Genetically Encodable Contrast Agents for Optical Coherence Tomography

Optical coherence tomography (OCT) has gained wide adoption in biological research and medical imaging due to its exceptional tissue penetration, 3D imaging speed, and rich contrast. However, OCT plays a relatively small role in molecular and cellular imaging due to the lack of suitable biomolecular contrast agents. In particular, while the green fluorescent protein has provided revolutionary capabilities to fluorescence microscopy by connecting it to cellular functions such as gene expression, no equivalent reporter gene is currently available for OCT. Here, we introduce gas vesicles, a class of naturally evolved gas-filled protein nanostructures, as genetically encodable OCT contrast agents. The differential refractive index of their gas compartments relative to surrounding aqueous tissue and their nanoscale motion enables gas vesicles to be detected by static and dynamic OCT. Furthermore, the OCT contrast of gas vesicles can be selectively erased in situ with ultrasound, allowing unambiguous assignment of their location. In addition, gas vesicle clustering modulates their temporal signal, enabling the design of dynamic biosensors. We demonstrate the use of gas vesicles as reporter genes in bacterial colonies and as purified contrast agents in vivo in the mouse retina. Our results expand the utility of OCT to image a wider variety of cellular and molecular processes. ; © 2020 American Chemical Society. Received: October 24, 2019; Accepted: February 5, 2020; Published: February 5, 2020. The authors thank Changhuei Yang for helpful discussion and Theodore Chang for assistance with initial experiments. Electron microscopy was performed at the Beckman Institute Resource Centre for Transmission Electron Microscopy at Caltech. This research was supported by the National Institutes of Health (Grants K99EB024600 to G.J.L.; K12EY024225 and P30EY022589 to D.L.C.; R44HL129496, R43HD071701, and R44CA177064 to T.R.; and R01EB018975 to M.G.S.), the Defense Advanced Research Projects Agency (HR0011-17-2-0037 to M.G.S.), the ...