The stiffness tomography is a new imaging mode developed in the laboratory of physics of living matter in EPFL.
This imaging mode is described in a paper published in Biophysical Journal in 2009.
How does it works ?
Atomic force microscope has several imaging mode. The force spectroscopy mode permits to use the AFM as a nano-indenter.
The data resulting from this imaging mode is a set of force distance curve that informs on how the cantilever deflects in function of the sample height. From this curve, we can deduce the force indentation curve which informs on how much force we need to indent into a certain depth in the sample. By fitting these curves with theoretical models (like the Hertz model), one can estimate the Young modulus of the indented substrate.
If one examines the force indentation curve, he can observe that a stiff inclusion into the sample modifies the shape of the curve. The position of the modification depends on the depth where the inclusion is located.
The idea behind the stiffness tomography is to segment the force indentation curve in several segment of a defined depth size and fit each of these segments with the theoretical model (like Hetz model). The stiffness nanotomography results then from the segmentation of all force indentations curves of the force volume image.
An Example ?
Here is the stiffness tomography of a neurite scanned at 2µm size. Some structures are clearly visible inside the neurite.