Biomedical Engineering Reference
In-Depth Information
group studied the design and synthesis of ligands functionalized with a biotin end
group. The designed ligands had a central tetraethylene glycol (TEG) segment, a
dithiol terminal group for anchoring on the QD surface and a lateral biotin. Attach-
ing biotin at the end of QD surface-attached ligands provided an avidin bridge for
avidin-biotin binding for attachment of proteins and other biomolecules on the
QD surface. Exchange reactions were carried out with mixed ligands and binding
assays of the biotin-coated water-soluble QDs to NeutrAvidin-functionalized sub-
strates showed specific capture through avidin-biotin interactions.
Chitosan, a polysaccharide consisting of randomly distributed β-(1-4)-linked
D-glucosamine (deacetylated unit) and
N
-acetyl-D-glucosamine (acetylated unit)
provides a natural, biocompatible, cationic, and hydrophilic polymer coating
that is suitable for affinity purification of proteins and magnetic bioseparation.
95
Chitosan-coated SPIONs that were used to label fibroblasts improved their inva-
sive potential under a magnetic force, showing promise for tissue engineering.
98
Dextran, a polysaccharide, has also been applied in coating NMs. For bio-
logical applications, SPIONs are usually coated with organic biodegradable
compounds such as dextran or carbohydrate derivatives that are commonly used
as plasma expanders that have very high affinity to iron oxides.
99
Several such
formulations are now commercially available for human consumption such as
Ferridex, Resovist, Combidex, and AMI-288/ferumoxytol that are successfully
used as magnetic resonance imaging (MRI) contrast agents.
100
Biocompatible polymers that are amphiphilic in nature have been reported for
coating NPs to make them hydrophilic.
101,102
Hu's group reported the epoxidation
of the surface OA ligand and further coupling with polyethylene glycol mono-
methyl ether (mPEG-OH) to coat the surface of nanophosphors.
102
The effective
coating of the surface of the nanophosphors with mPEG-OH was confirmed by
1
H NMR spectrometry, Fourier-transform infrared (FTIR) spectroscopy, and
dynamic light scattering (DLS) studies, but TEM and PL spectroscopy showed no
obvious variations in the morphologies and luminescence before and after coating.
3.2.4.1 Protocol for Amphiphilic Polymer Coating of NMs
The following protocol was adopted from Hessel's paper.
101
Part 1. Synthesis of the amphiphilic polymer
(1)
In a capped, single neck round-bottom flask, place 100 mL anhydrous
tetrahydrofuran (THF), 15 mmol dodecylamine (about 3.45 mL), and
poly(isobutylene-
alt
-maleic anhydride) (20 mmol of monomer units,
3.084 g) sequentially to form a turbid white solution.
(2)
Sonicate the flask for 1 min to suspend the insoluble polymer.
(3)
Heat the suspension to 60 °C for 3 h under vigorous stirring. The suspen-
sion will become clear after 15 min of stirring, indicating that the poly-
mer became soluble in THF after covalently coupling with hydrophobic
dodecylamine molecules.
(4)
Cool the solution down to RT.
(5)
Using a rotary evaporator, reduce the volume to 20 mL.
