Quantum sensors harness the high sensitivity of quantum systems to external perturbations to accurately measure various physical quantities. Among the quantum systems employed for sensing purposes, the nitrogen-vacancy (NV) defect in diamond has garnered considerable attention as a magnetometer and opened new perspectives in nanomagnetism imaging after its integration as a sensor to scanning probe microscopy. However, the use of NV centers is not limited to magnetometry, as they are also sensitive to electric field. The aim of the project QUAMION is to evidence the relevance of scanning NV center electrometry as a tool for imaging ferroelectric order, with the asset of being quantitative and non-perturbative. In order to reach the needed sensitivity, I will rely on spin echo sequences synchronised with the local probe's movement, which also allows static parasitic fields to be ignored. Furthermore, I will demonstrate the possibility of combining magnetic and electric field sensing in a joined measurement. I will achieve this by adjusting the direction of a external bias magnetic field, which switches the sensitivity of the NV center between magnetic and electric fields. Such a multifunctional scanning microscope will provide a unique solution to probe coexisting and interacting orders, which I will show by mapping together the magnetic and electric components of multiferroic textures. The project QUAMION will thus establish quantum sensing with NV centers as a key technique to address emerging topics like multiferroic topological textures or the exploration of 2D multiferroic materials.

Novel analysis techniques are actively sought to hold the promise of personalized DNA sequencing and high-throughput screening of proteins at affordable cost and viable time. Among those, nanopore sensing of single biomolecules represents a path-breaking technology because it represents a label-free and amplification-free approach that is scalable for high-throughput analysis. Most research to date has focused on biological nanopores and on nanoperforations drilled in thin solid-state membranes. These nanopores yielded many remarkable results but also have important limitations such as the difficulty to engineer them with atomic scale precision. Sequencing systems based on such nanopores are announced for commercialization in 2013 once their error rate has been lowered to acceptable values. However, it is unlikely that a single type of nanopore will fulfil the requirements for all the applications envisioned for nanopore sensing; different types of nanopores will be required for different types of applications. Actually, synthetic nanochannels having a versatile and perfectly-defined atomic structure do exist in the form of single-walled carbon nanotubes (SWNTs). Our previous works notably established methods to prepare long and individual SWNTs, characterize their atomic structures by optical spectroscopy and integrate them in functional devices. This project aims at exploring the potential of SWNTs for nanopore sensing, as an alternative to the short biochannels and nano-perforations essentially used so far. Specifically, we will investigate the aptitude of SWNT devices for discriminating single small biomolecules, using nucleotides and amino acids as model compounds. To do so, we will fabricate microfluidic devices integrating individual SWNTs previously identified by Raman spectroscopy. We will perform patch-clamp-type experiments to investigate and rationalize the parameter dependence of the ionic conductance in SWNT channels. We will investigate the electrophoretic translocation of nucleotides and amino acids in individual SWNTs and evaluate the identification accuracy relying on both the conductance drop and dwell time of the current blocking events. This research is expected to result in an improved understanding of molecular transport in nanochannels and in the development of an accurate identification method of single small biomolecules. Such a method is expected to be extremely valuable for both basic biological research and bioanalytical applications.

Efficient coupling between electronic and biological systems requires an interface for converting electronic signals into ionic (or chemical) signals, and vice versa, ideally with high sensitivity and speed. Unfortunately, the performances and functionalities of present electro-ionic devices poorly compare with those of their electronic and biological counterparts (e.g. transistors and synapses). Emerging fields such as iontronics, bioelectronics, or bioprotonics aim at developing a sophisticated control and sensing of the motion of ions and molecules to record and modulate biological processes, or to perform logic operations mimicking the functioning of the brain. Our project aims at exploring the potential of single-walled carbon nanotubes (SWCNTs) for 1) actively controlling and sensing the motion of ions by an unprecedently large coupling between ions (in the channel) and electrons (in the channel wall) and 2) investigating the new transport phenomena specific to the subcontinuum regime such as ionic capillary evaporation (ICE) and ionic Coulomb blockades (ICBs). Our project gathers experts with strong and complementary skills covering all project needs: SWCNT growth and characterization, fabrication and study of SWCNT-based nanofluidic and FET devices, theoretical modelling and numerical simulations of ion transport in nanochannels. All the partners have successfully collaborated in the past, notably in the frame of the ANR TRANSION project (2012-2016). METHODOLOGY. To address the objectives of the project, our methodology combines: 1) Two types of electro-nanofluidic devices allowing ion and electron transport through a single SWCNT or several SWCNTs in parallel (planar devices for their robustness, thin membranes devices for studying short SWCNTs); 2) Molecular dynamics simulations of ionic transport as a function of the surface charge and edge functions optimized using quantum calculations ; 3) Theoretical modeling (both numerical and analytical) using a variational field-theoretic approach to compute the ionic concentration and the ionic transport. PROGRAM. First, we will control the chemical moieties at tube ends to optimize their selectivity for specific types of ions (objective 1). To do so, we will i) measure ion transport through SWCNT with controlled edge functions, ii) simulate ion transport through SWCNTs with specific edge functionalization, and iii) develop theoretical models of energy-barrier regulation for reproducing the experimental features. Second, we will actively control the electronic charge of a metallic SWCNT and study the effect on the transport of ions through its inner channel (objective 2). With an application focus, we will study the performances (gating response and speed) of this ultimate ionic transistor whose ionic channel is optimally coupled to an all-around electronic gate. In experiments and simulations, we will look for i) stochastic fluctuations of conductance to evidence ICE, and for ii) periodic oscillations of conductance, the expected signature of ICBs. Third, we will investigate the ion species and surface charges in the inner channel of a semiconducting SWCNT by using it as a sensitive electronic FET sensor (objective 3). To strongly enhance the detection range and sensitivity, we will test gating methods known for their higher efficiency (solid top-gate and liquid electrolyte gate) and model the coupling between the ions inside the SWCNT and an outer electrolyte.

The general character of dynamic transitions of colloids have attracted the attention of a vast part of the soft matter community, since achieving the on-the-fly control of colloidal states, from solid to liquid and vice versa, is a possible path towards “smart” materials with switchable properties.In this context, the “contamination” of colloidal suspensions with smaller particles or polymers has been one of the most adopted strategies to tune colloidal dynamics and explore the possibility to tailor new materials. However, despite their importance to understand the fundamental behavior of soft matter, all model systems (like model hard spheres) employed up to now to investigate such transitions are quite uncommon in nature, since they disregard the effect of charges on both colloids and (non-adsorbing) “contaminants”. Indeed, all colloids and polymers dissolved in polar solvents, such as water, very often bear ionizable groups. In aqueous solutions, for example, polyelectrolytes (PE) and oppositely charged colloids, due to electrostatic interactions, self-assemble into complex aggregates. Although PE-colloid complexation has been observed in a variety of mixtures under different conditions, in all reported studies the surface charge density of the colloids was fixed, or, at least, it could not be changed without changing the chemistry of the suspending medium, limiting to a large extent the on-the-fly control of PE adsorption. Recently, I and my coworkers [Soft Matter 14, 4110 (2018)] have shown that ionic colloids with stimuli-responsive charge density, like PniPam microgels, give the opportunity to tune finely the adsorption of oppositely charged species simply by modulating the stimulus concerned, i.e. temperature. This opens a new route to trigger PE or nanoparticle (NP) adsorption onto microscopic soft substrates, to tailor the structure and the dynamics of soft binary ionic mixtures and to remove ionic contaminants in a controlled manner. These issues represent the core of THELECTRA. In particular, this action aims at investigating how electrostatic adsorption of charged polyelectrolytes (PE) affects the structure and the rheology of oppositely charged ionic microgel suspensions, and to use the latter as eco-friendly adsorbent flocculants, i.e. as systems capable to adsorb physically a wide class of ionic wastes. I will investigate for the first time the state diagram of PE-microgel complexes in terms of rheology and microscopic dynamics, by doping dense and dilute microgel suspensions with model nano-contaminants (PE). We will use a set of complementary experimental techniques, including a unique rheo-light scattering setup, to determine the microscopic dynamics of PE-microgel complexes formed at high concentrations, both at rest and under large shear deformations. This will allow measuring the rheological response and the microscopic dynamics of concentrated suspensions at different PE concentrations and across fluid-solid transitions. A quantitative comparison between the microscopic dynamics (e.g. mean square displacement and dynamic structure factor) and macroscopic mechanical properties (e.g. elastic and viscous moduli) of microgel-PE suspensions will be performed. This will elucidate the microscopic origin of their rheological properties, including yielding, ageing and possibly thixiotropy. Such a fundamental understanding will be utilized to provide a robust proof of concept for a fully functioning water treatment cell for grey water purification. Taking advantage of the thermosensitive charge density of microgels, waste encapsulation at high temperature (T>33°C) results in the formation of reversible large aggregates that are easily filtered, while microgels can be recycled for successive remediation cycles. THELECTRA is the first attempt to use PniPam microgels for wastewater remediation on their own (i.e. when they are not involved in a composite material) by exploiting their electrostatic properties.

Motivated by recent and engaging results showing the fundamental role of chirality in the dynamic of soft matter systems and the technological need of the pharmaceutical industry for chiral differentiation, the CHIRALGHOST research project proposes to examine new possibilities of achieving the separation of enantiomeric entities of various sizes using chiral soft matter systems. The primary objective of this project is to design and implement new experimental systems and theoretical models, based on confined chiral liquid crystals, allowing to specifically determine how the chirality of a fluctuating host environment interacts with the structural chirality of guest objects at the molecular and mesoscopic scales when these objects diffuse or are dragged. More specifically, the possibility of dynamically separating enantiomeric chiral guest molecules diffusing in a confined chiral liquid crystal host will be examined by using specifically designed chiral fluorescent molecules and a combination of fluorescence and light scattering microscopy observations. Moreover, the diffusive and dynamical properties of colloidal particles with a chiral shape and more complex patterns localized in the orientational field of the CLC molecules will be experimentally characterised and quantitatively described in the same confined chiral liquid crystal systems. With a unique combination of experimental and theoretical approaches unlocked by recent advances made by the main coordinator, the CHIRALGHOST project will generate new knowledge regarding multiscale chiral interactions in soft condensed matter. A comprehensive description of chirality-tuned diffusive phenomena in liquid crystals will be established, with a direct impact on the understanding of more complex phenomena such as the self-assembly of chiral objects in complex chiral environments.