SMU and the University of Rhode Island have developed a groundbreaking method for creating solid-state nanopores (SSNs) that is both cost-effective and user-friendly. Furthermore, this innovation enables self-cleaning of clogged nanopores, addressing significant challenges that have limited the widespread use of SSNs in biosensor applications.
The patented technique, known as chemically tuned controlled dielectric breakdown (CT-CDB), tackles two main issues that have limited the use of solid-state nanopores, which are too small to be seen by the human eye. These issues have hindered the more widespread use of solid-state nanopores in the construction of biosensors capable of measuring biological and chemical reactions in a given sample.
Biosensors have broad medical applications, providing fast, early, and efficient disease diagnosis and monitoring.
“We produced nanopores that vastly surpassed legacy drawbacks associated with solid-state nanopores (SSNs) using this technique,” said one of the patent holders, MinJun Kim, who is the Robert C. Womack Chair in the Lyle School of Engineering at SMU and principal investigator of the BAST Lab.
SSN devices are made up of a minuscule opening called a nanopore, which is located within a membrane. This membrane is a thin material that acts as a separator between two reservoirs that are filled with ionic solutions.
When a voltage is applied across the membrane, an ionic current moves through the nanopore.
In order to acquire more knowledge about a specific substance, scientists guide a small sample through the nanopore into one of the reservoirs. Each biomolecule then produces its unique signal as it travels through the nanopore, caused by a modification in the electric field. These signals of electrical current enable the determination of the biological and chemical properties of the substance.
“A fast and simple approach for fabricating a single nanopore is by using controlled dielectric breakdown, or CDB, at the nanoscale,” Kim said.
When exposed to high voltage, an electrically insulating material experiences dielectric breakdown, causing it to transition from an insulator to a conductor, enabling the flow of current. Dielectric breakdown involves applying a voltage across an insulating membrane to create a strong electric field and monitoring the resulting leakage current. The leakage current is a result of electron tunneling through traps or inherent defects within the membrane. Over time, the accumulation of charged traps leads to a dielectric breakdown in the membrane, resulting in the formation of a single nanopore.
However, there are two consistent issues associated with pores created using this method: fluctuations in open-pore current and irreversible sticking of analytes. Changes or fluctuations in the baseline current flowing through a nanopore when it is unobstructed are known as drifts in open-pore current. These drifts can impact the precision and dependability of measurements conducted using solid-state nanopores.
The permanent binding of the substance being measured or analyzed, known as the analyte, to the nanopore instead of traversing through it, is referred to as irreversible analyte sticking.Both of these issues have the potential to disrupt researchers’ ability to obtain consistent, long-term measurements from nanopores.
Researchers from SMU and the University of Rhode Island have come up with a technique to alter CDB using a chemical additive called sodium hypochlorite, or NaOCl, for creating SSNs with thin silicon nitride membranes.
The addition of sodium hypochlorite led to the creation of nanopores that were much less likely to get blocked compared to traditionally manufactured nanopores. Furthermore, it resulted in pores that were free from fluctuations in open-pore currents, as discovered by the researchers. These advantages reduced the duration of downtime between experiments.
“This resulted in dramatically different nanopore surface chemistry, which significantly improved their performance,” Kim said.