Lysing bacterial spores by sonication through a flexible interface in a microfluidic system

Cell disruptions using ultrasonic energy transmitted through a flexible int erface into a liquid region has limitations because the motion of the vibra ting tip is not completely transferred into the liquid. To ensure that some degree of contact will be maintained between the ultrasonic horn tip and t he flexible interface, the liquid must be pressurized. The pressure conditi ons that yield consistent coupling between the ultrasonic horn tip and the liquid region were explored in this study by using an analytical model of t he system and test fixture experiments. The nature of the interaction betwe en the horn tip and the flexible interface creates pulses of positive press ure rises, increase in temperature, streaming flow, and almost no cavitatio n in the liquid. There was sufficient energy to create a cloud of microsphe res, or beads, that maintain a consistent pattern of ballistic motion in th e liquid. The sonication was found to be repeatable by studying video recor dings of bead motion and was shown to be statistically consistent using mea surements of temperature rise. Sonication of bacterial spores to obtain mea surements of released nucleic acid and SEM images of damaged spores were us ed to verify the effects of liquid pressure on the horn-interface-liquid co upling.