Biomedical Engineering Reference
In-Depth Information
with different fluorescent emission wavelengths have been produced with various
DNA sequences as the stabilizers [
101
]. Contrary to tremendous reports on DNA-
templated Ag NCs, studies on the synthesis of luminescent Au NCs with DNA as
the capping agents are scarce. Only Chen et al. reported that the atomically mono-
disperse Au NCs could be obtained by etching gold particles with the help of
amino acids, proteins, and DNA under sonication in water [
102
]. Unlike DNA oli-
gonucleotides, proteins as the scaffolds offer more potentials in fluorescent Au NC
formation. The first fluorescent protein-templated Au NCs were reported by Ying
and coworkers in 2009. They developed a simple, green synthetic route for the
preparation of Au NCs with red emissions based on the capability of bovine serum
albumin (BSA) to sequester and reduce Au precursors [
103
]. Except BSA, other
proteins such as lysozyme [
104
], transferrin [
105
], and HRP enzyme [
106
] have
also been proved to act as efficient scaffolds for producing fluorescent Au NCs.
In 2007, Dickson et al. reported a significant advance in producing fluorescent
Ag NCs in vivo by ambient temperature photoactivation with nucleolin protein as
the scaffold. Inspired by this, they further designed a short peptide incorporating
the specific amino acids most prevalent in nucleolin and several cysteine groups
to stabilize fluorescent Ag NCs directly in phosphate buffer [
107
]. Details about
thiol-containing molecules, dendrimers, and polymers as the scaffold for the syn-
thesis of Au and Ag NCs can be referred to other reviews [
100
,
108
-
110
]. The
main synthetic approaches for DNA-templated Ag NCs and BSA-stabilized Au
NCs are illustrated in Fig.
2.3
.
Fig. 2.4
Schematic presentation of various methods for the preparation of QD bioconjugates.
a
Electrostatic interaction between a positively charged protein and a negatively charged QD
surface or between a negatively charged oligonucleotide and a positively charged QD surface.
b
Amide bond formation between carboxyl and amino groups by EDC/NHS chemistry.
c
Coupling
between amine and thiol groups via the cross-linker SMCC.
d
Conjugation between hydroxyl
and thiol groups.
e
Hydrophobic interactions between alkyl on QD surface and lipid or liposome
