Biomedical Engineering Reference
In-Depth Information
the US Environmental Protection Agency and the Center for Defense Information.
Ricin has high potential for use as an agent of biological warfare, a weapon of mass
destruction (WMD), and a terrorist weapon. Ricin protein consists of the A chain
and B chain. The A chain has the toxic enzymic activity (an RNA N-glycosidase)
of the protein and the B chain responsible for binding to cells and being taken up
by them. The dimension of ricin A protein is ~6.1 nm
2.4 nm [
119
] (Fig.
3.8a
).
The toxicity of ricin is activated only when the A chain meets with B chain.
The RNA aptamer targeting ricin A protein has been created by Ellington and
co-workers [
39
]. Recently the ricin A aptamer has been successfully integrated into
the chip for ricin detection [
65
]. However, the detection requires fluorescent-
labeling of the ricin protein.
By comparing, aptamer-encoded nanopore provides a novel, label-free method
of detecting single ricin molecules (Fig.
3.8a
)[
22
]. Similar to the IgE with its
aptamer, the presence of low concentration of ricin can generate a series of stepwise
blocks that can be attributed to the capture of single ricin molecules (Fig.
3.8b
).
Again, no discrete current increase observed for the release of ricin from its
aptamer, suggested a long binding time for A
ricin
ricin, in concordance with the
a
Ricin A chain
Aptamer
b
c
10
2
n
th
3
rd
10
1
2
nd
4 mins
10
0
1st ricin bound
(at 12.4 mins)
10
0
10
1
10
2
10
3
10
4
[Ricin A protein]
in exterior solution (nM)
−
67.5 nA
Fig. 3.8 Single-molecule detection of ricin A-chain protein in the external solution using an
A
ricin
-encoded nanopore. (a) A model showing the single ricin A-chain molecule binding to the
RNA aptamer immobilized in the nanopore. (b) Current in a 56-nm A
Ricin
-encoded nanopore
at
100 mV, with 100 nM ricin A-chain protein in the external solution. (c) The detection time
interval between the first and the second ricin block (
t
1
t
2
) in various concentrations of ricin
A-chain protein [
22
]. Reprinted with permission from
Anal.Chem.
81:6649-6655 (2009)
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