Morphology visualization of irregular shape bacteria by electron holography and tomography

Abstract

In the current work, irregular morphology of Staphylococcus aureus bacteria has been visualized by phase retrieval employing off-axis electron holography (EH) and 3D reconstruction electron tomography using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Bacteria interacting with gold nanoparticles (AuNP) acquired a shrunken or irregular shape due to air dehydration processing. STEM imaging shows the attachment of AuNP on the surface of cells and suggests an irregular 3D morphology of the specimen. The phase reconstruction demonstrates that off-axis electron holography can reveal with a single hologram the morphology of the specimen and the distribution of the functionalized AuNPs. In addition, EH reduces significantly the acquisition time and the cumulative radiation damage (in three orders of magnitude) over biological samples in comparison with multiple tilted electron expositions intrinsic to electron tomography, as well as the processing time and the reconstruction artifacts that may arise during tomogram reconstruction.

Macro to nano specimen measurements using photons and electrons with digital holographic interferometry: a review

“…The latter gives an extraordinary opportunity to study a wide variety of physical parameters in-on and around the specimen. Next, a couple of examples are given that involve the shape quantification of gold (Au) nano particles [85] and the 3D visualization of a bacteria [86].…”

“…To gain a better understanding of the location and effects of Ab-functionalized Au nano particles on S. aureus off-axis electron holographic interferometry (EHI) was used to determine the 3D sample structure and the location of particles attached on cell walls. The three dimensional reconstruction can be achieved by acquiring several holograms from different observation or electron illumination positions [86]. A set of holograms were acquired by tilting the sample from − 30°to + 30°in steps of 15°as shown in Fig.…”

“…In that paper the authors did not measure the exact position of this nano particle. Reprint from [86]. displacement and imaging a characteristic unwrapped phase maps, one might associate it with the biomechanical condition or inside changes.…”

“…Fig.34a set of electron holograms at different tilting angles, b reconstructed phases and c unwrapped phases taken using a biprism voltage of 20 V. The red circles show the location of a single Au nano particle that can be observed with the naked eye. The original images can be seen in the results presented in reference[86]. In that paper the authors did not measure the exact position of this nano particle.…”

“…In that paper the authors did not measure the exact position of this nano particle. Reprint from[86].Copyright[2017], WILEY…”