LGS shear horizontal SAW devices for biosensor applications

Low cost, highly sensitive biosensors for the selective detection of pathogens in liquids are urgently needed. These sensors can play a major role in limiting the threat of hazardous microbial agents introduced into food and water supplies accidentally or through acts of terrorism. Surface acoustic wave (SAW) sensors utilizing the shear horizontal (SH) mode together with a nucleic acid recognition technique called rolling circle amplification (RCA) represent an attractive technology for this type of application due to reduced acoustic wave attenuation of the SH mode in aqueous environments when compared to generalized SAW. Langasite (LGS) offers high coupling for the SH SAW mode, temperature compensated SH SAW orientations, and high dielectric permittivity aqueous solutions. These properties have been discussed in a previous work by M. Pereira da Cunha et al. (2002). This paper reports on LGS SH SAW delay lines that have been designed and fabricated with a gold shorted delay path as the sensing area, in which biomolecule sensing is performed as a model for the RCA recognition layer. Proteins were sequentially bound to a cysteamine-modified gold surface. With each protein addition, marked changes in the delay line phase were recorded, indicating the functionality of the biosensor as a platform for the RCA layer.