表面增强拉曼光谱（SERS）因其高达单分子检测的表面灵敏度而广受青睐, 其增强机理主要包括电磁场增强效应（EM）和电荷转移增强（CT）。 通常, 前者占主导作用, 且局域电磁场可极大地增强表面吸附分子的拉曼信号。 而介质通常对局域电磁场和EM增强有一定影响, 从而影响SERS检测, 通过壳层隔绝纳米粒子（SHINs）可避免介质与SERS增强源间的直接接触。 但迄今为止, 几乎未见有关介质对其增强拉曼光谱（SHINERS）影响的研究, 主要因SERS基底均匀性较差所致。 制备了两种探针分子内嵌且Au核尺寸不同的核壳纳米粒子, 即(55 nm Au-PNTP)@SiO2和(110 nm Au-pMBA)@SiO2, 壳层厚度分别为3.5和4.0 nm, 壳层结构连续且无针孔效应。 采用液-液两相成膜法制备其单层膜, 转移至固相基底上可作为SERS基底, (55 nm Au-PNTP)@SiO2单层膜上SERS谱峰强度的相对标准偏差约为5.38%, (110 nm Au-pMBA)@SiO2单层膜上相对标准偏差约为5.97%, 其重现性及均匀性优良, 符合作为SERS基底的要求。 研究它们分别在空气和水两种介质中的SERS效应, 结果表明Au核被致密无针孔效应的SiO2壳层包裹, 且探针分子内嵌其中, 由此完全隔绝了电磁场增强源内核Au纳米粒子与介质的直接接触, 当改变基底所处的环境时, 其实际介质仍为SiO2, 因此在两种介质中SERS信号几乎不发生改变。 内嵌探针分子的PNTP或pMBA被包裹在SiO2壳层内, 溶剂及氧气等均无法参与反应, 因此探针分子未发生SPR催化反应, 保持稳定的光谱特征。 由此可见内嵌探针分子的SERS信号强度及光谱特征不受介质的影响, 可望作为多介质环境使用的高灵敏度SERS检测以及稳定内标或标记的重要基底。

Surface-enhanced Raman spectroscopy (SERS) has been developed as a powerful tool in surface science due to its ultrahigh surface sensitivity up to the single molecular detection. The enhancement mechanisms include electromagnetic enhancement mechanism (EM) andchemical enhancement mechanism (CM). In general, the dominant contributor to most SERS processes is the EM, and the local electromagnetic field in the EM greatly enhance the surface Raman signal intensity of the adsorbed molecules. In addition, the medium has traditionally played a vital role in SERS measurements, as the medium also exhibits a certain influence on the local electromagnetic field as well as the EM enhancements. Shell-isolated nanoparticles (SHINs) can avoid direct contact between the medium and SERS enhancement source through the inert shell on the surface of the particles. However, up to now, few studies have been conducted on the effect of dielectrics on the shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), which is often due to the poor homogeneity of SERS substrates. Herein, two core-shell nanostructures embedded with probe molecules were fabricated successfully, i. e. (55 nm Au-PNTP)@SiO2 and (110 nm Au-pMBA)@SiO2 with the shell thickness of about 3.5 and 4.0 nm, respectively. The continuous shell layer covered the Au core nanoparticles compactly without pinhole effect. The core-shell nanoparticles monolayer layer was assembled at the liquid-liquid interface, and it was transferred to flat solid surface as SERS substrate. The monolayer film of (55 nm Au-PNTP)@SiO2 exhibited the uniform SERS effect with the relative standard deviation (RSD) of about 5.38%, while RSD of 5.97% for (110 nm Au-pMBA)@SiO2. Therefore, the reasonable performance of the monolayer film allowed serving as qualified SERS substrate. The medium effect was explored on the monolayer film in the water and air system. It demonstrated that the pinhole free continuous shell and the probe embedded into the shell brought isolation of the EM source and the probes with the medium condition. Although the outside medium (condition) was changed from air to water, the real medium of the probes and the Au core was still surrounded by the SiO2 shell. Consequently, the SERS signal intensity was independent of the outside medium. The probe molecules of PNTP and pMBA was embedded into the SiO2 shell, and the SPR catalysis reaction was absent due to the isolation of oxygen and solvent. Thus the spectral feature of probes was quite stable. It indicated that no influence on the SERS effect was observed by different medium for the probes embedded nanostructures. It was expected to develop the probes embedded nanostructures as SERS substrate for the sensitive detection in a different medium, and as an internal standard for calibration of SERS effect.