Helium Ion Microscopy

Biological and environmental research often requires high-resolution inspection of surface details, such as soil organic matter (SOM)-mineral interactions, ice nucleation in aerosols, and microbial communities in soils. Obtaining true surface details from these materials has historically been challenging, though, since the samples often consist of low atomic number materials.

The newly developed Helium Ion Microscope, or HIM, improves on older techniques that researchers used to image materials. HIM is similar to a scanning electron microscope (SEM), except it uses helium ions, instead of electrons, as a probing beam. There are unique advantages to using helium ions over electrons, including smaller and focused probe size, beam/sample interactions, and sample charge control. In particular, the instrument’s high-resolution (0.35 nm) and outstanding depth of field (microns) for imaging uncoated organic and biological material makes it especially suitable for biological and environmental research.

Current applications of HIM include

• Ultra-high-resolution imaging of bio samples
• Analysis of soot samples
• Study of plant anatomy
• Aerosol analysis
• Bio mineralization studies
• Mineral weathering studies.

Research applications

Supporting the Biogeochemical Transformations Integrated Research Platform, researchers can use HIM for

• High-resolution imaging of organic matter: High-resolution images of inorganic and organic surfaces in nano scales (few-nm resolution) can be obtained using HIM. It is well suited for imaging low Z materials, because the damage caused by the helium beam at the surface is much smaller compared to electron beams. We use HIM to image environmental samples, sub-cellular structures, minerals, and atmospheric aerosols. Special organic features that are difficult to measure with other techniques can be obtained using HIM. Organic and inorganic aerosols can be imaged with a nm resolution. And because of high resolution, we have the unprecedented ability to map specific microenvironments surrounding (and their interactions) microbial cells.
• Pore architecture: Nanometer-to-micrometer-scale pore systems have been found in the organic matter and matrix of inorganic grains of shale reservoirs and soils, which have significant influence on gas storage and fluid transportation. Scientists have identified a variety of pore types in reservoir rocks, such as pores associated with organic matter (organic pores), interparticle mineral pores, intraparticle mineral pores (inorganic pores), and microfractures. HIM provides the necessary information (pore structure distribution/pore network) about pores in nanometer scales (< 10 nm). 
• Mineral weathering studies: There is limited understanding of fundamental biogeochemical mechanisms that transform microbe-mineral interfaces at submicron scales, particularly in complex field systems. The HIM can analyze micro-organism- (fungal, bacteria) driven mineral weathering, as well as others such as biomechanical weathering, secondary mineral precipitation, biofilm formation, and grain coatings.

Supporting the Structural Biology Integrated Research Platform, researchers can use HIM for

• Ultra-high-resolution imaging of bio samples: For biological tissues and cells, the major advantage of HIM compared to other techniques (like SEM) is the large depth of field, combined with the ability to avoid sample charging by using the electron flood gun. Hence, imaging can be done without coating the sample with a conductive metal film that would cover (alter) the fine structures on the cell surface or tissue sections. With sub-nanometer resolution, researchers can gain new insights into the ultrastructure of bacteria, viruses, fungi, single cells, and model plants.
• Cellular interactions: We can image how cellular ultrastructures in microbial systems interact with one another and how organisms respond within a microbial consortium or to environmental stresses.

Supporting the Terrestrial-Atmospheric Processes Integrated Research Platform, researchers can use HIM for

• Analysis of soot samples: The HIM’s high lateral resolution is essential for studying particulate matter in combustion science. It is also used to measure the size and morphology of soot particles with a diameter as small as 2 nm.
• Aerosol analysis: HIM can analyze airborne soil organic particles and ice nucleating particles, and it can study the organic/inorganic interfaces within the particles.
• Bio mineralization studies: HIM can study the bio mineralization process and organic-mineral interfaces.

Supporting the Rhizosphere Function Integrated Research Platform, researchers can use HIM for

• Characterizing rhizosphere and phyllosphere microbiome structure and function, including soil properties and plant-microbe interactions.
• Creating high-resolution images (> nm) of microbial surfaces, interfaces between roots, interaction between microbes and soil, secondary mineral phases and microbial colonies, and bio film formation.

Tips for success

• Mineral and aerosol samples can be analyzed as prepared or as collected states.
• Biological samples typically require critical point drying in order to prepare the samples for imaging. Users can dry the samples and send them to EMSL or the EMSL team can prepare the samples on site.