Dr. H. J. Lewerenz

H. J. Lewerenz, Ph.D.
Professor of Physics
Technical University
Berlin, Germany

Head Interface
Engineering Group,
Helmholtz Center Berlin
for Materials and Engergy

Enzyme - Semiconductor Interactions: Fundamental Aspects and Routes to Photoactive Devices

Immobilization of enzymes (proteins) on nanostructured surfaces of MoTe₂ and Si is made based on so-called DLVO¹ and non-DLVO interaction forces. Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) experiments at protein-semiconductor systems show well resolved tertiary structures of the reverse transcriptases (RT) of HIV 1 and of the RT of AMV (avian myeloblastosis virus). The data are analyzed using concepts from applied semiconductor physics, such as Fermi level pinning and MIS (metal-insulator-semiconductor) junction electronics. Working hypotheses for the interpretation of STM images are presented that refer to the charge transfer from semiconductor to enzyme and the successive charge transport to the STM tip. The observation of uninhibited conductivity in the constant current STM experiments is attributed to solvation-assisted release of electrons from trap sites that exist along the polypeptide chains. Charge transport is proposed to occur at the circumference of the enzymes where biological water is present. Consequently, conventional modes of charge injection into catalytic centers of enzymes such as hydrogenase or water oxidase of Photosystem I and II with subsequent electron transfer to the active sites appear difficult to realize. Possibilities of radiation-less long-distance excitation energy transfer based on the Förster mechanism, its multichromic extension and on Dexter exciton hopping are considered for catalytically active hybrid inorganic/organic absorber-enzyme systems.

¹ Dejarguin, Landau, Verwey, Overbeek: Theory of the Stability

of Lyophobic Colloids (Elsevier, Amsterdam, 1948).

Joachim Lewerenz is a Professor of Physics at the Institute for Solid State Physics at the Technical University Berlin and is head of the Interface Engineering Group in the Division of Solar Energy of the Helmholtz Center Berlin for materials and Energy (HZB). His research is concerned with wet processing of semiconductors for solar applications, development of novel solar cell concepts, materials characterization with a wide variety of surface analytical methods including synchrotron radiation photoelectron spectroscopy (SRPES) and Brewster angle spectroscopy and, in an international cooperation, the investigation of the semiconductor-protein contact. Wet conditioning of semiconductors is predominantly using electrochemical and photoelectrochemical methods that allow high process control and exceptionally high surface sensitivity in the modification process. Recent accomplishments include the development of a novel nanoemitter Schottky-type solar cell for photovoltaic and photoelectrocatalytic operation (patent applied 2003) with 11.2% efficiency, the observation and interpretation of tertiary structure-resolved scanning tunnelling microscopy images of proteins and the replacement of the toxic cyanide etch step in the processing of CuInS₂ solar cell absorbers by a photoelectrochemical process that has been patented, The group has a yearly (federal and DFG) funding of 790 000 Euro (2003-2008)