Microflow-mediated optical assembly of nanoparticles with femtogram protein via shrinkage of light-induced bubbles

Bottom-up processing of nanobiomaterials enables the creation of a variety of macroscopic structures in natural systems. Here, we use optical means to produce macroscopic-assembled structures of nanoparticles (NPs) from protein molecules by using light-induced bubble (LIB) generation under asymmetric pressure-driven flow in a microchannel. The broadband optical response of assembled NPs facilitates the application of photon pressure and photothermal convection when irradiated by using an infrared laser. The presence of a large amount of protein allows the generation of a vast number of stable LIBs from optically assembled metallic NP-fixed beads (MNFBs). In the case of more diluted albumin solutions, the shrinking of a single LIB can cause the aggregation of MNFBs via fg-level albumin (3.4 fg in the observation region), like a microscale bubblegum. The size of the resulting aggregate can be controlled by changing the concentration of protein. These findings can be used to devise production methods not only for broadband optical nanocomposites but also for label-free methods to detect an extremely small amount of protein