Combining diagnostic and therapeutic processes into one (theranostics) and improving their selectivity to the cellular level may offer significant benefits in various research and disease systems and currently is not supported with efficient methods and agents. We have developed a novel method based on the gold nanoparticle-generated transient photothermal vapor nanobubbles, that we refer to as plasmonic nanobubbles (PNB). After delivery and clusterization of the gold nanoparticles (NP) to the target cells the intracellular PNBs were optically generated and controlled through the laser fluence. The PNB action was tuned in individual living cells from non-invasive high-sensitive imaging at lower fluence to disruption of the cellular membrane at higher fluence. We have achieved non-invasive 50-fold amplification of the optical scattering amplitude with the PNBs (relative to that of NPs), selective mechanical and fast damage to specific cells with bigger PNBs, and optical guidance of the damage through the damage-specific signals of the bubbles. Thus the PNBs acted as tunable theranostic agents at the cellular level and in one process that have supported diagnosis, therapy and guidance of the therapy.