SAW sensor for anti-human-immuno-globulin G molecule detection

We developed surface acoustic wave (SAW) sensors to detect human-immuno-globulin G molecule applying a particular antibody thin film on the delay line of transverse SAW devices. The mass loading effect was given by the antibody-antigen bonding of the target molecules on the delay line. The sensor consists of twin SAW delay lines operating at 100 MHz fabricated on 36 degrees rotated Y-cut X-propagation LiTaO₃ piezoelectric single crystals. The sensor structure was optimized to achieve the highest signal to noise ratio with the least energy leakage to the protein solution. In addition, the input IDT of the sensor was configured as a single-phase-unidirectional-transducer (SPUDT) for more stable operation. The sensitive channel of the SAW sensor was coated with a gold film on which an antibody layer was immobilized. The antibody investigated was human-immuno-globulin G (HigG) and protein A molecules were coupled with the HigG molecules to work as an immobilizer layer to hold the antigens (anti-HigG). For proper immobilization of the detection molecules, Bovine Serum Albumine worked as a blocking layer to prevent the adhesion of any other molecules different from the anti-HigG to the SAW delay line. The relative change in the frequency of the two oscillators was monitored to measure the anti-HigG concentration in the protein solution. The sensor showed linear response to the mass loading effects of the anti-HigG molecules with the sensitivity up to 10.7 ng/ml/Hz.