Sol–gel-derived thick-film conductometric biosensor for urea determination in serum

A conductometric urea biosensor based on sol–gel-immobilized urease on a screen-printed inter-digitated array (IDA) electrode has been developed. The screen-printed thick-film IDA electrode has proven to be an excellent conductometric transducer in which the admittance signal was dominated by the conductance signal and the resulting dynamic range was wide enough to be employed for the construction of conductometric urea biosensor. Urease was immobilized by a conventional sol–gel process using tetramethyl orthosilicate as a precursor. The sol–gel-derived urea biosensor showed a reasonably wide linear dynamic range 0.03–2.5 mM in 5.0 mM imidazole–HCl buffer at pH 7.5 (detection limit = 30 mM, signal : noise = 2), thus enabling it to be used to monitor urea in a diluted serum sample with the differential measurement format consisting of an active IDA electrode with sol–gel-immobilized urease and a control IDA electrode with sol–gel-immobilized bovine serum albumin. The urea biosensor exhibited good sensor-to-sensor reproducibility (4.4%) and storage stability (63% of its original activity retained after 25 days). The coupling of the sol–gel immobilization method and screen-printing technology can offer mass production of a durable urea biosensor. ©2000 Elsevier Science B.V. All rights reserved.