ZnO Nanogold Doping: A Bioinorganic Paradigm for Sensing and Optical Security Applications

Protein-mediated doping of ZnO with plasmonic nanoparticles offers control over surfaces, electronic states, carrier dynamics, and spectral fingerprints. Here, we report on ZnO-nano-Au bioinorganic heterostructures prepared using a chimeric polypeptide that combines most of the ZnO-binding sequence GLHVMHKVAPPR and the gold-binding AYSSGAPPMPPF sequence. The one-pot peptide-mediated synthesis was performed in the presence and absence of HAuCl4 to determine the impact of the peptide and metallic component on the structural and electronic properties of the ZnO assembly. Electron microscopy confirms that the chimera polypeptide promotes the synthesis of both spherical and nonspherical gold nanoparticles, which are properly embedded in ZnO. The optical absorption spectra describe a complex palette of plasmon modes, while the luminescence spectra show a dominant subset of near-infrared spectral fingerprints that suggest an increasing role of surfaces in carrier relaxation. Simulations using finite difference time-domain theory describe collective plasmon phenomena specific to gold nanoparticles embedded in ZnO. Furthermore, to confirm experimental data, theory suggests an interinclusion nanogold spacing of 10 nm or less. Flexibility of the primary sequence of the chimera in the synthesis of ZnO-nano-Au composites opens up possibilities for plasmon-modulated ZnO junctions with Ohmic contacts as sought in sensor technologies and for security applications.