Kyoungja Woo

Bright dual-mode green emission from selective set of dopant ions in β-Na(Y,Gd)F 4 :Yb,Er/β-NaGdF 4 :Ce,Tb core/shell nanocrystals

Bright dual-mode green-emitting core/shell nanoparticles (NPs) were synthesized by doping selective set of lanthanide ions. Up-conversion (UC) green-emitting β-NaY0.2Gd0.6F4:Yb0.18,Er0.02 NPs (8.3 nm) were used as core material. Bright down-conversion (DC) green-emitting β-NaGd0.8F4:Ce0.15,Tb0.05 NPs showed ca. 31 times higher photoluminescence (PL) intensity than β-NaGdF4:Tb NPs and they were served as shell material with their excellent PL properties. The UC/DC core/shell NPs showed bright green light under excitations of 980 nm near infrared (NIR) light and 254 nm ultraviolet (UV) light, respectively. The UC/DC core/shell NPs showed ca. 11 times higher UC PL intensity than core UCNPs. Consequently, the core/shell NPs doped with selective set of lanthanide ions showed bright dual-mode green emission under excitations of NIR light and UV light, indicating that they are promising for application to optical imaging.

Highly bright multicolor tunable ultrasmall β-Na(Y,Gd)F4:Ce,Tb,Eu/β-NaYF4 core/shell nanocrystals

Herein, we report highly bright multicolor-emitting β-Na(Y,Gd)F₄:Ce,Tb,Eu/β-NaYF₄ nanoparticles (NPs) with precise color tunability. First, highly bright sub-20 nm β-Na(Y,Gd)F₄:Ce,Tb,Eu NPs were synthesized via a heating-up method. By controlling the ratio of Eu(3+) to Tb(3+), we generated green, yellow-green, greenish yellow, yellow, orange, reddish orange, and red emissions from the NP solutions via energy transfer of Ce(3+)→ Gd(3+)→ Tb(3+) (green) and Ce(3+)→ Gd(3+)→ Tb(3+)→ Eu(3+) (red) ions under ultraviolet light illumination (254 nm). Because of Ce(3+) and Gd(3+) sensitization, Tb(3+) ions exhibited strong green emission. The decay time of Tb(3+) emission decreased from 4.0 to 1.4 ms as the Eu(3+) concentration was increased, suggesting that energy was transferred from Tb(3+) to Eu(3+). As a result, Eu(3+) emission peaks were generated and the emission color was transformed from green to red. Monodisperse sub-6 nm β-Na(Y,Gd)F₄:Ce,Tb,Eu NPs were synthesized through a simple reduction of the reaction temperature. Although fine color tunability was retained, their brightness was considerably decreased owing to an increase in the surface-to-volume ratio. The formation of a β-NaYF₄ shell on top of the sub-6 nm NP core to produce β-Na(Y,Gd)F₄:Ce,Tb,Eu/β-NaYF₄ significantly increased the emission intensity, while maintaining the sub-10 nm sizes (8.7-9.5 nm). Quantum yields of the ultrasmall NPs increased from 1.1-6.9% for the core NPs to 6.7-44.4% for the core/shell NPs. Moreover, highly transparent core/shell NP-polydimethylsiloxane (PDMS) composites featuring a variety of colors, excellent color tunability, and high brightness were also prepared.

Facile synthesis and optical properties of colloidal silica microspheres encapsulating a quantum dot layer

We present colloidal silica microspheres encapsulating a homogeneous quantum dot layer at radial equidistance from the centre by utilizing electrostatic interaction between surface-engineered silica microspheres and QDs. The microspheres show dramatically enhanced optical absorption and emission with an appropriate silica shell thickness.

Surface modification of hydrophobic iron oxide nanoparticles for clinical applications

Monodisperse superparamagnetic iron oxide nanoparticles (SPIONs) were prepared by thermal decomposition of Fe(CO)/sub 5/ and by consecutive aeration in organic medium. The resultant hydrophobic SPION surface was modified to be hydrophilic via Fe-S covalent bond with bi-functional 3-mercaptopropionic acid and then, the terminal carboxylic acid group was esterified with dextran for biocompatibility. Analysis by water dispersity, transmission electron microscopy, X-ray diffraction, and Fourier transformed infrared spectroscopy are reported.

Core-shell bimetallic nanoparticles robustly fixed on the outermost surface of magnetic silica microspheres.

The major challenges in practically utilising the immense potential benefits of nanomaterials are controlling aggregation, recycling the nanomaterials, and fabricating well-defined nanoparticulate materials using innovative methods. We present a novel innovative synthetic strategy for core–shell bimetallic nanoparticles that are well-defined, ligand-free, and robustly fixed on the outermost surface of recyclable magnetic silica microspheres. The strategy includes seeding, coalescing the seeds to cores, and then growing shells from the cores on aminopropyl-functionalised silica microspheres so that the cores and aminopropyl moieties are robustly embedded in the shell materials. The representative Au–Ag bimetallic nanoparticles fixed on the microsphere showed excellent catalytic performance that remained consistent during repeated catalytic cycles.

Antiviral properties of silver nanoparticles on a magnetic hybrid colloid.

ABSTRACT Silver nanoparticles (AgNPs) are considered to be a potentially useful tool for controlling various pathogens. However, there are concerns about the release of AgNPs into environmental media, as they may generate adverse human health and ecological effects. In this study, we developed and evaluated a novel micrometer-sized magnetic hybrid colloid (MHC) decorated with variously sized AgNPs (AgNP-MHCs). After being applied for disinfection, these particles can be easily recovered from environmental media using their magnetic properties and remain effective for inactivating viral pathogens. We evaluated the efficacy of AgNP-MHCs for inactivating bacteriophage ϕX174, murine norovirus (MNV), and adenovirus serotype 2 (AdV2). These target viruses were exposed to AgNP-MHCs for 1, 3, and 6 h at 25°C and then analyzed by plaque assay and real-time TaqMan PCR. The AgNP-MHCs were exposed to a wide range of pH levels and to tap and surface water to assess their antiviral effects under different environmental conditions. Among the three types of AgNP-MHCs tested, Ag30-MHCs displayed the highest efficacy for inactivating the viruses. The ϕX174 and MNV were reduced by more than 2 log10 after exposure to 4.6 × 109 Ag30-MHCs/ml for 1 h. These results indicated that the AgNP-MHCs could be used to inactivate viral pathogens with minimum chance of potential release into environment.

Acute toxicity and tissue distribution of CdSe/CdS-MPA quantum dots after repeated intraperitoneal injection to mice

Quantum dots (QDs) are novel tools with multiple biological and medical applications because of their superior photoemission and photostability characteristics. However, leaching of toxic metals from QDs is of great concern. Therefore, for the successful application of QDs in bioscience, it is essential to understand their biological fate and toxicity. We investigated toxicological effects and tissue distribution of mercaptopropionic acid‐conjugated cadmium selenide/cadmium sulfide (CdSe/CdS‐MPA) QDs after repeated intraperitoneal injection into BALB/c mice. The mice were injected every 3 days with various doses of QDs (0, 5, 10 and 25 mg kg−1). The subsequent effects of QDs on plasma levels of various biomarkers were evaluated at different time points (at 0, 1, 4, 7, 10, 13 and 15 days). Various tissue samples (spleen, liver, lung, kidneys, brain, heart and thymus) were collected for toxicity analysis, distribution testing, histopathological examination and inflammation assessment. No abnormal clinical signs or behaviors were recorded but the body weight of mice treated with 25 mg kg−1 QDs was significantly decreased from day 7 compared with control mice. QDs were observed in the liver, spleen, lung and kidneys, but not in brain or heart. Significantly higher levels of lactate dehydrogenase and nicotinamide adenine dinucleotide phosphate oxidase were found in the plasma, liver and spleen. Histopathological examination did not show any tissue toxicity but the levels of interleukin‐6, a pro‐inflammatory marker, were increased in the plasma, liver and spleen. All of these findings provide insight into the observed toxicological effect levels and tissue‐specific distribution of CdSe/CdS‐MPA QDs. Copyright

Magnetic hybrid colloids decorated with Ag nanoparticles bite away bacteria and chemisorb viruses

Magnetic hybrid colloids (MHCs) decorated with different-sized Ag nanoparticles (Ag07@MHC, Ag15@MHC, and Ag30@MHC denote MHCs decorated with ∼7 nm, ∼15 nm, and ∼30 nm AgNPs, respectively) are synthesized and used to investigate their antimicrobial efficacy and mechanism. An MHC (diameter ∼ 0.6 μm) is a cluster of superparamagnetic Fe3O4 nanoparticles (∼10 nm) encapsulated with a silica shell (thickness ∼ 0.1 μm). The Ag30@MHC was prepared using the seed-growth method with Ag seeds self-assembled on the aminopropyl-functionalized MHC, and its surface is covered with AgNPs and Ag+ ions. The Ag07@MHC and Ag15@MHC were prepared using the seeding, coalescing, and growing strategy with Au seeds, and these MHCs released substantially less Ag+ ions than Ag30@MHC due to the contribution of the Au core. The Ag30@MHC exhibited the greatest antimicrobial efficacy towards E. coli CN13 (6-log reduction) and the bacteriophage MS2 (2-3 log reduction) due to the synergistic effect of the 3D architecture decorated with AgNPs and Ag+ ions as well as the already-known effects of free AgNPs. On the 3D architecture, the AgNPs abstract Mg2+ or Ca2+ ions from the bacterial membrane and the Ag+ ions grab the microorganisms by forming a complex with the thiol groups imbedded in the membrane, which bites away bacteria and completely ruptures the cell structure. The Ag30@MHC is easily collectible from the reaction mixture using an external magnet without detachment of AgNPs, and it is re-dispersible. Overall, Ag30@MHC is believed to be a promising antimicrobial material for practical applications.

Synthesis of blue emitting InP/ZnS quantum dots through control of competition between etching and growth

Blue (<480 nm) emitting Cd-free quantum dots (QDs) are in great demand for various applications. However, their synthesis has been challenging. Here we present blue emitting InP/ZnS core/shell QDs with a band edge emission of 475 nm and a full width at half maximum of 39 nm (215 meV) from their quantum confined states. The drastic temperature drop immediately after mixing of the precursors and holding them at a temperature below 150 °C was the critical factor for the synthesis of blue emitting QDs, because the blue QDs are formed by the etching of ultra-small InP cores by residual acetic acid below 150 °C. Etching was dominant at temperatures below 150 °C, whereas growth was dominant at temperatures above 150 °C. ZnS shells were formed successfully at 150 °C, yielding blue emitting InP/ZnS QDs. The colour of the InP/ZnS QDs depicted on the CIE 1931 chromaticity diagram is located close to the edge, indicating a pure blue colour compared to other InP-based QDs.

Facile synthesis of intense green light emitting LiGdF4:Yb,Er-based upconversion bipyramidal nanocrystals and their polymer composites

A pathway for achieving intense green light emitting LiGdF4:Yb,Er upconversion nanophosphors (UCNPs) via Y(3+) doping is demonstrated. It was revealed that Y(3+) doping initiated the formation of a tetragonal phase and affected the particle size. Single tetragonal-phase LiGd0.4Y0.4F4:Yb(18%),Er(2%) (LGY0.4F:Yb,Er) UCNPs exhibited strong upconversion (UC) green luminescence and tetragonal bipyramidal morphologies. They showed 1325 and 325-fold higher photoluminescence intensity than the 0 and 80 mol% Y(3+)-doped LiGdF4:Yb,Er UCNPs, respectively. Additionally the particle size (edge length) of LiGdF4:Yb,Er-based upconversion tetragonal bipyramids (UCTBs) was controlled from 60.5 nm to an ultrasmall size of 9.3 nm with varying Y(3+) doping concentration. In an LGY0.4F:Yb,Er UCTB, uniform distribution of all constituent elements was directly confirmed by using high-angle annular dark-field scanning transmission electron microscopy and energy-filtered transmission electron microscopy (EFTEM) image analyses. In particular, existence of activator Er(3+) ions with extremely small quantity was clearly seen over a particle on the EFTEM image. Moreover, the LGY0.4F:Yb,Er UCTBs were successfully incorporated into the polydimethylsiloxane (PDMS) polymer and the highly transparent UCTB-PDMS composites showed bright green light under the excitation of 980 nm infrared light.