Microfluidics/chips/devices

Fig. 2.6.11 Flow dispersion profiles obtained with (a) a capillary, (b) with a model microfluidic chip device containing a channel enlargement, directly connected to a capillary and (c) with the same microfluidic chip connected to a capillary via a small mixing volume. A sketch of the model microfluidic device is placed at the right side of each image, drawn to...

Microfluidic chip devices are also shown to be attractive platforms for performing microscale voltammetric analysis and for integrating voltammetric procedures (linear-sweep, square-wave and adsorptive-stripping voltammetry) with on-chip chemical reactions and fluid manipulations [97]. 

Recently, a new approach was proposed to overcome these problems, based on a microfluidic chip device (Agilent, 2007) (Fig. 1.11). This finding includes the enrichment column, the separation column, and the nanospray emitter. By use of a robotic system, the chip is automatically positioned in front of the entrance orifice of the mass spectrometer. 

Lin, S. S., Fischl, A. S., Bi, X. H., and Parce, W., Separation of phospholipids in microfluidic chip device apphcation to high-throughput screening assays for lipid-modifying enzymes. Analytical Biochemistry 314, 97-107, 2003. 

In droplet-based microfluidics, these reaction vessels are formed by droplets of a dispersed phase, which are embedded into a continuous phase. Both liquid phases are immiscible. A huge amount of such droplet reactors can be generated, transported, controlled, and processed in parallel in a droplet-based lab-on-a-chip device. These devices can be characterized as application specific microfiuidic networks that implement and automate a conventional laboratory workflow in a microfluidic chip device or system. They are built up by appropriately intercoimecting microfluidic operation units, which provide the required laboratory operations at the microscale. Consequently, for each conventional laboratory operation, its microscale counterpart is required. 

STATE-OF-THE-ART OF BIOOBJECTS ASSAY IN MICROFLUIDIC LAB-ON-A-CHIP DEVICES... 

Miniaturized fluid handling devices have recently attracted considerable interest and gained importance in many areas of analytical chemistry and the biological sciences [50], Such microfluidic chips perform a variety of functions, ranging from analysis of biological macromolecules [51, 52] to catalysis of reactions and sensing in the gas phase [53, 54], They commonly consist of channels, valves and reaction... 

Mapping of transport parameters in complex pore spaces is of interest for many respects. Apart from classical porous materials such as rock, brick, paper and tissue, one can think of objects used in microsystem technology. Recent developments such as lab-on-a-chip devices require detailed knowledge of transport properties. More detailed information can be found in new journals such as Lab on a Chip [1] and Microfluidics and Nanofluidics [2], for example, devoted especially to this subject. Electrokinetic effects in microscopic pore spaces are discussed in Ref. [3]. 

However, current forms of LOAC devices have many components external to the microfluidic chip such as valves, pumps, power supplies, electronic circuitry, and reagent/waste storage units. While these devices are a major advance on pre-existing autonomous instruments and could be deployed on a reasonable scale, they are typically too large, consume too much power and are too expensive for high-density deployment. 

This chapter demonstrated that microchip electrophoresis reached maturity and is appropriate for analysis of nitrated explosives. However, to create easy-to-operate field portable instruments for pre-blast explosive analysis would require incorporation of world-to-chip interface, which would be able to continuously sample from the environment. Significant progress towards this goal was made and integrated on-chip devices which allow microfluidic chips to sample from virtually any liquid reservoir were demonstrated [25,31]. 

The use of ELISA is broad and it finds applications in many biological laboratories over the last 30 years many tests have been developed and vahdated in different domains such as clinical diagnostics, pharmaceutical research, industrial control or food and feed analytics for instance. Our work has been to redesign the standard ELISA test to fit in a microfluidic system with disposable electrochemical chips. Many applications are foreseen since the biochemical reagents are directly amenable from a conventional microtitre plate to our microfluidic system. For instance, in the last 5 years, we have reported previous works with this concept of microchannel ELISA for the detection of thromboembolic event marker (D-Dimer) [4], hormones (TSH) [18], or vitamin (folic acid) [24], It is expected that similar technical developments in the future may broaden the use of electroanalytical chemistry in the field of clinical tests as has been the case for glucose monitoring. This work also contributes to the novel analytical trend to reduce the volume and time consumption in analytical labs using lab-on-a-chip devices. Not only can an electrophoretic-driven system benefit from the miniaturisation but also affinity assays and in particularly immunoassays with electrochemical detection. 

A series of papers have concerned the incorporation of various sensors into lab-on-a-chip devices with, for example, conductivity measurements being combined with poly(methyl methacrylate) microfluidic devices to analyse mixtures of mono- and polyanionic molecules such as proteins [148]. 

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