Tissue biopsy is often required for cancer diagnosis and prognosis. However, tissue biopsy is highly invasive for most primary tumors and metastatic diseases, especially brain cancer, lung cancer, and ovarian cancer, which require difficult surgeries. The obtained tissue quality and quantity highly determine the diagnostic precision at the molecular level, including mutation characterization. Tumor tissues are heterogeneous and evolve over time. Sampling of entire tissue with dynamic representatives is not possible. Therefore, assessment of the molecular makeup of tumors from a biofluid sample is of great research interest.
Recent research of extracellular vesicles (EVs) and exosomes has revealed that early-stage tumors constitutively release vesicles carrying various tumor markers. Exosomes, which are membrane vesicles of endocytic origin, are systemically detectable in the blood of various cancer patients and have been shown to correlate well with tumor progression, immune response suppression, angiogenesis, and metastasis. Exosomes are stable carriers of enriched genetic material and proteins from their cell of origin, thereby holding great promise for identifying early-stage tumors. Compared to well-studied circulating tumor cells (1–10 circulating tumor cells [CTCs]/mL of blood), exosome release from tumor cells is an active process with concentrations of ≥109 vesicles/mL in blood. Exosomes sensitively reflect tumor status; therefore, substantial investigations have focused on the essential physiologic and pathophysiologic functions of circulating exosomes as a surrogate for tumor liquid biopsy.
Microfluidic lab-on-a-chip technology has recently been spotlighted as a promising approach for exosome isolation and molecular analysis, owing to its low-volume consumption, high capability of functional module integration, quick analysis time, and high sensitivity, as well as a sample-to-answer format.Several microfluidic approaches, such as isolation, quantification, and molecular profiling, have been previously developed for exosome study.
Microfluidic analysis of exosomal protein markers for liquid biopsy of cancer
(a) Polydimethylsiloxane chip containing a microchannel network for cascading exosome analysis. (b) Integration of streamlined on-chip immunomagnetic isolation of exosomes, chemical lysis, and intravesicular protein analysis. (c) Setup of ExoSearch chip for continuous mixing, isolation, enrichment, and multimarker probing of circulating exosomes. (d) Expression level and ROC analysis (e,f) of three tumor markers (CA125, p < 10–4; EpCAM, p = 0.0009; CD24, p = 0.003) from blood plasma–derived exosomes (nOvCa = 15, nhealthy = 5) using ExoSearch chip, compared to standard Bradford assay and NTA analysis of ultracentrifugation-purified exosomes from matched human subjects. Ovarian cancer patients are represented by red dots, and healthy controls are represented by blue dots. (Figures are adapted with permission from the Royal Society of Chemistry.)