title: Nanointerrogation of ultrasonic contrast agent microbubbles using atomic force microscopy.
abstract: Predicting the acoustic response of an encapsulated microbubble to ultrasound requires an accurate assessment of the mechanical properties of the microbubble shell. Atomic force microscopy (AFM) provides an unprecedented spatial and force resolution of the order of Angstroms and subnanonewtons, respectively. It is introduced here as a means to interrogate microbubbles manufactured for ultrasonic imaging. The advantage of AFM over scanning electron microscopy (SEM) is that the microbubbles need not be subjected to a low temperature or low-pressure environment. The microbubbles were interrogated in a liquid environment, which could potentially be a simulated physiological environment. AFM was used in tapping mode imaging to reveal topographical detail of biSphere microbubbles. Because microbubbles are large objects compared with the overall size of usual AFM tips, a convolution between the AFM tip and the microbubble was typical of the acquired topographies. However, a part of the top half of the bubble was imaged with nanometer resolution, and roughness measurements are reported. Force-distance curves were captured using contact mode AFM. The range of stiffness or effective spring constant of biSphere was found to be between 1 and 6 N m(-1). In conclusion, the AFM is proposed here for the first time as a tool to image the surface of bubbles at the nanometer range in liquid and to perform reproducible measurements on the mechanical properties of individual microbubbles.
authors.affiliation: Medical Physics, School of Clinical Sciences and Community Health, University of Edinburgh, Edinburgh, UK. Vassilis.Sboros@ed.ac.uk
authors.forename: V
authors.initials: V
authors.lastname: Sboros
authors.forename: E
authors.initials: E
authors.lastname: Glynos
authors.forename: S D
authors.initials: SD
authors.lastname: Pye
authors.forename: C M
authors.initials: CM
authors.lastname: Moran
authors.forename: M
authors.initials: M
authors.lastname: Butler
authors.forename: J
authors.initials: J
authors.lastname: Ross
authors.forename: R
authors.initials: R
authors.lastname: Short
authors.forename: W N
authors.initials: WN
authors.lastname: McDicken
authors.forename: V
authors.initials: V
authors.lastname: Koutsos
mesh_terms: D001696:Biomechanical Phenomena; D003287:Contrast Media; D004548:Elasticity; D006801:Humans; D021621:Imaging, Three-Dimensional; D045423:Microbubbles; D018625:Microscopy, Atomic Force / Q000379:methods; D036103:Nanotechnology; D013314:Stress, Mechanical; D013499:Surface Properties; D014463:Ultrasonography / Q000379:methods*
chemical_list: D003287:Contrast Media