Tribo-electrochemical surface modification of tantalum using in situ AFM techniques

Resolving electrical stimulus triggered molecular binding and force modulation upon thrombin-aptamer biointerface

Experimental and computational approaches are utilized to investigate the influence of electrostatic fields on the binding force between human coagulation protein thrombin and its DNA aptamer. The thiolated aptamer was deposited onto gold substrate located in a liquid cell filled with binding buffer, then the thrombin-functionalized atomic force microscopy (AFM) probe was repeatedly brought into contact with the aptamer-coated surface under applied electrical potentials of -100, 0, and 100 mV respectively. Force drops during the pull-off process were measured to determine the unbinding forces between thrombin and aptamer in a range of loading rates spanning from ~3 × 10² to ~1 × 10⁴ pN/s. The results from experiments showed that both of the binding strength and propensity of the complex are drastically diminished under positive electrode potential, whereas there is no influence on the molecular binding from negative electrode potential. We also used a theoretical analysis to explain the nature of electrostatic potential and field inside the aptamer-thrombin layer, which in turn could quantify the influence of the electrostatically repulsive force on a thrombin molecule that promotes dissociation from the aptamer due to positive electrode potential, and achieve good agreement with the experimental results. The study confirms the feasibility of electrostatic modulation upon the binding interaction between thrombin and aptamer, and implicates an underlying application perspective upon nanoscale manipulation of the stimuli responsive biointerface.

Degradation of polyvinyl alcohol under mechanothermal stretching

Mechanical and thermal properties of polyvinyl alcohol (PVA) are characterized and analyzed using in situ X-ray photoelectron spectroscopy (XPS) and quantum chemistry calculations. It is found that the carbon peaks-commonly used as the reference for spectroscopic analysis-shift under mechanical and thermal stretching. Results also indicate that, at different temperatures and among the various functional groups present in PVA, the carbon in the C-O group is the most stable. Computational calculations showed that Hartree-Fock/10-31G (d) reproduces the binding energy of core carbon electrons with an accuracy of 95%, which is enough to characterize bonds, allowing the results of the spectroscopic analysis to be corroborated.