Liquid biopsy offers non‐invasive and real‐time molecular profiling of individual patients, and is thus considered a revolutionary technology in precision medicine. Exosomes have been acknowledged as significant biomarkers in liquid biopsy, as they play a central role in cell–cell communication and are closely related to the pathogenesis of most human malignancies. Nevertheless, in biofluids exosomes always co‐exist with other particles, and the cargo components of exosomes are highly heterogeneous. Thus, the isolation and molecular characterization of exosomes are still technically challenging. Microfluidics technology effectively addresses this challenge by virtue of its inherent advantages, such as precise manipulation of fluids, low consumption of samples and reagents, and a high level of integration. Recent advances in microfluidics allow in situ exosome capture and molecular detection with unprecedented selectivity and sensitivity. In this review, the state‐of‐the‐art developments in microfluidics‐based exosome research, including exosome isolation approaches and molecular detection strategies, with highlights of the characterization of exosomal biomarkers in cancer liquid biopsy is summarized. The major challenges are also discussed and some perspectives for the future directions of exosome‐based liquid biopsy in microfluidic systems are presented.

MicroRNAs (miRNAs) in tumor-derived extracellular vesicles (tEVs) are important cancer biomarkers for cancer screening and early diagnosis. Multiplex detection of miRNAs in tEVs facilitates accurate diagnosis but remains a challenge. Herein, we propose an encoded fusion strategy to profile the miRNA signature in tEVs for pancreatic cancer diagnosis. A panel of encoded-targeted-fusion beads was fabricated for the selective recognition and fusion of tEVs, with the turn-on fluorescence signals of molecule beacons for miRNA quantification and barcode signals for miRNA identification using readily accessible flow cytometers. Using this strategy, six types of pancreatic-cancer-associated miRNAs can be profiled in tEVs from 2 μL plasma samples (n = 36) in an isolation-free and lysis-free manner with only 2 h of processing, offering a high accuracy (98%) to discriminate pancreatic cancer, pancreatitis, and healthy donors. This encoded fusion strategy exhibits great potential for multiplex profiling of miRNA in tEVs, offering new avenues for cancer diagnosis and screening.

MicroRNAs (miRNAs) have been extensively studied as non-invasive biomarkers for cancer diagnosis and prognosis, while the clinical application was constrained by the heterogeneous miRNA sources in plasma and the tedious assay processes. Here we developed a one-pot assay called dual-Surface-protein-guided Orthogonal Recognition of Tumor-derived Exosomes and in-situ profiling of microRNAs (SORTER) for rapid and precise diagnosis of prostate cancer. The SORTER utilizes the orthogonal barcoding of two allosteric aptamers against exosomal marker CD63 and tumor marker EpCAM to recognize and sort tumor-derived exosome subtypes. Furthermore, the labeled barcode on tumor-derived exosomes guided the targeted fusion with liposome miRNA detection probes, enabling in-situ profiling of tumor-derived exosomal miRNAs. With a signature of six miRNAs, SORTER differentiated prostate cancer and benign prostatic hyperplasia with a sensitivity, specificity, and accuracy of 100% in the training and validation cohorts. The SORTER provides a promising tool to advance the clinical adaptability of miRNA-based liquid biopsy.