Model‐Free Rheo‐AFM Probes the Viscoelasticity of Tunable DNA Soft Colloids

Atomic force microscopy rheological measurements (Rheo‐AFM) of the linear viscoelastic properties of single, charged colloids having a star‐like architecture with a hard core and an extended, deformable double‐stranded DNA (dsDNA) corona dispersed in aqueous saline solutions are reported. This is ac...

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Bibliographic Details
Published in:Small (Weinheim an der Bergstrasse, Germany) Germany), 2019-10, Vol.15 (42), p.e1904136-n/a
Main Authors: Moreno‐Guerra, José A., Romero‐Sánchez, Ivany C., Martinez‐Borquez, Alejandro, Tassieri, Manlio, Stiakakis, Emmanuel, Laurati, Marco
Format: Article
Language:English
Subjects:
AFM
Atomic force microscopy
brush
Colloids
Density
Deoxyribonucleic acid
DNA
dsDNA
Formability
Fourier transforms
Indentation
Nanotechnology
Polyelectrolytes
Reduction
Rheological properties
Saline solutions
Softening
Star formation
Stiffness
Storage modulus
Viscoelasticity
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Summary:Atomic force microscopy rheological measurements (Rheo‐AFM) of the linear viscoelastic properties of single, charged colloids having a star‐like architecture with a hard core and an extended, deformable double‐stranded DNA (dsDNA) corona dispersed in aqueous saline solutions are reported. This is achieved by analyzing indentation and relaxation experiments performed on individual colloidal particles by means of a novel model‐free Fourier transform method that allows a direct evaluation of the frequency‐dependent linear viscoelastic moduli of the system under investigation. The method provides results that are consistent with those obtained via a conventional fitting procedure of the force‐relaxation curves based on a modified Maxwell model. The outcomes show a pronounced softening of the dsDNA colloids, which is described by an exponential decay of both the Young's and the storage modulus as a function of the salt concentration within the dispersing medium. The strong softening is related to a critical reduction of the size of the dsDNA corona, down to ≈70% of its size in a salt‐free solution. This can be correlated to significant topological changes of the dense star‐like polyelectrolyte forming the corona, which are induced by variations in the density profile of the counterions. Similarly, a significant reduction of the stiffness is obtained by increasing the length of the dsDNA chains, which we attribute to a reduction of the DNA density in the outer region of the corona. A model‐free atomic force microscopy rheological measurement (Rheo‐AFM) method allows the measurement of the viscoelastic properties of DNA star‐like colloids in aqueous solution, revealing a pronounced softening of the particle with increasing salt concentration. This is related to a critical reduction of the corona size due to topological changes of the DNA chains. The method can be applied to determine the viscoelasticity of soft colloids and nanoparticles.
ISSN:1613-6810
1613-6829
DOI:10.1002/smll.201904136