Formaldehyde is one of the most important chemicals widely used in industry. Its classification as a mutagen and human carcinogen has motivated a strong need for formaldehyde control in environment and food. In order to measure the concentration of formaldehyde, a highly selective and stable biosensor is required, which can be based on the yeast cells capable of metabolizing formaldehyde. In the present study we tested the possibility to use living and permeabilized cells of the yeast Hansenula polymorpha for construction of amperometric biosensors selective to formaldehyde. The following experimental methods have been used: (i) measurement of the current produced by the cells in the presence of mediators based on the methodologies proposed in [1,2]; and (ii) measurement of oxygen consumption with a biosensor based on immobilized yeast cells. (i) It was found that both type of yeast cells produced rather high current in the presence of mediators. However, the current did not depend quantitatively on the formaldehyde concentration in the case of permeabilized cells. It was shown that digitonin used for the permeabilisation produces distortions of some essential membrane structures responsible for the normal work of the respiratory electron transport chain. Indeed, a biosensor based on living yeast cells was designed and its basic parameters, such as detection limit (0.5 mM), linear dinamic range (1-10 mM), long-term and operation stabilities were determined. (iii) The device with immobilized permeabilized yeast cells allowed determination of formaldehyde concentration only up to 4 mM at 24ºC. Similar results were obtained in a previously reported work [3] by using the pH-FET-based potentiometric biosensors. We can suggest that the rapid limitation of output signal with formaldehyde concentration is caused by regulatory properties of the complex AOX/membrane. A marked decrease in respiratory activity of permeabilised cells was observed at formaldehyde concentrations greater than 4 mM, probably as a result of a deterious effect of formaldehyde on the yeast cells.

[1] B.A. Kuznetsov et al., Bioelectrochem., 64 (2004) 125.
[2] A. Heiskanen et al., Electrochem. Commun., 6 (2004) 219.
[3] Y. I. Korpan et al., Biosens. Bioelectron., 15 (2000) 77.

Acknowledgement. The work was supported by INTAS Open Call project No. 03-51-6278

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