Summary of the operation of the physical sensor for viruses (Elsevier 2020).The coronavirus pandemic highlights the importance of testing for viruses; a simple physical procedure might make it easier, cheaper and quicker.The coronavirus pandemic highlights the importance of testing for viruses; a simple physical procedure might make it easier, cheaper and quicker.
With the new coronavirus pandemic in full flow, testing for viruses is in the public consciousness. But the tests can be complex and expensive procedures performed by skilled professionals. They also generally require a sophisticated combination of chemicals to amplify and detect viral components. A physical method for detecting specific viruses, being developed in Russia, avoids the need for complex chemistry and professional expertise. It might transform testing if future developments can build successfully on an early demonstration using influenza viruses, reported in the journal Results in Materials.
The basic idea is very simple. Extremely narrow pits, just the right size to entrap the specific virus to be detected, are etched into the surface of a silicon wire. The presence of the viruses when they are adsorbed inside the pits changes the electrical properties of the silicon. This generates a signal detected by apparatus called an impedance spectrometer.
“This could form the basis of a very simple device, not only for use in clinical settings but even as a personal sensor for use at home,” says Maxim Gongalsky, who worked with colleagues to develop the device at Lomonosov Moscow State University.
Gongalsky says the procedure could be ideally suited for detecting coronaviruses, including the SARS-CoV-2 virus causing the current pandemic, because these are unusually large viruses at 500 nanometres compared to the 80-120 nanometres of influenza viruses.
The pits are etched into the silicon using a simple mixture of hydrofluoric acid and ethanol. This procedure also creates a surface roughness that encourages binding to glycoprotein molecules that protrude from the outer coat of a virus.
It might seem surprising that a detection system for specific viruses could be based simply on size and the electrical effects caused by the viruses’ own electrical properties, but the test results with influenza viruses are promising. The specificity for the influenza virus and sensitivity of detection are both sufficient to encourage the research group to explore the possibilities further. The detected signals vary in proportion to the concentration of the viruses, offering opportunities for quantifying the level of viruses in addition to simply indicating their presence.
Gongalsky explains that the next steps will be focused on further improving the sensitivity and selectivity of the system. By controlling the precise size of the pits the team hope they can refine it to reliably detect a range of different viruses, including SARS-CoV-2.
“Potentially, the sensing circuit might be able to be connected to a cell phone,” says Gongalsky. This would avoid the current requirement for expensive impedance analysing equipment.
The initial focus on a specific strain of influenza virus was driven by the serious seasonal outbreaks of influenza that hit Russia, especially Moscow with its very high population density.
“Now the study will get even more personal, as the Covid-19 disease spreads through Russia, and the wider world,” project supervisor Liubov Osminkina concludes.
Looking to the possibilities of new viral threats, the researchers point out that the procedure may be especially useful in the early days of an epidemic, as conventional tests can take longer to develop.
(The work was supported by the Russian Science Foundation (Grant N17-12-01386)
Article details:
Gongalsky, M. B. et al.: “Double etched porous silicon nanowire arrays for impedance sensing of influenza viruses,” Results in Materials (2020)