Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 241

The selectivity of the probe for Hg 2+ ions can be further improved
by adding a chelating ligand (2,6-pyridinedicarboxylic acid) to the
sample solutions when using Au NPs capped with mercaptopropionic
acid. This approach provides an LOD of 2.0 ppb for Hg 2+ ions, a
selectivity 50 times that of other metal ions.
Use of DNA-functionalized Au NPs and OliGreen, a dye that binds
speciically to DNA, is selective and sensitive for the detection of
Hg 2+ ions. When OliGreen binds to DNA on the Au NPs surfaces, its
luorescence is weak as a result of Au NP quenching. Once Hg 2+ ions
interact with the thymidine units of the DNA molecules on the Au
NPs, the conformations of these DNA derivatives change from linear
to hairpin structures (see Fig. 10.13). 105
Figure 10.13 Schematic representation of Hg 2+ nanosensors at various
DNA-to-Au NPs molar ratios: <30 (A), 30-50 (B), and >60
(C). Reprinted with permission from Ref. 105.
As a result, some of the DNA-OliGreen complexes release from
the surface of the Au NPs into the bulk solution, leading to increased
luorescence. This system is the irst that allows for the detection
of Hg 2+ ions based on the release of DNA molecules induced by
conformational changes on Au NP surfaces. The sensitivity of