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Exosomes are a subset of extracellular vesicles that play critical roles in normal and disease physiology. Their roles are currently the subject of intense interest; however, their small size (typically less than 150 nm in diameter) makes them challenging to study. Thus, improved methods for sensing, isolating, and analyzing exosomes and, more broadly, extracellular vesicles are badly needed. Zhang et al. have developed a device for extremely sensitive detection of exosomes, enabling the detection of as few as ten exosomes per microliter. Their microfluidic device uses three-dimensional herringbone nanopatterns, which promote exosome–surface interactions for improved binding. They used their device to study exosomes from people with ovarian cancer and from healthy controls. Their results identified a potential biomarker for early detection of ovarian cancer and highlight the benefits of such a sensitive platform.