Researchers Develop Smallest Free-Floating Bubbles for Medical Imaging U ltrasound 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. A team of researchers from Rice University have introduced 50-nm gas-filled protein nanostructures derived from genetically engineered gas vesicles(GVs) that are referred to as 50 nmGVs. 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 nmGVs can be produced in a Zongru Li (left) and George Lu (Image: Anna Stafford/Rice University) b 50AuNp & 50nmGVs c d Figure 1. Purification and additional characterization of 50nmGVs. a) Representative phase contrast images of 50nmGV-expressing E.coli. E.coli cells with strong GV expression have visible reflecting dots in the phase contrast imaging (Farhadi et al., 2020) as indicated by the red arrows. Scale bars = 5 µm. b) A transmission electron microscopy (TEM) image of 50nmGVs mixed with commercial 50-nm gold nanoparticles (50AuNPs) for the comparison of their structural properties. 50AuNPs appear as darker contrast and GVs appear as lighter contrast on TEM images. Scale bar = 200nm. (c) A representative camera image of a 1.5 mL tube containing floating 50nmGVs and a TEM image of clustered 50nmGVs. Right after cell lysis, the clustered 50nmGVs are visually discernible as a floating white layer. d) A representative camera image and TEM image of 50nmGVs unclustered by 6 M urea treatment as described in previous protocols (Lakshmanan et al., 2017). 18 Photonics & Imaging Technology, November 2024