Chip on valve

One example of application of these chips is Chip on valve (ChOV). ChOV is a microfluidic methodology that consists on a chip mounted atop a selection valve. A schematic depiction of one of the first prototypes is shown in Figure 1.25. 

Draw of the piece to be built. Figure 4.12 shows the design and drawing made exploiting VCarve to build a chip on valve. 

Chip on valve design and drawing exploiting VCarve. (For color version of this figure, the reader is referred to the online version of this book.)... 

Some methacrylate chips built by combined use of VCarve and MACHS, (a) Chip on valve mounted atop the selection valve, (b) Chip designed for cross-injection analysis, (c) Chip especially used in kinetic methods. (For color version of this figure, the reader is referred to the online version of this book.)... 

When elution chromatography is used in both dimensions, the valve configurations are similar for the different column combinations. However, when CE is utilized as the second dimension, other types of interfaces not based on valves have been implemented with unique advantages. These and the microfluidic implementation of sampling systems for chip-based two-dimensional separations will be discussed below. 

An IEF/CGE separation for proteins has been achieved on a PDMS chip. Microfluidic valves were used to prevent intermixing between the two separation buffers used in IEF and CGE separations. The IEF ampholyte was very sensitive to high buffer concentration, but a small amount of ampholyte in the CGE did not affect its separation resolution [449]. 

Figure 6 Chip component of the MicroChannel assay system, (a) Overview of the entire chip, (b) detail of capillary pumps, which provide autonomous filling of each channel by capillary action, (c) each capillary retention valve prevents drainage of a channel s reaction zone after the fill port has emptied, and (d) a chip with an attached PDMS cube is fdled by a standard pipette. By placing the chip on 2 aluminum blocks, whose temperature is individually controlled by 2 Peltier elements, differential evaporation allows extremely low flow rates...

J.-H. Wang, Lab-on-valve mesofluidic analytical system and its perspectives as a world-to-chip front end, Anal. Bioanal. Chem. 381 (2005) 809. 

Currently, pTAS [112] and sequential injection systems using the lab-on-valve approach [22] are more popular. The former exploits hydrodynamic injection and is now known as Lab-on-Chip due to the extreme reduction in dimensions. Reproducible analytical channels are made by micro-drilling, etching, photolithography or laser erasing, and different channel profiles can be obtained at a reasonable cost. 

Microfluidic large scale integration describes a microfluidic channel circuitry with chip-integrated valves based on a flexible membrane between a liquid-guiding and a pneumatic control-channel layer. The valves are closed (opened) by applying an overpressure (underpressure) on the control-channel, leading to deflection (withdrawal) of the membrane into the liquid-guiding channel. 

Lab-on-a-chip (LOG) and lab-on-valve (LOV) devices are versions of pTAS where fluids are manipulated to give a complete assay on a microfabricated chip. Their main goal is the scaling down of laboratory processes onto a chip-based platform. 

Lab-on-valve (LOV) is a development of FI A whereby a microchannel chip (microconduit) is combined with a switching valve. It is a type of pTAS system. The function of the... 

FIGURE 33.6 (a) Manifold interface for providing fluidic interconnects between on-chip microchannels and off-chip pumps, valves, and electrodes and (b) manifold with integrated valves positioned above an lEF/SDS-CGE chip during testing. 

Concentration Gradient Generation and Controi, Fig. 7 (a) Schematic design of the microfluidic multiinjector (MMI). Crossings of control channels and fluidic channels make up the on-chip barrier valves (V1,V2,V3). These valves were actuated by pressurizing the control charmel and deforming the membrane between the channels to close the fluidic channel. These valves controlled the pulsatile release of solution into the reservoir to... 

Lab-on-valve , Lab-on-chips , Micro Total Analytical Systems (p-TAS) or Micro Electro Mechanical Systems (MEMS) that operate on micro- and nanometer scales are good examples of new trends and achievements in the area of instrumentation. These enable complex processes such as sampling, reagent addition, calibration, temperature control, and analysis, to be incorporated into... 

In 1999 an incident at Uljin Nuclear Power Station Unit 3 in Korea corrupted data on the performance net of the plant control computer [2]. The incident was caused by the failure of an application-specific integrated circuit (ASIC) chip on a rehostable module, which is part of a network interface module. Several non-operational pumps started without any demand, some closed valves opened and other open valves closed, and some circuit breakers switched on or off. There was also some relay chattering. Due to the response of the operators and because of diverse systems, the incident was mitigated without adverse consequences. 

Lab-on-valve is similar in concept to sequential injection, but involves integration of all flow manifold elements and the detector flow cell into a microconduit attached to the back of the selection valve [151]. Only one method based on this methodology for AA determination has been published. Sorouraddin et al. [152] applied an on-chip microdetermination device, integrating the FIA system, to l-AA and DHAA determination in urine and pharmaceutical samples. The manifold components are used for flow, mixing, reaction, and detection. The reaction system is a coupled redox-complexation reaction between AA and a l,10-phenanthroline-Fe(III) and a photothermal microscope is used for the ultrasensitive detection of the nonfluorescent reaction product (ferroin). For DHAA determination, dithiothreithol is used as reducing agent and the total AA is determined. 

HPLC with microchip electrophoresis. Capillary RPLC was used as the first dimension, and chip CE as the second dimension to perform fast sample transfers and separations. A valve-free gating interface was devised simply by inserting the outlet end of LC column into the cross-channel on a specially designed chip. Laser-induced fluorescence was used for detecting the FITC-labeled peptides of a BSA digest. The capillary HPLC effluents were continuously delivered every 20 s to the chip for CE separation. 

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