Single Microbubble Measurements for Bound and Unbound Conditions

Abstract

We show here that adhesion to a solid substrate increases the resonance frequency of a lipid-coated microbubble by causing an apparent increase in shell stiffness. Using our previously developed photoacoustic measurement technique to drive individual microbubbles into small-amplitude oscillations, we found that biotinylated microbubbles adherent to a streptavidin-coated glass coverslip had much higher resonance frequencies than unbound microbubbles. The frequency responses of the bound microbubbles agree well with a linearized form of the modified Rayleigh-Plesset model with an added increase of shell elasticity. The apparent shell elasticity increased from 0.5 N/m for unbound microbubbles to 2.6 N/m. These findings may be used to better understand microbubble dynamics for applications in ultrasound imaging and therapy.