A Low-cost, Highly-stable Surface Enhanced Raman Scattering Substrate by Si Nanowire Arrays Decorated with Au Nanoparticles and Au Backplate

Bi-Shen Lee,Ta-Jen Yen,Ding-Zheng Lin

doi:10.1038/s41598-017-04062-4

Abstract

We present a facile and cost-effective manner to fabricate a highly sensitive and stable surface enhanced Raman scattering (SERS) substrate. First, a silicon nanowire array (SiNWA) is tailored by metal-assisted chemical etching (MaCE) method as a scaffold of the desired SERS substrate. Next, with an oblique angle deposition (OAD) method, optimized gold nanoparticles (AuNPs) are successfully decorated on the surface of the SiNWA. These AuNPs enable a strong localized electric field, providing abundant hot spots to intensify the Raman signals from the targeting molecules. By applying a well-established methodology, Taguchi method, which is invented for designing experiments, the optimized combination of parameters is obtained efficiently. The experimental results are also confirmed by finite-difference time-domain (FDTD) simulation calculations. Besides, a gold metal backplate (AuMBP) is applied to further enhancing the Raman signal intensity. Based on this developed SERS substrate, we demonstrated an enhancement factor (EF) of 1.78 × 106 and a coefficient of variation (CV) of 4.2%. Both EF and CV indicate a highly stable property and the optimized SERS substrate substantially outperform the commercial product. In the end, we also demonstrate a quantitative measurement on practical application of detecting malachite green (MG) with concentration from 10 nM to 100 μM.

Highlights

Further improve the surface enhanced Raman scattering (SERS) effect, gold quasi-3D array[16], ordered nanoporous AuNP array[17], gold nanofingers[18], and especially the glass nanopillar array covered with silver nanoislands[19] were proposed
Based on the measured Raman intensities of nine trials, we conducted an analysis of variance (ANOVA) to identify the significance of four individual parameters, and concluded the optimal combination of A2B2C3D3, which denoted 300 nm-long Si nanowire arrays (SiNWA) with 70° oblique angle deposition (OAD), 30 nm-thick AuNPs and 20 nm-thick Au metal backplate (AuMBP), respectively (Refer to Supplementary Material, Table S1 and Figure S1)
We demonstrated a practical application of detecting malachite green (MG)

Summary

Introduction

Further improve the SERS effect, gold quasi-3D array[16], ordered nanoporous AuNP array[17], gold nanofingers[18], and especially the glass nanopillar array covered with silver nanoislands[19] were proposed. The glass nanopillar array involves expensive reactive ion etching (RIE) fabrication process and the silver is not chemically stable as gold. These two issues impede its employment for fast screening and practical applications. We utilized a metal-assisted chemical etching (MaCE) method to fabricate Si nanowire arrays (SiNWA)[20, 21], which function as a high surface-to-volume scaffold. The scaffold was deliberately deposited AuNPs by oblique angle deposition to yield strong localized surface plasmon resonance for enhancing the Raman signal. An Au metal backplate (AuMBP) was introduced to preventing the light trapping by SiNWA25, leading to a further enhancement of our engineered SERS substrate

Methods

Results

Conclusion