Introductory Remarks

Heterogeneity in size and function of intracellular organelles is intimately associated with dynamic cellular processes. Such processes include fusion, fission, biomolecular synthesis within the organelle, biomolecular transport, and degradation. Organelle morphology relates to the dysfunction of cellular processes such as organelle quality control, oxidative stress, decreased respiratory chain function in mitochondria, lipid storage, and programmed cell death, which are associated with diseases including Alzheimer’s disease, cardiovascular disease, diabetes, cancer, and aging among others. Organelle subpopulations thus play critical roles in the onset of disease and their recovery, extraction and purification from cells and tissue is imperative to unravel the underlying biological mechanisms related to size and function. Current methods to separate organelles can however not access subpopulations by size and in most cases, organelle recovery is scarce and impurities are common. Here, we present a novel ratchet-based separation method designed for the fractionation of sub-µm sized organelles. The migration mechanism requires tailored microenvironments as well as subtle tuning of electrokinetic and dielectrophoretic driving forces. To characterize the ratchet migration mechanism, we have thus developed a numerical model allowing to predict the regime of driving parameters under which it occurs. We demonstrate that the numerical model can be applied to hundreds of particles, allowing the study of the separation performance. Moreover, micrometer and sub-micrometer particles can be separated with baseline resolution in less than one minute. We further show that experimental observations match the numerical model in very good agreement for polystyrene particles and that mitochondria isolated from rat liver follow the predicted migration mechanism.