Research

Research Interests

My research interest involve biomineralization and interfacial phenomena. Nature is replete with examples of biominerals formed by the living organisms with complex architectures and advanced functionalities. Microbes and plants can also synthesize a wide variety of new nanomaterials, and are able to incorporate elements not commonly found in living organisms. My ongoing work involves understanding the role of biomineralization proteins in nucleation, growth, evolution and functional properties of resulting biominerals, within multidisciplinary research framework. Some examples include:

Biomineralization

1) Protein-mediated nucleation of inorganic materials. Biomineral crystal formation, evolution, and maturation
2) Metallization of DNA origami
3) Interfacial phenomena 

I am involved in development of advanced analytical techniques for characterization of biomineral formation and growth. These include  electron microscopy in liquid phase, correlative technique for characterization of organic-inorganic interfaces using combination of high-resolution electron microscopy and atom probe tomography (in collaboration with the group of Prof. Alberto Perez-Huerta at University of Alabama, Tuscaloosa), and visualization of electrostatic potentials and electromagnetic fields in the natural environment of the growing biomineral (in collaboration with Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich).

Current Research Projects

1) Liquid phase electron microscopy imaging of magnetotactic bacteria

The microorganisms are stained with mixture of fluorescent dyes and exposed to elelctron beam.
Fluorescent microscopy, after e-beam exposure, points to viable bacterial cells. 

 

Microscopy aided in many important discoveries in life sciences. Now, using the latest developments in the field of liquid phase electron microscopy, it is possible to image fully hydrated cells of various biological specimens in their natural liquid environment with nanometer resolution.  Magnetotactic bacteria biomineralize ordered chains of uniform magnetite or greigite nanocrystals, exhibiting nearly perfect crystal structures and consistent species-specific morphologies. This microorgamism can serve as a model system for the study of molecular mechanisms of magnetite biomineralization. 

Bacterial magnetite biomineralization is a complex process involving a number of simultaneously occurring different steps. There are many steps involved in magnetosome magnetite formation, and because of this complexity we need to to use a number of different characterization techniques. Instead of working with fixed or cryo-plunged samples, we image Magnetospirillum magneticum strain AMB-1 in its natural liquid environment with a continuous flow fluid cell specimen holder, by using a high angle annular dark field (HAADF) detector. 

 

2) Mapping of electrostatic potentials and magnetic fields in liquid phase using electron holography

(in collaboration with Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich).

It is important to know how individual nanoparticles interact with each in liquid phase. Off-axis electron holography, a transmission electron microscopy technique, was used to measure the magnetic induction of bacterial magnetite nanocrystals in a liquid environment. The liquid layer presents plenty of challenges. We are working to expand this technique to mapping of electrostatic potentials in liquid phase and for studying a variety of interfacial phenomena in liquids, with nanometer spatial resolution.

In the news: https://phys.org/news/2017-12-team-magnetic-fields-bacterial-cells.html

 

3) Liquid phase EM imaging of colloidal, soft, and biological materials

The findings obtaining with using magnetotactic bacteria as model system lend themselves naturally to the investigation of many real-world samples. Our current in situ liquid phase electron microscopy effort is focused on imaging of a variety of  biological, soft, and colloidal materials. The systems of interest span from characterization of colloidal suspensions and gel-based nanocomposites, to probing the interactions of living cells with engineered nanomaterials and monitoring biomass degradation.

Colloidal systems: 

Alumina nanoparticles are often used as model system. In aqueous solutions, these nanoparticles aggregate to form hydrated clusters with varying aspect ratio that are significantly larger than the primary particle. Such clusters with the surrounding hydration cloud increase the effective solids content of the suspensions and effectively decrease the available free liquid carrier, resulting in exceptionally high suspension viscosity. 

Gel-based nanocomposites:

 Structural characterization of aqueous polymeric gels is usually addressed by using Small Angle Scattering techniques, as the very nature of these sample limits direct imaging of the polymeric assembly to bright field cryo-TEM of thin sections of either freeze-dried or vitrified samples. We use fluid cell S/TEM to image nanoparticles as small as ~6 nm in thick polymeric gel-based nanocomposites. While every gel is different, our HAADF-STEM approach to nanoparticle imaging is robust.

DNA origami:  

DNA origami triangle
Top, Left: DNA origami triangles imaged with electron microscopy; Right: Fine structural details are revealed by high-resolution imaging.
Bottom, Left: Class-average image from a subset of images above; Right: histogram identifying nine helices along the side of the triangle.

For many practical uses, DNA origami nanostructures need to be metallized, yet the very nature of DNA-templated nanoparticle nucleation remains elusive. Our current work with DNA origami is focused on elucidating of mechanism of metallization. But first, we must visualize the DNA origami nanostructures themselves. We use advanced electron microscopy to probe the structure and spatio-chemical properties of DNA origami. 

 

In the news:https://phys.org/news/2019-09-microscopy-imaging-reveals-dna-origami.html

https://www.nanowerk.com/nanotechnology-news2/newsid=53515.php