TABLE 3.

Comparison of methods for detecting ExoPD-L1 in clinical samples.

Method	Instrument	Sample volume (μl)	Exosome isolation	Heterogeneous reaction system	Detection limitation	References
ELISA	Microplate reader	1000	Ultracentrifugation	Yes	200 pg/ml	Chen G. et al., 2018; Liu et al., 2018b; Theodoraki et al., 2018a, b, 2019; Fan et al., 2019; Li et al., 2019a; Lux et al., 2019; Cordonnier et al., 2020; Huang et al., 2020
HOLMES-Exo-PD-L1	Flow cytometer	1000	Ultracentrifugation	No	17.6 pg/ml	Huang et al., 2020
nPLEX assay	Compact SPR biosensor	50	Ultracentrifugation	No	Not given	Liu et al., 2018b
SERS immunoassay	Raman spectrometer	4	Fe3O4@TiO2 magnetic nanobeads	No	1 PD-L1+ exosome/μl	Pang et al., 2020

ELISA, enzyme linked immunosorbent assay; HOLMES-ExoPD-L1, homogeneous, low-volume, efficient, and sensitive ExoPD-L1; nPLEX, nanoplasmonic exosome; SPR, surface plasmon resonance; SERS, surface-enhanced Raman scattering.