Cu nanocrystal growth on peptide nanotubes by biomineralization: size control of Cu nanocrystals by tuning peptide conformation

Abstract

With recent interest in seeking new biologically inspired device-fabrication methods in nanotechnology, a new biological approach was examined to fabricate Cu nanotubes by using sequenced histidine-rich peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled as nanotubes, and the biological recognition of the specific sequence toward Cu lead to efficient Cu coating on the nanotubes. Cu nanocrystals were uniformly coated on the histidine-incorporated nanotubes with high packing density. In addition, the diameter of Cu nanocrystal was controlled between 10 and 30 nm on the nanotube by controlling the conformation of histidine-rich peptide by means of pH changes. Those nanotubes showed significant change in electronic structure by varying the nanocrystal diameter; therefore, this system may be developed to a conductivity-tunable building block for microelectronics and biological sensors. This simple biomineralization method can be applied to fabricate various metallic and semiconductor nanotubes with peptides whose sequences are known to mineralize specific ions.

Fig. 1.

Scheme of the Cu nanotube fabrication. (a) Immobilization of the sequenced HG12 peptide at the amide-binding sites of the template nanotubes. (b) The Cu ion–HG12 peptide complexation on the nanotube surfaces. (c) Cu nanocrystal growth on the nanotubes nucleated at Cu ion-binding sites after reducing trapped Cu ions with NaBH₄.

Fig. 2.

(a) Cu nanocrystals grown on the nanotube at pH 6. (Left) TEM image. (Center) Electron-diffraction pattern. (Right) Size distribution. (Inset) The TEM image in higher magnification. (b) Cu nanocrystals grown on the nanotube at pH 8. (Left) TEM image. (Center) Electron-diffraction pattern. (Right) Size distribution. (Inset) The TEM image in higher magnification. (c) Cu nanocrystals grown on the nanotube without the HG12 peptide at pH 6. (Left) TEM image. (Center) Electron-diffraction pattern. (Right) Size distribution. (Scale bar = 100 nm.)

Fig. 3.

UV-visible spectra of the nanotubes coated with Cu nanocrystals in a diameter of 10 nm, grown in pH 6 solution (dotted line) (a) and Cu nanocrystals in a diameter of 30 nm, grown in pH 8 solution (solid line) (b).

Fig. 4.

TEM images of the Cu nanocrystals grown in the HG12 peptide solution without the template nanotubes at pH 6 (a) and at pH 8 (b). Arrows show the edges of aggregated HG12 peptides. (Scale bar = 100 nm.)

Fig. 5.

IR spectra of the HG12 peptide–Cu(II) complexes on the nanotubes at pH 6 (dotted line) and pH 8 (solid line).

Fig. 6.

A proposed structure of the Cu nanocrystal–HG12 peptide complex on the template nanotube.