Unique Upconversion Luminescence Research Articles

ZnO Nanoparticles Modified by Carbon Quantum Dots for the Photocatalytic Removal of Synthetic Pigment Pollutants.

Synthetic pigment pollutants caused by the rapid development of the modern food industry have become a serious threat to people's health and quality of life. Environmentally friendly ZnO-based photocatalytic degradation exhibits satisfactory efficiency, but some shortcomings of large band gap and rapid charge recombination reduce the removal of synthetic pigment pollutants. Here, carbon quantum dots (CQDs) with unique up-conversion luminescence were applied to decorate ZnO nanoparticles to effectively construct the CQDs/ZnO composites via a facile and efficient route. The ZnO nanoparticles with a spherical-like shape obtained from a zinc-based metal organic framework (zeolitic imidazolate framework-8, ZIF-8) were coated by uniformly dispersive quantum dots. Compared with single ZnO particles, the obtained CQDs/ZnO composites exhibit enhanced light absorption capacity, decreased photoluminescence (PL) intensity, and improved visible-light degradation for rhodamine B (RhB) with the large apparent rate constant (k app). The largest k app value in the CQDs/ZnO composite obtained from 75 mg of ZnO nanoparticles and 12.5 mL of the CQDs solution (∼1 mg·mL-1) was 2.6 times that in ZnO nanoparticles. This phenomenon may be attributed to the introduction of CQDs, leading to the narrowed band gap, an extended lifetime, and the charge separation. This work provides an economical and clean strategy to design visible-light-responsive ZnO-based photocatalysts, which is expected to be used for the removal of synthetic pigment pollutants in food industry.

Engineered lanthanide-doped upconversion nanoparticles for biosensing and bioimaging application.

Various fluctuations of intracellular ions, biomolecules, and other conditions in the physiological environment play crucial roles in fundamental biological processes. These factors are of great importance for analysis in biomedical detection. Nevertheless, developments of the simple, rapid, and accurate proof for specific detection still encounter major challenges. Upconversion nanoparticles (UCNPs), which could absorb multiple low-energy near-infrared light (NIR) photon excitation and emits high-energy photons caused by anti-Stokes shift, show unique upconversion luminescence (UCL) properties, for example, sharp emission band, high physicochemical stability like near-zero photobleaching, photo blinking in biological tissues, and long luminescence lifetime. Furthermore, the NIR used for the light source to excite UCNPs enable lower photo-damage effect and deeper penetration of tissue, and in the meantime, it can avoid the auto-fluorescence and light scattering from biological tissue interference. Thus, the lanthanide-doped UCNP-based functional platform with controlled structure, crystalline phase, size, and multicolor emission has become an appropriate nanomaterial for bioapplications such as biosensing, bioimaging, drug release, and therapies. In this review, the recent progress about synthesis and biomedical applications of UCNPs related to sensing and bioimaging is summarized. Firstly, the different luminescence mechanisms of the upconversion process are presented. Secondly, four of the most common methods for synthesizing UCNPs are compared as well as the advantages and disadvantages of these synthetic routes. Meanwhile, the surface modification of lanthanide-doped UCNPs was introduced to pave the way for their biochemistry applications. Next, this review detailed the biological applications of lanthanide-doped UCNPs, particularly in bioimaging, including UCL and multi-modal imaging and biosensing (monitoring intracellular ions and biomolecules). Finally, the challenges and future perspectives in materials science and biomedical fields of UCNPs are concluded: the low quantum yield of the upconversion process should be considered when they are executed as imaging contrast agents. And the biosafety of lanthanide-doped UCNPs needs to be evaluated.

Recent advances in upconversion nanoparticle-based nanocomposites for gas therapy.

Gas therapy has attracted wide attention for the treatment of various diseases. However, a controlled gas release is highly important for biomedical applications. Upconversion nanoparticles (UCNPs) can precisely convert the long wavelength of light to ultraviolet/visible (UV/Vis) light in gas therapy for the controlled gas release owing to their unique upconversion luminescence (UCL) ability. In this review, we mainly summarized the recent progress of UCNP-based nanocomposites in gas therapy. The gases NO, O2, H2, H2S, SO2, and CO play an essential role in the physiological and pathological processes. The UCNP-based gas therapy holds great promise in cancer therapy, bacterial therapy, anti-inflammation, neuromodulation, and so on. Furthermore, the limitations and prospects of UCNP-based nanocomposites for gas therapy are also discussed.

High-Purity Carbon Dots Prepared by Modulating Morphology of Carbon Nano-Crystals: In Vitro and In Vivo Multi-Color Bioimaging

Due to the unique optical properties and excellent biological applications, carbon-based luminescent materials have become a research hotspot in recent years. In this paper, we report a synthesis method under mild condition, in which Carbon NanoCrystals (CNCs) were first prepared, and then high-purity multi-color carbon dots (HPMCCDs) were synthesized by modulating crystal morphology. The prepared nonfluorescent CNCs are, respectively, dissolved in a strong polar solvent and a weak polar solvent to prepare HPMCCDs. It exhibits the multi-excitation and multi-emission features (from green to yellow). The high-purity carbon dots (HPCDs) prepared by using this method demonstrate the higher quantum yields (QYs) (53.7%) than that of the carbon dots (CD) by traditional hydrothermal methods with dialysis, and make full use of the atomic economic model. Besides, it shows the unique up-conversion luminescence property (UCLP) at lower wavelength excitation and, which can also be placed for a long time at room temperature without being oxidized or deteriorated. Furthermore, we explored the regulation of polar-chromism mechanism of the CNCs. Finally, the HPMCCDs can be used for multi-color bioimaging in vivo and in vitro and as well as many other potential applications.

Ultrabright Full Color Carbon Dots by Fine-Tuning Crystal Morphology Controllable Synthesis for Multicolor Bioimaging and Sensing.

In this paper, two kinds of novel carbon nanocrystals (CNCs) with different crystal morphologies (the branch-chain young sprout form (CM1) and conifer-pine form (CM2)) were obtained in a controllable way. The mechanism of crystal morphological development was explored well. When the two kinds of the CNCs were dissolved in different polar solvents, they voluntarily become "ultrafine crystals" at the moment. After that, the ultrabright full color carbon dots (UBFCCDs) have been preliminarily prepared by fine-controlling. With the evaporation of the solvents, the CNCs crystallized again, which could repeat back and forth many times. After the conditions of preparing for CDs were optimized carefully, the as-prepared CDs exhibit ultrabright effects of multiexcitation and multiemission (from blue to red) and can show unique up-conversion luminescence characteristics under a lower excitation wavelength of 660 nm instead of a near-infrared wavelength of 980 or 808 nm. Significantly, the QY% of the UBFCCDs can reach 78.0%, which is higher than that of the traditional hydrothermal methods of discarding precipitation and carrying out dialysis (QY% = 69.0%). The as-prepared CDs can be used for multicolor biomedical imaging in vivo and in vitro and metal ion sensing and also show their potential value for industrial applications.

Recent Progress in 808 nm Excited Upconversion Nanomaterials as Multifunctional Nanoprobes for Visualized Theranostics in Cancers.

Near-infrared (NIR) light responsive nanomaterials have attracted considerable attention due to their location in the biological window. Especially, lanthanide-doped nanomaterials exhibit unique upconversion luminescence (UCL) properties with low background interference and long luminescence lifetime, which makes them promising in imaging diagnosis of cancers. Compared with traditional upconversion nanomaterials excited by 980 nm laser, 808 nm excitation can overcome the disadvantages of high heating effect and weak penetration depth induced by excitation source. Therefore, developing 808 nm excited upconversion nanoprobes will be important for the in vivo bio-imaging and visualized theranostics of tumors in deep-tissue. In the review paper, we systematically summarized the synthesis strategy and luminescence modulation of Nd3+-sensitized upconversion nanomaterials under 808 nm excitation, discussed the influence of excitation source on heating effect and penetration depth, and particularly focused on their applications in UCL imaging, multi-modal imaging and imaging-guided therapy of cancers.

Construction of Hierarchical Polymer Brushes on Upconversion Nanoparticles via NIR-Light-Initiated RAFT Polymerization

Photoinduced reversible addition-fragmentation chain transfer (RAFT) polymerization generally adopts high-energy ultraviolet (UV) or blue light. In combination with photoredox catalyst, the excitation light wavelength was extended to the visible and even near-infrared (NIR) region for photoinduced electron transfer RAFT polymerization. In this report, we introduce for the first time a surface NIR-light-initiated RAFT polymerization on upconversion nanoparticles (UCNPs) without adding any photocatalyst and construct a functional inorganic core/polymer shell nanohybrid for application in cancer theranostics. The multilayer core-shell UCNPs (NaYF4:Yb/Tm@NaYbF4:Gd@NaNdF4:Yb@NaYF4), with surface anchorings of chain transfer agents, can serve as efficient NIR-to-UV light transducers for initiating the RAFT polymerization. A hierarchical double block copolymer brush, consisting of poly(acrylic acid) (PAA) and poly(oligo(ethylene oxide)methacrylate-co-2-(2-methoxy-ethoxy)ethyl methacrylate) (PEG for short), was grafted from the surface in sequence. The targeting arginine-glycine-aspartic (RGD) peptide was modified at the end of the copolymer through the trithiolcarbonate end group. After loading of doxorubicin, the UCNPs@PAA-b-PEG-RGD exhibited an enhanced U87MG cancer cell uptake efficiency and cytotoxicity. Besides, the unique upconversion luminescence of the nanohybrids was used for the autofluoresence-free cell imaging and labeling. Therefore, our strategy verified that UCNPs could efficiently activate RAFT polymerization by NIR photoirradiation and construct the complex nanohybrids, exhibiting prospective biomedical applications due to the low phototoxicity and deep penetration of NIR light.

Tagged and enhanced interface of carbon fiber/epoxy by doping sizing agent with upconversion luminescent nanoparticles

A luminescent labeling method was developed to tag and enhance the carbon fiber (CF)/epoxy interface by doping sizing agent with upconversion luminescent nanoparticles (LNs). Morphology observation indicated that the value of surface roughness (Ra) decreased after sizing process and the sizing layer was about 110nm thick. With the addition of LNs, the CF/epoxy interface was tagged with green luminescence, which showed that the interface enlarged to 1.2μm due to interdiffusion between sizing layer and epoxy matrix. The LNs also presented a positive effect on the interfacial adhesion of CF/epoxy composites through chemical bonding among the LNs, sizing layer and matrix. The unique upconversion luminescence and reactive groups of LNs were responsible for the mechanism of luminescent labeling and interfacial enhancement, respectively.

Lanthanide-doped NaScF4 nanoprobes: crystal structure, optical spectroscopy and biodetection

Trivalent lanthanide ions (Ln(3+))-doped inorganic nanoparticles (NPs) as potential luminescent bioprobes have been attracting tremendous interest because of their unique upconversion (UC) and downconversion (DC) luminescence properties. NaScF4, as an important host material, has been rarely reported and its crystal structure remains unclear. Herein, based on the single crystal X-ray diffraction, the space group of NaScF4 crystals was determined to be P31 containing multiple sites of Sc(3+) with crystallographic site symmetry of C1, which was verified by high-resolution photoluminescence spectroscopy of Eu(3+) at low temperature (10 K). Furthermore, monodisperse and size-controllable NaScF4:Ln(3+) NPs were synthesized via a facile thermal decomposition method. The biotinylated NaScF4:Er(3+)/Yb(3+) NPs were demonstrated for their applications as a heterogeneous UC luminescence bioprobe to detect avidin with a detection limit of 180 pM. After bioconjugation with amino-terminal fragment (ATF) of urokinase plasminogen activator (uPA), NaScF4:Ln(3+) NPs also exhibited specific recognition of cancer cells overexpressed with uPA receptor (uPAR, an important marker of tumor biology and metastasis), showing great potentials in tumor-targeted bioimaging.

PEGylated denatured bovine serum albumin modified water-soluble inorganic nanocrystals as multifunctional drug delivery platforms.

A novel approach of using denatured bovine serum albumin (dBSA) to modify hydrophobic nanocrystals is reported. The dBSA layer outside of nanocrystals can adsorb water insoluble drugs excellently via hydrophobic interactions. Further PEGylation of the engineered nanocrystals greatly improves their aqueous stability. PEGylated dBSA modified upconversion nanoparticles, as a model for construction of integrating imaging and drug delivery platform, were also studied. The results demonstrated the modified upconversion nanoparticles not only maintain their unique up-conversion luminescence characters but also exhibit higher drug loading ability. Thus, such novel PEGylated dBSA modification approach expands the range of biological applications of inorganic nanocrystals.

The up-conversion luminescent properties and silver-modified luminescent enhancement of YVO4:Yb3+, Er3+ NPs

In this paper, the unique up-conversion luminescence (UCL) properties of as-prepared and annealing YVO(4):Yb(3+), Er(3+) nanoparticles (NPs, ∼100 nm) and the corresponding YVO(4):Yb(3+), Er(3+)@Ag hybrids under 980 nm excitation were systemically studied through power-dependent, temperature-dependent emission spectra and dynamics. It is interesting to determine that the radiative transition rate of (2)H(11/2)/(4)S(3/2)-(4)I(15/2) for Er(3+) ions in YVO(4) is about an order of magnitude faster than that in the other hosts due to the wave function coupling with the 3d orbital of V(5+) and, thus, the up-conversion (UC) green emissions of YVO(4):Yb(3+), Er(3+) NPs is efficient. In addition, efficient novel UC broad band centering around 630 nm (1.97 eV) was observed in YVO(4):Yb(3+), Er(3+) powders, which was attributed to defect emissions related to oxygen vacancies near V(5+) sites in the lattices of YVO(4). In as-prepared YVO(4):Yb(3+), Er(3+)@Ag hybrids colloids, more than one order UCL enhancement than YVO(4):Yb(3+), Er(3+) was observed. Powder and the annealing samples lead the UCL enhancement effect to disappear. The main UCL enhancement mechanism of YVO(4):Yb(3+), Er(3+)@Ag hybrids colloids was attributed to prevent YVO(4):Yb(3+), Er(3+) interaction with the solution, instead of surface plasmon enhancement (SPE) effect.

High uniformity and monodispersity of sodium rare-earth fluoride nanocrystals: controllable synthesis, shape evolution and optical properties

Highly uniform and monodispersed pure hexagonal phase NaReF4 (Re = Y, Pr–Nd, and Sm–Yb) nanocrystals with well-defined morphologies, including pills, rods, spheres, tubes, and plates, were systematically synthesized by a facile solution-based hydrothermal method using oleic acid as a stabilizing agent. Crystal phase, shape and size can be tuned readily by simply adjusting the molar ratio of F/Re and reaction temperature. Detailed experimental studies revealed that NaReF4 hosts strongly tend to form hexagonal phase nanocrystals with increasing rare earth ion radius. Based on the studies on crystal phase control and shape evolution of NaReF4 nanocrystals, the whole growth mechanism of nanocrystals can be concluded as a kinetic and thermodynamic growth process. Simultaneously, highly efficient up-conversion luminescence under 980 nm excitation was realized, such as eye-visible red, green, and blue up-conversion luminescence generated from NaYbF4 host doped with Er3+, Ho3+, and Tm3+, respectively. Due to their unique up-conversion luminescence, the highly uniform and monodispersed nanocrystals can be applied for biolabels, colour displays, light-emitting diodes, and solid-state lasers.

Laser Scanning Up-Conversion Luminescence Microscopy for Imaging Cells Labeled with Rare-Earth Nanophosphors

Because of the ability to selectively reveal the objects of interest with subcellular resolution, fluorescence microscopy provides widespread applications from basic biological research to clinical diagnosis. However, challenges still remain in reducing the degree of photobleaching and increasing the contrast between signal and noise. Herein, we found that rare-earth nanophosphors exhibit a unique up-conversion luminescence mechanism and imaging modality and developed a new three-dimensional visualization method of laser scanning up-conversion luminescence microscopy (LSUCLM) with little photobleaching and no background fluorescence, by introducing a reverse excitation dichroic mirror and the confocal pinhole technique. Moreover, we demonstrated the up-conversion emission imaging of thin films containing embedded rare-earth nanophosphors and cells multilabeled with the nanophosphors and organic dyes. These data show that LSUCLM not only shares noninvasive benefits and deep penetration of two-photon microscopy but also offers some distinct advantages, such as little photobleaching of both organic dyes and rare-earth nanophosphors, no background fluorescence from either endogenous fluorophores or colabeled fluorescent probes, and excellent compatibility with conventional confocal microscopy.