Biology Reference
In-Depth Information
probes onto electrode surface, because the molecular recognition
eventtypicallyoccursdirectlyonthesurfaceofthesignaltransducer.
The immobilization method will determine the sensitivity
and reproducibility of the genosensor. Several strategies for the
immobilizationofssDNAhavebeencarriedoutandwillbediscussed
in section 9.3.2. The ssDNA probe immobilized on the transducer
surface recognizes its complementary (target) DNA sequence via
hybridization. The DNA duplex is then converted into an analytical
signal by the transducer. Different strategies for electrochemical
detection have been performed and are mainly divided in two
groups:methodsusingdirectdetection(thoseinwhichtheintrinsic
electroactivity of DNA is involved) or indirect detection methods
(those whichimply the use of labels).
Electrochemical detection of hybridization is mainly based
on the differences in the electrochemical behavior of the labels
with or without double-stranded (dsDNA) or single-stranded DNA
(ssDNA). The labels for hybridization detection can be enzymes,
anticancer agents, organic dyes, colorants, metal complexes, or
metal nanoparticles among others.
9.3.1
Electrochemical Detection of Hybridization Reaction
As it has been mentioned previously, there are a wide range of
possibilities for the electrochemical detection of the hybridization
reaction, and they can be divided into two types, direct or indirect
methods.
9.3.1.1 Direct transduction methods
Direct transduction relies on the measurement of physico-chemical
changes occurring at the recognition layer induced by hybridization
event. These methods are generally based on the oxidation
processes of guanine or adenine that occur in an oligonucleotide
when the hybridization reaction takes place [1-16]. This is because
thenucleobasespresentinthedoublestrandareoxidizedinalower
extension than when they are forming a part of ssDNA, making the
analytical signal decrease, but at the same time the target strand
adds new bases increasing in part the analytical signal. This fact
