Spectroscopic Investigation of Local Mechanical Impedance of Living Cells

Abstract

We studied nanoscale mechanical properties of PC12 living cells with a Force Feedback Microscope using two experimental approaches. The first one consists in measuring the local mechanical impedance of the cell membrane while simultaneously mapping the cell morphology at constant force. As the interaction force is increased, we observe the appearance of the sub-membrane cytoskeleton. We compare our findings with the outcome of other techniques. The second experimental approach consists in a spectroscopic investigation of the cell while varying the tip indentation into the membrane and consequently the applied force. At variance with conventional dynamic Atomic Force Microscopy techniques, here it is not mandatory to work at the first oscillation eigenmode of the cantilever: the excitation frequency of the tip can be chosen arbitrary leading then to new spectroscopic AFM techniques. We found in this way that the mechanical response of the PC12 cell membrane is found to be frequency dependent in the 1 kHz - 10 kHz range. In particular, we observe that the damping coefficient consistently decreases when the excitation frequency is increased.

Custom AFM for X-ray beamlines:in situbiological investigations under physiological conditions

“…The AFM tip position is measured with a fiber-optic-based interferometer (Rugar et al, 1989). This detection operational scheme has already been employed for different experiments (Vitorino et al, 2015;Costa et al, 2014). A 125 mm-diameter cleaved optical fiber is brought to a distance of about 10 mm from the cantilever back-side by the inertial motors (SLC Smaract).…”

“…Users are encouraged to contact the Surface Science Laboratory staff to organize training periods and discuss the experiment and opportunities for collaborations. Depending on the users' scientific needs, two additional AFMs for beamlines might be employed: one for grazing-incidence experiments with larger scanning area (Costa et al, 2014) and one to couple fast AFM with X-ray techniques in normalincidence configuration (in commissioning).…”

Liquid–Liquid Interfacial Imaging Using Atomic Force Microscopy

“…Third, the softness of the liquid/liquid interface is another challenge over and above that of other interfaces usually investigated by AFM. Such an investigation typically requires the use of soft cantilevers as is often the case when studying living cells or soft materials both for AFM static and dynamic modes under bulk liquid at solid supports. Most importantly, liquids cannot support shear forces and consequently the interface has a time response in the vertical direction once it is displaced.…”

Synchronous, Crosstalk-free Correlative AFM and Confocal Microscopies/Spectroscopies

“…The same applies to the overall attractive force in the case of qp-BioAC. Those forces are not negligible and should be taken into account when measuring by AFM particularly soft interfaces such as living cells plasma membrane 42 or when unfolding single molecules 43 .…”