Exosomes has attracted tremendous research interests as they are emerging as a new paradigm of liquid biopsy. Although the concentration of exosomes in blood is relatively abundant, there still exists various vesicle-like nanoparticles, such as microvesicles, apoptotic bodies. It's an urgent need to isolate and enrich exosomes from the complex contaminants in biofluid samples. Moreover, the expressing level of exosomal biomarkers varies a lot, which make the sensitive molecular detection of exosomes in high demand. Unfortunately, the efficient isolation and sensitive molecular quantification of exosomes is still a major obstacle hindering the further development and clinical application of exosome-based liquid biopsy. Nanomaterials, with unique physiochemical properties, have been widely used in biosensing and analysis aspects, thus they are thought as powerful tools for effective purification and molecular analysis of exosomes. In this review, we summarized the most recent progresses in nanomaterials assisted exosome isolation and analysis towards liquid biopsy. On the one hand, nanomaterials can be used as capture substrates to afford large binding area and specific affinity to exosomes. Meanwhile, nanomaterials can also be served as promising signal transducers and amplifiers for molecular detection of exosomes. Furthermore, we also pointed out several potential and promising research directions in nanomaterials assisted exosome analysis. It's envisioned that this review will give the audience a complete outline of nanomaterials in exosome study, and further promote the intersection of nanotechnology and bio-analysis.

Exosomes are extracellular vesicles that actively secreted by most live cells via endosome pathway. They distribute ubiquitously in body fluids and play important roles in physiological and pathological processes. Recent studies have revealed that exosomes carry cell‐specific cargoes, such as proteins and nucleic acids, which have been recognized as emerging noninvasive biomarkers in liquid biopsy. Therefore, the molecular profiling of tumor‐derived exosomes is crucial in facilitating the discovery of cancer‐related biomarkers. Recently, various techniques have been proposed for sensitive, accurate, and rapid molecular characterization of these small vesicles. To meet the growing demands for multiplexed detection, microfluidics has been integrated with diverse traditional analytical methods as powerful components for exosomes analysis. Taking advantages of their inherent merits of great sensitivity, high analysis performance and system integration, short analysis time, low cost, small volume of sample, improved potential for control, automation, and disposability, microfluidic systems have significantly improved the molecular profiling of exosomes. In this review, we summarized the most recent progresses in microfluidic technologies for molecular profiling of tumor‐derived exosomes, including proteins, nucleic acids, metabolites, lipids. Furthermore, we discussed the major challenges and offered a perspective of the microfluidic strategy‐based exosomal biomarkers discovery. We expected that the in‐depth summary of microfluidic devices–assisted analysis of exosomes will greatly facilitate the discovery of biomarkers, thereby realizing highly efficient and accurate diagnosis, and prediction of cancers. Moreover, in view of the significance of this interesting approach in exosomes‐based liquid biopsy, this review will contribute to the translation of microfluidic technology into clinical applications.

Exosomes have been extensively studied as liquid biopsy biomarkers in the past decade. However, the origin and molecular heterogeneity of exosomes hinder the research development moving from proof-of-concept to clinical applications. Herein, we report an integrated microfluidic platform termed Sub-ExoProfile chip, to achieve the selective isolation and subsequent proteomic profiling of multiplex exosome subpopulations simultaneously. The Sub-ExoProfile chip comprises three cylindrical self-assembled nanopillars, on which specific exosome capture antibodies (CD81, EpCAM, HER2) were immobilized to capture and sort different exosome subpopulations. It is worth noting that the 3D porous nanopillars afford enhanced interface binding efficiency; thus, a tumor-specific exosome subpopulation with lowly-expressed surface marker was still isolated with satisfactory capture efficiency. Moreover, the amphiphilic mesoporous silica nanoparticle self-assembled nanopillars also served as a nanoreactor for the enrichment and in situ digestion of exosomal proteins, providing improved performance for the mass-spectrometry based molecular characterization of exosome subpopulations. The Sub-ExoProfile chip was investigated on standard exosome samples from different breast cancer cell lines. The isolation and quantitative detection of exosome subpopulations were in line with the molecular subtype of breast cancer cell lines, and the molecular makeup was confirmed using classic microplate ELISA. Clinical samples from HER2-positive and triple-negative breast cancer patients were also examined using the Sub-ExoProfile chip. The quantitative results of three exosome subpopulations distinguished the three subtypes of breast cancer significantly. Most importantly, the molecular characterization of three exosome subpopulations revealed that the distinct exosome subpopulation participated in a different signaling pathway and performed distinct biological functions. It is envisioned that the analysis of the exosome subpopulation on the Sub-ExoProfile chip will facilitate the screening of tumor-specific exosomal biomarkers and open a new avenue for exosome-based liquid biopsy.