Nanoparticules upconverting : vers la microscopie en super-résolution

Lanthanide-based Upconverting nanoparticles (UCNPs) show the fascinating property of converting low energy NIR photons into higher energy ones without requiring high laser fluences. This unique large anti-Stokes shift affords a higher signal-to-noise ratio than standard luminescent compounds. Associated to their photostability (non-blinking, non-bleaching), their size-independent emission spectrum and a limited toxicity, these inorganic materials have become an interesting tool in Biology besides Quantum Dots, especially for Bioimaging. However, the overall emission plummets sharply when the size is reduced. Therefore, efficient ultrasmall UCNPs are still challenging to obtain. The present work is dedicated to the design of innovative nanohybrid structures based on NaREF4 with ultrasmall sizes, in order to go towards super-resolution microscopy. Investigations were focused on three main issues. At first, we will describe how a size reduction from 10-20 nm to sub-5 nm UCNP can be envisioned. An appropriate composition choice, coupled to an improvement of the common thermal coprecipitation pathway was setup. Especially, we have shown the importance of the conjunction of a mixing strategy for the primo-precipitation and accurate monitoring of the high temperature step. Here, the use of microwave-assisted synthesis was found to be crucial for a precise control of the Ostwald ripening through an original cycling heating. Then, the photophysics of a library of different UCNPs were assessed in order to understand the complex energy redistribution within an NP, using different setups, home-made or thanks to collaborative work in specialized laboratories in Berlin or Lille. From these observations, the use of classic emission quantifiers was found to be inefficient and a first step towards a relevant kinetic model was initiated. Eventually, nanohybrids based on a photochromic hydrophilic polymer have been elaborated. Selection of the appropriate dye, and preliminary exploration of the photokinetic properties of the polymer have been undertaken. This approach, coupling our ultrastable nanolamp to a photochromic shutter, is aimed at developing an innovative stochastic method to compete with the recent successes of the use of UCNPs for super-resolution via a STED approach.Les nanoparticules Upconverting (UCNP) à base de lanthanides possèdent la propriété fascinante d’être capables de convertir des photons infrarouges en photons de plus haute énergie sans recourir à des fluences de laser élevées. Ce décalage Anti-Stokes conduit à rapport signal sur bruit meilleur que pour la luminescence classique. Associé à leur photostabilité (non clignotantes, non photolysables), un spectre d’émission indépendant de leur taille, une faible toxicité, ces matériaux inorganiques sont devenus un outil de choix en biologie, en particulier en imagerie biologique, à côté des Quantum Dots. Cependant, l’émission globale s’effondre rapidement quand la taille des UCNP est réduite. En conséquence la réalisation de particules ultra petites et efficaces reste un défi. Le présent mémoire s’intéresse au design de structures nanohybrides fondées sur des particules ultra petites de NaREF4, avec pour objectif la microscopie super-résolue. Le travail s’est organisé en trois phases. Tout d’abord nous avons étudié la réduction en taille des UCNP de 10-20 nm à moins de 5 nm, en se focalisant sur leur composition et l’amélioration du procédé de synthèse. En particulier nous avons montré l’importance de la conjonction du processus de mélange avec la conduite de l’étape à haute température. Pour cette dernière l’emploi du chauffage micro-onde, avec un cyclage en température original a permis de contrôler efficacement le mûrissement d’Ostwald. La librairie de particules ainsi construite a permis d’étudier la photophysique des processus de redistribution de l’énergie au sein des particules sur des montages « maison » ou des équipements dédiés grâce à des collaborations avec des équipes de Berlin ou Lille. Il en ressort que les quantificateurs usuels de luminescence sont inadéquats pour décrire le phénomène d’upconversion. Aussi avons-nous débuté l’élaboration d’un modèle cinétique approprié. Enfin, la construction de nanohybrides impliquant un polymère photochrome hydrophile a été explorée. La sélection du colorant approprié et les premières études photocinétiques ont été menées. Cette approche couplant nos « nanolampes » avec un « volet photochrome » a pour but de proposer une alternative innovante au développement de la super-résolution par STED

Upconversion nanoparticles : towards super-resolution microscopy

Les nanoparticules Upconverting (UCNP) à base de lanthanides possèdent la propriété fascinante d’être capables de convertir des photons infrarouges en photons de plus haute énergie sans recourir à des fluences de laser élevées. Ce décalage Anti-Stokes conduit à rapport signal sur bruit meilleur que pour la luminescence classique. Associé à leur photostabilité (non clignotantes, non photolysables), un spectre d’émission indépendant de leur taille, une faible toxicité, ces matériaux inorganiques sont devenus un outil de choix en biologie, en particulier en imagerie biologique, à côté des Quantum Dots. Cependant, l’émission globale s’effondre rapidement quand la taille des UCNP est réduite. En conséquence la réalisation de particules ultra petites et efficaces reste un défi. Le présent mémoire s’intéresse au design de structures nanohybrides fondées sur des particules ultra petites de NaREF4, avec pour objectif la microscopie super-résolue. Le travail s’est organisé en trois phases. Tout d’abord nous avons étudié la réduction en taille des UCNP de 10-20 nm à moins de 5 nm, en se focalisant sur leur composition et l’amélioration du procédé de synthèse. En particulier nous avons montré l’importance de la conjonction du processus de mélange avec la conduite de l’étape à haute température. Pour cette dernière l’emploi du chauffage micro-onde, avec un cyclage en température original a permis de contrôler efficacement le mûrissement d’Ostwald. La librairie de particules ainsi construite a permis d’étudier la photophysique des processus de redistribution de l’énergie au sein des particules sur des montages « maison » ou des équipements dédiés grâce à des collaborations avec des équipes de Berlin ou Lille. Il en ressort que les quantificateurs usuels de luminescence sont inadéquats pour décrire le phénomène d’upconversion. Aussi avons-nous débuté l’élaboration d’un modèle cinétique approprié. Enfin, la construction de nanohybrides impliquant un polymère photochrome hydrophile a été explorée. La sélection du colorant approprié et les premières études photocinétiques ont été menées. Cette approche couplant nos « nanolampes » avec un « volet photochrome » a pour but de proposer une alternative innovante au développement de la super-résolution par STED.Lanthanide-based Upconverting nanoparticles (UCNPs) show the fascinating property of converting low energy NIR photons into higher energy ones without requiring high laser fluences. This unique large anti-Stokes shift affords a higher signal-to-noise ratio than standard luminescent compounds. Associated to their photostability (non-blinking, non-bleaching), their size-independent emission spectrum and a limited toxicity, these inorganic materials have become an interesting tool in Biology besides Quantum Dots, especially for Bioimaging. However, the overall emission plummets sharply when the size is reduced. Therefore, efficient ultrasmall UCNPs are still challenging to obtain. The present work is dedicated to the design of innovative nanohybrid structures based on NaREF4 with ultrasmall sizes, in order to go towards super-resolution microscopy. Investigations were focused on three main issues. At first, we will describe how a size reduction from 10-20 nm to sub-5 nm UCNP can be envisioned. An appropriate composition choice, coupled to an improvement of the common thermal coprecipitation pathway was setup. Especially, we have shown the importance of the conjunction of a mixing strategy for the primo-precipitation and accurate monitoring of the high temperature step. Here, the use of microwave-assisted synthesis was found to be crucial for a precise control of the Ostwald ripening through an original cycling heating. Then, the photophysics of a library of different UCNPs were assessed in order to understand the complex energy redistribution within an NP, using different setups, home-made or thanks to collaborative work in specialized laboratories in Berlin or Lille. From these observations, the use of classic emission quantifiers was found to be inefficient and a first step towards a relevant kinetic model was initiated. Eventually, nanohybrids based on a photochromic hydrophilic polymer have been elaborated. Selection of the appropriate dye, and preliminary exploration of the photokinetic properties of the polymer have been undertaken. This approach, coupling our ultrastable nanolamp to a photochromic shutter, is aimed at developing an innovative stochastic method to compete with the recent successes of the use of UCNPs for super-resolution via a STED approach

A photochemical determination of luminescence efficiency ofupconverting nanoparticles

International audienceUpconverting nanoparticles are a rising class of non-linear luminescent probes burgeoning since the beginning of the 2000’s, especially for their attractiveness in theranostics. However, the precise quantification of the light delivered remains a hot problem in order to estimate their impact on the biological medium. Sophisticated photophysical measurements under near infrared excitation have been developed only by few teams. Here, we present the first attempt towards a simple and cheap photochemical approach consisting of an actinometric characterization of the green emission of NaYF4:Yb,Er nanoparticles. Using the recently calibrated actinometer 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene operating in the green region of the visible spectra, we propose a simple photochemical experiment to get an accurate estimation of the efficiency of these green-emitting “nanolamps”. The agreement of the collected data with the previous published results validates this approach

Versatile thiolactone-based conjugation strategies to polymer stabilizers for multifunctional upconverting nanoparticles aqueous dispersions

International audienceWell-defined phosphonic acid-terminated polymers were synthesized from amine-terminated polymer precursors and a phosphonated thiolactone and were used to prepare stable, water-dispersible multifunctional upconverting luminescent nanohybrids

Ionic Flash NanoPrecipitation (iFNP) for the facile, one-step synthesis of inorganic–organic hybrid nanoparticles in water

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Selective ion sensing in aqueous media with ESIPT active fluorescent probes – A particular case for hypochlorite detection

International audienceWe report two ESIPT active novel fluorescent probes, 1 and 2, based on benzoxazole and benzimidazole units, respectively. Their sensing aptitude towards metal ions in aqueous media is reported. A specific response of 1 to Al 3+ and, to a lesser extent, Zn 2+ , was found, while the emission of 2 is highly impacted by the Al 3+ , Cu 2+ , Fe 2+ and Fe 3+ metal ions by either a blue shift or a quenching of the emission. Emission of 2 also shows a relative sensitivity to the Ni 2+ and Hg 2+ cations. Anions sensing studies on 2 revealed a unique emission in presence of hypochlorite ions, while glyphosate and aminomethylphosphonic acid have the effect to decrease the emission intensity by 40% and 75%, respectively. Investigations on the recognition mechanism led to the conclusion that Al 3+ was inhibiting the ESIPT process by deprotonation of the phenol group, and that a fast but weak interaction was taking place between the hypochlorite ion and 2

Importance of the Mixing and High-Temperature Heating Steps in the Controlled Thermal Coprecipitation Synthesis of Sub-5-nm Na(Gd-Yb)FTm

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Top-down synthesis of luminescent microplastics and nanoplastics by incorporation of upconverting nanoparticles for environmental assessment

International audiencePolyethylene model particle is synthesized by a top-down approach with effective incorporation of upconverting nanoparticles. The particles with irregular shapes, similar to those found in the environment, are trackable under 980 nm irradiation

Top-Down Synthesis of Luminescent Microplastics and Nanoplastics by Incorporation of Upconverting Nanoparticles for Environmental Assessment

The occurrence of micro- and nanoplastics is a major environmental problem. Especially for nanoplastics due to their easy bioavailability and unknown impact on living organisms. The monitoring of these extremely small particles during their ingestion, tissue translocation and transfer through the trophic chain remains very challenging. This study aims to develop an environmentally relevant model of luminescent micro- and nanoplastics. First, lanthanide-based upconverting nanophosphors (20 nm) were incorporated in bulk polyethylene without modification of the polymer structure or morphology. Second, micrometric and nanometric particles were obtained after powdering. Two fractions were obtained with cascade filtration with average sizes of 5 µm and 150 nm and characterized in terms of size distribution, morphology and surface charge. The particles are very polydisperse with an irregular shape and a global negative charge; they exhibit morphological characteristics similar to those formed in the environment. Their luminescent properties upon NIR excitation at 980 nm open the possibility to track them in the tissues of organisms. The powdering method is very simple and compatible with many polymers pure or formulated. As a perspective, the use of weathered materials is possible with the proposed method and will allow the preparation of particles sharing additional properties with environmental micro- and nanoplastics

Quench ionic flash nano precipitation as a simple and tunable approach to decouple growth and functionalization for the one-step synthesis of functional LnPO 4 -based nanoparticles in water

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