Immobilization method of yeast cells for intermittent contact mode imaging using the atomic force microscope.

The atomic force microscope (AFM) is widely used for studying the surface morphology and growth of live cells. There are relatively fewer reports on the AFM imaging of yeast cells [1] (Kasas and Ikai, 1995), [2] (Gad and Ikai, 1995). Yeasts have thick and mechanically strong cell walls and are therefore difficult to attach to a solid substrate. In this report, a new immobilization technique for the height mode imaging of living yeast cells in solid media using AFM is presented. The proposed technique allows the cell surface to be almost completely exposed to the environment and studied using AFM. Apart from the new immobilization protocol, for the first time, height mode imaging of live yeast cell surface in intermittent contact mode is presented in this report. Stable and reproducible imaging over a 10-h time span is observed. A significant improvement in operational stability will facilitate the investigation of growth patterns and surface patterns of yeast cells.

Real time reduction of probe-loss using switching gain controller for high speed atomic force microscopy.

In this article, a switching gain proportional-integral-differential controller is used to reduce probe-loss affected regions in an image, obtained during tapping mode operation. Switching signal is derived from the "reliability index" signal, which demarcates regions where the tip has lost contact with the sample (probe-loss), within couple of cantilever oscillation cycles, thereby facilitating use of higher than optimal controller gain without deteriorating on-sample performance. Efficacy of the approach is demonstrated by imaging calibration sample at tip velocity close to 240 microm/s and plasmid DNA at tip velocity of 60 microm/s indicating significant reduction of probe-loss areas and recovery of lost sample features.