Optical microscopic and spectroscopic detection of exosomes

Exosomes are extracellular vesicles with a diameter of 30–150 nm, they can reflect the biological information of their parent cells and participate in intercellular communication. Exosomes have become one of the most promising markers for the early diagnosis and prognosis of cancers. With the development of modern optical technology and the emergence of high resolution optical microscopies, the micro/nanostructures of exosomes that have never been observed optically before can be observed now. In this review, we systematically introduce the optical techniques for the imaging and detection of exosomes up to date, including dark field microscopy, surface plasmon resonance, interference reflectance and interference plasmonic, fluorescence, surface enhanced Raman scattering, optical super resolution imaging, mass spectrometry, etc. We demonstrate the working principles, analysis performances, advantages and limitations of each detection technique through some typical examples. Furthermore, the challenges and opportunities of exosomes detection are also discussed in this review.