“Cloud” assemblies: quantum dots form electrostatically bound dynamic nebulae around large gold nanoparticles

“Cloud” assemblies: quantum dots form electrostatically bound dynamic nebulae around large gold nanoparticles†

G. Daniel Lilly,^a Jaebeom Lee^ab and Nicholas A. Kotov*^abcd

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* Corresponding authors

^a Department of Chemical Engineering, University of Michigan, Ann Arbor, USA
E-mail: kotov@umich.edu

^b Department of Nanomedical Engineering, Pusan National University, Pusan, Korea

^c Department of Material Sciences and Engineering, University of Michigan, Ann Arbor MI, USA

^d Department of Biomedical Engineering, University of Michigan, Ann Arbor MI, USA

Abstract

Dynamic self-assembled structures of nanoparticles can be produced using predominantly electrostatic interactions. Such assemblies were made from large, positively charged Au metal nanoparticles surrounded by an electrostatically bound cloud of smaller, negatively charged CdSe/ZnS or CdTe quantum dots. At low concentrations they are topologically similar to double electric layers of ions and corona-like assemblies linked by polymer chains. They can also be compared to the topological arrangement of some planetary systems in space. The great advantages of the cloud assemblies are (1) their highly dynamic nature compared to more rigid covalently bound assemblies, (2) simplicity of preparation, and (3) exceptional versatility in components and resulting optical properties. Photoluminescence intensity enhancement originating from quantum resonance between excitons and plasmons was observed for CdSe/ZnS quantum dots, although CdTe dots displayed emission quenching. To evaluate more attentively their dynamic behavior, emission data were collected for the cloud-assemblies with different ratios of the components and ionic strengths of the media. The emission of the system passes through a maximum for 80 QDs ∶ 1 Au NP as determined by the structure of the assemblies and light absorption conditions. Ionic strength dependence of luminescence intensity contradicts the predictions based on the Gouy–Chapman theory and osmotic pressure at high ionic strengths due to formation of larger chaotic colloidally stable assemblies. “Cloud” assemblies made from different nanoscale components can be used both for elucidation of most fundamental aspects of nanoparticle interactions, as well as for practical purposes in sensing and biology.

This article is part of the themed collection: Supraparticle physical chemistry

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Article information

DOI: https://doi.org/10.1039/C0CP00186D
Article type: Paper
Submitted: 11 Apr 2010
Accepted: 24 Jun 2010
First published: 29 Jul 2010

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Phys. Chem. Chem. Phys., 2010,12, 11878-11884

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