Effect Of Solution Conductivity On Resonance Frequency Of Quartz Crystal Microbalance

As a high-precision resonant sensor,quartz crystal microbalance(QCM)has been widely used in the fields of chemistry and biology.Thickness field excitation(TFE)QCM mainly detects the mass effect of the object and the mechanical properties of the solution.Lateral field excitation(LFE)QCM with different electrode structures can not only detect the mechanical properties of the solution but is more sensitive to electrical properties.The basic working principle of QCM and the relationship between QCM frequency shift and surface mass load are introduced.The reference resonant element is set to eliminate the influence of liquid mechanical characteristics and external disturbance using a dual-channel LFE-QCM.With the corresponding flow cell structure and flow injection system,a complete QCM liquid detection device is formed to study the influence of solution conductivity on QCM.The modified liquid phase equivalent circuit model is derived by establishing the corresponding boundary conditions when the liquid is in contact with sensing layer.Based on this,a liquid electrical characteristic equivalent circuit model is proposed.Through the impedance analyzer test,the basic electrical parameters of the QCM chip are obtained,and the Q values in the air and in the deionized water satisfy the stable oscillation condition of the resonator.The measurement of phosphate buffer by TFE-QCM proves that in biological immunization experiments,the conductivity will also have different effects on the traditional QCM,and this effect cannot be simply ignored.Using LFE-QCM measuring different solubility NaCl solution,the relationship between QCM frequency shift and conductivity is obtained,which provides a new direction for future conductivity detection technology.Combined with the detection results of different permittivity solutions,the correctness of the equivalent circuit model of liquid phase electrical properties is proved.Finally,the oscillating circuit is used to monitor the conductivity of the solution in real time,which proves that QCM can be applied to the detection of liquid electrical properties in the future.