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. 2021 Feb 13;5(3):256–274. doi: 10.7150/ntno.51676

Table 2.

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

Type Radionuclide Source of sEVs / EMVs; size; isolation method Radiolabelling condition Purification RLY In vitro stability; assessed by In vivo imaging Ref.
Surface radiolabelling 125I-biotin B16-BL6 mouse melanoma cells; 70 ± 3 nm; UC 30 min; 37°C;
10 µg		 Not reported ~ 80%* > 95% serum stability at 4 h; UF û 78
As above û 79
Na131I +
iodo-bead method		 Various 30 min; RT;
not reported		 UF = Nanosep 100k Omega >80% for 4T1 EVs* ca. 80% serum stability at 24 h*; iTLC √ 80
99mTc-tricarbonyl Human red blood cells; 188 ± 11 nm; UC + UF + SEC 30 min; RT;
0.6 mL		 Zeba spin desalting column 38.8 ± 6.2% No data given √ 81
99mTc-tricarbonyl HEK 293T human embryonic kidney cells; ~77 nm; not reported 1 h; 37°C;
20 µg		 None used > 98% 96% saline stability at 24 h; TLC √ 82
99mTc
(+ SnCl2)		 Goat milk; 122 ± 1 nm; UC and SEC 30 min; 37°C;
75 µg		 Exosome spin column 37 ± 9% 95% PBS stability at 48 h; iTLC √ 83
111In-DTPA B16-F10 mouse melanoma cells; 132 ± 6 nm; UC 30 min; 37°C;
1x1011 sEVs		 SEC = Sepharose CL-2B 19.2 ± 4.5% 86.8 ± 3.1% PBS stability, and 80.4 ± 1.6% serum stability at 24 h; iTLC √ 84
Intraluminal radiolabelling 111In-oxinate PC3 human prostate cancer cells; 140 ± 59 nm; UC 20 min; RT;
2.5-3.7 mg/mL		 SEC = P6 column 81% No data given û 85
MCF-7 human breast cancer cells; 130 ± 57 nm; UC 67%
111In-oxinate HEK 293 human embryonic kidney cells; 106 ± 14 nm; UF + UC 30 min; RT;
1x109 sEVs/mL		 UF = Amicon ultra 100 kDa > 98% > 92% serum stability at 24 h; iTLC √ 86
111In-tropolone B16-F10 mouse melanoma cells; 132 ± 6 nm; UC 20 min; 37°C;
1x1011 sEVs		 SEC = Sepharose CL-2B 4.7 ± 0.4% 43.4 ± 10.1% PBS stability, and 14.2 ± 2.8% serum stability at 24 h; SEC √ 84
99mTc-HMPAO Raw 264.7 mouse macrophages; 218 ± 8 nm; serial extrusion 1 h; RT;
100 µg		 SEC = PD-10, MW3000 spin column > 93% ~ 90% serum stability at 5 h; iTLC √ 87
99mTc
(+ SnCl2)		 Rat red blood cells; 201 ± 16 nm; serial extrusion 20 min; 37°C;
100 µg		 UC (only if RLY < 95% on iTLC) 100% 93 ± 3% serum stability at 24 h; iTLC √ 88