Plasmon Modulated Upconversion Biosensors

Over the past two decades, lanthanide-based upconversion nanoparticles (UCNPs) have been fascinating scientists due to their ability to offer unprecedented prospects to upconvert tissue-penetrating near-infrared light into color-tailorable optical illumination inside biological matter. In particular, luminescent behavior UCNPs have been widely utilized for background-free biorecognition and biosensing. Currently, a paramount challenge exists on how to maximize NIR light harvesting and upconversion efficiencies for achieving faster response and better sensitivity without damaging the biological tissue upon laser assisted photoactivation. In this review, we offer the reader an overview of the recent updates about exciting achievements and challenges in the development of plasmon-modulated upconversion nanoformulations for biosensing application.

Poly(4-Styrenesulfonic Acid-co-maleic Anhydride)-Coated NaGdF4:Yb,Tb,Nd Nanoparticles with Luminescence and Magnetic Properties for Imaging of Pancreatic Islets and β-Cells

Novel Yb,Tb,Nd-doped GdF₃ and NaGdF₄ nanoparticles were synthesized by a coprecipitation method in ethylene glycol (EG) in the presence of the poly(4-styrenesulfonic acid-co-maleic anhydride) stabilizer. The particle size and morphology, crystal structure, and phase change were controlled by adjusting the PSSMA concentration and source of fluoride anions in the reaction. Doping of Yb³⁺, Tb³⁺, and Nd³⁺ ions in the NaGdF₄ host nanoparticles induced luminescence under ultraviolet and near-infrared excitation and high relaxivity in magnetic resonance (MR) imaging (MRI). In vitro toxicity of the nanoparticles and their cellular uptake efficiency were determined in model rat pancreatic β-cells (INS-1E). As the NaGdF₄:Yb,Tb,Nd@PSSMA-EG nanoparticles were non-toxic and possessed good luminescence and magnetic properties, they were applicable for in vitro optical and MRI of isolated pancreatic islets in phantoms. The superior contrast was achieved for in vivo T₂*-weighted MR images of the islets transplanted under the kidney capsule to mice in preclinical trials.

Single-Source Precursors for Chemical Solution Deposition of Up-Converting NaLnF4 Thin Films

Novel single-source precursors based on sodium and lanthanide pentafluoropropionates have been developed for chemical solution deposition of NaLnF4 thin films (Ln = Y, Yb, Er, Tm). A series of [Ln2(pfp)6Qn] (Q = H2O, diglyme) and mixed-metal NaLn(pfp)4Qn were synthesized and characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TG-DTA). Thermal decomposition of individual Na(pfp) and Ln(pfp)3 occurs at different temperatures while single-source NaLn(pfp)4 decomposes with the transformation to NaLnF4 in a single stage at 280 °C. Further crystallization of NaLnF4 was studied by variable-temperature powder XRD, which shows two phase transformations from cubic NaLnF4 to hexagonal NaLnF4 at 310 °C and back to a high-temperature cubic phase at 560 °C. The thin films of NaY0.78Yb0.2Er0.02F4 prepared by the dip-coating technique on Al2O3 substrates showed intense up-converting luminescence in green and blue regions under 980 nm excitation.

Crystallization of Gd2O3 nanoparticles: evolution of the microstructure via electron-beam manipulation

NaGdF4 is one of the most commonly employed phosphor host matrices for lanthanide doping and is one of the most efficient infrared-to-visible up-conversion fluorescent host materials. Although the structure, morphology and luminescence properties of NaREF4 have been sufficiently investigated, there are very few reported instances of introducing localized order/crystallinity by electron-beam (e-beam) irradiation. In this work, we studied the phase transformation of Gd2O3 from an amorphous to crystalline form via manipulation by e-beam irradiation. The amorphous Gd2O3 occurs as an impurity in the cubic-NaGdF4 nanoparticles (NPs). The structural evolutions, including the transformation from amorphous to crystalline, the recrystallization process and the formation of the graphene@NP core-shell structure, are discussed in detail. We also propose an evolution scheme, in which the e-beam manipulation of the organic-containing NPs induces a subtle structural transformation, depending in principle on the microenvironment of the NPs.

Nanometric NaYF4 as an Unconventional Support for Gold Catalysts for Oxidation Reactions

The metal-support interaction plays an important role in gold catalysis. We employ here crystalline cubic (α-) and hexagonal (β-) phases of heterometallic fluoride NaYF₄ nanoparticles (NPs), obtained by the decomposition of a single source precursor [NaY(TFA)₄(diglyme)] (TFA = trifluoroacetate), as nonoxide supports for gold catalysts. Using an isostructural gadolinium analogue, we also obtained doped α-NaYF₄:Gd³⁺ and β-NaYF₄:Gd³⁺ NPs. A successful deposition of ∼1% by weight gold NPs of average size 5-6.5 nm on these doped and undoped metal fluorides using HAuCl₄·3H₂O afforded Au/NaYF₄ catalysts which were thoroughly characterized by using several physicochemical techniques such as X-ray diffraction, Brunauer-Emmett-Teller analysis, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. A comparative study of the above catalysts for different oxidation reactions show that while for the aerobic oxidation of trans-stilbene in solution phase, they are either better (in terms of stilbene conversion) or at par (in terms of trans-stilbene oxide yield) in comparison to the reference catalyst Au/TiO₂ of the World Gold Council, their activity toward CO oxidation reactions in gas phase remains much less than that of gold catalysts supported on metal oxides.

Asymmetrically substituted triazenes as poor electron donor ligands in the precursor chemistry of iron(ii) for iron-based metallic and intermetallic nanocrystals

First as precursors: Heteroleptic Fe^II complexes derived from new asymmetric triazene ligands t-BuNN-NHR (R = Et, i-Pr, n-Bu) show interesting molecular and precursor chemistry.