Shell Semiconductor Nanocrystals for Biological Labeling

Core-Shell Semiconductor Nanocrystals for Biological Labeling 

In this chapter, we discuss core-shell semiconductor quantum dots and their applications in biological labeling (Fig. 12.1). In comparison with organic dyes and fluorescent proteins, semiconductor quantum dots represent a new class of fluorescent labels with unique advantages and applications. For example, the fluorescence emission spectra of quantum dots can be continuously tuned by changing the particle size, and a single wavelength can be used for simultaneous excitation of all different-sized QDs. 

In semiconductor nanocrystals, optical absorption and photoluminescence are different from those in traditional, molecular systems. In semiconductors, the absorption of a photon causes a valence band electron to be promoted into the con- 

The Chemistry of Nanomaterials Synthesis, Properties and Applications, Volume 2. Edited by C. N. R. Rao, A. Muller, A. K. Cheetham 

Copyright 2004 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30686-2 

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I 72 Core-Shell Semiconductor Nanocrystals for Biological Labeling... 

Quantum dots (QDs) are semiconductor nanocrystals with unique and size-dependent electronic and fluorescent properties. The properties of QDs have sparked interest in many commercial applications, including computing, photovoltaic cells, and biological labeling. CdSe QDs are the most common type of QDs considered for use in biological applications. The CdSe core is often surrounded by another semiconductor shell, such as ZnS, to enhance emission properties. The shell of QDs can be capped with functionalized thiol molecules to make them water soluble and may be additionally coated with polymer or protein coatings to make them biologically compatible. 

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