Control of Submillimeter Phase Transition by Collective Photothermal Effect

Local molecular states and biological materials in small spaces ranging from the microscale to nanoscale can be modulated for medical and biological applications using the photothermal effect (PTE). However, there have been only a few reports on exploiting the collective phenomena of localized surface plasmons (LSPs) to increase the amount of light-induced heat for the control of material states and the generation of macroscopic assembled structures. Here, we clarify that microbeads covered with a vast number of Ag nanoparticles can induce a large PTE and generate a submillimeter bubble within several tens of seconds under the synergetic effect of the light-induced force (LIF) and photothermal convection enhanced by collective phenomena of LSPs. Control of the phase transition induced by such a "collective photothermal effect" enables rapid assembling of macroscopic structures consisting of nanomaterials, which would be used for detection of a small amount of proteins based on light-induced heat coagulation.