Microfluidic tools for improved sensing and dispensing

点击翻译按钮获取中文摘要

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.