Biology Reference
In-Depth Information
with excellent differentiation for single base mismatches. The use
of gold nanoparticles provided a significant signal amplification
effect in that hundreds of DNA reporter strands were immobilized
on each particle thus increasing the amount of reporter RuHex
molecules that could bind. A modified “bio-barcode” technique that
mixes both complementary and noncomplementary DNA probes
on the modified gold nanoparticles limits the number of strands
available for hybridization of target molecules on the surface
(Fig. 14.6B) [35]. This subsequently decreases the number of DNA
interconnects on the transducer surface and has a profound impact
onthereproducibilityandsensitivityofthetechnique.ADNAprobe
bridge could be constructed that could combine two different gold
nanoparticle bio-bar codes. The DNA bridge gold nanoparticle bio-
bar code conjugate contained three gold nanoparticle labels and
only one linking DNA molecule for target binding (Fig. 14.6C). The
resulting tri-gold nanoparticle DNA probe combined the maximum
synergy of signal amplification, from the electrostatic binding of
ruthenium hexamine onto 486 DNA reporter probes on the three
gold nanoparticles, and increased selectivity from the one-to-one
recognition of the single target binding site to achieve a detection
limit of 53 aM. Li
et al
. [36] reported another version of this tech-
nique where an avidin/polyamidoamine (PAMAM) dendrimer/3-
mercaptopropionic acid layer was used to immobilize DNA probes.
The use of the PAMAM served as an additional amplification effect,
along with the use of gold nanoparticles to bind RuHex, due to
the increased amount of DNA probes that could be attached when
compared to a flat substrate and led to a low detection limit of
1.4
10
−
14
molL
−
1
.
Enzymes have found wide use as labels in biological assays due
to their ability to produce catalytic signals from the generation of
electroactiveproducts.However,therearesomeinherentdrawbacks
with using biological labels associated with their thermal and
environmental instabilities. The large surface area-to-volume ratio
of nanoparticles makes them superior catalysts when compared to
their bulk metal counterparts. Taking advantage of these catalytic
properties, Willner and coworkers [37] introduced the use of metal
nanoparticles as inorganic analogues to traditional enzyme tags by
using single-stranded DNA probe-modified platinum nanoparticles
×
