Photothermal Off-Resonance Tapping for Rapid and Gentle Atomic Force Imaging of Live Cells

Imaging living cells by atomic force microscopy (AFM) promises not only high-resolution topographical data, but additionally, mechanical contrast, both of which are not obtainable with other microscopy techniques. Such imaging is however challenging, as cells need to be measured with low interaction forces to prevent either deformation or detachment from the surface. Off-resonance modes which periodically probe the surface have been shown to be advantageous, as they provide excellent force control combined with large amplitudes, which help reduce lateral force interactions. However, the low actuation frequency in traditional off-resonance techniques limits the imaging speed significantly. Using photothermal actuation, we probe the surface by directly actuating the cantilever. Due to the much smaller mass that needs to be actuated, the achievable measurement frequency is increased by two orders of magnitude. Additionally, photothermal off-resonance tapping (PORT) retains the precise force control of conventional off-resonance modes and is therefore well suited to gentle imaging. Here, we show how photothermal off-resonance tapping can be used to study live cells by AFM. As an example of imaging mammalian cells, the initial attachment, as well as long-term detachment, of human thrombocytes is presented. The membrane disrupting effect of the antimicrobial peptide CM-15 is shown on the cell wall of Escherichia coli. Finally, the dissolution of the cell wall of Bacillus subtilis by lysozyme is shown. Taken together, these evolutionarily disparate forms of life exemplify the usefulness of PORT for live cell imaging in a multitude of biological disciplines

Influence of an interfacial AlxIn1-xSb layer on the strain relaxation and surface morphology of thin GaSb layers epitaxially grown on GaAs(001)

This work focuses on the strain relaxation and surface morphology of 10 ML thick GaSb layers on GaAs. It is shown that full relaxation is never reached for this thickness. The use of an AlSb interfacial layer only slightly improves strain relaxation but greatly reduces surface roughness. Finally, first results are reported using an AlxIn1-xSb interfacial layer which allows reaching 100% relaxation. However, this implies to lower the growth temperature around 450C in order to avoid excessive surface roughning. Further reduction of the growth temperature leads to the development of a strong relaxation anisotropy