Fig. 4: Characterization of the helical peptide-based nanogenerator.

a Photograph and schematic configuration of coin-sized piezoelectric energy generation measurement set-up utilized as a direct power source with peptide assemblies as the active component. b, c Open-circuit voltage (b) and short-circuit current (c) of piezoelectric energy harvester in the forward connection. d, e The generated voltage output (d) and current output (e) in the reverse connection. f, g Variable external load was applied onto the device. The measured open-circuit voltage (f) and short-circuit current output (g) of Hyp-Phe-Phe under different applied force. h, i Linear dependence of the voltage (h) and current (i) output on the applied force. The black and red lines indicate forward and reverse connection, respectively. j–l Comparison of piezoelectric response of the engineered helical tripeptides with β-sheet forming Phe-Phe peptide assemblies. j The self-assembled nanostructures and β-sheet molecular arrangement in the crystal structure of Phe-Phe (CCDC ref. no 16340⁸³). k Short circuit current obtained from the generator using Phe-Phe assemblies as the active component upon applied force = 23 N. l Comparison of output current of Phe-Phe with helical peptides, Pro-Phe-Phe and Hyp-Phe-Phe. Error bars = SD (n = 3).