In addition, mismatches between probes and samples did not correlate with variation in between probe signals (Additional file 1: Table S4).
However, the use of STED on biological samples has been limited by the need for intense irradiation of the sample (>150 mW/μm), the use of scanning probes on soft samples poses challenges for maintaining the distance between probe and the sample, and the use of ZMWs requires the sample to penetrate into a narrow aperture.
The effects of various factors, namely the shape of the probe, the contact between the probe and sample and the modelling method, were also evaluated.
Yet, probing the surface of a soft material in a liquid environment is challenging, since the point of contact between a probe and sample surface during finite-rate indentation can be obscured by viscous squeeze-out effects of temporarily confined liquid.
The basic principle behind these techniques [5] is applying a direct current (DC) bias between the conductive probe and the sample to facilitate the recording of variations in the electrostatic force between the probe and sample.
The primary change between electron probes is not only the probe center position, but we can also vary coherent wave aberrations in the probe such as defocus or spherical aberration, change the probe size by modifying the probe semi-angle radius, and also include relative tilt between the probe and sample by moving the probe center away from (vec {q}= 0,0)).
AFM is based on the detection of forces acting between an AFM probe and sample surface.
Moreover, a comprehensive nonlinear interaction force is assumed between probe's and sample in order to reveal the response of the system more realistically.
Although it is not mandatory, the use of an index-matching medium is often useful to ensure a complete contact between the probe and the sample when the sample surface is rough.
