Flows of molecules at the nanometers scale play an important role in many biological, chemical and physical systems and have important applications in the near future. Nanofluidics is a very active topic of research and attracts different fields from biology, physics, chemistry to engineering.

Ions and macromolecules are transported across lipid membranes by highly selective nanoscale protein channels. The study of these processes and their imitation in artificial structures, fabricated by chemical synthesis or micro-fabrication, offers many opportunities for applications in ultrasensitive detection of molecules : rapid sequencing of DNA or RNA, studies of conformation (secondary structure of RNA, protein folding), or molecular interaction between proteins or between proteins and nucleic acids. The integration of channels and pores in the nanometer micro-fluidic devices or on deposited lipid bilayers on solid surfaces leads to the creation of new bio-sensors.

Furthermore, nanoscale channels, such as nanoslits or individual nanotubes offer the possibility to explore new phenomena appearing for molecular flows confined in nanometers scales. New transport behavior and functionalities can be developed by taking benefit of the specific couplings occurring at these scales (electrostatic, surface properties, ….). Applications are numerous in the domains of desalination, ultra-filtration, energy harvesting.

The highly intrincated nature of the interactions in nanochannels is a major challenge in order to rationalize and simulate transport in nanofluidic systems. The emerging consensus in the field is that a synergy between computational, theoretical, and new experimental approaches is required in the next few years.

This proposal follows the discussion meeting organized in Institut Henry Poincaré in May 2013 in the framework of the CFCAM node. A large part of the proposed participants were already attending to this meeting and have wished to be part of a CECAM workshop on the same thematics but with a larger scope in physics and biology.

The studies of these transport phenomena at the molecular scales are notoriously difficult and this was a real revolution when J. Kasianowicz, E. Brandin, D. Branton and D. Deamer [1] with G. Church and R. Baldarelli showed that one may observe directly - by a very simple electrical method - the passage of one single strand DNA or RNA molecule through a protein pore inserted in a bilayer lipid membrane.
This electrical method of detection is the same as the one used in the “Coulter counter” at a more macroscopic scale. In the biological context of the study of membrane proteins, it is quite close to the “patch-clamp” and “black lipid membrane” electrophysiological techniques [2].

Since this works, numerous teams in the world started to explore theoretically and experimentally [2,3] the numerous applications of the transport of molecules in nanopores. It concerns the ultrafast sequencing of DNA and RNA , the manipulation of biological macromolecules, the development of chemical and biological sensors, fundamental studies of confined polymer chains, … In parallel, this raised a strong interest to explore the new behaviour of fluids and ions in such nanoscale pores.

On the experimental side, advancing our fundamental understanding of fluid and molecule transport on the smallest scales requires fluid and molecular dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores. A major challenge for nanofluidics thus lies in building distinct and well-controlled nanochannels, amenable to the systematic exploration of their properties. There has been accordingly a intense effort to build new natural or artificial channels made either by transforming cyclic molecules, or based on the development of nanofabrication and heavy ions track etch techniques, such as focused ion beam [4] and electron beam. Furthermore channels made of individual carbon or boron-nitride nanotubes [4] were developed using nano-assembly techniques using nanotubes as nanoscale building blocks.

Nevertheless, many challenges are still ahead in this field. First, the fundamental physics of the transport in nanochannels are still poorly understood (force control during macromolecule translocation, explored energetic landscape, new fluid properties, …). Then, the studied channels are seen as passive objects and the idea of active biomimetic systems used to produce controlled nano-object still has to be developed.