Microfluidic Circuits

Henry, C. 2002. Microfluidic circuits Lab on a chip. Chemical and engineering news September 30 11. 

Fig. 21.3. Visual proteomics require samples to be prepared by a microfluidic circuit. Cells grown in microreactors are released and sorted to reach a device that lyses them. Various well-known separation circuits are used in series for generating suitable fractions of the lysate. Importantly, a spotting device akin to those used for DNA array production produces 10 pL droplets that are deposited on an EM grid. One cell will provide enough material to cover 1 to a few grids, when one droplet is deposited per grid square...

S.-K. Cho S.-K. Fan H. Moon H and C.-J. Kim, Towards digital microfluidic circuits creating, transporting, cutting and merging liquid droplets by electrowetting-based actuation, Tech. Dig. MEMS 2002 IEEE Inter Conf on Micro Electro Mechaiucal Systems, 11, 454-61 (2002). 

Easley, C.J., Karlinsey, J.M., Leslie, D.C., Begley, M.R., and Landers, J.R Directional and frequency-dependent flow control in microfluidic circuits using passive elastomeric components. Proceedings of the mTAS 2006 Conference, 10th International Conference on Miniaturized Systems for Chemistry and the Life Sciences (Tokyo), 2006, 2, 1064—1068. 

High pressure-rated channels allow a smaller construction of microfluidic assays at the same throughput, which arises due to higher possible flow rates. Such devices are of interest for the cost-effective integration of CMOS chips to microfluidic circuits [45]. 

Microfluidic Circuits Microfluidic Sample Manipulation Surface Tension, Capillarity, and Contact Angle... 

Cho SK, Moon H, Kim CJ (2003) Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits. J MEMS 12 70-80... 

Fluorescent Thermometry, Fig. 4 (a) Schematic of a microfluidic circuit through which flow is driven by electrokinetic pumping, (b-f) Temperatore fields through... 

However, in the great majority of microfluidic circuits, especially those that use electrophoretic... 

Microfluidic Boards Microfluidic board interconnection technologies seek to mimic the electronic printed circuit board for ease of use, reliability, and versatility. In microfluidic board technologies, the substrate contains the passive microfluidic channels and reservoirs, with active components (e.g., sensors, valves) mounted on top (e.g.. Ref. [2]) (see Fig. 1) similarly to electronic components mounted on a printed circuit board (PCB) or multichip modules (MCM) in surface-mount technologies (SMT). Electronic coimections between components are provided on top of the board, while fluidic interconnection is usually provided in the board material itself. Microfluidic circuit boards can be made from a variety of materials, including silicon, glass, and polymers, e.g., polydimethylsiloxane (PDMS), epoxy, or polymethyl methacrylate (PMMA). Microfluidic boards can be as simple... 

Structures to Facilitate Modular Assembly For many modular approaches and techniques, including microfluidic circuit boards, stacks, or freely joined modules assembled via robotic techniques, alignment keys and mechanical joints may facilitate microassembly, joint strength, or reworkability. 

Gray BL, Collins SD, Smith RL (2004) Interlocking mechanical and fluidic interconnections for microfluidic circuit boards. Sens Actuators A 112 18-24... 

Like electric circuits, fluidic circuits can craisist of individual components such as fluidic resistors, capacitors, inductors, and transistors. Brief descriptions of various components of microfluidic circuits are given below in this section. 

A typical value of the characteristic response time for water in an 800 pm capillary is approximately 20 ms, and so the typical frequencies in a microfluidic circuit are on the order of 100 Hz. 

A number of microfluidic circuits have been developed their principles of operation depend on the mechanism of fluid flow in the microchip. In this entry, we shall describe only the fluidic circuits used with pressure-driven flow and electrokinetically driven flow, as these are the two main pumping methods for continuous-flow microfluidic devices. Pressure-driven flow can be obtained by connecting the channel to a syringe pump or a compressed gas. Electroki-netic flow of an ionized electrolyte can be obtained by applying an electric field along the flow direction. 

Microfluidic Circuits, Table 1 Typical channel geometries used in microfluidic circuits [2] ... 

Fluidic control can be achieved by changing the impedance of the fluid path and/or by modulating the mass flow rate of the incoming fluid streams. The working principles of some recently tested pressure-driven microfluidic circuits are presented below. 

Microfluidic Circuits, Fig. 1 Schematic view of a four-channel microfluidic logic gate [3]. The lengths and cross-sectional areas of the input channels A and B are the same. The flow resistance of the output channel Y is higher than that of X owing to its smaller cross-sectional area... 

The basic operating principle of a bubble logic gate [3] is shown in Fig. 1. This microfluidic circuit consists of two input channels (A and B) and two output channels (Z and T). Channel X is shghtly wider than channel Y, i.e., channel X has a lower fluidic resistance than T. Hence, if a bubble reaches the junction by way of input channel A or B, then it will always take the output channel X owing to the lower fluidic resistance. But if two bubbles arrive simultaneously from input channels A and B, then the first bubble will take the output channel X. This first bubble increases the fluidic resistance of channel X and causes the other bubble to flow through channel Y. For detailed information on other microfluidic logic circuits, readers are advised to consult [3]. 

Microfluidic Circuits, Fig. 2 (a) Schematic view of an analog, or jet, interaction amplifier [11], The supply jet exits through both of the outputs 1 and 2. The ratio of the mass flow rate at output 1 to that at output 2 is determined by the control ports 1 and 2. (b) Schematic view of a digital, or wall attachment, amplifier and its working principle [11]. The supply jet exits through either output 1 or output 2. Switching between these outputs is guided by the control ports 1 and/or 2... 

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