Rapid, inexpensive, and accurate tests are still necessary for epidemiological surveillance and health care services to monitor and prevent the spread of SARS-CoV-2. Brazilian researchers have contributed to the efforts of this field by creating an electrochemical immunosensor that identifies antibodies against the virus.
The innovation is described in an article published in the journal ACS Biomaterials Science and Engineering.
In search of a novel diagnostic method, the group chose a material often used in metallurgy – zinc oxide – and combined it for the first time with fluorine-doped tin oxide (FTO) glass, 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 developed a surface capable of detecting antibodies against SARS-CoV-2. The result is shown as an electrochemical signal captured by the surface this,” said chemist Wendel Alves. , lead author of the article. Alves is a professor at the Center for Natural and Human Sciences, Federal University of the ABC (UFABC), state of Sao Paulo.
The electrode developed by the researchers detected COVID-19 antibodies in serum in about five minutes with 88.7% sensitivity and 100% specificity, which is more than the enzyme-linked immunosorbent assay (ELISA) test, the current gold-standard clinical diagnostic tool.
The research is supported by FAPESP through the National Science and Technology Institute for Bioanalysis and a Thematic Project.
According to Alves, who heads the Electrochemistry and Nanostructured Materials Laboratory of UFABC, prior knowledge of chemical properties such as the isoelectric point of the spike protein (S) of the virus, allowed the group to develop a platform for S to bind electrostatically to zinc oxide nanorods. Zinc oxide is increasingly used to make biosensors because of its versatility and unique chemical, optical and electrical properties.
Principle of Immunosensor Manufacturing
A method for directly connecting an electronic device to a biological environment is difficult due to the inherent complexity of biosensor development. Nanomaterials enable the miniaturization of devices, improving their sensitivity due to their higher surface area and long-range electron conductivity.
(72,73) ZnONRs create a favorable environment for biomolecules adsorption, maintaining their functionality and converting biological events into a stable, selective, and sensitively measurable signal.
The SARS-CoV-2 recombinant trimeric spike protein is the biomolecule used to develop an electrochemical biosensing detection platform for anti-spike antibodies because the S protein is the main target antigen component from all the structural proteins of SARS-CoV- 2. (74) When working at physiological pH (7.4), the IEP of the S protein (∼5) has a net negative surface charge, and the ZnONR matrix with a high isoelectric point (∼9.5) acquires a net positive surface charge density .
Thus, the negatively charged protein can be immobilized by electrostatic interaction on the surface of the positively charged ZnONR matrix. This principle is widely used for the development of multiple immunosensors.
Analysis and future use
A total of 107 blood serum samples were analyzed. They were divided into four groups: pre-pandemic (15), COVID-19 convalescents (47), vaccinated without a previous positive result for the disease (25), and vaccinated after a positive result (20). The vaccine is two doses of CoronaVac given four weeks apart. CoronaVac is produced by the Chinese company SinoVac in collaboration with the Butantan Institute (state of Sao Paulo).
The authors of the article – researchers affiliated with the UFABC and the Heart Institute (INCOR), managed by the University of Sao Paulo’s Medical School (FM-USP) – note that the device detected antibodies produced in response in both virus infection and vaccination, and shows great potential as a tool for monitoring seroconversion and seroprevalence. Determining the response to vaccination is important to help public health authorities assess the effectiveness of different vaccines and vaccination campaigns or programs, they stressed.
The device has been validated for detecting CoronaVac-induced immunity, but the group plans to extend its use to testing responses to Pfizer and AstraZeneca vaccines.
One of the advantages of the electrode they developed is its flexible architecture, which means it can be easily customized for other diagnostic and biomedical applications using different biomolecules on zinc oxide nanorods and other target analytes. .
“The technology is a versatile biosensing platform. As we developed it, it can be modified and customized for the serological detection of other diseases of public health interest,” said Alves.
Electrochemical Response Studies of ZnONRs/Spike Immunosensors
EIS, CV, and SWV were used to characterize the electrode at each manufacturing stage (Figure 4). It shows the Faradic impedance spectra for the redox of [Fe(CN)6]3–/4– measured at each stage of manufacturing. The imaginary part of the impedance (Z″) is shown as a function of the real part of the impedance (Z′), as shown in Figure 4A.
* with inputs from ANI
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