MolecularControl has addressed several soft matter contexts and probed the mechanisms for particle transport at small scales in diverse environments. These include transport in nanopores or nanochannels (Part 1) as well as the transport of complex small particles with multivalent ligand-receptors (Part 2).
Part 1 - Transport in nanopores
Fluctuations are ubiquitous in bio and artificial nanopores, and dramatically impact transport since the surface-to-volume ratio is exacerbated in small pores. Most of the time, fluctuations are seen as a negative feature that impedes for example signal measurements. Furthermore, fluctuations have entangled consequences, as they affect all dynamics and dynamics are not necessarily linear. Yet, biological pores (such as ion channels that serve as chemical pathways between cells) are still able to achieve complex tasks, including precise and rapid selection of particles, in spite of fluctuations.
To investigate the riddle of fluctuations in nanopore transport, we explored how fluctuations in the number of particles present within the pore affect signal measurements, and have published several original research articles on the subject.
Beyond number fluctuations, transport of ions and particles in small pores is strongly affected by hydrodynamic and electrokinetic effects, as we have further demonstrated.
Collaborating with researchers in Europe and at NYU, a methodological review was written to disseminate and communicate about modern tools and methods to account for such effects in small pores.
Part 2 - Transport of particles with sticky feet or multivalent ligand-receptors.
Particles with sticky feet - or nanoscale caterpillars - in biological or artificial systems, beat the paradigm of standard diffusion to achieve complex functions. Some cells (like leucocytes) use ligand-receptor contacts (sticky feet) to crawl and roll along vessels. Numerous viruses utilize proteins to stick and roll and crawl on mucus proteins before invading their host. Sticky DNA (another type of sticky feet) is coated on colloids to design programmable interactions and self-assembly.
We have rationalized what parameters control average feet attachment in a model system and how they can be compared to other existing systems, using modeling approaches and experiments.
We have investigated furthermore how various motion modes of such particles (sliding or hopping) may be favored over one another, especially depending on the number of feet attached. This was done building an advanced yet completely analytically solvable modeling approach, that showed predictive capabilities. After a series of experiments we were able to demonstrate these different motion modes on a model experimental system and showed how they depend on several parameters such as temperature.
Finally we have identified that such particles may diffuse with a diffusion coefficient that depends on their mass: this breaks the common physical paradigm where inertial effects do not arise in the diffusion of small scale systems.
All results have been published as green or gold open access publications, as well as open access codes; and have been broadly disseminated at multiple scales, in conferences, seminars, meetings and social media.
