介孔SiO2薄膜增敏SERS基底在消逝波激励下的特性表征

Characterization of Mesoporous Silica Film Sensitized SERS Substrates Based on Evanescent-Wave Excitation

采用溶胶-凝胶分子模板法在50 nm厚金膜表面制备约40 nm厚介孔二氧化硅(MPS)薄膜,然后在MPS薄膜表面静电自组装金纳米粒子(GNP)单层膜,形成的多层膜结构用作表面增强拉曼散射(SERS)基底.利用扫描电镜观测到MPS薄膜具有表面开口多孔结构,有助于小分子向薄膜内快速扩散.基于时域有限差分(FDTD)方法对电场分布的仿真结果指出,在表面等离子体共振(SPR)条件下分布于金膜与GNP之间的消逝场显著增强.由于空间重叠,该增强场能够高效激发MPS内富集的小分子拉曼信号,产生的拉曼信号还可免受金属作用的干扰.利用Kretschmann结构和尼罗蓝(NB)拉曼活性分子测试了Au/MPS/GNP基底在785 nm激发波长下的SERS效果,并与Au/GNP基底进行了比较.结果表明,在SPR条件下,Au/MPS/GNP基底能够导致较强的定向和背向拉曼信号,而且在586 cm-1处的背向拉曼信号强度是Au/GNP基底的40倍,这归功于MPS薄膜.进一步测试表明背向拉曼信号强度与NB浓度成正相关.这意味着Au/MPS/GNP基底具有良好的半定量检测本领.

Sol-gel copolymer templated mesoporous silica （MPS） films of^40 nm thickness were fabricated on the 50-nm-thick gold films sputtered on glass substrates. A top monolayer of gold nanoparticles （GNPs） was subsequently self-assembled on the MPS film to form an Au/MPS/GNP multilayer structure for surface-enhanced Raman scattering （SERS） spectroscopy based on evanescent wave excitation. The open-pore structure of the MPS films, which was conducive to the rapid diffusion of smal molecules into the film, was observed by scanning electron microscopy. Simulation using finite difference time domain （FDTD） solutions indicates that the evanescent field between the Au film and GNP layer of the Au/MPS/GNP substrate can be significantly enhanced under the surface plasmon resonance （SPR） condition. Owing to the complete spatial overlap, this enhanced field enables to superefficiently excite SERS signals from smal molecules adsorbed in the MPS film. Moreover, the MPS film can effectively prevent the direct metal-molecule interaction, making the SERS signal immune to the interference by the metal. The SERS effect of the Au/MPS/GNP substrate loaded with Raman-active Nile blue （NB） molecules was investigated at 785 nm excitation wavelength with the Kretschmann configuration,and the experimental results were compared with those obtained using the Au/GNP substrate. With the Au/MPS/GNP substrate very strong Raman signals were detected on the prism and air sides, respectively, under the SPR condition. The air-side Raman peak at 586 cm-1 is 40 times as high as that with the Au/GNP substrate. This enhancement is attributed to the open-pore MPS film. The further measurements reveal a positive correlation between the air-side Raman peak intensity and the NB concentration of the solution sample, giving a sign that the Au/MPS/GNP substrate could be used for quasi-quantitative analysis.