From the beginning of the project, several achievements have been reached, all of them based on the efficiency of thermophoresis to drive nano and micro objects in fluids.
I- Experimentally We first managed to master a chemical synthesis technique for the production of the gold nanoparticle samples used as photothermal transducers for all the tasks of the project. This technique is called block copolymer micellar lithography.
We also developed a novel methodology to achieve any microscale temperature distribution by shaping a laser beam and send to a gold nanoparticle layer (10.1038/s41598-019-40382-3). The achievement enabled precise control of microscale thermophoresis of microbeads, and is now used on a daily basis in the HiPhore project to drive molecules, particles and bacteria in fluids, under the field of view of a microscope. Along this line, we developed a hydrid phase/fluorescence microscopy technique to achieve metrological measurements of thermophoresis of nanoparticles. The approach does not suffer from the artefacts previously reported in the literature, when using fluorescent molecules to map temperature at the microscale, as our temperature microscopy technique is label-free (10.1021/acs.jpcc.1c06299 10.1038/s41598-022-07588-4 10.1021/acs.nanolett.0c03638).
In parallel, we managed to observe life at high temperature (80°C) under the field of view of a microscope thanks to the laser heating of gold nanoparticles. This achievement is one of the main milestones of the project (10.1038/s41467-022-33074-6).
We investigated in detail the possibility to measure the mass of individual micro-organisms using wavefront microscopy, with a sub-picogram sensitivity (10.1016/j.bpj.2023.06.020).
Investigations of the HiPhore project also led us to unexpected discoveries. In particular,
- We developed a technique to quantitatively measure all the optical properties of nano and microparticles (10.1364/OPTICA.381729).
- We understood what was hampering our culture of bacteria between coverslips. This claustrophobic behavior of bacteria is to be published soon (10.1039/d1ra00184a).
These 5 years have also been the occasion to try and make wavefront microscopy more popular, by attending several 10s of conference, but also by publishing review and tutorial articles (10.1088/1361-6463/abfbf9 10.1021/acsphotonics.2c01238 10.1016/j.optcom.2022.128577).
II - Numerically and theoretically,the project was also the occasion to investigate the origin of thermophoresis in liquid, especially from the team at LOMA (laboratoire Onde Matière d'Aquitaine, Bordeaux).
First, we have clarified the expression for the Seebeck coefficient in ionic conductors. As a main result we found that it depends on the boundary conditions and may even show opposite signs for open and closed systems (10.1103/PhysRevResearch.2.042030).
For ionic charge carriers in solid-state or gel matrices, we proposed a model based on hopping dynamics which provides a rationale for the giant Seebeck coefficients observed in these systems (10.1103/PhysRevLett.126.068001). In collaboration with an experimental group from Linköping University, Sweden, we compared this model with measured data and reviewed recent progress (10.1016/j.jechem.2021.02.022).
At present we work with Michel du Chalard de Taveau, Master student (March-June 2021), on the Seebeck coefficient of thermogalvanic cells.
In collaboration with experimental groups from University of Gothenburg and Chalmers University, Sweden, we studied the non-equilibrium properties of gold nanoparticles in a optical tweezers potential (10.1038/s41467-021-22187-z).
