The ANTQ300 designed by ANT is based on the principle of piezoelectric biosensor. It is made of three portions including electronic oscillation circuit, frequency counter, and piezoelectric quartz of fixed biosensor molecule¡]p-chip¡^ . Piezoelectric quartz crystal

consist of quartz crystal slab with a layer of gold electrode on each side¡]Figure 1a¡^.It is the signal conversion component of piezoelectric sensor chip and can convert the result sensed by the sensor molecule into electronic signal and being amplified. The function of gold electrodes are mainly to introduce an oscillating electric field perpendicular to the surface of the chip so that the internal of the chip generates mechanical oscillation due to

the piezoelectric effect¡]Figure 1b¡^. If the thickness of the quartz crystal is fixed, the mechanical oscillation will be generated at a fixed frequency. Using a suitable electronic oscillation circuit, the resonant frequency can be measured. According to Surgery equation, to the AT-cut quartz piezoelectric crystal, the variation in the mass on the surface of the electrode is linearly related to the variation of quartz oscillation frequency.

Therefore, to selectively measure a specific analyte it is only required to modify the surface of quartz crystal electrode with a layer of sensor molecule thin film with high specificity. Then, this sensor chip is placed in a test environment containing analyte so that the analyte could

be affinitively absorbed onto the sensor electrodes. From the attenuation in the oscillation frequency of the crystal after the attachment we can estimate the amount of attached analyte.