Biology Reference
In-Depth Information
materials to be performed thus enabling electrochemical sensing
with no need for electron-transfer mediators. Properties of gold
nanoparticles, such as their high surface-to-volume ratio, high
surfaceenergy,theabilitytodecreasethedistancebetweenproteins
and metal particles, and their performance as electron-conducting
pathways between the prosthetic groups and the electrode surface,
have been claimed as reasons to improve electron transfer between
redox proteins and electrodes [3]. Also, gold nanoparticles have
showntoconstituteusefulinterfacesfortheelectrocatalysisofredox
processes of molecules such as H
2
O
2
,O
2
,orNADHinvolvedinthe
biochemicalreactions withanalytical significance[4].
This chapter is devoted to electrochemical DNA biosensors
coupled with the use of gold nanoparticles to improve both
oligonucleotide immobilization on electrode surfaces and signal
amplification for sensitive detection of hybridization events. Elec-
trochemical genosensors have demonstrated in recent years to
constitute reliable alternatives for applications directed to gene
analysis, detection of genetic disorders, tissue matching and
forensics, due to their high sensitivity, small dimensions, low cost,
and compatibility with microfabrication technology. Besides tra-
ditional electrochemical transduction of DNA hybridization events
involving electroactive indicators/intercalators or enzyme tags,
the use of nanoparticles, especially of gold nanoparticles, offers
elegant pathways for interfacing such events with electrochemical
signal transduction and for amplification of the resulting electrical
response [5].
Gold nanoparticles can be employed for improving the immo-
bilization of DNA on electrode surfaces and thus for increasing
the hybridization capacity of the modified surface [6]. The use of
gold nanoparticles supporting films constructed by self-assembling
of 16-nm diameter colloidal gold onto a cystamine-modified gold
electroderesultedinsurfacedensitiesofoligonucleotidesashighas
4
×
10
14
moleculescm
−
2
,allowingadetection limitof500 pMto be
achieved.
The other fundamental advantage of gold nanoparticles-based
electrochemicalDNAbiosensorsisthedevelopmentofamplification
routesfortheDNAsensingevents.AccordingtoWillner
et al.
[7],the
concept of the amplified detection of DNA using gold nanoparticles
