Thesis presented December 20, 2023

Abstract:
Over the past few years, nanoparticles have sparked a great interest in the biomedical field. Examples include lipid nanoparticles as drug delivery systems for targeted therapy or biological nanoparticles such as extracellular vesicles, which are released by all human cells. Extracellular vesicles have been shown to be involved in many physiological and pathological mechanisms, demonstrating their strong potential as new biomarkers for the early detection of a number of diseases using liquid biopsy. Precise characterization of such particles is of utmost importance, to ensure quality control of samples dedicated to clinical use, or simply to characterize their biophysical properties (size, density, stiffness, etc.). However, due to their nanometric size and their potential heterogeneity, standard methods are usually not sufficient to characterize properly such particles. Over the past few years, MEMS technologies such as Suspended Microchannel Resonators (SMR) have already proven their potential to characterize precisely microparticles, at a single cell level. Such sensors are composed of a hollow microcantilever beam containing a buried nanofluidic channel, suspended in a vacuum cavity. This configuration allows the fluid to be confined inside the resonator, thus maintaining its mechanical properties and low damping in its environment. As an individual nanoparticle flows through the channel, it induces a transient shift in resonance frequency, which is directly proportional to its buoyant mass. Using fabrication methods derived from microelectronics, microscale dimensions of SMR sensors allows them to weigh single cells or bacteria with a resolution of 1 fg (10^-15 g).
The aim of this work is to use a miniaturized version of this technology, called SNR (Suspended Nanochannel Resonators), and to implement it to characterize lipid nanoparticles. Due to the reduced dimensions, it becomes possible to weigh single particles at the attogram scale (10^-18 g), such as 10-15 nm diameter gold nanoparticles. First, a test bench has been developed to conduct gold nanoparticle characterizations using this type of sensors. Then, this method has been challenged to weigh nanoparticles of biological origin, for which an efficient and robust passivation strategy is crucial to prevent non-specific adsorption of the sample to the channel walls. On the other hand, a new type of microfluidic architecture has been explored, containing two cantilevers connected in series, to measure the density of nanoparticles. Lastly, the test bench has been adapted to integrate and characterize miniaturized sensors, showing signs of enhanced sensitivity and a reduced limit of detection. In the future, the building blocks developed during this work could lead to a label-free, multiparametric characterization platform (mass, size, density, stiffness), using this unique technology to perform quality control measurements for bioproduction applications, to provide diagnostic or prognostic information, or to better understand physiological and pathological processes involving extracellular vesicles.

Keywords:
NEMS, Microfluidics, Extracellular Vesicles​