Saisai Gao

Large-area MoS2 thin layers directly synthesized on Pyramid-Si substrate for surface-enhanced Raman scattering

In our work, we directly synthesized few layer MoS2 on a pyramid-Si substrate to fabricate a surface-enhanced Raman scattering (SERS) substrate via thermally decomposing the precursor of ammonium thiomolybdate ((NH4)2MoS4). Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectra are employed to characterize the as-grown MoS2 layers. Adenosine and cytidine were selected as the probe molecules to investigate the SERS ability of the MoS2-pyramid-Si substrate, and have shown that the MoS2-pyramid-Si substrate can prominently suppress photobleaching and fluorescence of the probe molecule. Compared with the MoS2-flat-Si substrate (MoS2 layers synthesized on flat-Si substrate), the MoS2-pyramid-Si substrate has more significant SERS ability. The minimum detected concentration of both adenosine and cytidine on the MoS2-pyramid-Si substrate can reach 10−6 M. Importantly, the linear relationship between the Raman intensity and the concentration of adenosine or cytidine can apply to the bimolecular detection. This work may provide a new opportunity for the study of the chemistry mechanism (CM) and novel SERS substrate fabrication.

A sensitive, uniform, reproducible and stable SERS substrate has been presented based on MoS2@Ag nanoparticles@pyramidal silicon

By combining the excellent surface-enhanced Raman scattering (SERS) activity of Ag nanoparticles (AgNPs), the well-separated pyramid arrays of the pyramidal silicon (PSi) and unique physical/chemical properties of molybdenum disulfide (MoS2), the MoS2@AgNPs@PSi substrate shows high performance in terms of sensitivity, uniformity, reproducibility and stability. By using rhodamine 6G (R6G) as probe molecule, the SERS results indicate that the MoS2@AgNPs@PSi substrate is superior to the AgNPs@PSi, AgA@PSi (the second annealing of the AgNPs@PSi) and the MoS2@AgNPs@flat-Si substrate. The MoS2@AgNPs@PSi substrate also shows the reasonable linear response between the Raman intensity and R6G concentration. The maximum deviations of SERS intensities from 20 positions on a same MoS2@AgNPs@PSi substrate and 10 MoS2@AgNPs@PSi substrates in different batches are less than 7.6% and 9%, respectively, revealing the excellent uniformity and reproducibility of the substrate. Besides, the SERS substrate has a good stability, the Raman intensity of the MoS2@AgNPs@PSi substrate only drop by 15% in a month. The corresponding experimental and theoretical results suggest that our proposed MoS2@AgNPs@PSi substrate is expected to offer a new and practical way to accelerate the development of label-free SERS detection.

A sensitive 2D plasmon ruler based on Fano resonance

In this paper, we designed a 2D distance and rotation angle plasmon ruler based on Fano resonance of a trimer nanostructure, which consists of a concentric square nanoring–disk and an outside nanorod (CSRDR). The Fano dip energy and depth are fairly sensitive to the nanometer-scale displacements and rotations, when the nanodisk moves in all direction and rotates around its center. When the symmetry of the nanoring is broken, we can identify the moving and rotating direction of the nanodisk more accurately. We use the CSRDR nanostructure which supports a narrow line-width as a 2D plasmon ruler, which can enhance the sensitivity of a plasmon ruler significantly.

An optical fiber SERS sensor based on GO/AgNPs/rGO sandwich structure hybrid films

In this work, we present a novel optical fiber SERS (OF-SERS) sensor based on a sandwich structure of GO/AgNPs/rGO. Rhodamine 6G (R6G) was selected as the probe molecule to compare the SERS ability of different films composed of the bare optical fiber, GO, AgNPs, rGO/AgNPs, GO/AgNPs and GO/AgNPs/rGO. Raman spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were performed to characterize the sandwich structure hybrid films. Besides, the stability of GO/AgNPs and GO/AgNPs/rGO was compared on the optical fiber end face. The OF-SERS sensor based GO/AgNPs/rGO hybrid films had stable SERS performance even when exposed to ambient conditions for a prolonged time of 30 days. This work may provide a new strategy for an efficient stable OF-SERS sensor due to its simplicity, low-cost and long-term stability.