Biology Reference
In-Depth Information
damage to the guanine base and/or disintegration of DNA
molecules into small fragments [52]. With various biosensor
arrangements, effects of agents such as antitumor platinum
complexes [53] and various aromatic hydrocarbons derivatives
[54] on arsenic oxide [55] have been investigated using the
guanine response at the mercury-based electrodes. Besides
low specificity of this type of response, the general problem
of relatively low sensitivity is connected with the signal-off
approach.
(d) Detection of electroactive products of DNA damage. Some
products of DNA damage exhibit characteristic electrochemical
activity possessing a new signal. For example, 8-oxoguanine
(8-OG) is electrochemically oxidized at carbon electrodes at
a potential significantly less positive than the parent guanine
base [14, 38-40]. Compared with the previous one (described
under c), this approach exhibits much better sensitivity and
specificity. New species can be detected also using a redox
mediator.Thecomplexesofosmium(suchas[Os(bipy)
3
]
3
+
)and
ruthenium with different redox potentials have been shown as
electrocatalysts for8-OG and guanine,respectively [17, 56].
(e) Layered assemblies for genotoxicity screening. Multilayer
assemblies of cationic redox-active polymer films, DNA, and
heme proteins at carbon electrodes were designed for testing
thegenotoxicactivityofvariouschemicals[57].Inthesedevices,
layers of enzymatically active hemoproteins mimic metabolic
carcinogen activation processes (e.g., styrene is enzymatically
converted to styrene oxide). The activated species diffuse into
the DNA layer and attack guanine residues, and the damaged
DNA double helix is indicated by using guanine oxidation
mediated by acationicpolymeric film.
(f) A molecular beacon-like sensor for the evaluation of nuclease
and ligase activities. An electrochemical biosensor using a
hairpin DNA with an oxidizable ferrocene label was published
for the detection of activities of enzymes such as nucleases
(generating single-strand breaks) and DNA ligases (sealing the
break) [58]. At a single-strand break in the duplex part of the
hairpin structure, the ferrocene-labeled segment was removed
underconditionsofdanaturationwithdiminutionofthecurrent
