CD81 and neoplasm: To further confirm that BALF contains a higher proportion of tumor‐derived PD‐L1+ exosomes, exosomes were injected at a concentration of 108 particles mL−1 into the DP‐SIS sensor functionalized with exosome‐specific anti‐CD81 antibodies, followed by the injection of aPD‐L1 (1 μg mL−1).