Cell viability and probe-cell membrane interactions of XR1 glial cells imaged by atomic force microscopy

As atomic force microscopy (AFM) imaging of live specimens becomes more commonplace, at least two important questions arise: 1) do live specimens remain viable during and after AFM, and 2) is there transfer of membrane components from the cell to the AFM probe during probe-membrane interactions? We imaged live XR1 glial cells in culture by single- or dual-pass contact or tapping-mode AFM, examined cell viability at various postimaging times, and report that AFM-imaged live XR1 cells remained viable up to 48 h postimaging and that cell death rates did not increase. To determine if nonlethal, transient interactions between the AFM probe and cell membrane led to transfer of XR1 cell membrane phospholipid components on the probe, we treated the scanned probes with the lipid-binding fluorophore FM 1-43. Confocal microscopy revealed that phospholipid membrane components did accumulate on the probe, and to a generally greater extent during contact-mode imaging than during tapping-mode imaging. Moreover, membrane accumulations on the probe were greater when live XR1 cells were damaged or perturbed, yet membrane did not accumulate in fluorescently detectable quantities during repeated "force curves" during control experiments. Taken together, our data indicate that although AFM imaging of live cells in culture does not affect long-term cell viability, there are substantial probe-membrane interactions that lead to transfer of membrane components to the probe.