Star-Shaped Fe3-xO4-Au Core-Shell Nanoparticles: From Synthesis to SERS Application.

Thi Thuy Nguyen,Fayna Mammeri,Souad Ammar,Stephanie Lau-Truong

doi:10.3390/nano10020294

Abstract

In this work, the preparation of magneto-plasmonic granular nanostructures and their evaluation as efficient substrates for magnetically assisted surface enhanced Raman spectroscopy (SERS) sensing are discussed. These nanostructures consist of star-shaped gold Au shell grown on iron oxide Fe3-xO4 multicores. They were prepared by seed-mediated growth of anisotropic, in shape gold nanosatellites attached to the surface of polyol-made iron oxide polycrystals. In practice, the 180 nm-sized spherical iron oxide particles were functionalized by (3-aminopropyl) triethoxysilane (APTES) to become positively charged and to interact, in solution, with negatively charged 2 nm-sized Au single crystals, leading to nanohybrids. These hybrids acted subsequently as nucleation platforms for the growth of a branched gold shell, when they were contacted to a fresh HAuCl4 gold salt aqueous solution, in the presence of hydroquinone, a reducing agent, for an optimized nominal weight ratio between both the starting hybrids and the gold salt. As expected, the resulting nanocomposites exhibit a high saturation magnetization at room temperature and a rough enough plasmonic surface, making them easily attracted by a lab. magnet, while exhibiting a great number of SERS hot spots. Preliminary SERS detection assays were successfully performed on diluted aqueous thiram solution (10−8 M), using these engineered substrates, highlighting their capability to be used as chemical trace sensors.

Highlights

Star-shaped Fe3-xO4-Au core-satellites and core-shell nanoparticles provide interesting magnetic and optical properties, making them appealing to broaden advances in magnetically assisted surface-enhanced Raman spectroscopy (SERS) applications [1,2,3,4,5,6,7]
The magneto-plasmonic building blocks were consecutively fabricated, starting from (i) the precipitation in polyol of multicore iron oxide nanoparticles; (ii) their surface modification for the electrostatic attachment of ultrafine preformed negatively charged gold nanocrystals; and (iii) the use of the resulting hybrid particles as seeds to grow a rough gold shell thanks to the reduction of dissolved HAuCl4 salt in water with hydroquinone in the presence of citrates. Within these experimental conditions and by varying the weight ratio r between the hybrid seed particles and the gold salt precursor, a more or less continuous but anisotropic in shape gold layer can be formed around the iron oxide particles, leading to more or less efficient magneto-plasmonic nanostructures for SERS detection of analyte traces in water
It could be evidenced on the X-ray diffraction (XRD) patterns (Figure 6(2a) on which the high intensity diffraction peaks at 2Θ positions of 44.7, 52.1, 76.8, 93.5 and 99.1° correspond to the (111), (002), (022), (113) and (222) planes of facecentered cubic gold phase

Summary

Introduction

Star-shaped Fe3-xO4-Au core-satellites and core-shell nanoparticles provide interesting magnetic and optical properties, making them appealing to broaden advances in magnetically assisted surface-enhanced Raman spectroscopy (SERS) applications [1,2,3,4,5,6,7]. The magneto-plasmonic building blocks were consecutively fabricated, starting from (i) the precipitation in polyol of multicore iron oxide nanoparticles (core of the final hybrids); (ii) their surface modification for the electrostatic attachment of ultrafine preformed negatively charged gold nanocrystals (seed particles); and (iii) the use of the resulting hybrid particles as seeds to grow a rough gold shell thanks to the reduction of dissolved HAuCl4 salt in water with hydroquinone in the presence of citrates Within these experimental conditions and by varying the weight ratio r between the hybrid seed particles and the gold salt precursor, a more or less continuous but anisotropic in shape gold layer can be formed around the iron oxide particles, leading to more or less efficient magneto-plasmonic nanostructures for SERS detection of analyte traces in water

Chemicals

Characterization Tools

Results and Discussion

Toward Magnetically Assisted SERS Sensing

Conclusions