Patrice L. Baldeck

Long-Lived Two-Photon Excited Luminescence of Water-Soluble Europium Complex: Applications in Biological Imaging Using Two-Photon Scanning Microscopy

A new europium complex presenting good solubility and stability in water, intense emission in the red (616 nm), long luminescence lifetime, and significant two-photon absorption cross-section in the biological window has been designed and successfully used for two-photon scanning microscopy bioimaging experiments on fixed cancer cells.

Chitosan-coated triangular silver nanoparticles as a novel class of biocompatible, highly effective photothermal transducers for in vitro cancer cell therapy

One of the relevant directions that nanotechnology is taking nowadays is connected with nanomedicine and specifically related to the use of light and nanoparticles in early diagnosis and effective therapeutics of cancer. Noble-metal nanoparticles can act under laser irradiation as effective photothermal transducers for triggering localized hyperthermia of tumors. In this work we report the performance of newly synthesized chitosan-coated silver nanotriangles (Chit-AgNTs) with strong resonances in near-infrared (NIR) to operate as photothermal agents against a line of human non-small lung cancer cells (NCI-H460). The hyperthermia experiments were conducted by excitation of nanoparticles-loaded cells at 800 nm wavelength from a Ti:Sapphire laser. We found that the rate of cell mortality in the presence of Chit-AgNTs is higher than in the presence of thiolated poly(ethylene) glycol capped gold nanorods (PEG-AuNRs) - a common hyperthermia agent used as reference-, while no destructive effects were noticed on the control sample (cells without nanoparticles) under identical irradiation conditions. Additionally, we conducted cytotoxicity assays and found Chit-AgNTs to be efficiently uptaken by the cells while exhibiting good biocompatibility for healthy human embryonic cells (HEK), which is essential for any in vivo applications. Our results reveal a novel class of biocompatible plasmonic nanoparticles with high potential to be implemented as effective phototherapeutic agents in the battle against cancer.

Two-photon absorption and optical power limiting of bifluorene molecule

We have studied the nonlinear absorption spectra and optical limiting properties of 2,2′-(9,9-dihexyl) bifluorene. Measurements were done in chloroform solution, in the visible range (450–650 nm), and for nanosecond time-duration pulses. The two-photon absorption (TPA) spectrum, obtained by the up-conversion fluorescence method, shows a resonance at λ=534 nm with a cross-section σTPA=60 10−50 cm4⋅s/photon-molecule. Semiempirical quantum chemistry calculation on fluorene and bifluorene suggests an enhancement of the bifluorene TPA due to coupling effects between monomers. In nonlinear transmission measurements, two-photon absorption is reinforced by the excited-state absorption that occurs during the pulse duration. At resonance, the three-photon absorption coefficient is α3=14 000 cm3/GW2 for a bifluorene concentration of 600 g/L. This strong nonlinear absorption leads to an efficient optical power limiting in the green and blue parts of the spectrum. The maximum transmitted energy is lower than 10 μJ for an input energy of up to 200 μJ in a F/5 optical geometry.

Three-dimensional microfabrication by two-photon-initiated polymerization with a low-cost microlaser

Fabrication of submicrometer structures by two-photon-initiated polymerization is performed with an inexpensive and low-power microlaser. This is made possible by the design of photoinitiators with strong two-photon absorption cross sections. We analyze the influence of both material properties and irradiation conditions on the two-photon polymerization rate and show that resins based on our highly sensitive two-photon photoinitiator can be solidified with microlaser excitation, whereas commercial UV photoresins require ultrashort and intense laser pulses.

Design of Dipicolinic Acid Ligands for the Two-Photon Sensitized Luminescence of Europium Complexes with Optimized Cross-Sections

The multistep synthesis of an extensive series of push-pull donor-pi-conjugated dipicolinic acid ligands is described. The charge transfer character of the ligand can be tuned by changing the donor group (CH 2R, OR, SR, or NR 2) or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone). The photophysical properties of related D 3 symmetric europium complexes (absorption and luminescence) were measured. Experiments using two-photon sensitized luminescence of a Eu (III) complex reveal large two-photon absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide complexes.

Ytterbium-Based Bioprobes for Near-Infrared Two-Photon Scanning Laser Microscopy Imaging†

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Ytterbium-based bioprobes for near-infrared two-photon scanning laser microscopy imaging. Anthony D’Aléo, Adrien Bourdolle, Sophie Brustlein, Teddy Fauquier, Alexei Grichine, Alain Duperray, P. L. Baldeck, Chantal Andraud, Sophie Brasselet, Olivier Maury

Two-photon absorption spectrum of poly(fluorene)

Abstract We report here on the two-photon absorption (TPA) properties of poly(fluorene). The two-photon absorption spectrum has been characterized in the range 550–680 nm. A resonance at λ =625 nm is observed with a cross-section of 2×10 −46 cm 4 s/photon-molecule. This large value is interpreted as the result of dipolar coupling between 12 monomer units, i.e. the polymer coherence length. In the framework of a three-level model, the TPA transition is related to the second excited state 2A g lying at 6200 cm −1 above the lowest excited state 1B u .

Comparative Analysis of Conjugated Alkynyl Chromophore–Triazacyclononane Ligands for Sensitized Emission of Europium and Terbium

A series of europium and terbium complexes based on a functionalized triazacyclononane carboxylate or phosphinate macrocyclic ligand is described. The influence of the anionic group, that is, carboxylate, methylphosphinate, or phenylphosphinate, on the photophysical properties was studied and rationalized on the basis of DFT calculated structures. The nature, number, and position of electron-donating or electron-withdrawing aryl substituents were varied systematically within the same phenylethynyl scaffold in order to optimize the brightness of the corresponding europium complexes and investigate their two-photon absorption properties. Finally, the europium complexes were examined in cell-imaging applications, and selected terbium complexes were studied as potential oxygen sensors.

Folic Acid-Conjugated, SERS-Labeled Silver Nanotriangles for Multimodal Detection and Targeted Photothermal Treatment on Human Ovarian Cancer Cells

The effectiveness of a therapeutic agent for cancer stands in its ability to reduce and eliminate tumors without harming the healthy tissue nearby. Nanoparticles peripherally conjugated with targeting moieties offer major improvements in therapeutics through site specificity. In this study we demonstrate this approach by targeting the folate receptor of NIH:OVCAR-3 human ovary cancer cell line. Herein we used silver nanotriangles which were biocompatibilized with chitosan (bio)polymer, labeled with para-aminothiophenol (pATP) Raman reporter molecule, and conjugated with folic acid. The nanoparticles conjugation and efficient labeling was investigated by localized surface plasmon resonance (LSPR), zeta potential, and surface-enhanced Raman scattering (SERS) measurements. Conjugated particles were proven to be highly stable in aqueous and cellular medium. The targeted uptake of conjugated nanoparticles by human ovary cancer cells was confirmed by dark field microscopy and scattering spectra of the particles inside cells. Comparative studies revealed specific internalization of the conjugated nanoparticles in comparison with similar bare nanoparticles. Moreover, the SERS identity of the particles was proven to be highly conserved inside cells. Targeted cancer cell treatment conducted by irradiating the nanoparticle-treated cells with a continuous wave-nearinfrared (cw-NIR) laser in resonance with their plasmonic band proved an efficient therapeutic response. By integrating the advantages of multimodal optical imaging and SERS detection with hyperthermia capabilities through site specificity, these nanoparticles can represent a real candidate for personalized medicine.

Modulating the photophysical properties of azamacrocyclic europium complexes with charge-transfer antenna chromophores.

Two europium complexes with bis(bipyridine) azamacrocyclic ligands featuring pendant arms with or without π-conjugated donor groups are synthesized and fully characterized by theoretical calculations and NMR spectroscopy. Their photophysical properties, including two-photon absorption, are investigated in water and in various organic solvents. The nonfunctionalized ligand gives highly water-stable europium complexes featuring bright luminescence properties but poor two-photon absorption cross sections. On the other hand, the europium complex with an extended conjugated antenna ligand presents a two-photon absorption cross section of 45 GM at 720 nm but is poorly luminescent in water. A detailed solvent-dependent photophysical study indicates that this luminescence quenching is not due to the direct coordination of O-H vibrators to the metal center but to the increase of nonradiative processes in a protic solvent induced by an internal isomerization equilibrium.