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Soft and Hybrid Microscopy

(Supported by NSF-ECS, NSF-INT, DARPA, Baxter, SRC, CMRC, NMH)research4

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Soft materials, including biological structures, polymers and hybrid materials with soft and hard components, are used in a range of applications from medicine to electronics to optics. The characterization of soft and hybrid materials is essential for the understanding of the form-function relationship and must span length scales. Effectively characterizing these materials requires contrast enhancement because of the low atomic number of soft components as well as dose-reduction to avoid damaging beam-sensitive samples. Our work focuses on the synthesis of polymers and a variety of hybrid materials through DNA-mediated assembly as well as improvements in sample preparation and imaging methodologies.

Contrast enhancement for biological material is traditionally obtained through heavy metal staining, and we augment this sample preparation through imaging at lower voltage than in traditional transmission electron microscopy (TEM) in order to increase electron-sample interactions. We are able to image protein assemblies using a scanning electron microscope with transmission detection at voltages lower than 5 kV; in addition to improving contrast, this significantly increases the throughput for sample screening when compared with conventional TEM. We also implement targeted heavy metal staining with 3-dimensional electron tomography to observe the structure of chromatin in cell nuclei.

We analyze soft and hybrid polymeric materials using analytical electron microscopy techniques such as energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS). These spectroscopy techniques allow for spatial location of elements in the sample, tracking of changes in elemental bonding, and an analysis of sample damage under the beam. Through EELS, EDS, and standard imaging, we can better understand the polymer structure and the nature of the interface between hard and soft materials.  Previous work has analyzed polymeric bicontinuous nanospheres (BCNs) with EELS to track beam damage. BCNs loaded with iron nanoparticles were analyzed with EDS to uncover details of the hard-soft interface. When coupled with other characterization techniques, spectroscopy in a scanning transmission electron microscope is a powerful method to analyze the morphology of self-assembled polymer structures.

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Representative Publications:

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