Researchers studied electrical conduction and nanopore formation during the controlled breakdown technique for better nanopore technology.
Nanopores are anemometer sized holes in an insulating membrane. The holes allow ions to pass through the membrane when a voltage is applied, resulting in a measurable current. When a molecule passes through a nanopore, the current changes and the change in current can be used to identify individual molecules.
Nanopores are useful for detecting DNA, RNA, and even proteins. Recently, it has been used in the SARS-CoV-2 virus sequencing. Solid-state nanopores are fome on less than 50 nanometers thick material made from materials such as silicon nitride. Usually, they are fabricated by Controlled Breakdown (CBD) technique. This technique is quick, reduces fabrication costs, does not require specialized equipment, and can be automated.
In CBD, an electric field is applied across the membrane to induce a current. A spike in the current signifies pore formation. The voltage is then quickly reduced to ensure the fabrication of a single, small nanopore.
Researchers from Instituto de Tecnologia Química e Biológica António Xavier da Universidade NOVA de Lisboa (ITQB NOVA) created three devices in which the electric field is applied to the membrane (a silicon-rich SiNx membrane) in different ways: via metal electrodes on both sides of the membrane; via electrolyte solutions on both sides of the membrane; and via a mixed device with a metal electrode on one side and an electrolyte solution on the other.
The results showed that redox reactions must occur at the membrane-electrolyte interface, whilst the metal electrodes circumvent this need. The researchers demonstrate that because of this phenomenon, nanopore fabrication could be localized to certain regions by performing CBD with metal microelectrodes on the membrane surface.
“Controlling the location of nanopores has been of interest to us for a number of years”, says James Yates. Pedro Sousa adds that “our findings suggest that CBD can be used to integrate pores with complementary micro or nanostructures, such as tunneling electrodes or field-effect sensors, across a range of different membrane materials.” These devices may then be used for the detection of specific molecules, such as proteins, DNA, or antibodies, and applied to a wide array of scenarios, including pandemic surveillance or food safety.
The research was published in the journal Small.