The present invention relates to a magnetic gas bubble composition, comprising one or more gas bubbles in a liquid medium wherein magnetic particles are present at the interface of the gas bubble and the liquid medium. Further, the present invention relates to a functionalised magnetic particle composition comprising two or more magnetic particles that are according to a first state agglomerated and/or coupled-together in a spatially delimited way by a bond and/or by embedding in a solid or viscous medium which bond or embedding medium can be physically, chemically and/or biologically modified, dissolved and/or degraded to a second state of reduced agglomeration and wherein the average particle to particle distance between the magnetic particles is less than 10 times the average magnetic particle size. Further, the present invention relates to a magnetic gas bubble precursor for the manufacture of such a magnetic gas bubble composition.
