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 Topics:


 a. Bio-Molecular Motility – where Physics meets Biotech

b. Modifying the
Graphene Surface by Local Electron Irradiation
 
 c. Low Temperature
Scanning Tunneling Microscopy of Single Molecule Magnets


 
 Earlier Research

 

 

Research

a.       Bio-Molecular Motility – where Physics meets Biotech

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Physicists have a long history of making substantial contributions to our understanding of life. One of the first prominent examples is Erwin Schrödinger, who used general entropic arguments to show the necessity of macromolecular coding of life.[i] This seminal insight had a profound impact on the search for (and subsequent discovery of) DNA. More recently, the availability of powerful techniques, which physicists and engineers have developed for the “hard sciences”, has led to a distinct change in the research patterns in the life sciences: it enables controlled in-vitro experiments are now possible in place of in-vivo experiments. This seemingly benign step should not be underestimated. The descriptive nature of the early life sciences can be attributed to the overwhelming complexity of the in-vivo systems being studied, which often prevented sufficiently controlled experiments. With more controlled experiments causality can often better be established, which has introduced a more predictive approach to the life sciences. The study of interactions between and self-assembly of bio-molecular systems is one such area. Insights from surface science, coupled with experimental designs arising from nanotechnology now enable rather sophisticated in-vitro experiments. It is this general area that our studies on bio-molecular motility exploit. Specifically, we artificially fabricate the motor protein kinesin and the microtubular tracks on which these kinesin motors travel as well as lithographic electrodes to electrophoretially attract them to surfaces.[ii],[iii] Because we can control the specific properties of the constituents and the surface interactions on an artificial chip we can precisely analyze the resulting kinetic processes and determine causalities in the behavior. As a result, we could determine some of the underlying parameters and fabricate transport systems for a wide range of physical materials, ranging from quantum dots to carbon nanotubes.[iv],[v],[vi],[vii],[viii],[ix]

 

Bio-motility systems, comprising of microtubules (MTs) and kinesin, can provide molecular insight into neuronal transport and communication, with significant potential to understand diseases of societal impact. We have developed lab-on-a-chip based assays to mimic protein-protein interactions and to model motor protein movement, relevant to cellular mechanics. Changes of the biochemical nature of the microenvironment can alter the interaction of the sensory motif of the protein in cellular transport. Altering the environment with an inhibitor of protein dynamics at the mesoscopic scale (as shown in our rendering on the right),[x],[xi],[xii] we have investigated the co-relation of engineered proteins by using time lapse fluorescence microscopy and the mathematical modeling of particle dynamics.[xiii] In order to better understand the biomedical relevance of these in-vitro results, the relation to cellular systems needs to be investigated.

 

b.       Modifying the Graphene Surface by Local Electron Irradiation

Graphene is one of the most interesting materials for both fundamental and applied studies. Arising from the deceptively simple hexagonal organization of carbon in a monatomic sheet, the unusual electronic as well as mechanical properties are of interest. Our research is focused at our ability to locally alter the properties of graphene by inducing damage sites through electron beam patterning thus encoding lateral functional structure directly in the graphene sheet. We can do this by using the computer controlled electron beam in a nanopatterning system to locally functionalize the electronic properties which then can be measured through a 4-wire electronic measurement. As a result of the electron irradiation we have measured changes of the electronic properties, consistent with altered adsorption behavior on the graphene surface. [xiv],[xv]

 

c.       Low Temperature Scanning Tunneling Microscopy of Single Molecule Magnets

Single molecule magnets (SMMs) are macromolecular complexes composed of a magnetic core stabilized by organic ligands. The magnetic core of a typical SMM contains a number of magnetic centers which behave more or less independently at high temperature. As the temperature is lowered, the magnetic system enters a correlated state, i.e. the independence of the magnetic centers ceases as the entire molecule is governed by a correlated magnetic system. The ground state of this system is bi-stable with a substantial energy barrier preventing thermally activated transitions. As a result, the molecules can be prepared in a low temperature state which allows transitions only in a resonance tunneling event, called macroscopic quantum tunneling. This phenomenon accounts for a large part of the fundamental interest in this class of magnetic systems. In addition, substantial applied potential arises from these molecules facilitating quantum computing and data storage at the single molecule level. The most suitable instrument to study the intramolecular magnetic system at low temperature (T<3K) is a scanning tunneling microscope that allows the in-situ application of a magnetic field in all 3 dimensions (vector magnet). This type of system permits the in-situ alignment of the magnetic field direction with the relevant magnetic axis of the molecule while performing electronic tunneling measurements with sub-molecular resolution at low temperature. There are only a handful of instruments in the world that allow the simultaneous application of these conditions (particularly the vector magnet) and thus a suitable single molecule experiment. We have access to one of these instruments at Tohoku University’s AIMR and have performed some of the first experiments in this direction.[xvi] In collaboration with mathematicians, we have developed a general model to predict molecular stability based on graph theory,[xvii],[xviii] a concept which we are currently extending to include magnetic moments.



[i] Erwin Schrödinger, “What is life?”, Cambridge University Press (1992).

[ii] J. A. Noel, W. Teizer, and W. Hwang, ACS Nano 3, 1938 (2009).

[iii] J. Noel, W. Teizer, and W. Hwang, Journal of Visualized Experiments 30 (2009).

[iv] A. Sikora, J. Ramon, K. Kim, K. Reaves, H. Nakazawa, M. Umetsu, I. Kumagai, T. Adschiri, H. Shiku, T. Matsue, W. Hwang and W. Teizer. Nano Letters 14, 876-881 (2014).

[v] K. Kim, A. L. Liao, A. Sikora, D. Oliveira, H. Nakazawa, M. Umetsu, I. Kumagai, T. Adschiri, W. Hwang and W. Teizer. Biomedical Microdevices 16, 501-508 (2014).

[vi] K. Kim, A. Sikora, K. S. Nakayama, H. Nakazawa, M. Umetsu, W. Hwang and W. Teizer. Applied Physics Letters 105, 143701-1–143701-5 (2014).

[vii] K. Kim, A. Sikora, K. S. Nakayama, M. Umetsu, W. Hwang and W. Teizer. Journal of Applied Physics 117, 144701-1–144701-10 (2015).

[viii] A. Sikora, J. Ramón-Azcón, M. Sen, K. Kim, H. Nakazawa, M. Umetsu, I. Kumagai, H. Shiku, T. Matsue and W. Teizer. Biomedical Microdevices 17, 78:1-6 (2015).

[ix] A. Sikora, F. F. Canova, K. Kim, H. Nakazawa, M. Umetsu, I. Kumagai, T. Adschiri, W. Hwang, W. Teizer. ACS Nano 9, 11003-11013 (2015).

[x] S. Bhattacharyya, K. Kim, and W. Teizer. Advanced Biosystems 1, 1600034 (2017).

[xi] S. Bhattacharyya, K. Kim, H. Nakazawa, M. Umetsu, and W. Teizer. Integrative Biology 8, 1296-1300 (2016).

[xii] S. Bhattacharyya, K. Kim, and W. Teizer. Advanced Biosystems 1, 1700108 (2017).

[xiii] K. Kim, A. Sikora, K. S. Nakayama, H. Nakazawa, M. Umetsu, W. Hwang and W. Teizer. Physical Biology 13, 056002 (2016).

[xiv] S. O. Woo and W. Teizer. Applied Physics Letters 103, 041603 (2013).

[xv] S. O. Woo and W. Teizer. Carbon 93, 693-701 (2015).

[xvi] K. Reaves, K. Kim, K. Iwaya, T. Hitosugi, Helmut G. Katzgraber, H. Zhao, K. R. Dunbar, W. Teizer, SPIN 03, 1350004 (2013).

[xvii] D. M. Packwood, K. T. Reaves, F. L. Federici, H. G. Katzgraber and W. Teizer. Proceedings of the Royal Society A 469, 20130373 (2013).

[xviii] D. M. Packwood, H. G. Katzgraber, W. Teizer. Proceedings of the Royal Society A 472, 20150699:1-19 (2016).

 

 

 

© Copyright 2018 Winfried Teizer