Surface acoustic wave biosensors for biomolecular interaction analysis

HPSSW type, (horizontally polarized surface shear wave) surface acoustic wave (SAW) devices have been proven to be suitable for biosensing applications. They allow an easy and fast label free detection of molecules with biological relevance via direct detection of the adsorbed mass. However, SAW device structures are usually connected by bond wires. In consequence sampling chambers suffer from relatively big flow cell volumes ∼ 50 μl. We developed new resonator filter based HPSSW devices with gold transducers. They work at an operating frequency of 433.9 MHz on 36°YX LiTaO₃ as substrate material. Bonding wires could be eliminated as the sensor is capacitively coupled with the driving electronics via large contact pads. The new coupling concept (originally developed for our gas sensing approach) enables the reduction of the sample volume in the flow cell down to 60 nl. This decreases sample consumption and reduces the length of the measurement cycles. Affinity assays were realized using this SAW biosensor. Measurements with the systems urease/anti-urease and estradiol/estrogen receptor are shown exemplarily. In the latter case it could be shown that reference SAW surfaces without binding partner have the potential to enable the quantification of binding reactions even in complex media. For automated sample handling, the SAW detection unit is integrated in a flow injection analysis (FIA) system. A cost-effective, compact demonstration instrument for SAW biosensing was developed.