Hydrophilic Upconversion Nanoparticles Research Articles

Silk‐Based Functional Inks with Color‐Tunable Light Upconversion for Printing on Arbitrary Surfaces

AbstractA biocompatible and versatile silk‐based functional ink with hydrophilic upconversion nanoparticles (UCNPs) that can be printed or painted on arbitrary substrates, including biological surfaces is demonstrated. Hydrophilic UCNPs, ready to be dispersed in aqueous silk fibroin solution, are synthesized in large quantities via facile hydrothermal synthesis using citric acid. Based on a systematic study of dopant control to achieve robust red emission from citrate‐capped UCNPs, three primary colors are obtained, which serve as the basis for the expansion of the color palette. The synthesized UCNPs are homogeneously dispersed in regenerated silk fibroin solutions derived from Bombyx mori cocoons to produce water‐based functional inks. Cyan, magenta, and yellow (CMY) inks are created by combining red, green, and blue (RGB) inks. Demonstrator devices, where a variety of colorful patterns and codes are revealed only under near‐infrared irradiation, are realized through stencil printing or brush painting on flexible polymer films, fruit, leaves, silkworm cocoons, and pig skin. The patterns and codes are highly heat resistant (≈230 °C) and can be easily washed off with water after use. The printable/paintable inks and functions proposed here will provide new opportunities for applications where sustainability, biocompatibility, and intentional luminescence are simultaneously required.

Light-Emitting Diode Excitation for Upconversion Microscopy: A Quantitative Assessment

Lanthanide-based upconversion nanoparticles (UCNPs) generally require high power laser excitation. Here, we report wide-field upconversion microscopy at single-nanoparticle sensitivity using incoherent excitation of a 970 nm light-emitting diode (LED). We show that due to its broad emission spectrum, LED excitation is about 3 times less effective for UCNPs and generates high background compared to laser illumination. To counter this, we use time-gated luminescence detection to eliminate the residual background from the LED source, so that individual UCNPs with high sensitizer (Yb3+) doping and inert shell protection become clearly identified under LED excitation at 1.18 W cm-2, as confirmed by correlated electron microscopy images. Hydrophilic UCNPs are obtained by polysaccharide coating via a facile ligand exchange protocol to demonstrate imaging of cellular uptake using LED excitation. These results suggest a viable approach to bypassing the limitations associated with high-power lasers when applying UCNPs and upconversion microscopy to life science research.

Evaluation of Luminescence Properties of Single Hydrophilic Upconversion Nanoparticles by Optical Trapping

By using multifunctional optical tweezers (OT) equipped with a 980 nm continuous-wave single-mode diode laser and multiple detectors, we are able to trap single upconversion nanoparticles stably as...

β-NaYF4:Yb3+/Er3+ nanocrystals embedded sol-gel glass ceramics for self-calibrated optical thermometry

β-NaYF4:Yb3+/Er3+ nanocrystals embedded transparent glass ceramic has been successfully fabricated by direct incorporation of hydrophilic upconversion nanoparticles (UCNPs) into sol-gel silica glass and subsequent heat treatment. The temperature-sensitive upconversion luminescent behaviors of the as-fabricated UCNPs-silica glass ceramic are systemically investigated in order to investigate its potential application as luminescent thermometric medium. Impressively, benefiting from low-phonon-energy environment, highly UC emission for erbium ions in β-NaYF4 nanophase and high transparency, good chemical/mechanical stability of the oxide glass matrix, the investigated glass ceramic has superiorities of high relative temperature sensitivity (~ 1.16% K−1) and excellent thermal stability for accurate temperature sensing. This preliminary study not only provides a reference for fabricating other transparent bulk glass ceramics containing highly luminescent nanomaterials, but also exploits an effective approach for developing high-performance luminescent thermometers.

Nanohybrid scaffolds with luminescent remote control

We report on hybrid nanocomposite scaffolds on the base of cross-linked hyaluronic acid derivative with embedded upconversion nanoparticles (UCNPs). The unique photoluminescence properties of specially designed hydrophilic UCNPs enable visualization of hydrogel using NIR irradiation. Formation of scaffold structure can be produced by means of 3D printing or direct laser writing. For the first time, we present visualization of nanohybrid scaffolds in live small animal aiming to demonstrate new possibilities of their luminescent remote control for tissue engineering.

Simple synthesis of amino acid-functionalized hydrophilic upconversion nanoparticles capped with both carboxyl and amino groups for bimodal imaging.

The development of multimodal imaging probes carrying more than one modifiable site is very important in medical diagnosis. Herein, we demonstrate that amino acids, including acidic, neutral and basic amino acids, can be used as stabilizers and functional agents for the simple, one-step hydrothermal synthesis of hydrophilic upconversion nanoparticles (UCNPs) with a pure hexagonal phase and strong upconversion luminescence (UCL). The surface of the as-prepared UCNPs was capped with both carboxyl and amino groups, which not only provided the NPs with good dispersity in water, but also made further conjugation with two different biomolecules (e.g. targeted molecules and functional agents) possible. By co-doping different lanthanide ions, amino acid-functionalized UCNPs with different-colored UCL and different functions were obtained. For example, aspartate (Asp)-functionalized NaLuF4 co-doped with Tm3+ and Gd3+ not only emitted strong UCL in the range of the biological transparent window, but also has great potential as a T1-weighted magnetic resonance (MR) imaging contrast agent. The as-prepared Asp-NaLuF4:Gd/Yb/Tm UCNPs were successfully used in the UCL/MR bimodal in vivo imaging of nude mice.

A Facile Method for the One-Step Synthesis of Hydrophilic Up-Conversion Nanoparticles.

Up-conversion nanoparticles made from NaYF4:Yb3+, Er3+ have been used as imaging materials in many studies. These stable luminescence materials always needs hydrophilic modification to meet the challenges in biomedical applications. In our work, hydrophilic up-conversion nanoparticles (HUNPs) with stable luminescence character were prepared by a one-step method. The excitation wavelength of this type of nanoparticles is 980 nm. Furthermore, from the data of zeta potential measurement and energy dispersive X-ray (EDX) analysis, we deduced that these nanoparticles exhibited amino groups on the surface. MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide) study showed that the as-prepared up-conversion nanoparticles demonstrated low cytotoxicity and excellent biocompatibility.

Comparison of Two Methods for NaYF<SUB>4</SUB>: Yb, Er/Tm Hydrophilic Upconversion Nanoparticles Synthesis

Comparison of Two Methods for NaYF<SUB>4</SUB>: Yb, Er/Tm Hydrophilic Upconversion Nanoparticles Synthesis

Design of multifunctional alkali ion doped CaF2 upconversion nanoparticles for simultaneous bioimaging and therapy

Herein, alkali ion doped CaF2 upconversion nanoparticles (UCNPs) were first reported as a multifunctional theranostic platform for dual-modal imaging and chemotherapy. Interestingly, we found that the alkali ions doping approach could efficiently enhance the upconversion luminescence (UCL) intensity, whereas slightly affect the phase and morphology of the resulting products. In order to further improve the UCL efficacy for bioimaging, a pristine CaF2 shell was grown on the CaF2:Yb, Er core surface to enhance the UCL intensity. After being transferred into hydrophilic UCNPs, these water-soluble UCNPs could be served as contrast agents for in vitro/in vivo UCL imaging and X-ray computed tomography (CT) imaging. Furthermore, the as-prepared UCNPs could also be employed as nano-carriers for drug delivery. Doxorubicin (DOX) can be easily loaded onto the UCNPs and the DOX-loaded UCNPs exhibit a good cell killing ability. Therefore, the multifunctional core-shell CaF2 UCNPs with UCL/CT imaging and drug carrier properties may find extensive applications in simultaneous imaging diagnosis and therapy.

Water-Soluble Upconversion Nanoparticles by Micellar Route

Upconversion nanoparticles (UCNs) have been of interest in applications such as biological imaging and sensing because of properties like low autofluorescence and negligible photobleaching. In this paper, a micellar encapsulation route was worked upon to make hydrophilic UCNs that are compatible with biological systems and enable conjugation of biomolecules. Phospholipid micelles cannot be easily synthesized with chemical recognition groups of biological interest so synthetic amphiphiles with suitable functional head groups were used to encapsulate and solubilize the hydrophobic UCNs. The encapsulated nanoparticles were characterized using transmission electron microscopy, fluorescence spectroscopy, and dynamic light scattering. The micelle-encapsulated UCNs had an average diameter of 125 nm and the fluorescence emission at 540/660 nm of the bare UCNs did not show any shift after encapsulation. The cytotoxicity of the micelle-encapsulated UCNs was tested using lactose dehydrogenase/MTS (tetrazole salt) assays. The cell viability was estimated to be 80 % at the working concentration of the micelle-encapsulated UCNs. Finally, the micelle-encapsulated UCNs bearing Arg-Gly-Asp tripeptidic RGD surface functionalization were tested on cancer cells expressing integrins for specificity. The micelle-encapsulated UCNs were found to be suitable for cellular targeting and imaging.

Amphiphilic chitosan modified upconversion nanoparticles for in vivo photodynamic therapy induced by near-infrared light

Upconversion nanoparticles (UCNPs) have attracted much attention as potential photosensitizer carriers for photodynamic therapy (PDT) in deep tissues. In this study, hydrophilic UCNPs were prepared by coating amphiphilic chitosan (N-succinyl-N′-octyl chitosan, SOC) on the surface of hydrophobic oleic acid-capped NaYF4 UCNPs (OA-UCNPs). Water-insoluble photosensitizer zinc(II) phthalocyanine (ZnPc) was loaded into the SOC-coated UCNPs (SOC-UCNPs) via hydrophobic interactions to form a novel drug delivery system for in vivo deep tissue PDT triggered by near-infrared (NIR) light. The ZnPc-loaded SOC-UCNPs exhibited good dispersibility, excellent optical properties and good photostability. Under NIR light irradiation, the measurement of singlet oxygen production indicated that ZnPc effectively generated singlet oxygen induced by the emission from the UCNPs. Cell viability assays showed the low cytotoxicity of the UCNPs after surface modification. In vitro and in vivo therapeutic investigation evidenced the prominent PDT effects of ZnPc-loaded SOC-UCNPs upon NIR light irradiation. Furthermore, NIR imaging of ICG derivative-loaded SOC-UCNPs after intra-tumoral injection indicated the high retention of SOC-UCNPs only in the tumor site. Histological examination confirmed the negligible toxicity of ZnPc-loaded SOC-UCNPs on other organs. All the results demonstrate the promising potential of using SOC-UCNPs as new photosensitizer carriers for PDT of cancer and other diseases in deep tissues.