The selective and tunable transport of biomolecules is crucial to the function of biological cells. The modular design and rich functionalities of colloidal nanoparticles allow them to serve in a variety of systems, including as biomolecule-mimics. However, we still largely lack the ability to actively and specifically transport nanoparticles, relying instead on diffusion or bulk fluid flows. Biological systems often use the non-equilibrium <i>ratchet</i> transport mechanism, which eschews overall gradients in favor of local asymmetries, and rectifies non-directional forces such as chemical energy and Brownian motion. Common examples include the myosin-actin system responsible for muscle contraction, and the kinesin molecular transporter. The sensitive and selective properties of ratchets have proven a fascinating topic of study, both as model dynamic steady-state systems, and for their potential applications in microfluidics and energy devices. We have extensively explored ratchets transporting electrons and nanoparticles, using a combined theoretical-experimental approach. In this talk, I will discuss our theoretical studies of nanoparticle ratchets. We utilized a classical, particle-based approach to simulate the motion of electrostatically-charged colloidal nanoparticles under the influence of time-oscillating and spatially-varying electric fields. I will show how cooperative mechanisms of motion emerge from interparticle interactions, and how increasing the dimensionality of a ratchet drastically changes the observed behaviors.

Transporting colloidal nanoparticles using symmetry-breaking ratchets

ACS Spring Meeting 2021

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