Biosensors based on piezoelectric transducers

The development of immunosensors based on piezoelectric transducers is widely investigated due to their attractive applications in mass sensitive detection [1, 2]. The most classical transducer is based on the quartz crystal microbalance (QCM), adapted to the liquid medium, which gives a direct response signal which characterizes the binding event between a sensitive layer, grafted onto the surface transducer, and the analyte to be detected. This kind of transducers offers many applications and an increasing number of publications illustrates this phenomena [3]. However, for small biomolecule detection under minute concentration it is quite difficult to obtain an observable and direct signal. This is mainly due to the lack of mass sensitivity of the commonly used QCM as they are generally built with 5 to 10 MHz quartz crystals. For solving this problem, attemps were made by increasing the working frequencies of the devices as, in general, the mass sensitivity increseases at the same time. Several possibilities were examined : either by using classical QCM with a smaller crystal thickness which increased the resonant frequency or by developping interdigitated piezoelectric devices at higher working frequencies. Various mass sensitivities will be calculated in order to compare the mass sensitivities of the different piezoelectric transducers. Moreover, we insists on the part played by other physico-chemical effects than the mass and which affect the piezoelectric response.