Microalgae are sunlight-driven micro-organisms that convert carbon dioxide into valuable molecules of interest (i.e. lipids, proteins, carbohydrates and pigments) for a broad range of industrial applications such as energy, food, cosmetics and pharmaceuticals. They offer many advantages such as a rapid growth rate, a greenhouse gas fixation ability and high biomass and lipid productivities. Microalgae oil is therefore considered as a promising alternative energy source to fossil fuels. However, despite these advantages, several scientific, technological and economical bottlenecks remain in the different steps of the production, particularly in the culturing (growth and productivity) and downstreaming. Those must be overcome to envision the feasibility of large-scale production of algae-based biofuels. In the particular case of downstream processing (extraction and pretreatments), the very robust cell walls of microalgae influence significantly the efficiency. The development of alternative systems such as those based on microalgae-bacteria co-culturing techniques represent a great potential, with enhanced growth rates and lipid yield. Besides, we hypothesize a consequent effect on the cell wall structure and thus extraction efficiency. MicroPILOTING project deals with designing and developing a microfluidic platform to study the growth of bacteria and the growth and lipid productivity of microalgae in different co-culturing conditions. A predictive quantitative growth model involving iterative optimizations, will be established to investigate the mutual dependencies of the growth of microalgae and bacteria., via the production of CO2, O2 and vitamin B12. Such microfluidic tools combined with mathematical analysis, is very original, and will permit the determination of the best culturing and pretreatment conditions, thus improving the performance for conversion efficiency, and cost reduction for obtaining in-fine low-cost bioenergy carriers.

Understanding the stochastic dynamics of nanosystems is of significant interest since they lie at the heart of the dynamics of biological systems and is the cornerstone for nano-heat-engine development. In particular, an important effort has been devoted to the development of optimal protocols for thermodynamics state to state transformations. However, the experimental implementation of such protocols for general damping case, as well as there robustness to system imperfections have been mostly ignored. The OPLA project aimed at benefiting from the unique versatility of optical levitation of particle in vacuum to address these questions. It also proposes an approach for experimental determination of optimal protocols in the case of arbitrary complex transformations. These developments pave the way, among others, to the development of nano-heat engines and efficient simulated annealing protocols, and more generally to improve our understanding of out-of-equilibrium nano-thermodynamics.

Many molecules of interest, such as DNA and proteins, show no absorption in the visible range, but have strong absorption and high refractive indices in the UV range. One of the main goals of UV plasmonics is to detect the adsorption of these molecules on a metal nanostructure, with a higher sensitivity than that obtained in the visible range. Studies in the literature are still limited to isolated nanoparticles (NPs) and in the visible spectrum. It is promising to assemble the NPs in order to shift the plasmonic resonance, change their vibrational modes and improve their sensitivity. In this project, we will design colloidal active metasurfaces composed of plasmonic nanorods, in which external stimuli will adjust the distance between the NPs and modulate the temporal and spectral variation of the UV optical response. This project is an important step toward the development of ultrafast UV sensors. Irradiating plasmonic NPs with ultrashort laser pulses produces a series of transient phenomena, including ultrafast dynamics of the plasmon modes (LSPR) as well as acoustic modes. Noble metal NPs have often been proposed to be used as nanobalances by exploiting the load-dependence of their vibration mode frequencies. In preliminary works, we have shown recently that bimetallic silver coated gold nanorods (AuNR@Ag) are promising for LSPR sensing as well as nanobalances in the near UV region. In the CODENAME project, the NPs will be assembled into metasurfaces, in which the transverse modes could be selectively excited. We expect that the metasurface to be even more sensitive than dispersed NPs because of plasmonic coupling and collective acoustic modes. Depletion forces can be used to induce the self-assembly of AuNR@Ag in a reversible manner, using surfactant micelles as depletant. Depletion induced self-assembly has been used to separate plasmonic NPs of different shapes, but very little for its ability to shape reconfigurable materials. The rods will stack side by side due to shape anisotropy, resulting in a spectral shift of the plasmons modes and in oriented superstructures. We will control the distance between the NPs in situ by varying the depletion interaction through control of temperature and surfactant concentration. A methodological development will be implemented for in situ studies (self-powered microfluidics and acoustic levitation). The properties of the metasurfaces (structure, ultrafast optical response) will be probed by different techniques, including in-situ synchrotron X-ray scattering, and transient optical spectroscopy. We expect to modulate the temporal and spectral variation of the optical response in the near UV by adjusting plasmonic coupling in the metasurface. Within the metasurface, the nanorods tips will be more accessible than the side due to side-to-side packing, allowing for selective functionalization of the tips. By increasing nanoparticles interdistance in situ by mean of decreasing depletion interaction, molecules could intercalate between the NPs in the metasurface and it is expected that the transverse modes will be modified in a noticeable way. Indeed, intercalated molecules will act as nanosprings between NPs that tune mechanical coupling and affect the frequencies of the collective modes. This will affect the coupling between neighboring NPs, resulting in a more sensitive detection than the one achievable with isolated NPs. The ultimate goal is to design plasmonic sensors in the UV spectral region, which could detect NPs loads by a dual optical readout, based on plasmon and acoustic vibration frequency shifts.

Fascinating phenomena emerge from the appearance of far-from-equilibrium thermodynamic states, from active matter to protein folding dynamics, including non-trivial heat flows. Nevertheless, the complexity of these phenomena makes their fundamental understanding difficult. In this context, the FENNEC project aims at investigating experimentally and theoretically far-from-equilibrium nanothermodynamics through the careful engineering of colored heat baths of an optically levitated particle. First, it proposes to develop experimental and theoretical tools to generate and characterize out-of-equilibrium dynamics of the systems. Then, it addresses the stochastic energetics of the particle in controlled out-of-equilibrium states or during state-to-state transformations, introducing protocols that could improve and optimize such transformations. Finally, it proposes to take advantage of the out-of-equilibrium system dynamics to investigate and improve the efficiency of heat and particle transport. The FENNEC project will thus provide a unique experimental platform associated with innovative theoretical frameworks for studying far-from-equilibrium systems associated with colored heat baths. It will pave the way for developing efficient nanosystems for transport and sensing.

COupling Ultraquickly and Ultrastrongly Plasmonic and Photonic modes for Largely Efficient Sensing (COUUPPLES). Optical sensors allow contactless interrogation and rely on the availability of numerous sources and detectors. Metal nanoparticles (NPs) are largely used as their localized surface plasmon resonance is altered by small perturbations of their environment, enabling high detection sensitivity. We already demonstrated a spectacular enhancement of the ultrafast optical response of gold NPs once coupled with a resonant photonic mode of a 1D microcavity in the weak-coupling regime, together with a reduction of the resonance linewidth. It is even possible to reach the ultrastrong coupling regime. A laser pulse can induce switching from the strong to the weak coupling in less than a picosecond. Our project will first demonstrate this experimentally by inserting an array of aligned gold nanorods at the photonic antinode of a multi-layered cavity. The anticrossing behaviour of the polariton mode dispersion curve will be shown and the proof for ultrastrong coupling regime will be established. The high susceptibility to the NP environment of the polariton modes and their ultrafast dynamics will then be exploited to realize new plasmon-based sensors with high sensitivity and large effective volume. Hybrid cavities will be elaborated by mixed nanofabrication techniques and their optical response assessed and modelled. The near-field dynamics will be determined by via an original pump-probe fluorescence investigation. The cavities will then be integrated in a microfluidic environment and their potential for sensing will be tested through six different configurations with growing complexity, from the simple continuous monochromatic light interrogation to the exploitation of the spectral and temporal signatures of the device’s ultrafast transient optical response. The sensitivity of these sensing configurations to changes in the refractive index of the gold nanorod environment will be first determined. Then, a DNA aptamer will be grafted on the nanorod surface, able to bind with both large and small biomolecules. In order to establish the proof of concept of our new localized plasmon-based sensing pathways, we will chose as the analyte thrombin, a protein involved in several cardiovascular diseases, as well as small drug molecules possessing known anticancer and anti-viral activities. The project will be carried out through an interdisciplinary approach gathering three academic laboratories: LuMIn for the theoretical and experimental ultrafast optical response assessment, L2n for nanofabrication and optical characterization, and LBPA for biofunctionalization.