tx2003195_si_002.avi (7.93 MB)
Contrast of the Biological Activity of Negatively and Positively Charged Microwave Synthesized CdSe/ZnS Quantum Dots
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posted on 2011-12-19, 00:00 authored by Amber Nagy, Andrew Zane, Sara L. Cole, Michael Severance, Prabir K. Dutta, W. James WaldmanQuantum dots (QDs) are semiconductor nanocrystals that
have found
use in bioimaging, cell tracking, and drug delivery. This article
compares the cytotoxicity and cellular interactions of positively
and negatively charged CdSe/CdS/ZnS QDs prepared by a microwave method
using a murine alveolar macrophage-like cell culture model. Keeping
the core semiconductor the same, QD charge was varied by altering
the surface capping molecule; negatively charged QDs were formed with
mercaptopropionic acid (MPA-QDs) and positively charged QDs with thiocholine
(THIO-QDs). The size and charge of these two QDs were investigated
in three types of media (RPMI, RPMI + FBS, and X-VIVO serum-free media)
relevant for the biological studies. MPA-QDs were found to have negative
zeta potential in RPMI, RPMI + FBS, and serum-free media and had sizes
ranging from 8 to 54 nm. THIO-QDs suspended in RPMI alone were <62
nm in size, while large aggregates (greater than 1000 nm) formed when
these QDs were suspended in RPMI + FBS and serum-free media. THIO-QDs
retained positive zeta potential in RPMI and were found to have a
negative zeta potential in RPMI + FBS and nearly neutral zeta potential
in serum-free media. In a cell culture model, both MPA-QDs and THIO-QDs
caused comparable levels of apoptosis and necrosis. Both QDs induced
significant tumor necrosis factor-alpha (TNF-α) secretion only
at high concentrations (>250 nM). Both types of QDs were internalized
via clathrin-dependent endocytosis. Using real-time, live cell imaging,
we found that MPA-QDs interact with the cell surface within minutes
and progress through the endocytic pathway to the lysosomes upon internalization.
With the THIO-QDs, the internalization process was slower, but the
pathways could not be mapped because of spectroscopic interference
caused by QD aggregates. Finally, MPA-QDs were found to associate
with cell surface scavenger receptors, while the THIO-QDs did not.
This study indicates that the surface charge and aggregation characteristics
of QDs change drastically in biological culture conditions and, in
turn, influence nanoparticle and cellular interactions.
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mercaptopropionic acidendocytic pathwaycore semiconductorQD charge250 nMcell imagingRPMIsemiconductor nanocrystalssurface chargespectroscopic interferenceinternalization processcell surface scavenger receptorsmicrowave methodinfluence nanoparticleFBSQD aggregatescell surfaceaggregation characteristicsBiological Activity54 nmQDs changedrug deliveryculture conditions
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