Smartphone-interfaced lab-on-a-chip devices for field-deployable enzyme-linked immunosorbent assay

The emerging technologies on mobile-based diagnosis and bioanalytical detection have enabled powerful laboratory assays such as enzyme-linked immunosorbent assay (ELISA) to be conducted in field-use lab-on-a-chip devices. In this paper, we present a low-cost universal serial bus (USB)-interfaced mobile platform to perform microfluidic ELISA operations in detecting the presence and concentrations of BDE-47 (2,2′,4,4′-tetrabromodiphenyl ether), an environmental contaminant found in our food supply with adverse health impact. Our point-of-care diagnostic device utilizes flexible interdigitated carbon black electrodes to convert electric current into a microfluidic pump via gas bubble expansion during electrolytic reaction. The micropump receives power from a mobile phone and transports BDE-47 analytes through the microfluidic device conducting competitive ELISA. Using variable domain of heavy chain antibodies (commonly referred to as single domain antibodies or Nanobodies), the proposed device is sensitive for a BDE-47 concentration range of 10⁻³–10⁴μg/l, with a comparable performance to that uses a standard competitive ELISA protocol. It is anticipated that the potential impact in mobile detection of health and environmental contaminants will prove beneficial to our community and low-resource environments.     

劈尖干涉理论及应用

介绍了劈尖干涉的原理,利用分振幅法将一束光分为两束光,在介质膜上、下表面反射的光在膜的上表面附近相遇,而发生干涉,在介质表面就会观察到明暗相间、等间距的条纹。探讨了劈尖干涉理论在检查平面的平整度及计算平面凹凸的深度、测量微小长度、微小角度等很多实际应用的结论,改进了测量微笑长度的方法。     

Optofluidic microvalve-on-a-chip with a surface plasmon-enhanced fiber optic microheater

We present an optofluidic microvalve utilizing an embedded, surface plasmon-enhanced fiber optic microheater. The fiber optic microheater is formed by depositing a titanium thin film on the roughened end-face of a silica optical fiber that serves as a waveguide to deliver laser light to the titanium film. The nanoscale roughness at the titanium-silica interface enables strong light absorption enhancement in the titanium film through excitation of localized surface plasmons as well as facilitates bubble nucleation. Our experimental results show that due to the unique design of the fiber optic heater, the threshold laser power required to generate a bubble is greatly reduced and the bubble growth rate is significantly increased. By using the microvalve, stable vapor bubble generation in the microchannel is demonstrated, which does not require complex optical focusing and alignment. The generated vapor bubble is shown to successfully block a liquid flow channel with a size of 125 μm × 125 μm and a flow rate of ∼10 μl/min at ∼120 mW laser power.     

Antioxidant and lipid lowering activities of Indian black tea

Indian black tea; CTC leaf and dust, produced by Tata Tea Limited, Kolkata, (India) was studiedin vitro as potential scavenger of oxygen free radicals. Super oxide anions were generated in a system containing xanthine—xanthine oxidase (enzymic system) and by NADH- phenozine methosulphate (non enzymic system). Anions were assayed in terms of uric acid formation and reduction of nitroblue tetrazolium salt, which were shown to be suppressed by tea extracts. Extracts from both leaf and dust also inhibted the formation of hydroxyl radicalsin vitro in the enzymic system comprising hypoxanthine—Cu⁺²—sodium ascorbate and xanthine oxidase and in non enzymic system of deoxyribose—Cu⁺²—sodium ascorbate and H₂O₂ as well as the Cu⁺² induced lipid peroxidation in human low density lipoprotein. Feeding with black tea in normal rats for sixty days increased their antioxidant activity and their liver microsomes were shown to be protected against peroxidation of lipids as stimulated by metal ions with enzymic or non enzymic reactants. Furthermore feeding with tea extracts in normal as well as triton WR—1339 induced hyperlipidemic rats caused decrease in their plasma levels of total cholesterol, phospholipids and triglycerides. The antioxidant and lipid lowering activities of both extracts from CTC leaf and dust tea was comparable and may be due to the presence of natural products like catechin and others.     

不同土地利用类型下土壤-作物镉含量积累及其健康风险分析

镉(Cd)是一种剧毒重金属元素,可引起呼吸系统、肾损伤等多种疾病,对人体毒性极高,可通过多种途径暴露于人体,危害人体健康。土壤-植物-食品-人的迁移途径在人类对环境镉的暴露中占主导地位。近年来,Cd通过饮食途径对人体健康造成的风险日益引起人们的关注和重视。本文在对研究区不同土地利用类型下土壤和作物进行大规模采样调查的基础上,对其蔬菜、水稻、旱地、果园等4种土地类型土壤及其种植作物中镉含量积累进行了研究。结果表明,菜地和水稻地有明显的污染超标现象,其中菜地土壤镉含量最高。根据不同土地利用类型下各作物镉富集系数,进行聚类分析,比较其对镉富集能力的差异,结果表明水稻地稻米镉的富集能力最高,单独划为一类。利用定性风险分析技术,对不同土地利用类型下土壤镉对人体健康的风险商值进行了计算,结果表明不同土地类型下,作物镉风险商值为水稻>深色蔬菜>浅色蔬菜>水果>玉米。镉对个人致癌年风险的计算结果表明,水稻个人年致癌风险为0.6270×10^-4/年,高于防护委员会(ICRP)推荐的最大可接受年风险水平0.5×10^-4/年,为不可接受水平,居民面临较大的致癌风险,应采取积极措施对研究区土壤镉污染进行治理和修复。     

中国西北沙漠对东亚大气粉尘影响的数值试验研究

以塔克拉玛干沙漠为主的中国西北沙漠区是东亚地区主要沙尘释放源区之一。本文利用美国大气研究中心（NCAR）的公用气候模式（CCM3）与一个沙尘释放和沉降模式（DEAD）相嵌套、能够反映沙尘扬起及输送和沉降动态过程的耦合模式系统（CCM3-DEAD），通过改变中国西北沙漠-半沙漠区下垫面类型的数值模拟试验，对比分析了西北沙尘源区地表类型的改善对东亚地区沙尘释放及大气粉尘含量变化的可能影响。研究结果表明，地表覆盖状况与沙尘释放关系密切，沙尘源区地表类型的改善可明显抑制沙尘的释放。中国西北沙漠-半沙漠区地表的改善，可引起整个中国北方至蒙古国的大气粉尘含量减少，使大气环境明显改善。假设以塔克拉玛干为主的沙漠-半沙漠区不存在（当地地表类型若以温带草原植被为主），则整个中国北方沙尘释放和沉降通量仅为目前的50%左右。模式中分4个粒级描述沙尘释放及沉降通量，其中1.0~2.5μm和2.5~5.0μm两个粒级的贡献约占总通量的76%，对比试验显示在没有塔克拉玛干等沙漠存在的情况下这两个粒径释放通量大大降低。由西北沙漠-半沙漠区释放的沙尘，经大气环流传输可直接影响到我国东北、华北等东部地区的大气粉尘状况，并对日本、韩国及其周边地区也有一定影响。     

成都市空气污染指数、降水量小波分析

通过对2006～2010年成都市的空气污染指数及其2006～2010年每月降水量进行小波分析,以及对两者不同时间尺度下的小波系数进行滑动比较。得到如下结论:(1)在2006~2010年期间,成都市的空气污染状况以优良为主,冬季的污染较重,夏季较轻,变化周期为3个月,2006年、2008年和2010年波动较大;(2)成都市月降水量的变化周期也是3个月,2006～2008年和2010年其月降水量波动较大;(3)成都市的月平均空气污染指数与月降水量之间呈现负相关关系,其相关系数为-0.498,而两者的波动性呈现出一定的正相关关系。     

Increasing Glucose Concentrations Interfere with Estimation of Electrolytes by Indirect Ion Selective Electrode Method

The estimation of electrolytes like sodium (Na⁺), potassium (K⁺) and chloride (Cl⁻) using direct and indirect ion-selective electrodes (ISE) is a routine laboratory practice. Interferents like proteins, triglycerides, drugs etc. are known to affect the results. The present study was designed to look into the effect of increasing glucose concentrations on estimation of Na⁺, K⁺ and Cl⁻ by direct and indirect ISE. Pooled sera was mixed with glucose stock solution (20 g/dL) prepared in normal saline to obtain glucose concentrations ranging from ~100 to ~5000 mg/dL. Na⁺, K⁺ and Cl⁻ levels were estimated by direct and indirect ISE analyzers and results were statistically analysed using ANOVA and Pearson’s correlation. Similar experiment was also performed in 24 h urine sample from healthy subjects. Significant difference was observed between Na⁺ and Cl⁻ measurements by direct and indirect ISE, with indirect ISE values being consistently higher than direct ISE. Besides this, significant difference was observed amongst Na⁺ and Cl⁻ values from baseline values obtained by indirect ISE at glucose concentrations ≥2486 mg/dL. However, no such difference was observed with direct ISE. Na⁺ and Cl⁻ estimation by indirect ISE showed significant negative correlation with glucose concentration, more so, above ~2000 mg/dL. K⁺, however, showed no significant difference with varying glucose. Similar results were observed in 24 h urine samples with a significant difference observed amongst Na⁺ and Cl⁻ values at ≥2104 mg/dL glucose. Thus we conclude that high glucose concentrations interfere significantly in estimation of Na⁺ and Cl⁻ by indirect ISE in serum as well as urine.

Electronic supplementary material

The online version of this article (doi:10.1007/s12291-015-0522-0) contains supplementary material, which is available to authorized users.     

The magnetic deflection experiments of Curtiss and of Mott-Smith

We have carried out a geometrical analysis which applies to that type of cosmic ray deflection experiment in which an extended region of magnetic field lies between the lower two of three or more Geiger-Mueller counters arranged in line for counting coincident discharges. It is apparent that charged particles of sufficiently low energy will be deviated away from the last counter and that the counting rate will therefore be reduced by application of the field. This paper presents a method for computing what proportion of electrons of a given energy will be eliminated by application of the field. The method is extended to include a constant loss of energy per unit path length as the particle traverses an iron core. The results of the experiments of Curtiss and of Mott-Smith are interpreted in the light of these calculations. Curtiss' result could be explained if all rays were electrons of 4 × 10⁸ volts energy. One may conclude from his observation that if all the radiation consists of positive or negative electrons, the fraction between 2 × 10⁷ volts and 1.5 × 10⁸ volts is less than 30 per cent. of the total above 2 × 10⁷, and that the fraction between 2 × 10⁷ and 10⁹ is greater than 30 per cent. A comparison of Curtiss' and Mott-Smith's experiments yields no reason for doubting the correctness of using the magnetic induction B when computing the deflection within iron. Nor does it necessarily sustain this procedure. An experiment by W. F. G. Swann and the writer is at present under way for the purpose of securing, if possible, more conclusive evidence on this point.     

北京市沙尘暴天气环境质量等级划分

为进一步认知沙尘天气对北京空气质量的定量影响,本文通过对2001-2009年发生在我国北方显著沙尘天气过程的分析,结合同期北京空气污染指数(API)的变化,研究了沙尘天气对北京空气质量等级划分的影响。结果如下:①构建了一个空气质量等级划分的复合指标体系。将沙尘天气过程对北京空气质量的影响划分为4个等级。分别是覆盖型重污染、边缘型中度污染、远距离轻微污染和远距离无影响;②2001-2009年,我国北方共计发生136次沙尘天气过程,对北京大气环境质量影响贡献的最高值出现在秋末(11月)和冬初(12月),以覆盖型重污染等级为主,共计发生17次,期间北京地区平均API为306;③从传输路径上划分,则是以西北路径为主,共计发生59次,其中24次显著影响到北京,占41%。期间,北京地区平均API为242;④沙尘天气过程持续时间以2天为主,共计发生56次,共有14次显著影响到北京,占25%,期间北京地区平均API为216。     

塔克拉玛干沙漠腹地太阳紫外辐射特征

本文利用塔克拉玛干沙漠腹地(塔中站:83°40'E,39°01'N)2007年1月-12月紫外辐射和总辐射的观测资料,分析了塔克拉玛干沙漠腹地太阳紫外辐射的气候学特征。结果表明:①本地区太阳紫外辐射年总量为305.64MJ(/m2·a)。年平均日总量为0.84MJ/m2,大于黑河、太湖和青藏高原地区。紫外辐射年平均值在总辐射年平均值中所占比例为4.99%,小于太湖和北京,大于黑河地区和五道梁,月平均日总量7月最大;②其日变化,晴天呈现出标准的倒"U"型,即早晚小、中午大,正午达到一天中的最大值;③紫外辐射受云量、降水和沙尘的影响很大;④紫外辐射在总辐射中所占比例有明显的年、季节和日变化,其年变化分为三个明显不同的阶段,夏季大,冬季小。青藏高原地区春夏大,冬季小,北京地区和黑河地区相近,分别是冬季大,夏季小和冬季大,春夏小。     

IntoNews: Online news retrieval using closed captions

We present IntoNews, a system to match online news articles with spoken news from a television newscasts represented by closed captions. We formalize the news matching problem as two independent tasks: closed captions segmentation and news retrieval. The system segments closed captions by using a windowing scheme: sliding or tumbling window. Next, it uses each segment to build a query by extracting representative terms. The query is used to retrieve previously indexed news articles from a search engine. To detect when a new article should be surfaced, the system compares the set of retrieved articles with the previously retrieved one. The intuition is that if the difference between these sets is large enough, it is likely that the topic of the newscast currently on air has changed and a new article should be displayed to the user. In order to evaluate IntoNews, we build a test collection using data coming from a second screen application and a major online news aggregator. The dataset is manually segmented and annotated by expert assessors, and used as our ground truth. It is freely available for download through the Webscope program.¹ Our evaluation is based on a set of novel time-relevance metrics that take into account three different aspects of the problem at hand: precision, timeliness and coverage. We compare our algorithms against the best method previously proposed in literature for this problem. Experiments show the trade-offs involved among precision, timeliness and coverage of the airing news. Our best method is four times more accurate than the baseline.     

Hepatitis during respiratory syncytial virus infection – a case report

Introduction:

Respiratory syncytial virus (RSV) infection is the most common cause of hospitalization in infants and small children. The aim was to present a 13-months old boy diagnosed with acute airway infection, acute otitis media (AOM) and hepatitis during the RSV-infection.

Material and methods:

Serum catalytic activities of alkaline phosphatase (ALP), aspartate aminotranspherase (AST), alanine aminotranspherase (ALT), gamma glutamyl transpherase (GGT), lactate dehydrogenase (LD), and concentrations of bilirubin were monitored during hospitalization and at control examination.

Results:

The child had clinical signs and symptoms of respiratory failure, AOM, and laboratory findings of virus infection and liver disease. On admission, catalytic activities of enzymes were markedly increased, especially the activity of ALP (10333 U/L, i.e. 24-fold increase in comparison with the upper reference limit). The highest increased in AST (339 U/L, 4.5-fold), ALT (475 U/L, 10.3-fold) and LD (545 U/L, 1.5-fold) were registered on the 3^rd day, and the highest increase in GGT (68 U/L, 3.1-fold) occurred on the 11th day. Seven weeks after discharge AST, ALT, GGT and LD decreased into reference range, and ALP remain mildly increased (478 U/L, 1.1 fold increase). RSV was confirmed in nasal lavage fluid.

Conclusion:

Laboratory results in patient with RSV infection needs to be interpreted in the light of both, respiratory and extrapulmonary manifestations of the infection, respectively.     

2001-2010 年东北三省植被净初级生产力模拟与时空变化分析

本文基于改进的CASA光能利用率模型,利用遥感数据、气象数据、土地覆盖类型数据作为模型输入参数,估算了中国东北三省2001-2010年的植被净初级生产力(NPP),并利用MOD17A3 NPP产品与本文估算NPP进行了精度对比分析。结果表明,东北三省10a平均的植被NPP为304.643g C/(m2·a)。不同土地覆盖类型NPP差异明显,阔叶林>混交林>针叶林>农田>灌木>草地>城镇>未利用地>水体。年NPP在2001-2005年间出现了上下波动的趋势,且不同土地覆盖类型NPP的时空变化趋势不同,森林覆盖区域具有明显的逐年下降趋势(-1.217g C/(m2·a)),未利用地则具有明显的逐年上升趋势(2.35g C/(m2·a))。通过对3个气象因子(降水、辐射量、温度)、3个模型参数因子(APAR累积量、光能利用率ε、NDVI累积量)与NPP的相关性分析可知,APAR累积量与NPP的相关性最大,研究区平均相关系数达到了0.703,温度与NPP的相关系数最小,研究区平均相关系数为0.011。     

Biomineralization of a calcifying ureolytic bacterium Microbacterium sp. GM-1

BackgroundBiomineralization is a significant process performed by living organisms in which minerals are produced through the hardening of biological tissues. Herein, we focus on calcium carbonate precipitation, as part of biomineralization, to be used in applications for environmental protection, material technology, and other fields. A strain GM-1, Microbacterium sp. GM-1, isolated from active sludge, was investigated for its ability to produce urease and induce calcium carbonate precipitation in a metabolic process.ResultsIt was discovered that Microbacterium sp. GM-1 resisted high concentrations of urea up to 60 g/L. In order to optimize the calcification process of Microbacterium sp. GM-1, the concentrations of Ni^2 + and urea, pH value, and culture time were analyzed through orthogonal tests. The favored calcite precipitation culture conditions were as follows: the concentration of Ni^2 + and urea were 50 μM and 60 g/L, respectively, pH of 10, and culture time of 96 h. Using X-ray diffraction analysis, the calcium carbonate polymorphs produced by Microbacterium sp. GM-1 were proven to be mainly calcite.ConclusionsThe results of this research provide evidence that Microbacterium sp. GM-1 can biologically induce calcification and suggest that strain GM-1 may play a potential role in the synthesis of new biominerals and in bioremediation or biorecovery.     

Reproducibility, accuracy and concordance of Accutrend Plus for measuring circulating lipid concentration in adults

Introduction

The determination of lipid biomarkers by capillary sampling may be useful in the screening, diagnosis and/or personal management of hyperlipidemia and cardiovascular risk. It remains unclear whether the use of the Accutrend^® Plus system is appropriate. This study aimed to assess its reproducibility, accuracy and concordance for blood lipid profiling in adults.

Materials and methods:

Fasting capillary total cholesterol (TC) and triglyceride (TG) concentration on Accutrend^® Plus were compared with their venous analogues obtained by a laboratory reference method in sixty-one adults (27 men and 34 women, aged 33.0 years). Supplementary capillary sampling was performed at two consecutive days taking into account macro-nutrient intake.

Results:

The day-to-day reproducibility of the Accutrend^® Plus system proved to be high for TC (ICC = 0.85, P < 0.001), but moderate for TG (ICC = 0.68, P < 0.001). Strong correlations (r ≥ 0.80, P < 0.001) with the reference method were found for TC and TG. Mean difference (limits of agreement) were: 0.26 mmol/L (−0.95, 1.47) for TC, and −0.16 mmol/L (−1.29, 0.98) for TG. The concordance for subject classification according to the National Cholesterol Education Program (NCEP) guidelines was significant (P < 0.001), with substantial agreement for TC (κ_w = 0.67), and moderate agreement for TG (κ_w = 0.50).

Conclusions:

Day-to-day reproducibility of the Accutrend^® Plus device for TC and TG is not optimal and lacks accuracy when compared to the reference laboratory method. The concordance between both methods for classifying subjects according to the NCEP is inadequate. Accutrend^® Plus device should not be interchangeably used as a substitution for the standard laboratory methods in the diagnosis of hyperlipidemia.     

Syringe-vacuum microfluidics: A portable technique to create monodisperse emulsions

We present a simple method for creating monodisperse emulsions with microfluidic devices. Unlike conventional approaches that require bulky pumps, control computers, and expertise with device physics to operate devices, our method requires only the microfluidic device and a hand-operated syringe. The fluids needed for the emulsion are loaded into the device inlets, while the syringe is used to create a vacuum at the device outlet; this sucks the fluids through the channels, generating the drops. By controlling the hydrodynamic resistances of the channels using hydrodynamic resistors and valves, we are able to control the properties of the drops. This provides a simple and highly portable method for creating monodisperse emulsions.Droplet-based microfluidic devices use micron-scale drops as “test tubes” for biological reactions.^{1, 2, 3} With the devices, the drops are loaded with cells, incubated to stimulate cell growth, picoinjected to introduce additional reagents, and sorted to extract rare specimens.^{4, 5, 6} This allows biological reactions to be performed with greatly enhanced speed and efficiency over conventional approaches: by reducing the drop volume, only picoliters of reagent are needed per reaction, while through the use of microfluidics, the reactions can be executed at rates exceeding hundreds of kilohertz. This combination of incredible speed and efficient reagent usage is attractive for a variety of applications in biology, particularly those that require high-throughput processing of reactions, including cell screening, directed evolution, and nucleic acid analysis.^{7, 8} The same advantages of speed and efficiency would also be beneficial for applications in the field, in which the amount of material available for testing is limited, and results are needed with short turnaround. However, a challenge to using these techniques in field applications is that the control systems developed to operate the devices are intended for use in the laboratory: to inject fluids, mechanical pumps are needed, while computers must adjust flow rates to maintain optimal conditions in the device.^{9, 10, 11, 12} In addition to significantly limiting the portability of the system, these qualities make them impractical for use outside the laboratory. For droplet-based microfluidic techniques to be useful for applications in the field, a general, robust, and portable system for operating them is needed.In this paper, we introduce a general, robust, and portable system for operating droplet-based microfluidic devices. In this system, which we call syringe-vacuum microfluidics (SVM), we load the reagents needed for the emulsion into the inlets of a microfluidic drop maker; using a standard plastic syringe, we generate a vacuum at the outlet of the drop maker,¹³ sucking the reagents through the channels, generating drops, and transporting them to different regions for visualization and analysis. By controlling the vacuum strength and channel resistances using hydrodynamic resistors^{14, 15, 16} and single-layer membrane valves,^{17, 18} we are able to specify the flow rates in different regions of the device and to adjust them in real time. No pumps, control computers, or electricity is needed for these operations, making the entire system portable and of potential use for field applications. To characterize the adjustability and precision of this system, we vary channel resistances and vacuum pressures while measuring the effects on drop size and production frequency. We also show how to use this to form drops of many distinct reagents simultaneously using only a single vacuum syringe.Monodisperse drop formation is the central operation in droplet-based microfluidics but can be quite challenging due to the need for precise, steady pumping of reagents; forming monodisperse drops with controlled properties is thus a stringent demonstration of the effectiveness of a control system. While there are many geometries available for microfluidic drop formation,¹⁹ in this discussion we use a simple cross-junction for its proven ability to form uniform emulsions at high rates of speed,^{20, 21} a schematic of which is shown in Fig. ​Fig.1.1. The devices are fabricated in poly(dimethylsiloxane) (PDMS) using soft lithography.²² The drop formation channels have dimensions of 25 μm in width and 25 μm in height. To enable production of aqueous drops in oil, which are the most useful for biological assays, we require hydrophobic devices, which we achieve using an Aquapel chemical treatment: we flow Aqualpel through the channels for a few seconds, flush with air, and then bake the devices for 20 min at 65 °C. After this treatment, the channels are permanently hydrophilic, as is needed for forming aqueous-in-oil emulsions. To introduce reagents into the device, we use 200 μl plastic pipette tips inserted into the channel inlets. To apply the suction, we use a 10 ml Bectin-Dickenson plastic syringe coupled to the device through a 16 G needle and PE∕5 tubing. The other end of the tubing is inserted into the outlet of the device.Open in a separate windowFigure 1Schematic of the microfluidic drop maker for use with SVM. To form water drops in oil, the device must be hydrophobic, which we achieve by treating the channels with Aquapel. The water and surfactant-containing oil are loaded into pipette tips inserted into the device inlets at the locations indicated. To pump the fluids through the drop maker, a syringe applies a vacuum to the outlet; this sucks the fluids through the drop maker, forming drops. The drops are collected into the suction syringe, where they can be stored, incubated, and reintroduced into a microfluidic device for additional processing.To begin forming drops, we fill the device with HFE-7500 fluorocarbon oil, displacing trapped air bubbles that could restrict flow and interfere with drop formation. Pipette tips containing reagents are then inserted into the device inlets, as shown in Fig. ​Fig.11 and pictured in Fig. ​Fig.2a;2a; during this step, care must be taken to not trap air bubbles under the pipette tips, as they would restrict flow. For the fluids, we use distilled water for the droplet phase and HFE-7500 with the ammonium salt of Krytox 157 FSL at 1.8 wt % for the continuous phase. The suction syringe is then connected to the device outlet; to initiate drop formation, the piston is pulled outward and locked in place with a 1 in. binder clip, as shown in Fig. ​Fig.2a.2a. This expands the air in the syringe, generating a vacuum that is transferred to the device through tubing. Since the inlet reagents are open to the atmosphere and thus maintained at a pressure of 1 atm, this creates a pressure differential through the device that pumps the fluids. As the fluids flow through the cross-channel, forces are generated that create drops, as shown in Fig. ​Fig.2b2b (enhanced online). Due to the very steady flow, the drops are highly monodisperse, as shown in Fig. ​Fig.2c.2c. After they are formed, the drops flow out of the device through the suction tube and are collected into the syringe. Depending on the emulsion formulation, drops may coalesce on the metal needle of the syringe; if so, an Upchurch fitting should be used to couple the tubing instead. The collected drops can be stored in the syringe, incubated, and reintroduced into additional microfluidic devices, as needed for the assay.Open in a separate windowFigure 2Photograph of the microfluidic drop formation device with pipette tips containing emulsion reagents and vacuum syringe for pumping (a). Distilled water is used for the droplet phase and HFE-7500 fluorocarbon oil with fluorinated surfactant for the continuous phase. The vacuum applies a pressure differential through the device that pumps the fluids through the drop maker (b) forming drops. The drops are monodisperse, due to the controlled properties of drop formation in microfluidics (c). The scale bars denote 50 μm (enhanced online).In many biological applications, drop size must be precisely controlled. This is essential, for example, when encapsulating molecules or cells in the drops, in which the number encapsulated depends on the drop size.^{3, 23, 24} With SVM, the drop size can be precisely controlled. Our strategy to accomplish this is motivated by the physics of microfluidic drop formation. In microfluidic devices, the capillary number of the flow is normally small, Ca<0.1; as a consequence, the drop formation physics follows a plugging∕squeezing mechanism, in which the drop size depends on the flow rate ratio of the dispersed-to-continuous phase.^{20, 25} By adjusting this ratio, we can thus control the drop size. To adjust this ratio, we use hydrodynamic resistor channels.^{14, 15, 16} These channels are analogous to electronic resistors in that for a fixed pressure drop (voltage) the flow rate through them (current) is inversely proportional to their resistance. By making the resistors longer or shorter, we adjust their resistance, thereby controlling the flow rate.To use resistors to control the drop size, we place three on the inlets of the cross-junction, at the locations indicated in Fig. ​Fig.3a.3a. In this configuration, the flow rate ratio depends on the resistances of the central and side resistors: shortening the side resistors increases the continuous phase flow rate with respect to the dispersed phase, thereby reducing the ratio and, consequently, the drop size, whereas lengthening it increases the drop size. By varying the ratio, we produce drops over a range of sizes, as shown in Fig. ​Fig.3b3b (enhanced online). The drop size is linear in the resistance ratio, indicating that it is linear in the flow rate ratio, as is expected for plugging∕squeezing drop formation [Fig. ​[Fig.3b3b].^{20, 25} This behavior is identical to that of pump-driven fluidics, demonstrating that SVM affords similar control.Open in a separate windowFigure 3Drop properties can be controlled using resistor channels. The resistors are placed on the inlets of the drop maker at the locations indicated in (a). The resistors enable the flow rates of the inner and continuous phases to be controlled. By varying the length ratio of the inlet resistors, we control the flow rate ratio in the drop maker. This allows the drop volume to be controlled, as shown by drop volume plotted as a function of inlet resistor length ratio in (b); varying this ratio does not significantly affect the drop formation frequency, as shown in (c). By varying the length of the outlet resistor, we control the total flow rate through the device; this allows us to form drops of constant volume, but at a different formation frequency, as shown by the plots of volume and frequency as a function of the inverse of the outlet resistor length in (d) and (e), respectively. The measured hydrodynamic resistance of a resistor channel with water as a function of length is shown as inset into (d) (enhanced online).We can also control the frequency of the drop formation using resistor channels. We place a resistor on the outlet of the device; this sets the total flow rate through the device, thereby adjusting drop frequency, as shown in Fig. ​Fig.3e3e (enhanced online). To confirm that the size and frequency control are independent, we plot size as a function of the outlet resistance and frequency as a function of the resistance ratio [Figs. ​[Figs.3c,3c, ​,3d];3d]; both are constant as a function of these parameters, again demonstrating independent control. Frequency can also be adjusted by changing the strength of the vacuum, which can be accomplished by loading a prescribed volume of air into the syringe before expansion. In this case, the vacuum pressure applied is P_fin=V_in∕V_fin×P_in, where V_in is the initial volume of air in the syringe, V_fin is the volume after expansion, and P_in is the initial pressure, which is 1 atm. By loading a prescribed volume of air into the syringe before connecting it to the device and pulling the piston, the expansion factor can be reduced, thereby lowering the vacuum strength.The flow rates through the microfluidic device depend on the applied pressure differential, which, in turn, depends on the value of the ambient pressure. Since ambient pressure may vary due to differences in altitude, the drop formation may also vary. However, since ambient pressure variations affect the inner and outer phase flows equally, this should alter the total flow rate but not the flow rate ratio. Consequently, we expect it to alter drop formation frequency but not drop size because while the frequency depends on absolute flow rate [as illustrated by Fig. ​Fig.3e],3e], drop size depends on the flow rate ratio [as illustrated in Fig. ​Fig.3b].3b]. Based on normal variations in atmospheric pressure on the surface of the Earth, we expect this to produce differences in the drop formation frequency of ∼25%, for example, when operating a device at sea level compared to at the top of a moderately sized mountain.Resistor channels allow drop properties to be controlled, equivalent to what is possible with pump-driven flow; however, they do not allow real-time control because their dimensions are fixed during the fabrication. Real-time control is often needed, for example, as it is when performing reactions in drops for the first time, in which the optimal drop size is not known. To enable real-time control, we must adjust flow rates, which can be achieved using the fluidic analog of electronic potentiometers. Single-layer membrane valves are analogous fluidic components, consisting of a control channel that abuts a flow channel.^{17, 18} By pressurizing the control channel, the thin PDMS membrane between these channels is deflected laterally, constricting the flow channel, thereby increasing its hydrodynamic resistance and reducing its flow rate.¹⁸ To use these membrane valves to vary drop size, we replace the inlet resistors with inlet valves, as shown in Fig. ​Fig.4a.4a. To set the flow rate through a path, we actuate the valve with a defined pressure. To actuate the valves, we use air-filled syringes: a 1 ml syringe is filled with air and connected to the valve control channel through tubing; an additional component, a three-way stopcock is inserted between the syringe and needle, allowing the pressure to be locked in after optimal actuation conditions are obtained. We use one syringe to control the dispersed phase valves and another to control the continuous phase valves. The valves are pressurized by compressing the air in the syringes to a defined degree using the marked graduations; this is achieved by pressing the piston to a defined graduation mark, compressing the air contained within it, thus increasing pressure. The stopcock is then switched to the off position, locking in the actuation. This simple scheme allows precise actuation of the valves, for accurate, defined flow rates in the drop maker, and controlled drop size, as shown in Figs. ​Figs.4b,4b, ​,4c4c (enhanced online). The drop size can be varied at a rate of several hertz without noticeable loss of control; moreover, changing the drop size does not affect the frequency, indicating that, again, these properties are independent, as shown by the constant drop frequency with varying pressure ratio in Fig. ​Fig.4d4d.Open in a separate windowFigure 4Single-layer membrane valves allow the drop size to be varied in real time to screen for optimal reaction conditions. The valves are positioned on the inner and side inlets, as indicated in (a). By adjusting the actuation pressures of the valves, we vary the flow rates in the drop maker, thereby changing the drop size (b), as shown by the plot of drop volume as a function of the actuation pressure ratio in (c). Varying the inlet resistance ratio does not significantly alter drop formation frequency, as shown by frequency as a function of the pressure ratio in (d). A movie of drop formation during actuation of the valves are available in the supplemental material (Ref. ²⁹). The scale bars denote 100 μm (enhanced online).Another useful attribute of SVM is that it readily lends itself to parallel drop formation²⁶ because the pressure that pumps the fluids through the channels is supplied by the atmosphere and is applied evenly over the whole outer surface of the device. This allows fluids to be introduced at equal pressures from different inlets, for forming drops with identical properties in different drop makers. To illustrate this, we use a parallel drop formation device to emulsify eight distinct reagents simultaneously; the product of this is an emulsion library, consisting of drops of identical size in which different drops encapsulate distinct reagents, useful for certain biological applications of droplet-based microfluidics.⁷ The microfluidic device consists of eight T-junction drop makers.²⁵ The drop makers share one oil inlet and outlet but each has its own inner-phase inlet, as shown in Fig. ​Fig.5.5. The oil and outlet channels are wide, ensuring negligible pressure drop through them, so that all T-junctions are operated under the same flow conditions. A distinct reagent fluid is introduced into the inner phase of each T-junction, for which we use eight concentrations of the dye Alexa Fluor 680 in water. After loading these solutions into the device through pipette tips, a syringe applies the vacuum to the outlet, sucking the reagents through the T-junctions, forming drops, as shown by the magnified images of the T-junctions during drop formation in Fig. ​Fig.5.5. Since the drop makers are identical and operated under the same flow conditions, the drops formed are of the same size, as shown in the magnified images in Fig. ​Fig.55 and in a movie available in the supplemental material.²⁹Open in a separate windowFigure 5Parallel drop formation device consisting of eight T-junction drop makers. The drop makers share a common oil inlet and outlet, both of which are wide to ensure even pressure distribution to all drop makers; support posts prevent these channels from collapsing under the suction. Each drop maker has its own inner-phase inlet, allowing emulsification of a distinct reagent. Since the drop maker dimensions and pressure differentials are constant through all drop makers, the drops formed are of the same size, as shown in the magnified images. The drops are ∼35 μm in diameter.To verify that the dye solutions are successfully encapsulated, we image a sample of the collected drops with a fluorescent microscope. The drops are confined in a monolayer between two glass plates so they can be individually imaged. They are of the same size but have distinct fluorescence intensities, as shown in Fig. ​Fig.6a.6a. To quantify these differences, we measure the intensity of each drop and plot the results as a histogram [see Fig. ​Fig.6b].6b]. There are eight peaks in the histogram, corresponding to the eight dye concentrations, demonstrating that all dyes are encapsulated successfully. The peak areas are also similar, demonstrating that drops of different types are formed in equal amounts due to the uniformity of the parallel drop formation.Open in a separate windowFigure 6Fluorescent microscope image of emulsion library created with parallel T-junction device (a). In this demonstration, eight concentrations of Alexa Fluor 680 dye are emulsified simultaneously, producing an emulsion library of eight elements. The drops are of the same size but encapsulate distinct concentrations of the dye solution, as demonstrated by the eight peaks in the intensity histograms in (b). The scale bar denotes 100 μm.SVM is a simple, accessible, and highly controlled way to form monodisperse emulsions for biological assays. It allows controlled amounts of different reagents to be encapsulated in individual drops, drop size to be precisely controlled, and the ability to form drops of different reagents at the same time, in a parallel drop formation device. These properties should make SVM useful for biological applications of monodisperse emulsions;^{1, 2, 3} the portability of SVM should also make it useful for applications in the field, particularly when no electrical power source is available. The parallel emulsification technique should also be useful for particle templating from drops, in which the particles must be of the same size but composed of distinct materials.^{26, 27, 28, 29}     

一种喷淋式霾尘空气净化器

为了减轻严重雾霾天气的危害,可推广应用一种喷淋式霾尘空气净化器。该种空气净化器不仅结构简单、排风量大,而且由于采用水为过滤介质,因而可对霾尘空气中包含2．5PM和以下细微的尘粒、烟粒、盐粒及各种水溶性有害气体进行净化。     

Asymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcation

In microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear, and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations, human red blood cells suspended in dextran 40 with about 14% of hematocrit level (14 Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0 × 10⁻¹² m³/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region.