Influenza has been the main cause of critical respiratory infections over the years. It is caused by a number of strains of various subtypes of the influenza virus. Therefore, quick diagnosis or detection and classification of the influenza in its early stages of development is pivotal for efficient treatment implementing antiviral drugs and in identifying pandemic occurrences. Immunoassay-based detection of the virus implementing antibody-antigen interactions offers a potential means of detection owing to their unique binding affinity and specificity.
Various approaches have been developed for influenza virus detection, for instance, enzyme-linked immunosorbent assay and fluorescence immunosensors. However, the methods have demonstrated a number of insufficiencies in their implementation and use. For example, the immunosorbent assay has slow throughput and results in time consuming protocols. Researchers have however developed spectro-electrochemical alternatives. This is where the wavelength of the probing light is spectrally tuned in order to interrogate optical transition that is linked to the electrochemically driven electro-transfer process of the redox molecules and is optically blind to ions present in the sample.
Researchers led by Professors Sergio B. Mendes (Physics) and Martin O’Toole (Bioengineering) from the University of Louisville developed a novel immunosensor-based approach for direct detection of viral pathogens by using a sandwich bioassay on a single mode electron active integrated optical waveguide platform. In their study, they targeted the hemagglutinin protein for the H5N1 avian influenza A virus in a bid to show the capacity of the waveguide platform device for detection as well as classification of a selected influenza antigen. Their work is published in Optics Letters.
The authors selected an immunoassay with a monoclonal anti-H5 antibody, which was bound to the electro-active integrated optical waveguide gadget to develop an interface that was prepared to detect and capture the target hemagglutinin protein. When the protein antigens were captured on the surface of the gadget, they initiated the immobilization of polyclonal antibody that was marked with methylene blue dye. Methylene blue dye has reversible changes in optical absorption throughout a transition in the oxidation state, therefore, presenting a characteristic optical probe that can be electrically tuned.
Once the researchers determined the optimal angular frequency for modulating the optical signal of the redox process, they applied an AC voltammetric approach at varying DC bias potentials. They then tested virus protein solutions with different concentrations.
When the DC bias potential was detuned from the formal potential, the signal probe decreased towards zero. The optically measured peak intensity of the faradic current density associated with the redox probe was found to be proportional to the concentration of the antigen and provided a direct path for quantifying the virus analyte.
From the experimental data obtained from this study, a 3-sigma limit detection was realized to be 4 ng/mL for the virus antigen. This figure is perhaps the best performance reported so far. It surpasses several technologies deployed in most clinics.
The analytical signal implemented in this study was linked to electrochemical and spectral attributes of a redox probe designed to detect the target antigen. These selective features are critical in minimizing the unwanted signals from interferents in clinical samples. The spectro-electrochemical approach in the single-mode electro-active optical waveguide platform offers a detection protocol for direct detection and quantification of the virus analyte. The results for the influenza A (H5N1) HA protein obtained in this paper, surpassed an outstanding level of detection.
Jafar H. Ghithan, Monica Moreno, Guilherme Sombrio, Rajat Chauhan, Martin G. O’toole, And Sergio B. Mendes. Influenza virus immunosensor with an electro-active optical waveguide under potential modulation. Vol. 42, No. 7 / April 1 2017 / Optics Letters.