Biology Reference
In-Depth Information
Figure 14.19. ElectrochemicalDNAdetectionusingALP-loadedCNTtags.
with a second DNA probe, which hybridized to a complementary
oligonucleotide. This complex then hybridized with DNA probes
attached to the CNT-enzyme conjugates, demonstrating the first
example of using DNA for linking particles to CNTs, as shown
in Fig. 14.19. The catalytic hydrolysis of
α
-naphthylphosphate to
the electrochemically detectable
-naphthol product by the bound
enzymes gave a 10 4 -fold improvement in the sensitivity compared
to a single ALP tag. Further amplification was achieved by using
a CNT-modified glassy carbon electrode, increasing the electrode
area for the chronopotentiometric detection of the enzymatic
product. Coupling the two amplification steps (CNT-enzyme tags
and preconcentration of CNT transducers) yielded a dramatic
enhancement in sensitivity, allowing an extremely low detection
limit of 1.3 zmol in a 25 μ l sample. This corresponds to 820 copies
in the sample size. Further amplification, with detection of DNA
down to 80 copies, was achieved with the enzyme-coated CNT tags
when they were prepared by using a layer-by-layer self-assembly
technique, maximizing the ratio of enzyme tags per binding event
[108].
A sensitive, indirect method of detecting hybridized DNA was
conducted by preparing ferrocene (Fc)-SWCNT adducts coupled
with a DNA probe [109]. Ferrocene noncovalently interacts with
SWCNTs through π - π interactions. The Fc-SWCNT adducts were
then further conjugated with DNA probes covalently through the
amide linkage between the primary amine at the 3 end of the DNA
probe and the carboxylic acid groups on the CNTs. The Fc-SWCNT-
DNA probe hybridized to a target sequence already hybridized
α
 
Search WWH ::




Custom Search