Biology Reference
In-Depth Information
deposited onto a
p
-aminothiophenol SAM on an Au electrode by
eitherelectrodepositionoftheSiNPsfromasilicasol,oradsorption
of the Si NPs upon dipping the SAM-modified electrode into a silica
sol/Si NP solution for several hours. Electrodeposition of the Si
NP provided the best Si NP loading, increasing immobilized ssDNA
probe density and improved electron-transfer kinetics compared
to the SAM-modified electrode alone. FIS allowed for detection
of target DNA hybridization with a detection limit of 1.5 pM and
discrimination between single or double base pair mismatched
DNA sequences. A similar Si NP-SAM-modified Au electrode system
employing [Co(bpy)
3
]
3
+
as the electroactive reporter and differen-
tial pulse voltammetry for DNA detection has also been reported
[72].
14.3.8
Liposomes
Liposomes are aggregates of amphiphilic block copolymers or sur-
factant molecules that self-assemble into spherical nanostructures
in aqueous solution. Typically, liposomes consist of a bilayer in
which hydrophilic blocks of the polymer form the outer and inner
shell of the bilayer while the hydrophobic blocks lie between the
inner and outer shell. This configuration shields the hydrophobic
blocks from the external aqueous solution and the aqueous internal
core of the liposome. Liposomes can be functionalized with various
biomolecules and loaded during the self-assembly process with
reporters facilitating use of liposomes as effective labels for DNA
detection.
Patolsky
et al.
[73] reported the use of 220
20 nm diam-
eter negatively charged liposomes with maleimide functionality
for electrochemical detection of DNA. Thiol-terminated detection
probe DNA was immobilized onto the maleimide functionalized
liposomes yielding 50 to 60 bound DNA probes per liposome.
These DNA-modified liposomes were hybridized to captured target
DNA which was previously immobilized onto a probe DNA-
modified Au electrode in a sandwich assay format, as shown in
Fig.14.15A.ThestrongnegativesurfacechargeoftheDNA-modified
liposomes prevented nonspecific interactions with the negatively
charged electrode surface, providing very low background signals.
±
