Quantum dots (QDs) are semiconductor nanocrystals with extensive imaging and diagnostic capabilities, including the
potential for single molecule tracking. Commercially available QDs offer distinct advantages over organic fluorophores,
such as increased photostability and tunable emission spectra, but their cadmium selenide (CdSe) core raises toxicity
concerns. For this reason, replacements for CdSe-based QDs have been sought that can offer equivalent optical
properties. The spectral range, brightness and stability of InP QDs may comprise such a solution. To this end,
LANL/CINT personnel fabricated moderately thick-shell novel InP QDs that retain brightness and emission over time in
an aqueous environment. We are interested in evaluating how the composition and surface properties of these novel QDs
affect their entry and sequestration within the cell. Here we use epifluorescence and transmission electron microscopy
(TEM) to evaluate the structural properties of cultured Xenopus kidney cells (A6; ATCC) that were exposed either to
commercially available CdSe QDs (Qtracker® 565, Invitrogen) or to heterostructured InP QDs (LANL). Epifluorescence
imaging permitted assessment of the general morphology of cells labeled with fluorescent molecular probes (Alexa
Fluor® ® phalloidin; Hoechst 33342), and the prevalence of QD association with cells. In contrast, TEM offered unique
advantages for viewing electron dense QDs at higher resolution with regard to subcellular sequestration and
compartmentalization. Preliminary results show that in the absence of targeting moieties, InP QDs (200 nM) can
passively enter cells and sequester nonspecifically in cytosolic regions whereas commercially available targeted QDs
principally associate with membranous structures within the cell. Supported by: NIH 5R01GM084702.
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