Piezoelectric properties of single-strand DNA molecular brush biolayers

Abstract

The paper is devoted to investigations on nanomechanical behaviors of biochips in label-free biodetections. The chip consists of Si-layer, Ti-layer, Au-layer and single-strand DNA (ssDNA) molecular brush biolayer immobilized by self-assembly technology of thiol group. Unlike previous viewpoints, such as force-bending, entropy-bending and curvature electricity effect, etc., the piezoelectric effect of the biopolymer brush layer is viewed as the main factor that induces nanomechanical bending of biochips, and a classical macroscopic piezoelectric constitutive relation is used to describe the piezoelectric effect. A new laminated cantilever beam model with a piezoelectric biolayer in continuum mechanics, the linearized Poisson-Boltzmann equation in statistical mechanics and the scaling method in polyelectrolyte brush theory are combined to establish a relationship between the nanomechanical deflection of DNA chips and the factors such as nanoscopic structural features of ssDNA molecules, buffer salt concentration, macroscopic mechanical/piezoelectric parameters of DNA chips etc. Curve fitting of experimental data shows that the sign of the piezoelectric constant of the biolayer may control the deflection direction of DNA chips during the packaging process.

Nanomechanical behaviors of microcantilever-based single-stranded DNA chips induced by counterion osmotic effects

“…Considering nanomechanical deflections and detection precisions (0.1 nm) in the present chip system, an alternative two-variable method (Zhang and Xing 2006;Zhang et al 2007;Zhang and Chen 2008, 2009b, 2010 is used in order to describe the chip deformation more accurately. If the curvature radius at the neutral axis (for zero normal strain) is ρ, the normal strain ε at the location y is…”

“…In recent years, microcantilever-based biosensors have attracted much attention (Fritz et al 2000;Wu et al 2001;Hagan et al 2002;Liu et al 2003;Alvarez et al 2004;Hansen and Thundat 2005;Stachowiak et al 2006;Zhang et al 2007;Zhang and Shan 2008;Finot et al 2008;Fritz 2008;Zhang and Chen 2009a;). The low-cost sensors not only exhibit fast response, high sensitivity, and suitability for parallelization into arrays, but also provide common platforms for label-free analyses, such as DNA hybridization, antigen-antibody binding, and drug discovery.…”

“…Based on Strey's empirical potential (Strey et al 1997(Strey et al , 1999 for a double-stranded DNA (dsDNA) systems, Hagan et al (2002) provided a theoretical framework for such microcantilever-dsDNA chips (corresponding to detection process) and showed that the dominant contribution to hybridization deflections comes from hydration forces. Using an alternative two-variable method (Zhang and Xing 2006;Zhang et al 2007;Zhang and Chen 2008, 2009b, 2010 for laminated cantilever beams, Zhang et al formulated a four-layer energy model for microcantilever-dsDNA chips (Zhang and Shan 2008) and investigated stochastic effect (Zhang and Shan 2008), hybridization exothermic effect ) as well as compressive elastic modulus (Zhang and Chen 2009a) of dsDNA-biolayer. In the process of modeling ssDNA chips (corresponding to packing process), Hagan et al (2002) pointed out that there is relatively little information about the segment-segment interactions in ssDNA, and therefore estimated the ssDNA free energy by utilizing several methods commonly used to examine polymer brushes, e.g., scaling laws, self-consistent-field methods, and Monte Carlo simulations.…”

“…First, Hagan's model for a cylindrical polyelectrolyte brush system based on Poisson- Boltzmann distribution hypothesis is employed to estimate the counterion osmotic energy in the ssDNA-biolayer with weak interactions. Second, Zhang's two-variable method (Zhang and Xing 2006;Zhang et al 2007;Zhang and Chen 2008, 2009b, 2010 is used to describe the deformation field of the chip as well as the mechanical energy of three nonbiological layers. Third, the principle of minimum energy is adopted to predict the packing deflection and study the influence of grafting density, chain length and buffer salt concentration.…”

Effect of Conformational Entropy on the Nanomechanics of Microcantilever-Based Single-Stranded DNA Sensors

“…Zhang et al [15] developed a phenomenological model to interpret this phenomenon considering the piezoelectric effect. Curve fitting with the related experimental data showed that the sign of the piezoelectric constant of ssDNA biofilm may control the deflection direction of ssDNA sensors.…”