Lab-on-a-chip devices

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

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]. 

Recent developments in microsystems technology have led to the widespread application of microfabrication techniques for the production of sensor platforms. These techniques have had a major impact on the development of so-called Lab-on-a-Chip devices. The major application areas for theses devices are biomedical diagnostics, industrial process monitoring, environmental monitoring, drug discovery, and defence. In the context of biomedical diagnostic applications, for example, such devices are intended to provide quantitative chemical or biochemical information on samples such as blood, sweat and saliva while using minimal sample volume. 

Lee, K. J. Tosser, K. A. Nuzzo, R. G. 2005. Fabrication of stable metallic patterns embedded in poly(dimethylsiloxane) and model applications in non-planar electronic and lab-on-a-chip device patterning. Adv. Funct. Mater. 15 557-566. 

The analysis of biomolecules by AFM is sometimes [3] referred to as surface biology, as opposed to the so-called test-tube biology, because the immobilisation of oligonucleotides on sohd surfaces is central to the design, fabrication and operation of DNA-based microdevices, such as biosensors, DNA micro- and nanoarrays, microPCR and lab-on-a-chip devices. As the analysed biomolecules are in close contact and very often in intimate interaction with the surface, sample preparation for the AFM analysis of surface-immobihsed biomolecules is both critical and dehcate. The biomolecules need to be firmly anchored on the substrate, which has to have a sufficiently minimal or easily discriminated topography [1]. The Kleinschmidt method [6] for the DNA... 

The versatility of lab-on-a-chip devices has been exploited for developing a novel and effective protocol for rapid screening/waming followed by detailed... 

Unlike capillary electrophoresis, wherein absorbance detection is probably the most commonly utilized technique, absorbance detection on lab-on-a-chip devices has seen only a handful of applications. This can be attributed to the extremely small microchannel depths evident on microchip devices, which are typically on the order of 10 pm. These extremely small channel depths result in absorbance pathlengths that seriously limit the sensitivity of absorbance-based techniques. The Collins group has shown, however, that by capitalizing on low conductivity non-aqueous buffer systems, microchannel depths can be increased to as much as 100 pm without seeing detrimental Joule heating effects that would otherwise compromise separation efficiencies in such a large cross-sectional microchannel [38],... 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

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. 

Gambari R, Borgatti M, Altomare L, et al. Applications to cancer research of lab-on-a-chip devices based on dielectrophoresis (DEP). Technol Cancer Res Treat 2003 2(1) 31 10. 

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]. 

Hasselbrink, E.F., Jr., Shepodd, T.J., Rehm, J.E., High-pressure microfluidic control in lab-on-a-chip devices using mobile polymer monoliths. Anal. Chem. 2002, 74(19), 4913—4918. 

Chin CD, Linder V, Sia SK (2007) Lab-on-a-chip devices for global health. Lab Chip 7 41-57... 

An important component of many bio- or chemical lab-chips is the microfluidic dispenser, which employs electroosmotic flow to dispense minute quantities (e.g., 300 pico-liters) of samples for chemical and biomedical analysis. The precise control of the dispensed sample in microfluidic dispensers is key to the performance of these lab-on-a-chip devices. 

There has been a trend toward electrochemical reactions in lab-on-a-chip devices in the last few years.51,52 This is mainly because miniaturized electrodes can be fabricated using microfabrication methods and solutions can be transferred by microfluidics approaches.5354 Flow injection analysis and sequential injection analysis techniques were also employed for electrochemical enantioselective high-throughput screening of drugs.55... 

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