Biology Reference
In-Depth Information
interface and suppressed diffusion-limited electrochemical behav-
ior. Interestingly, upon binding of thiolated probe DNA to 3-
mercaptopropyl trimethoxysilane-modified GaN nanowires, two
semicircles were observed. The first semicircle was now indicative
of charge transfer at the GaN-DNA interface, with the second
semicircle indicative of charge transfer at the DNA-electrolyte
interface. These two phenomena are more clearly observed in the
two peaks in the Bode plot shown in Fig. 14.12B. The deconvolution
of the charge transfer properties of these two interfaces allowed for
monitoring the extent of DNA hybridization (decrease in resistance
to charge transfer in the semicircle corresponding to the GaN/DNA
interface, shown in Fig. 14.12A) while the second interface served
as a fingerprint for modification of the nanowires with DNA.
Picomolar concentrations of target DNA, even in the presence of
noncomplementary and mismatched sequences, were reported.
14.3.5
Dendrimers
Dendritic polymers, or dendrimers, are three-dimensional nano-
sized synthetic molecules possessing a regularly branched tree-
like structure. Dendrimers can be described as covalent micelles
havingwell-definedcavities,beingnontoxic/biocompatible,andcan
contain several functional groups allowing for functionalization
and/or immobilization of the dendrimers [57]. Several schemes
utilizing dendrimers for electrochemical detection of DNA have
been reported. In these reports dendrimers are either loaded
with electroactive reporter molecules and used as labels for DNA
detection, or immobilized on electrodes as scaffolds for DNA
immobilization providing higher probe densities and improved
electron transfer to theelectrode.
Commercially available poly(amidoamine) (PAMAM)
dendrimers are the most commonly used dendrimers for electro-
chemicalDNAdetection.Recently,Zhuandcoworkers[58]reported
the use of a new class of PAMAM dendrimers with a trimesyl core
and terminal carboxyl groups for DNA detection. Amine-modified
target DNA was immobilized to the dendrimer using carbodiimide
chemistry. Amine functionalized probe DNA was also immobilized
toamercaptoaceticacidself-assemblingmonolayer(SAM)-modified
