Anal. Chem. 2000, 72, 5225-5232
A Transducer Based on Enzyme-Induced Degradation of Thin Polymer Films Monitored by Surface Plasmon Resonance Claire Sumner, Andrea Sabot, Katrina Turner, and Steffi Krause*
Department of Chemistry, University of Sheffield, S3 7HF, U.K.
The degradation of a thin film in the presence of an analyte or the reaction product of an analyte can be utilized to produce highly sensitive transducers for disposable biosensors. This sensing principle has proven particularly effective if the degradation is caused by an enzymatic reaction. Recent work in this area lead to the development of a new sensor based on the measurement of capacitance changes produced during enzyme-catalyzed dissolution of polymer coatings on electrodes. Thin films of pH-sensitive polymers, e.g., a copolymer of methyl methacrylate and methacrylic acid, were deposited onto gold-coated electrodes. A localized increase in pH, caused by the enzymatic action of urease on urea, triggered the dissolution of the polymer films. Degradation of the films was accompanied by an increase in capacitance of up to 4 orders of magnitude. The method was developed into a fast and simple disposable sensor for urea in serum and whole blood.1,2 Further-
more, it was demonstrated that the high sensitivity and fast response of the technique could be utilized for immunosensing, using urease as the enzyme label.1 A disadvantage of this system is that the polymer film is not degraded directly by the enzyme, but by the pH change produced during the enzymatic reaction, i.e., pH and buffer capacity of the sample to be analyzed can influence the sensor response. Saum et al. used ac impedance spectroscopy to follow the proteolytic digestion of gelatin-coated interdigitated electrodes in order to detect collagenase activity.3 However, this system is only suitable for measurements at very low electrolyte concentrations (
