Hybrid Enhancement of Surface-Enhanced Raman Scattering Using Few-Layer MoS2 Decorated with Au Nanoparticles on Si Nanosquare Holes.

Tsung-Shine Ko,Yen-Lun Chen

doi:10.3390/nano12050786

Abstract

By combining the excellent biocompatibility of molybdenum disulfide (MoS2), excellent surface-enhanced Raman scattering (SERS) activity of Au nanoparticles (Au NPs), and large surface area of Si nanosquare holes (NSHs), a structure in which MoS2 is decorated with Au NPs on Si NSHs, was proposed for SERS applications. The NSH structure fabricated by e-beam lithography possessed 500 nm of squares and a depth of approximately 90 nm. Consequently, a few-layer MoS2 thin films (2–4 layers) were grown by the sulfurization of the MoO3 thin film deposited on Si NSHs. SERS measurements indicated that MoS2 decorated with Au NPs/Si NSHs provided an extremely low limit of detection (ca. 10−11 M) for R6G, with a high enhancement factor (4.54 × 109) relative to normal Raman spectroscopy. Our results revealed that a large surface area of the NSH structure would probably absorb more R6G molecules and generate more excitons through charge transfer, further leading to the improvement of the chemical mechanism (CM) effect between MoS2 and R6G. Meanwhile, the electromagnetic mechanism (EM) produced by Au NPs effectively enhances SERS signals. The mechanism of the SERS enhancement in the structure is described and discussed in detail. By combining the hybrid effects of both CM and EM to obtain a highly efficient SERS performance, MoS2 decorated with Au NPs/Si NSHs is expected to become a new type of SERS substrate for biomedical detection.

Highlights

Surface-enhanced Raman scattering (SERS) has become a powerful method for the detection of biomolecules, owing to its many excellent advantages, including improvement of the Raman scattering efficiency, high sensitivity at the single-molecule level, and high accuracy in biomedical detection [1–3]
By combining the hybrid effects of both chemical mechanism (CM) and electromagnetic mechanism (EM) to obtain a highly efficient SERS performance, MoS2 decorated with Au nanoparticles (Au NPs)/Si nanosquare holes (NSHs) is expected to become a new type of SERS substrate for biomedical detection
Since the difference in wavenumber between the E1 2g and A1 g modes could reflect the number of layers for MoS2 in terms of a few-layer structure [23,24], we suggested that the thickness of the MoS2 coated on the lateral wall and basin surfaces into the NSHs would be probably two to three layers, and that on the platform would be approximately four layers

Summary

Introduction

Surface-enhanced Raman scattering (SERS) has become a powerful method for the detection of biomolecules, owing to its many excellent advantages, including improvement of the Raman scattering efficiency, high sensitivity at the single-molecule level, and high accuracy in biomedical detection [1–3]. The EM effect is attributed to the local electromagnetic field enhancement at the metal surface owing to the surface plasmon polaritons, yielding an excellent SERS enhancement [11]. Noble metals, such as Au and Ag, are widely used as SERS substrates due to the existence of EMs. the main disadvantages of using noble metals as SERS substrates are their high cost, poor stability, and strong carbonization effects [12–14]. The SERS enhancement of the CM effect owing to a charge transfer (CT) between the probe molecule and semiconductor is relatively weaker than that of the EM effect. A hybrid SERS substrate that combines the advantages of the EM and CM effects should be developed and investigated

Methods

Results

Conclusion