Radial excursions of bound and non-bound targeted lipid-coated single microbubbles

Abstract

One of the main challenges for ultrasound molecular imaging is acoustically distinguishing non-bound microbubbles from those that have bound to their molecular target. We previously showed that biotinylated DPPC-based microbubbles (16 C-atoms) had a larger binding area and a more domed shape when bound to a streptavidin-coated surface than DSPC-based microbubbles (18 C-atoms) [1]. In the present in vitro study, we used the Brandaris 128 ultrahigh-speed camera (~15 Mfps) to compare the acoustical responses of biotinylated DPPC and DSPC-based microbubbles in a non-bound configuration and bound to a streptavidin-coated membrane, aiming to acoustically discriminate them from each other. The microbubbles were driven at a pressure of 50 kPa and at frequencies between 1 and 4 MHz. The main difference between bound and non-bound microbubbles was the lower radial excursion at the fundamental frequency for bound microbubbles. Resonance frequencies and subharmonic responses were the same for bound and non-bound micr...