The feasibility of protein-mediated doping of zinc oxide with nanogold (ZnO nano-Au) particles for sensing and optical security applications has recently been explored. Published in the journal ACS Applied Nano Materials, researchers present a novel technique for preparing ZnO-nanogold composites using a chimeric protein.
Study: ZnO Nanogold Doping: A Bioinorganic Paradigm for Sensing and Optical Security Applications. Image Credit: Sergey Nivens/Shutterstock.com
This method for synthesizing ZnO-nano-Au composites offers the chimeric protein's primary sequence flexibility, which is desired in sensor technologies and security applications.
Applications and Limitations of ZnO-Gold Nano Composites
In the last two decades, zinc oxide-gold nanocomposites have gained a great deal of interest as a way to produce more efficient photoelectric and enhanced catalytic devices. These composites are made up of ZnO nano-and micro-assemblies, as well as gold (Au) nanostructures, all of which have different electrical and optical characteristics.
Zinc oxide is an n-type semiconductor with a large bandgap that exhibits a significant charge carrier binding affinity and prominent energy bands in the UV and visible regions. By altering the layer formation or synthesis processes and by infusing the composites with dopants, ZnO's optical and electrical qualities may be modified to meet the requirements of a particular product, such as light-emitting diodes (LEDs).
Although Zinc oxide is a potential candidate for various applications such as solar coatings, LEDs, and sensors, its electrical and optical uses are hampered by the material's high UV bandgap. However, by designing ZnO with dopants, these limitations may be addressed.
It is understood that nanoscale metallic materials, like gold, can generate a localized surface plasmon oscillation, which leads to optical absorption in the visual spectrum when exposed to visible light.
The morphology of the layer and the size of the nanoparticles, as well as the surrounding medium, have a significant impact on the site of the absorption.
Flexible Protein-Meditated Doping: a Novel Technique
Previous methods for fabricating ZnO-Au nanocomposites have included coating nanogold on ZnO surfaces, irradiation, heat-assisted chemical processing, photocatalytic metal deposition, and incorporating natural thiol linkers.
To formulate gold-coated ZnO nanocomposites, the latter technique makes use of pre-synthesized ZnO and Au compounds that are joined using an organic thiol linker and then dried. However, all of these methods are either expensive or extremely complex.
In this study, a protein linker was substituted for the naturally occurring thiol linker, allowing the researchers to use a unique peptide-mediated one-pot technique to manufacture ZnO-Au nanomaterials where the Au nanocrystals are incorporated inside the ZnO substrate.
The protein linker is a unique hybrid sequence constructed to have particular ZnO-and Au-binding capability by combining a ZnO binder with a well-known Au binder known as A3. Using a protein linker rather than an organic thiol linker allows for more flexibility and other desired features in the nanocomposites, which are beneficial in advanced sensing applications such as biosensors and medical imaging.
For both the nano Au and ZnO composites, a one-pot process was used to fabricate the materials, enabling the peptide to mediate the formations more easily. The reaction solution was first cultured at 20 degrees Celsius for 24 hours before being warmed to 68 degrees Celsius for another 48 hours. Following incubation, the residue was removed from the reaction media by centrifugation, resulting in the formation of ZnO-Au nanocomposites.
It was discovered that there were short gold intrusions implanted inside the ZnO-Au complex, with tips of varying radii. The observed features are due to gold nanoparticles aggregating and fusing to generate thermodynamically favorable features.
The optical absorptions of the produced particles exhibit the classic ZnO edge characteristic of the conduction band, with a minor widening of ZnO spectrum characteristics in ZnO-ZA2-Au owing to the inclusion of nano-Au specks. Furthermore, the ZnO nanogold composites' spectrum exhibited a spectral signature linked to the presence of the Au plasmon resonance in the ZnO-ZA2-Au matter, which was investigated using both Mie and FDTD techniques.
Significance of Protein-Meditated Doping Technique in Sensing Applications
The researchers present a novel method for preparing ZnO-Au nanocomposites using flexible peptide linkers in this study. This approach can be used to develop ZnO composites with a dense population of ingrained gold nanoparticles that influence the electronic and optical properties of the ZnO, making it suitable for advanced sensing applications.
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Oliver, D. J. et al. (2021) ZnO Nanogold Doping: A Bioinorganic Paradigm for Sensing and Optical Security Applications. ACS Applied Nano Materials. Available at: https://pubs.acs.org/doi/abs/10.1021/acsanm.1c03805