Fig. 1

Strategy for visualization of EVs. The size of EVs is around 100 nm, which restricts direct imaging with optical microscopy. Recently, several labeling methods have been developed. Lipophilic fluorescence dye is simple and commonly used to track EVs. Reporter imaging using fluorescence or bioluminescence combined with transmembrane proteins could provide information more specific to EVs than direct dye labeling. For clinical application and deep tissue imaging, radionuclide imaging or MRI could be possible using ¹¹¹In-oxine, ^99mTc-HMPAO, and iron oxide nanoparticles. GFP green fluorescent protein