ABSTRACT
Fluorescent semiconductor nanocrystals, also called quantum dots (QDs), have
been widely used and investigated in the fields of analytical chemistry and
bioengineering, especially in fluorescent labeling for both in vivo cellular and
molecular imaging and in vitro assay detection. Applications of QDs include
serving as specific markers for cellular and molecular structures, tracing cell
line age, monitoring physiological events in live cells, measuring cell motility, and
tracking cells in vivo. Comparedwith the organic dyemolecules, QDs have several
advantages. Organic dye molecules have narrow absorption bands which make it
difficult to excite multiple colors with a single excitation source. The emission
density of organic dye molecules relies on the environment. They could not
offer long-term photostability. They suffer from fast photobleaching and broad,
overlapping emission lines (Gerion et al., 2001). The biological applications of
the traditional organic dye are thus limited. Instead, QDs give several interesting
and powerful optical properties, such as tunable emission from visible to
infrared wavelengths by changing their size and composition, broad excitation
spectra with higher absorption coefficients, high quantum yield of fluorescence,
stronger brightness and photostability, and high resistance to photobleaching.
All those features have attracted tremendous interest in exploiting biomedical
applications of QDs (Alivisatos et al., 2005; Ballou et al., 2004).
