The helium ion microscope (HIM) probes light elements (e.g. C, N, O, P) with high
contrast due to the large variation in secondary electron yield, which minimizes the
necessity of specimen staining. A defining characteristic of HIM is its remarkable
capability to neutralize charge by the implementation of an electron flood gun, which
eliminates the need for coating non-conductive specimens for imaging at high
resolution. In addition, the small convergence angle in HeIM offers a large depth of field
(~5× FE-SEM), enabling tall structures to be viewed in focus within a single image.
Taking advantage of these capabilities, we investigate the interactions of engineered
nanoparticles (NPs) at the surface of alveolar type II epithelial cells grown at the airliquid
interface (ALI). The increasing use of nanomaterials in a wide range of
commercial applications has the potential to increase human exposure to these
materials, but the impact of such exposure on human health is still unclear. One of the
main routs of exposure is the respiratory tract, where alveolar epithelial cells present a
vulnerable target at the interface with ambient air. Since the cellular interactions of NPs
govern the cellular response and ultimately determine the impact on human health, our
studies will help delineating relationships between particle properties and cellular
interactions and response to better evaluate NP toxicity or biocompatibility.
The Rutherford backscattered ion (RBI) is a helium ions imaging mode, which
backscatters helium ions from every element except hydrogen, with a backscatter yield
that depends on the atomic number of the target. Energy-sensitive backscatter analysis
is being developed, which when combined with RBI image information, supports
elemental identification at helium ion nanometer resolution. This capability will enable
distinguishing NPs from cell surface structures with nanometer resolution.