Stochastic Detection of Terrorist Agents and Biomolecules in a Biological Channel
Stochastic sensing can detect analytes at the single-molecule level, in which a biological ion channel embedded in a lipid bilayer or a nano-scale sized pore fabricated in a solid-state membrane is used as the sensing element. By monitoring the ionic curr
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Stochastic Detection of Terrorist Agents and Biomolecules in a Biological Channel Xiyun Guan, Ranulu Samanthi S. de Zoysa, Dilani A. Jayawardhana, and Qitao Zhao
Abstract Stochastic sensing can detect analytes at the single-molecule level, in which a biological ion channel embedded in a lipid bilayer or a nano-scale sized pore fabricated in a solid-state membrane is used as the sensing element. By monitoring the ionic current modulations induced by the passage of the target analyte through the single pore, both the concentration and the identity of the analyte can be revealed. In this chapter, we highlight recent advances in the stochastic detection of terrorist agents and biomolecules, and in real-world sample analysis using alpha-hemolysin protein ion channels. Keywords Stochastic sensing • Ion channel • Lipid bilayer • Alpha-hemolysin • Artificial nanopore • Single-channel recording • Terrorist agents • Peptides • DNA • Real-world sample analysis
13.1
Introduction
Nanopore stochastic sensing is currently an active research area. In large part this growing interest is driven by the discovery that nanopore sensors can successfully detect analytes at the single-molecule level, potentially offering a highly sensitive, rapid, and multi-functional sensing system [1, 2]. Nanopore detection is achieved by monitoring the ionic current flowing through a single pore at a fixed applied potential. Typically a buffer solution containing a high salt concentration (e.g., 1 M NaCl or KCl) at or near pH 7.4 (i.e., physiological pH) is used to produce the open channel X. Guan (*) Department of Chemistry and Biochemistry, The University of Texas at Arlington, 700 Planetarium Place, Arlington, TX 76019-0065, USA e-mail: [email protected] S.M. Iqbal and R. Bashir (eds.), Nanopores: Sensing and Fundamental Biological Interactions, DOI 10.1007/978-1-4419-8252-0_13, # Springer Science+Business Media, LLC 2011
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Recognition site
cis
α-hemolysin Lipid bilayer
trans τon
Open channel current
Amplitude τoff
Fig. 13.1 Schematic representation of nanopore stochastic sensing
current which is monitored. In the absence of compounds, the channel is always open and a constant ionic current (called open-channel current) could be observed. In contrast, when a target molecule enters the pore, it will physically block the channel, thus resulting in a decrease in the ionic current flowing through the pore; when the molecule leaves the channel, the pore re-opens and the ionic current will increase (back to the open-channel state). In this way, a sequence of individual singlemolecule binding events can be detected as transient modulations in the recorded current. Although each individual current blockage event is random, the statistical mean values of the residence time (toff) and amplitude of the events are reproducible and are also unique for different analytes. Hence, toff and amplitude can serve as a characteristic current signature to reveal the identity of an analyte (Fig. 13.1). Furthermore, the concent
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