Available online at www.sciencedirect.com Talanta 75 (2008) 786–791 Direct detection of formaldehyde in air by a novel NAD + - and glutathione-independent formaldehyde dehydrogenase-based biosensor S. Achmann a,∗ , M. Hermann b , F. Hilbrig b , V. J´ erˆ ome b , M. H¨ ammerle a , R. Freitag b , R. Moos a a Chair of Functional Materials, University of Bayreuth, 95440 Bayreuth, Germany b Chair for Process Biotechnology, University of Bayreuth, 95440 Bayreuth, Germany Received 30 July 2007; received in revised form 29 November 2007; accepted 7 December 2007 Available online 23 December 2007 Abstract An amperometric enzyme-based sensor-system for the direct detection of formaldehyde in air is under investigation. The biosensor is based on a native bacterial NAD + - and glutathione-independent formaldehyde dehydrogenase as biorecognition element. The enzyme was isolated from Hyphomicrobium zavarzinii strain ZV 580, grown on methylamine hydrochloride in a fed-batch process. The sensor depends on the enzymatic conversion of the analyte to formic acid. Released electrons are detected in an amperometric measurement at 0.2 V vs. Ag/AgCl reference electrode by means of a redox-mediator. To optimize the sensing device, Ca 2+ and pyrroloquinoline quinone (PQQ) were added to the buffer solution as reconstitutional substances. At this stage, the sensor shows linear response in the tested ppm-range with a sensitivity of 0.39 A/ppm. The signal is highly reproducible with respect to sensitivity and base line signal. Reproducibility of sensitivity is more than 90% within the same bacterial batch and even when enzyme of different bacterial batches is used. © 2007 Elsevier B.V. All rights reserved. Keywords: Enzyme sensor; Gas-phase; Gas sensor; Amperometric biosensor; Dye-linked formaldehyde dehydrogenase; Hyphomicrobium zavarzinii 1. Introduction In spite of their high sensitivity and selectivity the use of biosensors for industrial or medical analysis is still restricted. Enzyme-based sensor-systems still suffer from their low long- time stability often provoked by the low stability of their biological components [1]. They are also often restricted to analytes in solvent or fluidic analysis-systems, because an appro- priate medium (solvent or gel) adjusted to the used enzymatic system [2] is needed, to gain optimum activity and stability of the enzyme and other biological components. Thus, for gas phase analysis additional sampling and accumulation steps have to be incorporated prior to the real measurement, showing a few draw- backs such as high cost for technical equipment, longer sampling time and sometimes reduction of measuring-range. ∗ Corresponding author at: Chair of Functional Materials, University of Bayreuth, FAN-A Room A 0.09, 95440 Bayreuth, Germany. Tel.: +49 921 557412; fax: +49 921 557405. E-mail address: Sabine.Achmann@uni-bayreuth.de (S. Achmann). The enzyme-based sensor-system investigated here is designed to avoid some of the difficulties mentioned above. In contrast to existing systems [3–5], the amperometric biosensor detects the analyte formaldehyde directly from the gas phase without prior accumulation or sampling steps. So, it can be used as an online detection system to monitor the formaldehyde concentration in ambient air. Unlike other biosensors detecting formaldehyde, which often use commercially available formaldehyde dehydrogenase from P. putida [6,7], or another NAD + - and/or glutathione-dependent formaldehyde dehydrogenase [8], the novel biosensor uses a dye-linked formaldehyde dehydrogenase from H. zavarzinii strain ZV 580 as biorecognition element. This enzyme catal- yses the conversion of the analyte without the need of NAD + , a cofactor which is very well known in the literature [9] for its instability in different buffers, its high over potential for direct re-oxidation, and a proposed radical reaction mechanisms dur- ing re-oxidation [10]. Therefore, a NAD-independent system is expected to show a better long-term stability than the available systems. 0039-9140/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2007.12.015