high-resolution-physical-characterization-single-metallic

High Resolution Physical Characterization of Single Metallic Nanoparticles

Individual molecules can be detected and characterized by measuring the degree by which they reduce the ionic current flowing through a single ...

National Institute of Standards and Technology

Columbia University

Columbia College

We developed a generalized technique to characterize polymer-nanopore interactions via single channel ionic current measurements. Physical interactions between analytes, such as DNA, proteins, or synthetic polymers, and a nanopore cause multiple discrete states in the current. We modeled the transitions of the current to individual states with an equivalent electrical circuit, which allowed us to describe the system response. This enabled the estimation of short-lived states that are presently not characterized by existing analysis techniques. Our approach considerably improves the range and resolution of single-molecule characterization with nanopores. For example, we characterized the residence times of synthetic polymers that are three times shorter than those estimated with existing algorithms. Because the molecule's residence time follows an exponential distribution, we recover nearly 20-fold more events per unit time that can be used for analysis. Furthermore, the measurement range was extended from 11 monomers to as few as 8. Finally, we applied this technique to recover a known sequence of single-stranded DNA from previously published ion channel recordings, identifying discrete current states with subpicoampere resolution. 

Quantifying short-lived events in multistate ionic current measurements.

We report a new method to identify metallic nanoclusters (polyoxometalate structures) in solution at the single molecule limit using a nanometer-scale pore. The technique allows the measurement of polyoxometalates with over 2 orders of magnitude lower analyte concentration than conventional analytical chemistry tools. Furthermore, pH-dependent structural changes in phosphotungstic acid are measured with protein nanopores and validated with NMR. We further demonstrate that the method can also discriminate [PW9O34](9-) structural isomers. The results suggest this technique can serve as a complementary approach to traditional methods.

Single Molecule Discrimination of Heteropolytungstates and Their Isomers in Solution with a Nanometer-Scale Pore.

Biological and solid-state nanometer-scale pores are the basis for numerous emerging analytical technologies for use in precision medicine. We developed Modular Single-Molecule Analysis Interface (MOSAIC), an open source analysis software that improves the accuracy and throughput of nanopore-based measurements. Two key algorithms are implemented: ADEPT, which uses a physical model of the nanopore system to characterize short-lived events that do not reach their steady-state current, and CUSUM+, a version of the cumulative sum statistical method optimized for longer events that do. We show that ADEPT detects previously unreported conductance states that occur as double-stranded DNA translocates through a 2.4 nm solid-state nanopore and reveals new interactions between short single-stranded DNA and the vestibule of a biological pore. These findings demonstrate the utility of MOSAIC and the ADEPT algorithm, and offer a new tool that can improve the analysis of nanopore-based measurements.

MOSAIC: A Modular Single-Molecule Analysis Interface for Decoding Multistate Nanopore Data.

Nanometer-scale pores have been developed for the detection, characterization, and quantification of a wide range of analytes (e.g., ions, polymers, proteins, anthrax toxins, neurotransmitters, and synthetic nanoparticles) and for DNA sequencing. We describe the key requirements that made this method possible and how the technique evolved. Finally, we show that, despite sound theoretical work, which advanced both the conceptual framework and quantitative capability of the method, there are still unresolved questions that need to be addressed to further improve the technique.

Article	Year
Quantifying short-lived events in multistate ionic current measurements. ACS nano\| PubMed ID: 24397836	2014
Single Molecule Discrimination of Heteropolytungstates and Their Isomers in Solution with a Nanometer-Scale Pore. Journal of the American Chemical Society\| PubMed ID: 27203713	2016
MOSAIC: A Modular Single-Molecule Analysis Interface for Decoding Multistate Nanopore Data. Analytical chemistry\| PubMed ID: 27797501	2016
Determining the Physical Properties of Molecules with Nanometer-Scale Pores. ACS sensors\| PubMed ID: 29381331	2018

Jessica Ettedgui

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