-on-chip devices, where chemical and biological reagents are enclosed within plugs separated
from each other by an immiscible fluid, offers significant advantages for the development of devices with high throughput
of individual heterogeneous samples. Lab-on-chip devices designed to perform the polymerase chain reaction (PCR) are a prime
example of such developments. The internal circulation within the plugs used to transport the reagents affects the efficiency
of the chemical reaction within the plug, due to the degree of mixing induced on the reagents by the flow regime. It has been
hypothesised in the literature that all plug flows produce internal circulation. This work demonstrates experimentally that
this is false. The particle image velocimetry (PIV) technique offers a powerful non-intrusive tool to study such flow fields.
This paper presents micro-PIV experiments carried out to study the internal circulation of aqueous plugs in two phase flow
within 762 μm internal diameter FEP Teflon tubing with FC-40 as the segmenting fluid. Experiments have been performed and
the results are presented for plugs ranging in length from 1 to 13 mm with a bulk mean flow velocity ranging from 0.3 to 50 mm/s.
The results demonstrate for the first time that circulation within the plugs is not always present and requires fluidic design
considerations to ensure their generation. 相似文献
15.
Zongbo Zhang Yi Luo Xiaodong Wang Yingsong Zheng Yanguo Zhang Liding Wang 《Microsystem Technologies》2010,16(4):533-541
Bonding is a bottleneck for mass-production of polymer microfluidic devices. A novel ultrasonic bonding method for rapid and
deformation-free bonding of polymethyl methacrylate (PMMA) microfluidic chips is presented in this paper. Convex structures,
usually named energy director in ultrasonic welding, were designed and fabricated around micro-channels and reservoirs on
the substrates. Under low amplitude ultrasonic vibration, localized heating was generated only on the interface between energy
director and cover plate, with peak temperature lower than T
g (glass transition temperature) of PMMA. With the increasing of temperature, solution of PMMA in isopropanol (IPA) increases
and bonding was realized between the contacting surfaces of energy director and cover plate while no solution occurs on the
surfaces of other part as their lower temperature. PMMA microfluidic chips with micro-channels of 80 μm × 80 μm were successfully
bonded with high strength and low dimension loss using this method. 相似文献
16.
《Sensors and actuators. B, Chemical》2006,113(1):376-381
We present and evaluate a new approach to cell immobilization for use in cell-based biosensors. We have fabricated a microfluidic channel using poly(dimethylsiloxane) (PDMS) with cell entrapment posts for the gentle packing and immobilization of yeast cells. This method of immobilization allows for a density of metabolically active cells greater than 8.0 × 106 cells/mm3. The packed microcolumn approach addresses simple diffusional limitations inherent in traditional suspension and membrane entrapment techniques. By utilizing genetically engineered whole cells, rather then cellular components, the sensor is capable of detecting and responding to a wide range of biologically active compounds. In this study, Saccharomyces cerevisiae was genetically engineered to produce yellow fluorescent protein (YFP) when exposed to galactose. Fluorescence response of packed cells (G1 phase) to galactose required 40% longer than the fluorescent response of cells grown in suspension. To address concerns of long-term viability (>60 days) and cell overgrowth, stationary phase cells were also tested in the microfluidic channel. Response time required approximately 50% longer than non-stationary phase cells packed inside the microfluidic channel. Additionally, cellular response as a function of the target analyte concentration was investigated and response time versus analyte concentration is reported. This report demonstrates proof-of-concept of using protein expression-based biosensors, based upon a packed, microcolumn architecture, as a dependable long-term storage platform. 相似文献
17.
Winnie W. Y. Chow Yanli Qu Wen J. Li Steve C. H. Tung 《Microfluidics and nanofluidics》2010,8(5):631-640
We have developed SWCNT sensors for air-flow shear-stress measurement inside a polymethylmethacrylate (PMMA) “micro-wind tunnel”
chip. An array of sensors is fabricated by using dielectrophoretic (DEP) technique to manipulate bundled single-walled carbon
nanotubes (SWCNTs) across the gold microelectrodes on a PMMA substrate. The sensors are then integrated in a PMMA micro-wind
tunnel, which is fabricated by SU-8 molding/hot-embossing technique. Since the sensors detect air flow by thermal transfer
principle, we have first examined the I–V characteristics of the sensors and confirmed that self-heating effect occurs when the input voltage is above ~1 V. We then
performed the flow sensing experiment on the sensors using constant temperature (CT) configuration with input power of ~230 μW.
The voltage output of the sensors increases with the increasing flow rate in the micro-wind tunnel and the detectable volumetric
flow is in the order of 1 × 10−5m3/s. We also found that the activation power of the sensors has a linear relation with 1/3 exponential power of the shear stress
which is similar to conventional hot-wire and polysilicon types of convection-based shear-stress sensors. Moreover, measurements
of sensors with different overheat ratios were compared, and results showed that sensor is more sensitive to the flow with
a higher overheat ratio. 相似文献
18.
Filtration for microfluidic sample-collection devices is desirable for sample selection, concentration, preprocessing, and
manipulation, but microfabricating the required sub-micrometer structures is an elaborate process. This article presents a
simple method to integrate filters in polydimethylsiloxane (PDMS) devices to sample microorganisms in aqueous environments.
An off-the-shelf membrane filter with 0.22-μm pores was embedded in a PDMS layer and sequentially bound with other PDMS channel
layers. No leakage was observed during filtration. This device was validated by concentrating a large amount of biomass, from
15 × 107 to 3 × 108 cells/ml of cyanobacterium Synechocystis in simulated sample water with consistent performance across devices. The major advantages of this method are low cost, simple
design, straightforward fabrication, and robust performance, enabling wide-utility of chip-based devices for field-deployable
operations in environmental microbiology. 相似文献
19.
Neus Godino Detlef Snakenborg Jörg P. Kutter Jenny Emnéus Mikkel Fougt Hansen F. Xavier Muñoz F. Javier del Campo 《Microfluidics and nanofluidics》2010,8(3):393-402
This work presents the fabrication and characterisation of a versatile lab-on-a-chip system that combines magnetic capture
and electrochemical detection. The system comprises a silicon chip featuring a series of microband electrodes, a PDMS gasket
that incorporates the microfluidic channels, and a polycarbonate base where permanent magnets are hosted; these parts are
designed to fit so that wire bonding and encapsulation are avoided. This system can perform bioassays over the surface of
magnetic beads and uses only 50 μL of bead suspension per assay. Following detection, captured beads are released simply by
sliding a thin iron plate between the magnets and the chip. Particles are captured upstream from the detector and we demonstrate
how to take further advantage of the system fluidics to determine enzyme activities or concentrations, as flow velocity can
be adjusted to the rate of the reactions under study. We used magnetic particles containing β-galactosidase and monitored
the enzyme activity amperometrically by the oxidation of 4-aminophenol, enzymatically produced from 4-aminophenyl-β-d-galactopyranoside. The system is able to detect the presence of enzyme down to approximately 50 ng mL−1. 相似文献
20.
Taotao Fu Denis Funfschilling Youguang Ma Huai Z. Li 《Microfluidics and nanofluidics》2010,8(4):467-475
The present study aims at scaling the formation of slug bubbles in flow-focusing microfluidic devices using a high-speed digital
camera and a micro particle image velocimetry (μ-PIV) system. Experiments were conducted in two different polymethyl methacrylate
square microchannels of respectively 600 × 600 and 400 × 400 μm. N2 bubbles were generated in glycerol–water mixtures with several concentrations of surfactant sodium dodecyl sulfate. The influence
of gas and liquid flow rates, the viscosity of the liquid phase and the width of the microchannel on the bubble size were
explored. The bubble size was correlated as a function of the width of the microchannel W
c, the ratio of the gas/liquid flow rates Q
g/Q
l and the liquid Reynolds number. During the pinch-off stage, the variation of the minimum width of the gaseous thread W
m with the remaining time could be scaled as
_boxclose_boxclose ()^ - 0.15 (T - t)^1/3 . W_{\text{m}} \propto ({\frac{{Q_{\text{g}} }}{{Q_{\text{l}} }}})^{ - 0.15} (T - t)^{1/3} . The velocity fields in the liquid phase around the thread, determined by μ-PIV measurements, were obtained around a forming
bubble to reveal the role of the liquid phase. 相似文献