Analytical microsystems

A. Rios, A. Escarpa, M.C. Gonzalez and A.C. Crevillen, Challenges of analytical microsystems, Trends Anal. Chem., 25 (2006) 467-479. 

A.J. Blasco, I. Barrigas, M.C. Gonzalez and A. Escarpa, Fast and simultaneous detection of prominent natural antioxidants using analytical microsystems for capillary electrophoresis with a glassy carbon electrode A new gateway to food environments, Electrophoresis, 26 (2005) 4664-4673. 

Electrochemical detection offers also great promise for CZE microchips, and for other chip-based analytical microsystems (e.g., Lab-on-a-Chip) discussed in Section 6.3 (77-83). Particularly attractive for such microfluidic devices are the high sensitivity of electrochemical detection, its inherent miniaturization of both the detector and control instrumentation, low cost, low power demands, and compatibility with micromachining technologies. Various detector configurations, based on different capillary/working-electrode... 

A wide number of companies across the world are offering SPR devices, as it is shown in Table 5.3. Some of these companies are Jandratek [38], GWC [39], Ibis [40], Leica [41], Autolab, NLE (SPR670) [42], HTS Biosystems [43], Texas Instrmnents (Spreeta) [44], DKTOA, Analytical Microsystems (Bio-suplar), Sensia S.L., Vir Biosensor. Texas Instrtunents (Dallas, USA) was the first in the development of a miniaturized integrated SPR sensor called TI-SPR-1 Spreeta [44]. The device of Texas Instruments is a novel miniature... 

BIAcore (BIAcore AB), www.biacore.com Jandratek, Leica, Ibis, Autolab, Texas Instruments (Spreeta), DKTOA, Analytical Microsystems (Biosuplar), NLE (SPR670), HTS Biosystems, Applied Biosystems, GWC, Sensia S.L., Vir Biosensor ASI (Artiflcial Sensing Instrument)... 

Assembling the PCB microfluidic with the biosensor array results in the bio-analytical microsystem with a flow cell volume of 150 nl and a mixing coU volume... 

The toner material and the direct-printing approach may not only be used for PT microchannel fabrication but also to produce a great variety of features, devices, or elements for analytical microsystems. For example, other essential elements for electrophoresis microchips are the... 

Rapp, M., Boss, B., Voigt, A., Gemmeke, H. and Ache, H. J. (1995) Development of an analytical microsystem for organic gas-detection based on surface-acoustic-wave resonators. Fresenius Journal of Analytical Chemistry 352, 699-704. 

Ney H et al (2009) Fabrication of a multichannel PDMS/glass analytical microsystem with integrated electrodes for amperometric detection. Lah Chip 9 115-121... 

However, one of the most relevant characteristics of these analytical microsystems is the possibility of handling fluidics on the nanoliter and even picoliter scale, which has widened the scope of micro-TAS to microfluidics, defined as the science and technology of systems that process or manipulate small amounts of fluidics (10 -10 1), using channels measuring from tens to hundreds of micrometers [1]. 

Detection has been one of the main challenges for analytical microsystems, as very sensitive techniques are needed as a consequence of the ultrasmall sample volumes used in micron-sized environments. Electrochemical detection (ED) is a very suitable detection principle to be coupled in microchips because it presents the inherent ability for miniaturization without loss of performance and its high compatibility with microfabrication techniques. Similarly, it possesses high sensitivity, its responses are not dependent on the optical path length or sample turbidity, and it has low power supply requirements which are its additional advantages [5-9]. 

Nowadays, it is clear that nanotechnology offers valuable tools for building new architectonics for analytical microsystems. Apart from their high sensitivity and inherent miniaturization, another added functionality of ED is the opened opportunity to modify these surfaces suitably with nanomaterials to break frontiers in new food analysis applications. In food microfluidic analysis, two relevant nanomaterial examples have been explored as novel electrochemical detectors coupled to ME carbon nanotubes (CNTs) [45, 46] and metallic nanowires (MNWs) [47]. 

Classical methods of sampling and sample pretreatment are not well adapted to microsystems. The advantages of miniature dimensions are lost if e.g. a blood sample must be taken by a traditional syringe or if manual extraction or filtration operations must precede the final measuring process. On the other hand, such peripheral operations must be done also with miniature systems. Obviously, such preceding or subsequent operations attracated increased interest with the advent of analytical microsystems. Some examples of successful integration of sample preparation are discussed below. 

Electrodes modified with MN4 complexes were also used recendy to develop detection systems for thiols in analytical microsystems, allowing minimum volume of sample to be analyzed. These miniaturized setups are of particular interest for biological samples, to minimize the required volume and be able to analyze a drop of blood for example, with minimal cost and lower solvent and consumables use. Martin et al. [182] have developed carbon ink microelectrodes containing CoPc for the detection of thiols in simple monochannel microchip. The microsystem was applied to the detection of cysteine, homocysteine and glutathione of artificial sample and in buffer at pH 5.5. The electro-oxidation of cysteine and glutathione occurs at +0.5 V while that of homocysteine occurs at +0.35 V at such modified microelectrode. The microelectrode was then used as amperometric sensor in... 

The final aim of analytical miniaturized systems is represented by the micro total analysis systems p-TAS concept was developed from the modification of the TAS by downsizing and integrating the analytical process steps onto single monolithic devices. In essence, a p-TAS is a device that improves the performance of an analysis by virtue of its reduced size. Besides analytical tasks can be performed into a miniaturized system, other chemical functions such as synthesis can be also performed. For this reason, today, p-TAS concept has also been called by lab-on-a-chip . On the other hand, it has to be pointed out that miniaturization is more than simply the scaling down of well-known systems since the relative importance of forces and processes changes with scale. One of the most relevant characteristics of analytical microsystems is the omnipresence of laminar flow (Reynold s number... 

Micro-TAS, lab-on-a-chip devices or microfluidics in Analytical Chemistry can be seen as different analytical microsystems comprising (1) the direct measurement of one or a few components with little or no sample preparation (p-sensors) (2) the measurement of one or a few components which require some treatment of the sample (pFlA) (3) the analysis of more complex samples involving the separation of their components (p-HPLC and p-CE). In all cases, one of the oldest and most important challenges in analytical chemistry is chased the accurate measurement of a specific compound in a complex matrix. Taking in consideration these principles, the aim of this chapter would be mainly focus on the integration of sensors or sensor-like systems in microfluidic systems as platforms for electrochemical sensing in the environmental field. 

In this sense, MCE was one of the earliest examples of pTAS, and it constitutes one of the most representative examples of analytical microsystems. Using this performance, analysis times can be reduced to seconds and extremely high separation efficiencies can be achieved. The easy microfabrication of a network of channels using materials of well-known chemistiy, and the possibility of using the electrokinetic phenomena to move fluids are among the most important factors to understand the relevance of CE microchips to miniaturization. Due to its relevance, even in the environmental monitoring field, a wider description of the foundations and specific examples on environmental MCE will be provided below. 

Rios A, Escarpa A, Gonzalez MC, Crevillen AG (2006) Challenges of analytical microsystems. Trends Anal Chem 25 467-479... 

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