50‐nm Gas‐filled Protein Nanostructures to Enable the Access of Lymphatic Cells by Ultrasound Technologies

Abstract Ultrasound imaging and ultrasound‐mediated gene and drug delivery are rapidly advancing diagnostic and therapeutic methods; however, their use is often limited by the need for microbubbles, which cannot transverse many biological barriers due to their large size. Here, the authors introduce 50‐nm gas‐filled protein nanostructures derived from genetically engineered gas vesicles(GVs) that are referred to as 50 nm GVs. These diamond‐shaped nanostructures have hydrodynamic diameters smaller than commercially available 50‐nm gold nanoparticles and are, to the authors’ knowledge, the smallest stable, free‐floating bubbles made to date. 50 nm GVs can be produced in bacteria, purified through centrifugation, and remain stable for months. Interstitially injected 50 nm GVs can extravasate into lymphatic tissues and gain access to critical immune cell populations, and electron microscopy images of lymph node tissues reveal their subcellular location in antigen‐presenting cells adjacent to lymphocytes. The authors anticipate that 50 nm GVs can substantially broaden the range of cells accessible to current ultrasound technologies and may generate applications beyond biomedicine as ultrasmall stable gas‐filled nanomaterials.