Self-assembly of unidirectionally polarized piezoelectric peptide nanotubes using environmentally friendly solvents

Diphenylalanine (FF) peptide nanotubes are considered to be particularly promising biomaterials for bio-implantable devices due to their unique characteristics, such as strong piezoelectricity, remarkable physical properties, and chemical stability. However, the 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)-water co-solvent system, which is often used for FF nanotube synthesis, is toxic and expensive. These are limitations for the development of eco-friendly and practical biocompatible piezoelectric devices. In this study, we developed an eco-friend and cost-effective approach for aligning piezoelectric FF nanotubes using an ethanol–water solvent system. First, we fabricated horizontally aligned FF nanotubes via a meniscus-driven self-assembly process. The fabricated FF nanotubes using ethanol exhibited unidirectional polarization and strong piezoelectric properties comparable to HFIP solvent based FF nanotubes. In addition, the FF-based piezoelectric nanogenerator generates voltage, current, and power of up to 1.66 V, 19.4 nA, and 19.2 nW, respectively, with a force of 40 N. These FF-based piezoelectric nanogenerators will be applicable as a compatible energy source for future biomedical applications.