containing vials as evident from the change in color from
pinkish red into purple grey (Fig. 1D) [13]. In another study, a
species-specific nanobiosensor was fabricated by integrating a
27-nt AluI fragment with 3-nm citrateetannate-coated GNPs
[12]. Structurally, the nanobiosensor was composed of a
single-stranded DNA covalently linked to 3-nm GNPs via sulfuregold
bond at one end and a fluorescent dye at the other
end. The higher the fluorescence emission, the greater the
degree of target DNA binding, with the baseline and
maximum fluorescence being observed in the absence of any
target DNA and by saturating the probe with target DNA,
respectively. The underlying mechanism of this method involves
three oligonucleotide probes flanked by a hexyl-A
spacer at both sides, while the alkane thiol cap at one end
and fluorophore at the other end are shown to self-organize in
a constrained arch-like structure [12]. In the absence of any
complementary target, the fluorophore is quenched by GNPs.
However, upon target binding, the structure of probe is
transformed into a rod-like conformation emitting fluorescence
due to separation of fluorescence dye from the nanoparticle.
In addition, the distinct change in fluorescence
intensity was shown to occur among noncomplementary,
complementary, and single mismatched targets as compared
with that for free probe, demonstrating the high specificity of
this method (Fig. 1E). Moreover, this swine-specific biosensor
could detect 100% pork and 1e50% pork in ready-to-eat
meatballs prepared from porkebeef mixtures with high
sensitivity and specificity. Commercial meatballs made from
beef, chicken, mutton, and chevon also showed significant
difference in fluorescence intensity when compared with free
probe (Fig. 1F) [12].