Since the beginning of the project, manifold tasks towards the development of active nanofluidics have been accomplished. However, several key milestones have been already achieved:
(1) First, we have developed a detailed understanding of the ionic Coulomb blockade [Kavokine et al., Nature Nano 2019], showing that Coulomb blockade occurs in ionic systems due to a fractional Wien effect, associated with the dissociation of Bjerrum pairs with the gate charge. This mechanism leads unexpectedly to quantized ionic transport in a non-quantum system. Furthermore this active device paves the way to fabricate artificial ionic pumps.
(2) On the theoretical side, we made a breakthrough in the understanding of the ‘bizarre’ water-carbon interface. It emerges from our (and others) experimental reports in distinct systems that water behaves in a most peculiar way close to graphitic interfaces, with numerous examples showing how graphite ‘outperforms’, in some way or the other, alternative confining materials. We have demonstrated that these specific properties take their roots in quantum effects at the water carbon interface. This is a groundbreaking step and in the context of active nanofluidics, reveiling that a ‘quantum engineering’ of fluid and ion transport is possible. This paper was published in Nature in 2022.
(3) Second, a strong experimental effort has been achieved to develop active nanofluidic devices, in particular the so-called “Single Digit Nanopores” (SDN), with a size below 10nm, which have highlighted many peculiar transport properties. This relies on our expertize to fabricate 1D and 2D nano-assemblies. A key experimental result in both 1D and 2D SDNs is the demonstration of stimulated transport [Mouterde et al., Nature 2019; Marcotte et al., Nature Materials, 2020; Emmerich, Nature Materials 2022]. The ionic conduction is shown to be non-linearly modulated by the mechanical stimuli, here the applied pressure, akin a mechanical transistor. These responses echo directly the behaviour of some biological channels, which exhibit activated responses under various stimuli, such as the mechanosensitive channels such as Piezos, which are involved in touch sensing and in hearing.
(4) Then, we have thoroughly explored the non-linear ionic response in two dimensions - in direct line with the experimental systems – and we have unveiled a very specific Wien effect in the 2D ionic systems. A groundbreaking outcome in 2D is that the non-linear ionic transport results in memory dependent conduction, due to the slow time dynamics of the pairing. In other words, these 2D systems behave as memristors. Coupling two of these ionic 2D-memristors, in the spirit of Hodgkin-Huxley model of neuronal dynamics, we have shown that this nanofluidic device highlight autonomous spiking, in full analogy to real neurons. This serendipitous outcome is a quantum leap to develop artificial neural machines, in particular in view of the accessibility to fabricate such 2D systems in the lab. This paper was published in the review Science in 2021.
(5) Last, and a kind of climax of the project, a strong experimental effort has been achieved to explore these phenomena in experimental nanofluidic devices. We have extended our know-how to fabricate 2D systems and heterostructures, in the footsteps of recent advances achieved on 2D slits. A key experimental result is that we fully confirmed the predictions for the occurrence of ionic memristors in confined 2D systems. Going beyond, we showed that these systems allowed to perform Hebbian learning, just like biological synapses. This is the first ionic analogue of such an advanced functionality. This paper was published in the review Science in 2023.
Altogether this fully achieves the original goals of Shadoks: developing active nanofluidics to created biomimetic ionic machines mimicking their biological (in particular neuronal) counterparts.
Nanofluidics is an emerging field with high potential in terms of fundamental science, but also in terms of applications at the water-energy nexus.
In terms of dissemination, a series of lectures explaining the emerging field of nanofluidics and the molecular mechanics of fluids has been realized at College de France in 2023 (
https://www.college-de-france.fr/fr/agenda/cours/la-mecanique-moleculaire-des-fluides-un-champ-innovation-pour-eau-et-energie(opens in new window)).
