Self-assembled bifunctional surface mimics an enzymatic and templating protein for the synthesis of a metal oxide semiconductor

doi:10.1073/pnas.0508488103

Self-assembled bifunctional surface mimics an enzymatic and templating protein for the synthesis of a metal oxide semiconductor

*Institute for Collaborative Biotechnologies,
^†Materials Research Laboratory and California NanoSystems Institute, and
^§Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106-9610

Edited by John A. Carbon, University of California, Santa Barbara, CA, and approved February 14, 2006 (received for review September 28, 2005)

Abstract

The recent discovery and characterization of silicatein, a mineral-synthesizing enzyme that assembles to form the filamentous organic core of the glassy skeletal elements (spicules) of a marine sponge, has led to the development of new low-temperature synthetic routes to metastable semiconducting metal oxides. These protein filaments were shown in vitro to catalyze the hydrolysis and structurally direct the polycondensation of metal oxides at neutral pH and low temperature. Based on the confirmation of the catalytic mechanism and the essential participation of specific serine and histidine residues (presenting a nucleophilic hydroxyl and a nucleophilicity-enhancing hydrogen-bonding imidazole nitrogen) in silicatein’s catalytic active site, we therefore sought to develop a synthetic mimic that provides both catalysis and the surface determinants necessary to template and structurally direct heterogeneous nucleation through condensation. Using lithographically patterned poly(dimethylsiloxane) stamps, bifunctional self-assembled monolayer surfaces containing the essential catalytic and templating elements were fabricated by using alkane thiols microcontact-printed on gold substrates. The interface between chemically distinct self-assembled monolayer domains provided the necessary juxtaposition of nucleophilic (hydroxyl) and hydrogen-bonding (imidazole) agents to catalyze the hydrolysis of a gallium oxide precursor and template the condensed product to form gallium oxohydroxide (GaOOH) and the defect spinel, gamma-gallium oxide (γ-Ga₂O₃). Using this approach, the production of patterned substrates for catalytic synthesis and templating of semiconductors for device applications can be envisioned.

Footnotes

^¶To whom correspondence should be sent at the ∗ address. E-mail: d_morse{at}lifesci.ucsb.edu
↵ ^‡Present address: Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho Koganei, Tokyo 184-8588, Japan.
Author contributions: D.K. and D.E.M. designed research; D.K., Q.T., Y.A., and J.C.W. performed research; D.K. and D.E.M. analyzed data; and D.K. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations:

GaOOH,

gallium oxohydroxide;

γ-Ga2O3,

gamma-gallium oxide;

HB,

hydrogen-bonding;

NP,

nucleophilic;

SAM,

self-assembled monolayer;

TEM,

transmission electron microscopy.