Self-assembly of diphenylalanine peptide with controlled polarization for power generation

Abstract

Peptides have attracted considerable attention due to their biocompatibility, functional molecular recognition and unique biological and electronic properties. The strong piezoelectricity in diphenylalanine peptide expands its technological potential as a smart material. However, its random and unswitchable polarization has been the roadblock to fulfilling its potential and hence the demonstration of a piezoelectric device remains lacking. Here we show the control of polarization with an electric field applied during the peptide self-assembly process. Uniform polarization is obtained in two opposite directions with an effective piezoelectric constant d₃₃ reaching 17.9 pm V^-1. We demonstrate the power generation with a peptide-based power generator that produces an open-circuit voltage of 1.4 V and a power density of 3.3 nW cm^-2. Devices enabled by peptides with controlled piezoelectricity provide a renewable and biocompatible energy source for biomedical applications and open up a portal to the next generation of multi-functional electronics compatible with human tissue.

Figure 1. Growth of vertical FF peptide microrod arrays with controlled polarization.

(a,b) Schematic of the positive-EF (electric field) growth (a) and the negative-EF growth (b). The large arrows are the directions of the applied electric fields, and the plus and minus signs indicate the polarizations of the FF molecules and FF microrods. (c,d) Cross-section views of arrays from the positive-EF growth (c) and the negative-EF growth (d). Scale bars in (c) and (d) are 100 μm. (e) High-magnification view of vertical microrods. Scale bar, 20 μm. (f) Photography of vertical FF peptide microrod array grown on a gold-coated substrate. The yellow gold layer is visible owing to the vertical alignment of microrod arrays and good optical waveguide properties along their axial directions.

Figure 2. PFM and SKPM characterization of the microrod arrays.

(a,b) PFM phase image and corresponding SKPM surface potential map of a microrod from the positive-EF growth (a) and a microrod from the negative-EF growth (b). The phase and surface potential distributions are shown by the colour overlaid on the topography of the top of the microrod. (c) Statistics of the piezoelectric phase for the arrays from the positive-EF growth, negative-EF growth and no-EF growth. Detailed data for this chart is provided in Supplemental Table 1. (d) Linear dependence of the PFM amplitude on the applied voltage for FF peptide microrods from growth with different electric fields. The slopes of the lines provide effective piezoelectric coefficients d₃₃, which are 17.9, 11.7 and 9.3 pm V⁻¹ for microrods from the negative-EF growth, positive-EF growth and no-EF growth, respectively. Error bar: s.d.

Figure 3. Characterization of the FF peptide-based power generators.

(a) Schematic of the FF peptide-based generator connected to the measurement equipment. Bottom-right inset: photography of a real device. (b) Schematic of the measurement set-up in which a linear motor pushes with controlled forces on the top electrode in (a). The linear motor was programmed to always keep contact with the top electrode to minimize the effect of static charges. (c,d) Open-circuit voltage (c) and short-circuit current (d) from a generator using microrods from positive-EF growth. (e) Dependence of the power output from the generators on the resistance of the external load under 50 N applied force. (f) Linear dependence of the open-circuit voltage on the applied force. Error bar: s.d.

Figure 4. Demonstration of the FF peptide-based generator as a practical power source.

(a,b) Open-circuit voltage over time as the generator was pressed under 50 N force for over half an hour at 0.5 Hz (a), and the enlarged view of the voltage output (b). The time was limited by the storage of our measuring instrument. The background shift due to long time measurement was subtracted from the recorded signal for clarity. (c) Photograph of the generator as a direct power source for an LCD. (d,e) Photograph of the LCD before (d) and after (e) the generator in (c) was pressed by a human finger.