Keywords: lab-on-a-chip design, microscale reactors, reduced order models
IntroductionMicrototal analysis systems (TAS), also known as "Labon-a-Chip," 1 are terms used to connote the miniaturization of chemical, biological and biochemical analysis devices. 2,3 A Lab-on-a-Chip (LoC) system is a microfluidic device that mimics the functions of a standard analytical chemistry laboratory: sample preparation, mixing, reaction, injection, separation, and detection. 3 Miniaturization provides LoC devices with some key benefits: the drastic reduction of reagent consumption, which translates to cost savings; integration, which offers the advantages of faster analysis and sometimes novel, synergistic capabilities that may not be attainable otherwise; automation, that allows more precise and reproducible operations resulting in higher data quality. 2 LoC systems have various applications in clinical diagnosis, such as analysis of drugs in biological fluids, 4 DNA separation and detection, 5 and immunoassay. 6 A LoC device can also be used for countering bioterrorism threats and is typically capable of performing sampling and real time testing of samples for biochemical toxins. 7 There exist a large variety of LoC devices that differ in their functional tasks, as well as detection methods. Consequently, using a library of generic LoC designs for all applications may either fail for some analytical procedures or be over designed as for performances, costs and chip size. To avoid these problems, a design methodology is needed to make it easy to customize LoC devices according to applications.
LoC designWhile the advantages of microfluidic systems have been demonstrated, 8 systematic design methods are only begun to emerge. 7,9,10 Most often, to design a LoC device with optimized geometry and performance, the designer is reduced to using trial-and-error approaches that involve a large number of experimental tests and long development cycles. This deficiency becomes even more acute when large-scale microfluidic integration is needed. 11 Our long term goal is to develop a fast, robust, and accurate design methodology for integrated and multiplexed microfluidic systems. This general methodology will accelerate the design and customization of LoC devices for specific applications. In our approach to automated LoC design, the inner loop, that is, the evaluation of a particular layout instance of the unit operation, must be solved a large number of times; the typical place-and-route algorithms from integrated circuit design take on the order of ten to hundred thousand iterations. It is, thus, computationally intractable to even think about approaches where the evaluation of single unit operations are measured in minutes.In LoC devices, the subsystem design and ultimate chip layout are intimately linked due to the influence that channel geometry has on device performance. 9 The different operations of a LoC requires modules for subsystems: mixing, reaction, injection, and separation. Several component modules have already been develop...