Transport in solution at the nanoscale is of crucial interest for biology or energy conversion. The dynamics of single objects flowing in a liquid, and fluid transport properties are intimately related. Dynamics is mostly associated to the behavior of single object, whereas transport refers to the massive or global dynamics of a set of individuals. The gap in between these two views is very thin, as a global transport can be understood under a scale transformation of the behavior of one s! ingle component. This statement constitutes the basis of modern condensed matter physics. In this work we considered the behavior of individual diluted objects transported in solution from two vantages. First the dynamics of single "perfect" objects were investigated toward the characterization of micro-environments. Then, in a second time, we investigated the dynamics of single objects under-controlled environment aiming at elucidating the physical laws describing their behavior. We developed a new method for characterizing sub-micron confined flows. We derived a theoretical model based on nanospheres velocity probability density. This model was validated using in-house Brownian dynamics simulations of particles flowing in laminar Poiseuille flows. These numerical and analytical approaches were confronted to experiments of single nanospheres conveyed in pressure-driven flows in nanofluidic devices. We detected giant lift force, leading to cross-streamline migration away from the wall even at vanishing Reynolds number. These forces are not described in the literature, leading us to characterize their physical properties. We then switched to the study of dynamical properties of DNA molecules in solution in confined environment under an hybrid actuation involving hydrodynamics and electrokinetics. The use of a non-newtonian buffer solution led to observe a non-linear combination of the actuations. Experimental strategies were then developed to map the inhomogeneous transverse probability of density of molecules inside the channels. This specific phenomenon allow for the design of a new way of resolving biomolecules by size in free solution. Overall, this experimental work at the nexus of fluid physics, micro-fabrication engineering and statistical physics, allowed us for the design of a new nano-velocimetry, and other experimental methods which help us decipher transverse migration of diluted solid and flexible objects in solution. Furthermore, hybrid mode actuation of DNA in non-Newtonian fluids led us to design of new way of separating biomolecules by size. We think that this work is a leap forward for an easy characterization of nanoflows and particle transports at the nanoscale.
