Biomedical Engineering Reference
In-Depth Information
atoms from groups II to VI, with CdSe and CdTe being the most commonly
used for biological applications.
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2.1.1 QD Core Synthesis Protocol
One of the many ways by which QDs are synthesized (
Figure 2.2
) uses high-
temperature reaction of organometallic precursors in a mixture of trioctylphos-
phine/trioctylphosphine oxide (TOP/TOPO) and alkylamine.
22,24,50-52
The
TOP/TOPO-capped QDs are allowed to undergo cap exchange with the newly
synthesized ligands to achieve water solubility.
53-55
The CdSe core nanocrystals are synthesized from CdO and elemental Se
using a kinetic growth method, where particle size depends on reaction time.
56
To carry out this process the following protocol is followed:
(1)
Prepare a stock solution of Se precursor by combining 30 mg of Se and
5 mL of 1-octadecene (90%) in a 10-mL round-bottom flask that is con-
tinuously stirred with a magnetic stirrer.
(2)
Use a syringe to add 0.4 mL of TOP.
(3)
Add a magnetic stir bar to stir the solution on a magnetic stir plate.
(4)
Warm the solution to dissolve the Se.
(5)
The stock solution can be stored at room temperature (RT) in a sealed
container.
(6)
This stock solution has enough Se precursor for five preparations.
(7)
For each CdSe preparation, make the Cd precursor by adding 13 mg of
CdO to a 25-mL round-bottom flask in a heating mantle.
(8)
Add 0.6 mL of oleic acid and 10 mL of octadecene.
(9)
Insert a thermometer that is capable of measuring 225 °C.
(10)
Heat the setup to 225 °C and add 1 mL of the RT Se precursor.
(11)
Begin the timer upon the addition of the Se precursor because the proper-
ties of the QDs are size-dependent.
(12)
Use a 9-inch Pasteur pipette to quickly remove and quench about 1-mL
samples at regular time intervals from the start and when a noticeable
color change is detected.
(13)
Obtain nine or 10 samples within 2-3 min (
Figure 2.3
).
(14)
Record the visible absorption and emission spectra of individual samples to
find the maximum wavelength peaks at an excitation wavelength of 400 nm.
Caution:
56
(a)
All synthesis must be performed inside the fume hood wearing goggles,
nitrile gloves, and long sleeve lab gown covering arms.
(b)
Octadecene vapor should not be inhaled, and contact with skin and eyes
should be avoided.
(c)
Use a syringe to transfer TOP because it is corrosive and causes burns.
(d)
Oleic acid is air, light, and heat sensitive and irritates the eyes, the respira-
tory system, and the skin.
