Biomedical Engineering Reference
In-Depth Information
2.2.6.1.3 Method for 7 nm MnFe
2
O
4
NP Synthesis
112
(1)
Mix Mn(acac)
2
(1 mmol), Fe(acac)
3
(2 mmol), 1,2-hexadecanediol
(10 mmol), oleic acid (6 mmol), oleyl amine (6 mmol), and benzyl ether
(20 mL) with magnetic stirrer under a flow of nitrogen.
(2)
Heat the mixture to 200 °C for 2 h.
(3)
Reflux at ~300 °C for 1 h under a blanket of nitrogen.
(4)
Remove from heat source and cool the black mixture down to RT.
(5)
Repeat steps 5-10 in the methods for Fe
3
O
4
.
(6)
A black-brown hexane dispersion of 7 nm MnFe
2
O
4
NPs is produced.
Using the above protocols, IOMNPs with various sizes were made by choos-
ing different solvent for the reaction, or by controlling the concentration of
the metal precursors and metal/surfactant ratio. The protocols produced up to
15-nm diameter NPs.
2.2.6.2 Surface Modification of the Iron Oxide NPs
The synthesis of iron oxide NPs leads to hydrophobic MNPs that are not biocom-
patible. The non-water soluble properties of the MNPs require further surface
chemical modifications in order to ensure safety and good dispersibility in aque-
ous media. Various approaches have been developed for converting the MNPs
into their water-soluble form. Such approaches utilize procedures that can involve
(i) the exchange of the hydrophobic ligand surfactant coatings on the NP surface
with more hydrophilic ligands;
53,126,127
(ii) the growth of a water soluble protecting
layer material around the original NPs;
128,129
(iii) the complete encapsulation of the
hydrophobic NP within an amphiphilic polymeric shell.
58,59,130,131
One protocol for
the conversion of organic soluble MNPs to their water-soluble form is as follows.
2.2.6.2.1 Protocol for MNP Modification
(1)
Evaporate the hexane under a flow of nitrogen gas and collect the black
solid residue of iron oxide NPs.
(2)
Dissolve the residue in chloroform at a concentration of 0.5 mg particles/
mL solution.
(3)
Add 1 mL of chloroform solution of DSPE-PEG(2000)Biotin (10 mg/mL)
to every 2 mL of the NP dispersion.
(4)
Put the mixture in a shaker for 1 h and evaporate the solvent under nitrogen gas.
(5)
Disperse the residue in PBS solution.
(6)
Filter off undissolved residue with a 0.2-µm syringe filter.
(7)
Purify using a Nanosep 100K Omega to remove unreacted DSPE-
PEG(2000)Biotin or use a magnetic separator (
Figure 2.8
).
The most important aspect of MNPs for medical and other biological applica-
tions is biocompatibility and surface engineering. Surface engineering of MNPs
allows for the introduction of (a) ligands that are used for specific cell/tissue/
