In this study, various types of acoustic waves were compared for their sensitivity, and a waveguided shear horizontal surface acoustic wave was used as a biosensor for the detection of the food pathogenic Escherichia coli O157: H7 (E. coli O157:H7), a dangerous strain among the > 200 E. coli unique serotypes. The presence of higher than 1 cfu E. coli O157:H7 in 25 g of food is considered a dangerous level. The biosensor was fabricated on a 640 YX LiNbO3 substrate, and was enhanced by depositing a 130 nm thin layer of SiO2 nanostructures with a particle size of < 70 nm. A specific DNA sequence from E. coli O157:H7 has 22 mers, and an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization. The sensor was able to attain the sensitivity of 0.6439 nM/0.1 kHz, and the detection limit was down to 1.8 femtomolar (1.8 x 10- 15 M), with the specific oligonucleotide target.
