RESUMO
A heme peptide-modified quartz crystal oscillator is fabricated as a dual-response biosensor, giving electrochemical and piezoelectric responses simultaneously. Binding of a ligand to heme peptide causes inhibition of its catalytic activity, which is observed as the electrochemical response, and a mass increase is monitored as the piezoelectric response. The dual-response sensor can give two independent pieces of information at the same time. That is, qualitative (identification of the species) and quantitative (determination of its concentration) analyses can be made simultaneously. Simultaneous quantitative analysis for two components is also possible. These two modes are theoretically explained and then experimentally demonstrated employing imidazole and histidine as interferants.
RESUMO
The converse piezoelectric effect, in which an electric field applied across a piezoelectric material induces a stress in that material, has spurred many recent developments in mass measurement techniques. These methods commonly rely on the changes in the vibrational resonant frequency of piezoelectric quartz oscillators that result from changes in mass on the surface of the oscillator. The dependence of frequency on mass has been exploited extensively for mass measurements in vacuum or gas phase, for example, thickness monitors for thin-film preparation and sensors for chemical agents. Advances in piezoelectric methodology in the last decade now allow dynamic measurements of minute mass changes (< 10(-9) grams per square centimeter) at surfaces, thin films, and electrode interfaces in liquid media as well. Mass measurements associated with a diverse collection of interfacial processes can be readily performed, including chemical and biological sensors, reactions catalyzed by enzymes immobilized on surfaces, electron transfer at and ion exchange in thin polymer films, and doping reactions of conducting polymers.
