Resistive pulse sensing represents a very attractive method for identifying and quantifying biomedical species such as drugs, DNA, proteins, and viruses in solution. This method involves measuring changes in the ionic current across a membrane containing a single nanometer-sized pore that separates two electrolyte solutions. As the biological analytes make their way through the pore, they induce transient downward current pulses in the ionic current by transiently blocking the nanopore. The frequency, duration, and magnitude of the current pulse contain telltale information that aids the identification and quantification of the analyte. A biological nanopore, á-hemolysin, supported by a lipid bilayer membrane, works well in the detection of various analytes.
However, a major impediment to this system is its lack of mechanical robustness. Indeed, these biological membranes tend to rupture within a few hours, thus precluding their application in practical sensing devices. Now a team of researchers at the University of Florida have come up with a major breakthrough that will aid the reproducible fabrication of robust synthetic single-nanopore membranes.
The nanopores are prepared by a track-etching method. In this approach, a high-energy particle is passed through a synthetic polymer membrane to create a damage track, which is then chemically etched to convert the track to a pore. A major challenge has been ensuring control and reproducibility of the diameter of the resulting pore. Charles R. Martin and his colleagues have developed a two-step etching method to reproducibly fabricate conical pores in polymer membranes with predictive control of the diameters of the pore openings. The conical pores have two openings on opposite faces: a large-diameter base and a small-diameter tip. Much of the sensing action occurs at the tip, since the bioanalytes block the tip while moving across the membrane. It is thus imperative to control the size of this tip opening.
The researchers use the first etch step to define the base and the tip of the conical pores in the membrane. Subsequently, they use a second etching step, while continuously monitoring the ion current, and stop the etching process when the ion current across the membrane reaches a certain value, corresponding to a well-defined tip diameter. This method allows the predictive and reliable fabrication of conical pores with tip openings varying from 10 to 60 nm, which is in the right regime for detecting biological analytes. Martin and his colleagues have illustrated the dramatic potential of these membranes by detecting a protein analyte, bovine serum albumin, using nanopore sensors with two different tip diameters. The protein more effectively blocks the pores of a nanopore sensor with a tip diameter of 17 nm as compared to a sensor with 27-nm tips, and this is reflected in the current pulse data. “This method may allow us to take artificial nanopore sensors from the bench top to the practical prototype-device development stage”, said Martin, emphasizing that the reproducible preparation of artificial nanopores is critical for the development of resistive-pulse sensors.
Author: Charles R. Martin, University of Florida (USA), http://www.chem.ufl.edu/~crmartin/
Title: A Method for Reproducibly Preparing Synthetic
About Small: Micro and Nano: No small Matter. Science at the nano- and microscale is currently receiving enormous wordwide interest. Published by Wiley-VCH, Small provides the very best forum for experimental and theoretical studies of fundamental and applied interdisciplinary research at these dimensions. Read an attractive mix of peer-reviewed Communications, Reviews, Concepts, Highlights, Essays, and Full Papers.
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy