Maximum separation-distance for a separated-electrode piezoelectric sensor in non-electrolyte liquids. Application to determination of the adsorption human immunoglobulin G onto quartz surface

Abstract In a separated-electrode piezoelectric sensor (SEPS), the two excitation electrodes are separated by solution layers. An oscillation condition expressed as, 2PN≤(β+ 1+β 2 ) , is given for the SEPS to set up its stable oscillation in a non-electrolyte liquid. Here, P =1+ C o / C 1 + C o / C 2 , N = R q ωC o , ω =2 πF . C o , R q and F are the static capacitance, motional resistance, oscillation frequency of the quartz crystal, respectively. C 1 and C 2 are the solution capacitance. β is a parameter related to the phase of oscillator. According to this oscillation condition, there is a maximum separation-distance ( D max ) between the two excitation electrodes. It is shown that the D max values is proportional to the permittivity of the liquid and decreases with increasing viscosity and density of the liquid phase. The SEPS was applied for the determination of the adsorption density of human immunoglobulin G onto quartz surface.