Development of highly selective and stable potentiometric sensors for formaldehyde determination

Two types of biosensors selective to formaldehyde have been developed on th e basis of pH-sensitive field effect transistor as a transducer. Highly or partially purified alcohol oxidase (AOX) and the permeabilised cells of met hylotrophic yeast Hansenula polymorpha (as a source of AOX) have been used as sensitive elements. The response time in steady-state measurement mode i s in the range of 10-60 s for the enzyme-based sensors and 60-120 s for the cell-based sensor. When measured in kinetic mode the response time of all biosensors developed was less than 5 s. The linear dynamic range of the sen sor output signals corresponds to 5-200 mM formaldehyde for highly and part ially purified alcohol oxidase, and 5-50 mM formaldehyde for the cells. The operational stability of the biosensors is not less than 7 h, and the rela tive standard deviation of intra-sensor response is approximately 2 and 5% for the enzyme- and cell-based sensors, respectively. When stored at 4 degr ees C, the enzyme and cell sensor responses have been found stable for more than 60 and 30 days, respectively. Both types of biosensors demonstrate a high selectivity to formaldehyde with no potentiometric response to primary alcohols, including methanol, or glycerol and glucose. The possible reason s of such unexpected high selectivity of AOX-based FET-sensors to formaldeh yde are discussed. The influence of the biomembrane composition and the eff ect of different buffers on the sensor response to formaldehyde are also di scussed. (C) 2000 Elsevier Science S.A. All rights reserved.