Biomedical Engineering Reference
In-Depth Information
glutamate-activated a-amino-3-hydroxy-5-methyl-isoxazole propionate (AMPA)
channels/receptors with good specifi city (Howarth et al. 2005 ). Pinaud et al. have
designed a synthetic cysteine-rich phytochelatin-related peptide and used it to coat
QDs (Pinaud et al. 2004 ). QDs coated with peptides containing glutamic acid resi-
dues showed good solubillization, stability and unaltered photophysical properties.
The authors also showed successful labeling of cells expressing avidin-CD14
chimeric proteins with biotinylated peptide coated QDs. It is to be expected that
future surface modifi cations using alternative organic QD coatings such as these
peptides will improve the size and stability of QDs for biological applications.
Quantum Dot Toxicity
Due to their heavy metal cadmium and selenium composition, there have been con-
cerns related to the potential toxicity of QDs. Currently, most reports have not found
evidence for QD cytoxicity as assessed by change in cell morphology in in vitro cell
cultures (Jaiswal et al. 2003 ), and by injecting them into embryos and other animals
models for up to 4 months (Dubertret et al. 2002 ; Alivisatos et al. 2005 ) . The release of
Cd 2+ , enhanced by UV surface oxidation of QDs, has been reported to harm cultured
cells, but this effect has been shown to be signifi cantly repressed by the formation
of a ZnS shell around the QD CdSe core (Derfus et al. 2004b ) . Other sources of
cytotoxicity could originate not from release of Cd 2+ but rather from the biomolecu-
lar QD surface coatings or from potential aggregation that surface coating may
produce (Hoshino et al. 2004 ; Kirchner et al. 2005 ). It has also been proposed that
the size of QDs, once they get endocytosed, could interfere with normal cell func-
tion, and produce toxic effects though this has not yet been thoroughly investigated
(Shiohara et al. 2004 ). The potential harmful effects of QDs will depend on param-
eters that differ from study to study, such as specifi c chemical composition of the
QD core and shell (ZnS shell, polyethylene glycol coat), as well as environmental
conditions, such as illumination, time scale of exposure, and quantities exposed.
More studies that use more stringent toxicological criteria will be needed to exam-
ine factors that may bring about QD longer periods of time.
Current Applications of Quantum Dots to Neuroscience
Quantum Dots for Immunolabeling Neural Receptors
Receptor composition, distribution, and dynamics play a central role in initiating
various signaling pathways in the nervous system mediated by any single type of
particular ligand, or chemical group such as a neurotransmitter, antigen, hormone or
synthetic drug analog (Gur and Yarden 2004 ). The composition of receptors on any
neuron varies in population and density as a function of space and time. Commonly
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