Pulsating tandem microbubble for localized and directional single-cell membrane poration

The interaction of laser-generated tandem microbubble (maximum diameter of about $50\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) with single (rat mammary carcinoma) cells is investigated in a $25\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{m}$ liquid layer. Antiphase and coupled oscillation of the tandem microbubble leads to the formation of alternating, directional microjets (with max microstreaming velocity of $10\text{ }\text{ }\mathrm{m}/\mathrm{s}$) and vortices (max vorticity of $350\text{ }000\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$) in opposite directions. Localized and directional membrane poration (200 nm to $2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ in pore size) can be produced by the tandem microbubble in an orientation and proximity-dependent manner, which is absent from a single oscillating microbubble of comparable size and at the same stand-off distance.