Bioconjugation of Noble Metal Nanoparticles and Their Applications to Biolabeling and Bioimaging - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 13

Bioconjugation of noble metal nanoparticles mainly takes
place through covalent bonds and electrostatic interactions. 8-11
Common covalent bond-conjugation methods use metal-thiol bonds
directly between noble metal nanomaterials and biomolecules
or cross-link agents such as (1-ethyl-3-(3-dimethylaminopropyl)
carbodiimide) (EDC), which links amine and carboxylic acid groups;
4-( N -Maleimidomethyl)cyclohexane-1-carboxylic acid 3-sulfo- N -
hydroxysuccinimide ester (sulfo-SMCC), which links amine and
thiol groups; and the azide-acetylene system. 12 For electrostatic
interactions, the nanoparticles and biomolecules should be
oppositely charged. The formation of covalent bonds is stronger
compared to electrostatic interactions, and hence, the biomolecules
are dificult to detach from the nanoparticle surface. In addition,
electrostatic adsorption offers very little control over the orientation
of bound molecules. Orientation and conformational changes in
biomolecules during adsorption on nanoparticles can reduce their
binding afinities and activities. 13 Non-speciic conjugation sites
(random conjugations) of biomolecules result in some problems, for
example, the active sites of biomolecules may be blocked and the
activities disappear. Generally, the activities of biomolecules are
affected (increase or decrease) when their conformation produces
some changes. Hence, it is important that the activities of biomolecules
are kept after conjugation with noble metal nanoparticles and still
show functional performance.
To achieve the Great Aspiration for reduction of death for cancer
patients, a new approach in detecting cancer in the early stage is
highly desired. Biomedical imaging provides contrast information
to interest tissues and organs for analytic and diagnostic purpose.
Therefore, it is requisite to develop helpful imaging methods to
improve sensitivity and resolution of biological imaging. The time
of data acquisition and inancial cost are also required to consider
for further biomedical development. Furthermore, different imaging
techniques may provide complementary information in biological
interpretation.
Since the 1950s, Au nanoparticles have been used as radioactive
agents. 14 Additionally, Au nanoparticles conjugated to antibodies
have been used for biological staining in electron microscopy
since the 1980s. 15,16 Nanoparticles provide an opportunity to
develop non-invasive methodologies as multifunctional diagnostic
and therapeutic agents ranging from clinical diagnosis to cellular