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The need for chemical sensor systems is expanding rapidly. By employing an array format the sensor systems with different sensor materials might be more generic and also more universal in their applications. The peculiarity of such array-based systems is that utilizing already available signal processing schemes and pattern recognition methods, it is possible to characterize an analytical sample as a whole. This means that a sensor array development should be application driven and sensitive materials, as well as types of transducers comprising the array, should be considered for each application. Microelectronic technology has large experience in fabrication of chemical sensors based on ion-selective field effect transistors (ISFET) and other types of transducers, like amperometric or conductimetric, utilising thin film technology. Though large ISFETs arrays have been reported (T. Yeow et al. Sensors and Actuators B 44 (1997) 434–440) they are produced on the same silicon substrate that prevents simultaneous measurements of all the devices. To resolve this problem complementary metal-oxide semiconductor (CMOS) technology was proposed to isolate individual ISFETs by a p-n junction (S. Martinoia et al. Biosensors and Bioelectronics 16 (2001) 1043–1050); but this results in high leakage currents and cross-talking of sensors that shows that they must be isolated. The latest achievements in microelectronic micromachining gave rise to production of new starting materials like BESOI (silicon on insulator) that can be used as a base for the development of a liquid multi-sensor array containing different types of chemical and physical sensors and that permit to integrate NMOS and thin film technologies.

Express immunochemical techniques for determination of toxic compounds and pathogenic cells have been developed. Separation of reactants based on interaction between oppositely charged polyelectrolytes, namely polycation poly-N-ethyl-4-vinylpyridium and polyanion polymethacrylate, were used to reduce assay time. An extremely high rate and affinity of this interaction allowed formation of an immune complex in the solution followed by a quick separation of reactants. The polyelectrolyte-based assays were performed in both homogeneous and filtration formats. Total duration of the assay was 15– 20 min, limit of pesticides detection — down to 0.2 ng/ml. The polyelectrolyte separation has been also used in electrochemical immunosensors. The assay protocol is based on the measurement of pH changes induced by a peroxidase label. A field-effect transistor is the sensitive element of the sensor, and specific immune complexes are formed at disposable porous membranes. An alternative approach is based on the application of screen-printed electrode with impregnated peroxidase. The set of reactants was used together with a portable amperometric device designed for express monitoring of hazardous compounds under out-of-lab conditions. The total assay time was 20 min, and the detection limit was 0.2 ng/ml. Immunochromatographic tests based on colloidal gold particles conjugated with antibodies have been developed for detection of low molecular weight antigens and bacterial cells. The method allows detection of bacterial cells including and during 10 min in concentrations down to 10 cell/ml

The main principles used for creating biosensing units based on application of the double-stranded DNA liquid crystalline dispersions are considered. A broad rande of analytical abilities of these units is illustrated. These multifunctional biosensing units are capable of detecting various chemical or biologically active compounds (genotoxicans, such as antitumor drugs, antibiotics, proteins, etc.) influencing the DNA secondary structure or destroying the additional nanosized sensing elements, incorporated between the neighboring the DNA in the spatial structure of the liquid crystalline dispersions and forming artificial nanobridges between fixed in the structure of particles of LCD DNA molecules. Some unsolved problems are outlined.