Biomedical Engineering Reference
In-Depth Information
Exposure of breast cancer cells SK-BR3 to QDs leads to attachment of the
QDs to the cell surface.
4,130
This occurs with or without receptor targeting espe-
cially when QDs with positive zeta potential are used. In
Figure 8.3
, the cells
which accumulated the QDs show specks of fluorescent material on the cell
surface when observed under the microscope.
In vitro studies on QD toxicity was carried out at Ocean NanoTech as part of
a small business innovations research funded by the national Science Founda-
tion (NSF, USA).
131
Although the project was focused on the use of NMs for the
enhancement of antibody production through effective presentation of antigens
to antigen presenting cells,
14,131,132
the effect of NMs on the viability of cells
were evaluated (
Figure 8.3
). Two methods were used in evaluating QD toxicity
in vitro as described in the succeeding sections.
8.2.2.1 Procedure for the Evaluation of QD Toxicity to Cancer Cell
Lines, U937
The effect of QDs at various concentrations to the cell growth was evaluated
using water-soluble QDs. The QDs were made of CdSe/ZnS or CuInS2 that
were coated with amphiphilic polymer.
132
(1)
Grow the U937 cells from newly harvested suspension in culture flasks
following the manufacturer's recommendation.
(2)
Harvest the cells when they reach about 70-80% confluence.
(3)
Place 10
5
cells from the newly harvested suspension in individual centri-
fuge tubes.
(4)
Add enough QDs to each tube to attain the final concentrations of 0.025,
0.5, and 2 µM aqueous solutions using the medium as diluent.
(5)
Incubate at 37 °C in 5% CO
2
for 1, 4, and 24 h.
(6)
Spin the cells down at 3000 rpm for 3-4 min to collect the cells.
(7)
Wash the cells three times with 1× DPBS (Dulbecco's Phosphate-Buffered
Saline) to remove NPs.
(8)
Resuspend the cells in 1× DPBS and place in a 96-well plate.
(9)
Perform MTT assay following the manufacturer's recommendation.
(10)
Dissolve the crystals formed in 50 uL of MTT buffer.
(11)
Scan the solutions at 595 nm and subtract the background signal.
The MTT assay results in
Table 8.2
indicated that the CdSe/ZnS with car-
boxyl on the surface showed toxicity to the cells even at concentrations
down to 0.025 µM. Unlike the cadmium containing QDs, the CuInS
2
was
very slightly toxic after 4 or 24 h of exposure to 0.05 µM concentration.
However, the results were highly variable and some data had very low stan-
dard deviation while others had very high standard deviations. A confir-
matory test was performed by actually counting the number of viable and
non-viable cells after exposure to the QDs. The process is presented in the
next section.
