(a) Peptide-based nanotubes aligned across interdigitated electrodes under the influence of an external voltage. (b) Scanning electron microscope images of the aligned peptide-based nanotubes. (c) The bending stage used to flex the substrate. The substrates were flexed such that the aligned peptide-based nanotubes were bent as indicated in the inset, where the region of highest stress is indicated in red. Image: Sawsan Almohammed.Nanogenerators capable of converting mechanical energy into electricity are typically made from metal oxides and lead-based perovskites. But these inorganic materials aren't biocompatible, so the race is on to create natural biocompatible piezoelectric materials for energy harvesting, electronic sensing, and stimulating nerves and muscles.
Researchers at University College Dublin in Ireland and the University of Texas at Dallas decided to investigate the piezoelectric properties of peptide-based nanotubes, as they would be an appealing option for use within electronic devices and for energy harvesting applications. "The piezoelectric properties of peptide-based materials make them particularly attractive for energy harvesting, because pressing or bending them generates an electric charge," explained Sawsan Almohammed, lead author and a postdoctoral researcher at University College Dublin.
There's also an increased demand for organic materials to replace inorganic materials, which tend to be toxic and difficult to make. "Peptide-based materials are organic, easy to make, and have strong chemical and physical stability," Almohammed said.
To be able to take advantage of their piezoelectric properties, peptide-based nanotubes must be horizontally aligned with each other, which the researchers achieved by patterning a wettability difference onto the surface of a flexible substrate. This creates a chemical force that pushes the peptide nanotube solution from the hydrophobic region, which repels water and has a high contact angle, to the hydrophilic region, which attracts water and has a low contact angle.
As well as improving the alignment of the tubes, the researchers also improved their conductivity by making composite structures with graphene oxide.
"It's well known that when two materials with different work functions come into contact with each other, an electric charge flows from low to high work function," explained Almohammed. "The main novelty of our work is that controlling the horizontal alignment of the nanotubes by electrical field and wettability-assisted self-assembly improved both the current and voltage output, and further enhancement was achieved by incorporating graphene oxide."
The group's work, which is reported in a paper in the Journal of Applied Physics, will lead to organic materials, especially peptide-based ones, being used more widely within electronic devices and sensors, as well as for energy-harvesting. This is because the two key limitations of peptide nanotubes – alignment and conductivity – have been improved.
"We're also exploring how charge transfer processes from bending and electric field applications can enhance Raman spectroscopy-based detection of molecules," Almohammed added. "We hope these two efforts can be combined to create a self-energized biosensor with a wide range of applications, including biological and environmental monitoring, high-contrast imaging, and high-efficiency light-emitting diodes."
This story is adapted from material from the American Institute of Physics, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.