Biomedical Engineering Reference
In-Depth Information
RLS techniques are useful for the determination of analytes based
on the biocatalytic enlargement of Au NPs.
35
For example, H
2
O
2
, an
important metabolite that is generated by many biocatalytic reactions
can be determined by RLS (375 nm) because it effectively induces
growth of the Au NP seeds. As the size of Au NPs increases, the RLS
signal also intensiies (Fig. 8.4A). Thus, quantitative detection of
H
2
O
2
by RLS can be readily achieved (Fig. 8.4B). This RLS approach
provides detection of glucose over a linear range of 1.0-110 μM, with
an LOD of 0.68 μM.
Solutions containing Au NPs and rare-earth europium ions
(Eu
3+
) are interesting RLS systems because Au NPs can enhance the
RLS signals of the metal ions.
36
In the absence of Au NPs, a solution
containing Eu
3+
has two RLS peaks at wavelengths of 400 and
780 nm, as shown in Fig. 8.5. When the solution contains Au NPs
and Eu
3+
, however, the two RLS peaks are both enhanced, mainly
due to the energy transfer from the local ield in Au NPs to Eu
3+
ions. The RLS technique may also be utilized when investigating the
interaction of 11-mercaptoundecanoic acid (MUA) capped Au NPs
with Eu
3+
ions and amino acids.
37
Figure 8.5
RLS spectra of solution containing only Eu
3+
and solution
containing both Au NPs and Eu
3+
. Reprinted from Ref. 36 with
permission.
Figure 8.6 conceptually illustrates how Eu binding events, in
the presence of lysine, induce a change in the spacing and shape of
the Au NPs. Aggregation of Au NPs, through the binding of Eu
3+
to the
carboxylate ions on the outer surface, results in the modiication of
most nanodots into nanorods. In the absence of Eu
3+
ions, repulsive
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