Investigation of Microbubble Composition on Ultrasonic Dispersion Properties for Biosensing Applications

Abstract

Lipid shelled microbubbles are gaining attention as possible biosensors for monitoring the microbubble's in-vivo environment. These novel applications require the microbubble shell and gas components to be readily responsive to environmental changes. Since the ultrasonic properties of the microbubbles, for instance the resonance frequency or attenuation, are inherently related to the material properties of the monolayer shell such as visco-elasticity and thickness as well as on the physical properties of the encapsulated gas, it is important to investigate the influence of the shell composition and gas content on the ultrasonic behavior as well as the change in response after modifications of the microbubble environment. In this study, homemade microbubbles are characterized using ultrasonic through-transmission measurements in the range of 125kHz to 10MHz, thereby providing the dispersion relations of phase velocity and attenuation. Using this approach, the evolution of the dispersion properties of such bubbly media in time has been followed in order to detect changes in microbubble stability. In addition, several microbubble populations have been subjected to thermal changes to investigate their temperature dependence. The experimental observations have been compared to results from a nonlinear least squares fitting procedure with a theoretical model accounting for linear as well as nonlinear bubble behaviour. As such, the model allows to give a semi-quantitative interpretation of the dynamic behaviour and evolution of a microbubble population in the medium.