Voltage and blockade state optimization of cluster-enhanced nanopore spectrometry

Abstract

Recent work described the use of thiolate-capped gold clusters (Au25(SG)18) with nanopore sensing to increase the residence time of polyethylene glycol (PEG) in an alpha hemolysin pore [Anal. Chem., 2014, 86, 11077]. It was shown that the residence time enhancement narrows the peaks in the PEG-induced current blockade distribution, thus increasing the resolving power of the single molecule nanopore spectrometry (SMNS) technique. Here, we further study the interaction between the cluster and PEG with the goal of optimizing the residence time enhancement for SMNS detection. Specifically, we report the voltage dependence of the enhancement effect and show that, under the conditions studied, the cluster-enhanced residence time is maximized at an applied transmembrane potential near 60 mV. Additionally, we show that the PEG residence time depends on the degree to which the cluster blocks current through the pore and that the PEG on-rate to the pore can be more accurately measured with a cluster in the pore. Finally, we develop a model that describes the cluster-induced shift of the PEG current blockade distribution. We use this model to characterize the interaction between the cluster and PEG and show that it scales linearly with the applied voltage as expected from the proposed enhancement mechanism.

High Temperature Extends the Range of Size Discrimination of Nonionic Polymers by a Biological Nanopore

“…It seems evident that the single-monomer resolution of size-discrimination observed with the PEG/ α -hemolysin system, and recently also with PEG/metallic-clusters/ α -hemolysin1521, with PEG/aerolysin20 and with short oligonucleotides/aerolysin22, can only occur if each monomer contributes to the current blockade, i.e. when the polymer is fully accommodated in the pore.…”

“…However, this term may be somewhat misleading, as this technique does not discriminate molecules on the basis of their mass, but rather by their size, as mentioned in ref. 15. Thus we prefer to use the term “nanopore-based single-molecule size discrimination” (Np-SMSD) in what follows.…”

Interactions of a Polypeptide with a Protein Nanopore Under Crowding Conditions

“…These interactions can be detected by monitoring the changes that occur in transmembrane ionic current as a result of the application of a voltage bias. 6,[8][9][10][11][12][13][14][15][16][17][18] However, crowding agents, such as neutral, watersoluble, and flexible polymers, partition into a nanoscale protein pore in a size-dependent manner. [19][20][21][22][23][24] Given this interesting property, recent studies have highlighted the importance of selective pore penetration by smaller polymers against larger, less-penetrating polymers.…”

Determining the Physical Properties of Molecules with Nanometer-Scale Pores

“…The residence time of an analyte in the nanopore is influenced by several factors including interactions of the molecule with the pore wall, ,, the magnitude of the applied potential, and molecules (either free to enter and leave the pore or that are bound to the pore) that reversibly bind to the analyte. ,− The residence time can also be altered by another molecule that does not bind to the analyte, as was shown for the metallic nanocluster-enhanced increase in PEG residence time in the αHL pore (Figure ). , Negatively charged gold nanoclusters stabilized with glutathione (Au 25 SG 18 ) and PEG weakly bound with cations were added to the cis and trans sides of the phospholipid membrane, respectively. A negative applied electrostatic potential (with respect to the trans side) forces both analytes into the pore.…”