The present paper is a review of own publications of the authors concerning the development of conductometric enzyme biosensors for direct substrates or inhibitors analysis. Such biosensors were designed by using immobilised enzymes and planar thin-films interdigitated electrodes. Highly specific, sensitive, simple, fast and cheap determination of different substances renders them as promising tools for needs of medicine, biotechnology, environmental control, agriculture and food industry.

The characteristics of thin-films conductometric interdigitated electrodes as transducers were studied using impedance spectroscopy. The optimal materials for electrodes and support, the characteristic dimensions of electrodes as well as proper working conditions were chosen for enzyme biosensors designing.

Conductometric enzyme biosensors based on direct enzyme analysis for determination of concentrations of different substrates (glucose, urea, penicillin, formaldehyde, etc.) have been developed and their laboratory prototypes were fabricated. Improvement of analytical characteristics of such conductometric enzyme biosensors may be achieved by using: differential mode of measurement; working buffer solutions with different concentrations; potassium hexacyanoferrate(III) as an oxidising agent replacing O₂ in the case of  glucose biosensors; negatively or positively charged additional membranes. These approaches give a possibility to decrease the effect of the buffer capacity influence on the sensor response, to increase the sensitivity of the biosensors and to extend their dynamic ranges.

Conductometric enzyme biosensors for determination of concentrations of different toxic substances (organophosphorus pesticides, heavy metal ions, etc.) were designed on the basis of enzyme inhibition effect. The conception of enzyme multibiosensor for determination of toxic substances based on the enzyme inhibition effect is described.

The respective advantages and disadvantages of conductometric enzyme biosensors developed are discussed.