Biology Reference
In-Depth Information
extensive growth in nanobiotechnology has been in the area of DNA
analysis. Electrochemical DNA biosensors are powerful tools for
nucleic acid analysis because they are often simple, rapid, reliable,
and cost effective. The transduction of DNA hybridization events
into electrical signals to construct sensing devices has potential
applications ranging from molecular diagnostics, drug screening,
medical diagnosis, food analysis, and environmental monitoring.
As a material system approaches molecular dimensions, it can
exhibitnoveloptical,electrical,mechanical,andchemicalproperties
that can be further manipulated and tailored by varying the size,
shape, and composition of the nanoscale material. The unique
electronic and structural properties of nanomaterials have enabled
new ultrasensitive electrochemical sensors [2] that would not have
been possible without the nanomaterials' unique properties. The
progressmadetowardchemicalfunctionalizationofthesematerials
has led to successful interfacing of biomolecules, such as DNA,
with electrochemical signal transduction platforms providing an
enhanced electrochemical response.
For example, a number of different electrochemical techniques
such as cyclic voltammetry, differential pulse voltammetry, and
potentiometric stripping analysis can be used in combination with
nanomaterialstoquantitativelydetectextremelylowconcentrations
of oligonucleotides. This is due, in part, to the highly sequence-
specific hybridization of DNA coupled with the extraordinary
electron-transport properties, catalytic properties, and high surface
area of various nanomaterials. DNA hybridization is detected
on nanomaterial-modified electrodes using either a direct label-
free detection scheme or indirect methods. Direct methods are
usually based on the redox signal of DNA bases, most notably
the oxidation of guanine which can be further amplified using
electrocatalytic mediators such as [Ru(bpy)
3
]
2
+
,orbymeasuring
changes in the interfacial properties of the nanomaterial-modified
electrode including impedance and conductivity. Indirect methods
make use of electroactive indicators that either intercalate into
hybridized double-stranded DNA (ethidium bromide, daunomycin)
oremploylabelssuchasmetalnanoparticleswhichenableavariety
of electrochemical enhancements. In comparison to nonmodified
surfaces, these electrochemical assays exhibit orders of magnitude
