Table 3.

Summary of reports of EV radiolabelling with PET radioisotopes. The hydrodynamic size of EVs are stated for unmodified EVs before radiolabelling, as appropriate. Radiolabelling conditions column shows EV and radiotracer co-incubation time, temperature, and the amount of EVs used per reaction. Data shown as reported by the authors. RLY = radiolabelling yield, UC = ultracentrifugation, SEC = size exclusion chromatography, RT = room temperature, iTLC = instant thin layer chromatography; * data taken from the figures.

Type	Radionuclide	Source of sEVs; size; isolation method	Radiolabelling conditions	Purification	RLY	In vitro stability; assessed by	In vivo imaging	Ref.
Surface radiolabelling	Na124I + iodogen method	MLP29 mouse liver cells; ~130 nm; UC	2 h; 25°C; 0.4 µg	SEC = Sephadex G25 (DNA grade)	Glycosylated = 17 ± 2% Non-glycosylated = 19 ± 1%	> 90% PBS stability at 72 h; iTLC	√	89
	64Cu-DOTA	Human umbilical cord blood mononuclear cells; ~110 nm; UC	1 h; RT; > 300 µg	MW3000 exosome spin column	16 - 25%	94% serum stability at 24 h, 95% blood stability at 1 h; iTLC	√	90
	64Cu-NOTA	4T1 mouse breast cancer cells; 106.3 ± 0.3 nm (volume weighted); UC	30 min; 37°C; 300 µg	SEC = PD-10	Non-PEGylated = 91.2 ± 0.2% PEGylated = 85.7 ± 0.7%	Non-PEGylated = 80.4 ± 1.3% PEGylated = 95.7 ± 0.9% serum stability at 24 h; iTLC	√	91
	64Cu-NOTA-Cy7	4T1 mouse breast cancer cells; ~100 nm; ExoQuick®	5 min; 37°C; 100 µg	ExoQuick®	~ 98%	> 95% serum stability at 36 h*; iTLC	√	92
	68Ga-NOTA-Cy7		30 min; 25°C; 100 µg		Not reported	Not reported
Intraluminal radiolabelling	89Zr-oxinate	B16-F10.GFP mouse melanoma cells; 146 ± 2 nm; ExoQuick®	1 h; 37°C; 1x1010 sEVs	MW3000 exosome spin column	6 ± 1%	Not reported	û	93
		MDA-MB-231.CD63-GFP human breast cancer cells; 121 ± 14 nm; UC	20 min; 37°C; 1x1010 sEVs	SEC = Sepharose CL-2B	6 ± 1%		û
		PANC1 human pancreatic cancer cells; 97 ± 4 nm; UC	20 min; 37°C; 1x1011 sEVs		23 ± 7%	76 ± 3% PBS stability at 26 h; iTLC (37°C)	√