Microfluidic tools for improved sensing and dispensing

数字微流体（DMF）能够控制和操纵从皮升到微升的微小和离散流体单位，并为患者提供快速个性化诊断的长期潜力，例如，跟踪肥胖治疗效果。在典型的封闭结构中，液滴被限制在两个平行的衬底之间。定义电极网格的底部衬底和作为电地的顶部电极。通过在电极之间施加电场，液滴可以被精心安排和操纵，例如使其合并、分裂或突出成更小的液滴。由于操作程序离散，通常与生化方案和分析相关的液体控制和处理可以通过数字微流控装置完全模拟。液滴可以作为隔离的运输胶囊，同时也可以作为微反应器进行化学反应。流体体积可以急剧减少，扩散和反应速率可以加快。通过这种方式，DMF设备利用了在微观尺度上占主导地位的现象，而不是像许多连续流设备那样与它们作对。常见的检测方法，如光学检测，已经变得越来越难以与微型设备集成，特别是由于需要便携式，即时护理应用。虽然与流体控制和处理相关的组件的尺寸已经大大减小，但化学反应检测的外部光学仪器的类似缩小则更加困难。电化学检测是一种非常实用的DMF器件检测技术。它可以集成由于简单的传感器设计与微加工技术兼容。此外，电化学换能器可以与廉价的仪器相结合，并且具有低功耗，高灵敏度，低检测限和可调选择性

Digital Microfluidics (DMF) enables the control and manipulation of minute and discrete units of fluid from the picoliter to microliter scale and offers the long-term potential for fast personalized diagnosis for patients, for example, to track obesity treatment effectiveness. In typical closed configurations, droplets are confined between two parallel substrates. A bottom substrate defining a grid of electrodes, and a top electrode to act as an electrical ground. By applying an electric field between the electrodes, droplets can be orchestrated and manipulated, such as to be made to merge, split, or protrude into smaller droplets. Due to the discrete operating procedure, liquid control and handling that is usually associated with biochemical protocols and assays can be fully emulated by the digital microfluidic device. Droplets can be used as isolated transport capsules, and at the same time function as microreactors for chemical reactions to take place. Fluid volumes can be drastically decreased and diffusion and reaction rates increased. In this way, DMF devices leverage phenomena that are dominant at the microscale instead of working against them like many continuous flow devices. Common detection methods, such as optical detection, have become harder to be integrated with microdevices, especially by virtue of the need for portable, point-of-care applications. While the size of the components related to fluidic control and handling has been dramatically reduced, similar downscaling of external optical instruments for chemical reaction detection is more difficult. Electrochemical detection is a very practicable technique for DMF devices. It can be integrated due to simple sensor designs compatible with microfabrication technologies. Also, electrochemical transducers can be combined with inexpensive instrumentation, and have low power consumption, high sensitivity, low detection limits, and adjustable selectivity Ongoing work in my group has concentrated on steps that could lead to for chemical analysis including (a) novel methods of filtration of particles from droplets, (b) the automated detection of droplet composition based on electrochemical properties and (c) bridging these samples to an electrospray. By bridging this to an Ion Mobility Spectrometer (IMS), a sensor that tracks ion mobility within an electric field, improved sensing capability is possible. Using valving and capillary loading methods developed as part of other work I have led, it is possible to perform many sample preparation and chemical analysis steps on the DMF platform and load an electrospray. Successful implementation requires an improved grasp of the electrospray used to ionize the sample and high resolution over short distances. This would focus on controlling pulsing behavior of the electrospray and electronics-independent timing of the sample ejection for improved drift-time measurement.