Periodic Reporting for period 4 - HiPhore (High-temperature Thermophoresis using advanced optical microscopies)
Okres sprawozdawczy: 2022-09-01 do 2023-08-31
What is the problem/issue being addressed?
Thermophoresis denotes the motion of dissolved species in fluids created by temperature gradients. In water, the origin of thermophoresis is multiple, complex and still a matter of active research activities for solutes such as proteins, DNA or colloids.
Thermophoresis at small scales (sub-100 µm) aroused a strong interest this last decade because it makes the diffusion process faster and because of the development of breakthrough applications, e.g. in life sciences (PCR [1], bioanalytics [2], ...). However, reducing the spatial scale makes quantitative and non-invasive measurements of temperature and molecular concentration more challenging. Today the techniques developped for the study of thermophoresis at small scales are slow and invasive.
The HiPhore project aims to provide the research community working on thermophoresis at small scale with innovative tools that enable a faster collection of data and that are label-free.
Why is it important for society?
The most important benefit for society is related to the development of a technique capable of observing living hyperthermophilic bacteria. These organisms live at temperature as high as 121°C, making it impossible to observe them alive under an optical microscope. The project was aimed to make them alive under the field of view of a microscope by microscale optical heating using a laser and gold nanoparticles as light absorbers, as a means to observe hyperthermophilic organisms living and interacting, and the amount of knowledge that the society could gather from this kind of observation is limitless. Hyperthermophilic organisms are already at the basis of the technique called PCR (polymerase chain reaction) to replicate DNA, a gold standard in molecular biology to make several copies of a specific DNA segment.
What are the overall objectives?
Using gold nanoparticles under illumination as nanosources of heat and advanced microscopy tools, I wish to achieve major breakthroughs in the field of microscale thermophoresis in liquids (MTL): - (i) developing new instrumentations for MTL
(ii) make the basics of MTL richer (clarify the enigmatic mechanism of protein thermophoresis and introducing a new concept: superthermophoresis)
(iii) introduce new applications of MTL in life sciences.
Thermophoresis denotes the motion of dissolved species in fluids created by temperature gradients. In water, the origin of thermophoresis is multiple, complex and still a matter of active research activities for solutes such as proteins, DNA or colloids.
Thermophoresis at small scales (sub-100 µm) aroused a strong interest this last decade because it makes the diffusion process faster and because of the development of breakthrough applications, e.g. in life sciences (PCR [1], bioanalytics [2], ...). However, reducing the spatial scale makes quantitative and non-invasive measurements of temperature and molecular concentration more challenging. Today the techniques developped for the study of thermophoresis at small scales are slow and invasive.
The HiPhore project aims to provide the research community working on thermophoresis at small scale with innovative tools that enable a faster collection of data and that are label-free.
Why is it important for society?
The most important benefit for society is related to the development of a technique capable of observing living hyperthermophilic bacteria. These organisms live at temperature as high as 121°C, making it impossible to observe them alive under an optical microscope. The project was aimed to make them alive under the field of view of a microscope by microscale optical heating using a laser and gold nanoparticles as light absorbers, as a means to observe hyperthermophilic organisms living and interacting, and the amount of knowledge that the society could gather from this kind of observation is limitless. Hyperthermophilic organisms are already at the basis of the technique called PCR (polymerase chain reaction) to replicate DNA, a gold standard in molecular biology to make several copies of a specific DNA segment.
What are the overall objectives?
Using gold nanoparticles under illumination as nanosources of heat and advanced microscopy tools, I wish to achieve major breakthroughs in the field of microscale thermophoresis in liquids (MTL): - (i) developing new instrumentations for MTL
(ii) make the basics of MTL richer (clarify the enigmatic mechanism of protein thermophoresis and introducing a new concept: superthermophoresis)
(iii) introduce new applications of MTL in life sciences.
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).
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).
Progress beyond the state of the art is listed below:
- We developed a new label-free optical microscopy technique to image concentration of molecules at the microscale in the context of thermophoresis experiments
- We developed a procedure to shape any tempeture profile at the microscale using a spatially contrasted laser beam and a layer of gold nanoparticles
- We developed a technique to optically characterize nano- microparticles (determination of all the optical cross sections at once)
- We developed a methodology to observe life at high temperature
- We were able to measure the mass of single bacteria with a sub-picogram precision.
- We theoretically showed that for ionic conductors cations and anions, the Seebeck coefficient obtained from a current measurement differs from that obtained from the thermopotential.
- We rationalized the giant Seebeck coefficients observed since 2017 for various ionic conductors.
- We studied various ideas developed since almost 20 years on the temperature dependence of the Soret coefficient of organic solutes (expansivity of water, viscoelectric effect of surface charges) and found that none of them provided a satisfactory explanation for data on proteins, DNA, polystyrene beads, charged and uncharged micelles.
- We developed a new label-free optical microscopy technique to image concentration of molecules at the microscale in the context of thermophoresis experiments
- We developed a procedure to shape any tempeture profile at the microscale using a spatially contrasted laser beam and a layer of gold nanoparticles
- We developed a technique to optically characterize nano- microparticles (determination of all the optical cross sections at once)
- We developed a methodology to observe life at high temperature
- We were able to measure the mass of single bacteria with a sub-picogram precision.
- We theoretically showed that for ionic conductors cations and anions, the Seebeck coefficient obtained from a current measurement differs from that obtained from the thermopotential.
- We rationalized the giant Seebeck coefficients observed since 2017 for various ionic conductors.
- We studied various ideas developed since almost 20 years on the temperature dependence of the Soret coefficient of organic solutes (expansivity of water, viscoelectric effect of surface charges) and found that none of them provided a satisfactory explanation for data on proteins, DNA, polystyrene beads, charged and uncharged micelles.