Effect of surface charge state on the surface stress of a microcantilever

Abstract

The surface charge state at a liquid-solid interface is important to the variations in the physical/chemical properties of adsorbate film such as surface stress and the ensuing tip deflection of the microcantilever. The well-known Stoney's equation, derived more than 100 years ago, conceals the film electrical properties with the replacement of substrate deformation induced by adsorptions of particles. This implicit expression provides a shortcut to circumvent the difficulty in identifying some film properties, however, it limits the capacity to ascertain the relation between surface stress variation and the surface charge state. In this paper, we present an analytical expression to quantify the cantilever deflection/surface stress and the film potential difference by combining the piezoelectric theory and Poisson-Boltzmann equation for electrolyte solution. This updated version indicates that the two linear correlations between surface stress and surface charge density or the bias voltage are not contradictory, but two aspects of one thing under different conditions. Based on Parsegian's mesoscopic interaction potential, a multiscale prediction for the piezoelectric coefficient of double-stranded DNA (dsDNA) film is done, and the results show that the distinctive size effect with variations in salt concentration and nucleotide number provides us with an opportunity to obtain a more sensitive potential-actuated microcantilever sensor by careful control of packing conditions.

Synthesis, Assembly, and Applications of Hybrid Nanostructures for Biosensing

“…However, like many other sensors within real-life biofluid environments, nonspecific adsorption is still the main technical obstacle to overcome if microcantilever-based biodetection were to succeed in practical conditions. As recent studies demonstrated, the reproducibility of the microcantilever-based biosensors can be improved as the surface charge and stress states of biofluid-microcantilever interfaces are better understood . Furthermore, the sensitivity of microcantilever sensors can be enhanced by integration or combination with other detection schemes, such as SPR, to create opto-mechanical hybrid sensors …”

The effect of microscopic attractive interactions on piezoelectric coefficients of nanoscale DNA films and its resultant mirocantilever-based biosensor signals

“…First, based on a macroscopic piezoelectric theory, an analytical relation between the cantilever deflection and the electric potential of the adsorbate film is recited here as in the previous works [21], where the adsorbate film was viewed as a kind of piezoelectric materials [16], while the substrate was treated as an elastic material.…”

“…As for the cantilever deformation, it could be obtained by the energy approach. The Hamiltonian for the adsorbate film is given as [21]…”

“…While Zhang et al [19,20] proposed an alternative mechanism to interpret the relation between the change of the microcantilever's bending direction and the piezoelectric coefficient of the immobilized DNA film. Furthermore, Zhang et al [21] studied the size effect of the piezoelectric coefficient for DNA films in NaCl solutions. However, the piezoelectric behavior of DNA films and the resultant signals of microcantilever-based biosensors in multivalent salt solutions are not considered.…”

“…In this paper, first, two different analytical models for microcantilever deflections based on macroscopic piezoelectric theories [21][22][23] or mesoscopic liquid crystal theories for nanoscale DNA films [2,6], are recited to obtain a multiscale prediction of piezoelectric coefficient for DNA films. Second, two interaction potentials of free energy for repulsion-dominated DNA films in NaCl solutions or attractionrepulsion-coexisted DNA films in multivalent salt solutions are used to compare the piezoelectric effect and the resultant cantilever bending in different packing conditions.…”