Optical characterization of an individual polymer-shelled microbubble structure via digital holography

Microbubbles are often used as ultrasound contrast agents for sonography. However, polymer-shelled microbubbles have the potential to support also additional functionalities such as, for example, targeted drug delivery. Using digital holographic microscopy we demonstrate that structural information on individual bubbles can be retrieved with high precision combined with low costs and short acquisition time. We have characterized the distributions of size, shell thickness and refractive index for hundreds of polymeric microbubbles showing that shell thickness displays a large variation that is strongly correlated with its refractive index. A large thickness corresponds to a smaller refractive index indicating a possible mechanism of progressive shell swelling with water.