Potential biosensor system employing acoustic impulses in thin polymer films

Abstract

Piezoelectric biosensors usually employ quartz crystals, either as resonating crystals (quartz crystal microbalance), or as bulk or surface acoustic wave devices. Their action depends on changes in bound mass with the sensitivity of most systems being inversely proportional to the crystal thickness (minimum 150 µm), which is inadequate for many applications. A system is described in which acoustic impulses are launched across a very thin (9 µm), tensioned polymer film consisting of adjacent control and measurement channels. Bound mass causes small changes (ns) in the transit time (µs), which is monitored sequentially on the two sensing areas. Because the polymer films are so thin, a 30-fold increase in sensitivity over quartz crystals can be achieved as was shown previously for a system using two separate resonant polymer film sensors. However, the original system had limited immunity to interfering effects, especially temperature, which the new system is designed to overcome. Results show that changes in temperature and viscosity acting on both channels are well compensated, which should allow the determination of very small mass changes on the measurement area.