Figure 3.

Images of glass microbubbles labeled with PE-conjugated biotin. Unmodified glass microbubbles (as shown in the phase-contrast image a) are not labeled with PE-conjugated biotin as there is no fluorescence shown in the fluorescence image b, where as the surface-modified glass microbubbles (as shown in the phase-contrast image c) have bright ring-shaped fluorescence shown in image d, indicating that the PE-conjugated biotin molecules are immobilized on the surface of glass microbubbles by their NeutrAvidin coating (scale bar = 50 μm).