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.
Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory
How cheetahs stay fit and healthy
24.03.2017 | Forschungsverbund Berlin e.V.
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy