Highly effective and chemically stable surface enhanced Raman scattering substrates with flower-like 3D Ag-Au hetero-nanostructures

Abstract

We demonstrated flower-like 3D Ag-Au hetero-nanostructures on an indium tin oxide glass (ITO glass) for surface enhanced Raman scattering (SERS) applications. The flower-like 3D Ag nanostructures were obtained through electrodeposition with liquid crystalline soft template which is simple, controllable and cost effective. The flower-like 3D Ag-Au hetero-nanostructures were further fabricated by galvanic replacement reaction of gold (III) chloride trihydrate (HAuCl₄·3H₂O) solution and flower-like Ag. The flower-like Ag-Au hetero-nanostructure exhibited stronger SERS effects and better chemical stability compared with flower-like Ag nanostructure. The localized surface plasmon resonance (LSPR) spectra, field emission scanning electron microscope (FESEM) photos and Ag-Au ratios were studied which show that the surface morphology and shape of the flower-like Ag-Au hetero-nanostructure play significant roles in enhancing SERS. The flower-like 3D Ag-Au hetero-nanostructures fabricated by electrodeposition in liquid crystalline template and galvanic replacement reaction are simple, cheap, controllable and chemical stable. It is a good candidate for applications in SERS detection and imaging.

Figure 1

Typical characterizations of flower-like silver nanostructure substrates. (a–c) Are FESEM pictures of silver flower nanostructure substrates obtained for 0.5 h, 2 h and 5 h, respectively. (d) Is the top view of single silver flower. (e) Is the image from the bottom of silver flowers. (f) is the side view of the nanostructure substrate. (g) Is EDS spectrum of sliver flowers.

Figure 2

FESEM images of flower-like Ag nanostructures and flower-like Ag-Au hetero-nanostructures. (a) Is the image of silver flower before reacting with the HAuCl₄. (b–d) Are images of flower-like Ag-Au hetero-nanostructures obtained by reacting with 0.05 mM aqueous solutions of HAuCl₄ for 10 min, 30 min and 40 min respectively. (e–f) Are images of flower-like Ag-Au hetero-nanostructures obtained by reacting with 0.5 mM aqueous solutions of HAuCl₄ for 10 min and 30 min respectively. (g–l) Are the single flower images of (a–f). (m–r) Are the magnified images of (g–l).

Figure 3

EDS spectra of Ag nanostructures and Ag-Au hetero-nanostructures. (a) Is the spectrum of silver flower before reacting with the HAuCl₄. (b–d) Are spectra of Ag-Au hetero-nanostructures obtained by reacting with 0.05 mM aqueous solutions of HAuCl₄ for 10 min, 30 min and 40 min respectively. (e–f) Are spectra of Ag-Au hetero-nanostructures obtained by reacting with 0.5 mM aqueous solutions of HAuCl₄ for 10 min and 30 min respectively. The inserted tables are the Au:AuAg ratios in the different nanostructures.

Figure 4

LSPR spectra of flower-like Ag nanostructures and flower-like Ag-Au hetero-nanostructures. (a) Is the spectrum of flower-like silver nanostructures before reacting with the HAuCl₄. (b–d) Are spectra of Ag-Au hetero -nanostructures obtained by reacting with 0.05 mM aqueous solutions of HAuCl₄ for 10 min, 30 min and 40 min respectively. (e–f) Are spectra of Ag-Au hetero-nanostructures obtained by reacting with 0.5 mM aqueous solutions of HAuCl₄ for 10 min and 30 min respectively.

Figure 5

SERS effect for flower-like silver nanostructure substrates with different growth time. (a) SERS spectra of 4-MBA for substrates of 0.5 h, 2 h, 5 h deposition time respectively. (b) Is the relation between enhancement factor and deposition time.

Figure 6

SERS effects of Ag-Au hetero-nanostructure substrates with different reaction time compared with SERS effect of silver nanostructure substrate. (a) SERS spectra and Raman spectra of 4-MBA for flower-like Ag-Au hetero-nanostructure substrates and flower-like silver nanostructure substrate respectively. (b) Is the relation between enhancement factor and gold ratio in the hetero-nanostructure substrate.

Figure 7

The FESEM pictures of Ag-Au hetero-nanostructures and flower-like Ag nanostructures as a function of time reaction with H₂O₂. (a–c) Are the FESEM pictures of the flower-like Ag-Au hetero-nanostructures after etching for 5 h, 10 h and 24 h by H₂O₂, respectively. (d–f) Are the FESEM pictures of the flower-like Ag nanostructures after etching for 5 h, 10 h and 24 h by H₂O₂, respectively.