Size and surface charge characterization of nanoparticles with a salt gradient

TLDR

Exosomes are nanometer‑sized lipid vesicles used as biomarkers for diseases such as cancer and Alzheimer’s, yet their purification and size and surface charge characterization remain time‑consuming and lack a single‑step measurement. This study aims to concentrate exosomes from dilute solutions and determine their size and zeta potential in a single measurement using a salt‑gradient capillary system. The salt gradient drives opposite particle and fluid transport that traps exosomes, and fitting their spatial distribution in a low‑cost polymer capillary yields both size and surface charge. The technique increases exosome concentration by more than two orders of magnitude within minutes and is also applicable to other nanoparticle types.

Abstract

Abstract Exosomes are nanometer-sized lipid vesicles present in liquid biopsies and used as biomarkers for several diseases including cancer, Alzheimer’s, and central nervous system diseases. Purification and subsequent size and surface characterization are essential to exosome-based diagnostics. Sample purification is, however, time consuming and potentially damaging, and no current method gives the size and zeta potential from a single measurement. Here, we concentrate exosomes from a dilute solution and measure their size and zeta potential in a one-step measurement with a salt gradient in a capillary channel. The salt gradient causes oppositely directed particle and fluid transport that trap particles. Within minutes, the particle concentration increases more than two orders of magnitude. A fit to the spatial distribution of a single or an ensemble of exosomes returns both their size and surface charge. Our method is applicable for other types of nanoparticles. The capillary is fabricated in a low-cost polymer device.