Biomedical Engineering Reference
In-Depth Information
circulation by the RES (e.g., in the liver and the spleen), depending on their size and
surface characteristics. (6) The chemicals used should be of high purity.
4 Surface Modifying Agents
4.1 Capping and Passivating Agents
Capping agents provide biocompatibility besides controlling the particle size.
Passivation is achieved mostly by capping the particles with organic materials,
but inorganic materials are also used. Organic ligands such as thiopyridines and
thiolates have been reported to minimize surface defects and increase luminescence
efficiencies. Several capping agents such as silica [
22
], starch, biotin, citric acid
[
23
], polyvinyl pyrollidine, polyvinyl alcohol, oleic acid, and cytosine [
24
] have
been regularly used for diverse biomedical applications. In view of the diverse
applications of these nanoparticles in biology and medicine, hundreds of capping
strategies have been studied. Many of these typically involve some kind of polymer
such as poly(ethylene glycol) (PEG) [
25
-
29
], poly(lactic-
co
-glycolic acid) (PLGA),
or a polysaccharide [
30
-
32
]; natural macromolecules such as oligonucleotides [
33
],
peptides, and proteins [
34
-
39
]; poly(vinyl alchohol), poly(vinyl pyrolline), silica etc.
Sharma et al. [
40
] have shown the surface modification of nanoparticles by embedding
ZnO nanoparticles in SiO
2
matrix and measuring the luminescence. The luminescence
properties and structure of these ZnO nanoparticles embedded in SiO
2
matrix are
shown in Fig.
3
.
Sharma et al. [
40
] have used tetra-ethyl-ortho-silicate (TEOS) for the formation
of SiO
2
matrix. The chemical structure of TEOS can be represented as shown in
Fig. 3 Prepared ZnO QDs embedded in SiO
2
matrix under (a) ordinary and (b) UV (365 nm
excitation) lamps. (
A
) Solid samples, (
B
) samples dissolved in ethanol, and (
C
) samples dissolved
in water. Photographs were taken with a digital camera just after completion of synthesis.
(c) TEM Image of symmetrically dispersed ZnO QDs embedded in SiO
2
matrix. (Figure adapted
from [
40
])
