AFM Investigation of Avian Influenza Viruses
The present paper describes a direct label-free diagnostic method that uses atomic force microscopy (AFM) to identify avian influenza virus strains through their electrical properties. In this method, a single virus particle is sandwiched between a rigid, conductive substrate and a conductive AFM tip (radius ∼ 8nm). Electrical characterization is achieved by probing the complex impedance spectrum of the sandwiched virus while mechanical characterization is achieved through nanoindentation. A total of three virus strains (inactivated) with different combinations of glycoprotein subtypes (H2N2, H3N5 and H4N6) were tested. Results from the electrical characterization indicate that the impedance spectra of different virus strains are indeed different. While the average electrical capacitance of a virus particle is about 17pF, the variation from one strain to another can be as high as 70%. A COMSOL Multiphysics™ simulation was carried out to estimate the electrical properties of the glycoproteins on the virus particle by comparing the simulated capacitance to the experimentally obtained values. The result indicates that the electrical conductivity of the glycoproteins is in the range of 9 to 14 mS and the dielectric constant value is around 2. The present results strongly suggest the possibility of using AFM as a diagnostic tool for direct recognition of avian influenza virus strains.