Inverse piezoelectricity of single-stranded DNA film on microcantilever

The paper aims to reveal the relation between the inverse piezoelectricity of single-stranded DNA (ssDNA) film and the origin and sign of the deflection of microcantilever produced by the DNA immobilization. By using Zhang´s two-variable method for strain field of laminated beam and the linearized Poisson-Boltzmann equation for bioelectric potential of polyelectrolyte brush, an approximate model is presented to confirm the previous conjecture that the sign of the piezoelectric constant of ssDNA film might decide the sign of the surface stress. There is only one fitting parameter (piezoelectric stress constant) needed in the simplified model, which greatly reduces the difficulty of identifying the nanoscale electrical/mechanical properties of DNA film. Numerical fitting curves based-on the analytical models agree well with the pertinent experimental dada. The difference between the previous four-layered model and the present two-layered approximate model is also compared.