A versatile approach for the preparation of thermosensitive PNIPAM core-shell microgels with nanoparticle cores.
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Journal Article↗
Biomedical subjects
Luis M Liz-Marzán
Publications and source records attributed to Luis M Liz-Marzán.
Seeded growth of submicron Au colloids with quadrupole plasmon resonance modes.
A modified seeded growth process has been used for the controlled synthesis of quasispherical, CTAB-stabilized gold nanoparticles from 12 up to 180 nm with narrow size distributions. The UV-visible spectra of the aqueous colloids show distinct bands corresponding to dipole and quadrupole plasmon modes, for diameters above 100 nm, in close agreement with predictions based on Mie theory. The assignment of the modes is demonstrated by calculation of near field enhancement maps based on the boundary element method. Apart from other applications, since absorption is drastically reduced above 600 nm, while scattering is largely increased, these particles open new possibilities for construction of highly efficient photonic structures.
Journal Article↗
Tailoring surface plasmons through the morphology and assembly of metal nanoparticles.
Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.
Journal Article↗
Carbon nanotubes encapsulated in wormlike hollow silica shells.
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Carbon↗
Synthesis of core-shell nanoparticles using organic surface-functionalized gold and Au@SiO2 nanoparticles as multifunctional initiators in atom transfer radical polymerization.
Gold and Au@SiO2 nanoparticles were synthesized and surface-functionalized by initiators for atom transfer radical polymerization (ATRP), either using a thiol or a trialkoxysilane anchor group for the immobilization of the initiating functionality. The thus obtained initiator-capped gold systems were applied in polymerizations of various monomers, such as styrene, methacrylic acid trimethyloxysilyl propylester and isoprene and copolymers thereof. The final inorganic-organic core-shell nanoparticles were characterized applying different techniques such as electron microscopy and light scattering. Kinetic studies of the polymerizations revealed that they were highly controlled and therefore the thickness of the polymer shell could be easily adjusted. The obtained nanoparticles formed stable suspensions in various organic solvents and can therefore be used as building blocks for polymer nanocomposites.
Gold↗
Optically active poly(dimethylsiloxane) elastomer films through doping with gold nanoparticles.
Poly(dimethylsiloxane) (PDMS) elastomer films synthesized through a cross-linking reaction between hydroxyl-terminated or vinyl-terminated PDMS have been homogeneously doped with silica-coated Au nanoparticles. The nanocomposite synthesis involves mixing a preformed colloid of surface-modified metal nanoparticles with the elastomer film precursors. The homogeneous distribution of nanoparticles is demonstrated through the presence of well defined plasmon absorbance bands in the visible, which clearly show that the composites retain the characteristic optical properties of single Au nanoparticles. The metal particle concentration could be easily tailored either through the amount or the concentration of the nanoparticle colloid added. Since the Au nanoparticles are not cross-linked to the polymer and the concentration of particles is relatively low, we postulate that the presence of the nanoparticles does not affect the mechanical properties of the films, though this remains to be confirmed.
Dimethylpolysiloxanes↗
On the temperature stability of gold nanorods: comparison between thermal and ultrafast laser-induced heating.
The response of gold nanorods to both thermal and ultrafast laser-induced heating has been examined. The thermal heating experiments show structural changes that occur on timescales ranging from hours to days. At the highest temperature examined (250 degrees C) the nanorods are transformed into spheres within an hour. On the other hand, no structural changes are observed in the laser-induced heating experiments up to temperatures of 700 +/- 50 degrees C. This is attributed to thermal diffusion in the laser experiments. Measurements of the period of the extensional mode of the nanorods using time-resolved spectroscopy show a significant softening at high pump laser powers. However, the decrease in the period is less than expected from bulk Young's modulus vs. temperature data.
Journal Article↗
Spatially-directed oxidation of gold nanoparticles by Au(III)-CTAB complexes.
Gold nanoparticles are readily oxidized by Au(III) in the presence of cetyl-trimethylammonium bromide (CTAB). Oxidation occurs preferentially at surface sites with higher curvature. Conversely, oxidation with cyanide ions in the absence of CTAB leads to uniform oxidation over the whole surface. Examples of the spatially directed oxidation are provided using large, irregular spheres, nanocubes, and nanorods. We conclude that the mechanism of oxidation depends on whether the oxidant is attached to CTAB micelles. It is postulated that the CTAB micelles approach the nanoparticles preferentially at the tips, leading to spatially directed oxidation.
Letter↗
Aligning Au nanorods by using carbon nanotubes as templates.
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Journal Article↗
XPS characterization of Au (Core)/SiO2 (shell) nanoparticles.
Core-shell nanoparticles with ca. 15-nm gold core and 6-nm silica shell were prepared and characterized by XPS. The Au/Si atomic ratio determined by XPS is independent of the electron takeoff angle because of the concentric spherical shape of the nanoparticles. The formula given by Wertheim and DiCenzo (Phys. Rev. B 1988, 37, 844) for spherical nanoparticles and the modified one by Yang et. al. (J. Appl. Phys. 2005, 97, 024303) for core-shell nanoparticles are used to correlate the XPS-derived composition with the geometry of the nanoparticles only after significantly modifying either the bulk density of the silica shell or the attenuation length of the photoelectrons.
Letter↗
Silica coating of silver nanoparticles using a modified Stober method.
Silver nanoparticles prepared through a borohydride-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stober method. Various amine catalysts were used for initialization of a sol-gel reaction of TEOS with no need for a prior surface modification. Use of dimethylamine (DMA) as a catalyst was found to be necessary to obtain a proper coating. The silica shell thickness was varied from 28 to 76 nm for TEOS concentrations of 1-15 mM at 11.1 M water and 0.8 M DMA. The optical spectra of the core-shell silver-silica composite particles show a qualitative agreement with predictions by Mie theory.
Journal Article↗
Optical properties of nanoparticle-based metallodielectric inverse opals.
Metallodielectric inverse opals were prepared by co-crystallizing silica-coated gold nanoparticles and polymer spheres, followed by removal of the crystal template. The inverse opals exhibit a distinct reflectance peak, which results from Bragg diffraction due to the highly ordered 3D macroporous structure. Photonic band-structure calculations indicate that the characteristic reflectance peaks observed are signatures of the directional gap at the L point. It is demonstrated that the optical properties (the position and magnitude of the electromagnetic bandgaps) of the gold-silica nanocomposite inverse opals can be engineered by varying the nanoparticle morphology (core size and shell thickness) and/or the nanoparticle volume-filling ratio of the composite. The use of metallodielectric nanoparticles to form inverse opals offers a versatile approach to prepare photonic materials that may exhibit absolute bandgaps.
Crystallization↗
Flexible ureasil hybrids with tailored optical properties through doping with metal nanoparticles.
Hybrid organic-inorganic nanocomposites containing uniform distributions of metal nanoparticles have been prepared by mixing a preformed nanoparticle colloid with the precursors of a ureasil, prior to the sol-gel transition. These nanocomposites possess not only high optical quality and optical features dictated by the size and shape of the nanoparticle dopants but also a high degree of flexibility, which can largely enhance the range of applications in practical devices. The deposition of a uniform silica shell on the nanoparticle surface prior to the sol-gel transition was found to be required to maintain the colloidal stability during the process and, thus, to retain the optical properties in the final nanocomposite material. This method can be readily extended to other materials, such as semiconductor and magnetic nanoparticles.
Journal Article↗
Water-based ferrofluids from FexPt1-x nanoparticles synthesized in organic media.
This paper describes an effective method to transfer oleic acid/oleylamine-capped colloidal FePt nanoparticles dispersed in hexane into water, using tetramethylammonium hydroxide (TMAOH) as a phase transfer agent. FexPt1-x nanoparticles with different compositions (x = 0.32, 0.40, 0.48, 0.60, 0.66, 0.69) in the size range of 2-4 nm were synthesized by a high-temperature organometallic route with oleic acid and oleylamine as stabilizers. The surface of such nanoparticles was modified through removal of the organic, hydrophobic layer and adsorption of TMAOH, which provides the nanoparticles with sufficient surface charge so that an electrostatic double layer builds up, and the FePt nanoparticles can be fully redispersed in aqueous solution, even with high concentrations. The water-dispersible FePt nanoparticles were characterized by transmission electron microscopy, electrophoretic mobility, X-ray diffraction, and Fourier transform infrared spectroscopy.
Journal Article↗
AuAg bimetallic nanoparticles: formation, silica-coating and selective etching.
A time-resolved study of the formation of AuAg alloy nanoparticles during boiling of AgNO3 and HAuCl4 in the presence of sodium citrate has been performed by monitoring the UV-visible spectra of the solutions. This study reveals clear differences with respect to the formation of pure Au particles, and suggests that gold and silver nanoparticles nucleate separately, but lattice rearrangement eventually leads to formation of alloy nanoparticles with the expected composition, which was confirmed by high resolution TEM. Additionally, we studied the chemical reaction of the alloy nanoparticles with NH4OH, observing that part of the Ag atoms get oxidized, but reorganization of the crystal lattice during the reaction prevents full transformation into pure gold nanoparticles. This allows the synthesis of silica-coated bimetallic particles with tailored plasmon resonance between ca. 430 and 520 nm, as well as homogeneous incorporation of the coated alloy nanoparticles within silica gels.
Journal Article↗
Direct coating of gold nanoparticles with silica by a seeded polymerization technique.
Gold nanoparticles prepared through a conventional citrate-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stöber method. The method required no surface modification. The addition of tetraethylorthosilicate and water prior to ammonia was found to be critical to obtain a proper coating. The silica shell thickness was varied from 30 to 90 nm for TEOS concentrations of 0.0005-0.02 M at 10.9 M of water and 0.4 M of ammonia. The optical spectra of the core-shell gold-silica composite particles agreed with predictions of Mie theory.
Journal Article↗
Synthesis and assembly of SiO2-coated Bi2S3 nanofibers.
The SiO2 coating of Bi2S3 nanofibers using the alkaline hydrolysis of Si(OEt)4 is reported. A comparative study on the optical and morphological properties of the starting Bi2S3 nanofibers and the final SiO2 coated nanomaterials are presented and discussed. A SiO2 cap covering homogeneously single Bi2S3 nanofibers was obtained when the hydrolysis of Si(OEt)4 was performed under sonication treatment to maintain the fibers well separated during the coating process. These coated nanofibers were then used in a layer-by-layer deposition process to produce multilayered nanostructured films.
Journal Article↗
Multicolor luminescence patterning by photoactivation of semiconductor nanoparticle films.
Indiscriminate adsorption of nanoparticles (NPs) significantly complicates the preparation of mesoscale NP patterns considered as enabling technology for many devices and processes. Instead of selected chemical functionalization of the substrate surface prior to the assembly of nanocolloids, the required optical properties - in our case, high quantum yield luminescence - are imparted to the layer-by-layer assembled films by spatially selected photoactivation. The films are made by sequential adsorption of a positively charged polyelectrolyte and a negatively charged CdSe/CdS aqueous dispersion with an initial quantum yield of 0.5-2%. The photoactivation process takes place in the presence of oxygen and may be accompanied by photoetching. A 50-500-fold increase in the luminescence intensity of CdSe/CdS citrate-stabilized particles (quantum yield 25-45%) after visible light illumination provides excellent pattern contrast. Micron scale luminescence patterns were produced from NPs of various CdSe core diameters with red, yellow, and green emission. It was also demonstrated that different emission colors such as orange and green can be combined in one image by taking advantage of spatially selective photoetching. The presented optical patterning technique significantly simplifies the preparation of luminescence patterns as compared to conventional methods. The high signal-to-noise ratio associated with it is essential for optical devices, information processing, and biophotonics. The most immediate use of this approach is expected in cryptography and cell monitoring.
Cadmium Compounds↗