Modulating Semiconductor Surface Electronic Properties by Inorganic Peptide–Binders Sequence Design

The use of proteins and peptides as part of biosensors and electronic devices has been the focus of intense research in recent years. However, despite the fact that the interface between the bioorganic molecules and the inorganic matter plays a significant role in determining the properties of such devices, information on the electronic properties of such interfaces is sparse. In this work, we demonstrate that the identity and position of single amino acid in short inorganic binding protein-segments can significantly modulate the electronic properties of semiconductor surfaces on which they are bound. Specifically, we show that the introduction of tyrosine or tryptophan, both possessing an aromatic side chain which higher occupied molecular orbitals are positioned in proximity to the edge of GaAs valence band, to the sequence of a peptide that binds to GaAs (100) results in changes of both the electron affinity and surface potential of the semiconductor. These effects were found to be more pronounced than the effects induced by the same amino acids once bound on the surface in a head-tail configuration. Furthermore, the relative magnitude of each effect was found to depend on the position of the modification in the sequence. This sequence dependent behavior is induced both indirectly by changes in the peptide surface coverage, and directly, probably, due to changes in the orientation and proximity of the tyrosine/tryptophan side group with respect to the surface due to the preferred conformation the peptide adopts on the surface. These studies reveal that despite the use of short protein oligomers and aiming at a non-natural-electronic task, the well-known relations between the proteins' structure and function is preserved. Combining the ability to tune the electronic properties at the interface with the ability to direct the growth of inorganic materials makes peptides promising building blocks for the construction of novel hybrid electronic devices and biosensors.