Viscoelasticity of single biopolymers using atomic force microscopy

Abstract

Viscoelasticity of single protein molecules is essential to fully understand their dynamicproperties and functions It is also believed that the initial collapse in protein foldingis governed by their viscoelasticity Dynamic atomic force microscopy is recognised asa powerful tool for direct measurement of viscoelasticity in the single molecules Thismethod had also been vastly applied to understand the dynamic properties of the nanoconfinedliquids The estimated viscoelasticity using this method is always debated dueto the complex dynamic behaviour of AFM cantilever beam in liquid environment Inorder to resolve this issue understanding the cantilever dynamics under the influence ofinteraction force in liquid environment is essential We have done a comprehensive workto precisely determine the interaction viscoelasticity using amplitude modulation atomicforce microscopy AM AFM Single protein molecule titin I278 has been chosen as amodel system for the study We have applied two types of AFMs slope detection based commercial and displacement detection based interferometer based home built AFM Twotypes of cantilever excitation mechanisms have been used acoustic excitation cantileverbaseis excited using dither piezo and magnetic excitation cantilever tip is excited usingthe magnetic excitation Experiments were performed at truly off resonance regime toavoid the complexities arising at on resonance operation Data has been analyzed using twomathematical models continuous beam CB and point mass PM model The experimentsperformed using different AFMs and using different cantilever excitation schemes and dataanalyzed using different models have been compared and an unified understanding have beentried building up to understand the AM AFM measurements and its outcomes We found thatthere are various sources which can introduce errors artefacts in final results such as offset in newline newline