12
Core–Shell Semiconductor Nanocrystals for
Biological Labeling
R. E. Bailey and S. Nie
12.1
Introduction
Extensive research in nanomaterials has been mainly directed towards their potential use in microelectronics, optoelectronics, and high-density memory devices
[1–10]. Recent progress has also demonstrated that nanostructured materials such
as semiconductor quantum dots (QDs) have important applications in biology and
medicine [11, 12]. This fusion of nanotechnology and biotechnology is creating a
new frontier in which multifunctional or ‘‘smart’’ structures could be designed for
disease detection, diagnosis, and treatment [13]. Current efforts in this area have
produced biocompatible nanoparticles conjugated to peptides [14], proteins [15–
17], and DNA [18, 19]. These nanobioconjugates are useful for homogeneous bioassays [20–22], as multicolor luminescent labels [15–19], as well as for bottom-up
assembly of novel materials [23, 24]. For semiconductor nanocrystals, major improvements have occurred in both chemical synthesis [25] and surface conjugation
[15, 16], producing large quantities of high-quality and commercially available
luminescent nanoparticles.
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.
12.2
Optical Properties
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 con405
Core–Shell Semiconductor Nanocrystals for
Biological Labeling
R. E. Bailey and S. Nie
12.1
Introduction
Extensive research in nanomaterials has been mainly directed towards their potential use in microelectronics, optoelectronics, and high-density memory devices
[1–10]. Recent progress has also demonstrated that nanostructured materials such
as semiconductor quantum dots (QDs) have important applications in biology and
medicine [11, 12]. This fusion of nanotechnology and biotechnology is creating a
new frontier in which multifunctional or ‘‘smart’’ structures could be designed for
disease detection, diagnosis, and treatment [13]. Current efforts in this area have
produced biocompatible nanoparticles conjugated to peptides [14], proteins [15–
17], and DNA [18, 19]. These nanobioconjugates are useful for homogeneous bioassays [20–22], as multicolor luminescent labels [15–19], as well as for bottom-up
assembly of novel materials [23, 24]. For semiconductor nanocrystals, major improvements have occurred in both chemical synthesis [25] and surface conjugation
[15, 16], producing large quantities of high-quality and commercially available
luminescent nanoparticles.
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.
12.2
Optical Properties
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 con405