Development of a Shear Horizontal SAW RFID Biosensor

RFID tags have been used for passive retrieval of information via retransmission of interrogative radio frequency signals. This paper presents the development of a shear horizontal surface acoustic wave (SH-SAW) RFID biosensor. A 220 MHz SAW device was fabricated on LiNbO₃ substrate; composed of an interdigitated transducer (IDT), a dummy electrode, reflectors and a bio-sensitive layer. As the RF interrogation system sends a short RF pulse to the SAW device, the apparent pulse frequency of the return signal shifts due to binding of the biological target which decreases the velocity of the traveling pulse. The biosensor was functionalized by immobilizing anti-FITC on the dummy electrode, and tested against FITC and biocytin (negative control). The frequency shifted by 250 kHz with FITC, and 20 kHz with biocytin. Real-time monitoring of mass loading with deionized water and acetone on the device showed a 3 MHz shift. In addition, the effects of acetone evaporating on the sensor were observed as the device returned to the base frequency.