Thomas Maldiney

Controlling Electron Trap Depth To Enhance Optical Properties of Persistent Luminescence Nanoparticles for In Vivo Imaging

Focusing on the use of nanophosphors for in vivo imaging and diagnosis applications, we used thermally stimulated luminescence (TSL) measurements to study the influence of trivalent lanthanide Ln(3+) (Ln = Dy, Pr, Ce, Nd) electron traps on the optical properties of Mn(2+)-doped diopside-based persistent luminescence nanoparticles. This work reveals that Pr(3+) is the most suitable Ln(3+) electron trap in the diopside lattice, providing optimal trap depth for room temperature afterglow and resulting in the most intense luminescence decay curve after X-ray irradiation. This luminescence dependency toward the electron trap is maintained through additional doping with Eu(2+), allowing UV-light excitation, critical for bioimaging applications in living animals. We finally identify a novel composition (CaMgSi(2)O(6):Eu(2+),Mn(2+),Pr(3+)) for in vivo imaging, displaying a strong near-infrared afterglow centered on 685 nm, and present evidence that intravenous injection of such persistent luminescence nanoparticles in mice allows not only improved but highly sensitive detection through living tissues.

EFFECT OF CORE DIAMETER, SURFACE COATING, AND PEG CHAIN LENGTH ON THE BIODISTRIBUTION OF PERSISTENT LUMINESCENCE NANOPARTICLES IN MICE

A growing insight toward optical sensors has led to several major improvements in the development of convenient probes for in vivo imaging. Efficient optical detection using quantum dots (QDs) as well as near-infrared organic dyes relies on several key driving principles: the ability to lower background absorption or autofluorescence from tissue, a good photostability of the probe, and a high quantum yield. In this article, we report the real-time biodistribution monitoring of lanthanide-doped persistent luminescence nanoparticles (PLNP), emitting in the near-infrared window, in healthy and tumor-bearing mice. We focused on the influence of hydrodynamic diameter, ranging from 80 to 180 nm, and polyethylene glycol (PEG) surface coating on the behavior of our probes. Tissue distribution was found to be highly dependent on surface coverage as well as core diameter. The amount of PLNP in the blood was highly increased for small (d < 80 nm) and stealth particles. On the opposite, PEG shield molecular weight, ranging from 5 to 20 kDa, had only negligible influence on the in vivo biodistribution of our silicate-based material.

In vivo optical imaging with rare earth doped Ca 2 Si 5 N 8 persistent luminescence nanoparticles

Ca2Si5N8:Eu2+,Tm3+ presents outstanding long lasting luminescence at about 610 nm. However, to be useful for in vivo optical imaging, persistent luminescence materials should possess high optical performance combined with sizes in the nanoscale. With this aim, we investigated two different techniques for the preparation of nanoparticles from Ca2Si5N8:Eu2+,Tm3+ bulk powder. First, nanoparticles were successfully prepared with the pulsed laser ablation method in liquid (abbreviated as PLAL). Secondly, nanoparticles obtained by selective sedimentation from the bulk compound resulted in satisfactory yield and allowed to perform the first real-time in vivo imaging with Ca2Si5N8:Eu2+,Tm3+ host. Finally the influence of surface functionalization on the biodistribution of the probe after systemic injection is discussed.

In Vitro Targeting of Avidin-Expressing Glioma Cells with Biotinylated Persistent Luminescence Nanoparticles

Far red emitting persistent luminescence nanoparticles (PLNP) were synthesized and functionalized with biotin to study their targeting ability toward biotin-binding proteins. First, the interaction of biotin-decorated PLNP with streptavidin, immobilized on a plate, was shown to be highly dependent on the presence of a PEG spacer between the surface of the nanoparticles and the biotin ligand. Second, interaction between biotin-PEG-PLNP and free neutravidin in solution was confirmed by fluorescence microscopy. Finally, in vitro binding study on BT4C cells expressing lodavin fusion protein, bearing the extracellular avidin moiety, showed that such biotin-covered PLNP could successfully be targeted to malignant glioma cells through a specific biotin-avidin interaction. The influence of nanoparticle core diameter, incubation time, and PLNP concentration on the efficiency of targeting is discussed.

Chemically engineered persistent luminescence nanoprobes for bioimaging

Imaging nanoprobes are a group of nanosized agents developed for providing improved contrast for bioimaging. Among various imaging probes, optical sensors capable of following biological events or progresses at the cellular and molecular levels are actually actively developed for early detection, accurate diagnosis, and monitoring of the treatment of diseases. The optical activities of nanoprobes can be tuned on demand by chemists by engineering their composition, size and surface nature. This review will focus on researches devoted to the conception of nanoprobes with particular optical properties, called persistent luminescence, and their use as new powerful bioimaging agents in preclinical assays.

Synthesis and functionalization of persistent luminescence nanoparticles with small molecules and evaluation of their targeting ability

We have recently reported the design and use of inorganic nanoparticles with persistent luminescence properties. Such nanoparticles can be excited with a UV lamp for 2min and emit light in the near-infrared area for dozen of minutes without any further excitation. This property is of particular interest for small animal optical imaging, since it avoids the autofluorescence of endogenous fluorophores which is one major problem encountered when using fluorescent probes. We report herein the synthesis of persistent luminescence nanoparticles (PLNPs) and their functionalization with two small targeting molecules: biotin and Rak-2. We provide characterization of each PLNP as well as preliminary evidence of the ability of PLNP-PEG-Biotin to target streptavidin and PLNP-PEG-Rak-2 to bind prostate cancer cells in vitro.

Non‐Aqueous Sol–Gel Synthesis of Ultra Small Persistent Luminescence Nanoparticles for Near‐Infrared In Vivo Imaging

Ultra-small ZnGa2 O4 :Cr(3+) nanoparticles (6 nm) that exhibit near-infrared (NIR) persistent luminescence properties are synthesized by using a non-aqueous sol-gel method assisted by microwave irradiation. The nanoparticles are pegylated, leading to highly stable dispersions under physiological conditions. Preliminary in vivo studies show the high potential for these ultra-small ZnGa2 O4 :Cr(3+) nanoparticles to be used as in vivo optical nanotools as they emit without the need for in situ excitation and, thus, avoid the autofluorescence of tissues.

Trap depth optimization to improve optical properties of diopside-based nanophosphors for medical imaging

Regarding its ability to circumvent the autofluorescence signal, persistent luminescence was recently shown to be a powerful tool for in vivo imaging and diagnosis applications in living animal. The concept was introduced with lanthanide-doped persistent luminescence nanoparticles (PLNP), from a lanthanide-doped silicate host Ca0.2Zn0.9Mg0.9Si2O6:Eu2+, Mn2+, Dy3+ emitting in the near-infrared window. In order to improve the behaviour of these probes in vivo and favour diagnosis applications, we showed that biodistribution could be controlled by varying the hydrodynamic diameter, but also the surface charges and functional groups. Stealth PLNP, with neutral surface charge obtained by polyethylene glycol (PEG) coating, can circulate for longer time inside the mice body before being uptaken by the reticulo-endothelial system. However, the main drawback of this first generation of PLNP was the inability to witness long-term monitoring, mainly due to the decay kinetic after several decades of minutes, unveiling the need to work on new materials with improved optical characteristics. We investigated a modified silicate host, diopside CaMgSi2O6, and increased its persistent luminescence properties by studying various Ln3+ dopants (for instance Ce, Pr, Nd, Tm, Ho). Such dopants create electron traps that control the long lasting phosphorescence (LLP). We showed that Pr3+ was the most suitable Ln3+ electron trap in diopside lattice, providing optimal trap depth, and resulting in the most intense luminescence decay curve after UV irradiation. A novel composition CaMgSi2O6:Eu2+,Mn2+,Pr3+ was obtained for in vivo imaging, displaying a strong near-infrared persistent luminescence centred on 685 nm, allowing improved and sensitive detection through living tissues.

Highly cohesive dual nanoassemblies for complementary multiscale bioimaging

Innovative nanostructures made of a high payload of fluorophores and superparamagnetic nanoparticles (NPs) have simply been fabricated upon self-assembling in a two-step process. The resulting hybrid supraparticles displayed a dense shell of iron oxide nanoparticles tightly attached through an appropriate polyelectrolyte to a highly emissive non-doped nanocore made of more than 105 small organic molecules. Cooperative magnetic dipole interactions arose due to the closely packed magnetic NPs at the nanoarchitecture surface, causing enhanced NMR transverse relaxivity. Large in vivo MRI T2 contrast was thus obtained with unusually diluted solutions after intravenous injection in small rodents. Two-photon excited fluorescence imaging could be performed, achieving unprecedented location resolution for agents combining both magnetic nanoparticles and fluorescence properties. Finally, TEM imaging of the sectioned mouse tissue succeeded in isolating the core-shell structures, which represents the first image of intact complex magnetic and fluorescent nanoassemblies upon in vivo injection. Such highly cohesive dual nanoarchitectures should open great horizons toward the assessment with high spatial resolution of the drug or labeled stem cell biodistribution.

Persistent Luminescence Nanoparticles for Bioimaging

Optical imaging is a rapidly developing field of research aimed at noninvasive monitoring of disease progression, evaluating the effects and pharmacokinetic of a drug, or identifying pathological biomarkers . To this end, it requires the development of targeting and highly specific contrast agents . In fluorescence imaging, an external light of appropriate wavelength is used to excite the fluorescent molecule, followed almost immediately by the release of longer wavelength, lower energy light for imaging. Fluorescence is increasingly used for imaging and has provided remarkable results. However this technique presents several limitations, especially due to tissue autofluorescence under external illumination and weak tissue penetration of low wavelength excitation light. To overcome these drawbacks, we have developed an innovative technique using persistent luminescence nanoparticles (PLNP) for optical imaging in small animal. Such nanoparticles can be excited before systemic injection, and their biodistribution monitored in real-time for dozen of minutes without the need for any external illumination source. This review article will focus on recent works undertaken in our laboratory on the synthesis of PLNP, their surface modifications and applications for bioimaging.