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Nanotechnology-based quantifications of nanoparticles from human cerebrospinal fluid: comparison of Atomic Force Microscopy and Tunable Resistive Pulse Sensing

Nanoparticles are natural components of body fluids and include diverse nanosized structures produced by various tissues and secreted for different purposes. Extracellular vesicles (EVs) are currently the most intensively studied type of nanoparticles because of their potential usage as diagnostic and prognostic markers. Namely, EVs are secreted by practically all cells and their molecular composition reflects the type and state of originating cells. However, research of EVs is hampered due to lacking methods for precise and reliable quantification. The goal of our study was to improve EV size measurement in their natural environment by applying novel technologies able to measure individual nanoparticles directly and in liquid phase. Such quantification is obtained by Tunable Resistive Pulse Sensing (TRPS) and Atomic Force Microscopy (AFM). We determined the size and concentration of EVs in cerebrospinal fluid (CSF) from patients with severe traumatic brain injury (TBI), a condition in which EVs have been previously described to change their physical properties. TRPS measurements of the CSF sample showed a mean EV diameter of 61.5 nm ± 22.8 nm and an EV concentration of 1.31 x 109 particles/ml. The same CSF sample was used for the AFM measurement for which we introduced a novel protocol in tapping mode to obtain images in a liquid environment. Particle diameter distribution was calculated from a 1.5 x 5 µm image containing 100 nanoparticles, resulting in a mean diameter of 66.7 nm ± 21.9 nm. However, no EV concentration was determined by AFM since the detected signal does not include volume measurement. Thus, the current AFM technology is not suitable to measure EV concentration. Overall, our results show that both AFM and TRPS nanotechnologies provide comparable EV diameter measurements. Yet, TRPS brings a clear advantage in a more reliable measurement of EV concentration. This research will further contribute to the characterization of quantitative changes of nanoparticles in biofluids.

extracellular vesicles (EVs) ; traumatic brain injury (TBI) ; cerebrospinal fluid (CSF) ; Atomic Force Microscopy (AFM) ; Tunable Resistive Pulse Sensing (TRPS)

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