In vitro Preparation and Characterization of Magnetic Nanobubbles

Lipid-shelled magnetic bubbles are widely researched for potential applications as multi-functional contrast agents for ultrasound and magnetic resonance imaging and for drug delivery applications. In this study, we prepared nano-sized magnetic bubbles using a magnetic lipid solution created by first forming a homogeneous phospholipid solution in phosphate buffered saline (PBS) containing glycerol and propylene glycol and followed by adding superparamagnetic iron oxide nanoparticles with a diameter of 10 nm. Bubbles were generated by mechanical agitation using a dental amalgamator, and magnetic nanobubbles were isolated by centrifugation at 50 g for 5 min. Prepared magnetic nanobubbles had a mean diameter of 308 +/- 105 nm and a concentration of (1.68 x 10(10) bubbles/mL), as determined by resonant mass measurement. Stability of the magnetic nanobubbles over time was evaluated by measuring the acoustic signal decay. Magnetic nanobubbles showed a 27% and 83% signal decay after 1 and 2 h at room temperature, respectively. The response of the magnetic nanobubbles to a magnetic field was examined by measuring T2 relaxation times at different bubble/iron concentrations. Magnetic nanobubbles showed an r2 relaxivity of 144.6 mM(-1)s(-1). This study demonstrates feasibility of preparing magnetic nanobubbles using a simple self-assembly process. The constructs could be more effective in multimodality molecular imaging and extravascular drug delivery compared to magnetic microbubbles, due to their submicron size.