Investigation of the morphology, viability and mechanical properties of yeast cells in environmental SEM

The mechanical properties of biological cells at nanoscale may be characterized using an environmental scanning electron microscopy (ESEM) combined with a force measurement device. However, the electron beam radiation in an ESEM may damage a specimen. So far, little is known about the radiation damage to biological cells. In this work, single yeast cells were imaged using an ESEM under both high and low vacuum modes. The changes in their morphology and viability were monitored as a function of radiation time for a given beam current of 538 pA corresponding to 10 kV accelerating voltage and spot size 4. Under the two modes, the radiation damage to the morphology of yeast cells became evident after an exposure time of 3 min, but under the low vacuum mode, the damage to their morphology was more severe. However, all cells lost their viability after 5 min under the high vacuum mode with the electron beam off from an initial viability of 95+/-1%. In contrast, the viability of cells under the low vacuum mode was found to be approximately 20% after 20 min. In addition, a newly developed ESEM-based nanomanipulation technique was applied to measure the force imposed on single yeast cells and their deformation, including contact diameter and central lateral diameter for the compression of single yeast cells to a given displacement within a time frame of 1 min, and the data obtained may be used to validate mathematical modeling of the stress-strain relationship for the compression of cells in order to determine their intrinsic mechanical property parameters. SCANNING 30: 435-442, 2008. (c) 2008 Wiley Periodicals, Inc.