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Anal Chem. 2017 Mar 7;89(5):3184-3190. doi: 10.1021/acs.analchem.6b05037. Epub 2017 Feb 10.

Concentration-Normalized Electroanalytical Assaying of Exosomal Markers.

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Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QZ, United Kingdom.
Nuffield Department of Clinical Neurosciences, University of Oxford , John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.


Exosomes are both active in mediating intracellular communication and potentially present a potent cargo of disease biomarkers to an assay. The robust evaluation of exosomal markers could lead to a paradigm shift in clinical analysis and associated care. To date, much of this has been hindered by issues of sample preparation and assay signal-to-noise. We introduce here the use of ultrasensitive electrochemical impedance spectroscopy to quantify both external (tetraspanin) and internal (syntenin) exosome-specific markers. Associated exosome detection limits are 1.9 × 105 particles mL-1 (equivalent to 320 aM or 9500 exosomes in 50 μL) for intact exosomes and 3-5 picomolar for internal exosomal syntenin levels with almost 5 decades of linear dynamic range. Sample preparation can be carried out by simple fine filtering of cell-conditioned medium prior to a non-NTA-determined (i.e., nanoparticle tracking analysis) exosome concentration analysis, lysing, and subsequent internal syntenin quantification. Such concentration-normalized dual-marker analysis can be used to define "analytical zones" in a manner which is then independent of absolute exosome concentration and sample preparation.

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