Figure 2: In vitro magnetic microbubble (MMB) characterisation. (a) Size distribution plot obtained from 30 images of magnetic microbubbles using the image processing software. (b-c) Microscope images of magnetic microbubbles (20x objective). (b) Brightfield (33 ms exposure, 1x gain) and (c) fluorescence (TRITC filter, 500 ms exposure, 1x gain) images of the same field of view. (d) Brightfield and (e) fluorescence (TRITC filter) microscope images of magnetic microbubbles (4x objective) under influence of a magnet. Microbubbles were pipetted into a droplet and the field of view positioned towards the left edge of the droplet. A 1.5 T permanent magnet was held above the left side of the slide and is visible as the dark region to the left of the brightfield image. Microbubbles were observed to move towards the magnet and gather on the side of the droplet closest to the magnet under both brightfield and fluorescence imaging. Arrow in (d) indicates direction of microbubble motion. Inset in (d) shows initial distribution of microbubbles in centre of droplet prior to application of magnetic field taken at 1x magnification (scale bar 2000 m).