Sen Liang

Colorful detection of organic solvents based on responsive organic/inorganic hybrid one-dimensional photonic crystals

Solvent sensitive organic/inorganic hybrid one-dimensional photonic crystals (1DPCs) were prepared through alternating thin films of poly methyl methacrylate-co-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate (PMMA-co-PHEMA-co-PEGDMA) and titania nanoparticle sol by spin-coating. Since the titania layer has a higher refractive index compared with the polymer layer, an obvious photonic stop band (PSB) can be easily obtained in several layers. Meanwhile, the materials take on evident color as the PSB falls into the visible region. The PSB can be reversibly tuned by introducing or removing organic solvents. Due to different interactions between the polymer and solvent molecules, the PSB can be shifted to different positions when introducing different solvents. At the same time, the 1DPCs present different colors, and the solvents used can be differentiated by the naked eye through color change. The solvent responsive process is very quick and the solvent sensitivity is very high. Almost all common solvents can be distinguished in this way. As well as pure solvents, mixtures can also be detected through the changes of optical properties. The shift of the PSB and the response speed can be modulated by changing the thickness of the polymer layer, while the thickness of the titania layer has little influence on them.

A pluronic F127 coating strategy to produce stable up-conversion NaYF4:Yb,Er(Tm) nanoparticles in culture media for bioimaging†

Up-conversion nanoparticles (UCNPs) have exhibited great potential in biological imaging and labeling. The further development of the correlated techniques strongly depends on the stability of UCNPs in buffers and biological growth media. In this paper, Pluronic F127, a nonionic triblock copolymer of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO), is applied to coat the originally hydrophobic NaYF4:Yb,Er(Tm) UCNPs, leading to an oil-to-water phase transfer. After the phase transfer, F127-coated UCNPs are well dispersed in water with more than 43% UC luminescence preserved. Because of the nonionic nature of F127, the F127-coated UCNPs are quite stable in culture media, and exhibit excellent biocompatibility and low toxicity. The biocompatible decoration using F127 is facile and repeatable, thus facilitating the biological applications of UCNPs. As an example, the bioimaging of caenorhabditis elegans is demonstrated.

Fabrication of CdTe nanoparticles-based superparticles for an improved detection of Cu2+ and Ag+

Detection of highly toxic and bioaccumulative heavy metal ions using fluorescent semiconductor nanoparticles (NPs) has stimulated recent research interests, but the separation of NPs after detection has failed to be achieved. In this paper, fluorescent CdTe NPs-based superparticles (SPs) were fabricated using oil droplets in microemulsion as templates. By controlling the experimental variables, SPs with different fluorescence and composition were obtained. In particular, CdTe/Fe3O4 binary SPs simultaneously exhibited strong fluorescence and magnetism, thus achieving the separation of SPs. These CdTe-based SPs showed an improved detection of Cu2+ and Ag+.

Polymer Bragg stack as color tunable photonic paper

Polymer 1D photonic crystals with perfect optical tuning and distinctive brilliant colors are successfully fabricated through alternating thin films of PMMA and PNIPAM-co-PGMA, which can be easily processed as photonic paper by combining with top-down assisted photolithograph. The photonic paper is prewritten by ultraviolet light cross-linking with a photo mask and read with water as ink. The writing and erasing process is smoothly reversible by repeatedly exposing the material to water and air. The color of letters written on the paper can be modulated by tuning the cross-linking density and ink temperature. Moreover, multicolors can be integrated onto the photonic paper simultaneously by making the degree of cross-linking of different regions of the photonic paper different. The fabrication method is simple and low-cost, and the photonic paper can be easily manufactured in large areas. The integrated multicolor and its diverse change with external stimuli promises the photonic paper lots of potential applications, such as colorful sensors, security labels, full-color printing, displays and so on.

Patterning organic/inorganic hybrid Bragg stacks by integrating one-dimensional photonic crystals and macrocavities through photolithography: toward tunable colorful patterns as highly selective sensors.

Herein, we report a simple method to fabricate patterned organic/inorganic hybrid 1DPCs by top-down assisted photolithography. Versatile colorful pattern with different size and shape can be produced by selectively exposing the 1DPCs under UV light with predesigned photomask directly. The period change, especially the thickness variation of the top polymer layer, is the main reason for the colorful pattern generation. Because of the swelling property of the polymer layers, the pattern color can be modulated by introducing or taking off organic solvents, leading the as-prepared patterned 1DPCs to be effective sensors with high selectivity.

Decoration of up-converting NaYF4:Yb,Er(Tm) nanoparticles with surfactant bilayer. A versatile strategy to perform oil-to-water phase transfer and subsequently surface silication

Up-conversion rare-earth nanoparticles (UCNPs) are potential alternatives to down-conversion fluorescent quantum dots for biolabeling, and the prerequisite for biological applications is the enhancement of surface hydrophilicity and physiological stability of UCNPs. In this work, we demonstrated a facile method to modulate the surface functionality of original hydrophobic UCNPs by forming a surfactant bilayer, which made UCNPs dispersible in water. After oil-to-water phase transfer, more than 30% up-conversion luminescence was preserved. It was found that the key to avoiding the aggregation of bilayer-modified UCNPs was the concentration of surfactant. High concentration of surfactant led to bilayer-modified individual UCNPs, whereas insufficient surfactant generated the water-dispersible aggregates of UCNPs, namely UCNP superstructures. Various commercially available surfactants, such as cationic cetyltrimethylammonium bromide, anionic sodium dodecyl sulfate, and nonionic polyethylene glycol tert-octylphenyl ether, were practical, making the current method versatile for anchoring functional groups on UCNPs. Moreover, bilayer-modified UCNPs could act as a platform to perform surface silication, thus further improving the biocompatibility and stability of UCNPs.

Preparation of quantum dots-montmorillonite nanocomposites with strong photoluminescence for light-emitting diodes

CdTe quantum dots (QDs)/montmorillonite (MMT)-Na+ nanocomposites with tunable fluorescence colors and stable photoluminescence quantum yields (PLQYs) are used as the color convertors in commercial light-emitting diodes (LEDs) for the first time. By controlling the size of the CdTe QDs, the fluorescence colors of the nanocomposites can cover the range from green to red. Because of the high reducibility of N2H4, the current CdTe QDs synthesized through the N2H4-promoted strategy possess improved PL stability compared with those through the conventional reflux growth method. Furthermore, a freeze-drying instead of a precipitation pathway is employed for the separation of the nanocomposites from solvent, which efficiently avoids the aggregation induced by centrifugation. Owing to the great photoluminescence (PL) properties of the CdTe QDs/MMT-Na+ nanocomposites, the as-fabricated LEDs exhibit promising potential.