Microfluidic Device for the Manipulation of Microparticles for Flow Cytometry Application

This work produces a unique microfluidic device that acts as a “lab on a chip,” conducting separation, mixing, and concentration of microparticles similar to that required by cell sorting flow cytometry applications. The passive two-dimensional device shows to be successful at separating polystyrene (PS) beads between 5 and 20 µm in diameter, mixing them with an external media, and concentrating them by 250% continuously with minimal sample preparation, while still being inexpensive, and effective. By implementing the microfluidic device, the processing steps are done within seconds due to its high throughput of 2 mL min⁻¹, wherein different hydrodynamic phenomena such as Dean's forces, inertial lift forces, and enhanced diffusion are taken advantage of.     

基于微泡共振的快速微流体声学混合方法研究

微流体在生物医学、化学工程等领域应用广泛,并具有重大意义.在预处理中,液体混合也是关键且最为必要的前序.为了提高微流控腔道内液体混合的效率,本文提出基于单微泡振动的声学混合器,通过微泡共振,产生声微流,声微流形成的剪切力将在流体中产生微扰动,实现液体的混合.设计了底面直径为40μm的微孔结构,由于液体表面张力作用形成微泡,在共振频率为165 kHz的压电换能器激励下,气泡发生共振产生声微流.通过对压电换能器输入不同能量,获取混合液体的最优参数,可在37.5 ms内实现混合效果,混合均匀度达到92.7%.本文设计的单微泡振动混合器结构简单、混合效率高、混合时间短、输入能量低,可为生物化学等方面的研究提供强有力的技术支撑.     

Three-dimensional chemical concentration maps in a microfluidic device using two-photon absorption fluorescence imaging

Two-photon absorption fluorescence is employed within a microfluidic device to create a three-dimensional chemical concentration map for mixing uniformity characterization. This multiphoton technique images fluorescence intensity directly and provides a simple, rapid, and readily employed route to composition characterization within microfluidic systems.     

Enhancement of mixing by microbubble emission boiling in a microfluidic device

The effect of microbubble emission boiling (MEB) on the mixing of two fluids in a microfluidic device was studied experimentally. When MEB occurred on an electric heater made of a platinum wire with a diameter of 30 micrometers, the mixing of the two fluids increased markedly. However, nucleate boiling had no significant effect on the mixing. A high-speed video showed that the very rapid growth and collapse of micro boiling bubbles on the heater causes the strong mixing of the two fluids. The coexistence of highly superheated and highly subcooled water near the heater seems to be the reason for such enhanced mixing.     

Hybrid approach to high-frequency microfluidic mixing

We report the experimental verification of the predicted chaotic mixing characteristics for a polydimethylsioxane microfluidic chip, based on the mechanism of multistage cross-channel flows. While chaotic mixing can be achieved within short passage distances, there is an optimal side channel flow pulsation frequency beyond which the mixing becomes ineffective. Based on the physical understanding of a Poincaré section analysis, we propose the installation of passive flow baffles in the main microfluidic channel to facilitate high-frequency mixing. The combined hybrid approach enables chaotic mixing at enhanced frequency and reduced passage distance in two-dimensional flows.     

Spectrally resolved flow imaging of fluids inside a microfluidic chip with ultrahigh time resolution

Microfluidics has advanced to become a complete lab-on-a-chip platform with applications across many disciplines of scientific research. While optical techniques are primarily used as modes of detection, magnetic resonance (MR) is emerging as a potentially powerful and complementary tool because of its non-invasive operation and analytical fidelity. Two prevailing limitations currently inhibit MR techniques on microfluidic devices: poor sensitivity and the relatively slow time scale of dynamics that can be probed. It is commonly assumed that the time scale of observation of one variable limits the certainty with which one can measure the complementary variable. For example, short observation times imply poor spectral resolution. In this article, we demonstrate a new methodology that overcomes this fundamental limit, allowing in principle for arbitrarily high temporal resolution with a sensitivity across the entire microfluidic device several orders of magnitude greater than is possible by direct MR measurement. The enhancement is evidenced by recording chemically resolved fluid mixing through a complex 3D microfluidic device at 500 frames per second, the highest recorded in a magnetic resonance imaging experiment. The key to this development is combining remote detection with a time ‘slicing’ of its spatially encoded counterpart. Remote detection circumvents the problem of insensitive direct MR detection on a microfluidic device where the direct sensitivity is less than 10^-5 relative to traditional NMR, while the time slicing eliminates the constraints of the limited observation time by converting the time variable into a spatial variable through the use of magnetic field gradients. This method has implications for observing fast processes, such as fluid mixing, rapid binding, and certain classes of chemical reactions with sub millisecond time resolution and as a new modality for on-chip chromatography.     

Time-of-flight flow imaging of two-component flow inside a microfluidic chip

Here we report on using NMR imaging and spectroscopy in conjunction with time-of-flight tracking to noninvasively tag and monitor nuclear spins as they flow through the channels of a microfluidic chip. Any species with resolvable chemical-shift signatures can be separately monitored in a single experiment, irrespective of the optical properties of the fluids, thereby eliminating the need for foreign tracers. This is demonstrated on a chip with a mixing geometry in which two fluids converge from separate channels, and is generally applicable to any microfluidic device through which fluid flows within the nuclear spin-lattice relaxation time.     

Effect of flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip

The detection of samples in a microfluidic nuclear magnetic resonance chip is generally performed under flow condition. To study the effect of sample flow on the apparent transverse relaxation time in a microfluidic nuclear magnetic resonance chip, theoretical calculations were performed on three microfluidic samples (including deionized water, absolute ethanol, and copper sulfate pentahydrate) for flow velocities in the range 1.7–25?mm/s. A microfluidic nuclear magnetic resonance device with a low cost microfluidic solenoid coil was fabricated to verify the theoretical calculations by experiments. The results show that the apparent transverse relaxation time of the sample is a monoexponential decay with respect to flow velocity. In addition, it was found that the experimental values and the theoretical values of the apparent transverse relaxation time are identical when the samples are prepolarized completely; but for the samples that are not prepolarized completely, all the experimental values are smaller than the theoretical values and their difference increases with the flow velocity of the sample. After further study, it was discovered that the relative error between the experimental values and the theoretical values is a monoexponential decay to the level of the sample to be prepolarized. This discovery is very useful, because it can be used to modify the theoretical calculation model of the apparent transverse relaxation time for the samples that are prepolarized incompletely, as well as improve the application of microfluidics on nuclear magnetic resonance.     

Microfluidic transport of photopolymerizable species for laser source integration in lab-on-a-chip photonic devices

We recently developed a novel composite photopolymerizable material which allows the holographic recording of diffraction gratings with optimal optical and mechanical properties (high diffraction efficiency, transparency and spatial resolution, low shrinkage, long time stability). This material was successfully used to produce a low cost and easy to make optically pumped, organic distributed feedback laser, working on the first diffraction order of a high quality Bragg grating doped with a photoluminescent dye. Here we show the possibility of positioning these micrometer sized light sources at any point of a generic lab-on-a-chip device by borrowing experimental techniques commonly used in the fields of microfluidics and optofluidics. In particular, a microfluidic channel has been imprinted by soft lithography in a polydimethylsiloxane substrate in order to convey the photopolymerizable mixture to a particular area of the sample, where the laser device has been holographically recorded. A characterization of the lasing properties of this device has been carried out. The proposed approach allows a better confinement of the emitted light and overcomes some physical constrains (resolution, aspect ratio) of PDMS based microfluidic laser thus opening new possibilities for the complex integration of organic laser sources in lab-on-a-chip devices.     

基于微流控混合器的连续流动态同步辐射圆二色谱发展

基于微流控混合器,采用连续流探测方法,在北京同步辐射装置真空紫外光谱实验站发展了毫秒动态圆二色谱探测方法。石英微流控混合器采用深度离子刻蚀技术加工,通道深度44.5 μm。混合器采用蛇形通道实现溶液的快速混合。通过荧光倒置显微镜,在模拟真实实验条件的高粘度溶液中,观察蛇形通道内溶液混合的荧光图像,进行混合效率测试。500 μL·min-1流量下,目前可实现4.5～270 μs的时间尺度探测。利用微流控混合器进行动态探测,同步辐射紫外光必须聚焦,但由于聚焦透镜波长色散引起的焦点位移,导致圆二色谱发生畸变。通过精确测试不同波长对应焦点的相对位置,然后在圆二色谱扫描中实现波长和焦点位置精确的反馈控制,获得准确的圆二色谱。利用所发展的方法,测试了去折叠状态下的细胞色素c恢复折叠的动态同步辐射圆二色谱,在4.5 μs处折叠恢复54%。这种方法将为生物大分子折叠动力学研究提供新的探测手段。     

荧光寿命显微成像技术及应用的最新研究进展

由于荧光寿命不受探针浓度、激发光强度和光漂白效应等因素影响,荧光寿命显微成像技术(fluorescence lifetime imaging microscopy, FLIM)在监测微环境变化、反映分子间相互作用方面具有高特异性、高灵敏度、可定量测量等优点,近年来已被广泛应用于生物医学等领域.然而,尽管FLIM的发明和发展已历经数十年时间,其在实际应用中仍然面临着许多挑战.例如,其成像分辨率受衍射极限限制,而其成像速度与成像质量和寿命测量精度则存在相互制约的关系.近几年来,相关硬件和软件的快速发展及其与其他光学技术的结合,极大地推动了FLIM技术及其应用的新发展.本文简要介绍了基于时域和频域的不同寿命探测方法的FLIM技术的基本原理及特点,在此基础上概述了该技术的最新研究进展,包括其成像性能的提升和在生物医学应用中的研究现状,详细阐述了近几年来研究者们通过硬件和软件算法的改进以及与自适应光学、超分辨成像技术等新型光学技术的结合来提升FLIM的成像速度、寿命测量精度、成像质量和空间分辨率等方面所做的努力,以及FLIM在生物医学基础研究、疾病诊断与治疗、纳米材料的生物医学研究等方面的应用,最后对其未来发展趋势进行了展望.     

Dye-sensitized solar cell module realized photovoltaic and photothermal highly efficient conversion via three-dimensional printing technology

Three-dimensional(3D) printing technology is employed to improve the photovoltaic and photothermal conversion efficiency of dye-sensitized solar cell(DSC) module. The 3D-printed concentrator is optically designed and improves the photovoltaic efficiency of the DSC module from 5.48% to 7.03%. Additionally, with the 3D-printed microfluidic device serving as water cooling, the temperature of the DSC can be effectively controlled, which is beneficial for keeping a high photovoltaic conversion efficiency for DSC module. Moreover, the 3D-printed microfluidic device can realize photothermal conversion with an instantaneous photothermal efficiency of 42.1%. The integrated device realizes a total photovoltaic and photothermal conversion efficiency of 49% at the optimal working condition.     

Effect of korteweg stress in miscible liquid two-layer flow in a microfluidic device

Miscible liquid two-layer flow in a Y-shaped microfluidic device, which consists of microchannels with 120 μm in width and 35 μm in depth, is investigated by particle image velocimetry (PIV) to clarify the flow characteristics at fluid interfaces. The obtained velocities with a spatial resolution of 5.9 x 1.5 μm² around the interface between water and ethanol indicate an imbalance in shear stress at interface. The reason of the imbalance is to be the Korteweg stress generated by interfacial tension gradient due to a concentration gradient by diffusion in a miscible two-layer flow. The stress may cause an interfacial instability and destroy a uniform mixing in two flowing fluids in the case of large concentration gradient.     

燃料射流与空气协流混合中的自点火预测研究

预混燃烧室燃料与空气混合过程中出现的自点火会引起回火与挂火,烧毁燃料喷嘴。针对这一问题,利用实验台模拟贫燃燃烧室预混过程,燃料射流与预热后的空气协流同向喷入石英管预混段中,研究自点火现象。本文结合机器学习和物理规律分析,开展湍流混合过程的自点火预测研究。基于二元逻辑回归建立了机器学习模型,模型的特征由分析影响自点火的物理规律得到,训练和校验模型所需的数据由燃料射流-空气协流的自点火实验获得。结果显示,机器学习方法能快速、准确地预测混合过程中自点火的发生和火焰类型,并揭示其关键影响因素。与传统的数值计算方法相比,机器学习方法预测自点火所需的时间仅为传统数值模拟方法的几千分之一。     

Dielectrophoresis based cell switching in continuous flow microfluidic devices

This article presents a novel negative-dielectrophoresis based approach for switching of a focused stream of micro-sized particles, including cells, to desired locations inside a continuous flow microfluidic device. The first section, of the device, focuses the incoming stream of micro-sized particles while the second section switches this focused stream of micro-sized particles. The microfluidic device consists of a glass substrate and a PDMS layer. The microfluidic device is realized using standard microfabrication. Tests are carried out using blood cells to demonstrate the efficacy of the approach in switching a stream of micro-sized particles to multiple locations inside the microchannel.     

A Feasible Add-On Upgrade on a Commercial Two-Photon FLIM Microscope for Optimal FLIM-FRET Imaging of CFP-YFP Pairs

Fluorescence lifetime imaging microscopy (FLIM) based on time-correlated single photon counting (TCSPC) is a widely used method for fluorescence resonance energy transfer (FRET). Here we report a feasible add-on approach to upgrade a commercial two-photon FLIM microscope into a single-photon FLIM microscope which provides optimal FLIM-FRET imaging of FRET pairs consisting of cyan fluorescent proteins (CFPs) as the donor and yellow fluorescent proteins (YFPs) as the acceptor. The capability of the upgraded system is evaluated and discussed, and the imaging performance of the system is demonstrated using FLIM-FRET experiments with a representative CFP-YFP FRET pair (mCerulean-mCitrine).     

Modelling of particle paths passing through an ultrasonic standing wave

Within an ultrasonic standing wave particles experience acoustic radiation forces causing agglomeration at the nodal planes of the wave. The technique can be used to agglomerate, suspend, or manipulate particles within a flow. To control agglomeration rate it is important to balance forces on the particles and, in the case where a fluid/particle mix flows across the applied acoustic field, it is also necessary to optimise fluid flow rate. To investigate the acoustic and fluid forces in such a system a particle model has been developed, extending an earlier model used to characterise the 1-dimensional field in a layered resonator. In order to simulate fluid drag forces, CFD software has been used to determine the velocity profile of the fluid/particle mix passing through the acoustic device. The profile is then incorporated into a MATLAB model. Based on particle force components, a numerical approach has been used to determine particle paths. Using particle coordinates, both particle concentration across the fluid channel and concentration through multiple outlets are calculated. Such an approach has been used to analyse the operation of a microfluidic flow-through separator, which uses a half wavelength standing wave across the main channel of the device. This causes particles to converge near the axial plane of the channel, delivering high and low particle concentrated flow through two outlets, respectively. By extending the model to analyse particle separation over a frequency range, it is possible to identify the resonant frequencies of the device and associated separation performance. This approach will also be used to improve the geometric design of the microengineered fluid channels, where the particle model can determine the limiting fluid flow rate for separation to occur, the value of which is then applied to a CFD model of the device geometry.     

High-speed wide-field time-gated endoscopic fluorescence-lifetime imaging

We report the development of a high-speed wide-field fluorescence-lifetime imaging (FLIM) system that provides fluorescence-lifetime images at rates of as many as 29 frames/s. A FLIM multiwell plate reader and a potentially portable FLIM endoscopic system operating at 355-nm excitation have been demonstrated.