Upconversion nanoparticles with a strong acid-resistant capping

Abstract

Water-dispersible upconversion nanoparticles (β-NaYF4:Yb(3+),Er(3+), UCNP) coated with a thin shell of a biocompatible copolymer comprising 2-hydroxyethylmethacrylate (HEMA) and 2-acrylamido-2-methyl-1-propanesulphonsulphonic acid (AMPS), which we will term COP, have been prepared by multidentate grafting. This capping is remarkably resistant to strong acidic conditions as low as pH 2. The additional functionality of the smart UCNP@COP nanosystem has been proved by its association to a well-known photosensitizer (namely, methylene blue, MB). The green-to-red emission ratio of the UC@COP@MB nanohybrid exhibits excellent linear dependence in the 7 to 2 pH range as a consequence of the release of the dye as the pH decreases.

Surface chemistry modified upconversion nanoparticles as fluorescent sensor array for discrimination of foodborne pathogenic bacteria

“…As an excellent anti-stokes luminescent element, the fluorescence emission spectra of the three UCNPs@ COPs materials under 980 nm excitation wavelengths were further investigated in physiological saline solution/ DMSO (9:1). As expected, the prominent fluorescence emission spectra of the three UCNPs@COPs materials showed the typical green upconversion emissions of NaYF 4 : Er 3+ , Yb 3+ (the characteristic of Er 3+ corresponded to the ( 2 H11/2 and 4 S3/2) → 4 I15/2 transitions) [27], and the fluorescence emission intensity of the three UCNPs@COPs materials decreased slighter than that of the bare UCNPs at the same concentration, which was attributed to the weakened luminescence caused by the capping agents COPs (Additional file 1: Figure S7A). Meanwhile, the capping agents COPs with different functional groups did give rise to certain difference of fluorescence emission intensity.…”

“…Moreover, UCNPs-based probes have excellent photo-stability, multicolor tunable property, less toxic elements, negligible autofluorescence background and the minimal photo blinking and photo bleaching [10-12, 21, 25], which can heavily improve the sensitivity and reliability of detection. In addition, surface chemistry modification further endows UCNPs materials versatile properties and enables these functional UCNPs materials to realize the tunable charges and solubility, and target diversity, which provides a large library for sensor selection [10,12,22,26,27].…”

Lengthening the Lifetime of Common Emissive Probes to Microseconds by a Jigsaw‐Like Construction of NIR‐Responsive Nanohybrids

“…The chemical strategies usually employed to load a high concentration of a desired molecule of interest (e.g., biomolecules, probes, chromophores, or drugs) on an UCNP surface or its periphery are interdigitation of amphiphilic molecules, covalent linkage, ligand exchange or oxidation, and electrostatic interactions. [ 13,18,19 ] In the last few years, we have used strategies that are now well known to design smart photoactive upconversion nanohybrids for different purposes (e.g., colocalization of different payloads, [ 20 ] photodynamic therapy, [ 21,22 ] pH‐triggered release of a photosensitizer loaded on polymer coated‐UCNPs that are very resistant to strong acidic pHs, [ 23,24 ] etc.). Among them, cucurbituril‐capped UCNPs (UC@CB), easily prepared by reaction of bare UCNPs with CB, proved to be useful as a scaffold for cationic dyes, such as methylene blue, [ 25 ] thanks to the high electron density at the free CB carbonyl portal.…”

Systematic Investigation of Functional Ligands for Colloidal Stable Upconversion Nanoparticles

“…16 Among surface modication methods, polymers containing single or multiple anchoring ligands, such as hydroxyl, amine, carboxylic acid, sulphonic acid, phosphonate and phosphate groups, have been extensively studied to modify the positively charged surface of UCNPs and other inorganic nanoparticles. 15,[17][18][19] However, to our best knowledge, there is no report that specically focuses on the inuence of structural variation of functional ligands on the coating density, dispersity and more importantly, the extended colloidal stability of polymer functionalized UCNPs. To ll this knowledge gap, our work provides a systematic study of competitive adsorption at the nanocrystal surface between multidentate phosphate, carboxylic and sulphonic acids with oleate ligands.…”