Noncontact microrheology at acoustic frequencies using frequency-modulated atomic force microscopy


We report an atomic force microscopy (AFM) method for assessing elastic and viscous properties of soft samples at acoustic frequencies under non-contact conditions. The method can be used to measure material properties via frequency modulation and is based on hydrodynamics theory of thin gaps we developed here. A cantilever with an attached microsphere is forced to oscillate tens of nanometers above a sample. The elastic modulus and viscosity of the sample are estimated by measuring the frequency-dependence of the phase lag between the oscillating microsphere and the driving piezo at various heights above the sample. This method features an effective area of pyramidal tips used in contact AFM but with only piconewton applied forces. Using this method, we analyzed polyacrylamide gels of different stiffness and assessed graded mechanical properties of guinea pig tectorial membrane. The technique enables the study of microrheology of biological tissues that produce or detect sound.

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Figure 1: Concept of FM-AFM to measure mechanical properties of soft samples.
Figure 2: Estimation of mechanical properties through measurement of frequency shifts.
Figure 3: Effective probe area of pyramidal-probe C-AFM versus FM-AFM.


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We thank T.B. Friedman and K.H. Iwasa for critical input. This work was supported by the Intramural Program of the US National Institute of Deafness and Other Communication Disorders.

Author information




N.G. conceived, designed and performed the experiments, analyzed the data and wrote the paper. R.S.C. developed the hydrodynamic lubrication theory, conceived and designed the experiments and wrote the paper.

Corresponding author

Correspondence to Richard S Chadwick.

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The authors declare no competing financial interests.

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Supplementary Figures 1–4, Supplementary Table 1 and Supplementary Notes 1–3 (PDF 430 kb)

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Gavara, N., Chadwick, R. Noncontact microrheology at acoustic frequencies using frequency-modulated atomic force microscopy. Nat Methods 7, 650–654 (2010).

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