A multiscale model for inverse flexoelectricity and inverse piezoelectricity of layered nucleic acid adsorbed film in the deflection signals of microcantilevers

In recent years, the global spread of infectious diseases has spurred a rapid development of detection techniques by a novel nucleic acid probe microcantilever. However, challenges remain in quantitatively characterizing the electromechanical properties of adsorbed films and detection signals in microcantilever biosensors. This paper focuses on the multiscale correlation between detection conditions, the electromechanical coupling effect of adsorbed films, and microcantilever signals in novel techniques. First, considering the heterogeneous distribution and zonal characteristics of substrate-confined particles, novel three-zone models are proposed to predict the electric field distribution and mesoscopic free energy of the adsorbed film. Second, treating the nucleic acid solution as an adsorbed film with inverse flexoelectric/piezoelectric effects, effective electromechanical coefficients are characterized by using a deformation equivalence method and the above proposed mesoscopic energy model. Subsequently, a multiscale analytical model is established to interpret the deflection signals contributed from inverse flexoelectricity and inverse piezoelectricity of the layered adsorbed film. The validity of the analytical model is verified through nucleic acid probe-microcantilever experiments and x-ray photoelectron spectroscopy experiments. The study demonstrates that microscopic interactions such as electrostatic force, hydration force, and configurational entropy govern the dependence of the electromechanical coefficients of the heterogeneous layered adsorbed film on probe type and hybridization conditions, while the synergy and competition between macroscopic inverse flexoelectricity and inverse piezoelectricity contribute to the variation in microcantilever signals. These findings not only clarify the mechanism by which detection conditions influence the electromechanical coupling effects in heterogeneous adsorbed films and the relevant microcantilever signals but also provide insights for the design of high-sensitivity biosensors.