Detecting of the Cu2+ Ion in kiwifruit using QCM sensor based on phase measurement principle

QCM(Quartz crystal microbalance) sensor can convert the mechanical vibration signal into electrical signal due to the piezoelectric effect. It is often acts as an ultra-sensitivity mass sensing device to detect the tiny mass change. The shift of the resonant frequency is the measurable parameter currently used for a rapid evaluation of this change in typical QCM applications. The linear expression between mass change and frequency shift of QCM is given by Sauerbrey, which reveals that frequency decrease is proportional to the mass that was added to the surface of the QCM. In this paper, another characterization of QCM is revealed, the phase-mass relation of QCM sensor in air-phase application is derived based on wave equation. Taking Cu²⁺ in kiwifruit detection as an example, changes in frequency and phase of the QCM sensor was measured respectively. By applying the Sauerbrey´s equation and the newly derived phase-mass equation, the quantity of the Cu²⁺ in kiwifruit were calculated and compared. Experimental result shows that the phase-mass relation is agree well with that of the classical Sauerbrey´s equation. The study reveals that the method based on phase measurement principle of the QCM sensor is also useful.