Figure 3.

Principle and results of the robotic fluidic force microscopy (FluidFM BOT) measurements. (a) Workflow of the cell adhesion strength measurement using the FluidFM method. The hollow cantilever is approached to the adhered cell (top frame). Upon contact, vacuum is applied to fix the top of the cell to the cantilever (middle frame). Once a stable connection is established, the cantilever is retracted while its bending is recorded by the reflected laser beam deflection (red arrow). (b) The custom-made biosensor insert holder positioned in the sample holder of FluidFM BOT device. The photograph is made from below showing the objectives of the inverted microscope of the FluidFM BOT, the two circular wells, the sensor surfaces (reflective colored squares in the right well) and the probe on the upper side of the sensor insert. (c) Live view image of the fluidic force microscopy measurement: the picture shows the cantilever (and the purple laser spot on it) with surrounding adhered cells (scale bar: 40 μm). Inset: scanning electron microscopy image of the top of the cantilever. The aperture with an 8 µm diameter can be clearly seen. Scale bar: 8 μm (Image provided by Cytosurge AG). (d) Photograph showing the FluidFM BOT device on an anti-vibration table. The stage is fixed on an inverted microscope with the head unit above the objective. The inserted biosensor plate is seen at the right. (e) A typical force-distance curve of a measured cell and its evaluation. The adhesion energy is given by integrating the area under the curve from the point of contact (blue area). The adhesion force is defined as the maximal value of the force exerted by the cell-surface contact to the cantilever (green circle). (f) Plot showing the correlation between the adhesion force and adhesion energy values of the cells measured in our fluidic force microscopy experiments. While the two values both characterize the strength of the adhesion, they can represent different biological information.