Biomedical Engineering Reference
In-Depth Information
a
56
.9 n
A
1
st
IgE bound
(at 3.9 mins)
2
nd
3
rd
b
4 mins
A
IgE
IgE
n
th
Sensing
zone
Fig. 3.7 Capture of single IgE molecules by immobilized aptamers in the nanopore. The sequence
of IgE aptamer is 5
0
-GGGGCACGTTTATCCGTCCCTCCTAGTGGCGTGCCCC [
122
], the
voltage was given from the electrode in the pipette and the external bath was grounded.
(a) Current in a 63-nm A
IgE
-encoded nanopore at +100 mV with 5 nM IgE in the pipette. Stepwise
discrete current blocks are due to individual IgE molecule binding to the immobilized aptamers
(b) Sensing zone at the narrow opening of the nanopore [
22
]. Reprinted with permission from
Anal.Chem.
81:6649-6655 (2009)
The electroosmotic flowcan also be identified based on the voltage polarity-dependent
blocks, i.e. stepwise block can only observed at positive voltage, but not negative
voltage. The voltage polarity switches the direction of the electroosmotic flow, thus
enhancing or weakening the binding frequency [
28
].
According to the number of IgE blocks in a recording, we infer that there is a
sensing zone in the nanopore (Fig.
3.7b
)[
22
]. Only single IgE molecules captured
by aptamers in the sensing zone generated pronounced signal blocks, whereas
molecules outside of the sensing zone yielded signal blocks that are too weak to
be detected. Based on the wineglass-shaped profile, we approximated the thickness
of sensing zone.
Protein detection with aptamer-encoded nanopore is highly selective, as charac-
teristic stepwise blocks cannot be found if IgG is added to the IgE aptamer-modified
nanopore or if a mutant IgE aptamer that has a single nucleotide removed from the
recognizing domain (loop). The result of the mutant aptamer further suggests the
nanopore's ability in probing aptamer-target interaction [
122
].
3.4.5 Detection of Bioterrorist Agent Ricin with
RNA Aptamer in Nanopore
The aptamer-encoded nanopore is highly programmable and can be versatile to any
aptamers. For example, besides DNA, the RNA aptamers targeting high impact
substances can use applied. The bioterrorist agent ricin from the castor bean plant is
the third-most toxic substance, after plutonium and botulinum toxin, according to
Search WWH ::
Custom Search