Formaldehyde assay by capacitance versus voltage and impedance measurements using bi-layer bio-recognition membrane

A novel formaldehyde sensitive biosensor based on bacterial formaldehyde dehydrogenase (FDH) as a bio-recognition element has been developed. The bio-recognition membrane had bi-layer architecture and consisted of FDH, cross-linked with albumin, and of the cofactor NAD at a high concentration level (first layer). The second layer was a negatively charged Nafion membrane, which prevented a leakage of negatively charged NAD molecules from the bio-membrane. As transducers, gold electrodes SiO2/Si/SiO2/Ti/Au and electrolyte-insulator-semiconductor Si/SiO2 (EIS) structures have been used. Changes in capacitance and impedance properties of the bio-recognition membrane have been used for monitoring formaldehyde concentration in a bulk solution. It has been shown that formaldehyde can be detected within a concentration range from 1 μM to 20 mM depending on the type of transduction used, with a detection limit of 1 and 100 μM for gold-based and EIS-based transducers, respectively.