The New Challenges of Chemical and Biological Sensing

Issued as final repor

Design of advanced sensing materials

Issued as final reportNational Science Foundation (U.S.

Chemical Electronics

Jiri Janata, Professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology, presented a lecture at the Nano@Tech Meeting on January 13, 2009 at 12 noon in room 102 of the Microelectronics Research Center.Runtime: 55:07 minutesIntegration of chemical recognition elements with solid state electronic devices has been subject of intense interest for over three decades, with some notable achievements achieved in electroanalytical chemistry. Initially, the “chemistry” has been added to more or less conventional silicon electronics with advantages in miniaturization, noise reduction and promise of multivariate analysis. That was the era of chemically sensitive field-effect transistors (CHEMFET), i.e. ion-sensitive field-effect transistors and enzymatic field-effect transistors. In the second phase, it has been recognized that modulation of electronic properties of organic semiconductors leads to creation of solid state work function sensors for gases, again based on the traditional silicon platform. Development of organic electronics took place almost in parallel. In that case silicon, as the functional material, has been replaced with organic semiconductors. The motivation for this development has been the promise of flexible and inexpensive electronics. What has not been recognized is that the physics of operation of so-called organic field-effect transistors (OFET) is fundamentally different from the physics of their silicon-based counterparts. In the last decade the chemically responsive OFETs have been added to the toolbox of electroanalytical chemistry. All chemically sensitive silicon based field-effect transistors are high input impedance potentiometric sensors. In such case the transistor current passes only through silicon, which is protected from the environment by nearly ideal passivation with silicon dioxide/silicon nitride. The corollary of this fact is that WF of silicon does not change and the WF-FET sensors do not require separate reference electrode. On the other hand in OFETs the transistor current passes through the organic semiconductor, which is subject to modulation by the operating environment. The chemical response to gases and vapors then originates at multiple points in the device. The contacts, the bulk of the organic semiconductor and all the interfaces can be involved making the interpretation of the response very difficult. Because of this fact OFETs are chemiresistors and can be classified as conductimetric chemical sensors

A.T.F. Investigation of Doping

Jiri Janta presented a lecture at the Nano@Tech Meeting on November 29, 2011 at 12 noon in room 1116 of the Marcus Nanotechnology Building.Professor Jiri Janata is Georgia Research Alliance Eminent Scholar in the School of Chemistry and Biochemistry at Georgia Tech. Between 1991 and 1997 he was an Associate Director of the Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, in Richland, Washington. Prior to that appointment he was Professor of Materials Science and Professor of Bioengineering at the University of Utah for 17 years. Professor Janata was born in Czechoslovakia where he received his Ph.D. degree in analytical chemistry from the Charles University (Prague) in 1965. His current interests include interfacial chemistry, chemical sensors and electroanalytical chemistry with particular emphasis on development of chemical sensors for environmental and security applications.Runtime: 49:43 minutesIn organic electronics doping can be a sin or a virtue. Two kinds of doping, primary and secondary, will be shown and the implications on function and operation of solid state devices containing organic semiconductors will be discussed

Conducting polymers in electronic chemical sensors

Chemical sensors for gases are at the forefront of the information acquisition chain about the environment in which we live. The quality of the air we breathe is one of the most important concerns of a modern society. A large number of gas sensors use conducting polymers (CPs) because they offer great design flexibility 1,2. They can form selective layers in which the interaction between the analyte gas and the conducting matrix generates the primary change of a physical parameter in the transduction mechanism. On the other hand, their performance in devices that form circuit elements such as transistors has been less than ideal 3,4.The abundant literature dealing with various applications of CPs can be divided into two groups: CPs in electronic 5, optoelectronic 6 and electromechanica

Evolution-guided adaptation of an adenylation domain substrate specificity to an unusual amino acid.

Adenylation domains CcbC and LmbC control the specific incorporation of amino acid precursors in the biosynthesis of lincosamide antibiotics celesticetin and lincomycin. Both proteins originate from a common L-proline-specific ancestor, but LmbC was evolutionary adapted to use an unusual substrate, (2S,4R)-4-propyl-proline (PPL). Using site-directed mutagenesis of the LmbC substrate binding pocket and an ATP-[32P]PPi exchange assay, three residues, G308, A207 and L246, were identified as crucial for the PPL activation, presumably forming together a channel of a proper size, shape and hydrophobicity to accommodate the propyl side chain of PPL. Subsequently, we experimentally simulated the molecular evolution leading from L-proline-specific substrate binding pocket to the PPL-specific LmbC. The mere change of three amino acid residues in originally strictly L-proline-specific CcbC switched its substrate specificity to prefer PPL and even synthetic alkyl-L-proline derivatives with prolonged side chain. This is the first time that such a comparative study provided an evidence of the evolutionary relevant adaptation of the adenylation domain substrate binding pocket to a new sterically different substrate by a few point mutations. The herein experimentally simulated rearrangement of the substrate binding pocket seems to be the general principle of the de novo genesis of adenylation domains' unusual substrate specificities. However, to keep the overall natural catalytic efficiency of the enzyme, a more comprehensive rearrangement of the whole protein would probably be employed within natural evolution process