ABSTRACT
This chapter focuses on the potential use of piezoelectric crystals as analytical sensors in which biological components serve as coating materials. It presents both liquid-phase and gas-phase applications. Antigen-coated crystals were proven applicable for the determination of the corresponding antibody concentration in solution. After the development the use of antigens, antibodies, and enzymes as specific coatings in piezoelectric biosensors has been widespread in liquid-phase analysis and, more recently, in gas-phase analysis. The piezoelectric effect is due to the fact that certain crystals contain positively and negatively charged ions, which separate when the crystals are subjected to stress. One of the simplest crystals, zinc sulfide, can be used to illustrate this phenomenon. The frequency output from the oscillator, which is identical to the resonant frequency of the crystal, can be measured by a frequency counter. Biological materials as piezoelectric crystal coatings were first demonstrated by Shons et al.
