Micro total analysis systems

One expected advantage of the application of the micro total analysis systems (mTAS) was the integration of the whole analytical process, i.e. the sequential operations like sampling, sample pre-treatment, analytical separation, chemical reaction, analyte detection, and data analysis would be performed in one analytical microdevice (thus the expression: lab-on-chip originated). mTAS finds typical applications in biology and medicine during DNA, genome, and clinical measurement [1].

The concept of mTAS was introduced in the early 1990's [2,3] and originally the first structures were fabricated using conventional micromachining technologies based on silicon wafers. Nowadays, many polymers (polydimethylsiloxane, polymethylmethacrylate, epoxy resin) are also utilised in mTAS design. The advantages of mTAS are evident if construction details are considered. The analysis performed in such a system requires a very small sample to be delivered, the reagents' consumption is also reduced, the separation obtained is much better than in ordinary bench-type measurements, and the time of the analysis is quite short. Nevertheless, new problems were faced by the designers like hydrodynamics of fluids in small channels, novel phenomena in very small channels, chemical resistivity of the silicon wafer to a variety of chemical compounds etc. Also the technology of a bonding, i.e. the assembly of the substrate materials to form the final mTAS structure, is not very compatible with the immobilised chemicals in the channels or reactors. The traditional bonding process involves anodic or thermal bonding and these operations, being carried out at high temperatures, are harmful to the chemicals on the chip. Thus for many years of mTAS development chemical sensors were very rarely used as detectors. Most systems were based on optical detection carried out by means of laboratory spectrometers or fluorometers. Recently, a new concept of chemical sensor construction for the microsystem has been proposed [4]. The flow-through type ion-selective electrodes were made of a dialyse tube for measurements of pH, Na⁺, K⁺, and Li⁺.

The advantages of the mTAS can be summarised as follows:

• Ultra small volume of the sample
• Low chemicals consumption
• Fast analysis
• Low cost of the analysis

References

1. Van den Berg A., Olthius W., Bergveld P. (eds.), Proceedings of the mTAS 2000 (Micro Total Analysis Systems 2000), Kluwert Academic Publishing, Boston/London, 2000.
2. Manz A., Graber N., Widmer H.M., Miniaturised total chemical analysis systems: a novel concept for chemical sensing, Sens. Actuators B, 1, 244 (1990).
3. Manz A., Harrison D.J., Verpoorte E.M.J., Fettinger J.C., Paulus A., Ludi H., Widmer H.M., Planar chips technology for miniaturisation and integration of separation techniques into monitoring systems. Capillary electrophoresis on a chip, J.Chromatogr. B, 539, 253 (1992).
4. Boehm S., Olthuis W., Bergveld P., A generic design of a flow-through potentiometric sensor array, Microchim. Acta, 134, 237 (2000).

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