Biomedical Engineering Reference
In-Depth Information
3.2.3 Encapsulation of NMs
Encapsulation with amphiphilic diblock or triblock copolymers
82
or in silica
shells,
59,83
phospholipid micelles,
84
or polymer shells is another way to convert
NMs into their water soluble form.
19
The encapsulation process introduces new
functional groups on the surface of NMs such as carboxylic acids, amines, or
hydroxides. These functional groups can be used to attach different biomol-
ecules including drugs and vaccines on the surface of NMs (
Figure 3.2
).
Silanes have been used to functionalize semiconductor QDs leading to
multiple advantages. The siloxane shell gives extra stability to nanostruc-
tures, and the silanized nanosystems remain stable over a wide range of pH
and impede the release of undesirable heavy elements. Silanization can be
carried out by Stöber-process-based approaches, in which alkoxysilanes are
condensed in acidic or basic medium
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that lead to synthesis of highly fluo-
rescent silica-coated QDs with various surface charges by adopting a process
similar to Stöber's process. One of the disadvantages of silanization is the self-
condensation between the silane molecules. To overcome this, Yang and Gao
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employed the reverse microemulsion method to coat CdTe nanocrystals with
silica. Various organosilanes in toluene are used to treat nanocrystals to carry
out multifunctionalization of semiconductor QDs.
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Silane, such as 3-mercaptopropyltrimethoxysilane, is directly adsorbed
on the nanocrystals to displace the TOPO molecules and form a silica/silox-
ane shell on the surface by introduction of a base and hydrolysis of the silanol
groups. The polymerization of the silanol groups stabilizes the nanocrystals
against aggregation making the QDs soluble in intermediate polar solvents,
such as methanol and dimethylsulfoxide. Reaction with bifunctional methoxy
Biocompatible
coating
QD
QD
Drug
Antibody
Drug
FIGURE 3.2
Schematic of hydrophilic carboxyl-functionalized NMs carrying a drug (left) or a
drug and an Ab (right).
(For color version of this figure, the reader is referred to the online version
of this topic)
