共查询到20条相似文献，搜索用时 15 毫秒
1.
Cytokines are small proteins secreted by leukocytes in blood in response to infections, thus offering valuable diagnostic information. Given that the same cytokines may be produced by different leukocyte subsets in blood, it is beneficial to connect production of cytokines to specific cell types. In this paper, we describe integration of antibody (Ab) microarrays into a microfluidic device to enable enhanced cytokine detection. The Ab arrays contain spots specific to cell-surface antigens as well as anti-cytokine detection spots. Infusion of blood into a microfluidic device results in the capture of specific leukocytes (CD4 T-cells) and is followed by detection of secreted cytokines on the neighboring Ab spots using sandwich immunoassay. The enhancement of cytokine signal comes from leveraging the concept of reconfigurable microfluidics. A three layer polydimethylsiloxane microfluidic device is fabricated so as to contain six microchambers (1 mm × 1 mm × 30 μm) in the ceiling of the device. Once the T-cell capture is complete, the device is reconfigured by withdrawing liquid from the channel, causing the chambers to collapse onto Ab arrays and enclose cell/anti-cytokine spots within a 30 nl volume. In a set of proof-of-concept experiments, we demonstrate that ∼90% pure CD4 T-cells can be captured inside the device and that signals for three important T-cell secreted cytokines, tissue necrosis factor-alpha, interferon-gamma, and interleukin-2, may be enhanced by 2 to 3 folds through the use of reconfigurable microfluidics. 相似文献
2.
Samuel M. Stavis St��phane C. Corgi�� Benjamin R. Cipriany Harold G. Craighead Larry P. Walker 《Biomicrofluidics》2007,1(3)
Laser induced fluorescence in submicrometer fluidic channels was used to characterize the synthesis of polymerase chain reaction (PCR) products from a model bacterial system in order to explore the advantages and limitations of on chip real time single molecule PCR analysis. Single oligonucleotide universal bacterial primers and PCR amplicons from the 16S rDNA of Thermobifida fusca (325 bp) were directly detected at all phases of the reaction with low sample consumption and without post-amplification purification or size screening. Primers were fluorescently labeled with single Alexa Fluor 488 or Alexa Fluor 594 fluorophores, resulting in double labeled, two color amplicons. PCR products were driven electrokinetically through a fused silica channel with a 250 nm by 500 nm rectangular cross section. Lasers with 488 nm and 568 nm wavelengths were focused and overlapped on the channel for fluorescence excitation. All molecules entering the channel were rapidly and uniformly analyzed. Photon burst analysis was used to detect and identify individual primers and amplicons, and fluorescence correlation and cross-correlation spectroscopy were used to account for analyte flow speed. Conventional gel and capillary electrophoresis were also used to characterize the PCR amplification, and the results of differences in detection sensitivity and analyte discrimination were examined. Limits were imposed by the purity and labeling efficiency of the PCR reagents, which must be improved in parallel with increases in detection sensitivity. 相似文献
3.
Using a membrane emulsification method based on porous hollow-fiber membranes in combination with an aqueous two-phase system (ATPS), we are able to produce “water-in-water” droplets with narrow-dispersed size distributions. The equilibrium phases of the aqueous two-phase system polyethylene glycol-dipotassium hydrogen phosphate are used for this purpose. The droplet diameter of a given fluid system is determined by the flow rates of the continuous and disperse phase as well as the hollow fiber dimensions. When diluting the disperse phase and thus moving the ATPS system out of equilibrium, the droplet size can be further reduced in comparison to the equilibrium case. Generally, droplets formed with this method have diameters 20%–60% larger than the inner hollow fiber diameter. The new strategy of diluting the disperse phase allows the production of droplet diameter below the inner diameter of the membrane. 相似文献
4.
This paper presents a low-cost, power-free, and easy-to-use spotter system for fabrication of microarrays. The spotter system uses embedded dispensing microchannels combined with a polydimethylsiloxane (PDMS) membrane containing regular arrays of well-defined thru-holes to produce precise, uniform DNA or protein microarrays for disease diagnosis or drug screening. Powered by pre-evacuation of its PDMS substrate, the spotter system does not require any additional components or external equipment for its operation, which can potentially allow low-cost, high-quality microarray fabrication by minimally trained individuals. Polyvinylpyrrolidone was used to modify the PDMS surface to prevent protein adsorption by the microchannels. Experimental results indicate that the PDMS spotter shows excellent printing performance for immobilizing proteins. The measured coefficient of variation (CV) of the diameter of 48 spots was 2.63% and that of the intensity within one array was 2.87%. Concentration gradient experiments revealed the superiority of the immobilization density of the PDMS spotter over the conventional pin-printing method. Overall, this low-cost, power-free, and easy-to-use spotting system provides an attractive new method to fabricate microarrays. 相似文献
5.
Two simple gold nanoparticle (GNP)-based DNA analysis methods using a microfluidic device are presented. In the first method, probe DNA molecules are immobilized on the surface of a self-assembled submonolayer of GNPs. The hybridization efficiency of the target oligonulceotides was improved due to nanoscale spacing between probe molecules. In the second method, target DNA molecules, oligonulceotides or polymerase chain reaction (PCR) amplicons, are first bound to GNPs and then hybridized to the immobilized probe DNA on a glass slide. With the aid of GNPs, we have successfully discriminated, at room temperature, between two PCR amplicons (derived from closely related fungal pathogens, Botrytis cinerea and Botrytis squamosa) with one base-pair difference. DNA analysis on the microfluidic chip avoids the use of large sample volumes, and only a small amount of oligonucelotides (8 fmol) or PCR products (3 ng), was needed in the experiment. The whole procedure was accomplished at room temperature in 1 h, and apparatus for high temperature stringency was not required. 相似文献
6.
本文研究了水雾与浸没在多孔介质中的乙醇火焰间的相互作用。探讨了水雾喷射压力,燃料预燃时间以及多孔介质类型对水雾灭火规律的影响。实验结果表明燃料预燃时间相同时,水雾喷射压力越大,火焰区及燃料床内部的温度变化越快,火焰熄灭时间也越短。当水雾喷射压力相同时,预燃时间越长,火焰越容易被熄灭,此外多孔介质类型对水雾灭火效果有重要影响。 相似文献
7.
Along with other cultural organizations, newspapers, through waves of digital disruption, have become subject to a dominant narrative of crisis. But newspapers have long participated in change. A constructivist approach, qualified by consideration of media materiality, draws attention to diverse but essential processes of innovation around them. We see a contraflow of migration from digital to print, opening up a shared media space; bonding strategies are bringing multimedia to ink on paper, while bridging via boundary objects such as QR (Quick Response) codes are connecting the two. Among other initiatives, development of automation of news production and experiments with transparency are further evidence of an active embrace of change by newspapers that calls into question the discourse on their demise. This analysis inductively develops a nuanced account of the role of the newspaper as an object and as an institution. It suggests a hybrid, multifaceted, enduring presence of print in the complex media ecology of the future. 相似文献
8.
Zhichao Guan Yuan Zou Mingxia Zhang Jiangquan Lv Huali Shen Pengyuan Yang Huimin Zhang Zhi Zhu Chaoyong James Yang 《Biomicrofluidics》2014,8(1)
Although digital detection of nucleic acids has been achieved by amplification of single templates in uniform microfluidic droplets and widely used for genetic analysis, droplet-based digital detection of proteins has rarely been reported, largely due to the lack of an efficient target amplification method for protein in droplets. Here, we report a key step towards digital detection of proteins using a highly parallel microfluidic droplet approach for single enzyme molecule detection in picoliter droplets via enzyme catalyzed signal amplification. An integrated microfluidic chip was designed for high throughput uniform droplet generation, monolayer droplet collection, incubation, detection, and release. Single β-galatosidase (β-Gal) molecules and the fluorogenic substrate fluorescein di-β-D-galactopyranoside were injected from two separated inlets to form uniform 20 μm droplets in fluorinated oil at a frequency of 6.6 kHz. About 200 000 droplets were captured as a monolayer in a capture well on-chip for subsequent imaging detection. A series of β-Gal solutions at different concentrations were analyzed at the single-molecule level. With no enzyme present, no droplets were found to fluoresce, while brightly fluorescent droplets were observed under single-enzyme molecule conditions. Droplet fluorescence intensity distribution analysis showed that the distribution of enzyme molecules under single-molecule conditions matched well with theoretical prediction, further proving the feasibility of detecting single enzyme molecules in emulsion droplets. Moreover, the population of fluorescent droplets increased as the β-Gal concentration increased. Based on a digital counting method, the measured concentrations of the enzyme were found to match well with input enzyme concentration, establishing the accuracy of the digital detection method for the quantification of β-Gal enzyme molecules. The capability of highly parallel detection of single enzyme molecules in uniform picoliter droplets paves the way to microdroplet based digital detection of proteins. 相似文献
9.
为研究共享汽车租赁网络扩张特征和布局策略,将网络效应考虑在内,分别分析单个租赁网点在租赁网络扩张中的利润特征及不同网络结构下租赁网络的利润情况,最后给出共享汽车租赁网络的布局建议。研究发现,正网络外部性占主导时,租赁网点的边际利润随网络的扩展呈现出一种先递减再递增的趋势;当租赁网点受到负网络外部性主导时,其边际利润随网络扩展呈现出先增后减的趋势;网络布局受路径依赖效应的影响,先布设受正网络外部性影响较大的网点时,网络所获的累计利润将更高;最后给出了网络扩张中,各网点布局的条件。 相似文献
10.
Dielectrophoretic nanocolloid assay is a promising technique for sensitive molecular detection and identification, as target molecule hybridization onto the probe-functionalized nanocolloids can change their surface conductance and consequently their dielectrophoretic crossover frequencies. Thus, instead of relying on surface charge density increase after hybridization, as in many capacitive and field effect transistor impedance sensing techniques, the current assay utilizes the much larger surface conductance (and dielectrophoresis crossover frequency) changes to effect sensitive detection. Herein, we present a Poisson–Boltzmann theory for surfaces with finite-size molecular probes that include the surface probe conformation, their contribution to surface charge with a proper delineation of the slip and Stern planes. The theory shows that the most sensitive nanocolloid molecular sensor corresponds to a minimum in the dielectrophoretic crossover frequency with respect to the bulk concentration of the molecular probes (oligonucleotides in our case) during nanocolloid functionalization. This minimum yields the lowest number of functionalized probes that are also fully stretched because of surface probe-probe interaction. Our theory provides the surface-bulk oligonucleotide concentration isotherm and a folding number for the surface oligonucleotide conformation from the crossover frequency, the zeta potential, and the hydrodynamic radius data. 相似文献
11.
偏远型景区有其自身的特点,其旅游资源开发受到诸多因素的影响.本文以青海省三江源地区达那河谷景区为例,运用层次分析法构建了偏远型景区旅游资源开发影响因素分析的指标体系,计算了各影响因素的影响力权重,并针对各影响因素提出了旅游资源开发的一些行为对策;进而对实施这些行为对策的投资成本进行了估计,结合各行为对策所对应因素的权重及实施该行为对策的预期成本大小,将这些行为对策分为4种类型;最后认为在偏远型景区旅游资源开发实践中,应综合考虑影响作用及实施成本的大小来进行各种资源的优先配置,并以此为依据确定各种行为对策的优先度次序. 相似文献
12.
We demonstrate here the discovery of a unique and direct three-dimensional biomicrofabrication concept possessing the ability to revolutionize the jet-based fabrication arena. Previous work carried out on similar jet-based approaches have been successful in fabricating only vertical wall∕pillar-structures by the controlled deposition of stacked droplets. However, these advanced jet-techniques have not been able to directly fabricate self-supporting arches∕links (without molds or reaction methods) between adjacent structures (walls or pillars). Our work reported here gives birth to a unique type of jet determined by high intensity electric fields, which is derived from a specially formulated siloxane sol. The sol studied here has been chosen for its attractive properties (such as an excellent cross-linking nature as well as the ability to polymerize via polycondensation on deposition to its biocompatability), which promotes direct forming of biostructures with nanometer (<50 nm) sized droplets in three dimensions. We foresee that this direct three-dimensional biomicrofabrication jet technique coupled with a variety of formulated sols having focused and enhanced functionality will be explored throughout the physical and life sciences. 相似文献
13.
旅游景区（点）系统空间结构关联维数分形研究——以南京市景区（点）系统为例 总被引：16，自引：0，他引：16
本文以南京市旅游景区（点）系统为例,采用测算与分析空间关联分形维数的方法对景区（点）系统的空间结构进行了研究。根据旅游景区（点）系统空间结构的无标度特性和遵循的进化过程,认为对其空间结构进行分形研究是可行的。南京市景区（点）系统的空间结构是分形的,具有景点系统空间结构演化自组织优化的趋势,在地理区域分布上表现为景点空间分布较集中的特性。同时认为景区（点）系统空间结构具有自仿射性分形特征,景点系统从中心向外围有递变的趋势,且在不同方向上递变的比率是不同的,在地理区域上表现为景点的空间分布越往外围越集中（或均衡）,且不同方向上的集中性程度是不同的;具体到南京市来说是递减的,向南部递减的较慢,向北部递减的较快。同时系统的空间结构也基本具有分形对称性特征。 相似文献
14.
In order to fully explore and utilize the advantages of droplet-based microfluidics, fast, sensitive, and quantitative measurements are indispensable for the diagnosis of biochemical reactions in microdroplets. Here, we report an optical detection technique using two-photon fluorescence lifetime imaging microscopy, with an aligning-summing and non-fitting division method, to depict two-dimensional (2D) maps of mixing dynamics by chaotic advection in microdroplets with high temporal and spatial resolution. The mixing patterns of two dye solutions inside droplets were quantitatively and accurately measured. The mixing efficiency in a serpentine droplet mixer was also quantified and compared with the simulation data. The mapped chaotic mixing dynamics agree well with the numerical simulation and theoretical prediction. This quantitative characterization is potentially applicable to the real-time kinetic study of biological and chemical reactions in droplet-based microfluidic systems. 相似文献
15.
偏远型景区有其自身的特点,其旅游资源开发受到诸多因素的影响.本文以青海省三江源地区达那河谷景区为例,运用层次分析法构建了偏远型景区旅游资源开发影响因素分析的指标体系,计算了各影响因素的影响力权重,并针对各影响因素提出了旅游资源开发的一些行为对策;进而对实施这些行为对策的投资成本进行了估计,结合各行为对策所对应因素的权重及实施该行为对策的预期成本大小,将这些行为对策分为4种类型;最后认为在偏远型景区旅游资源开发实践中,应综合考虑影响作用及实施成本的大小来进行各种资源的优先配置,并以此为依据确定各种行为对策的优先度次序. 相似文献
16.
基于九寨沟景点负荷均衡的时空分流导航研究 总被引：2，自引：1，他引：1
全球旅游业的发展趋势对现代旅游管理提出了新的要求,如何实现旅游业的经济效益、社会效益与生态效益的协调发展逐渐成为社会各界关注的焦点。研究在对九寨沟进行了全面考查的基础上,分析了旅游旺季景区内客流的时空变化特征,指出由于游客在时间和空间上的分布不均衡,导致各景点负荷差异明显,使旅游和生态不能协调发展。因此有必要设计合理的游客分流方案,实现景区生态保护与经济发展的协调。文章研究内容属于景区时空分流导航研究的理论基础,它构建了面向景点负荷均衡的数学定量描述,从建立数学规划模型和动态预测调度两个方面提供了问题分析思路,并提出在预测调度中嵌套车辆调度。 相似文献
17.
An experimental study on isotachophoresis (ITP) in which an emulsion is used as leading electrolyte (LE) is reported. The study aims at giving an overview about the transport and flow phenomena occurring in that context. Generally, it is observed that the oil droplets initially dispersed in the LE are collected at the ITP transition zone and advected along with it. The detailed behavior at the transition zone depends on whether or not surfactants (polyvinylpyrrolidon, PVP) are added to the electrolytes. In a system without surfactants, coalescence is observed between the droplets collected at the ITP transition zone. After having achieved a certain size, the droplets merge with the channel walls, leaving an oil film behind. In systems with PVP, coalescence is largely suppressed and no merging of droplets with the channel walls is observed. Instead, at the ITP transition zone, a droplet agglomerate of increasing size is formed. In the initial stages of the ITP experiments, two counter rotating vortices are formed inside the terminating electrolyte. The vortex formation is qualitatively explained based on a hydrodynamic instability triggered by fluctuations of the number density of oil droplets. 相似文献
18.
网络化是旅游目的地空间演化的基本规律。本文以野三坡旅游地为案例,基于ArcGIS与UCINET软件平台,利用社会网络理论和空间分析方法,从网络规模、网络中心性以及网络结构演化三方面入手,揭示了1986—2015年野三坡旅游目的地网络的空间演变过程,并对其影响因素进行简要分析。研究发现：①野三坡旅游地网络日趋形成,网络规模不断扩大,网络联系逐渐增强,但空间分布不均衡,呈现以百里峡景区（核心景区）为核心,由西南向东北逐渐递减的空间格局。②整个网络的中心性呈现下降趋势,网络结构趋于均衡,网络节点具有明显的层次性,核心景区与中心城镇相较于周边的乡村社区与特色园区来说中心性指数更高,占据核心地位。③野三坡旅游地网络演化经历了单核集聚-双核共生-多核等级化-链式全域化四个空间过程,交通网络及可达性、旅游消费者、社区参与与旅游企业、政府政策与规划是影响旅游地网络形成和演化的四个重要因素。景区、城区、社区以及园区一体化发展的旅游产业集聚区作为旅游地网络研究的最小单元,为旅游地研究提供了新的理论范式,成为未来研究的重要趋势。 相似文献
19.
Meng-chun Liu 《Research Policy》2012,41(6):1107-1120
China has become a hot spot of R&D internationalization and a growing number of Taiwan-based firms have indeed set up R&D units in China. Taking into account China's substantial regional variations in economic development, innovation capacity, and knowledge productivity, such notions as regional innovation system (RIS) and local innovative milieu may become more relevant to the study on relationships between China and its inward R&D internationalization. Therefore, the key issue for this paper is what locational advantages of an RIS within a host country affect the network linkages and networking strategy of multinational corporations’ (MNCs’) offshore R&D units. The paper aims to enrich the current understanding of R&D internationalization in several ways. First, the paper attempts to examine the R&D networking underlying R&D internationalization by Taiwan-based firms in China, with particular reference to the sub-national level inside China. Second, the paper tries to establish a link between the literature of R&D internationalization and that of RIS, with a modified version of Dunning's eclectic paradigm. Efforts are made to map the relationship between foreign subsidiaries’ local R&D networks and their host RISs inside China. Third, the paper takes advantage of a government databank to adopt a quantitative approach, the Seemingly Unrelated Bivariate Probit Regression model, with foreign subsidiaries as the unit of analysis, to highlight the role played by some aspects of the RIS in determining the local R&D networking of Taiwanese subsidiaries in China. Our evident shows that MNCs’ offshore R&D units that purse home-based technology exploitation strategy, the mainstream strategy regarding the developing host country, tend to be located in a host region with a strong knowledge application and exploitation subsystem, while an RIS with a strong knowledge generation and diffusion subsystem, within such a developing country as China, may induce MNCs’ local R&D units to pursue home-base technology augmenting strategy. On balance, not only the location choice but also the local R&D linkages of MNCs’ offshore subsidiaries are related to appropriate fits between the RIS and the subsidiaries’ innovation network inside the host country. 相似文献
20.
用蒙特卡洛方法研究了夸克喷注和反夸克喷注内部的动力学起伏。夸克和反夸克喷注从91．2GeV正负电子湮灭的2-喷注事件中在部分子层次上被区分出来．结果显示，在这两种喷注中都存在着一个转变点．在转变点处，动力学起伏在纵-横平面内是各向异性的，而在横平面内是各向同性的，由此得到了实验中可观察喷注的物理标度。 相似文献