POTENTIAL BIOSENSOR SYSTEM EMPLOYING ACOUSTIC IMPULSES IN THIN POLYMER-FILMS

Piezoelectric biosensors usually employ quartz crystals, either as res onating crystals (quartz crystal microbalance), or as bulk or surface acoustic wave devices. Their action depends on changes in bound mass w ith the sensitivity of most systems being inversely proportional to th e crystal thickness (minimum 150 mum), which is inadequate for many ap plications. A system is described in which acoustic impulses are launc hed across a very thin (9 mum), tensioned polymer film consisting of a djacent control and measurement channels. Bound mass causes small chan ges (ns) in the transit time (mus), which is monitored sequentially on the two sensing areas. Because the polymer films are so thin, a 30-fo ld increase in sensitivity over quartz crystals can be achieved as was shown previously for a system using two separate resonant polymer fil m sensors. However, the original system had limited immunity to interf ering effects, especially temperature, which the new system is designe d to overcome. Results show that changes in temperature and viscosity acting on both channels are well compensated, which should allow the d etermination of very small mass changes on the measurement area.