Small particles are prolific in many different areas of science and present technical challenges to characterize in solution. In particular, lipid particles such as lipoproteins, synaptic vesicles, and exosomes are of fundamental importance, both for biological function and their potential as biomarkers for disease. For example, lipoproteins vary in size, shape, lipid composition, and protein content and these heterogeneous properties cannot be distinguished by traditional bulk measurements which may average out crucial features. We have developed an experimental method to track individual lipid particles and measure their properties by confining them in an easily constructed confinement chamber (~100 nm thickness). The diffusion of the particles is used to determine their relative sizes and total bound protein content is quantified by fluorescence intensity. We have applied this technique to studies of lipoproteins and lipid vesicles. Using lipoproteins, which have well-defined size regimes, we have demonstrated that a lipid particle down to a radius of 5 nm can be tracked. Further, we have extended this method to study α-synuclein, a neuronal protein involved in Parkinson disease, and its membrane interactions at the single-vesicle level to understand the biophysical basis for curvature sensing by α-synuclein. We envisage this method will have broad applicability for the study of heterogeneous particles including colloids and nanomaterials.

Single-particle tracking of lipoproteins and lipid vesicles

251st National Meeting (2016)

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