Formaldehyde-sensitive conductometric sensors based on commercial and recombinant formaldehyde dehydrogenase

Novel formaldehyde-sensitive conductometric biosensors have been developed that are based on commercial bacterial formaldehyde dehydrogenase (FDH) from Pseudomonas putida and recombinant formaldehyde dehydrogenase (rFDH) from the yeast Hansenula polymorpha as the bio-recognition elements. The bio-recognition membranes have mono-layer architecture and consist of enzyme cross-linked with albumin and of the cofactors NAD (for FDH-based sensor) or NAD and glutathione (for rFDH-based sensor). This architecture of the biosensor allows the determination of formaldehyde without adding NAD and glutathione to the analyzed sample at every analysis and conducting measurements on the same transducer without cofactors regeneration since the bio-membrane contains it at high concentration (100 mM for NAD and 20 mM for glutathione). The response is linear in the range from 10 to 200 mM of formaldehyde concentration depending on the enzyme used. The dependence of the biosensor output signals on pH and buffer concentration as well as operational/storage stability and selectivity/specificity of the developed conductometric biosensors have been investigated. The relative standard deviation of the intra-sensor response did not exceed 4% and 10% for rFDH- and FDH-based sensors, respectively. The relative standard deviation of the inter-sensor response constituted 20% for both dehydrogenases used. The biosensors have been validated for formaldehyde detection in some real samples of pharmaceutical (Formidron), disinfectant (Descoton forte) and an industrial product (Formalin). A good correlation does exist between the concentration values measured by the conductometric biosensor developed in this work, an enzymatic method, amperometric biosensors developed earlier, and standard analytical methods of formaldehyde determination.