Biomedical Engineering Reference
In-Depth Information
These particles are intrinsically water soluble and are very useful in biologi-
cal environments. The surface-modified NMs require biological interfacing in
order to be useful for specific applications.
3.3.1 NM Bioconjugation Techniques
The surface-functionalized NMs are conjugated to biomolecules making it use-
ful for various biological and medical applications. Conjugation can be done
using conventional conjugation techniques depending upon the surface func-
tional group on the NM and on the biomolecule.
108
Conjugation to NMs may
be done through ligand-like attachment by chemisorption to the NMs' core as
in the case of sulfur-containing groups,
12,109
electrostatic adsorption (includ-
ing those involving engineered proteins),
12,109
hydrophobic interactions,
12,97,110
conjugation by covalent binding of groups on both particle and the surface
modifier,
12,111
or through a receptor-ligand interaction as in the case of avidin-
biotin system.
12
Table 3.1
shows a list of various functional groups on the sur-
face of NMs that can be used for the attachment of a biomolecule.
Studies have been reported on the use of thioctic acid and PEGs in simple
esterification schemes, followed by reduction of the 1,2-dithiolane to synthe-
size a series of PEG-terminated dihydrolipoic acid (DHLA-PEG)
24,97
capping
substrates. The exchange reaction of TOP/TOPO-capped QDs with these mate-
rials led to the production of water-soluble NMs that were stable over long
time points over a broad pH range from weakly acidic (pH 5) to basic condi-
tions (pH 12). However, although highly stable, these ligands did not possess
TABLE 3.1 Common NMs' Bioconjugation Techniques to load NM
With Drugs, Gene, or Proteins
Molecule to be coupled
with the NM
Cross-linker/mediator/
reagent
NMs' functional group
Amine (-NH2)
Drug-NH
2
Disuccinymidyl
glutarate
106
DNA
Succinymydyl-[4-
(psoralen-8-yloxy)]-
butyrate
106
Protein-NH
2
Disuccinymidyl
glutarate
106
Carboxyl (-COOH)
Drug-NH
2
; protein-NH
2
;
DNA-NH
2
Carbodiimide
42,107
Sulfhydryl (-SH)
Protein; drug
Maleimide
108
Biotin
Streptavidin-protein
Buffer