Microfluidic Device-Based <i>In Vivo</i> Detection of PD-L1-Positive Small Extracellular Vesicles and Its Application for Tumor Monitoring

Abstract

Liquid biopsy is of great significance in tumor early diagnosis and treatment stratification. PD-L1-positive small extracellular vesicles (PD-L1⁺ sEVs) are closely related to tumor growth and immunotherapy response, which are considered valuable liquid biopsy biomarkers. In contrast to conventional <i>in vitro</i> detection, <i>in vivo</i> detection has the ability to improve the detection efficiency and enable continuous or real-time dynamic monitoring. However, <i>in vivo</i> detection of PD-L1⁺ sEVs has multiple difficulties, such as high cell background, complex blood environments, and lack of a specific and stable detection method. Herein, the <i>in vivo</i> detection of PD-L1⁺ sEVs method was constructed, which efficiently separated sEVs based on the microfluidic device and quantitatively analyzed PD-L1⁺ sEVs by aptamer recognition and hybridization chain reaction. The concentration of PD-L1⁺ sEVs was continuously monitored, and significant differences at different stages of tumor as well as a correlation with tumor volume were found. Diseased and healthy individuals could also be effectively distinguished based on the concentration of PD-L1⁺ sEVs. The method with good stability, biocompatibility, and detection performance provided a powerful means for <i>in vivo</i> detection of PD-L1⁺ sEVs, contributing to the clinical diagnosis and treatment of tumor.