Colorimetric Bioassay Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 44

This temperature is always greater than the melting temperature of
the corresponding duplex without Au NPs. The exact temperature at
which the color change occurs is thought to depend on a mechanism
in which the melting of one linker sequence promotes the melting
of others. 78 Interestingly, the melting proile of the DNA-Au NP
aggregation is extraordinarily sharp, occurring over a temperature
range much narrower than that of the original DNA. By controlling
the temperature, this approach provides a limit of detection (LOD)
down to the nanomolar level for DNA with a single base mismatch
resolution.
Figure 3.7 Aggregation of ssDNA-modiied Au NPs by the addition of the
DNA complementary to the DNA on the Au surface.
In order to further improve the sensitivity, researchers have
demonstrated bio-barcode ampliication approaches, using Au NPs
and magnetic microparticles. 79-81 Each magnetic microparticle that
has a magnetic iron oxide core with an amine-modiied silane coating
is functionalized with alkanethiol-capped oligonucleotides that are
complementary to one 12-mer portion (5 ′ -ATTGATAAGGAT-3 ′ ) of
a target sequence using a sulfosuccinimidyl 4- N -maleimidomethyl
cyclohexane-1-carboxylate linker. The second probe is a 30 nm Au NP
modiied with two types of oligonucleotides; one is complementary
to the target sequence of interest (5 ′ -GGATTATTGTTAAAT-3 ′ ), and
the other is complementary to a barcode sequence that is a unique
identiication tag for the target sequence. After hybridization,
the signal can be detected by using a spectrophotometer or a
scanometric detection system after further ampliication by using
silver enhancement. The LODs for the two detection modes are 100