Encapsulation of InP/ZnS Quantum Dots into MOF-5 Matrices for Solid-State Luminescence: Ship in the Bottle and Bottle around the Ship Methodologies.

The utilization of InP-based quantum dots (QDs) as alternative luminescent nanoparticles to cadmium-based QDs is actively pursued. However, leveraging their luminescence for solid-state applications presents challenges due to the sensitivity of InP QDs to oxidation and aggregation-caused quenching. Hence, an appealing strategy is to protect and disperse InP QDs within hybrid materials. Metal-organic frameworks (MOFs) offer a promising solution as readily available crystalline porous materials. Among these, MOF-5 (composed of {Zn4O}6+ nodes and terephthalate struts) can be synthesized under mild conditions (at room temperature and basic pH), making it compatible with InP QDs. In the present work, luminescent InP/ZnS QDs are successfully incorporated within MOF-5 by two distinct methods. In the bottle around the ship (BAS) approach, the MOF was synthesized around the QDs. Alternatively, in the ship in the bottle (SIB) strategy, the QDs were embedded via capillarity into a specially engineered, more porous variant of MOF-5. Comparative analysis of the BAS and SIB approaches, evaluating factors such as operational simplicity, photoluminescence properties, and the resistance of the final materials to leaching were carried out. This comparative study provides insights into the efficacy of these strategies for the integration of InP/ZnS QDs within MOF-5 for potential solid-state applications in materials chemistry.

Ligand Tail Controls the Conformation of Indium Sulfide Ultrathin Nanoribbons.

We report the conformational control of 2D ultrathin indium sulfide nanoribbons by tuning their amine ligands' alkyl chain. The initial orthorhombic InS nanoribbons bare n-octylamine ligands and display a highly curved geometry with a characteristic figure of eight shapes. Exchanging the native ligand by oleylamine induces their complete unfolding to yield flat board-shaped nanoribbons. Significant strain variations in the InS crystal structure accompany this shape-shifting. By tuning the linear alkyl chain length from 4 to 18 carbon atoms, we show using small-angle X-ray scattering in solution and transmission electron microscopy that the curvature of the nanoribbon subtly depends on the ligand-ligand interactions at the nanoribbon's surface. The curvature decreases gradually as the chain length increases, while carbon unsaturation has an unexpectedly significant effect at constant chain length. These experiments shed light on the critical role of the ligand monolayer on the curvature of ultrathin 2D crystalline nanosheets and demonstrate that weak supramolecular forces within the organic part of colloidal nanocrystals can dramatically impact their shape. This transduction mechanism, in which changes in the organic monolayer impact the shape of a nanocrystal, will help to devise new strategies to design stimuli-responsive systems that take advantage of both the flexibility of organic moieties and the physical properties of the inorganic core.

Metal Fluorides Passivate II-VI and III-V Quantum Dots.

Quantum dots (QDs) with metal fluoride surface ligands were prepared via reaction with anhydrous oleylammonium fluoride. Carboxylate terminated II-VI QDs underwent carboxylate for fluoride exchange, while InP QDs underwent photochemical acidolysis yielding oleylamine, PH3, and InF3. The final photoluminescence quantum yield (PLQY) reached 83% for InP and near unity for core-shell QDs. Core-only CdS QDs showed dramatic improvements in PLQY, but only after exposure to air. Following etching, the InP QDs were bound by oleylamine ligands that were characterized by the frequency and breadth of the corresponding ν(N-H) bands in the infrared absorption spectrum. The fluoride content (1.6-9.2 nm-2) was measured by titration with chlorotrimethylsilane and compared with the oleylamine content (2.3-5.1 nm-2) supporting the formation of densely covered surfaces. The influence of metal fluoride adsorption on the air stability of QDs is discussed.

A First Wide-Open LDH Structure Hosting InP/ZnS QDs: A New Route Toward Efficient and Photostable Red-Emitting Phosphor.

The architecture of Zn-Al layered double hydroxides (LDHs), organo-modified with bola-amphiphiles molecules, is matching its interlayer space to the size of narrow-band red-emitting InP/ZnS core-shell quantum dots (QDs) to form original high-performance functional organic-inorganic QD-bola-LDH hybrids. The success of size-matching interlayer space (SMIS) approach is confirmed by X-ray diffraction, small angle X-ray scattering (SAXS), TEM, STEM-HAADF, and photoluminescence investigations. The QD-Bola-LDH hybrid exhibits a photoluminescence quantum yield three times higher than that of pristine InP/ZnS QDs and provides an easy dispersion into silicone-based resins, what makes the SMIS approach a change of paradigm compared to intercalation chemistry using common host structures. Moreover, this novel hybrid presents low QD-QD energy transfer comparable to that obtained for QDs in suspension. Composite silicone films incorporating InP/ZnS (0.27 wt%) QD-bola-LDH hybrids further show remarkable improved photostability relative to pristine QDs. An LED overlay consisting of a blue LED chip and silicone films loaded with QD-bola-LDH hybrids and YAG:Ce phosphors exhibits a color rendering index close to 94.

Synthesis and in vitro preliminary evaluation of prostate-specific membrane antigen targeted upconversion nanoparticles as a first step towards radio/fluorescence-guided surgery of prostate cancer.

Over the last decade, upconversion nanoparticles (UCNP) have been widely investigated in nanomedicine due to their high potential as imaging agents in the near-infrared (NIR) optical window of biological tissues. Here, we successfully develop active targeted UCNP as potential probes for dual NIR-NIR fluorescence and radioactive-guided surgery of prostate-specific membrane antigen (PSMA)(+) prostate cancers. We designed a one-pot thermolysis synthesis method to obtain oleic acid-coated spherical NaYF4:Yb,Tm@NaYF4 core/shell UCNP with narrow particle size distribution (30.0 ± 0.1 nm, as estimated by SAXS analysis) and efficient upconversion luminescence. Polyethylene glycol (PEG) ligands bearing different anchoring groups (phosphate, bis- and tetra-phosphonate-based) were synthesized and used to hydrophilize the UCNP. DLS studies led to the selection of a tetra-phosphonate PEG(2000) ligand affording water-dispersible UCNP with sustained colloidal stability in several aqueous media. PSMA-targeting ligands (i.e., glutamate-urea-lysine derivatives called KuEs) and fluorescent or radiolabelled prosthetic groups were grafted onto the UCNP surface by strain-promoted azide-alkyne cycloaddition (SPAAC). These UCNP, coated with 10 or 100% surface density of KuE ligands, did not induce cytotoxicity over 24 h incubation in LNCaP-Luc or PC3-Luc prostate cancer cell lines or in human fibroblasts for any of the concentrations evaluated. Competitive binding assays and flow cytometry demonstrated the excellent affinity of UCNP@KuE for PSMA-positive LNCaP-Luc cells compared with non-targeted UCNP@CO2H. Furthermore, the binding of UCNP@KuE to prostate tumour cells was positively correlated with the surface density of PSMA-targeting ligands and maintained after 125I-radiolabelling. Finally, a preliminary biodistribution study in LNCaP-Luc-bearing mice demonstrated the radiochemical stability of non-targeted [125I]UCNP paving the way for future in vivo assessments.