Stochastic Detection of Terrorist Agents and Biomolecules in a Biological Channel - Nanopores: Sensing and Fundamental Biological Interactions - page 329

13.5 Nanopore Analysis of Real World Samples

In addition to the development of various nanopore sensors for a variety of analytes,
efforts are under way to transition the protein-based nanopore technology to
deployable sensor applications. As overviewed in the introduction section, one
key challenge to nanopore stochastic sensing using protein channels is the fragility
and the long-term stability of the lipid bilayers. The recent advance in the protein
pore technology demonstrated that this limitation could be potentially overcome by
using a protein nanopore chip [ 45 ], or employing lipid bilayer supported by a glass
nanopore membrane [ 46 ]. Another challenge to nanopore (including both protein
pore and synthetic nanopore) stochastic sensing is how effective this approach
is used for the analysis of a real-world sample. It is likely that a number of
components in the sample matrix could potentially interfere with the target analyte
detection since the nanopore sensor is semi-selective. To address this issue,
recently, simulated contaminated water samples were analyzed by nanopore sensor
for the first time [ 15 ]. Among them, one water sample served as the false positive,
which was obtained by spiking methyl phosphonic acid, ethyl methylphosphonic
acid, and 2-(dimethylamino) ethanethiol in tap water. Other water samples served
as real alarms. In addition to the three organophosphate compounds, these samples
also contained different concentrations of pinacolyl methylphosphonic acid
(PMPA). The experimental results showed that if the sample only contained false
positives, no current blockage events were observed. In contrast, current modula-
tions were identified in all of the samples that contained the target compound (i.e.,
PMPA) [ 15 ]. Furthermore, the concentrations of pinacolyl methylphosphonic acid
in the real alarm samples obtained by using the nanopore sensor were in agreement
with their corresponding theoretical values (Table 13.1 ). The results showed that
the nanopore sensing method could indeed differentiate the target compound from
false positives, and even allowed the accurate identification and quantification of
PMPA in the presence of a mixture of structure-similar compounds, thus demon-
strating the feasibility of utilizing nanopore sensors for real-world sample analysis.

Table 13.1 Recovery of PMPA from liquid samples a by use of the nanopore stochastic sensing
method
Sample number

Theoretical value ( m M) Experimental value SD ( m M)

1 0 not detected
2 10.0 10.6 0.4
3 15.0 14.2 0.9
4 20.0 18.8 1.7
Each experimental value represents the mean of three replicate analyses one standard deviation.
The experiments were performed at 80 mV with mutant a HL (M113K/F147N) 7 pore in the
presence of 40 m M b CD. Table reprinted with permission from [ 15 ], Copyright 2009 Elsevier B.V.
a

All of the four liquid samples contained additional 100 m M of methyl phosphonic acid, ethyl
methylphosphonic acid, and 2-(dimethylamino) ethanethiol.