Capture, characterization and reactions of nanoparticles in a diffusiophoretic trap

Martin Kjærulf Rasmussen

Research output: Book/ReportPh.D. thesis

Abstract

Nanometer-sized biocolloids including synthetic liposomes and naturally occurring exosomes are promising for drug delivery in cancer treatment and as biomarkers for early stage diagnosis of cancer, respectively. Purification and subsequent particle characterization are essential for exosome-based diagnostics. However, purification is time consuming and can damage the sample while characterization often requires several independent experiments.
Size and zeta potential are two important parameters as they affect the interaction between the nanoparticles and cells, and they are therefore crucial in the design process of liposomes as drug delivery vehicles. To increase the lifetime and target specificity, the surface of liposomes designed for drug delivery are often modified with macromolecules, but the funtionalization efficiency is challenging to evaluate. In this thesis, a diffusiophoretic trap is developed to capture, concentrate and characterize nanoparticles in a nanochannel using a salinity gradient. The diffusiophoretic trap is based on balancing the oppositely directed diffusiophoretic particle transport and diffusioosmotic fluid transport arising in a nanochannel due to a salinity gradient. A model is developed to extract the nanoparticles' diameter and zeta potential related to the surface charge from a single measurement of the nanoparticles spatial distribution in the diffusiophoretic trap. The trap is demonstrated as a size and zeta potential sensor on liposomes and exosomes. The obtained particle parameters are consistent with values measured using established methods such as Dynamic Light Scattering and Laser Doppler Electrophoresis and the diffusiophoretic trap can even resolve samples too heterogeneous for these standard methods. The trapping and characterization is tuned to occur at physiological salinity conditions and are demonstrated to yield consistent results for measurements at different salinity gradients. The analysis is demonstrated to be able to characterize both ensembles and individual nanoparticles. Exosome and liposome concentrations in the trap are shown to increase ∼ 400 times the samples initial concentration in 90 s. As the trapping position in the nanochannel depends on the particle's zeta potential, subpopulations with different zeta potentials can be separated and analyzed in the trap. This is demonstrated with a liposome population containing two subpopulations of liposomes with different lipid compositions.
The trapping position's zeta potential dependence and the ability to introduce reactants while maintaining the trap is leveraged to develop a label-free method for monitoring ligand binding to macromolecules on the surface of nanoparticles. As charged ligands binds to the receptors the liposome shift position in the trap, and hence the reaction can be monitored. This method is demonstrated on liposomes decorated with DNA probes which hybridize with DNA targets introduced into the nanochannel. This use has potential for analysis of surface functionalization efficiency or for biorecognition of macromolecules and biomarkers such as proteins, peptides and antigens on exosomes. The trap is demonstrated as a biorecognition sensor by detecting biotin on the surface of exosomes through binding of streptavidin protein in the trap. The diffusiophoretic trap is shown to have a sensitivity to changes in total particle surface charge down to 1:5%. The diffusiophoretic trap is finally demonstrated for monitoring particle-particle interaction in the form of DNA induced liposome fusion. Here the particles in the trap are monitored during the reaction without the need to immobilize them on a surface. The trap concentrates the particle and thereby increase the reaction speeds. The reaction rates in the trap are then measured for liposomes with different surface parameters.
Original languageEnglish
PublisherDTU Health Technology
Number of pages129
Publication statusPublished - 2020

Fingerprint

Dive into the research topics of 'Capture, characterization and reactions of nanoparticles in a diffusiophoretic trap'. Together they form a unique fingerprint.

Cite this