Biology Reference
In-Depth Information
silver deposition versus the use of another substrate such as
p
-
aminophenyl phosphate that is more unstable and produces higher
background signals.
Moreover, the hybridization reaction with noncomplementary
target does not occur for all concentrations assayed (see the
voltammogram in Fig. 9.13B for the highest concentration of
noncomplementary target assayed, 700 fg/
μ
L). This fact shows that
non-specificadsorptionsarenotobserved.Regardingtheselectivity
of the genosensor, this system has been studied in the previous
section and this is able to discriminate one-base mismatched
strands.
9.4.3
Genosensor for SARS Virus Detection Based on Gold
Nanostructured Screen-Printed Carbon Electrode
In this section, a DNA hybridization assay with enzymatic electro-
chemical detection was carried out on a disposable gold nanos-
tructuredscreen-printedcarbonelectrode(SPCnAuE),whichallows
working with small volumes. Gold nanoparticles (NPs) which are
formed
in situ
byapplyingaconstantcurrentintensityduringafixed
time act as an immobilization and transduction surface. Although
thick gold substrates are reported in the literature for enzymatic
DNAdetection(screen-printedgoldelectrodes[46],2mmthickfilm
gold electrodes [66], or gold disk electrodes [69]), gold NPs have
beenunusuallyusedaselectrochemicaltransducers,despiteoftheir
widespreaduseasDNAlabelsduetotheelectrochemicalproperties
of goldNPs [70].
The sequence chosen as target is included in the 29 751-base
genomeoftheSARS(severeacuterespiratorysyndrome)-associated
coronavirus. A 30-mer oligonucleotide with bases comprised
between numbers 29 218 and 29 247, both included, was chosen.
This is the causative agent of an outbreak of atypical pneumonia,
first identified in Guangdong Province, China, that has spread to
several countries. The sequence corresponds to a gene that encodes
the nucleocapsid protein (422 amino acids), specifically a short
lysine-rich region that appears to be unique to SARS and suggestive
of a nuclear localizationsignal.
