软物质类外文文献翻译、微流控智能电敏滴中英文翻译、外文翻译

附录    软物质  引用： DOI： 10.1039/c2sm26286j /softmatter (/ softmatter) 微流控智能电敏滴  回顾 ：  2012 年 6 月 4 日收到，  2012 年 8 月 26 日接受  DOI： 10.1039/c2sm26286j 我们给液滴微流控技术的一个简短的回顾，重点对 ''''聪明滴，这是基于上，可以积极地控制并通过外部刺激如压力操纵的材料，温度， pH，和电场或者磁场。特别是，重点是产生和操纵这是基于巨电流变流体（ GERF）液滴。我们详细说 明编制及 GERF，相关微流控芯片的格式，以及特色产生和使用 GERF 如任一小滴或载体流体液滴的控制。一个重要的应用GERF 液滴，在实现第一个通用微流控逻辑装置可以执行 16 布尔逻辑运算，详述。  1.引言  在 80 年代后期， 在对固体第五届国际会议  国家传感器和执行器，曼茨和合作者先进  的“总化学分析系统程式（ MTA） '的概念 1 的强调微型器件在化学的重要性，并  生物测试。随后，这个一般概念催生了  调查与描述性词语，如多元化的领域“微流控技术”，“生物微机电系统”，“实验室在单芯片”等微流体，  尤其是有关涉及运输的 新学科现象和基于流体的装置在微米尺度。在过去的  几十年来，这个地区经历了爆炸式的发展，服务作为共同的平台，工程师，物理学家，化学家，生物学家和其他人可以进行交互和创新上的研究方向和应用范围浩大从传感器，化学 /生物合成，微反应器，以药物发现和点关心（ POC）诊断 .1-3微流控技术已受聘于发展喷墨打印头， 4 个实验室在一个芯片技术， 5 微型热技术， 6 等有巨大潜力的微流体将使多个步骤的复杂的整合分析程序，微到纳升消费试剂 /样本，以及进行所有的承诺与可移植性 .7-9 流程。  目前，微流体技术有两种不同的  方法：连续流微流 体和微流体液滴。都有自己的特点和应用。连续流微流控技术更成熟，滴  微流体从其独特的获得认可和控制。  连续流动设备提供流微调控制  的特性，其比例最多是一个挑战，因为的大小几乎呈线性平行通道的数量。在  相反，液滴的基于微流体，其中有大量的  反应可以在平行而不必增加运行的装置规模和复杂性，吸引了越来越多的兴趣爱好者 .10 化学反应和生物测试可以独立成微小的液滴从纳米到微微升的大小。这可以作为小滴基础上具有得天独厚的优势microfluidics.11， 12 下面我们进一步阐述了这  一点。  物理，科学香港大学和技术，清 水湾，九龙，香港，中国。电子邮箱：  phwenust.hk先进的研究，科学的香港大学和技术，清水湾，九龙，香港，中国。电子邮箱： shengust.hk  吴金波的研究兴趣主要集中在液滴型微流体，生物芯片 PCR 和表面改性与  图案。卫嘉的主要研究  兴趣包括软凝聚态  凝聚态物理，电流变  （ ER）和磁（ MR）液，  布局和结构转换，微和纳米流体控制，微球和纳米捏造，  薄膜物理，带隙材料，超材料和非线性光学材料。   以液滴的形式，试剂在精确输送离散量，可作为血管的试剂，从而实现了单细胞操纵生物testing11 ，  13,14 和高通量化学 reactions.1 ，  15 它提供了一个有前途的途径，空间和时间分辨化学，其中 1 可用于便宜的和潜在改进的测量动力学和结合常数，以及测量多组分的相和反应图解的各方面 systems.16 ，  17 混合液滴的试剂已被证明是在几毫秒内实现，因此多步化学反应通过微流体液滴已被证明是 possible.18 液滴的微流体的另一个优点是该试剂 /化学 /颗粒 /细胞中的每个液滴是很好的隔离，从而减少固体墙和潜在的污染接触。液滴的微流体芯片更趋于多功能，用一个简单和小型化的结构。目前，液滴微流体不仅在DNA 和蛋白质分析应用 19-23 immunoassay24 和化学，  25,26 ，但也一直发现在某些物理测量，  27 是不可或缺的液滴和气泡的逻辑，  28 以及临床 applications.29 ，  30    液滴微流控涉及的产生，检测和  操作里面 microdevices.18 不连续的水滴， 31 在  接下来，我们在调查第二节为代方法  和操纵液滴。在第三节的重点是  这是基于巨电流的 ''''聪明滴流体（ GERF）。特别是，在制备智能液滴，相关微流控芯片设计，并且  机动和智能墨滴的控制详述。部分四，介绍了智能电敏的一个 重要应用在实现微流控逻辑门飞沫最终可以使之在自立运行微流控芯片只需极少的外部控制。我们结论在第五节与言论有关的潜在未来发展。  盛平是香港科技大学威廉教授纳米科学的博士生。  他的研究兴趣在复杂的领域流体，流体动力学边界的条件下，电流变流体，光子与声子材料，  和碳纳米管超导性。  二液滴生成和操作  2.1 液滴生成  液滴微流控系统的特殊效用在于形成均匀的液滴和颗粒。固有的这种  系统，以及最重要的，是的精确控制尺寸，形状和液滴的单分散性。微流控流动聚焦（ MFF）的方法通常是在液滴 /气泡用形成， 32,33 双乳液的生成 ,34-36 多功能颗粒和 microbeads.37 韦茨的研究小组已经开发出新颖，轻便，并采用玻璃毛细管的可扩展技术生产单，双，和高阶单分散乳液具有卓越的精度。这些乳液是一种有用的各种各样的应用范围从微粒制造（多层，多核或非球面），以囊泡的形成和化学合成的高通量筛选，其中每个  液滴供应来封装单个细胞，基因，或反应物。  另一种基于几何的产生方法使用的丁字路口构，其中两种不混溶流体被带到在一起。基础研究到这种方法已经被进行地震的研究小组， 41 韦茨的 group42others.43 许多活跃发电控制方法已经被开发出来 ，如误吸， 44 外力， 45 声波， 46 电解，高电压 47 脉冲和热毛细。  2.2 液滴操控  不同于连续微流体，液滴微流体系统让液滴的独立控制，使产生的飞沫可以单独拆分，混合，运输和分析 50 液滴操作可以包括核裂变，聚变，排序，混合增强和检测。无论是被动和主动方法已被用在液滴操作。  2.2.1 被动操作  被动的方法通常依赖上的信道结构，可以在二维或三维。通道树枝或障碍物的目的是创造一个剪切力分裂 droplets.51 -53 当液滴被压入到分路结，分支可以拉对液滴，使其断裂成两个，或对称或不对称。在这些设计，液滴裂变可通过流 量控制。融合液滴通常是通过将两个或更多个液滴进行接近彼此，直到流体形式的薄膜时，在连接为此目的设计 的 interface.54 通 道的几何 形状可 以包括侧 通道地 漏之间的 连续相droplets.51 ，液滴内 55 混合是另一个重要的问题液滴微流控。在液滴触及的每一半的通道壁，等于重新循环流可以生成。从而在液滴的每一半流体充分混合但两半保持每个other.49 被动混合液滴分离通常由一个弯弯曲曲的通道折叠，伸展和重新调整增强该droplets.16 ，  17 被动液滴的排序往往取决于液滴尺寸。通道的几何形状和分支机构可仔细 设计用于区分大小 differences.56 被动运输单个液滴的控制注意到仍然是一个挑战。  2.2.2 主动操纵   许多主动控制方法有已经实现，例如通过流体静力学压力，  57温度平盛梯度，  58 热膨胀，  59 光学电有关的包括静电，  66 电效应，其中，上电润湿电介质（  EWOD ）  69,74,75 已被证明是非常有效的切割，合并，创建和运输液滴。这样一个类型的技术已被表示为数字微流体（  DMF ）  ，如此命名是因为它的微调 '' ''数字化控制液滴。所有的液滴操作，配药，移动，分裂和合并，通过使用 EWOD 驱动进行的 液滴运动，与外部定义的每一个步骤控制。与此相反，对于智能液滴逻辑门描述下面，逻辑运算都是通过互动液滴中，这大大简化了为控制必要的用于实现逻辑操作。  2.3 智能墨滴  聪明滴基于智能或智能材料可以对外界刺激如压力，温度， pH 响应，  和电场或磁场field.76 相对于传统的液滴中，智能的生成和操作液滴可以更容易地通过外部刺激以控制积极的态度。  至目前为止，几种智能（响应）液滴已经根据其响应于外部报告和分类控制。  （ 1）热响应液滴。通过将二氧化钛纳米 particles77 或其他材料，如 wax78 成液滴，流体液滴的表面张力或粘度可以使  是温度依赖的。特别是，塞弗特等和 Shah 等人。已经形成温敏智能微凝胶从大分子前体胶囊和证明他们的实用程序，用于封装和控释应用。 79,80 （ 2）对 pH 值敏感的液滴。  Khan等。制作涂有 pH 敏感的聚合物水凝胶的智能乳剂其表面电荷性质可以通过外部 pH 值来改变value.81 ，  82 （  3 ）光响应液滴。  Matsumoto 等人。成功开发出光响应凝胶液滴可在紫外光 exposure.83 转化为溶胶状态（  4 ）磁响应水滴如铁磁流体液滴。铁磁流体液滴可致动的磁场中，通过改变其磁流变 properties.84 ，  85 也可以在所述致动使用泵或 valve86 并已由 Nguyen.87 评论（ 5）电响应水滴如电流变液液滴。通过采用巨电流变液（  GERF ）  ，  88 全系列芯片嵌入式软 valves89 ，  90 和中流体为基础的自动智能系统已经实现。下面我们专注于 GERF 作为智能有利的材料液滴。相比，所有其他智能液滴，电敏智能墨滴提供的不仅是优势对自己的 '智能 ' ，但也可以用于控制其他类型的的液滴。这一点下面将详细进行进一步的讨论。  表 1 总结，以图形的方式，将 5 类型的智能  上述液滴。  表 1     插图的 5 种智能墨滴的。  （ 1）液滴的大小  随着温度（ 2）所述的液滴是正  被控在 pH4，而它原来的中性 pH 值两个 9.91（ 3）外壳  液滴，在紫外光照射下，变成溶胶状态的凝胶状态，  和两个液滴融合成 one.83（ 4）磁性颗粒悬浮在当磁场是 applied.86（ 5）介电液滴形式链  颗粒悬浮在液滴形式链时受到电领域。   聪明滴  举例  （ 1）热响应滴   （ 2）对 pH 值敏感滴   （ 3） 光响应滴  （ 4）磁敏感滴  （ 5）电响应滴   电流变流体（  ERF）是一种智能材料其包括介电粒子悬浮在绝缘 oil.92 由于在固体之间的介电常数的对比度粒子和分散液，固体颗粒被极化根据施加的电场，从而导致诱导偶极时刻（图 1）  。所得  到的偶极  - 偶极相互作用和最小化的要求支配，该粒子将聚集形成柱沿外加电场方向。这结构转  型，它可以发生在几毫秒内，导致电流变液表现出粘度增加，甚至固体状的行为，即维持能力的剪切 stress93 -101（图 1）  。  ERF 可以作为电  - 机械接口，并且加上传感器时，触发时间和幅度所施加  的电场，它可以呈现许多设备，如电脑配件，阀门，风门等人，成为活跃的机械能够应对环境变化的元素 - 因此智能 流体的外延。然而，尽管有在设想不同的应用，实际广泛的兴趣实现这些有用的潜力已经阻碍了不足的 ER 效应展出由传统的 ERF 。相当大的改进工作已经进入准备另类悬浮颗粒 ,102- 104 ，但无明显的效果。  一个突破是在 2003 年实现（参见 88）与发现巨型流体（ GERF），包括尿素包衣草酸氧钛钡的纳米颗粒悬浮在硅油。该 GER 效果代表从不同的范式因为它是基于分子传统的 ER 机制偶极子，而不是诱导偶极的。它提供了一个显著 effect.88 在一个适度的电场， GERF 可以改造成各向异性的固体，具有的数量级上的屈服应力  100-300 千帕，在 4 千伏毫米？ 1的电场。这些流变变异可以发生在 10 毫秒内和是可逆的当该字段被删除。有了这样的显着特点，一范围的设备 applications88 ,105-108，以及微流控微阀，微泵，具有很强的可操作性等，已经实现。  在下文中，我们详细 GERF 的生成过程液滴和流和液滴列车操作，可以是实现的。在与使  用的 Ag-PDMS 的结合复合材料作为导电线和微流体通道作为的电气电路的电容 /电阻部分，它表明逻辑功能可实现对微流控芯片，通过该 GERF 液滴的非线性电流响应。   图 1。介电微球的下一个 1 的构造演 化增强的电场。从左至右依次为：无场，一个温和的字段和强场。  三 GERF 的智能墨滴  3.1 GERF 组成及特点  用于在微流体的上下文中使用的 GERF，它是要避免硅油，传统的吸收  悬浮液 GERF，由基本的芯片材料硅橡胶。因此，对于微流体应用的 GER颗粒悬浮在向日葵油来代替，以 5-40的重量比 GER 颗粒。将混合物过滤，用筛子（孔径为 10mm 左右），以除去大的聚集体。  下一个应用领域 >1 千伏毫米  ？ 1， GERF 展品行为，例如，对发送的剪切应力的能力。该向日葵油  基 GERF 的测量动态剪切应力相当于，根据硅酮油为基 础 GERF 的类似的电场。作为 GERF 具有大得多的 ER 在相同的外加磁场（图 2）响应与比较传统的 ERF，温和的电场足以减缓下来或停止微流体流动，同时为液滴生成和操作流程。这是一个重要的方面已启用 GERF 的智能墨滴的发展在微流控。  3.2 芯片制造  控制 GERF 液滴，电极必须被集成进入 PDMS 微流控芯片。然而，金属确实良好的 PDMS，由于其低的表面能。至克服这个问题，导电性粒子，例如碳  纤维 /碳黑色或银纳米粒子嵌入或附加成的 PDMS，以形成导电，可以是复合材料通过软 lithography.114， 115 两种类型的兼 容处理 - 基于 PDMS 的导电复合材料（银 /碳的 PDMS 银 / C PDMS）已经开发了牛等 al.116这些的混合物，可制成薄膜具有所需的厚度或构图成结构和嵌入的 PDMS 微流体芯片通过软光刻技术。平面和三维导电的微观结构，从几十到几百微米的，已成功集成到基于 PDMS 的芯片。  通过使用导电复合材料的 PDMS，对平行的和通道壁嵌入电极可穿过安装微流体通道。与输入的电信号，电控制和传感成为实现作为 GERF 液滴的一部分控制。在电容特别是非常小的  变化当液滴穿过两者之间，可以检测电极。由于电极的设计和反馈的电子大小，形状 的电路，精确的实时决心和液滴的组合物已被证实（图 3）。该操作频率可达 10 千赫，一个速度，这是难以通过常规的光学装置来实现。因此，它可以在原位检测和控制用于便携式实验室芯片的液滴。测试的电容的信号，可以直接使用  原位标记，分类和液滴操控。  3.3 GERF 作为液滴或作为载流体  有施加 GERF 到微流体的两种方式  引导液滴操作。第一是形成 GERF 通过另一种流体通过，而第二个是用滴 GERF 作为载流体，以控制其它的液滴或气泡。这两种情况的示意图如图所示。图 4（ a）和（ b）所示。放置在微流体通道的两侧的电极可以将电 场施加到流动 GERF，无论是在液滴的形式，或作为载体流体。在电极芯片的液滴产生部分位于靠近结面积，从而控制了 GERF 流的定时，从而液滴的产生提供控制。下游电极提供进一步的流量控制中的形式检测，路由和 /或分选。   图 2。 2 校准的两个葵花籽油为基础的 GERF 的电流变效应  为 20和 40的纳米粒子的浓度。动态剪切应力被绘制为时间的函数。  1 kV 到 5 kV 的方波直流  电压脉冲被施加到样品两端 1 毫米间隙 . 图 3。一组离子水液滴具有不同的图 3（ a）光学图像尺寸。少量的染料（而不引起的变化检测介电常数为微滴）溶 液中加入用于标记。检测到的信号被描绘在（ b）所示。  （三），箭头指向的检测信号对应的液滴：染色 DI 水（暗）和乙二醇（光）。    图 4。该 GERF4 示意图为：（ a） droplets113 及（ b）承运人 fluid118 在微流体通道。   图 5。图 5（ a）智能墨滴产生不同 GERF 流速下，与液滴的长度（由流量归一化）绘制的函数电气控制 signals.113 的周期 T（ F）光学显微图像两组 GERF 液滴通过控制电信号的产生  （红线）。  下面我们回顾这两种情况 GERF 为飞沫或作为载体流体，并且它们各自的功能。  3.3.1 GERF 智能墨滴的生成。在第一种方法中，  由流聚焦方法被生成为 GERF 液滴图示意性示出。图 4（ a）所示。当在一对的电压在上述液滴生成部电极被设置为零， GERF 液滴可以以被动方式来生成。图的边界（ b）所示。  5 示出了单分散的液滴形成时的流速 GERF是 0.2 毫升水 1 和硅油的比（作为载体液），以 GERF 流量是 3： 1，然而，当流速高（ 4 毫升水 1）和油的比例增加至 10： 1（参看（ C），则生成 GERF 液滴具有高得多的聚分散度。  GERF 液滴也可以在活动计划，通过产生在此对申请方波脉冲电场信号电极。非常 均匀的液滴，稳定在一个较宽的范围内流速，示于图 5 （  D， E ）  。电的周期 T 脉冲被注意到是为稳定 GERF 的关键参数液滴生产。特别是，不稳定的设置当 T 除此之外，已被确定为有一定的工作范围范围从 100 毫秒到 1000 毫秒，在 GERF 的流速  0.4 毫升 1。通过使用两个或多个独立的 GERF 入口，两在稳定的政权运营，  GERF 液滴同步和相对相位变化可以容易地实现。生成的液滴长度被绘制为 T 的图的函数。图 5（ a ）为 4 种流量。此外，电信号不需要是周期性的。任意的脉冲序列可以用来生成 GERF 液滴链具有所需液滴尺寸和距 离。二例子示于图 5 （  f）所示。在所有情况下液滴生成和所施加的电信号被很好地匹配，即GERF 液滴链通过电信号进行编码。在的情况下热响应性智能材料，穆尔希德等。有表明温度的纳米流体液滴尺寸的依赖在生成过程中，  77 而塞弗特等。有显示该液滴（微粒凝胶粒）的大小也可以变化为函数的温度，从 60 毫米至 120mm 代以后。  3.3.2 流量控制与 GERF 聪明滴。图 6 所示两种类型 GERF 智能液滴具有两个不同的生成纳米粒子的浓度。顶部三面围板，图图 6（ a ）  - （三）涉及到与 40 重量的纳米粒子的液滴，而图图 6（ d ）为 GERF 液滴具有较低百分比的纳米粒子，  5 重量。图。图 6（ a ）示出了一个智能液滴与没有电场适用。它具有球形形状。在图图 6（ b ）所示，当一个（  1500 V 毫米 1）被施加时，液滴被看作是细长的带的两端接触的电极。这会减慢甚至停止这种液滴的运动。当该字段为除去，液滴恢复其原来的球形和提出再次，如图所示。图 6（ c ）  。观察封装 GER颗粒更清楚，一些聪明的变形用较低浓度的纳米颗粒的液滴中示出图。图 6（  d）所示。在左侧的液滴是的影响外电场，并且具有球形形状。但是，对于那些下施加电场，每个液滴被拉伸时，伴随着 纳米颗粒的自的清晰可见的分离葵花子油。特别是，链 /柱的形成纳米颗粒是清楚地识别，而向日葵油是看到被向前推，以形成一个弧形的前与硅氧烷油，由于通过所产生的压力差慢通道流动。  图 6（ e）显示测得的差压 DPP1 ？  P2由 GERF 液滴在两个不同的纳米颗粒持续  浓度。可以看出，增加的  压力显示一个非线性行为，与饱和度在较高的电场强度，它是从接近线性的不同动态剪切应力的依赖关系。详细检查所述第二插入图图 6（ e）显示，该颗粒具有小于密度接近通道壁比在中间。然而，本最大压差超过 90 千帕毫米  为 1GERF 液用 40 重量 的纳米颗粒。这种差对于大多数微流体 applications.119 的压力是足够的的压力差引起的智能液滴可容易地通过改变电场的强度调整，液滴尺寸和纳米粒子的浓度在 GERF。     附录  英语原文  Soft Matter < Cite this: DOI: 10.1039/c2sm26286j /softmatter Smart electroresponsive droplets in microfluidics Jinbo Wu,a Weijia Wen*a and Ping Sheng*ab Received 4th June 2012, Accepted 26th August 2012 DOI: 10.1039/c2sm26286j We give a short review of droplet microfluidics with the emphasis on smart droplets, which are based on materials that can be actively controlled and manipulated by external stimuli such as stress, temperature, pH, and electric field or magnetic field. In particular, the focus is on the generation and manipulation of droplets that are based on the giant electrorheological fluid (GERF). We elaborate on the preparation and characteristics of the GERF, the relevant microfluidics chip format, and the generation and control of droplets using GERF as either droplets or the carrier fluid. An important application of the GERF droplets, in the realization of first universal microfluidic logic device which can execute the 16 Boolean logic operations, is detailed. I. Introduction In the late 1980s, at the 5th International Conference on Solid-State Sensors and Actuators, Manz and collaborators advanced the concept1 of total chemical analysis system (mTAS) thatemphasized the importance of microdevices in chemistry andbio-testing. Subsequently, this general concept has spawned a diverse field of investigation with descriptive terms such asmicrofluidics, bio-MEMS, lab-on-a-chip, etc. Microfluidics,in particular, relates to the new discipline involving the transport phenomena and fluid-based devices at the micron scale. In pastdecades, this area has undergone explosive development, servingas the common platform upon which engineers, physicists, chemists, biologists and others can interact and innovate on a vast array of research directions and applications that range from sensors, chemical/biological synthesis, microreactors, to drug discovery and point-of-care (POC) diagnostic.13 Microfluidics technology has been employed in the development of inkjet print-heads,4 lab-on-a-chip technology,5 microthermal technologies,6 etc. There is great promise that microfluidics would enable the integration of multiple steps of complex analytical procedures,  micro- to nanoliter consumption of reagents/samples, as well as carrying out all the promised processes with portability.79 At present, microfluidics technology has two different approaches: continuous flow microfluidics and droplet microfluidics. Both have their own special characteristics and applications.Continuous flow microfluidics is more mature, droplet microfluidics is gaining recognition from its distinct micromaneuverability and control.Continuous-flow devices offer fine-tuned control of flow characteristics, its scaling up is a challenge as the size of devices increases almost linearly with the number of parallel channels. In contrast, droplet-based microfluidics, in which a large number of reactions can be run in parallel without having to increase the device size or complexity, has attracted more and more interest.10 Chemical reactions and biological testing can be independently minitrarizied into tiny droplets ranging from nano- to picoliters in size. This can serve as a unique advantage of droplet-based microfluidics.11,12 Below we further elaborate on this point. In the form of droplets, reagents are conveyed precisely in discrete volumes that can act as vessels for reagents, thereby enabling single-cell manipulation in bio-testing11,13,14 and highthroughput chemical reactions.1,15 It provides a promising avenue for spatially and temporally resolved chemistry,16 which can be used for inexpensive and potentially improved measurements of kinetic and binding constants, as well as measuring aspects of phase and reaction diagrams of multi-component systems.16,17 Mixing of reagents in droplets has been proven to be achievable within milliseconds, hence multistep chemical reactions via droplet microfluidics has been shown to be possible.18 Another advantage of droplet microfluidics is that the reagents/ chemical/particles/cells in each droplet are well isolated, thus reducing contact with solid walls and potential contamination. The droplet microfluidic chip tends to be more multi-functional,with a simple and miniaturized structure. At present, droplet microfluidics is not only applied in DNA and protein analysis,1923 immunoassay24 and chemistry,25,26 but has also been found to be indispensable in some physical measurements,27 droplet and bubble logic,28 as well as clinical applications.29,30m  Droplet microfluidics involves the generation, detection andm manipulation of discrete droplets inside microdevices.18,31 In what follows, we survey in Section II the approaches for generation and manipulation of droplets. In Section III the focus is on the smart droplets that are based on the giant electrorheological fluid (GERF). In particular, the preparation of the smart droplets, the relevant microfluidic chip design, and the maneuver and control of the smart droplets are detailed. Section IV presents an important application of the smart electroresponsive droplets in realizing the microfluidic logic gates that can eventually enable the self-sustaining operation of the microfluidic chips requiring minimal external control. We conclude in Section V with remarks regarding potential future developments. II. Droplets generation and manipulation 2.1 Droplets generation The special utility of droplet-based microfluidic systems lies in the formation of uniform droplets and particles. Intrinsic to such systems, and of utmost importance, is the precise control of the size, shape and monodispersity of the droplets. The microfluidic flow-focusing (MFF) method is often used in droplet/bubble formation,32,33 the generation of double emulsions,3436 multifunctional particles and microbeads.37 Weitzs group has developed novel, facile, and scalable techniques using glass capillary for producing single, double, and higher order monodisperse emulsions with exceptional precision. These emulsions are useful for a variety of applications ranging from microparticle fabrication (multilayers, multicore or non-spherical) to vesicle formation and chemical synthesis to high-throughput screening where each droplet serves to encapsulate single cells, genes, or reactants.3840 Another geometry-based generation method uses the T-junction configuration, by which two immiscible fluids are brought together. Basic research into this method has been conducted by Quakes group,41 Weitzs group42 and others.43 Many active generation control methods have been developed, such as aspiration,44 external force,45 acoustic wave,46 electrolysis,47 highvoltage pulses,14 electrowetting48 and thermocapillary.49 2.2 Droplets manipulation Unlike continuous microfluidics, droplet microfluidic systems allow independent control of droplets, so that generated droplets can be individually split, mixed, transported and analyzed.50 Droplet operations can include fission, fusion, sorting, mixing enhancement, and detection. Both the passive and active methods have been utilized in droplet manipulation. 2.2.1 Passive manipulation. Passive methods usually depend on the channel structure, either in 2D or 3D. Channels with branches or obstructions are designed to create a shear force for splitting droplets.5153 When a droplet is pushed to the bifurcating junction, the branches can pull on the droplet, causing it to break up into two, either symmetrically or asymmetrically. In these designs, droplet fission may be controlled by flow rates. Fusion of droplets is usually conducted by bringing two or more droplets close to each other until a thin film of fluid forms, connecting the interface.54 Channel geometries designed for this purpose can include side channels to drain the continuous phase between the droplets.51,55 Mixing within a droplet is another important issue for droplet microfluidics. In each half of a droplet that touches the channel wall, equal recirculation flow can be generated. Thus fluids in each half of the droplet are well-mixed but the two halves remain separated from each other.49 Passive droplets mixing is usually enhanced by a winding channel to fold, stretch and reorient the droplets.16,17 Passive droplet sorting often depends on the droplet size. Channel geometry and branches can be carefully designed to differentiate size  differences.56 Passive transport control of individual droplet is noted to still remain a challenge. 2.2.2 Active manipulation. Many active control methods have been realized, such as via hydrostatic pressure,57 temperature Ping Sheng gradient,58 thermal expansion,59 optical approaches,6062 magnetic field63 and electric-related approaches13,64,65 that include electrostatic,66 electrokinetic effect,67 dielectrophoresis68 and electrowetting.48,6973 Among them, electrowetting on dielectric (EWOD)69,74,75 has been proven to be very effective for cutting, merging, creating and transporting liquid droplets. Such a type of technology has been denoted as digital microfluidics (DMF), so named because of its finely tuned digital control of droplets. All droplet manipulationsdispensing, moving, splitting and mergingare conducted by using EWOD to drive the droplet movement, with every single step defined by external control. In contrast, for the smart droplet logic gate described below, logic operations are carried out through interaction among the droplets, which greatly simplifies the control that is necessary for realizing the logic operations. 2.3 Smart droplets Smart droplets are based on smart or intelligent materials that can respond to external stimuli such as stress, temperature, pH,and electric field or magnetic field.76 Compared to the conventional droplets, the generation and manipulation of the smart droplet can be more easily controlled by external stimuli in an active manner. To date, several kinds of smart (responsive) droplets have been reported and classified according to their response to external control. (1) Thermal responsive droplets. By incorporating TiO2 nano particles77 or other materials such as wax78 into droplets, the surface tension or viscosity of the fluid droplets can be made to be temperature dependent. In particular, Seiffert et al. and Shah et al. have formed thermoresponsive smart microgel capsules from macromolecular precursors and demonstrated their utility for encapsulation and controlled-release applications.79,80 (2) pH responsive droplets. Khan et al. fabricated smart emulsion coated with a pH-sensitive polymeric hydrogel whose surface charge property can be changed by external pH value.81,82 (3) Photo responsive droplets. Matsumoto et al.successfully developed a  photo-responsive gel droplets which can transform to the sol state under UV exposure.83 (4) Magnetic responsive droplets such as ferrofluid droplets. Ferrofluid droplets can be actuated in a magnetic field, by changing its magnetic rheological properties.84,85 It can also be used in the actuation of a pump or valve86 and has been reviewed by Nguyen.87 (5) Electric responsive droplets such as electrorheological fluid droplets. By employing the giant electrorheological fluid (GERF),88 a series of fully chip-embedded soft-valves89,90 and a fluidic-based automatic smart system have been realized. Below we focus on the GERF as the enabling material for the smart droplets. Compared to all the other smart droplets, the electroresponsive smart droplets offer the advantage of not only being smart on their own, but can also be used to control other types of droplets. This point will be further discussed in detail below. Table 1 summaries, in pictorial form, the five types of smart droplets described above.  Table 1 Illustration of 5 types of smart droplets. (1) The droplet size decreases as the temperature increases.84,85 (2) The droplet is positively charged at pH ? 4 while it turns neutral at pH ? 9.91 (3) The shell of two droplets, under UV irradiation, turns into the sol state from the gel state, and the two droplets fuse into one.83 (4) Magnetic particles suspended in a droplet form chains when a magnetic field is applied.86 (5) Dielectric particles suspended in a droplet form chains when subjected to an electric field92 Electrorheological fluid (ERF) is a type of smart material comprising dielectric particles suspended in an insulating oil.92 Owing to the contrast in the dielectric constant between the solid particles and the dispersing liquid, solid particles are polarized under an applied electric field, leading to an induced dipole moment (Fig. 1). The resulting dipoledipole interaction and the energy minimization requirement dictate that the particles would aggregate to form columns along the applied field direction. This structural transformation, which can occur within a few milliseconds, causes the ER fluid to exhibit increased viscosity or even solid-like behavior, i.e., the ability to sustain the shear stress93101 (Fig. 1). ERF can serve as an electricalmechanical interface, and when coupled with sensors to trigger the timing and magnitude of the applied electric field, it can render many devices such as clutches, valves, dampers and others to become active mechanical elements capable of responding to environmental variations hence the denotation of smart fluid. However, in spite of broad interest in the envisioned diverse applications, actual realization of these useful potential has been hampered by the inadequate ER effect exhibited by the traditional ERF.Considerable  improvement efforts have gone into the preparation of alternative suspended particles,102104 but to no appreciable effect. A breakthrough was achieved in 2003 (ref. 88) with the discovery of the giant electrorhelogical fluid (GERF), comprising urea-coated barium titanyl oxalate nanoparticles suspended in silicone oil. The GER effect represents a different paradigm from the conventional ER mechanism as it is based on molecular dipoles instead of induced dipoles. It offers a significantly higher ER effect.88 Under a moderate electric field, GERF can transform into an anisotropic solid, with a yield stress on the order of 100300 kPa at 4 kV mm_1 of the electric field. These rheological variations can occur within 10 milliseconds and are reversible when the field is removed. With such remarkable features, a range of device applications88,105108 as well as microfluidic microvalve, micropump, and highly maneuverable microplatforms etc., have been realized.89,90,109112 Fig. 1 The structural evolution of dielectric microspheres under an increasing electric field. From left to right: no field, a moderate field and a strong field. In what follows we detail the generation process of GERF droplets and the flow and droplet train manipulations that can be achieved. In conjunction with the use of the AgPDMS composite as conducting wires and the microfluidic channel as part of electrical circuits capacitance/resistance, it is shown that logic functions can be realized on microfluidic chips, through the nonlinear electrical-flow response of the GERF droplets. III. GERF-based smart droplets 3.1 GERF composition and characteristics For the GERF to be used in the microfluidics context, it is necessary to avoid the absorption of silicone oil, the traditional suspending fluid for GERF, by the basic chip material PDMS.Hence for microfluidic applications the GER particles are suspended in sunflower oil instead, with a weight ratio of 540%GER particles. The mixture is filtered with sieves (with pore size around 10 mm) to remove the large aggregates. Under an applied field >1 kV mm_1, the GERF exhibits solidlike behavior, e.g., the ability to transmit the shear stress. The measured dynamic shear stress of the sunflower oil-based GERF is   comparable to that of the silicone oil-based GERF under similar electric fields. As the GERF has a much larger ER response under the same applied field (Fig. 2) compared with the traditional ERF, a moderate electric field is sufficient for slowing down or stopping the microfluidic flow, for both the droplet generation and manipulation processes. This is a crucial aspect that has enabled the development of GERF-based smart droplets in microfluidics. 3.2 Chip fabrication To control the GERF droplets, electrodes have to be integrated into the PDMS microfluidic chips. However, metal does not adhere well to the PDMS, owing to its low surface energy. To overcome this problem, conductive particles such as carbon fibers/carbon black or Ag nanoparticles were embedded or added into PDMS, to form conducting composites that can be compatibly processed through soft lithography.114,115 Two types of PDMS-based conducting composites (silver/carbon  PDMS Ag/C PDMS) have been developed by Niu et al.116 These mixtures can be made into a thin film with desired thickness or patterned into structures and embedded in PDMS microfluidic chips by soft-lithography. Planar and 3D conducting microstructures, ranging from tens to hundreds of micrometers, have been successfully integrated into PDMS-based chips.   Fig. 3 (a) Optical image of a group of DI water droplets with different sizes. A small amount of dyes (without causing detectable variation of the dielectric constant for the droplets) was added for labeling. The detected signals are depicted in (b). (c) Detected signals with arrows pointing to the corresponding droplets: dyed DI water (dark) and ethylene glycol (light).117 By using the PDMS conducting composites, pairs of parallel and channel-wall-embedded electrodes can be installed across the microfluidic channel. With the input electric signal, electrical control and sensing become achievable as part of GERF droplet control. In particular, very small variations in the capacitance can be detected when a droplet passes through between the two electrodes. Due to the electrodes design and feedback electronic circuit, accurate real-time determination of size, shape andcomposition of droplets has been demonstrated (Fig. 3). The operational frequency can reach up to 10 kHz, a speed which is difficult to be  realized by conventional optical means. Thus, it can be used in portable lab-chip for in situ detection and control of droplets. The tested capacitance signals can be used directly for in situ labeling, sorting and droplet manipulation. 3.3 GERF as droplets or as a carrier fluid There are two ways of applying the GERF into the microfluidic channel for droplet manipulations. The first is to form GERF droplets carried by another fluid, while the second is to use GERF as the carrier fluid to control other liquid droplets or bubbles. A schematic of the two cases is  shown in Fig. 4(a) and (b). The electrodes placed on the sides of microfluidic channels can apply the electric field to the flowing GERF, either in the form of droplets or as the carrier fluid. The electrodes at the droplet generation section of the chip are located near the junction area so as to control the timing of the GERF flow, thereby giving control to the generation of droplets. Downstream electrodes provide further flow control in the form of sensing, routing, and/or sorting.                   Fig. 4 Schematic view of the GERF as (a) droplets113 and (b) the carrier fluid118 in the microfluidic channels. Below we review the two cases of GERF as droplets or as a carrier fluid, and their respective capabilities. 3.3.1 GERF smart droplet generation. In the first approach, GERF droplets are generated by the flow-focusing approach as shown schematically in Fig. 4(a). When the voltage on a pair of electrodes at the droplet generation section is set to zero, GERF droplets can be generated in a passive manner. Inset (b) of Fig. 5 shows mono-dispersed droplet generation when the flow rate of GERF is at 0.2 ml h_1 and the ratio of silicone oil (as the carrier fluid) to GERF flow is 3 : 1. However, when the flow rate is high(4 ml h_1) and the oil ratio is increa