Surface/Interface Effect Of Adsorbed DNA Film And Its Influence On Detection Signals Of Microbeam Sensors

Taking DNA-microcantilever in label-free biodetection as object of study,in this paper we formulated multi-scale models correlating microscopic effect of buffer solution,mechanical properties of DNA film and mechanical response of DNA microbeam systems,and studied the influence of the adsorption-related surface effect,end effect,buckling effect and nonlinear effect on the detection signal of microbeam.The relevant models,methods and conclusions not only enrich the theoretical framework of soft matter mechanics,but also provide reference and new ideas for the development of DNA chip technology and the potential application of DNA film in biomedicine and nanomaterials.The main work is as follows:(1)As for the problem of capturing the local deformation of DNA fragments under low buffer salt concentration and low DNA strand packing density,we developed a new coarse-grained DNA bead-chain model.In the new model,we modified the Yukawa potential which describes the interaction between DNA strands.Then,we predicted the elastic properties of DNA film by thought experiment method,and sampled the stable configuration of DNA strand by Monte Carlo simulation.The results showed that the complex microscopic interaction in buffer solution results in the variability of DNA nanoscale structure,which endows the diversity of mechanical properties of DNA film on the substrate.(2)As for the linear detection mode under higher buffer salt concentration and DNA strand packing density,by using thought experiment method,empirical potential of mesoscopic free energy of DNA film and Hamilton principle,we formulated a multi-scale model correlating microscopic effect of buffer solution,macroscopic mechanical properties of DNA film and mechanical response of DNA microbeam systems.Then,we studied the effect of DNA film microscopic interactions on the system's detection signal,and revealed the possible physical mechanism of DNA condensation in living organisms and system's anomalous detection signal.The results showed that the dominating attractive interaction between DNA strands in high valence salt solution endows adsorbed DNA film with metamaterial propertites(negative elastic modulus),and the competition of attractive and repulsive interactions will lead to the change of bending direction and the positive or negative shift of natural frequency of the microbeam.(3)As for the linear detection mode under normally eccentric loading of uniform surface stress,based on the principle of virtual work,we established a mathematical model of DNA-microcantilever which exactly satisfies the displacement and force boundary conditions,and proposed a general solution to a class of variable coefficient differential equations,analytically predicted the static response of the system,thereout pointed out the shortcomings of the previous approximate models with concentrated load assumption.The results showed that the adsorption induced non-uniform deformation at fixed end makes the uniform curvature bending assumption of classical concentrated load models no longer applicable,the system curvature approximately linearly decreases along the axis,and the influence of the end effect on static deflection of the system should be considered in certain parameter spaces.(4)As for the discussed new-type linear dynamic detection mode based on nonlinear buckling configuration,considering the geometric nonlinear of von Karman type,based on Hamilton principle,we established a nonlinear mathematical model of DNA-microbeam with double fixed supports before and after buckling,and studied system's nonlinear buckling problem and linear vibration characteristics before and after buckling,thereout reasonably explained the phenomenon of anomalous frequency shift found in experiments,and revealed the ultra-high sensitivity of the system in the postbuckling vibration mode.The results showed that the thinner the substrate thickness or the softer the substrate material,the more likely the DNA-microbeam system occurred to be buckled;due to the competition between stiffness effect and axial force effect caused by DNA adsorption,the linear vibration natural frequency of postbuckling system will change from negative shift to positive.(5)As for the discussed new-type nonlinear dynamic detection mode based on nonlinear buckling configuration,considering the competition between square nonlinearity induced by the change of buckling static equilibrium position and cubic nonlinearity,based on Hamilton principle,we established a nonlinear dynamical model of DNA microbeam before and after buckling.By using spatial domain Galerkin method and temporal domain multi-scale method,we analytically predicted the nonlinear dynamic characteristics of the system,and revealed the ultra-high sensitivity of the system in the nonlinear detection mode,thereout discussed the stability and final state sensitivity of the nonlinear solution.The results showed that due to the competition between square nonlinearity and cubic nonlinearity,the system vibration presents a transition of nonlinear hardening and softening before and after buckling;in addition,the stable solution branch of the non-chaotic attractor is strongly sensitive to the system parameters.