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Concentrated DNA Rheology and Microrheology

Published online by Cambridge University Press:  10 February 2011

T. G. Mason ,
A. Dhople  and
D. Wirtz
T. G. Mason
Affiliation:
Department of Chemical Engineering, Johns Hopkins University, 24 NEB, 3400 N. Charles St., Baltimore, MD 21218, Email: tgmason@jhu.edu
A. Dhople
Affiliation:
Department of Chemical Engineering, Johns Hopkins University, 24 NEB, 3400 N. Charles St., Baltimore, MD 21218.
D. Wirtz
Affiliation:
Department of Chemical Engineering, Johns Hopkins University, 24 NEB, 3400 N. Charles St., Baltimore, MD 21218.
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Abstract

We present mechanical measurements of the frequency-dependent linear viscoelastic storage and loss moduli, G′(ω) and G″(ω), and the yield stress, τy, and yield strain, γy, for calf thymus DNA (13 kbp) over a range of mitotically relevant concentrations from CDNA = 1 to 10 mg/ml. For large CDNA, we find a dominant plateau elasticity, G′p, at high ω. As ω decreases, G′ falls until it is equal to G′ at the crossover frequency, ωc, below which G″ dominates. We measure G′p ∼ CDNA2.25 and ωc ∼ CDNA−2.4, consistent with scaling exponents for classical polymer solutions. The mechanical |G*(ω)| agree well with those measured using a new microrheological technique based on video tracking microscopy of thermally-driven fluorescent colloidal spheres and a frequency-dependent Stokes-Einstein equation. We have developed this technique to probe how enzymes, typically available in small quantities, can affect the rheology of the DNA. Using it, we report preliminary measurements of a higher ωc for a DNA network in which the ATP-powered enzyme Topoisomerase II transiently cuts and rebinds the DNA, thereby relaxing entanglements.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 463: Symposia EE – Statistical Mechanics in Physics and Biology , 1996 , 153
Copyright
Copyright © Materials Research Society 1997

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References

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