Exploitation of Luminescent Lanthanide Nanoparticles for a Sensitivity-Enhanced ELISA Detection Method.

A new detection method based on the photoluminescence properties of dye-sensitized lanthanide nanoparticles (Ln NPs) was developed for enzyme-linked immunosorbent assays (ELISAs). In this method, the horseradish peroxidase (HRP) enzyme catalyzes the oxidation of phenol derivatives in the presence of hydrogen peroxide, providing dimers that are able to interact with the Ln NP surface and to efficiently photosensitize the Ln ions. Due to the very long emission lifetime of Ln, the time-gated detection of Ln NP luminescence allows the elimination of background noise due to the biological environment. After a comparison of the enzyme-catalyzed oxidation of various phenol derivatives, methyl 4-hydroxyphenyl acetate (MHPA) was selected as the most promising substrate, as the highest Ln emission intensity was observed following its HRP-catalyzed oxidation. After a meticulous optimization of the conditions of both the enzymatic reaction and the Ln sensitization (buffer, pH, concentration of the reactants, NP type, etc.), this new detection method was successfully implemented in a commercial insulin ELISA kit as a proof-of-concept, with an increased sensitivity compared to the commercial detection method.

Structure-Activity Optimization of Luminescent Tb-doped LaF3 Nanoparticles.

A series of Tb-doped LaF3 nanoparticles (NPs) was prepared by systematically varying the Tb doping rate from 0 to 100%. The elemental composition was confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis, and the size, morphology, and crystal structure were determined in the solid state by transmission electron microscopy and X-ray diffractometry, while the size and ζ-potential of the NPs in solution were studied by dynamic light scattering, Taylor dispersion analysis, and laser Doppler electrophoresis. While the crystal structure appears to be hexagonal for a doping rate of up to 70%, an admixture of hexagonal and orthorhombic phases is observed for 80 and 90% Tb contents with a pure orthorhombic phase being obtained for TbF3. The spectroscopic properties of the NPs were studied for bare NPs and in the presence of dipicolinic acid as a surface-capping antenna ligand in solution. The coverage of the NPs by the ligand resulted in an increase in the luminescence lifetime of the emitting Tb centers, as a consequence of a better protection toward luminescence quenching from water molecules, as well as a large improvement in the brightness of the NPs. Taking into account the various parameters, a doping rate of 40% Tb was shown to be the best compromise for the development of such NPs for bioanalytical applications.

Ultrabright Terbium Nanoparticles for FRET Biosensing and in Situ Imaging of Epidermal Growth Factor Receptors*.

Lanthanide-doped nanoparticles (LnNPs) have become an important class of fluorophores for advanced biosensing and bioimaging. LnNPs that are photosensitized by surface-attached antenna ligands can possess exceptional brightness. However, their functional bioconjugation remains an important challenge for their translation into bioanalytical applications. To solve this problem, we designed a ligand that can be simultaneously applied as efficient light harvesting antenna for Tb surface ions and strong linker of biomolecules to the LnNPs surfaces. To demonstrate generic applicability of the photosensitized TbNP-bioconjugates, we applied them in two prototypical applications for biosensing and bioimaging. First, in-solution biorecognition was shown by time-resolved Förster resonance energy transfer (FRET) between streptavidin-functionalized TbNPs to biotinylated dyes (ATTO 610). Second, in situ detection of ligand-receptor binding on cells was accomplished with TbNP-antibody (Matuzumab) conjugates that could specifically bind to transmembrane epidermal growth factor receptors (EGFR). High specificity and sensitivity were demonstrated by time-gated imaging of EGFR on both strongly (A431) and weakly (HeLa and Cos7) EGFR-expressing cell lines, whereas non-expressing cell lines (NIH3T3) and EGFR-passivated A431 cells did not show any signals. Despite the relatively large size of TbNP-antibody conjugates, they could be internalized by A431 cells upon binding to extracellular EGFR, which showed their potential as bright and stable luminescence markers for intracellular signaling.

Oxidative Damages on the Alzheimer's Related-Aß Peptide Alters Its Ability to Assemble.

Oxidative stress that can lead to oxidation of the amyloid-ß (Aß) peptide is considered a key feature in Alzheimer's disease (AD), influencing the ability of Aß to assemble into ß-sheet rich fibrils that are commonly found in senile plaques of AD patients. The present study aims at investigating the fallouts of Aß oxidation on the assembly properties of the Aß peptide. To accomplish this, we performed kinetics and analysis on an oxidized Aß (oxAß) peptide, resulting from the attack of reactive oxygen species (ROS) that are formed by the biologically relevant Cu/Aß/dioxygen/ascorbate system. oxAß was still able to assemble but displayed ill-defined and small oligomeric assemblies compared to the long and thick ß-sheet rich fibrils from the non-oxidized counterpart. In addition, oxAß does affect the assembly of the parent Aß peptide. In a mixture of the two peptides, oxAß has a mainly kinetic effect on the assembly of the Aß peptide and was able to slow down the formation of Aß fibril in a wide pH range [6.0-7.4]. However, oxAß does not change the quantity and morphology of the Aß fibrils formed to a significant extent. In the presence of copper or zinc di-cations, oxAß assembled into weakly-structured aggregates rather than short, untangled Cu-Aß fibrils and long untangled Zn-Aß fibrils. The delaying effect of oxAß on metal altered Aß assembly was also observed. Hence, our results obtained here bring new insights regarding the tight interconnection between (i) ROS production leading to Aß oxidation and (ii) Aß assembly, in particular via the modulation of the Aß assembly by oxAß. It is the first time that co-assembly of oxAß and Aß under various environmental conditions (pH, metal ions …) are reported.

Bioconjugation studies of an EGF-R targeting ligand on dendronized iron oxide nanoparticles to target head and neck cancer cells.

A major challenge in nanomedicine is designing nanoplatforms (NPFs) to selectively target abnormal cells to ensure early diagnosis and targeted therapy. Among developed NPFs, iron oxide nanoparticles (IONPs) are good MRI contrast agents and can be used for therapy by hyperthermia and as radio-sensitizing agents. Active targeting is a promising method for selective IONPs accumulation in cancer tissues and is generally performed by using targeting ligands (TL). Here, a TL specific for the epidermal growth factor receptor (EGFR) is bound to the surface of dendronized IONPs to produce nanostructures able to specifically recognize EGFR-positive FaDu and 93-Vu head and neck cancer cell lines. Several parameters were optimized to ensure a high coupling yield and to adequately quantify the amount of TL per nanoparticle. Nanostructures with variable amounts of TL on the surface were produced and evaluated for their potential to specifically target and be thereafter internalized by cells. Compared to the bare NPs, the presence of the TL at the surface was shown to be effective to enhance their internalization and to play a role in the total amount of iron present per cell.

Dye-sensitized lanthanide containing nanoparticles for luminescence based applications.

Due to their exceptional luminescent properties, lanthanide (Ln) complexes represent a unique palette of probes in the spectroscopic toolkit. Their extremely weak brightness due to forbidden Ln electronic transitions can be overcome by indirect dye-sensitization from the antenna effect brought by organic ligands. Despite the improvement brought by the antenna effect, (bio)analytical applications with discrete Ln complexes as luminescent markers still suffers from low sensitivity as they are limited by the complex brightness. Thus, there is a need to develop nano-objects that cumulate the spectroscopic properties of multiple Ln ions. This review firstly gives a brief introduction of the spectral properties of lanthanides both in complexes and in nanoparticles (NPs). Then, the research progress of the design of Ln-doped inorganic NPs with capping antennas, Ln-complex encapsulated NPs and Ln-complex surface functionalized NPs is presented along with a summary of the various photosensitizing ligands and of the spectroscopic properties (excited-state lifetime, brightness, quantum yield). The review also emphasizes the problems and limitations encountered over the years and the solutions provided to address them. Finally, a comparison of the advantages and drawbacks of the three types of NP is provided as well as a conclusion about the remaining challenges both in the design of brighter NPs and in the luminescence based applications.

Receptor-Ligand Interaction Measured by Inductively Coupled Plasma Mass Spectrometry and Selenium Labeling.

In the search for an alternative strategy to the radioactivity measurement conventionally performed to probe receptor-ligand interactions in pharmacological assays, we demonstrated that selenium labeling of the studied ligand combined with elemental mass spectrometry was as efficient and robust as the reference method but devoid of its environmental and health hazards. The proof-of-concept was illustrated on two GPCR receptors, vasopressin (V1A) and cholecystokinin B (CCK-B), involving peptides as endogenous ligands. We proposed several methodologies to produce selenium-labeled ligands according to peptide sequences along with binding affinity constraints. A selection of selenopeptides that kept high affinities toward the targeted receptor were engaged in saturation and competitive binding experiments with subsequent sensitive RP-LC-ICP-MS measurements. Experimental values of affinity constant ( Ki) were perfectly correlated to literature data, illustrating the general great potency of replacing radioactive iodine by selenium for ligand labeling to further undergo unaffected pharmacology experiments efficiently monitored by elemental mass spectrometry.

Identification of key structural features of the elusive Cu-Aß complex that generates ROS in Alzheimer's disease.

Oxidative stress is linked to the etiology of Alzheimer's disease (AD), the most common cause of dementia in the elderly. Redox active metal ions such as copper catalyze the production of Reactive Oxygen Species (ROS) when bound to the amyloid-ß (Aß) peptide encountered in AD. We propose that this reaction proceeds through a low-populated Cu-Aß state, denoted the "catalytic in-between state" (CIBS), which is in equilibrium with the resting state (RS) of both Cu(i)-Aß and Cu(ii)-Aß. The nature of this CIBS is investigated in the present work. We report the use of complementary spectroscopic methods (X-ray absorption spectroscopy, EPR and NMR) to characterize the binding of Cu to a wide series of modified peptides in the RS. ROS production by the resulting Cu-peptide complexes was evaluated using fluorescence and UV-vis based methods and led to the identification of the amino acid residues involved in the Cu-Aß CIBS species. In addition, a possible mechanism by which the ROS are produced is also proposed. These two main results are expected to affect the current vision of the ROS production mechanism by Cu-Aß but also in other diseases involving amyloidogenic peptides with weakly structured copper binding sites.

Is ascorbate Dr Jekyll or Mr Hyde in the Cu(Aß) mediated oxidative stress linked to Alzheimer's disease?

Evaluation of the pro versus antioxidant activity of ascorbate regarding Cu(Aß) induced reactive oxygen species production in the context of Alzheimer's disease shows that a protective activity can only be observed at high ascorbate concentration for exogenous molecules but not for the amyloid-ß peptide itself.

Metal-catalyzed oxidation of Aß and the resulting reorganization of Cu binding sites promote ROS production.

In the context of Alzheimer's disease (AD), the production of HO˙ by copper-amyloid beta (Aß) in the presence of ascorbate is known to be deleterious for the Aß peptide itself and also for the surrounding molecules, thus establishing a direct link between AD and oxidative stress. The metal-catalyzed oxidation (MCO) of Aß primarily targets the residues involved in copper coordination during HO˙ production. In the present work, we demonstrate that the oxidative damage undergone by Aß during MCO lead to a change in copper coordination, with enhanced catalytic properties that increases the rates of ascorbate consumption and HO˙ production, and the amount of HO˙ released by the system. This phenomenon is observed after the peptide has been sufficiently oxidized.