Fast, cheap and accurate tests remain essential for epidemiological surveillance and for health services to monitor and contain the spread of SARS-CoV-2. Brazilian scientists have contributed to efforts in this area by developing an electrochemical immunosensor that detects antibodies against the virus.
In search of a new diagnostic method, the group opted for a material frequently used in metallurgy – zinc oxide – and combined it for the first time with fluorine-doped tin oxide glass ( FTO), a conductive material used in electrodes for photovoltaics and other advanced applications.
“With this unusual combination and the addition of a biomolecule, the viral spike protein, we have developed a surface capable of detecting antibodies against SARS-CoV-2. The result is displayed in the form of an electrochemical signal picked up by this surface,” explains chemist Wendel Alves, lead author of the article. Alves is a professor at the Center for Natural and Human Sciences of the Federal University of ABC (UFABC), State of São Paulo.
The electrode made by the researchers detected COVID-19 antibodies in serum in approximately five minutes with 88.7% sensitivity and 100% specificity, even surpassing the enzyme-linked immunosorbent assay (ELISA), l reference clinical diagnostic tool.
The research was supported by FAPESP through the National Institute of Science and Technology for bioanalysis and a thematic project.
According to Alves, who directs UFABC’s Electrochemistry and Nanostructured Materials Laboratory, prior knowledge of chemical properties such as the isoelectric point of the virus’ spike protein (S), has enabled the group to develop a platform form allowing S to electrostatically bind to zinc oxide nanorods. Zinc oxide is increasingly used to fabricate biosensors due to its versatility and unique chemical, optical and electrical properties.
The immunosensor is easy to manufacture and use, and its production cost is relatively low. “The group succeeded in developing the device thanks to its solid knowledge of new materials and the synthesis of zinc oxide nanorods,” Alves said. The nanorods form a film on the conductive surface of the FTO, creating a favorable molecular microenvironment for protein S immobilization and making the construct a simple way to detect these antibodies.
Researchers will now adapt the platform to make it portable and connectable to mobile devices for use in diagnosing COVID-19 and other infectious diseases.
Analysis and future uses
A total of 107 blood serum samples were analyzed. They were divided into four groups: pre-pandemic (15), COVID-19 convalescents (47), vaccinated without previous positive results for the disease (25) and vaccinated after a positive result (20). The vaccine consisted of two doses of CoronaVac given four weeks apart. CoronaVac is produced by the Chinese company SinoVac in partnership with the Butantan Institute (State of São Paulo).
The authors of the article – researchers affiliated with UFABC and the Institute of Cardiology (INCOR), which is run by the Faculty of Medicine of the University of São Paulo (FM-USP) – note that the The device detects antibodies produced in response to both virus infection and vaccination, and has excellent potential as a tool for monitoring seroconversion and seroprevalence. Detecting the response to vaccination is important to help public health authorities assess the effectiveness of different vaccines and vaccination campaigns or programs, they point out.
The device has been validated to detect CoronaVac-induced immunity, but the group plans to expand its use in vaccine response tests from Pfizer and AstraZeneca.
One of the advantages of the electrode they developed is its flexible architecture, which means it can easily be customized for other diagnostic and biomedical applications by using different biomolecules on the zinc oxide nanorods and other target analytes.
“The technology is a versatile biosensing platform. As developed by us, it can be modified and customized for the serological detection of other diseases of public health interest,” Alves said.
Reference: Nunez FA, Castro ACH, de Oliveira VL, et al. Electrochemical immunosensors based on zinc oxide nanorods for the detection of antibodies against the spike protein of SARS-CoV-2 in convalescent and vaccinated persons. ACS Biomater Sci Eng. 2022: acsbiomaterials.2c00509. doi:10.1021/acsbiomaterials.2c00509
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