Biology Reference
In-Depth Information
NP-modified screen-printed carbon electrodes, the reporter DNA-
modified liposomes hybridized directly to thiol-terminated capture
probesboundtotheAuNPsviaAu-thiolinteraction.Inthepresence
of target DNA strands specific to
E. coli
O157, liposome-labeled
reporter DNA was displaced from the electrode surface. Remaining
[Ru(NH
3
)
6
]
3
+
loaded liposomes were quantified via square wave
voltammetry.This“signal-off”mechanismprovidedadetectionlimit
of 150 fM (0.75 amol in 5
μ
L).
14.4 DNA Detection Using Carbon Nanotubes
There is enormous interest in utilizing carbon nanotubes (CNTs)
in biosensors primarily due to the high surface area, extraordinary
mechanical properties, electron-transport properties, and high
thermal and electrical conductivity of these materials. These one-
dimensional materials (1D) are attractive for the detection of
minor surface perturbations due to binding events. In the case of
single-walled carbon nanotubes (SWCNTs) the structure is such
that every carbon atom is on the surface, thus any event such
as DNA hybridization strongly influences the electronic behavior
of the material. Based on their structure, CNTs can be either
single- or multiwalled (MWCNTs), and envisioned as cylindrical
roll-ups of one or more sheets of graphene. These nanomaterials
have a high aspect ratio with diameters as small as 0.4 nm
for SWCNTs and 2 to 100 nm for MWCNTs and lengths from
tens of nanometers to several micrometers. Although both have
been studied as biosensor materials, MWCNTs, because of their
higher complexity, have been studied more frequently as a bulk
material where ordered structuring may not be as critical. When
integrating CNTs onto a substrate, controlling geometric structure
and orientation can provide enhanced electrochemical responses
due to their fast electron-transfer characteristics.
Their unique structural, mechanical, and electrical properties
differ greatly from other carbon materials used in electrochemical
measurements such as diamond, graphite, and glassy carbon. As
compared to graphite, SWCNTs have a greater surface area and
a much lower density. The unique differences of these materials
