High-frequency SAW oscillator sensor to measure DNA immobilization and hybridization

Abstract

We developed SH (shear horizontal) surface acoustic wave (SAW) sensors for detection of the immobilization and hybrdization of DNA (deoxyribonucleic acid) on the gold coated delay line of transverse SAW devices. The experiments of DNA immobilization and hybridization were performed with 15-mer oligonucleotides (probe and complementary target DNA). The sensor consists of twin SAW delay line oscillators (sensing channel and reference channel) fabricated on 36° rotated Y-cut X-propagation LiTaO 3 piezoelectric single crystals. The relative change in the frequency of the two oscillators was monitored to detect the immobilization of probe DNA with thiol group on the Au coated delay line and the hybridization between target DNA and immobilized probe DNA in pH 7.4 PBS (phosphate buffered saline) solution. In our previous work, we reported the sensitivity of 1.26 ng/ml/Hz with 100 MHz SAW sensors. Sensitivity of the SAW sensor is in nonlinear proportion to the oscillation frequency of the SAW device. Significant improvement of the sensitivity of the SAW DNA sensor has been achieved by increasing the oscillation frequency to 200 MHz. The sensitivity was improved to as high as 135 pg/ml/Hz. We addressed many engineering problems required for the increase of the oscillation frequency such as electromagnetic noise isolation, mechanical vibration isolation, acoustic noise absorbing, and digital signal processing.