Quantum Dot Imaging of Neural Cells and Tissue - Nanotechnology for Biology and Medicine - page 152

could serve as useful nanoscale platforms to target, probes, and deliver chemicals to
specifi c subcellular structures.
A unique class of nanoparticles is quantum dots (QDs). QDs are fl uorescent
spherical nanoparticles that have extremely well-controlled size dimensions and
exhibit novel photophysical properties, including extended photostability and mul-
ticolor excitation. The unique physical properties of QDs have only begun to be
understood and their application to biology is very recent. However, even at these
early stages, it is clear that QDs offer capabilities that will make signifi cant future
contributions to biology. In the past few years, there has been rapid progress along
the lines of QD synthesis and surface chemical developments. As the properties of
QDs and their interaction in physiological systems become more clearly under-
stood, QD-based biological applications are poised for further development of more
sophisticated and specialized biological and disease-oriented problems.
The nervous system is a complex organ that presents unique challenges for study
at the systems, tissue, and cellular level. Knowledge about the fundamental central
and peripheral neural processes underlying neuronal signaling, development, learn-
ing, and sensing have been enabled by crucial technological advances in physics,
chemistry, and engineering. We believe that QD nanoparticles can further enable
signifi cant technological advances in neuroscience. In this chapter we review the
history and development of QDs and their initial application in biology, specifi cally
concentrating on current QD-neuroscience applications. We also discuss specifi c
areas of neuroscience that would benefi t from development of future QD applica-
tions. QDs are largely used in biological studies as substitutes for fl uorescent tags,
but they are yet to be fully developed to address a variety of specifi c and signifi cant
questions in neuroscience basic research and biomedical therapies. The successful
results of QD-based work in a broad range of cell systems and applications indicate
that the convergence of development of QDs for neuroscience will prove to be a
rewarding area of future technology advancement.

2 Unique Challenges Presented by Neuroscience

The problem of trying to understand the brain is an immense and demanding chal-
lenge. The brain is the most complex tissue in the body, with a greater diversity of
cell types than all other organs and tissues combined. Furthermore, 100 billion of
neurons each make synaptic connections to one another, processing and propagat-
ing dynamic information that serves as the underlying mechanism of behavior, cog-
nition, neural development, learning, and sensory and autonomic processing. The
nanometer size and complexity of neuroanatomical structures, small quantities of
neurochemicals, rapid time course of exchange, and dynamic fl exibility of this pro-
cess present signifi cant challenges for understanding fundamental neural function.
Neurotransmission is mediated by the release of neurotransmitter ligands from as
little as a one vesicle, a spherical structure 30-50 nm in diameter, into a synaptic
cleft measuring 30 nm in width (Rieke and Schwartz 1996 ; Zhai and Bellen 2004 ;