Extracellular vesicles including exosomes have the potential to be used in therapeutic and diagnostic applications. Towards the noninvasive diagnosis of prostate cancer using urinary exosomes, technical challenges lie in developing precise methods of analyzing exosomes. Previously, we developed an on-chip microcapillary electrophoresis (µCE) system equipped with a laser dark-field microscope. The zeta potential of exosomes of cancer cells was found to be larger than that of normal cells. In this study, the zeta potential of exosomes of normal and cancer prostate cells was evaluated using this system after treating with sialidase. The large negative charge of cancer exosomes was found to be due to the large amount of sialic acids. These results suggest that an on-chip µCE system is useful for the accurate evaluation of events that occur on the exosome surfaces at the single-particle level and promising for the prescreening of prostate cancer exosomes without the need for labeling.

Cell-secreted nanovesicles called exosomes are expected as a promising candidate biomarker of various diseases. Toward the future application of exosomes as a disease biomarker for low-invasive diagnostics, challenges remain in the development of sensitive and precise analysis methods for exosomes. In this study, we performed the electrokinetic evaluation of individual exosomes by the combined use of on-chip microcapillary electrophoresis and laser dark-field microscopy. We extracted exosomes from six types of human cell cultured in a serum-free medium by differential ultracentrifugation and their zeta potential (electrophoretic mobility) were evaluated. We demonstrated that the proposed electrophoresis apparatus is particularly suitable for the tracking analysis of the electrophoretic migration of individual exosomes and enables the accurate evaluation of the zeta potential distribution of exosomes, for the first time. From the experimental results, we found that there is a strong correlation between the average zeta potentials of exosomes and their cells of origin.

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A microfluidic-chip-based analysis platform specially tuned for characterizing individual nanobio-particles has been developed. Using this platform, both artificial nanobioparticles (polyion complex vesicles) and cell-secreted exosomes with diameter down to 50 nm can be observed. The zeta potential distribution of the exosomes was obtained by measuring the zeta potential of individual exosomes. Since the number of surface molecules on nanobioparticles can be estimated by applying a particle immunoelectrophoresis method, this platform is promising for obtaining profiles of heterogeneous nanobioparticles including nanoDDS carriers and exosomes.