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Abstract

The diffusion of nanoparticles can be used to determine the structure of complex media, or as a probe to detect binding of an analyte. Two methods of diffusion measurements are presented to investigate nanoparticle diffusion mechanisms in different environments. One is used to detect the presence of DNA biomarkers, which is important for medical diagnosis. A biomarker can connect two DNA origami structures, causing a decrease in the diffusion coefficient of the origami structure, which is a means to detect the biomarker. Measurements at picomolar concentration by Fluorescence Nanoparticle Tracking Ana\-ly\-sis are shown to detect a random DNA sequence and a characteristic sequence of an antibiotic resistance gene within a few minutes. The method shows that diffusion can be a tool for detecting DNA and suggests an application in the sensing of biologically relevant analytes. Further, Pulsed Field Gradient Nuclear Magnetic Resonance of liquid core particles enables direct, label-free diffusion measurements, even in complex or optically opaque media. It is shown that this permits the mesh size of a hydrogel to be probed, suggesting that this method may be used to characterize the microstructure of living tissue and other biologically relevant media.