Search query: Metal-enhanced fluorescence of colloidal nanocrystals with nanoscale control

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abstract: Engineering the spectral properties of fluorophores, such as the enhancement of luminescence intensity, can be achieved through coupling with surface plasmons in metallic nanostructures1,2,3,4,5,6,7,8,9,10,11. This process, referred to as metal enhanced fluorescence, offers promise for a range of applications, including LEDs, sensor technology, microarrays and single molecule studies. It becomes even more appealing when applied to colloidal semiconductor nanocrystals, which exhibit size dependent optical properties, have high photochemical stability, and are characterized by broad excitation spectra and narrow emission bands12. Other approaches have relied upon the coupling of fluorophores (typically organic dyes) to random distributions of metallic nanoparticles or nanoscale roughness in metallic films1,2,3,4,6,8. Here, we develop a new strategy based on the highly reproducible fabrication of ordered arrays of gold nanostructures coupled to CdSe/ZnS nanocrystals dispersed in a polymer blend. We demonstrate the possibility of obtaining precise control and a high spatial selectivity of the fluorescence enhancement process.
author_names: Pier Paolo Pompa

Luigi Martiradonna

Antonio Della Torre

F Della Sala

Liberato Manna

Massimo de Vittorio

Franco Calabi

Roberto Cingolani

Rosaria Rinaldi
title: Metal enhanced fluorescence of colloidal nanocrystals with nanoscale control
venue: Nature nanotechnology
year: 2006

abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2 3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling To whom correspondence should be addressed. E mail: dvtalapin@uchicago.edu. The University of Chicago. Argonne National Lab. Chem. Rev. 2010, 110, 389 458 389
author_names: Dmitri V Talapin

Jong-Soo Lee

Maksym V Kovalenko

Elena V Shevchenko
title: Prospects of colloidal nanocrystals for electronic and optoelectronic applications.
venue: Chemical reviews
year: 2010

abstract: Colloidal metal nanoparticles are emerging as key materials for catalysis, plasmonics, sensing, and spectroscopy. Within these applications, control of nanoparticle shape lends increasing functionality and selectivity. Shape controlled nanocrystals possess well defined surfaces and morphologies because their nucleation and growth are controlled at the atomic level. An overall picture of shaped metal particles is presented, with a particular focus on solution based syntheses for the noble metals. General strategies for synthetic control are discussed, emphasizing key factors that result in anisotropic, nonspherical growth such as crystallographically selective adsorbates and seeding processes.
author_names: Andrea R Tao

Susan E Habas

Peidong Yang
title: Shape Control of Colloidal Metal Nanocrystals
year: 2008

abstract: We present an experimental and theoretical study of the fluorescence rate of a single molecule as a function of its distance to a laser irradiated gold nanoparticle. The local field enhancement leads to an increased excitation rate whereas nonradiative energy transfer to the particle leads to a decrease of the quantum yield (quenching) Because of these competing effects, previous experiments showed either fluorescence enhancement or fluorescence quenching. By varying the distance between molecule and particle we show the first experimental measurement demonstrating the continuous transition from fluorescence enhancement to fluorescence quenching. This transition cannot be explained by treating the particle as a polarizable sphere in the dipole approximation.
author_names: Pascal Anger

Palash Bharadwaj

Lukas Novotny
title: Enhancement and quenching of single molecule fluorescence.
venue: Physical review letters
year: 2006

abstract: Nanometre size inorganic dots, tubes and wires exhibit a wide range of electrical and optical properties that depend sensitively on both size and shape, and are of both fundamental and technological interest. In contrast to the syntheses of zero dimensional systems, existing preparations of one dimensional systems often yield networks of tubes or rods which are difficult to separate. And, in the case of optically active II VI and III V semiconductors, the resulting rod diameters are too large to exhibit quantum confinement effects. Thus, except for some metal nanocrystals, there are no methods of preparation that yield soluble and monodisperse particles that are quantum confined in two of their dimensions. For semiconductors, a benchmark preparation is the growth of nearly spherical II VI and III V nanocrystals by injection of precursor molecules into a hot surfactant. Here we demonstrate that control of the growth kinetics of the II VI semiconductor cadmium selenide can be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rod like one, with aspect ratios as large as ten to one. This method should be useful, not only for testing theories of quantum confinement, but also for obtaining particles with spectroscopic properties that could prove advantageous in biological labelling experiments and as chromophores in light emitting diodes.
author_names: Xiaogang Peng

Liberato Manna

Weidong Yang

Juanita Wickham

Erik C Scher

Andreas V Kadavanich

A Paul Alivisatos
title: Shape control of CdSe nanocrystals
venue: Nature
year: 2000

abstract: Abstract Solution phase syntheses and size selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ~1 to 20 nm and monodisperse to =5% are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals) Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter particle separations 5 100 A, dipole dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass.
author_names: Christopher B Murray

Cherie R Kagan

Moungi G Bawendi
title: Synthesis and Characterization of Monodisperse Nanocrystals and Close Packed Nanocrystal Assemblies
year: 2000

abstract: The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications1,2,3. The synthesis of monodisperse nanocrystals (size variation <5% is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal based optical devices is strongly dependent on the uniformity of the nanocrystals3,4,5,6, and monodisperse magnetic nanocrystals are critical for the next generation multi terabit magnetic storage media7,8,9. For these monodisperse nanocrystals to be used, an economical mass production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub gram quantities of monodisperse nanocrystals were produced. Uniform sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15) Co (refs 16 18) g Fe2O3 (refs 19,20) and Fe3O4 (refs 21,22) have been synthesized by using various synthetic methods23. Here, we report on the ultra large scale synthesis of monodisperse nanocrystals using inexpensive and non toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.
author_names: Jongnam Park

Kwang Jun An

Yosun Hwang

Je-Guen Park

H J Noh

Jae-Young Kim

Jae-hoon Park

Nong-Moon Hwang

Taeghwan Hyeon
title: Ultra large scale syntheses of monodisperse nanocrystals
venue: Nature materials
year: 2004

abstract: Due to their interesting properties, research on colloidal nanocrystals has moved in the last few years from fundamental research to first applications in materials science and life sciences. In this review some recent biological applications of colloidal nanocrystals are discussed, without going into biological or chemical details. First, the properties of colloidal nanocrystals and how they can be synthesized are described. Second, the conjugation of nanocrystals with biological molecules is discussed. And third, three different biological applications are introduced: (i) the arrangement of nanocrystal oligonucleotide conjugates using molecular scaffolds such as single stranded DNA, (ii) the use of nanocrystal protein conjugates as fluorescent probes for cellular imaging, and (iii) a motility assay based on the uptake of nanocrystals by living cells.
author_names: Wolfgang J Parak

Daniele Gerion

Teresa Pellegrino

Daniela Zanchet

Christine M Micheel

Shara C Williams

Rosanne Boudreau

Mark A Le Gros

Carolyn A Larabell

A Paul Alivisatos
title: Biological applications of colloidal nanocrystals
year: 2003

abstract: Metallic particles and surfaces display diverse and complex optical properties. Examples include the intense colors of noble metal colloids, surface plasmon resonance absorption by thin metal films, and quenching of excited fluorophores near the metal surfaces. Recently, the interactions of fluorophores with metallic particles and surfaces (metals) have been used to obtain increased fluorescence intensities, to develop assays based on fluorescence quenching by gold colloids, and to obtain directional radiation from fluorophores near thin metal films. For metal enhanced fluorescence it is difficult to predict whether a particular metal structure, such as a colloid, fractal, or continuous surface, will quench or enhance fluorescence. In the present report we suggest how the effects of metals on fluorescence can be explained using a simple concept, based on radiating plasmons (RPs) The underlying physics may be complex but the concept is simple to understand. According to the RP model, the emission or quenching of a fluorophore near the metal can be predicted from the optical properties of the metal structures as calculated from electrodynamics, Mie theory, and/or Maxwell's equations. For example, according to Mie theory and the size and shape of the particle, the extinction of metal colloids can be due to either absorption or scattering. Incident energy is dissipated by absorption. Far field radiation is created by scattering. Based on our model small colloids are expected to quench fluorescence because absorption is dominant over scattering. Larger colloids are expected to enhance fluorescence because the scattering component is dominant over absorption. The ability of a metal's surface to absorb or reflect light is due to wavenumber matching requirements at the metal sample interface. Wavenumber matching considerations can also be used to predict whether fluorophores at a given distance from a continuous planar surface will be emitted or quenched. These considerations suggest that the so called "lossy surface waves" which quench fluorescence are due to induced electron oscillations which cannot radiate to the far field because wavevector matching is not possible. We suggest that the energy from the fluorophores thought to be lost by lossy surface waves can be recovered as emission by adjustment of the sample to allow wavevector matching. The RP model provides a rational approach for designing fluorophore metal configurations with the desired emissive properties and a basis for nanophotonic fluorophore technology.
author_names: Joseph R Lakowicz
title: Radiative decay engineering 5: metal enhanced fluorescence and plasmon emission.
venue: Analytical biochemistry
year: 2005

abstract: Since the use of magnetic nanocrystals as probes for biomedical system is attractive, it is important to develop optimal synthetic protocols for high quality magnetic nanocrystals and to have the systematic understanding of their nanoscale properties. Here we present the development of a synthetically controlled magnetic nanocrystal model system that correlates the nanoscale tunabilities in terms of size, magnetism, and induced nuclear spin relaxation processes. This system further led to the development of high performance nanocrystal antibody probe systems for the diagnosis of breast cancer cells via magnetic resonance imaging.
author_names: Young-wook Jun

Yong-Min Huh

Jin-Sil Choi

Jae-Hyun Lee

Ho-Taek Song

Sungjun Kim

Sarah Yoon

Kyung-sup Kim

Jeon-Soo Shin

Jin-Suck Suh

Jinwoo Cheon
title: Nanoscale size effect of magnetic nanocrystals and their utilization for cancer diagnosis via magnetic resonance imaging.
venue: Journal of the American Chemical Society
year: 2005